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1

Short-Arc Correlation and Initial Orbit Determination For Space-Based Observations  

Microsoft Academic Search

Initial orbit determination (IOD) of space debris is an important segment of space situational awareness and is often coupled with the problem of track correlation, since in order to determine the orbit of an observed object, multiple observations must be combined. It is generally uncertain, however, whether two arbitrary tracks are of the same object. Recently, Fujimoto and Scheeres have

K. Fujimoto; D. Scheeres

2011-01-01

2

Short-Arc Correlation and Initial Orbit Determination For Space-Based Observations  

NASA Astrophysics Data System (ADS)

Initial orbit determination (IOD) of space debris is an important segment of space situational awareness and is often coupled with the problem of track correlation, since in order to determine the orbit of an observed object, multiple observations must be combined. It is generally uncertain, however, whether two arbitrary tracks are of the same object. Recently, Fujimoto and Scheeres have proposed a novel and rigorous track correlation and IOD technique where each observation is assigned an “admissible region” in state space based on some physical constraints. The relationship of two observations is then determined by finding whether these regions intersect via Bayes’ rule. In this paper, we propose a new application of this method to space-based observations. Preliminary results show robustness to classically singular geometries, such as GEO-on-GEO observations. Admissible regions were first proposed by Milani et al. for heliocentric orbits, and Tommei et al. expanded this concept to Earth orbiting objects. Maruskin et al. was first to introduce the concept of intersecting multiple admissible regions to correlate tracks and obtain an initial orbit estimate, albeit the correlation was conducted in 2-dimensional subspaces of the state space. Fujimoto and Scheeres fully developed ways of characterizing intersections of admissible regions in the full 6-dimensional state space. They showed through topological arguments that a positive correlation also simultaneously provides an initial orbit estimate. A method of linearly mapping admissible regions to the state space was introduced in order to improve computational turn-around, and was validated with a series of numerical tests. For space-based observations, the observation location vector, previously assumed to be Earth-fixed, is now allowed to propagate under two-body dynamics. Several technical challenges arise when we make this change. First, the admissible region spans over a larger region in the state space, making the correlation process more computationally intensive. Second, a modification must be made to the correlation process as the observer's state is always a valid solution. That is, any admissible region map from a space-based observation will intersect with any other map from the same observing satellite at the observing satellite's state. This problem is circumvented by automatically refining the state space discretization and throwing away solutions near the observing satellite's state. Numerical examples for several observation scenarios are discussed in this paper, including LEO-on-GEO and GEO-on-GEO observations. The LEO satellite is in a circular sun-synchronous orbit at 630 km altitude, much like the SBSS System. For existing IOD techniques there are known observation geometries that experience singularities such as the GEO-on-GEO case. Preliminary results show that our method does not suffer such singularities for the GEO-on-GEO observation scenario. This outcome is most likely due to the fact that we are combining 2 observations for a total of 8 observable variables, instead of the minimum 6, to obtain an initial orbit estimate. We believe this additional information removes the singularity from the problem.

Fujimoto, K.; Scheeres, D.

2011-09-01

3

India’s first lunar mission Chandrayaan-1 initial phase orbit determination  

Microsoft Academic Search

India’s first Moon mission Chandrayaan-1 carrying eleven scientific instruments for the purpose of expanding scientific knowledge about the Moon was launched on 22 October 2008. The spacecraft was put into Moon’s polar, circular orbit of about (100×100)km on 12 November 2008 by carrying out a sequence of Earth bound and Lunar bound maneuvers. Precise orbit determinations are carried out during

N. V. Vighnesam; Anatta Sonney; N. S. Gopinath

2010-01-01

4

Viking satellite orbit determination  

Microsoft Academic Search

During the summer of 1976, the two Viking spacecraft, each consisting of an orbiter-lander combination, were inserted into orbit about Mars. The paper describes the experiences of the Viking Satellite Orbit Determination Team in determining Mars centered ephemerides of the orbiters and positions of the landers from the two-way Doppler and range data, and synthesizes the different phases of the

C. E. Hildebrand; E. J. Christensen; D. H. Boggs; G. H. Born; H. Hokikian; J. F. Jordan; W. B. Howard

1977-01-01

5

Initial Orbit Determination using Short-Arc Angle and Angle Rate Data  

Microsoft Academic Search

The population of space objects (SOs) is tracked with sparse resources and thus tracking data are only collected on these objects for a relatively small fraction of their orbit revolution (i.e., a short arc). This contributes to commonly mistagged or uncorrelated SOs and their associated trajectory uncertainties (covariances) to be less physically meaningful. The case of simply updating a catalogued

Kyle J. DeMars; Moriba K. Jah; Paul W. Schumacher

2012-01-01

6

Lunar Prospector Orbit Determination Results.  

National Technical Information Service (NTIS)

The orbit support for Lunar Prospector (LP) consists of three main areas: (1) cislunar orbit determination, (2) rapid maneuver assessment using Doppler residuals, and (3) routine mapping orbit determination. The cislunar phase consisted of two trajectory ...

M. Beckman M. Concha

1998-01-01

7

Transfer orbit determination accuracy for orbit maneuvers  

NASA Astrophysics Data System (ADS)

This work intends to show the accuracy of the orbital elements determined during transfer orbit as a function of data span, as well as the feasibility of performance maneuvers. The orbit estimator used is a weighted least squares algorithm. The observation vector is composed of angle data (azimuth and elevation) and range data and are from the Astra IC mission. The state vector is either propagated by Brower model or numerical integration (for small eccentricities and inclination). The complete software to determine the orbit has been developed by Hughes Aircraft and been used for all Hughes satellite mission.

Pinheiro, Mery Passos

8

Orbit Determination and Data Fusion in GEO  

NASA Astrophysics Data System (ADS)

This paper proposes a simple yet reliable method for performing orbit determination or track initiation in the geosynchronous (GEO) regime of space using angle-only sensor observations. The main discovery communicated in this paper is a new online metric which allows the operator to assess in realtime if there is adequate observational data to solve the orbit determination problem and hence initiate a robust track state estimate and consistent covariance.

Horwood, J.; Poore, A.; Alfriend, K.

2011-09-01

9

NEMETODE: The Network for Meteor Triangulation and Orbit Determination. System Overview and Initial Results from a UK Video Meteor Network  

NASA Astrophysics Data System (ADS)

An overview is provided and first results presented from NEMETODE, The Network for Meteor Triangulation and Orbit Determination. This is a network of four low-light video cameras based in the North of England in the United Kingdom that use UFOCapture, UFOAnalyser and UFOOrbit to capture and analyse meteor data. NEMETODE is intended to supplement the increasing number of comparable teams around the world who are using similar networks. Many of these networks have been established to ascertain if the suspected meteor showers listed on the International Astronomical Union's Meteor Data Center actually exist and if so, determine if they can be associated with known parent bodies. This paper provides a detailed description of the equipment used and the techniques employed to collect and analyse the data. The results from the first full collaborative month of operation, 2012 August, are presented, with specific focus given to the 007 PER (Perseids) meteor shower. The Perseids are a well characterised shower and were selected to verify if the results from NEMETODE were consistent with currently accepted parameters.

Stewart, William; Pratt, Alex R.; Entwisle, Leonard

2013-06-01

10

Asteroid searching and orbit determination  

NASA Astrophysics Data System (ADS)

This lecture reviews some basic information on asteroids relating to the ASTROD project, as well as the current progress on asteroid searching. The online resources on asteroid orbit determination are also introduced.

Zhu, Jin; Gao, Jian; Guan, Min; Yang, Bin

11

Geostationary orbit determination using SATRE  

NASA Astrophysics Data System (ADS)

A new strategy of precise orbit determination (POD) for GEO (Geostationary Earth Orbit) satellite using SATRE (SAtellite Time and Ranging Equipment) is presented. Two observation modes are proposed and different channels of the same instruments are used to construct different observation modes, one mode receiving time signals from their own station and the other mode receiving time signals from each other for two stations called pairs of combined observations. Using data from such a tracking network in China, the results for both modes are compared. The precise orbit determination for the Sino-1 satellite using the data from 6 June 2005 to 13 June 2005 has been carried out in this work. The RMS (Root-Mean-Square) of observing residuals for 3-day solutions with the former mode is better than 9.1 cm. The RMS of observing residuals for 3-day solutions with the latter mode is better than 4.8 cm, much better than the former mode. Orbital overlapping (3-day orbit solution with 1-day orbit overlap) tests show that the RMS of the orbit difference for the former mode is 0.16 m in the radial direction, 0.53 m in the along-track direction, 0.97 m in the cross-track direction and 1.12 m in the 3-dimension position and the RMS of the orbit difference for the latter mode is 0.36 m in the radial direction, 0.89 m in the along-track direction, 1.18 m in the cross-track direction and 1.52 m in the 3-dimension position, almost the same as the former mode. All the experiments indicate that a meter-level accuracy of orbit determination for geostationary satellite is achievable.

Lei, Hui; Li, Zhigang; Yang, Xuhai; Wu, Wenjun; Cheng, Xuan; Yang, Ying; Feng, Chugang

2011-09-01

12

Orbit Determination from the Satellite.  

National Technical Information Service (NTIS)

The paper presents simple methods for determining moderately eccentric orbits from the satellite; linear combinations of time-of-flight measurements are used exclusively. The method is based on a third-order expansion of the satellite law of motion in ter...

A. Braga-Illa

1968-01-01

13

A Study on the Strategies of the Positioning of a Satellite on Observed Images by the Astronomical Telescope and the Observation and Initial Orbit Determination of Unidentified Space Objects  

NASA Astrophysics Data System (ADS)

An optical tracking system has advantages for observing geostationary earth orbit (GEO) satellites relatively over other types of observation system. Regular surveying for unidentified space objects with the optical tracking system can be an early warning tool for the safety of five Korean active GEO satellites. Two strategies of positioning on the observed image of Communication, Ocean and Meteorological Satellite 1 are tested and compared. Photometric method has a half root mean square error against streak method. Also null eccentricity method for initial orbit determination (IOD) is tested with simulation data and real observation data. Under 10 minutes observation time interval, null eccentricity method shows relatively better IOD results than the other time interval. For follow-up observation of unidentified space objects, at least two consecutive observations are needed in 5 minutes to determine orbit for geosynchronous orbit space objects.

Choi, Jin; Jo, Jung Hyun; Choi, Young-Jun; Cho, Gi-In; Kim, Jae-Hyuk; Bae, Young-Ho; Yim, Hong-Suh; Moon, Hong-Kyu; Park, Jang-Hyun

2011-12-01

14

Determination and prediction of Magellan's orbit  

Microsoft Academic Search

The Magellan spacecraft has been systematically mapping the surface of Venus since September 15, 1990, using a synthetic aperture radar. The spacecraft orbit about Venus is nearly polar, with an orbital period of 3.26 hours and periapsis altitude of 295 km. The radiometric measurements and the data reduction method used to determine and predict the spacecraft state are described. Orbit

D. B. Engelhardt; J. B. McNamee; S. K. Wong; F. G. Bonneau; E. J. Graat; R. J. Haw; G. R. Kronschnabl; M. S. Ryne

1991-01-01

15

Orbit determination study results for the Venus Radar Mapper orbiter  

Microsoft Academic Search

The Venus Radar Mapper (VRM), to be launched by the U.S. in July 1988 is described and Doppler-only and Doppler plus N-Delta-VLBI data analyses are contrasted in order to evaluate the importance of VLBI data to VRM orbit determination (OD). VRM OD study results are summarized by showing the accuracy of various orbital parameters for ten cases selected over a

P. B. Esposito; S. Demcak

1986-01-01

16

Precision Orbit Determination for the Lunar Reconnaissance Orbiter  

NASA Astrophysics Data System (ADS)

The Lunar Reconnaissance Orbiter (LRO) spacecraft was launched on June 18, 2009. In mid-September 2009, the spacecraft orbit was changed from its commissioning orbit (30 x 216 km polar) to a quasi-frozen polar orbit with an average altitude of 50km (+-15km). One of the goals of the LRO mission is to develop a new lunar reference frame to facilitate future exploration. Precision Orbit Determination is used to achieve the accuracy requirements, and to precisely geolocate the high-resolution datasets obtained by the LRO instruments. In addition to the tracking data most commonly used to determine spacecraft orbits in planetary missions (radiometric Range and Doppler), LRO benefits from two other types of orbital constraints, both enabled by the Lunar Orbiter Laser Altimeter (LOLA) instrument. The altimetric data collected as the instrument's primary purpose can be used to derive constraints on the orbit geometry at the times of laser groundtrack intersections (crossovers). The multi-beam configuration and high firing-rate of LOLA further improves the strength of these crossovers, compared to what was possible with the MOLA instrument onboard Mars Global Surveyor (MGS). Furthermore, one-way laser ranges (LR) between Earth International Laser Ranging Service (ILRS) stations and the spacecraft are made possible by the addition of a small telescope mounted on the spacecraft high-gain antenna. The photons received from Earth are transmitted to one LOLA detector by a fiber optics bundle. Thanks to the accuracy of the LOLA timing system, the precision of 5-s LR normal points is below 10cm. We present the first results of the Precision Orbit Determination (POD) of LRO through the commissioning and nominal phases of the mission. Orbit quality is discussed, and various gravity fields are evaluated with the new (independent) LRO radio tracking data. The altimetric crossovers are used as an independent data type to evaluate the quality of the orbits. The contribution of the LR data is assessed. Multi-arc solutions over entire months are presented, which allow to strengthen the LR data because fewer clock-related parameters need to be adjusted. Finally, a preliminary 1-month solution with altimetric crossover constraints is evaluated and discussed

Lemoine, F. G.; Mazarico, E.; Rowlands, D. D.; Torrence, M. H.; McGarry, J. F.; Neumann, G. A.; Mao, D.; Smith, D. E.; Zuber, M. T.

2010-05-01

17

Precise Method of Orbit Height Determination  

NASA Astrophysics Data System (ADS)

The problem of satellite orbit determination is a very important one, you can determine the orbit height of a low Earth orbiting (LEO) artificial satellite by using the satellite's apparent travel when the satellite appears to be near your local zenith, Or for most precise between two points of observation in earth. By using the determined orbit height, you can also determine the approximate orbit period of the satellite, this method takes advantage of the fact that the satellite's true velocity can be seen when it is nearly overhead. This paper illustrate how to obtain the height of the satellite using two observers method and by using MATLAB program then comparing this method with one observer method and illustrating how to increase the accuracy and take the measurement not limited to the local zenith only, but to any place of the orbit if you have an estimated period time for the satellite also these calculations depends on the data from NASA site.

Elbanna, Ahmed

18

Orbit determination and control for the European Student Moon Orbiter  

NASA Astrophysics Data System (ADS)

This paper presents the preliminary navigation and orbit determination analyses for the European Student Moon Orbiter. The severe constraint on the total mission ?v and the all-day piggy-back launch requirement imposed by the limited available budget, led to the choice of using a low-energy transfer, more specifically a Weak Stability Boundary one, with a capture into an elliptic orbit around the Moon. A particular navigation strategy was devised to ensure capture and fulfil the requirement for the uncontrolled orbit stability at the Moon. This paper presents a simulation of the orbit determination process, based on an extended Kalman filter, and the navigation strategy applied to the baseline transfer of the 2011-2012 window. The navigation strategy optimally allocates multiple Trajectory Correction Manoeuvres to target a so-called capture corridor. The capture corridor is defined, at each point along the transfer, by back-propagating the set of perturbed states at the Moon that provides an acceptable lifetime of the lunar orbit.

Zuiani, Federico; Gibbings, Alison; Vetrisano, Massimo; Rizzi, Francesco; Martinez, Cesar; Vasile, Massimiliano

2012-10-01

19

Precision Orbit Determination for the Lunar Reconnaissance Orbiter  

NASA Astrophysics Data System (ADS)

The U.S. Lunar Reconnaissance Orbiter (LRO) mission will be launched in October 2008, and will carry out a detailed mapping of the Moon using a science payload of multiple instruments, including the Lunar Orbiter Laser Altimeter (LOLA), and the Lunar Reconnaissance Orbiter Camera (LROC) (Chin, 2007). One of the primary goals of the LRO mission is develop a geodetic grid for the planet. A subsidiary goal is the improvement of the lunar gravity field. The environment for POD on LRO is especially challenging. The spacecraft will orbit the Moon at a mean altitude of 50 km, and the expected error from the Lunar Prospector series of gravity models (to degree 100 or to degree 150) can be expected to be hundreds of meters. LRO will be tracked by S Band Doppler from White Sands, New Mexico, and Dongara, Australia, as well as by one-way laser ranging from Satellite Laser Ranging (SLR) tracking stations on the Earth. However, unlike the Japanese lunar mission SELENE (Kaguya), no direct tracking will be available while the spacecraft is over the lunar farside. We review the status of orbit modelling for LRO, for both the geopotential modelling and the nonconservative force models, as well as anticipated improvements. We discuss the modelling for the one-way laser ranging observable, and how the data from the one-way laser ranging (LR) system will be acquired from selected stations of the global stations of the SLR network. We discuss the orbit determination strategies which we expect to implement on this mission, including the use of altimeter crossovers from the LOLA instrument to supplement the Earth-based tracking and we review the projected orbit determination accuracies that will be attainable.

Lemoine, Frank; Rowlands, David; McGarry, Jan; Neumann, Gregory; Chinn, Douglas; Mazarico, Erwan; Torrence, Mark

20

Determination and prediction of Magellan's orbit  

NASA Astrophysics Data System (ADS)

The Magellan spacecraft has been systematically mapping the surface of Venus since September 15, 1990, using a synthetic aperture radar. The spacecraft orbit about Venus is nearly polar, with an orbital period of 3.26 hours and periapsis altitude of 295 km. The radiometric measurements and the data reduction method used to determine and predict the spacecraft state are described. Orbit determination and prediction results are given for the first 146 days of mapping (through February 8, 1991, 60 percent of the first rotation of Venus). Orbit accuracy requirements of 150 meters in the radial position, and 1 km in the along-track and cross-track positions are shown to be met, but with exceptions. All error requirements were exceeded during a combined period of limited in-plane orbit observability due to earth-orbit relative geometry, and increased measurement noise due to superior conjunction.

Engelhardt, D. B.; McNamee, J. B.; Wong, S. K.; Bonneau, F. G.; Graat, E. J.; Haw, R. J.; Kronschnabl, G. R.; Ryne, M. S.

21

Orbit Determination from Minitrack Observations.  

National Technical Information Service (NTIS)

Although Minitrack observations are only accurate to about 1 minute of arc, accurate orbits have been obtained for a number of satellites. This is due to the excellent global coverage of the NASA Minitrack network. The accuracy obtained for eccentricity i...

R. H. Gooding

1966-01-01

22

Spacecraft orbit determination using GPS navigation solutions  

Microsoft Academic Search

The orbit determination using the GPS navigation solutions for the KOMPSAT-1 spacecraft has been studied. The Cowell method of special perturbation theories was employed to develop a precision orbit propagation, and the perturbations due to geopotential, the gravity of the Sun and the Moon, solid Earth tides, ocean tides, the Earth's dynamic polar motion, solar radiation pressure, and atmospheric drag

Jae-Cheol Yoon; Byoung-Sun Lee; Kyu-Hong Choi

2000-01-01

23

GPS orbit processing in support of low earth orbiter precise orbit determination  

Microsoft Academic Search

There are currently an increasing number of LEO missions incorporating dual frequency GPS receivers for Satellite to Satellite Tracking. The majority of LEO precise orbit determination (POD) strategies rely on high quality GPS orbits and clocks such as those supplied by the IGS Final product. The availability of these products may not satisfy operational requirements due to their ten day

I. Romero; H. Boomkamp; J. Dow; C. Garcia

2003-01-01

24

Short Arc Orbit Determination for Anna Satellite.  

National Technical Information Service (NTIS)

A differential orbit correction procedure and its application to observations distributed over short arcs of the geodetic satellite ANNA are presented in this report. Also included is an analysis of the accuracy achieved in determining the position and ve...

J. P. Rossoni P. Sconzo D. Winfield

1964-01-01

25

Formation Flying In Highly Elliptical Orbits Initializing the Formation.  

National Technical Information Service (NTIS)

In this paper several methods are examined for initializing formations in which all spacecraft start in a common elliptical orbit subsequent to separation from the launch vehicle. The tetrahedron formation used on missions such as the Magnetospheric Multi...

L. Mailhe C. Schiff S. Hughes

2000-01-01

26

Satellite-to-satellite tracking orbit determination  

Microsoft Academic Search

In the 1980's, low-earth-satellite orbits will be determined from one-way or relayed range and range-rate measurements to high-altitude orbiting spacecraft such as the two geo-synchronous satellites in the NASA Tracking and Data Relay Satellite System (TDRSS) and the 24 twelve-hour period, 63 deg inclination spacecraft in the DOD Global Positioning System (GPS). In this study, error analysis methods for satellite-to-satellite

B. T. Fang

1978-01-01

27

Comparison of four European orbit determination systems  

NASA Astrophysics Data System (ADS)

The objective of this paper is to present the activities and the main conclusions of the IOI (In-Orbit Infrastructure) Flight Dynamics Working Group. This IOIFDWG is an inter-agency working group composed of flight dynamics experts coming from the following space agencies: ASI, DLR, ESA and CNES. These agencies are in charge of elements of the future European orbital infrastructure such as the space station, the launcher, the vehicles, relay satellites or the ground control center. During the operations they will have to exchange flight dynamics data; therefore the main objective of the group was to analyze the compatibility of the orbit determination systems at the participating agencies. In order to identify the origin of possible discrepancies in the complex orbit determination process, the comparisons have been performed in three successive steps: first the orbit propagation software modules have been compared, then the tracking measurements modules have been compared and, finally the orbit estimation software modules themselves. After a short description of the software systems used at each agency, with their main features, this paper presents, for each step, the description of the tests and the main results. Then, the significant differences are discussed and in particular, the major contribution due to the atmospheric drag modeling is shown; finally, the main conclusions are summarized and recommendations for the exchange of state vectors are proposed including a list of data to be harmonized between agencies.

Alby, F.; Bianco, G.; Fourcade, J.; Gill, E.; Kirschner, M.; Luceri, V.; Mesnard, R.; Montenbruck, O.; Schneller, M.; Schoemaekers, J.

28

I: PRECISE ORBIT DETERMINATION AND GRAVITY FIELD MODELLING: Strategies for Precise Orbit Determination of Low Earth Orbiters Using the GPS  

NASA Astrophysics Data System (ADS)

Considerable experience accumulated during the past decade in strategies for processing GPS data from ground-based geodetic receivers. First experience on the use of GPS observations from spaceborne receivers for orbit determination of satellites on low altitude orbits was gained with the launch of TOPEX/POSEIDON ten years ago. The launch of the CHAMP satellite in July 2000 stimulated a number of activities worldwide on improving the strategies and algorithms for orbit determination for Low Earth Orbiters (LEOs) using the GPS. Similar strategies as for ground-based receivers are applied to data from spaceborne GPS receivers to determine high precision orbits. Zero- and double-differencing techniques are applied to obtain kinematic and/or reduced-dynamic orbits with an accuracy which is today at the decimeter level. Further developments in modeling and processing strategies will continuously improve the quality of GPS-derived LEO orbits in the near future. A significant improvement can be expected from fixing double-difference phase ambiguities to integer numbers. Particular studies focus on the impact of a combined processing of LEO and GPS orbits on the quality of orbits and the reference frame realization.

Hugentobler, U.; Beutler, G.

2003-07-01

29

Orbit Determination in the Pluto System  

NASA Astrophysics Data System (ADS)

The once simple binary system of Pluto and Charon has, until now, eluded a precise description of its orbital motion. The most important component that makes this system so difficult is a consequence of its fully relaxed spin-orbit state. The surface of Pluto has a highly variable albedo that also changes with time. These albedo variations lead to a shift of the photocenter relative to the center of the body. The synchronicity of the rotation of Pluto and the orbit of Charon couples the albedo pattern to the astrometry and lead, if uncorrected, to erroneous values for the orbital elements. In this presentation we will show results based on astrometry with the Hubble Space Telescope that now span nearly 20 years. We use two-body Keplerian orbit fits to describe the motions of all satellites as a tool to understand and remove the astrometric effects of the albedo pattern. The most immediate result of this work is a demonstration that the orbit of Charon is very close to circular (1-sigma limit is 3 km out of round). We also present an analysis of the degree to which albedo effects (spatial and temporal) impact the astrometry the resulting orbit determinations. These considerations show the value and necessity of combining photometric and astrometric data to further improve the dynamical description of this system. This work is a necessary precursor to upcoming New Horizons encounter with Pluto as well as our on-going work to determine the masses of the outer satellites. This work was supported by grants from NASA Planetary Astronomy and from the Space Telescope Science Institute.

Buie, Marc W.; Grundy, W. M.; Tholen, D. J.

2012-05-01

30

ROSACE orbit determination using telescope and CCD  

Microsoft Academic Search

This paper describes the ROSACE system, a low cost ground system using optical devices (telescope and CCD) in order to achieve high precision orbit determination. The elementary measurements are angular separations between the satellite spot and the dotted path of a known star. Those measurements are performed without any onboard equipment, thus allowing ROSACE to be used in contingency cases

Luc Maisonobe; Genevieve Campan; Pascal Brousse

1994-01-01

31

GPS-LEO orbiter occultation orbital analyses and event determination  

NASA Astrophysics Data System (ADS)

A good knowledge of the vertical profiles of temperature and humidity throughout the atmosphere are crucial to understand the present state of the Earth's atmosphere and it's modeling. The application of radio occultation technique has a heritage of over 2 decades in NASA's planetary exploration program to study the atmosphere of most of the major bodies in the solar system. Results from NASA's planetary program experiment have proven to be very effective at characterizing the atmosphere of a planet. However, the use of radio occultation technique to remote sensing the Earth's atmosphere is only practical to be implemented recently with the advent of the matured Global Positioning System (GPS). The GPS occultation technique is well suited to observe the Earth's atmosphere, due to it excellent geographical coverage, all weather capability, long-term stability, self-calibration and high vertical resolution. The GPS/MET (GPS Meteorology) experiment launched in April 1995 is the proof-of-concept of this technique. The results from this experiment is appealing and shown that the GPS occultation technique is a promising candidate to monitor the Earth's atmosphere. With the advancement of receiver technologies and lower system cost, the GPS occultation technique is a promising tool to predict the long-term climatic changes and numerical weather modeling of the Earth's atmosphere at a higher precision. This paper briefly describes the radio occultation concept and the GPS satellite systems, which form the basis understanding of this subject matter. This is followed by a detail description of the occultation geometries between the GPS satellites and a LEO orbiter. A method to determine the occultation event is discussed and thoroughly analyzed in terms of orbit inclinations, altitudes, receiver sampling rates, antenna positioning (aft and fore pointing), and antenna mask angles. A simulator is developed using MATLAB for the orbital analyses and occultation determination in 2-D and 3-D display and in GISO (Gall Isographic) map to give the overall picture on the total occultation events per day. Finally, results are presented and discussed.

Abdul Rashid, Z. A.; Cheng, P. P.

2003-04-01

32

Orbit determination of Tance-1 satellite using VLBI data  

NASA Astrophysics Data System (ADS)

On 30 December, 2003, China successfully launched the first satellite Tance-1 of Chinese Geospace Double Star Exploration Program, i.e. "Double Star Program (DSP)", on an improved Long March 2C launch vehicle. The Tance-1 satellite is operating at an orbit around the earth with a 550km perigee, 78000km apogee and 28.5 degree inclination.VLBI technique can track Tance-1 satellite or even far satellites such as lunar vehicles. To validate the VLBI technique in the on-going Chinese lunar exploration mission, Shanghai Astronomical Observatory (SHAO) organized to track the Tance-1 satellite with Chinese three VLBI stations: Shanghai, Kunming and Urumchi Orbit Determination (OD) of the Tance-1 satellite with about two days VLBI dada, and the capability of OD with VLBI data are studied. The results show that the VLBI-based orbit solutions improve the fit level over the initial orbit. The VLBI-delay-based orbit solution shows that the RMS of residuals of VLBI delay data is about 5.5m, and about 2.0cm/s for the withheld VLBI delay rate data. The VLBI-delay-rate-based orbit solution shows that the RMS of residuals of VLBI delay rate data is about 1.3cm/s, and about 29m for the withheld VLBI delay data. In the situation of orbit determination with VLBI delay and delay rate data with data sigma 5.5m and 1.3cm/s respectively, the RMS of residuals are 5.5,m and 2.0cm/s respectively. The simulation data assess the performance of the solutions. Considering the dynamic model errors of the Tance-1 satellite, the accuracy of the position is about km magnitude, and the accuracy of the velocity is about cm/s magnitude. The simulation work also show the dramatic accuracy improvement of OD with VLBI and USB combined.

Huang, Y.; Hu, X. G.; Huang, C.; Jiang, D. R.

2006-01-01

33

Orbit determination for the GOCE satellite  

NASA Astrophysics Data System (ADS)

Precise Orbit Determination (POD) for the Gravity field and steady-state Ocean Circulation Explorer (GOCE), the first core explorer mission by the European Space Agency (ESA), forms an integrated part of the so-called High-Level Processing Facility (HPF). Two POD chains have been set up referred to as quick-look Rapid and Precise Science Orbit determination or RSO and PSO, respectively. These chains make use of different software systems and have latencies of 1 day and 2 weeks, respectively, after tracking data availability. The RSO and PSO solutions have to meet a 3-dimensional (3D) position precision requirement of 50 cm and a few cm, respectively. The tracking data will be collected by the new Lagrange GPS receiver and the predicted characteristics of this receiver have been taken into account during the implementation phase of the two chains. This paper provides an overview of the two POD processing chains and includes a description of the required input, auxiliary and output products. Both chains have been tested with real data from the German CHAMP and the EUMETSAT MetOp satellites, which carry a BlackJack and GRAS GPS receiver, respectively. The consistency between CHAMP and MetOp orbit solutions computed with the final implementation of the different chains was found to be better than 10 cm in 3D position when use is made of high-quality GPS ephemeris and clock solutions. In addition, test results with data from a GOCE End-to-End (E2E) simulator which incorporates a model of the Lagrange receiver have been included. The differences between all orbit solutions was found to be of the order of a few cm for all directions. The precision requirements for the two chains were thus not only met with E2E simulated data, but also with real data from CHAMP and MetOp.

Visser, P. N. A. M.; van den Ijssel, J.; van Helleputte, T.; Bock, H.; Jäggi, A.; Beutler, G.; Švehla, D.; Hugentobler, U.; Heinze, M.

2009-03-01

34

From Ancient Paradoxes to Modern Orbit Determination  

NASA Astrophysics Data System (ADS)

In the 5th century BC, Zeno advanced a set of paradoxes to show motion and time are impossible, hence an illusion. The problem of motion has since driven much scientific thought and discovery, extending to Einstein's insights and the quantum revolution. To determine and predict the motion of remote objects within the solar system, a methodology has been refined over centuries. It integrates ideas from astronomy, physics, mathematics, measurement, and probability theory, having motivated most of those developments. Recently generalized and made numerically efficient, statistical orbit determination has made it possible to remotely fly Magellan and other spacecraft through the turbulent atmospheres of Venus and other planets while estimating atmospheric structure and internal mass distributions of the planet. Over limited time-scales, the methodology can predict the position of the Moon within a meter and asteroids within tens of meters -- their velocities at the millimeter per second level -- while characterizing the probable correctness of the prediction. Current software and networks disseminate such ephemeris information in moments; over the last 12 years, 10 million ephemerides have been provided by the Horizons system, at the request of 300000 different users. Applications range from ground and space telescope pointing to correlation with observations recorded on Babylonian cuneiform tablets. Rapid orbit updates are particularly important for planetary radars integrating weak small-body echoes moving quickly through the frequency spectrum due to relative motion. A loop is established in which the predicted delay-Doppler measurement and uncertainties are used to configure the radar. Both predictions are then compared to actual results, the asteroid or comet orbit solution improved, and the radar system optimally adjusted. Still, after 2500 years and tremendous descriptive success, there remain substantial problems understanding and predicting motion.

Giorgini, Jon D.

2008-09-01

35

Initial observations from the Lunar Orbiter Laser Altimeter (LOLA)  

NASA Astrophysics Data System (ADS)

As of June 19, 2010, the Lunar Orbiter Laser Altimeter, an instrument on the Lunar Reconnaissance Orbiter, has collected over 2.0 × 109 measurements of elevation that collectively represent the highest resolution global model of lunar topography yet produced. These altimetric observations have been used to improve the lunar geodetic grid to ˜10 m radial and ˜100 m spatial accuracy with respect to the Moon's center of mass. LOLA has also provided the highest resolution global maps yet produced of slopes, roughness and the 1064-nm reflectance of the lunar surface. Regional topography of the lunar polar regions allows precise characterization of present and past illumination conditions. LOLA's initial global data sets as well as the first high-resolution digital elevation models (DEMs) of polar topography are described herein.

Smith, David E.; Zuber, Maria T.; Neumann, Gregory A.; Lemoine, Frank G.; Mazarico, Erwan; Torrence, Mark H.; McGarry, Jan F.; Rowlands, David D.; Head, James W.; Duxbury, Thomas H.; Aharonson, Oded; Lucey, Paul G.; Robinson, Mark S.; Barnouin, Olivier S.; Cavanaugh, John F.; Sun, Xiaoli; Liiva, Peter; Mao, Dan-dan; Smith, James C.; Bartels, Arlin E.

2010-09-01

36

Laplacian Orbit Determination and Differential Corrections  

Microsoft Academic Search

Laplace's method is a standard for the calculation of a preliminary orbit. Certain modifications, briefly summarized, enhance its efficacy. At least one differential correction is recommended, and sometimes becomes essential, to increase the accuracy of the computed orbital elements. Difficult problems, lack of convergence of the differential corrections, for example, can be handled by total least squares or ridge regression.

Richard L. Branham

2005-01-01

37

Jason-2 Precise Orbit Determination : current status and future improvements  

NASA Astrophysics Data System (ADS)

The JASON-2 satellite was launched on June 20, 2008 to continue the series of spaceborne radar altimeter missions initiated with TOPEX-POESEIDON in 1992 and continued by its follow-on, JASON-1, starting in 2002. From the very beginning, Precise Orbit Determination (POD) has been a key component of the success of these satellite altimeter missions. In order to meet the 1.5 cm radial accuracy required for the operational precise orbits included in the Geophysical Data Record (GDR), both JASON satellites are equipped with three state-of-the-art track-ing systems: Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) , Satellite Laser Ranging (SLR), and Global Positioning System (GPS). Over the past 10 years, several improvements in the quality as well as in the spatial and the temporal coverage of these tracking data, together with the enhancements in models and parameterization techniques, have made it possible to achieve the "1-cm" goal. Today, JASON-2 orbits computed by various research groups compare at the sub-centimeter level in terms of radial RMS over a few days. A significant effort is now committed toward reducing the latency of the precise orbit products while maintaining a high level of accuracy and operational robustness. Most important, as the altimeter data set now spans over almost two decades, scientists are able to reveal small climate signals such as a 3mm/year rise of the global Mean Sea Level (MSL) as well as interannual fluctuations of few mm amplitude. To maintain this level of performance, new requirements on the long term drifts of all components of the measurement system of future altimeter missions are needed. In this context, the stability of the radial orbit error properties over several years is increasingly important. Typically, global RMS values can cover systematic variations that have a particular spatial and temporal coherence, and which are of particular interest for the altimeter data analysts. In particular, errors in the DORIS, SLR and GPS realizations of the terrestrial reference system in which orbit solutions are computed, mismodeled surface forces and temporal variations of the gravity field are fundamental contributors to the orbit error budget at the global and local scales. Two years after launch, this talk addresses these topics with an overview of JASON-2 POD performance, both in term of short term and long term accuracy, outlining past progress and prospects for future improvements.

Cerri, Luca

38

Multiprocessor implementation of algorithms for multisatellite orbit determination  

Microsoft Academic Search

Previous studies of parallel processing methods for use with satellite related, many parameter estimation problems indicate the need for faster numerical integration methods. Parallel numerical integration methods for use in satellite orbit determination were studied and tested. Several methods such as parallel Runge-Kutta schemes showed improvement over serial methods when tested on the two body problem. Existing orbit determination routines

Peter Borden Nagel

1999-01-01

39

TAOS Orbit Determination Results lJsing Global Positioning Satellites  

Microsoft Academic Search

Orbit determination results for the Air Force Phillips Laboratory's Technology for Autonomous Operational Survivability (TAOS) satellite using a Rockwell AST V Global Positioning System (GPS) receiver are presented in this paper. Under a cooperative effort, GPS orbit determination technology developed at Jet Propulsion Laboratory (JPL) has been transferred to the U.S. Air Force. JPL's post processing differential GPS software MIRAGE

Joseph R; Bobby G. Williams; Peter J. Wolff

40

Evaluation of Improved Spacecraft Models for GLONASS Orbit Determination  

Microsoft Academic Search

High-fidelity spacecraft models become more important as orbit determination strategies achieve greater levels of precision and accuracy. In this presentation, we assess the impacts of new solar radiation pressure and attitude models on precise orbit determination (POD) for GLONASS spacecraft within JPLs GIPSY-OASIS software. A new solar radiation pressure model is developed by empirically fitting a Fourier expansion to solar

J. P. Weiss; A. Sibthorpe; N. Harvey; Y. Bar-Sever; D. Kuang

2010-01-01

41

Analysis of high area-to-mass ratio (HAMR) GEO space object orbit determination and prediction performance: Initial strategies to recover and predict HAMR GEO trajectories with no a priori information  

NASA Astrophysics Data System (ADS)

Optical deep space surveys are focusing on the study of a class of near Geosynchronous (GEO) objects characterized by high area-to-mass ratio (HAMR). Consistent cataloging and study of these HAMR objects requires repeated follow-up and tracking. The combination of lunar-solar gravitation, unmodeled solar radiation pressure dynamics, thermal emissions, and possibly passive electrostatic charging of the object interacting with the weak magnetic field at GEO results in unknown perturbations to the its trajectory. When these effects are combined with their apparent dim, time-varying reflective light intensity magnitudes, correctly identifying/associating tracks to the HAMR object is non-trivial. The focus of this work is to quantify the effects of the unmodeled accelerations on the reconstructed and predicted HAMR trajectory. Optical angle tracking data for several candidate HAMR objects were reduced and analyzed, and compared with results derived from the reduction of simulated optical angles data generated from the same sites, over comparable durations and using known dynamical models. Comparison of the orbit determination results provides insight into the effects of unmodeled errors on the estimated orbit parameters and their associated uncertainties. The results conclude that the orbit errors resulting from unmodeled rotational dynamics are significant, and can require the addition of process noise to properly account for the force model uncertainties to the total state error distribution. The results further demonstrate that the longer term solar radiation pressure effects are well determined with adequate observations, but determination of shorter term variations due to rotational dynamics are dependent on the area-to-mass ratio, measurement quality and estimation sampling interval.

Kelecy, T.; Jah, M.

2011-09-01

42

Precise orbit determination for the GOCE satellite using GPS  

NASA Astrophysics Data System (ADS)

Apart from the gradiometer as the core instrument, the first ESA Earth Explorer Core Mission GOCE (Gravity field and steady-state Ocean Circulation Explorer) will carry a 12-channel GPS receiver dedicated for precise orbit determination (POD) of the satellite. The EGG-C (European GOCE Gravity-Consortium), led by the Technical University in Munich, is building the GOCE HPF (High-level Processing Facility) dedicated to the Level 1b to Level 2 data processing. One of the tasks of this facility is the computation of the Precise Science Orbit (PSO) for GOCE. The PSO includes a reduced-dynamic and a kinematic orbit solution. The baseline for the PSO is a zero-difference procedure using GPS satellite orbits, clocks, and Earth Rotation Parameters (ERPs) from CODE (Center for Orbit Determination in Europe), one of the IGS (International GNSS Service) Analysis Centers. The scheme for reduced-dynamic and kinematic orbit determination is based on experiences gained from CHAMP and GRACE POD and is realized in one processing flow. Particular emphasis is put on maximum consistency in the analysis of day boundary overlapping orbital arcs, as well as on the higher data sampling rate with respect to CHAMP and GRACE and on differences originating from different GPS antenna configurations. We focus on the description of the procedure used for the two different orbit determinations and on the validation of the procedure using real data from the two GRACE satellites as well as simulated GOCE data.

Bock, H.; Jäggi, A.; Švehla, D.; Beutler, G.; Hugentobler, U.; Visser, P.

43

Satellite laser ranging and orbit determination at Nottingham University  

Microsoft Academic Search

SODAPOP (Satellite Orbit Determination and Analysis Package Of Programs) is a computer software package which has been written and developed over seven years at Nottingham University. It is a complete SLR analysis suite, capable of precise orbit integration and the processing of both raw full-rate data and pre-processed normal points. It has been used to investigate a number of geophysical

V. Ashkenazi; C. J. Hill; T. Moore

1990-01-01

44

Determination of Space Station on-orbit nondestructive evaluation requirements  

NASA Astrophysics Data System (ADS)

NASA has recently initiated a reassessment of requirements for the performance of in-space nondestructive evaluation (NDE) of the International Space Station Alpha (ISSA) while on- orbit. given the on-orbit operating environment, there is a powerful motivation for avoiding inspection requirements. For example the ISSA maintenance philosophy includes the use of orbital replacement units (ORUs); hardware that is designed to fail without impact on mission assurance or safety. Identification of on-orbit inspection requirements involves review of a complex set of disciplines and considerations such as fracture control, contamination, safety, mission assurance, electrical power, and cost. This paper presents background discussion concerning on-orbit NDE and a technical approach for separating baseline requirements from opportunities.

Salkowski, Charles

1995-07-01

45

Preliminary Evaluation of Radio Data Orbit Determination Capabilities of China's First Lunar Orbiter  

NASA Astrophysics Data System (ADS)

Orbit determination accuracies with radio tracking of China's first lunar orbiter (Chang'e-I) have been investigated. The challenge is that China has no global deep space network. Furthermore, two stations couldn't take rang and range-rate data simultaneously due to the platform's capability. The orbit determination will mostly be based upon a short arc of data observed by a single station and no differenced radio data could be employed. To obtain preliminary estimates of such radio navigation capabilities, simulations has been carried out with batch filtering of conventional radio data from separated stations. Analysis results indicate that navigation accuracy is associated with the geometry of the ground stations. Therefore the orbit determination capabilities could be enhanced with the availability of overseas stations' radio data.

Liu, Y.; Yu, Z.; Dong, G.

46

The Bootstrap Estimation of the Accuracy of Preliminary Orbit Determination  

NASA Astrophysics Data System (ADS)

From the point of view of the non-parametric statistics, a general estimation method of the accuracy and con?dence interval of preliminary orbit determination is proposed for the occasion without any other information but observational data. Based on the bootstrap method, the estimation relies only on the observational data and does not require the precise orbit determination as a reference, or the assumption of normal distribution of observational errors. Numerical experiments show that this method is very simple in implementa- tion, and may serve as an easy accuracy evaluation for the preliminary orbit determination and for the follow-up employments.

Wang, Xin

2013-07-01

47

Space Capsule Recovery Orbit Determination System and Performance  

NASA Astrophysics Data System (ADS)

Space Capsule Recovery (SRE), a small satellite, completely recoverable capsule was launched by the Polar Satellite Launch Vehicle (PSLV-C7) from the Indian spaceport Sriharikota on 10th January 2007 at 04:09UT along with Indian Remore Sensing Satellite CARTOSAT-2 and two micro satellites namely Nano- Peheunsat and Lapantubsat. The satellite was put into an almost nominal orbit of (630 X 638)km with an inclination of 97.94deg. The main objective of the SRE missions was to conduct microgravity experiment, de- orbit and recover it in Indian waters. The spacecraft was de-boosted after the payload operations in the micro- gravity environment. This was achieved in two steps. SRE was first placed from the injected circular orbit to Repetitive Elliptical Orbit (REO) and subsequently de- boosted for reentry and recovery. This paper describes the S-band based orbit determination system for SRE and its performance during different phases of the mission. Comparison of the inertial navigation system (INS) and nominal orbit with the achieved/estimated orbit was made. Orbit determination system was executed successfully through out the mission. Relatively large residues were observed in measurements during OD process due to continuous thruster activity through out the mission.

Vighnesam, N. V.; Sonney, A.; Soni, P. K.

2008-08-01

48

Reduced-Dynamic Precise Orbit Determination for Low Earth Orbiters Based on Helmert Transformation  

NASA Astrophysics Data System (ADS)

A model based on Helmert transformation is presented in reduced-dynamic Precise Orbit Determination (POD). As an implementation, a reduced-dynamic POD approach was developed. The approach includes two steps: firstly, kinematic POD and then reduced-dynamic POD. Based on the approach, a set of programs were developed. POD of CHAMP (CHAllenging Minisatellite Payload) and GRACE (Gravity Recovery And Climate Experiment) was then carried out. Kinematic and reduced-dynamic POD for CHAMP and GRACE satellite over 2 weeks time show that reduced-dynamic orbits of CHAMP have a mean 3D RMS of 0.26m compared to PSO orbit of GFZ, and the mean 3D RMS of GRACE-A has the same value compared to GNV1B orbit of JPL. The 3D RMS is reduced by up to 40% compared to kinematic solutions.

Chen, Junping; Wang, Jiexian

49

GPS single-frequency orbit determination for low Earth orbiting satellites  

NASA Astrophysics Data System (ADS)

The determination of high-precision orbits for Low Earth Orbiting (LEO) satellites (e.g., CHAMP, GRACE, MetOp) is based on dual-frequency tracking data from onboard GPS receivers. The two frequencies allow it to eliminate the first order ionosphere effects on the level of the carrier phase measurement noise. Data screening and precise orbit determination (POD) procedures are optimized under the assumption of the availability of two frequencies. If only single-frequency data are available, the algorithms have to be modified to consider the ionospheric effect. We develop and study different approaches for POD with single-frequency data. Reduced-dynamic as well as kinematic POD techniques are considered. The potential of single-frequency POD in different environments is assessed by comparing the results with dual-frequency POD for LEOs orbiting at different orbital heights. Moreover, the impact of different data sampling rates on single-frequency POD is considered. Our study helps to define requirements for GPS receivers and POD algorithms for future LEO missions for which only moderate orbit accuracy is needed.

Bock, Heike; Jäggi, Adrian; Dach, Rolf; Schaer, Stefan; Beutler, Gerhard

50

Evaluation of Improved Spacecraft Models for GLONASS Orbit Determination  

NASA Astrophysics Data System (ADS)

High-fidelity spacecraft models become more important as orbit determination strategies achieve greater levels of precision and accuracy. In this presentation, we assess the impacts of new solar radiation pressure and attitude models on precise orbit determination (POD) for GLONASS spacecraft within JPLs GIPSY-OASIS software. A new solar radiation pressure model is developed by empirically fitting a Fourier expansion to solar pressure forces acting on the spacecraft X, Y, Z components using one year of recent orbit data. Compared to a basic “box-wing” solar pressure model, the median 24-hour orbit prediction accuracy for one month of independent test data improves by 43%. We additionally implement an updated yaw attitude model during eclipse periods. We evaluate the impacts of both models on post-processed POD solutions spanning 6-months. We consider a number of metrics such as internal orbit and clock overlaps as well as comparisons to independent solutions. Improved yaw attitude modeling reduces the dependence of these metrics on the “solar elevation” angle. The updated solar pressure model improves orbit overlap statistics by several mm in the median sense and centimeters in the max sense (1D). Orbit differences relative to the IGS combined solution are at or below the 5 cm level (1D RMS).

Weiss, J. P.; Sibthorpe, A.; Harvey, N.; Bar-Sever, Y.; Kuang, D.

2010-12-01

51

Expected orbit determination performance for the TOPEX/Poseidon mission  

NASA Astrophysics Data System (ADS)

Each of the components required for the computation of precise orbits for the TOPEX/Poseidon (T/P) spacecraft - gravity field modeling, nonconservative force modeling, and satellite tracking technologies - is examined. The research conducted in the Space Geodesy Branch at Goddard Space Flight Center in preparation for meeting the 13-cm radial orbit accuracy requirement for the T/P mission is outlined. New developments in modeling the earth's gravitational field and modeling the complex nonconservative forces acting on T/P are highlighted. The T/P error budget is reviewed, and a prelaunch assessment of the predicted orbit determination accuracies is summarized.

Nerem, R. S.; Putney, Barbara H.; Marshall, J. A.; Lerch, Francis J.; Pavlis, Erricos C.; Klosko, Steven M.; Luthcke, Scott B.; Patel, Girish B.; Williamson, Ronald G.; Zelensky, Nikita P.

1993-03-01

52

Orbit determination for the Mariner Mark II Comet Rendezvous/Asteroid Flyby mission - The orbiting phase  

NASA Astrophysics Data System (ADS)

The Comet Rendezvous/Asteroid Flyby (CRAF) mission is the first of the Mariner Mark II mission set, designed to explore the outer solar system. Major objectives of orbit determination will be determine the positions and masses of the comet and asteroid and the relative position of the spacecraft, which is important to accurate pointing of the scan platform on which the narrow angle camera and scientific instruments are positioned. Position prediction is also important, since continuous commuication with the spacecraft will not be possible. The small gravitational attractions and poorly known ephemerides of the comet and asteroid, and the small, slow spacecraft orbit about the comet, pose significant new problems for orbit determination. Results of simulations studying the effectiveness of key data types, the accuracies of estimates, and prediction capabilities, are presented.

Weeks, C. J.

1986-08-01

53

Evaluation of semiempirical atmospheric density models for orbit determination applications  

NASA Astrophysics Data System (ADS)

This paper presents the results of an investigation of the orbit determination performance of the Jacchia-Roberts (JR), mass spectrometer incoherent scatter 1986 (MSIS-86), and drag temperature model (DTM) atmospheric density models. Evaluation of the models was performed to assess the modeling of the total atmospheric density. This study was made generic by using six spacecraft and selecting time periods of study representative of all portions of the 11-year cycle. Performance of the models was measured for multiple spacecraft, representing a selection of orbit geometries from near-equatorial to polar inclinations and altitudes from 400 kilometers to 900 kilometers. The orbit geometries represent typical low earth-orbiting spacecraft supported by the Goddard Space Flight Center (GSFC) Flight Dynamics Division (FDD). The best available modeling and orbit determination techniques using the Goddard Trajectory Determination System (GTDS) were employed to minimize the effects of modeling errors. The latest geopotential model available during the analysis, the Goddard earth model-T3 (GEM-T3), was employed to minimize geopotential model error effects on the drag estimation. Improved-accuracy techniques identified for TOPEX/Poseidon orbit determination analysis were used to improve the Tracking and Data Relay Satellite System (TDRSS)-based orbit determination used for most of the spacecraft chosen for this analysis. This paper shows that during periods of relatively quiet solar flux and geomagnetic activity near the solar minimum, the choice of atmospheric density model used for orbit determination is relatively inconsequential. During typical solar flux conditions near the solar maximum, the differences between the JR, DTM, and MSIS-86 models begin to become apparent. Time periods of extreme solar activity, those in which the daily and 81-day mean solar flux are high and change rapidly, result in significant differences between the models. During periods of high geomagnetic activity, the standard JR model was outperformed by DTM. Modification of the JR model to use a geomagnetic heating delay of 3 hours, as used in DTM, instead of the 6.7-hour delay produced results comparable to or better than the DTM performance, reducing definitive orbit solution ephermeris overlap differences by 30 to 50 percent. The reduction in the overlap differences would be useful for mitigating the impact of geomagnetic storms on orbit prediction.

Cox, C. M.; Feiertag, R. J.; Oza, D. H.; Doll, C. E.

1994-05-01

54

Determination of Eros Physical Parameters for Near Earth Asteroid Rendezvous Orbit Phase Navigation  

NASA Astrophysics Data System (ADS)

Navigation of the orbit phase of the Near Earth steroid Rendezvous (NEAR) mission will re,quire determination of certain physical parameters describing the size, shape, gravity field, attitude and inertial properties of Eros. Prior to launch, little was known about Eros except for its orbit which could be determined with high precision from ground based telescope observations. Radar bounce and light curve data provided a rough estimate of Eros shape and a fairly good estimate of the pole, prime meridian and spin rate. However, the determination of the NEAR spacecraft orbit requires a high precision model of Eros's physical parameters and the ground based data provides only marginal a priori information. Eros is the principal source of perturbations of the spacecraft's trajectory and the principal source of data for determining the orbit. The initial orbit determination strategy is therefore concerned with developing a precise model of Eros. The original plan for Eros orbital operations was to execute a series of rendezvous burns beginning on December 20,1998 and insert into a close Eros orbit in January 1999. As a result of an unplanned termination of the rendezvous burn on December 20, 1998, the NEAR spacecraft continued on its high velocity approach trajectory and passed within 3900 km of Eros on December 23, 1998. The planned rendezvous burn was delayed until January 3, 1999 which resulted in the spacecraft being placed on a trajectory that slowly returns to Eros with a subsequent delay of close Eros orbital operations until February 2001. The flyby of Eros provided a brief glimpse and allowed for a crude estimate of the pole, prime meridian and mass of Eros. More importantly for navigation, orbit determination software was executed in the landmark tracking mode to determine the spacecraft orbit and a preliminary shape and landmark data base has been obtained. The flyby also provided an opportunity to test orbit determination operational procedures that will be used in February of 2001. The initial attitude and spin rate of Eros, as well as estimates of reference landmark locations, are obtained from images of the asteroid. These initial estimates are used as a priori values for a more precise refinement of these parameters by the orbit determination software which combines optical measurements with Doppler tracking data to obtain solutions for the required parameters. As the spacecraft is maneuvered; closer to the asteroid, estimates of spacecraft state, asteroid attitude, solar pressure, landmark locations and Eros physical parameters including mass, moments of inertia and gravity harmonics are determined with increasing precision. The determination of the elements of the inertia tensor of the asteroid is critical to spacecraft orbit determination and prediction of the asteroid attitude. The moments of inertia about the principal axes are also of scientific interest since they provide some insight into the internal mass distribution. Determination of the principal axes moments of inertia will depend on observing free precession in the asteroid's attitude dynamics. Gravity harmonics are in themselves of interest to science. When compared with the asteroid shape, some insight may be obtained into Eros' internal structure. The location of the center of mass derived from the first degree harmonic coefficients give a direct indication of overall mass distribution. The second degree harmonic coefficients relate to the radial distribution of mass. Higher degree harmonics may be compared with surface features to gain additional insight into mass distribution. In this paper, estimates of Eros physical parameters obtained from the December 23,1998 flyby will be presented. This new knowledge will be applied to simplification of Eros orbital operations in February of 2001. The resulting revision to the orbit determination strategy will also be discussed.

Miller, J. K.; Antreasian, P. J.; Georgini, J.; Owen, W. M.; Williams, B. G.; Yeomans, D. K.

1995-01-01

55

Precision orbit determination for the Geosat Exact Repeat Mission  

NASA Astrophysics Data System (ADS)

Precise ephemerides have been determined for the U.S. Navy Geosat Exact Repeat Mission (ERM) using an improved gravity-field model, PTGF-4A (Shum et al. 1989). The Geosat orbits were computed in a terrestrial reference system which is tied to the reference system defined by satellite laser ranging (SLR) to Lageos through a survey between the Tranet Doppler receiver and the SLR system located at Wettzell, FRG. The remaining Doppler tracking station coordinates were estimated simultaneously with the geopotential in the PTGF-4A solution. In this analysis, three continuous 17-day Geosat orbits, which were computed using the 46-station Tranet data and global altimeter crossover data, have a crossover residual rms of 20 cm, indicating that the Geosat radial orbit error is of the order of 20 cm. The orbits computed based on data collected by a 7-station OPNET tracking network and crossover data have the same level of accuracy.

Shum, C. K.; Yuan, D. N.; Ries, J. C.; Smith, J. C.; Schutz, B. E.

1990-03-01

56

From Ancient Paradoxes to Modern Orbit Determination  

Microsoft Academic Search

In the 5th century BC, Zeno advanced a set of paradoxes to show motion and time are impossible, hence an illusion. The problem of motion has since driven much scientific thought and discovery, extending to Einstein's insights and the quantum revolution. To determine and predict the motion of remote objects within the solar system, a methodology has been refined over

Jon D. Giorgini

2008-01-01

57

The Effect of Equatorial Spread F on Relative Orbit Determination of GRACE Using Differenced GPS Observations  

Microsoft Academic Search

In this paper, relative orbit of Low Earth Orbit satellites is determined using only GPS measurements and the effects of Equatorial Spread-F (ESF), that is one of biggest ionospheric irregularities, are investigated. First, relative orbit determiation process is constructed based on doubly differenced GPS observations. In order to see orbit determination performance, relative orbit of two GRACE satellites is estimated

Kyoung-Min Roh; Hermann Luehr; Sang-Young Park; Jung-Ho Cho

2009-01-01

58

Implementation of a low-cost, commercial orbit determination system  

NASA Astrophysics Data System (ADS)

Traditional satellite and launch control systems have consisted of custom solutions requiring significant development and maintenance costs. These systems have typically been designed to support specific program requirements and are expensive to modify and augment after delivery. The expanding role of space in today's marketplace combined with the increased sophistication and capabilities of modern satellites has created a need for more efficient, lower cost solutions to complete command and control systems. Recent technical advances have resulted in commercial-off-the-shelf products which greatly reduce the complete life-cycle costs associated with satellite launch and control system procurements. System integrators and spacecraft operators have, however, been slow to integrate these commercial based solutions into a comprehensive command and control system. This is due, in part, to a resistance to change and the fact that many available products are unable to effectively communicate with other commercial products. The United States Air Force, responsible for the health and safety of over 84 satellites via its Air Force Satellite Control Network (AFSCN), has embarked on an initiative to prove that commercial products can be used effectively to form a comprehensive command and control system. The initial version of this system is being installed at the Air Force's Center for Research Support (CERES) located at the National Test Facility in Colorado Springs, Colorado. The first stage of this initiative involved the identification of commercial products capable of satisfying each functional element of a command and control system. A significant requirement in this product selection criteria was flexibility and ability to integrate with other available commercial products. This paper discusses the functions and capabilities of the product selected to provide orbit determination functions for this comprehensive command and control system.

Corrigan, Jim

1994-11-01

59

GPS single-frequency orbit determination for low Earth orbiting satellites  

NASA Astrophysics Data System (ADS)

The determination of high-precision orbits for Low Earth Orbiting (LEO) satellites (e.g., CHAMP, GRACE, MetOp-A) is based on dual-frequency tracking data from on-board GPS (Global Positioning System) receivers. The two frequencies allow it to eliminate the first order ionosphere effects. Data screening and precise orbit determination (POD) procedures are optimized under the assumption of the availability of two frequencies. If only single-frequency data is available, the algorithms have to be modified to consider the ionospheric effect. We develop and study different approaches for POD with single-frequency data. Reduced-dynamic as well as kinematic POD techniques using pseudorange and carrier phase GPS data are considered. One week of data in the year 2007 is used to assess the potential of single-frequency POD in different environments by comparing the results with dual-frequency POD for LEOs orbiting the Earth in different heights. Data from the two GRACE and the MetOp-A satellites is processed for this purpose. Moreover, the impact of different data sampling rates on single-frequency POD is considered. For this period with low solar activity a 3D orbit accuracy of 1 dm could be reached for one of the GRACE satellites. It could be shown that it is necessary to have a high data sampling of 10 s or more available when the impact of the ionosphere is high due to low altitude of the satellite or high solar activity. Our study helps to define requirements for GNSS (Global Navigation Satellite System) receivers and POD algorithms for future LEO missions for which only moderate orbit accuracy of about one to few decimeter is needed.

Bock, H.; Jäggi, A.; Dach, R.; Schaer, S.; Beutler, G.

2009-03-01

60

Prevalence and Nature of Systemic Involvement and Stage at Initial Examination in Patients With Orbital and Ocular Adnexal Lymphoma  

Microsoft Academic Search

Objective: To determine the stage at initial examina- tion and the prevalence of systemic involvement in pa- tients with orbital and ocular adnexal lymphoma. Methods: The medical records of all patients with or- bital and ocular adnexal lymphoma treated in a recent 7-year period were reviewed for stage at initial exami- nation, highest stage during the follow-up period, and recurrence-free

Elham Hatef; Dianna Roberts; Peter McLaughlin; Barbara Pro; Bita Esmaeli

2007-01-01

61

Atypical Presentation of Orbital Pseudotumor with Visual Loss as an Initial Manifestation  

PubMed Central

Background An orbital pseudotumor typically presents with periorbital pain, cranial nerve palsies and proptosis. Although visual deterioration is not unexpected in this pathology, its presentation solely with visual loss is unusual. Case Report In this short report, we summarize a case of orbital pseudotumor which presented solely with a decrease in visual acuity, and discuss the clinical and radiological findings. Conclusions This atypical presentation likely resulted from the orbital pseudotumor originating in the optic foramen, leaving the neurovascular structures of the superior orbital fissure untouched initially. In the early clinical period, an orbital pseudotumor may manifest itself solely by visual loss. It should therefore be included in the differential diagnosis of visual pathologies-even in the absence of orbital pain and symptoms related to ocular movements.

Turkoglu, Recai

2011-01-01

62

Precision orbit determination at the NASA Goddard Space Flight Center  

Microsoft Academic Search

The GEODYN Computer program has been developed by the Geodynamics Branch at the NASA Goddard Space Flight Center (GSFC) for accurate satellite orbit and tracking data analysis. The software is currently used for baseline solutions for the Crustal Dynamic Project (Smith et al. \\/1\\/), gravity field determination for the TOPEX\\/POSEIDON mission (Marsh et al. \\/2\\/), SEASAT and LAGEOS data analysis,

B. Putney; R. Kolenkiewicz; D. Smith; P. Dunn; M. H. Torrence

1990-01-01

63

Modeling GPS satellite attitude variation for precise orbit determination  

Microsoft Academic Search

High precision geodetic application of the Global Positioning System (GPS) require highly precise ephemerides of the GPS satellites. An accurate model for the non-gravitational forces on the GPS satellites is a key to high quality GPS orbit determination, especially in long arcs. In this paper the effect of the satellite solar panel orientation error is investigated. These effects are approximated

D. Kuang; H. J. Rim; B. E. Schutz; P. A. M. Abusali

1996-01-01

64

Topex/Poseidon Precision Orbit Determination Production and Expert System.  

National Technical Information Service (NTIS)

TOPEX/Poseidon (T/P) is a joint mission between NASA and the Centre National d'Etudes Spatiales (CNES), the French Space Agency. The TOPEX/Poseidon Precision Orbit Determination Production System (PODPS) was developed at Goddard Space Flight Center (NASA/...

B. Putney N. Zelensky S. Klosko

1993-01-01

65

Modeling GPS satellite attitude variation for precise orbit determination  

Microsoft Academic Search

High precision geodetic applications of the Global Positioning System (GPS) require highly precise ephemerides of the GPS satellites. An accurate model for the non-gravitational forces on the GPS satellites is a key to high quality GPS orbit determination, especially in long arcs. In this paper the effect of the satellite solar panel orientation error is investigated. These effects are approximated

D. Kuang; H. J. Rim; B. E. Schutz; P. A. M. Abusali

1996-01-01

66

Geos-C Orbit Determination with Satellite to Satellite Tracking.  

National Technical Information Service (NTIS)

The feasibility of employing satellite to satellite tracking in lieu of ground based tracking to satisfy the orbit determination requirements of the GEOS-C mission was studied. It is shown that with proper estimation procedures it is possible to obtain fr...

P. Argentiero

1974-01-01

67

GIOVE Orbit and Clock Determination Based on the CONGO Network  

NASA Astrophysics Data System (ADS)

As a prototype for the satellites of the future European Global Navigation Satellite System (GNSS) Galileo, the European Space Agency (ESA) launched two satellites (GIOVE-A and GIOVE-B) as part of the Galileo in Orbit Validation Element (GIOVE). To gain experience with the signals transmitted by these satellites and to estimate satellite orbit and clock parameters, a global network of GIOVE-capable receivers was established. This Cooperative Network for GIOVE Observations (CONGO) is operated by Deutsches Zentrum für Luft- und Raumfahrt (DLR, Oberpfaffenhofen, Germany) and Bundesamt für Kartographie und Geodäsie (BKG, Frankfurt, Germany) in cooperation with several local station hosts. The CONGO network currently consists of 10 globally distributed stations providing their observations in real-time. This network is used by Technische Universität München for an operational daily orbit and clock determination of the GIOVE satellites including orbit predictions. The strategy of the combined GPS and GIOVE processing is presented. The quality of the estimated GIOVE satellite orbits is evaluated by orbit fits and satellite laser ranging (SLR). The quality of the GIOVE satellite clocks, in particular the hydrogen maser of GIOVE-B, is discussed. As three different receiver types and two different satellite systems are considered in the CONGO processing, a special focus has to be put on the biases between the different receivers and GNSSs. Additionally, DLR's Real-Time Clock Estimation (RETICLE) system has been extended to provide clock offset estimates for the GIOVE satellites based on the real-time data streams from the CONGO network. The GIOVE clocks are estimated based on the predicted orbits mentioned above. The paper introduces the real-time clock estimation process and presents real-time clock results.

Steigenberger, Peter; Hauschild, André; Montenbruck, Oliver; Hugentobler, Urs; Hessels, Uwe; Weber, Georg; Noack, Thoralf

2010-05-01

68

Expected orbit determination performance for the TOPEX/Poseidon mission  

SciTech Connect

The TOPEX/Poseidon (T/P) mission, launched during the summer of 1992, has the requirement that the radial component of its orbit must be computed to an accuracy of 13 cm root-mean-square (rms) or better, allowing measurements of the sea surface height to be computed to similar accuracy when the satellite height is differenced with the altimeter measurements. This will be done by combining precise satellite tracking measurements with precise models of the forces acting on the satellite. The Space Geodesy Branch at Goddard Space Flight Center (GSFC), as part of the T/P precision orbit determination (POD) Team, has the responsibility within NASA for the T/P precise orbit computations. The prelaunch activities of the T/P POD Team have been mainly directed towards developing improved models of the static and time-varying gravitational forces acting on T/P and precise models for the non-conservative forces perturbing the orbit of T/P such as atmospheric drag, solar and Earth radiation pressure, and thermal imbalances. The radial orbit error budget for T/P allows 10 cm rms error due to gravity field mismodeling, 3 cm due to solid Earth and ocean tides, 6 cm due to radiative forces, and 3 cm due to atmospheric drag. A prelaunch assessment of the current modeling accuracies for these forces indicates that the radial orbit error requirements can be achieved with the current models, and can probably be surpassed once T/P tracking data are used to fine tune the models. Provided that the performance of the T/P spacecraft is nominal, the precise orbits computed by the T/P POD Team should be accurate to 13 cm or better radially.

Nerem, R.S.; Putney, B.H.; Marshall, J.A.; Lerch, F.J. (NASA/Goddard Space Flight Center, Greenbelt, MD (United States)); Pavlis, E.C. (Univ. of Maryland, College Park (United States)); Klosko, S.M.; Luthcke, S.B.; Patel, G.B.; Williamson, R.G.; Zelensky, N.P.

1993-03-01

69

Precise orbit determination of SPOT platform with DORIS  

NASA Astrophysics Data System (ADS)

DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) is a new precise orbit determination system developed by CNES to meet the high accuracy requirement of oceanographic altimetric missions of TOPEX/Poseidon. The system is based upon a worldwide network of about 50 ground transmitting beacons, a Doppler receiver onboard of the satellite, a ground segment to control the system and a new software called ZOOM to compute the orbit. To prepare the DORIS operational applications and to access the in flight performances, a first DORIS receiver was put on SPOT2 platform, the network of orbitography beacons was deployed, and the ZOOM software was tested with actual data. Since the SPOT2 launch of January 22, 1990, improvements have been made in orbit computation. The paper emphasizes the major points which contribute to high precision objectives, during the first year of DORIS/SPOT2 life.

Nouel, F.; Berthias, J. P.; Broca, P.; Deleuze, M.; Guitart, A.; Laudet, P.; Pierret, C.; Piuzzi, A.; Valorge, C.

1992-08-01

70

Theoretical study of the effect of atmospheric refraction correction on orbit determination accuracy of Symphonie in geostationary orbit  

Microsoft Academic Search

An error analysis program was used to determine the effect of atmospheric refraction correction on the orbit determination accuracy of the Symphonie satellite. It is found that the refraction correction has a unique effect on the determination of satellite length, irrespective of tracking strategy. The effect on other orbital elements depends on tracking strategy.

A. Leibold

1976-01-01

71

A simple procedure to extend the Gauss method of determining orbital parameters from three to N points  

NASA Astrophysics Data System (ADS)

A simple procedure is developed to determine orbital elements of an object orbiting in a central force field which contribute more than three independent celestial positions. By manipulation of formal three point Gauss method of orbit determination, an initial set of heliocentric state vectors r i and dot{{r}}i is calculated. Then using the fact that the object follows the path that keep the constants of motion unchanged, I derive conserved quantities by applying simple linear regression method on state vectors r i and dot{{r}}i. The best orbital plane is fixed by applying an iterative procedure which minimize the variation in magnitude of angular momentum of the orbit. Same procedure is used to fix shape and orientation of the orbit in the plane by minimizing variation in total energy and Laplace Runge Lenz vector. The method is tested using simulated data for a hypothetical planet rotating around the sun.

Mirtorabi, Taghi

2013-10-01

72

COS FUV Initial On-Orbit Turn-On  

NASA Astrophysics Data System (ADS)

This proposal specifies the procedure for SMOV initial HV turn-on and ramp-up of the COS FUV detector. {The FUV will have been commanded to its Operate state to support execution of proposal 11353.} The procudure is detailed in the Observing Description, but in summary, the following is done: The initial transition from FUV Operate to HVLow is broken into two parts, with a gap of 4 hours between turning on the HV and ramping to the HVLow {SAA} voltage. This will be followed by 5 cycles of HV ramp-up and return to HVLow. Cycles will ramp up to successively higher {magnitude} voltage, with the fifth cycle going to the nominal operating values. There will be a gap of at least 4 hours between cycles. All HV ramp-up will be done at 10 sec per HV "step". The step rate and cycle voltage values {for Sements A and B} must be patched in FSW in each cycle prior to the HV ramp commanding. Memory monitors will be set on the patched memory locations. Immediately after any HV commanding, and 4 hours after ramp-up commanding, the DCE memory will be dumped. Immediately after HV ramp-up commanding higher than HVLow, short DARK & WAVE exposures will be obtained. Visits 01 and 02, and all the subsequent even numbered visits {the ones 4 hours after HV ramp-ups}, end with NSSC-1 COS event flag 3 being set. If the flag remains set, subsequent FUV commanding will be skipped. Thus, Operations Requests must be in place to clear the flag prior to those subsequent visits. Real-time monitoring of the telemetry will be used to guide the decisions whether or not to clear the flag. The final visit {13} provides a scheduled final opportunity to clear flag 3, and if the flag is cleared, initiates nominal FUV HV commanding and requests a DARK exposure. Supports Activity COS-23;

Welty, Alan

2008-07-01

73

TRACE trajectory analysis and orbit determination program. Volume 13: Square root information filtering and smoothing  

Microsoft Academic Search

The TRACE Trajectory Analysis and Orbit Determination Program is a general purpose orbital analysis program. It was developed specifically to assist technical personnel in the analysis and design of satellite orbits and tracking systems. Volume 13 is a technical reference for the square root information filtering and smoothing (SRIF\\/S) capabilities, which are used for high precision orbit determination and error

L. A. Campbell

1991-01-01

74

Galileo orbit determination for the Gaspra asteroid encounter  

NASA Astrophysics Data System (ADS)

This paper presents an overview of the orbit determination for Galileo's epochal encounter with the asteroid Gaspra on October 29, 1991. Topics discussed are a ground-based observation campaign to improve Gaspra's ephemeris before encounter, and the use of optical navigation together with Doppler and range data. The paper concludes by noting the steady improvement in the B-plane dispersions during the two months prior to encounter.

Kallemeyn, P. H.; Haw, R. J.; Pollmeier, V. M.; Nicholson, F. T.

1992-08-01

75

Precision Assessment of Near Real Time Precise Orbit Determination for Low Earth Orbiter  

NASA Astrophysics Data System (ADS)

The precise orbit determination (POD) of low earth orbiter (LEO) has complied with its required positioning accuracy by the double-differencing of observations between International GNSS Service (IGS) and LEO to eliminate the common clock error of the global positioning system (GPS) satellites and receiver. Using this method, we also have achieved the 1 m positioning accuracy of Korea Multi-Purpose Satellite (KOMPSAT)-2. However double-differencing POD has huge load of processing the global network of lots of ground stations because LEO turns around the Earth with rapid velocity. And both the centimeter accuracy and the near real time (NRT) processing have been needed in the LEO POD applications--atmospheric sounding or urgent image processing--as well as the surveying. An alternative to differential GPS for high accuracy NRT POD is precise point positioning (PPP) to use measurements from one satellite receiver only, to replace the broadcast navigation message with precise post processed values from IGS, and to have phase measurements of dual frequency GPS receiver. PPP can obtain positioning accuracy comparable to that of differential positioning. KOMPSAT-5 has a precise dual frequency GPS flight receiver (integrated GPS and occultation receiver, IGOR) to satisfy the accuracy requirements of 20 cm positioning accuracy for highly precise synthetic aperture radar image processing and to collect GPS radio occultation measurements for atmospheric sounding. In this paper we obtained about 3-5 cm positioning accuracies using the real GPS data of the Gravity Recover and Climate Experiment (GRACE) satellites loaded the Blackjack receiver, a predecessor of IGOR. And it is important to reduce the latency of orbit determination processing in the NRT POD. This latency is determined as the volume of GPS measurements. Thus changing the sampling intervals, we show their latency to able to reduce without the precision degradation as the assessment of their precision.

Choi, Jong-Yeoun; Lee, Sang-Jeong

2011-03-01

76

Orbit determination error analysis for satellite-satellite\\/ground tracking systems  

Microsoft Academic Search

A statistical error analysis was made for the orbit determination process, where the observations from ground stations and\\/or from some orbiting spacecrafts, employed for tracking, are used. The various errors included in the analysis are errors in the tracking systems, uncertainty in the orbit model, inaccuracies of the ground station coordinates, and errors in the orbital elements of the tracking

C. K. Rajasingh

1977-01-01

77

Precise Orbit Determination of Earth's Satellites for Climate Change Investigation  

NASA Astrophysics Data System (ADS)

The tremendous improvement of the gravity field models which we are achieving with the last Earth's satellite missions like, CHAMP, GRACE and GOCE devoted to its recovery could make feasibile the use of precise orbit determination (POD) of Earth satellites as a tool for sensing global changes of some key atmosphere parameters like refractivity and extinction. Such improvements indeed, coupled with the huge number of running Earth's satellites and combinations of their orbital parameters (namely the nodes) in a gravity field free fashion (hereafter GFF) can magnify the solar radiation pressure acting on medium earth orbit satellites :GPS, Etalon and, in near real future GALILEO and its smooth modulation through the Earth's atmosphere (penumbra). We would remind that The GFF technique is able to cancel out with "n" satellite orbital parameters the first n-1 even zonal harmonics of the gravity field. Previously it was demonstrated that the signal we want to detect could in principle emerge from the noise threshold but, more refined models of the atmosphere would be needed to perform a more subtle analysis. So we will re-compute the signal features of penumbra by applying more refined atmospheric models. The analysis will be performed by including in GFF Earth's satellites equipped with DORIS systems (Jason, Spot 2-3-4-5, ENVISAT etc.) other than those ranged with SLR and GPS. The introduction of DORIS tracked satellites indeed will allow to cancel higher and higher order of even zonal harmonics and will make still more favourable the signal to noise budget. The analysis will be performed over a time span of at least few tens of years just to enhance probable climate signatures.

Vespe, Francesco

78

Orbit/Attitude Determination and Control for the UMRSAT Mission  

NASA Astrophysics Data System (ADS)

As satellite missions become increasingly complex, a need for accurate determination and control systems using low cost hardware arises. This is especially true for university satellite programs such as the University of Missouri - Rolla satellite design team, or UMR SAT. With limited resources, mission success relies on creative and innovative hardware and software designs. This paper describes the development of control algorithms that will be used onboard the UMR SAT satellite pair. Using novel attitude and orbit control techniques and magnetometer-only attitude determination, the mission can be accomplished with low cost COTS hardware. The UMR developed ?-D controller will be used to facilitate the attitude and formation control, and the ?-D filter will be used for orbit determination. The ?-D technique has been successfully applied to a wide variety of applications ranging from wing aeroelastic flutter suppression to hit-to-kill missile autopilot design to reusable launch vehicle control. The results of each application have been very promising and show the potential improvement over pre-existing control techniques offered by the ?-D method. Along with software development, this paper also provides high fidelity simulations of the determination and control system are presented to demonstrate the effectiveness of the algorithms.

Dancer, M. W.; Searcy, J. D.

2008-08-01

79

Initial on-orbit radiometric calibration of the Suomi NPP VIIRS reflective solar bands  

NASA Astrophysics Data System (ADS)

The on-orbit radiometric response calibration of the VISible/Near InfraRed (VISNIR) and the Short-Wave InfraRed (SWIR) bands of the Visible/Infrared Imager/Radiometer Suite (VIIRS) aboard the Suomi National Polar-orbiting Partnership (NPP) satellite is carried out through a Solar Diffuser (SD). The transmittance of the SD screen and the SD's Bidirectional Reflectance Distribution Function (BRDF) are measured before launch and tabulated, allowing the VIIRS sensor aperture spectral radiance to be accurately determined. The radiometric response of a detector is described by a quadratic polynomial of the detector's digital number (dn). The coefficients were determined before launch. Once on orbit, the coefficients are assumed to change by a common factor: the F-factor. The radiance scattered from the SD allows the determination of the F-factor. In this Proceeding, we describe the methodology and the associated algorithms in the determination of the F-factors and discuss the results.

Lei, Ning; Wang, Zhipeng; Fulbright, Jon; Lee, Shihyan; McIntire, Jeff; Chiang, Kwofu; Xiong, Xiaoxiong

2012-09-01

80

Application of variance component estimation to precise orbit determination for ERS-2  

NASA Astrophysics Data System (ADS)

Variance component estimation (VCE) is applied to precise orbit determination (POD) of the ERS-2 satellite. Twenty 5-day long arcs in the early three months in 1998 were calculated using the SLR and PRARE data. In the data the adjacent arcs overlap for two days except the intervals for orbit maneuver. The effect of VCE orbit determination on the calculation is investigated by an analysis of residuals and comparison of overlapping arcs, and the mean a posteriori standard deviation of each group of measured residuals is given. It is shown by the residuals analysis that the fitting of the measurements is significantly improved by VCD. However, according to Abbey criterion, VCD is not able to eliminate the systematic errors due to errors in the dynamic and geometric models. The results of the comparison of the overlapping arcs show that (1) VCE reduces the mean range deviation of overlapping arcs, especially where there are obviously unreasonable deviations, so that the orbit obtained has a more uniform precision; (2) By using VCE, adjacent arcs tend to close up and this is more apparent in the transverse direction. From the mean a posteriori standard error of each group of measurements, it can be seen that as far as the single normal point measurement is concerned, the data of some SLR stations are more important than other measurements in POD calculation. Generally speaking, determination of weighting by using VCE is more reasonable than by using initial standard deviation.

Zhang, Fei-peng; Huang, Cheng; Feng, Chu-gang; Dong, Xiao-jun; Liao, Xin-hao

2001-10-01

81

Detection and orbit determination of tethered satellite systems  

NASA Astrophysics Data System (ADS)

A systematic algorithm for determining which satellites are tether-connected is described. It is assumed that observations in the forms of range, azimuth and elevation data, for several satellites, including singles, two-satellite tethered systems, and three-satellite tethered systems are available. The detection process is performed using the dynamic model and a minimum variance batch filter to process simulated observations over a period of ten minutes. In the process, the estimated acceleration per unit length between pairs of satellites due to a tether is assumed to be constant during this "short arc" observation period. The values of acceleration per unit length are used as indicators of which pairs of satellites are connected. Use of the algorithm is illustrated by applying it to a set of nine satellites that includes two tethered pairs. For small librational motion of the tethered pairs, values of the constraint accelerations per unit length that are large relative to zero were obtained. On the other hand, values very close to zero were obtained for un-tethered pairs. These results indicate that non-librating, two-satellite tethered systems can be successfully identified (i.e. "detected") when perfect and small-level noise corrupted observations are available. However, identification of two-satellite tethered systems with the large libration angle, or those with a very short tether when medium and large levels of noise are present is more difficult. The detection of a three-satellite tethered system was also performed with the same algorithm. After detection of a two-satellite tethered system (or three-satellite) is performed, its orbit may be determined by using long arcs of observations (over one orbital period). In the long arc estimation process used herein, the constraint acceleration per unit length is considered to be a time-varying variable. For an exemplary set of satellites, results for long arc estimations were obtained. Since observation data for both satellites in a tethered system were used and few approximations of the tether dynamics were made, the results are very accurate. The orbital motion of the three-satellite tether system was found to be similar to that of two-satellite tether system when the librational motion was small. The major difference was that larger tether accelerations were present due to another tether connected body. It should be relatively easy to incorporate the new method for detection and motion determination developed in this study into a general orbit determination process. (Abstract shortened by UMI.)

Choe, Nammi Jo

82

Galileo orbit determination for the Venus and Earth-1 flybys  

NASA Astrophysics Data System (ADS)

This paper presents the orbit determination strategy and results in navigating the Galileo spacecraft from launch through its Venus and first earth flybys. Many nongravitational effects were estimated, including solar radiation pressure, small velocity impulses from attitude changes and eight trajectory correction maneuvers. Tracking data consisted of S-Band Doppler and range. The fitting of Doppler was difficult since one of the cpacecraft's two antennas was offset from the spin axis, thus producing the sinusoidal velocity fluctuation seen in the data. Finally, Delta Differential One-way Range data was used during the last three months of the earth approach to help deliver the spacecraft to within desired accuracy.

Kallemeyn, P. H.; Haw, R. J.; Pollmeier, V. M.; Nicholson, F. T.; Murrow, D. W.

1992-08-01

83

Samos 2 (1961 alpha 1): Orbit determination and analysis at 31:2 response  

NASA Astrophysics Data System (ADS)

Samos 2, 1961 alpha 1, launched on 31 January 1961, was the first satellite to enter a Sun-synchronous orbit at an inclination of 97.4 deg. The initial perigee and apogee heights were 474 km and 557 km respectively, the initial period was 94.97 min and the satellite decayed 21 October 1973 after more than 12 years in orbit. Samos 2 passed through the condition of 31:2 resonance in June 1971 and orbital parameters were determined at 22 epochs from 1974 observations using the RAE orbit refinement program, PROP, between mid April and mid September 1971. The variations of inclination and eccentricity during this time were analyzed and values for six lumped 31st order harmonic coefficients in the geopotential were obtained. These lumped harmonic coefficients were compared with those derived from the individual coefficients of order 31 and appropriate degrees, from the most recent Goddard Earth Model, GEM 10C. The decrease in inclination between launch and 1971 was examined. It is found to be caused mainly by a near resonant solar gravitational perturbation.

Walker, D. M. C.

1980-02-01

84

The Determination of the Orbits of the Outer Jovian Satellites  

NASA Astrophysics Data System (ADS)

The eight outer satellites of Jupiter may be divided into two groups of four. Those in the first group, Himalia, Elara, Lysithea, and Leda, are in high inclination direct orbits between 11 and 12 million km from Jupiter. Those in the second group, Pasiphae, Sinope, Carme, and Ananke, are in high inclination retrograde orbits between 20 and 24 million km from Jupiter. Rocher and Chapront (1996 A&A 311, 710) have published orbits for Himalia, Elara, Pasiphae, and Sinope fit to observations from their discoveries through 1993. Apparently, only Herget (1968 AJ, 73, 737) has published orbits for Lysithea, Carme, and Ananke. These were later extended by Aksnes (1973 AJ, 78, 121) who also determined an orbit for Leda (1978 AJ, 83, 1249). To support the Galileo Project, I fit numerical integrations of all eight satellites to observations from their discoveries through 1994. I have extended the fit to include observations through January 2000. Among the additional observations are highly accurate CCD measurements obtained at both the US Naval Observatory, Flagstaff Station (Stone & Harris, to appear in AJ), and JPL's Table Mountain Observatory (Owen, private communication). The table below gives the number of observations of each satellite and the root-mean-square (rms) of the post-fit residuals. Observation Residual Statistics - rms Timespan Satellite ? ? \\cos? No. ? ? 1894-2000 Himalia 736 1\\farcs18 737 0\\farcs92 1905-2000 Elara 345 0\\farcs95 345 0\\farcs82 1908-2000 Pasiphae 472 1\\farcs13 472 0\\farcs89 1914-1998 Sinope 210 1\\farcs19 210 0\\farcs98 1938-1998 Lysithea 124 0\\farcs75 124 0\\farcs72 1938-1998 Carme 145 1\\farcs01 145 0\\farcs81 1951-1998 Ananke 134 0\\farcs88 134 0\\farcs88 1974-1998 Leda 67 0\\farcs87 67 0\\farcs70 The current integration includes perturbations due to the Sun, Saturn, the Galilean satellites, and the oblateness (J2 only) of Jupiter. The masses of Jupiter and the perturbing satellites and the Jupiter J2 are from the Galileo data analysis. Ephemerides for the satellites are available electronically from the JPL Horizons on-line solar system data and ephemeris computation service.

Jacobson, R. A.

2000-05-01

85

Numerical black hole initial data with low eccentricity based on post-Newtonian orbital parameters  

NASA Astrophysics Data System (ADS)

Black hole binaries on noneccentric orbits form an important subclass of gravitational wave sources, but it is a nontrivial issue to construct numerical initial data with minimal initial eccentricity for numerical simulations. We compute post-Newtonian orbital parameters for quasispherical orbits using the method of Buonanno, Chen and Damour, (2006) and examine the resulting eccentricity in numerical simulations. Four different methods are studied resulting from the choice of Taylor-expanded or effective-one-body Hamiltonians, and from two choices for the energy flux. For equal-mass, nonspinning binaries the approach succeeds in obtaining low-eccentricity numerical initial data with an eccentricity of about e=0.002 for rather small initial separations of D?10M. The eccentricity increases for unequal masses and for spinning black holes, but remains smaller than that obtained from previous post-Newtonian approaches. The effective-one-body Hamiltonian offers advantages for decreasing initial separation as expected, but in the context of this study also performs significantly better than the Taylor-expanded Hamiltonian for binaries with spin. For mass ratio 4?1 and vanishing spin, the eccentricity reaches e=0.004. For mass ratio 1?1 and aligned spins of size 0.85M2 the eccentricity is about e=0.07 for the Taylor method and e=0.014 for the effective-one-body method.

Walther, Benny; Brügmann, Bernd; Müller, Doreen

2009-06-01

86

Trace66 Trajectory Analysis and Orbit Determination Program, Volume X. Lunar Gravity Analysis.  

National Technical Information Service (NTIS)

The TRACE66 Trajectory Analysis and Orbit Determination Program is a general-purpose orbital analysis program. It was written specifically for the CDC 6000 series computers to assist The Aerospace Corporation personnel in the analysis and design of satell...

D. C. Walker R. H. Prislin W. D. Downs

1971-01-01

87

Advances in precision orbit determination of GRACE satellites  

NASA Astrophysics Data System (ADS)

The twin Gravity Recovery And Climate Experiment (GRACE) satellites carry a complete suite of instrumentation essential for precision orbit determination (POD). Dense, continuous and global tracking is provided by the Global Positioning System receivers. The satellite orientation is measured using two star cameras. High precision measurements of non-gravitational accel-erations are provided by accelerometers. Satellite laser ranging (SLR) retroreflectors are used for collecting data for POD validation. Additional validation is provided by the highly precise K-Band ranging system measuring distance changes between the twin GRACE satellites. This paper presents the status of POD for GRACE satellites. The POD quality will be vali-dated using the SLR and K-Band ranging data. The POD quality improvement from upgraded modeling of the GPS observations, including the transition to the new IGS05 standards, will be discussed. In addition, the contributions from improvements in the gravity field modeling -partly arising out of GRACE science results -will be discussed. The aspects of these improve-ments that are applicable for the POD of other low-Earth orbiting satellites will be discussed as well.

Bettadpur, Srinivas; Save, Himanshu; Kang, Zhigui

88

Orbital  

NASA Astrophysics Data System (ADS)

ORBITAL requires the following software, which is available for free download from the Internet: Netscape Navigator, version 4.75 or higher, or Microsoft Internet Explorer, version 5.0 or higher; Chime Plug-in, version compatible with your OS and browser (available from MDL).

Hanson, Robert M.

2003-06-01

89

Orbit Determination of Spacecraft in Earth-Moon L1 and L2 Libration Point Orbits.  

National Technical Information Service (NTIS)

The ARTEMIS mission, part of the THEMIS extended mission, is the first to fly spacecraft in the Earth-Moon Lissajous regions. In 2009, two of the five THEMIS spacecraft were redeployed from Earth-centered orbits to arrive in Earth-Moon Lissajous orbits in...

B. Owens D. Cosgrove D. Folta J. Marchese M. Woodard P. Morinelli

2011-01-01

90

Application of variance component estimation to precision orbit determination for ERS-2  

NASA Astrophysics Data System (ADS)

The variance component estimation (VCE) method was applied to the precision orbit determination (POD) for ERS-2 satellite. Totally, 23 5-day-long maneuver-free arcs with 2 days overlap (when without orbit maneuver separation between the successive arcs) in the early three months of 1998 were computed using SLR and PRARE data. To inspect the effect of the VCE method on the POD computation, the measurement residuals were analyzed, and the overlapping arcs were compared. At last, the mean posteriori standard deviations of each group of measurement were given. The analyses of residuals show that using the VCE method improved the fitness of measurements. Using Abbey criterion to examine systematic error checked the residuals. The checking results show that the VCE method could not eliminate the systematic errors in the orbit caused by the errors in dynamic and geometric models. The comparison results of overlapping arcs show that (1) using the VCE method reduced the mean deviations of overlapping arcs and the obviously unreasonable deviations in some arcs, thus made the orbit have more uniform precision; (2) relatively?the reduction of the mean deviations is more apparent in the transverse direction. From the mean posteriori standard deviations of each group of measurements, we could see that, for single normal points, the data of several SLR stations are more important than other measurements in POD computation. In general, the yielded mean posteriori standard deviations are more reasonable than the initial standard deviations to weight the observations.

Zhang, F. P.; Huang, C.; Feng, C. G.; Dong, X. J.; Liao, X. H.

2001-05-01

91

Initial Determination of Low Earth Orbits Using Commercial Telescopes.  

National Technical Information Service (NTIS)

Within the last decade, many new technologies have significantly changed the face of private astronomy. Developments such as inexpensive but high-quality sensors, rapid personal computing, and easy networking inspire a reexamination of an old problem: how...

M. M. Schmunk

2008-01-01

92

Orbit determination covariance analysis for the Deep Space Program Science Experiment mission  

Microsoft Academic Search

To define an appropriate orbit support procedure for the DSPSE mission, detailed permission orbit determination covariance analyses have been performed for the translunar and trans-Geographos mission phases. Preliminary analyses were also performed for the lunar mapping mission phase. These analyses are designed to assess the tracking patterns and the amount of tracking data needed to obtain orbit solutions of required

M. Beckman; C. Yee; T. Lee; M. Hoppe; D. Oza

1993-01-01

93

The Determination of the Orbits of the Outer Jovian Satellites  

Microsoft Academic Search

The eight outer satellites of Jupiter may be divided into two groups of four. Those in the first group, Himalia, Elara, Lysithea, and Leda, are in high inclination direct orbits between 11 and 12 million km from Jupiter. Those in the second group, Pasiphae, Sinope, Carme, and Ananke, are in high inclination retrograde orbits between 20 and 24 million km

R. A. Jacobson

2000-01-01

94

Orbital Moment Determination in (MnxFe1-x)3O4 Nanoparticles  

SciTech Connect

Nanoparticles of (Mn{sub x}Fe{sub 1-x}){sub 3}O{sub 4} with a concentration ranging from x = 0 to 1 and a crystallite size of 14-15 nm were measured using X-ray absorption spectroscopy and X-ray magnetic circular dichroism to determine the ratio of the orbital moment to the spin moment for Mn and Fe. At low Mn concentrations, the Mn substitutes into the host Fe{sub 3}O{sub 4} spinel structure as Mn{sup 2+} in the tetrahedral A-site. The net Fe moment, as identified by the X-ray dichroism intensity, is found to increase at the lowest Mn concentrations then rapidly decrease until no dichroism is observed at 20% Mn. The average Fe orbit/spin moment ratio is determined to initially be negative and small for pure Fe{sub 3}O{sub 4} nanoparticles and quickly go to 0 by 5%-10% Mn addition. The average Mn moment is anti-aligned to the Fe moment with an orbit/spin moment ratio of 0.12 which gradually decreases with Mn concentration.

Pool, V. L.; Jolley, C.; Douglas, T.; Arenholz, E.; Idzerda, Y. U.

2010-10-22

95

Determining the eccentricity of the Moon's orbit without a telescope  

NASA Astrophysics Data System (ADS)

Prior to the invention of the telescope many astronomers worked out models of the motion of the Moon to predict the position of the Moon in the sky. These geometrical models implied a certain range of distances of the Moon from Earth. Ptolemy's most quoted model predicted that the Moon was nearly twice as far away at apogee than at perigee. Measurements of the angular size of the Moon were within the capabilities of pretelescopic astronomers. Such measurements could have helped refine the models of the motion of the Moon, but hardly anyone seems to have made any measurements that have come down to us. We use a piece of cardboard with a small hole in it which slides up and down a yardstick to show that it is possible to determine the eccentricity ?~0.039+/-0.006 of the Moon's orbit. A typical measurement uncertainty of the Moon's angular size is +/-0.8 arc min. Because the Moon's angular size ranges from 29.4 to 33.5 arc min, carefully taken naked eye data are accurate enough to demonstrate periodic variations of the Moon's angular size.

Krisciunas, Kevin

2010-08-01

96

Gravitational wave forms for a three-body system in Lagrange's orbit: Parameter determinations and a binary source test  

SciTech Connect

Continuing work initiated in an earlier publication [Y. Torigoe, K. Hattori, and H. Asada, Phys. Rev. Lett. 102, 251101 (2009)], gravitational wave forms for a three-body system in Lagrange's orbit are considered especially in an analytic method. First, we derive an expression of the three-body wave forms at the mass quadrupole, octupole, and current quadrupole orders. By using the expressions, we solve a gravitational-wave inverse problem of determining the source parameters to this particular configuration (three masses, a distance of the source to an observer, and the orbital inclination angle to the line of sight) through observations of the gravitational wave forms alone. For this purpose, the chirp mass to a three-body system in the particular configuration is expressed in terms of only the mass ratios by deleting initial angle positions. We discuss also whether and how a binary source can be distinguished from a three-body system in Lagrange's orbit or others.

Asada, Hideki [Faculty of Science and Technology, Hirosaki University, Hirosaki 036-8561 (Japan)

2009-09-15

97

GIOVE Orbit and Clock Determination Based on the CONGO Network  

Microsoft Academic Search

As a prototype for the satellites of the future European Global Navigation Satellite System (GNSS) Galileo, the European Space Agency (ESA) launched two satellites (GIOVE-A and GIOVE-B) as part of the Galileo in Orbit Validation Element (GIOVE). To gain experience with the signals transmitted by these satellites and to estimate satellite orbit and clock parameters, a global network of GIOVE-capable

Peter Steigenberger; André Hauschild; Oliver Montenbruck; Urs Hugentobler; Uwe Hessels; Georg Weber; Thoralf Noack

2010-01-01

98

Uncertainty in hybrid gravitational waveforms: Optimizing initial orbital frequencies for binary black-hole simulations  

NASA Astrophysics Data System (ADS)

A general method is presented for estimating the uncertainty in hybrid models of gravitational waveforms from binary black-hole systems with arbitrary physical parameters, and thence the highest allowable initial orbital frequency for a numerical-relativity simulation such that the combined analytical and numerical waveform meets some minimum desired accuracy. The key strength of this estimate is that no prior numerical simulation in the relevant region of parameter space is needed, which means that these techniques can be used to direct future work. The method is demonstrated for a selection of extreme physical parameters. It is shown that optimal initial orbital frequencies depend roughly linearly on the mass of the binary, and therefore useful accuracy criteria must depend explicitly on the mass. The results indicate that accurate estimation of the parameters of stellar-mass black-hole binaries in Advanced LIGO data or calibration of waveforms for detection will require much longer numerical simulations than are currently available, or more accurate post-Newtonian approximations—or both—especially for comparable-mass systems with high spin.

Boyle, Michael

2011-09-01

99

Advanced stellar compass onboard autonomous orbit determination, preliminary performance.  

PubMed

Deep space exploration is in the agenda of the major space agencies worldwide; certainly the European Space Agency (SMART Program) and the American NASA (New Millennium Program) have set up programs to allow the development and the demonstration of technologies that can reduce the risks and the cost of deep space missions. From past experience, it appears that navigation is the Achilles heel of deep space missions. Performed on ground, this imposes considerable constraints on the entire system and limits operations. This makes it is very expensive to execute, especially when the mission lasts several years and, furthermore, it is not failure tolerant. Nevertheless, to date, ground navigation has been the only viable solution. The technology breakthrough of advanced star trackers, like the advanced stellar compass (ASC), might change this situation. Indeed, exploiting the capabilities of this instrument, the authors have devised a method to determine the orbit of a spacecraft autonomously, onboard, and without a priori knowledge of any kind. The solution is robust and fast. This paper presents the preliminary performance obtained during the ground testing in August 2002 at the Mauna Kea Observatories. The main goals were: (1) to assess the robustness of the method in solving autonomously, onboard, the position lost-in-space problem; (2) to assess the preliminary accuracy achievable with a single planet and a single observation; (3) to verify the autonomous navigation (AutoNav) module could be implemented into an ASC without degrading the attitude measurements; and (4) to identify the areas of development and consolidation. The results obtained are very encouraging. PMID:15220158

Betto, Maurizio; Jørgensen, John L; Jørgensen, Peter S; Denver, Troelz

2004-05-01

100

Determining the Eccentricity of the Moon's Orbit without a Telescope  

NASA Astrophysics Data System (ADS)

Ancient Greek astronomers knew that Moon's distance from the Earth was not constant. Ptolemy's model of the Moon's motion implied that the Moon ranged in distance from 33 to 64 Earth radii. This implied that its angular size ranged nearly a factor of two. Tycho Brahe's model of the Moon's motion implied a smaller distance range, some ±3 percent at syzygy. However, the ancient and Renaissance astronomers are notably silent on the subject of measuring the angular size of the Moon as a check on the implied range of distance from their models of the position of the Moon. Using a quarter-inch hole in a piece of cardboard that slides along a yardstick, we show that pre-telescopic astronomers could have measured an accurate mean value of the angular size of the Moon, and that they could have determined a reasonably accurate value of the eccentricity of the Moon's orbit. The principal calibration for each observer is to measure the apparent angular diameter of a 91 mm disk viewed at a distance of 10 meters, giving a true angular size of 31.3 arcmin (the Moon's mean angular size). Because the sighting hole is not much bigger than the size of one's pupil, each observer obtains a personal correction factor with which to scale the raw measures. If one takes data over the course of 7 lunations (7.5 anomalistic months), any systematic errors which are a function of phase should even out over the course of the observations. We find that the random error of an individual observation of ±0.8 arcmin can be achieved.

Krisciunas, Kevin

2010-01-01

101

Samos 2 (1961 alpha 1): Orbit determination and analysis at 31:2 response  

Microsoft Academic Search

Samos 2, 1961 alpha 1, launched on 31 January 1961, was the first satellite to enter a Sun-synchronous orbit at an inclination of 97.4 deg. The initial perigee and apogee heights were 474 km and 557 km respectively, the initial period was 94.97 min and the satellite decayed 21 October 1973 after more than 12 years in orbit. Samos 2

D. M. C. Walker

1980-01-01

102

FIRST ORBIT AND MASS DETERMINATIONS FOR NINE VISUAL BINARIES  

SciTech Connect

This paper presents the first published orbits and masses for nine visual double stars: WDS 00149-3209 (B 1024), WDS 01006+4719 (MAD 1), WDS 03130+4417 (STT 51), WDS 04357+3944 (HU 1084), WDS 19083+2706 (HO 98 AB), WDS 19222-0735 (A 102 AB), WDS 20524+2008 (HO 144), WDS 21051+0757 (HDS 3004 AB), and WDS 22202+2931 (BU 1216). Masses were calculated from the updated Hipparcos parallax data when available and sufficiently precise, or from dynamical parallaxes otherwise. Other physical and orbital properties are also discussed.

Ling, J. F., E-mail: josefinaf.ling@usc.es [Departamento de Matematica Aplicada, Universidade de Santiago de Compostela (Spain)

2012-01-15

103

First Orbit and Mass Determinations for Nine Visual Binaries  

NASA Astrophysics Data System (ADS)

This paper presents the first published orbits and masses for nine visual double stars: WDS 00149-3209 (B 1024), WDS 01006+4719 (MAD 1), WDS 03130+4417 (STT 51), WDS 04357+3944 (HU 1084), WDS 19083+2706 (HO 98 AB), WDS 19222-0735 (A 102 AB), WDS 20524+2008 (HO 144), WDS 21051+0757 (HDS 3004 AB), and WDS 22202+2931 (BU 1216). Masses were calculated from the updated Hipparcos parallax data when available and sufficiently precise, or from dynamical parallaxes otherwise. Other physical and orbital properties are also discussed.

Ling, J. F.

2012-01-01

104

Applications of square-root information filtering and smoothing in spacecraft orbit determination  

NASA Astrophysics Data System (ADS)

The JPL (Jet Propulsion Laboratory) Orbit Determination Software System is a set of computer programs developed for the primary purpose of determining the flight path of deep-space mission spacecraft in NASA's Planetary Program and highly elliptical orbiting spacecraft in Earth orbit. The filtering processes available within the JPL Orbit Determination Software are discussed, and several examples are presented. In particular, solutions obtained by the Square Root Information Filter (SRIF) using Bierman's Estimation Subroutine Library (ESL) are discussed and compared with the solutions obtained by the singular value decomposition (SVD) technique. It is concluded that the SRIF filtering and smoothing algorithms are efficient and numerically stable for well-conditioned systems. The use of Bierman's ESL simplifies the task of maintaining the orbit determination software by providing efficient, tested filtering tools. For solving a large well-conditioned system (rank higher than 120), SRIF is approximately four times faster than SVD; however, for solving an ill-conditioned system, SVD is recommended.

Wang, Tseng-Chan; Collier, James B.; Ekelund, John E.; Breckheimer, Peter J.

105

49 CFR 554.10 - Initial determinations and public meetings.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 2012-10-01 false Initial determinations and public meetings...STANDARDS ENFORCEMENT AND DEFECTS INVESTIGATION § 554.10 Initial determinations and public meetings. (a) An initial decision of failure to...

2012-10-01

106

49 CFR 554.10 - Initial determinations and public meetings.  

Code of Federal Regulations, 2011 CFR

...2011-10-01 2011-10-01 false Initial determinations and public meetings...STANDARDS ENFORCEMENT AND DEFECTS INVESTIGATION § 554.10 Initial determinations and public meetings. (a) An initial decision of failure to...

2011-10-01

107

Initial Data for Binary Neutron Stars with Arbitrary Spin and Orbital Eccentricity  

NASA Astrophysics Data System (ADS)

The starting point of any general relativistic numerical simulation is a solution of the Hamiltonian and momentum constraint. One characteristic of the Binary Neutron Star (BNS) initial data problem is that, unlike the case of binary black holes, there are no formalisms that permit the construction of initial data for stars with arbitrary spins. For many years, the only options available have been systems either with irrotational or corotating fluid. Ten years ago, Marronetti & Shapiro (2003) introduced an approximation that would produce such arbitrarily spinning systems. More recently, Tichy (2012) presented a new formulation to do the same. However, all these data sets are bound to have a non-zero eccentricity that results from the fact the stars' velocity have initial null radial components. We present here a new approximation for BNS initial data for systems that possess arbitrary spins and arbitrary radial and tangential velocity components. The latter allows for the construction of data sets with arbitrary orbital eccentricity. Through the fine-tuning of the radial component, we were able to reduce the eccentricity by a factor of several compared to that of standard helical symmetry data sets such as those currently used in the scientific community.

Tsatsin, Petr; Marronetti, Pedro

2013-04-01

108

Long arc orbit determination solutions using Encke's method  

Microsoft Academic Search

The long term tracking of geodetic satellites using laser ranging has provided an opportunity to conduct various geophysical studies by solving for continuous, dynamically consistent trajectories that span up to tens of thousands of orbital revolutions. The process of computing these long arc solutions require a reliable technique that numerically integrates the equations of motion. Previous studies have demonstrated that

John B. Lundberg; S. Bettadpur; R. J. Eanes

2000-01-01

109

Determining the material type of man-made orbiting objects using low-resolution reflectance spectroscopy  

Microsoft Academic Search

The purpose of this research is to improve the knowledge of the physical properties of orbital debris, specifically the material type. Combining the use of the fast-tracking United States Air Force Research Laboratory (AFRL) telescopes with a common astronomical technique, spectroscopy, and NASA resources was a natural step toward determining the material type of orbiting objects remotely. Currently operating at

Kira Jorgensen; John L. Africano; Eugene G. Stansbery; Paul W. Kervin; Kris M. Hamada; Paul F. Sydney

2001-01-01

110

The Effect of Equatorial Spread F on Relative Orbit Determination of GRACE Using Differenced GPS Observations  

NASA Astrophysics Data System (ADS)

In this paper, relative orbit of Low Earth Orbit satellites is determined using only GPS measurements and the effects of Equatorial Spread-F (ESF), that is one of biggest ionospheric irregularities, are investigated. First, relative orbit determiation process is constructed based on doubly differenced GPS observations. In order to see orbit determination performance, relative orbit of two GRACE satellites is estimated for one month in 2004 when no ESF is observed. The root mean square of the achieved baselines compared with that from K-Band Ranger sensor is about 2 » 3 mm and average of 95% of ambiguities are resolved. Based on this performance, the relative orbit is estimated for two weeks of two difference years, 2003 when there are lots of ESF occurred, and 2004 when only few ESF occurred. For 2003, the averaged baseline error over two weeks is about 15 mm. That is about 4 times larger than the case of 2004 (3.6 mm). Ionospheric status achieved from K-Band Ranging sensor also shows that more Equatorial Spread-F occurred at 2003 than 2004. Investigation on raw observations and screening process revealed that the ionospheric irregualarities caused by Equatorial Spread-F gave significant effects on GPS signal like signal loss or enhancement ionospheric error, From this study, relative orbit determination using GPS observations should consider the effect of Equatorial Spread-F and adjust orbit determination strategy, especially at the time of solar maximum.

Roh, Kyoung-Min; Luehr, Hermann; Park, Sang-Young; Cho, Jung-Ho

2009-12-01

111

GPS-Based Navigation and Orbit Determination for the AMSAT Phase 3D Satellite.  

National Technical Information Service (NTIS)

This paper summarizes the results of processing GPS data from the AMSAT Phase 3D (AP3) satellite for real-time navigation and post-processed orbit determination experiments. AP3 was launched into a geostationary transfer orbit (GTO) on November 16, 2000 f...

G. Davis R. Carpenter M. Moreau F. H. Bauer A. Long D. Kelbel T. Martin

2002-01-01

112

Precise orbit determination and gravity field improvement for the ERS satellites  

Microsoft Academic Search

The radial orbit error has long been the major error source in ERS-1 altimetry, crippled by having only satellite laser ranging for precise tracking and relying on insufficiently accurate general-purpose gravity field models. Altimeter crossovers are used very effectively as additional tracking data to laser ranging. The ERS Tandem Mission even provides the unique possibility to simultaneously determine orbits of

Remko Scharroo; Pieter Visser

1998-01-01

113

Accurate determination of highly eccentric orbits in earth's gravitational field with axial symmetry  

Microsoft Academic Search

An algorithm is constructed for the determination of the perturbed motion, in both, the rectangular and the orbital elements of highly eccentric orbits in Earth's gravitational field with axial symmetry whatever the number N of the zonal harmonic coefficients may be. An application of the algorithm for the Explorer 28 satellite (e > 0.94) is given for two geopotential models

A. Abdel Aziz Bakry

1988-01-01

114

Accurate determination of highly eccentric orbits in earth's gravtational field with axial symmetry  

Microsoft Academic Search

In this paper, an algorithm is constructed for the determination of the perturbed motion, in both, the rectangular and the orbital elements of highly eccentric orbits in Earth's gravitational field with axial symmetry whatever the number N of the zonal harmonic coefficients may be. An application of the algorithm for the Explorer 28 satellite (e > 0.94) is given for

A. Abdel Aziz Bakry

1988-01-01

115

Satellite Orbit Determination Using GPS Carrier Phase in Pure Kinematic Mode  

NASA Astrophysics Data System (ADS)

The mainstream approach to satellite orbit determination has been a dynamic one. This approach is fine as long as the satellite dynamic model is accurate. When the dynamics model is not accurate, the reduced dynamic approach is better suited for orbit determination. Even a purely kinematic solution can be obtained by using the reduced dynamic approach. However, this method is computationally very extensive and still requires a reasonably good satellite dynamics model to compute its reference orbit. A new algorithm and computer program, KODAC (Kinematic Orbit Determination And Comparison), was developed for satellite orbit determination using a kinematic approach with the GPS carrier phase as observable. Since the GPS signal has enough spatial geometric information, it is possible to determine the satellite orbit using a purely kinematic approach. In this method both double and triple differenced GPS carrier phases are used as observables, and epoch by epoch satellite positions and DD ambiguities are estimated by assuming GPS ephemerides and ground station positions are known. TOPEX GPS data is used for this study, and the final radial rms orbit accuracy of 5 cm with respect to the MSODP (Multi Satellite Orbit Determination Program) dynamic solution is achieved. This new kinematic approach has the advantage of having consistent orbit accuracy regardless of satellite altitude. The same algorithm can be applied to any satellite with a GPS receiver due to the algorithm's non-dynamic approach. The TOPEX on-board receiver has only six channels, and its signal view angle is limited. With an improved on-board receiver equipped with more channels and a wider GPS view angle, an improvement in orbit accuracy can be expected for future satellite missions.

Byun, Sung Hun

116

Orbit determination of close binary systems using lucky imaging  

NASA Astrophysics Data System (ADS)

We present relative positions of visual binaries observed in 2009 with the FastCam 'lucky-imaging' camera mounted on the 1.5-m Carlos Sánchez Telescope at the Observatorio del Teide. We obtained 424 CCD observations (averaged in 198 mean relative positions) of 157 binaries with angular separations in the range 0.14-15.40 arcsec, with a median separation of 0.51 arcsec. For a given system, each CCD image represents the sum of the best 10-25 per cent images from 1000-5000 short-exposure frames. Derived internal errors were 7 mas in ? and 1?2 (9 mas) in ?. When comparing to systems with very well known orbits, we find that the rms deviation in ? residuals is 23 mas, while the rms deviation in ? residuals is 0?73/?. We confirmed 18 Hipparcos binaries and we report new companions to BVD 36 A and J 621 B. For binaries with preliminary orbital parameters, the relative radial velocity was estimated as well. We also present four new revised orbits computed for LDS 873, BU 627 A-BC, BU 628 and HO 197 AB. This work discusses the first results on visual binaries using the FastCam lucky-imaging camera.

Rica, F. M.; Barrena, R.; Vázquez, G.; Henríquez, J. A.; Hernández, F.

2012-01-01

117

Initial Mars Upper Atmospheric Structure Results from the Accelerometer Science Experiment aboard Mars Reconnaissance Orbiter  

Microsoft Academic Search

Designed for aerobraking, Mars Reconnaissance Orbiter (MRO) launched on August 12, 2005, achieved Mars Orbital Insertion (MOI), March 10, 2006, and successfully completed aerobraking on August 30, 2006. Atmospheric density decreases exponentially with increasing height. By small propulsive adjustments of the apoapsis orbital velocity, periapsis altitude was fine tuned to the density surface that safely used the atmosphere of Mars

G. M. Keating; S. W. Bougher; M. E. Theriot; R. H. Tolson; R. C. Blanchard; R. W. Zurek; J. M. Forbes; J. Murphy

2006-01-01

118

Subdeterminant approach for pseudo-orbit expansions of spectral determinants in quantum maps and quantum graphs  

NASA Astrophysics Data System (ADS)

We study the implications of unitarity for pseudo-orbit expansions of the spectral determinants of quantum maps and quantum graphs. In particular, we advocate to group pseudo-orbits into subdeterminants. We show explicitly that the cancellation of long orbits is elegantly described on this level and that unitarity can be built in using a simple subdeterminant identity which has a nontrivial interpretation in terms of pseudo-orbits. This identity yields much more detailed relations between pseudo-orbits of different lengths than was known previously. We reformulate Newton identities and the spectral density in terms of subdeterminant expansions and point out the implications of the subdeterminant identity for these expressions. We analyze furthermore the effect of the identity on spectral correlation functions such as the autocorrelation and parametric cross-correlation functions of the spectral determinant and the spectral form factor.

Waltner, Daniel; Gnutzmann, Sven; Tanner, Gregor; Richter, Klaus

2013-05-01

119

Can Milankovitch orbital variations initiate the growth of ice sheets in a general circulation model?  

NASA Astrophysics Data System (ADS)

The Goddard Institute for Space Studies climate model is used to investigate whether the growth of ice sheets could have been initiated by solar insolation variations. Three different orbital configurations are used, corresponding to 116 and 106 kyr B.P., and a modified insolation field with greater reductions in summer insolation at high northern latitudes. The time periods chosen are those in which geophysical evidence suggests ice sheets may have been growing rapidly. The reduced summer insolation field characteristic of all the experiments is thought to be a necessary condition for allowing snow to last through the summer, and ice sheets to build. The results show that the model fails to maintain snow cover through the summer at locations of suspected initiation of the major ice sheets, despite the reduced summer and fall insolation. When 10-m-thick ice was inserted in all locations where continental ice sheets existed during the Last Glacial Maximum, the model failed to maintain it as well, producing energy and mass imbalances which would remove the ice within 5 years. Only when the ocean surface temperatures were adjusted to their peak ice age values was the model able to keep any of the additional ice, and then only in a very restricted region of northern Baffin Island. The experiments indicate there is a wide discrepancy between the model's response to Milankovitch perturbations and the geophysical evidence of ice sheet initiation. As the model failed to grow or sustain low-altitude ice during the time of high-latitude maximum solar radiation reduction (120-110 kyr B.P.), it is unlikely it could have done so at any other time within the last several hundred thousand years. If the model results are correct, it indicates that the growth of ice occurred in an extremely ablative environment, and thus demanded some complicated strategy, or else some other climate forcing occurred in addition to the orbital variation influence (and CO2 reduction), which would imply we do not really understand the cause of the ice ages and the Milankovitch connection. If the model is not nearly sensitive enough to climate forcing, it could have implications for projections of future climate change.

Rind, D.; Peteet, D.; Kukla, G.

1989-01-01

120

Precise orbit determination for GRACE using GPS and K-band data  

NASA Astrophysics Data System (ADS)

The two GRACE satellites provide a unique platform to study precise orbit determination strategies for constellations of low Earth orbiters (LEOs) using GPS and inter-satellite K-band data. We apply pseudo-stochastic orbit modeling techniques to the two GRACE satellites to derive normal equation contributions from the K-band measurements and from orbit positions previously established for both satellites with GPS carrier phase measurements. The three contributions are combined on the normal equation level using appropriate weighting. Special attention is paid to the numerical stability of the procedure due to the very different accuracies of the GPS carrier phase and the ultra-precise K-band measurements. We use GRACE data for the year 2003 to study the mutual benefits for precise orbit determination of a LEO constellation based on GPS and K-band data. We discuss the differences to GPS-only orbit solutions and show that precisions of a few tens of micrometers in the relative orbit positions may be achieved by combining both measurement types without degrading the absolute orbit quality.

Jäggi, Adrian; Beutler, Gerhard; Mervart, Leos; Hugentobler, Urs

121

A Polynomial Force Model Representation for Determining Near-Equatorial, Near-Synchronous Satellite Orbits.  

National Technical Information Service (NTIS)

A method for accurately determining the orbits of near-equatorial, near-synchronous satellites is presented. The basic approach is to supplement the conventional spherical harmonics representation of the terrestrial gravity field with a forcing function h...

N. S. Hall R. H. Gersten

1968-01-01

122

Determination of Orbits of Objects in Outer Space with the Help of an Automated Measuring Complex.  

National Technical Information Service (NTIS)

Orbits of objects in outer space are determined by means of the application of contemporary automatic means of measurements, transmission and processing of data, and the creation of mathematical methods.

E. L. Akim M. L. Kislik P. E. Elyasberg T. M. Eneev

1965-01-01

123

Autonomous satellite constellation orbit determination using the star sensor and inter-satellite links data  

NASA Astrophysics Data System (ADS)

A method of autonomous orbit determination for a satellite constellation using a star sensor combined with inter satellite links (ISLs) is studied. Two types of simulated observation data, Three-Satellite Constellation ISLs and background stellar observations by a CCD star sensor, are first produced. Based on these data, an observation equation is built for the constellation joint autonomous orbit determination, in which the simulations are run. The accuracy of this method with different orbital determination models are analyzed and compared with regard to the effect of potential measurement errors. The results show that autonomous satellite constellation orbit determination using star sensor measurement and ISLs data is feasible. Finally, this paper arrives at several conclusions which contribute to extending this method to a more general satellite constellation.

Gan, Qingbo; Ma, Jianbo; Xu, Jin

2010-05-01

124

Orbit determination and analysis for 1970-97B at 14th-order resonance  

Microsoft Academic Search

The orbit of the satellite 1970-97B, the rocket of Cosmos 378, at inclination 74 deg, has been determined at 18 epochs between April and August 1971, when the effects of 14th-order resonance with the Earth's gravitational field were appreciable. The orbits were determined with the PROP 6 program from Hewitt camera, kinetheodolite, US Navy and visual observations, and an average

A. N. Winterbottom; D. G. King-Hele

1985-01-01

125

Orbit determination and analysis for Cosmos 482 from 1978 to 1981  

Microsoft Academic Search

The orbit of the satellite Cosmos 482 (1972-23A) has been determined at 77 epochs between November 8, 1977 and April 18, 1981 from 5650 optical and radar observations. The computations were made with the RAE orbit determination program PROP6, and an average accuracy of 150 m radial and cross-track was achieved. Cosmos 482 was a high-drag satellite in an eccentric

D. G. King-Hele; A. N. Winterbottom

1985-01-01

126

Orbit determination and analysis for 1970-97B at 14th-order resonance  

Microsoft Academic Search

The orbit of the satellite 1970-97B, the rocket of Cosmos 378, at inclination 74 deg, has been determined at 18 epochs between April and August 1971, when the effects of 14th-order resonance with the earth's gravitational field were appreciable. The orbits were determined with the PROP 6 program from Hewitt camera, kinetheodolite, U.S. Navy, and visual observations, and an average

A. N. Winterbottom; D. G. King-Hele

1986-01-01

127

Models of Solar Radiation Pressure in the Orbit Determination of GPS Satellites  

NASA Astrophysics Data System (ADS)

For the orbit determination of high-orbit satellites, such as GPS satellites, the largest error source is the perturbation of solar radiation pressure. In recent years, the precision of the GPS ephemerides provided by various IGS analysis centers has been continually improved, for which a very important factor is the continuous refinement of the solar radiation pressure model. After a detailed description of the currently used 7 solar radiation pressure models, they are used to integrate satellite orbits, for the purpose of comparing their accuracies in the orbit integration of GPS satellites. The results show that the 3 models provided by Bern University are the most accurate for simulating the solar radiation pressure, and the obtained GPS orbit precision from them are almost an order of magnitude better than the other 4 models.

Chen, Jun-ping; Wang, Jie-xian

2007-01-01

128

ORBIT DETERMINATION OF DOUBLE-LINED SPECTROSCOPIC BINARIES BY FITTING THE REVISED HIPPARCOS INTERMEDIATE ASTROMETRIC DATA  

SciTech Connect

Untill now, the Hipparcos intermediate astrometric data (HIAD) have contributed little to the full orbit determination of double-lined spectroscopic binaries (SB2s). This is because the photocenter of such a binary system is usually not far from the system mass center, and its orbital wobble is generally weak with respect to the accuracy of the HIAD. However, the HIAD have been recently revised and the accuracy is increased by a factor of 2.2 in the total weight. Therefore, it is interesting to see if the revised HIAD can be used in the orbit determination at least for some SB2s. In this paper, we first search the 9th Catalogue of Orbits of Spectroscopic Binaries (S{sub B{sup 9}}) for SB2s with reliable spectroscopic orbital solutions and with periods between 50 days and 3.2 years. This leaves us with 56 systems. The full orbital solutions of these systems are then determined from the HIAD by a highly efficient grid search method developed in this paper. The high efficiency is achieved by reducing the number of nonlinear model parameters to one, and by allowing all parameters to be adjustable within a region centered at each grid point. After a variety of tests, we finally accept orbital solutions of 13 systems. Among these systems, six (HIP 677, 20894, 87895, 95995, 101382, and 111170) are well resolved with reliable interferometric data. Orbital solutions from these data are consistent with our results. The full orbital solutions of the other seven systems (HIP 9121, 17732, 32040, 57029, 76006, 102431, and 116360) are determined for the first time.

Ren Shulin; Fu Yanning, E-mail: rensl@pmo.ac.c, E-mail: fyn@pmo.ac.c [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)

2010-05-15

129

The impact of GPS ephemeris on the accuracy of precise orbit determination for LEO using GPS  

NASA Astrophysics Data System (ADS)

Today more and more Low Earth orbiting satellites (LEOs) of new scientific missions are equipped with a GPS receiver for precise orbit determination (POD), on-board GPS has become one of the main POD approaches. However, the on-board GPS POD accuracy obviously relies on the accuracy of GPS orbit and clock products. Based on the zero-difference dynamic POD approach of SHORDE-III program, this paper shows the influence of GPS orbit and clock on the POD accuracy of LEO using real GRACE data and three types of IGS orbit products between 1 Aug. and 7 Aug. The results indicate that IGS final precise orbit product (igs) and rapid orbit product (igr) have the equal POD accuracy which is about 9.5cm, the POD accuracy using ultra-rapid orbit product (igu) is about 10.5cm which is a little worse than igs and igr; High-rate GPS clock products have an impact of about 1--6 cm on the POD accuracy of LEO.

Peng, D. J.; Wu, B.

2008-10-01

130

Orbit determination for Chang'E-2 lunar probe and evaluation of lunar gravity models  

NASA Astrophysics Data System (ADS)

The Unified S-Band (USB) ranging/Doppler system and the Very Long Baseline Interferometry (VLBI) system as the ground tracking system jointly supported the lunar orbit capture of both Chang'E-2 (CE-2) and Chang'E-1 (CE-1) missions. The tracking system is also responsible for providing precise orbits for scientific data processing. New VLBI equipment and data processing strategies have been proposed based on CE-1 experiences and implemented for CE-2. In this work the role VLBI tracking data played was reassessed through precision orbit determination (POD) experiments for CE-2. Significant improvement in terms of both VLBI delay and delay rate data accuracy was achieved with the noise level of X-band band-width synthesis delay data reaching 0.2-0.3 ns. Short-arc orbit determination experiments showed that the combination of only 15 min's range and VLBI data was able to improve the accuracy of 3 h's orbit using range data only by a 1-1.5 order of magnitude, confirming a similar conclusion for CE-1. Moreover, because of the accuracy improvement, VLBI data was able to contribute to CE-2's long-arc POD especially in the along-track and orbital normal directions. Orbital accuracy was assessed through the orbital overlapping analysis (2 h arc overlapping for 18 h POD arc). Compared with about 100 m position error of CE-1's 200 km×200 km lunar orbit, for CE-2's 100 km×100 km lunar orbit, the position errors were better than 31 and 6 m in the radial direction, and for CE-2's 15 km×100 km orbit, the position errors were better than 45 and 12 m in the radial direction. In addition, in trying to analyze the Delta Differential One-Way Ranging (?DOR) experiments data we concluded that the accuracy of ?DOR delay was dramatically improved with the noise level better than 0.1 ns and systematic errors better calibrated, and the Short-arc POD tests with ?DOR data showed excellent results. Although unable to support the development of an independent lunar gravity model, the tracking data of CE-2 provided evaluations of different lunar gravity models through POD. It is found that for the 100 km×100 km lunar orbit, with a degree and order expansion up to 165, JPL's gravity model LP165P did not show noticeable improvement over Japan's SGM series models (100×100), but for the 15 km×100 km lunar orbit, a higher degree-order model can significantly improve the orbit accuracy.

Li, PeiJia; Hu, XiaoGong; Huang, Yong; Wang, GuangLi; Jiang, DongRong; Zhang, XiuZhong; Cao, JianFeng; Xin, Nan

2012-03-01

131

GPS (Global Positioning System) orbit determination: Bootstrapping to resolve carrier phase ambiguity  

NASA Astrophysics Data System (ADS)

For Global Positioning System (GPS) satellite orbit determination, the most accurate observable available is carrier phase, differenced between observing stations and between satellites to cancel both transmitter and receiver related errors. For maximum accuracy, the integer cycle ambiguities of such observations must be resolved. To perform this ambiguity resolution, a bootstrapping strategy is effective. This strategy requires the tracking stations to have a wide ranging progression of spacings. Then, by conventional integrated Doppler processing of the observations from the most widely spaced stations, the orbits can be determined well enough to permit resolution can reduce the uncertainty of the orbit determination enough to enable ambiguity resolution for more widely spaced stations, which will reduce the orbital uncertainty further, and enable ambiguity resolution for still more widely spaced stations, and so on. This strategy is tested with two different tracking networks. This limited ambiguity resolution reduced both the formal and the actual errors of GPS orbit determinations by a factor of two. In the second twelve stations were arranged in a spiral with geometrically increasing spacings from 10 to 330 km. By bootstrapping, all ambiguities for baselines up to about 100 km long were resolved. The distance was limited by strong ionospheric variability. Still, orbit-determination uncertainty (3 sigma) was reduced to about 1:1,000,000.

Abbot, R. E.; Counselman, C. C., III; Gourevitch, S. A.; Ladd, J. W.

1989-02-01

132

U.S. initiatives in the international effort to mitigate the orbital debris environment  

NASA Astrophysics Data System (ADS)

Following release of the 1989 'Report on Orbital Debris' by the Interagency Group (Space) for the National Security Council, NASA undertook a series of extensive bilateral discussions with the major spacefaring nations on the topic of orbital debris. These discussions led to a greater understanding of both the cause and the effect of orbital debris. As a result of these discussions, the major spacefaring nations have taken definitive steps to redesign their launch vehicles and spacecraft so as to mitigate the production of orbital debris. In 1993 the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA), and Japan formed a multilateral Inter- Agency Orbital Debris Coordination Committee (IADC). Since that time the Russian Space Agency (RSA), the Chines National Space Agency (CNSA), the French National Space Agency (CNES), the British National Space Agency (BNSA), and the Indian Space Agency (ISRO) have jointed the IADC. In 1994 orbital debris discussions began in the United Nations under the auspices of the Scientific and Technical Subcommittee of the Committee on the Peaceful Uses of Outer Space (UNCOPUOS). In 1995 UNCOPUOS adopted a multi-year program for studying orbital debris. In 1993 the White House Office of Science and Technology Policy (OSTP) and the National Security Council (NSC) undertook an interagency review to revise and update the 1989 'Report on Orbital Debris.' In November 1995 Dr. John H. Gibbons, the Assistant to the President for Science and Technology, released the 'Interagency Report on Orbital Debris -- 1995.'

Levin, George M.

1996-10-01

133

Investigations to Determine the Origin of the Solar Wind with SPICE and SolarOrbiter  

NASA Astrophysics Data System (ADS)

At large spatial scales, the structure of the solar wind and it's mapping back to the solar corona, is thought to be reasonably well understood. However, the detailed structure of the various source regions at chromospheric and transition region heights is extremely complex, and less well understood. Determining this connection between heliospheric structures and their source regions at the Sun is one of the overarching objective of the Solar Orbiter mission. During perihelion segments of its orbit, when the spacecraft is in quasi-corotation with the Sun, Solar Orbiter will determine the plasma parameters and compositional signatures of the solar wind, which can be compared directly with the spectroscopic signatures of coronal ions with differing charge-to-mass ratios and FIP. One of the key instruments on the Solar Orbiter mission to make these remote sensing measurements is the SPICE (Spectral Imaging of the Coronal Environment) imaging spectrograph. SPICE will provide the images and plasma diagnostics needed to characterize the plasma state in different source regions, from active regions to quiet Sun to coronal holes. By comparing composition, plasma parameters, and low/high FIP ratios of structures remotely, with those measured directly at the Solar Orbiter spacecraft, Solar Orbiter will provide the first direct link between solar wind structures and their source regions at the Sun. This talk will provide a background of previous compositional correlation measurements and an outline of the method to be used for comparing the spectroscopic and in-situ plasma parameters to be measured with Solar Orbiter.

Hassler, Donald M.; DeForest, C.; Wilkinson, E.; Davila, J.; SPICE Team

2011-05-01

134

Orbit determination for a low-drag satellite with sparse observations  

NASA Astrophysics Data System (ADS)

The RAE orbit refinement program PROP has been used to determine the orbit of a low-drag satellite, 1971-110C, from 45 visual observations over 18 months between 30 June 1984 and 31 December 1985. The orbit is circular at a height of 100 km, and the inclination to the equator is 70 deg. With the aid of the related program PREP, predictions were made for April 1986 which proved to be in error by 12 seconds in time, and predictions have been provided for August and December 1986.

King-Hele, D. G.

1986-06-01

135

Initial investigation of circle-plus-arc orbit variants with a dedicated emission mammotomograph  

Microsoft Academic Search

A dedicated emission mammotomograph, uniquely capable of imaging in a hemisphere, is utilized to image the breast by way of complex acquisition orbits, completely sampling most of the breast. Orbits such as the circle-plus-arc (CPA) in particular provide for extended viewing times in a specific portion of the breast. This is advantageous in that as a diagnostic rather than screening

Caryl N. Archer; Martin P. Tornai; James E. Bowsher; Marques L. Bradshaw

2002-01-01

136

TerraSAR-X precise orbit determination with real-time GPS ephemerides  

NASA Astrophysics Data System (ADS)

For active and future Earth observation missions, the availability of near real-time precise orbit information is becoming more and more important. The latency and quality of precise orbit determination results is mainly driven by the availability of precise GPS ephemerides and clocks. In order to have high-quality GPS ephemerides and clocks available at real-time, the German Space Operations Center (GSOC) has developed the real-time clock estimation system RETICLE. The system receives data streams with GNSS observations from the global tracking network of the International GNSS Service (IGS) in real-time. Using the known station position, RETICLE estimates precise GPS satellite clock offsets and drifts based on the most recent available ultra rapid predicted orbits provided by the IGS. The clock offset estimates have an accuracy of better than 0.3 ns and are globally valid. The latency of the estimated clocks is approximately 7 s after the observation epoch. Another limiting factor is the frequency of satellite downlinks and the latency of the data transfer from the ground station to the operations center. Therefore a near real-time scenario using GPS observation data from the TerraSAR-X mission is examined in which the satellite has about one ground station contact per orbit or respectively one contact in 90 min. This test campaign shows that precise orbits can be obtained in near real-time. With the use of estimated clocks an orbit accuracy of better than 10 cm (3D-RMS) can be obtained. The evaluation of satellite laser ranging (SLR) observations shows residuals of 2.1 cm (RMS) for orbits using RECTICLE and residuals of 4.2 cm (RMS) for orbits using the IGS ultra rapid ephemerides and clocks products. Hence the use of estimated clocks improves the orbit determination accuracy significantly (˜factor 2) compared to using predicted clocks.

Wermuth, M.; Hauschild, A.; Montenbruck, O.; Kahle, R.

2012-09-01

137

Chang’E-1 precision orbit determination and lunar gravity field solution  

Microsoft Academic Search

In this paper we present results assessing the role of Very Long Baseline Interferometry (VLBI) tracking data through precision orbit determination (POD) during the check-out phase for Chang’E-1, and the lunar gravity field solution CEGM-01 based on the orbital tracking data acquired during the nominal phase of the mission. The POD of Chang’E-1 is performed using S-band two-way Range and

Yan Jianguo; Ping Jinsong; Li Fei; Cao Jianfeng; Huang Qian; Fung Lihe

2010-01-01

138

Determination of diatomic crystal bond lengths using atomic s-orbital radii  

Microsoft Academic Search

We develop a theory to determine the bond lengths of over 270 AB crystals having ZnS, NaCl, and CsCl structures, including intermetallic compounds. The first-principles pseudopotential s-orbital radius r\\/sub s\\/ is used, which contains no element-specific adjustable parameters. The good agreement found here between the calculated and measured bond lengths, along with the earlier successful applications of orbital radii for

S. B. Zhang; Marvin Cohen; J. C. Phillips

1988-01-01

139

Determination of diatomic crystal bond lengths using atomic s-orbital radii  

Microsoft Academic Search

We develop a theory to determine the bond lengths of over 270 AB crystals having ZnS, NaCl, and CsCl structures, including intermetallic compounds. The first-principles pseudopotential s-orbital radius rs is used, which contains no element-specific adjustable parameters. The good agreement found here between the calculated and measured bond lengths, along with the earlier successful applications of orbital radii for separating

S. B. Zhang; Marvin L. Cohen; J. C. Phillips

1988-01-01

140

Experimental determination of spin orbital coupling states of O2(-)  

NASA Astrophysics Data System (ADS)

Electron affinities, Ea, E1 and A1 are reported for the 12 primary X, A-K (27 spin) states of O2(-): KeqT3/2 = (SanQan)(2?mek/h2)3/2exp(Ea/RT) k1 = A1T-1/2exp(-E1/RT). These are obtained from pulsed discharge electron capture detector data by rigorously including literature values and uncertainties in a global non-linear least-squares adjustment. Simple molecular orbital theory predicts 27 bonding and 27 anti-bonding low-lying spin states. For the first time, the positive Ea for the 27 bonding states are reported. The partition function ratios of the negative ion and neutral (SanQan), the A1(X-E) and the spin separations are from fundamental constants. The Ea (in eV) are as follows (with the spin states in brackets): [1.050, 1.070]; [0.915, 0.935]; [0.698, 0.718, 0.746, 0.782]; [0.734, 0.754]; [0.559, 0.587]; 0.518; [0.430, 0.450]; 0.380; 0.354; [0.286, 0.298, 0.318, 0.346]; [0.232, 0.252]; [0.172, 0.184, 0.204, 0.232]. The activation energies (in eV) are as follows: E1(X-C) 1.0; E1(D,E) 1.0, 0.8, 0.6; E1(F-K) 0.12-0.08. The Ea and E1 are used to calculate bonding Herschbach ionic Morse-Person empirical curves.

Chen, Edward C. M.; Herder, Charles; Chang, Winston; Ting, Regina; Chen, Edward S.

2006-06-01

141

19 CFR 210.42 - Initial determinations.  

Code of Federal Regulations, 2013 CFR

... 210.42 Section 210.42 Customs Duties UNITED STATES INTERNATIONAL TRADE COMMISSION INVESTIGATIONS OF...determination pursuant to § 210.18; a motion for intervention pursuant to § 210.19; a motion for...

2013-04-01

142

Experimental study on the precise orbit determination of the BeiDou navigation satellite system.  

PubMed

The regional service of the Chinese BeiDou satellite navigation system is now in operation with a constellation including five Geostationary Earth Orbit satellites (GEO), five Inclined Geosynchronous Orbit (IGSO) satellites and four Medium Earth Orbit (MEO) satellites. Besides the standard positioning service with positioning accuracy of about 10 m, both precise relative positioning and precise point positioning are already demonstrated. As is well known, precise orbit and clock determination is essential in enhancing precise positioning services. To improve the satellite orbits of the BeiDou regional system, we concentrate on the impact of the tracking geometry and the involvement of MEOs, and on the effect of integer ambiguity resolution as well. About seven weeks of data collected at the BeiDou Experimental Test Service (BETS) network is employed in this experimental study. Several tracking scenarios are defined, various processing schemata are designed and carried out; and then, the estimates are compared and analyzed in detail. The results show that GEO orbits, especially the along-track component, can be significantly improved by extending the tracking network in China along longitude direction, whereas IGSOs gain more improvement if the tracking network extends in latitude. The involvement of MEOs and ambiguity-fixing also make the orbits better. PMID:23529116

He, Lina; Ge, Maorong; Wang, Jiexian; Wickert, Jens; Schuh, Harald

2013-03-01

143

Experimental Study on the Precise Orbit Determination of the BeiDou Navigation Satellite System  

PubMed Central

The regional service of the Chinese BeiDou satellite navigation system is now in operation with a constellation including five Geostationary Earth Orbit satellites (GEO), five Inclined Geosynchronous Orbit (IGSO) satellites and four Medium Earth Orbit (MEO) satellites. Besides the standard positioning service with positioning accuracy of about 10 m, both precise relative positioning and precise point positioning are already demonstrated. As is well known, precise orbit and clock determination is essential in enhancing precise positioning services. To improve the satellite orbits of the BeiDou regional system, we concentrate on the impact of the tracking geometry and the involvement of MEOs, and on the effect of integer ambiguity resolution as well. About seven weeks of data collected at the BeiDou Experimental Test Service (BETS) network is employed in this experimental study. Several tracking scenarios are defined, various processing schemata are designed and carried out; and then, the estimates are compared and analyzed in detail. The results show that GEO orbits, especially the along-track component, can be significantly improved by extending the tracking network in China along longitude direction, whereas IGSOs gain more improvement if the tracking network extends in latitude. The involvement of MEOs and ambiguity-fixing also make the orbits better.

He, Lina; Ge, Maorong; Wang, Jiexian; Wickert, Jens; Schuh, Harald

2013-01-01

144

32 CFR 1907.24. - Initial determination.  

Code of Federal Regulations, 2013 CFR

...National Defense CENTRAL INTELLIGENCE AGENCY CHALLENGES TO...section. (b) Within 10 business days of receipt of a challenge...response to a challenge within 60 business days of receipt. (d...a determination within 60 business days of receipt of the...

2013-07-01

145

GOCE orbit analysis: Long-wavelength gravity field determination using the acceleration approach  

NASA Astrophysics Data System (ADS)

The restricted sensitivity of the Gravity field and steady-state Ocean Circulation Explorer (GOCE) gradiometer instrument requires satellite gravity gradiometry to be supplemented by orbit analysis in order to resolve long-wavelength features of the geopotential. For the hitherto published releases of the GOCE time-wise (TIM) and GOCE space-wise gravity field series—two of the official ESA products—the energy conservation method has been adopted to exploit GPS-based satellite-to-satellite tracking information. On the other hand, gravity field recovery from data collected by the CHAllenging Mini-satellite Payload (CHAMP) satellite showed the energy conservation principle to be a sub-optimal choice. For this reason, we propose to estimate the low-frequency part of the gravity field by the point-wise solution of Newton's equation of motion, also known as the acceleration approach. This approach balances the gravitational vector with satellite accelerations, and hence is characterized by (second-order) numerical differentiation of the kinematic orbit. In order to apply the method to GOCE, we present tailored processing strategies with regard to low-pass filtering, variance-covariance information handling, and robust parameter estimation. By comparison of our GIWF solutions (initials GI for "Geodätisches Institut" and IWF for "Institut für WeltraumForschung") and the GOCE-TIM estimates with a state-of-the-art gravity field solution derived from GRACE (Gravity Recovery And Climate Experiment), we conclude that the acceleration approach is better suited for GOCE-only gravity field determination as opposed to the energy conservation method.

Baur, O.; Reubelt, T.; Weigelt, M.; Roth, M.; Sneeuw, N.

2012-08-01

146

New Technique for Determining the Shock Initiation Sensitivity of Explosives.  

National Technical Information Service (NTIS)

A new technique for determining the shock initiation sensitivity of explosives is described. It involves a flyer plate impinging upon the test explosive to induce initiation of detonation. An electrically exploded foil propels the flyer plate, which is a ...

A. C. Schwarz

1977-01-01

147

Altitude and orbit determination of a bright meteor  

Microsoft Academic Search

A description is presented of the procedures followed by amateur astronomers in West Germany in connection with photographic meteor observations, taking into account as example a specific case involving a bright meteor. Simultaneous observations from two stations were planned. The use of a third station is desirable for the determination of parameter data in cases in which the flight path

B. Schmitz

1979-01-01

148

TRACE trajectory analysis and orbit determination program. Volume 7: Usage guide. Part A: Input data (reissue B)  

Microsoft Academic Search

The Trajectory Analysis and Orbit Determination Program (TRACE) is a general purpose orbital analysis program. It was written and continues to be developed specifically to assist technical personnel in the analysis and design of satellite orbits and tracking systems. An input usage guide is presented that defines all input required to perform TRACE functions such as trajectory generation, data\\/observation generation,

W. D. Downs III; R. H. Prislin; D. C. Walker; R. J. Mercer

1974-01-01

149

Fractography: determining the sites of fracture initiation.  

PubMed

Fractography is the analysis of fracture surfaces. Here, it refers to quantitative fracture surface analysis (FSA) in the context of applying the principles of fracture mechanics to the topography observed on the fracture surface of brittle materials. The application of FSA is based on the principle that encoded on the fracture surface of brittle materials is the entire history of the fracture process. It is our task to develop the skills and knowledge to decode this information. There are several motivating factors for applying our knowledge of FSA. The first and foremost is that there is specific, quantitative information to be obtained from the fracture surface. This information includes the identification of the size and location of the fracture initiating crack or defect, the stress state at failure, the existence, or not, of local or global residual stress, the existence, or not, of stress corrosion and a knowledge of local processing anomalies which affect the fracture process. The second motivating factor is that the information is free. Once a material is tested to failure, the encoded information becomes available. If we decide to observe the features produced during fracture then we are rewarded with much information. If we decide to ignore the fracture surface, then we are left to guess and/or reason as to the cause of the failure without the benefit of all of the possible information available. This paper addresses the application of quantitative fracture surface analysis to basic research, material and product development, and "trouble-shooting" of in-service failures. First, the basic principles involved will be presented. Next, the methodology necessary to apply the principles will be presented. Finally, a summary of the presentation will be made showing the applicability to design and reliability. PMID:8621031

Mecholsky, J J

1995-03-01

150

Determination of Multiple Asteroid Orbits With a Genetic-Based Algorithm  

NASA Astrophysics Data System (ADS)

Over the past decade, discoveries of multiple asteroid systems have played a significant role in our general understanding of small solar system bodies. Direct observations of satellites of asteroids are rare and difficult since they require the use of already over-subscribed facilities such as adaptive optics (AO) on large 8-10 m class telescopes and the Hubble Space Telescope (HST). The scarcity of data and the long temporal baseline of observations (up to 10 years) significantly complicate the determination of the mutual orbits of these systems. We implemented a new approach presented in Vachier et al (A&A,2012), for determining the mutual orbits of directly-imaged multiple asteroids using a genetic-based algorithm. This approach was applied to several known binary asteroid systems (22 Kalliope, 3749 Balam, and 50 000 Quaoar) observed with AO systems and HST. From 10 years of observation, we derived an orbital solution for Linus, companion of (22) Kalliope, with an accuracy close to the astrometric limit provided by the AO observations, assuming a purely Keplerian orbit. A search for non-Keplerian orbit confirmed that a J2 0 is the best-fitting solution. We show that the precession of the nodes could be detected without ambiguity, implying that Kalliope's primary may have an inhomogeneous internal structure. HST astrometric observations of Weywot, companion of the trans-Neptunian object (50 000) Quaoar, were used to derive its mass and its bulk density, which appears to be higher than the density of other TNOs. Finally, we derived a bundle of orbital solutions for (3749) Balam, with equally good fits, from the limited set of astrometric positions. They provide a realistic density between 1.3 and 3.7 g/cm3 for this S-type asteroid. We will present additional mutual orbits determined using our method as they become available. This work has been supported by NASA grant NNX11AD62G

Vachier, Frederic; Berthier, J.; Marchis, F.

2012-10-01

151

Orbit determination errors for a new concept of geopositioning and navigation  

NASA Astrophysics Data System (ADS)

A brief description of a new concept for remote geopositioning time dissemination and navigation applicable over regional areas currently being developed in Brazil is presented It aims at an independent Brazilian wide location system using concepts different from conventional GPS Galileo or GLONASS systems Its implementation becomes particularly important to allow independent comparisons validate measurements taken by other systems and assess the proposed system The new system utilizes at least three reference bases on the ground with precisely determined geodetic positions carrying synchronized clocks a transmitter in one central base master base emitting time coded marks and one repeater a satellite in the sky An algorithm and a digital telecommunication set up demonstrate its operation It is shown that in the master base it is necessary the knowledge of the satellite orbit with consistent precision Assuming a repeater put aboard an artificial satellite and a favorable geometry errors in the instantaneous determination of the position were studied Orbit propagation errors for one orbit or more are also presented One of the error sources which affects the orbit determination accuracy comes from the measurement system involving the ground segment geometry between the orbit and the bases and equipment For the sake of this work three measurement error sources were considered here the station location error the oscillator stability and miscellaneous additional sources

Vilhena de Moraes, R.; Kuga, H. K.; Kaufmann, P. L.; Beraldo, L. A.

152

Improvement Of The Ephemeris And Mass Of The Martian Moons From MEX Precise Orbit Determination  

NASA Astrophysics Data System (ADS)

Because of the much larger eccentricity of the MEX orbit than that of the MGS orbit (eccentricity of 0.6 versus 0.01), MEX is more sensitive to the gravitational attraction of the Martian moons Phobos and Deimos. From the 2-way Doppler and range data provided by the MEX Radio Science (MaRS) experiment over the last three years, we perform MEX Precise Orbit Determination (POD) in order to improve both moons' ephemeris and mass. We use the GINS software developed by CNES and further adapted at ROB for planetary geodesy applications. We obtain an average precision of 20 meters or less on the MEX positioning around Mars. This represents an improvement by more than a factor 2 with respect to the MEX navigation orbit provided by the flight dynamics team of ESOC. Here, we show the impact of the improved MEX orbit on the Martian Moon ephemerides by using images of the moons taken by the camera (SRC) onboard MEX. We obtain estimates of the masses of Phobos and Deimos with formal errors that are comparable or better than previous estimates from MGS and Mars Odyssey. By using our accurate orbits of MEX, we also estimate the second order coefficients of the gravity field of Phobos, which can be used as a constraint on the internal mass distribution of Phobos.

Rosenblatt, P.; Lainey, V.; Le Maistre, S.; Marty, J.; Dehant, V.; Paetzold, M.; van Hoolst, T.; Hauesler, B.

2007-12-01

153

Orbit determination performances using single- and double-differenced methods: SAC-C and KOMPSAT-2  

NASA Astrophysics Data System (ADS)

In this paper, Global Positioning System-based (GPS) Orbit Determination (OD) for the KOrea-Multi-Purpose-SATellite (KOMPSAT)-2 using single- and double-differenced methods is studied. The requirement of KOMPSAT-2 orbit accuracy is to allow 1 m positioning error to generate 1-m panchromatic images. KOMPSAT-2 OD is computed using real on-board GPS data. However, the local time of the KOMPSAT-2 GPS receiver is not synchronized with the zero fractional seconds of the GPS time internally, and it continuously drifts according to the pseudorange epochs. In order to resolve this problem, an OD based on single-differenced GPS data from the KOMPSAT-2 uses the tagged time of the GPS receiver, and the accuracy of the OD result is assessed using the overlapping orbit solution between two adjacent days. The clock error of the GPS satellites in the KOMPSAT-2 single-differenced method is corrected using International GNSS Service (IGS) clock information at 5-min intervals. KOMPSAT-2 OD using both double- and single-differenced methods satisfies the requirement of 1-m accuracy in overlapping three dimensional orbit solutions. The results of the SAC-C OD compared with JPL’s POE (Precise Orbit Ephemeris) are also illustrated to demonstrate the implementation of the single- and double-differenced methods using a satellite that has independent orbit information available for validation.

Hwang, Yoola; Lee, Byoung-Sun; Kim, Haedong; Kim, Jaehoon

2011-01-01

154

Unbiased orbit determination for the next generation asteroid/comet surveys  

NASA Astrophysics Data System (ADS)

In the next generation surveys, the discovery of moving objects can be successful only if an observation strategy and the identification/orbit determination procedure are appropriate for the diverse apparent motions of the target sub-populations. The observations must accurately measure the displacement over a short interval of time; observations believed to belong to the same object have to be connected into tracklets. Information contained in tracklets is in most cases not sufficient to compute an orbit: two or more of them must be identified to provide an orbit. We have developed a method for recursive identification of tracklets allowing an unbiased orbit determination for all sub-populations and efficient enough to cope with the data flow expected from the next generation surveys. The success of the new algorithms can be easily measured only in a simulation, by consulting a posteriori some "ground truth".We present here the results of a simulation of the orbit determination for one month of operations of the future Pan-STARRS survey, based upon a Solar System Model with a downsized population of Main Belt asteroids and a full size populations of Trojans, NEO, Centaurs, Comets and TNO. The results indicate that the method already developed and tested to find identifications of NEO and Main Belt asteroids are directly applicable to Trojans. The more distant objects often require modified algorithms, fitting orbits with only 4 parameters in a coordinate system specially adapted to handle very short arcs of observations. These orbits are mostly used as intermediate results, allowing to find full solutions as more tracklets are identified.When the number density of detections is as large as expected from the next generation surveys, both joining observations into tracklets and identifying tracklets can produce some false results. The only reliable way to remove them is a procedure of tracklet/identification management. It compares the tracklets and the identifications with a complex logic, allowing to discard almost all the false tracklets and all the false identifications. However, the distant objects still present a challenge for orbit determination: they require three tracklets in separate nights. If this requirement is met we have found no problem in achieving an unbiased orbit determination for all populations. Further work will lead to more advanced simulations, in particular by introducing a realistic model for astrometric and photometric errors.

Milani, A.; Gronchi, G. F.; Kneževic, Z.; Sansaturio, M. E.; Arratia, O.; Denneau, L.; Grav, T.; Heasley, J.; Jedicke, R.; Kubica, J.

155

From Astrometry to Celestial Mechanics: Orbit Determination with Very Short Arcs  

NASA Astrophysics Data System (ADS)

Contemporary surveys provide a huge number of detections of small solar system bodies, mostly asteroids. Typically, the reported astrometry is not enough to compute an orbit and/or perform an identification with an already discovered object. The classical methods for preliminary orbit determination fail in such cases: a new approach is necessary. When the observations are not enough to compute an orbit we represent the data with an attributable (two angles and their time derivatives). The undetermined variables range and range rate span an admissible region of solar system orbits, which can be sampled by a set of Virtual Asteroids (VAs) selected by an optimal triangulation. The attributable results from a fit and has an uncertainty represented by a covariance matrix, thus the predictions of future observations can be described by a quasi-product structure (admissible region times confidence ellipsoid), which can be approximated by a triangulation with each node surrounded by a confidence ellipsoid. The problem of identifying two independent short arcs of observations has been solved. For each VA in the admissible region of the first arc we consider prediction at the time of the second arc and the corresponding covariance matrix, and we compare them with the attributable of the second arc with its own covariance. By using the penalty (increase in the sum of squares, as in the algorithms for identification) we select the VAs which can fit together both arcs and compute a preliminary orbit. Even two attributables may not be enough to compute an orbit with a convergent differential corrections algorithm. The preliminary orbits are used as first guess for constrained differential corrections, providing solutions along the Line Of Variations (LOV) which can be used as second generation VAs to further predict the observations at the time of a third arc. In general the identification with a third arc will ensure a least squares orbit, with uncertainty described by the covariance matrix.

Milani, Andrea; Kneževi?, Zoran

2005-04-01

156

Orbit-based representation of equilibrium distribution functions for low-noise initialization of kinetic simulations of toroidal plasmas  

NASA Astrophysics Data System (ADS)

This work deals with the initial loading of phase space markers for global gyrokinetic particle-in-cell (PIC) simulations of plasmas that are magnetically confined in a toroidally axisymmetric configuration. A method is presented, which allows to prepare a marker distribution that is independent of time. This is achieved by discretizing the phase space along lines of constants of motion, which allows to load markers on the toroidal surfaces of unperturbed guiding center orbits. On each orbit surface, markers are distributed uniformly in time, so their distribution represents the compressible motion of physical particles. This method allows to initialize global PIC codes with an accurate equilibrium distribution function for charged particles, taking into account prompt losses to the wall. It facilitates simulations with lower noise levels and minimal noise-signal correlation; especially, in the linear regime. The problem considered is the representation of energetic ions in tokamaks, which are characterized by large drifts across magnetic surfaces.

Bierwage, A.; di Troia, C.; Briguglio, S.; Vlad, G.

2012-05-01

157

DPOD2005 : Realization of a DORIS terrestrial reference frame for precise orbit determination  

NASA Astrophysics Data System (ADS)

Scientific studies related to altimetry data (mean sea level determination and its time evolution) require centimeter-level orbit determination in the radial component of the satellite. Change in station coordinates and velocities affect the orbit determination and the derived oceanographic results. Following the release of the ITRF2005, we conducted an extensive study related to the DORIS tracking network. For all ground beacons, we verified if the ITRF2005 position and velocity can be extrapolated in time without significant loss of precision. We tried to identified discontinuities in the DORIS coordinates time series, either caused by physical reason, such as Earthquakes, or by instrumental causes. We also identified time periods for which data for a specific station should not be used for orbit determination. In particular, specific stations such as Socorro Island, on which horizontal and vertical movements are detected from the DORIS results will be presented and can be explained by a volcano deformation. Finally, a more complex example will be provided for the Arequipa station, where a major Earthquake happened on June 23, 2001 and for which some relaxation effects are noticeable in the velocity determination even 2 years after the station displacement. A complete set of positions and velocities (by intervals) is given (DPOD2005) and will be used for Jason and TOPEX orbit determination.

Willis, Pascal; Ries, John C.; Soudarin, Laurent; Zelensky, Nikita; Pavlis, Erricos C.

158

Accurate orbit determination strategies for the tracking and data relay satellites  

NASA Astrophysics Data System (ADS)

The National Aeronautics and Space Administration (NASA) has developed the Tracking and Data Relay Satellite (TDRS) System (TDRSS) for tracking and communications support of low Earth-orbiting satellites. TDRSS has the operational capability of providing 85% coverage for TDRSS-user spacecraft. TDRSS currently consists of five geosynchronous spacecraft and the White Sands Complex (WSC) at White Sands, New Mexico. The Bilateration Ranging Transponder System (BRTS) provides range and Doppler measurements for each TDRS. The ground-based BRTS transponders are tracked as if they were TDRSS-user spacecraft. Since the positions of the BRTS transponders are known, their radiometric tracking measurements can be used to provide a well-determined ephemeris for the TDRS spacecraft. For high-accuracy orbit determination of a TDRSS user, such as the Ocean Topography Experiment (TOPEX)/Poseidon spacecraft, high-accuracy TDRS orbits are required. This paper reports on successive refinements in improved techniques and procedures leading to more accurate TDRS orbit determination strategies using the Goddard Trajectory Determination System (GTDS). These strategies range from the standard operational solution using only the BRTS tracking measurements to a sophisticated iterative process involving several successive simultaneous solutions for multiple TDRSs and a TDRSS-user spacecraft. Results are presented for GTDS-generated TDRS ephemerides produced in simultaneous solutions with the TOPEX/Poseidon spacecraft. Strategies with different user spacecraft, as well as schemes for recovering accurate TDRS orbits following a TDRS maneuver, are also presented. In addition, a comprehensive assessment and evaluation of alternative strategies for TDRS orbit determination, excluding BRTS tracking measurements, are presented.

Oza, D. H.; Bolvin, D. T.; Lorah, J. M.; Lee, T.; Doll, C. E.

1995-05-01

159

Nontraditional method for determining unperturbed orbits of unknown space objects using incomplete optical observational data  

NASA Astrophysics Data System (ADS)

A physical-geometrical method for computing the orbits of earth satellites on the basis of an inadequate number of angular observations (N3) was developed. Specifically, a new method has been developed for calculating the elements of Keplerian orbits of unidentified artificial satellites using two angular observations (alpha sub k, S sub k, k = 1). The first section gives procedures for determining the topocentric distance to AES on the basis of one optical observation. This is followed by description of a very simple method for determining unperturbed orbits using two satellite position vectors and a time interval which is applicable even in the case of antiparallel AED position vectors, a method designated the R sub 2 iterations method.

Perov, N. I.

1985-02-01

160

DIODE: A DORIS based real-time on-board orbit determination system for SPOT 4  

NASA Astrophysics Data System (ADS)

A space borne orbit determination system is being developed by the French Space Agency (CNES) for the SPOT 4 satellite. This system processing Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) measurements to produce an orbit in real-time and on-board of the satellite, with an accuracy better than 30 meters rms. Its goal is to provide spacecraft position and velocity information to ground centers processing SPOT 4 images. This paper gives some background on the on-board orbit determination project, its objectives and its organization. It explains how this new function will interact with the SPOT 4 and DORIS projects. The implementation both on-board and on the ground is described. Special emphasis is given to the flight software architecture and algorithms. Various tests of the algorithms, of the operational procedures, and of the numerical accuracy are presented and analyzed.

Berthias, Jean-Paul; Jayles, Christian; Pradines, Didier

161

Effect of ITRF2000 on TOPEX/POSEIDON Orbit Determination and Mean Sea Level Time Series  

NASA Astrophysics Data System (ADS)

The precision orbits produced by NASA for the TOPEX/POSEIDON altimeter satellite are based on a set of SLR and DORIS station coordinates determined in 1995 (CSR95L01 and CSR95D02). However, it is clear that this terrestrial reference system needs to be updated. In particular, the DORIS station velocities in CSR95D02 are not sufficiently well determined to accurately propagate the positions into the current years, much less into the Jason-1 follow-on mission. The ITRF2000 reference frame is a new solution for the SLR, DORIS and GPS tracking stations which is a significant improvement over previous solutions. The concern is that artificial trends can be introduced into the sea level observations from changes or errors in the reference system used for orbit determination. ITRF97 has a significant offset (2 cm) and drift (2 mm/yr) relative to the CSR system, so it was not adopted for the NASA orbit production. ITRF2000 has adopted the SLR determination of the terrestrial origin, which has substantially removed this offset and drift. By adopting ITRF2000, NASA and CNES should be able to adopt the same terrestrial reference frame for the transition from TOPEX/POSEIDON to Jason-1. The level of backward compatibility with the CSR95L01/D02 system is examined to determine if any significant artifacts in the sea level time series are introduced in the sea level time series based on the NASA orbits.

Ries, J. C.; Chambers, D. P.; Choi, K.; Eanes, R. J.

2001-12-01

162

Application of multi-source data fusion in navigation satellite autonomous orbit determination  

NASA Astrophysics Data System (ADS)

Aiming at the orbit floating or so called constellation rotation in navigation satellite autonomous orbit determination, an approach based on multi sources data fusion was introduced, that is to introduce angle observation from on board star sensor toward fixed star to fix the ascending node ?, one of the six orbit elements so as to avoid constellation rotation. During data processing, a generalized measurement model based on matrix Cholesky decomposition and the method of measurement noises de-correlation was adopted. On the foundation of roundly analysis of present theories and methods of multi sources data fusion, and characteristics of multi sources measurement data fusion taken into account, two sorts of multi sources data fusion measurement models based on independent same distribution and correlation of measurement noises were conducted. Theoretical analysis and simulation experiment show that navigation satellite autonomous orbit determination based on multi sources data fusion can well solve the problem of orbit floating contrasting against that of only inter-satellite observations used.

Hou, Fen; Liu, Hui

2009-10-01

163

Orbit Determination System with Reasonable Performance Using Low-Cost Ground Station for Nanosatellite Projects  

NASA Astrophysics Data System (ADS)

Recently the activities for the development of micro- and nano- satellites like a cubesat are being increased. A lot of satellites are operated at a ground station located in a university, but public orbit information is used. In this paper, the orbit determination system is constructed using observations of Doppler frequency at a low-cost ground station. The traditional batch state estimation filter is used, and the orbital elements of satellite position and velocity in inertia coordinates are determined from the Doppler frequency of receiving signals. The verification tests are conducted using UHF-band signals (about 430 MHz) received at an amateur radio station and S-band signals (about 2.2 GHz) received at a 2.4-m parabola antenna from real satellites, and the valid performance is conformed for tracking satellites not depending on public orbit information. The error is max. 0.3 degrees in direction and max. 3.9 km in position for UHF-band signals, and max. 1.1 degrees in direction and max. 37 km in position for S-band signals. This method is valid especially for low-earth-orbit satellites with large Doppler effect.

Sakamoto, Yuji; Yoneyama, Akari

164

Orbital Evolution and Determination of Trans-Neptunian Binaries and Multiples  

NASA Astrophysics Data System (ADS)

Numerous binary systems have been observed in the solar system beyond Neptune, including approximately one third of cold classical objects. These systems can be strongly perturbed by solar tides (Kozai cycles), dissipative body tides, spin-orbit interactions, and shape effects. Such perturbations can rapidly destabilize binary orbits, constraining both the allowed orbital solutions and the objects' physical properties. In addition, two hierarchical multiple systems are known, Pluto and (47171) 1999 TC36, and more will likely be discovered in the future. The hierarchical nature of these systems can cause rapid and complex orbital evolution over timescales fast enough to confuse a Keplerian fit. Precise modeling of these systems therefore requires a simulation that takes all these factors into account and which can easily interface with observational data. We are developing such a model by building an n-body simulator with shape-effects, torques, and body tides. In the process of fitting, it can constrain otherwise unobservable physical properties, such as shape, tidal dissipation, and masses for small satellites. In addition to better orbital determination, this model can also be used to test the stability of complex systems. Recent simulations have shown that a combination of Kozai cycles, body tides, and shape effects can dominate the evolution of trans-Neptunian binaries. This model can similarly determine which evolutionary paths can produce more complex trans-Neptunian systems.

Porter, Simon; Grundy, W.

2012-10-01

165

Orbit and Attitude Determination Results During Launch Support Operations for SBS-5. (Satellite Business Systems).  

National Technical Information Service (NTIS)

Presented are orbit and attitude determination results from the launch of Satellite Business Systems (SBS)-5 satellite on September 8, 1988 by Arianespace. SBS-5 is a (HS-376) spin stabilized spacecraft. The launch vehicle injected the spacecraft into a l...

K. R. Hartman P. J. Iano

1989-01-01

166

A Pegasus Computer Programme for the Assessment of the Accuracy of Satellite Orbit Determination.  

National Technical Information Service (NTIS)

A computer programme is described by means of which one may estimate the potential accuracy of the elements of a given satellite orbit, if determined from observational data of specified type and assumed accuracy. An application of the programme is made t...

R. H. Gooding

1965-01-01

167

A Study to Explore the Use of Orbital Remote Sensing to Determine Native Arid Plant Distribution.  

National Technical Information Service (NTIS)

Progress Report; A study to explore the use of orbital remote sensing to determine native arid plant distribution; UN 613; No ERTS-1 data has as yet been received; Eight desert vegetation sites were picked for intensive study along a 25 mile transect in t...

W. G. McGinnies

1972-01-01

168

Unbiased orbit determination for the next generation asteroid\\/comet surveys  

Microsoft Academic Search

In the next generation surveys, the discovery of moving objects can be successful only if an observation strategy and the identification\\/orbit determination procedure are appropriate for the diverse apparent motions of the target sub-populations. The observations must accurately measure the displacement over a short interval of time; observations believed to belong to the same object have to be connected into

A. Milani; G. F. Gronchi; Z. Knezevic; M. E. Sansaturio; O. Arratia; L. Denneau; T. Grav; J. Heasley; R. Jedicke; J. Kubica

2006-01-01

169

Unbiased orbit determination for the next generation asteroid\\/comet surveys  

Microsoft Academic Search

In the next generation surveys, the discovery of moving objects can be successful only if an observation strategy and the identication\\/orbit determination procedure are appropriate for the diverse apparent motions of the target sub-populations. The observations must accurately measure the displacement over a short interval of time; observations believed to belong to the same object have to be connected into

A. Milani; G. F. Gronchi; Z. Kne; M. E. Sansaturio; O. Arratia; L. Denneau; T. Grav; J. Heasley; R. Jedicke; J. Kubica

2005-01-01

170

Short arc orbit determination for altimeter calibration and validation on TOPEX/POSEIDON  

NASA Astrophysics Data System (ADS)

TOPEX/POSEIDON (T/P) is a joint mission of United States' National Aeronautics and Space Administration (NASA) and French Centre National d'Etudes Spatiales (CNES) design launched August 10, 1992. It carries two radar altimeters which alternately share a common antenna. There are two project designated verification sites, a NASA site off the coast at Pt. Conception, CA and a CNES site near Lampedusa Island in the Mediterranean Sea. Altimeter calibration and validation for T/P is performed over these highly instrumented sites by comparing the spacecraft's altimeter radar range to computed range based on in situ measurements which include the estimated orbit position. This paper presents selected results of orbit determination over each of these sites to support altimeter verification. A short arc orbit determination technique is used to estimate a locally accurate position determination of T/P from less than one revolution of satellite laser ranging (SLR) data. This technique is relatively insensitive to gravitational and non-gravitational force modeling errors and is demonstrated by covariance analysis and by comparison to orbits determined from longer arcs of data and other tracking data types, such as Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) and Global Positioning System Demonstration Receiver (GPSDR) data.

Williams, B. G.; Christensen, E. J.; Yuan, D. N.; McColl, K. C.; Sunseri, R. F.

171

Ers-1 Orbit Determination from Laser, Tranet, and Prare Tracking Data.  

National Technical Information Service (NTIS)

An error model for ERS-1 orbit determination was derived and was used for covariance analyses of 3-day, 2-revolution, and 15-min data arcs. For the 3-day and 2-revolution arcs, laser range and TRANET 2 range rate tracking concepts were studied. Laser and ...

K. F. Wakker B. A. C. Ambrosius

1983-01-01

172

Comet Halley Orbit Determination by Means of the Pathfinder Data: Methods Used and Results Obtained.  

National Technical Information Service (NTIS)

Use of the pointing angle from the Soviet spacecraft Vega-1 and Vega-2 to the nucleus of the comet, derived from attitude and camera data collected onboard the two spacecraft, to determine comet orbit for Halley flyby by Giotto is described. Pathfinder re...

P. Debroeck F. Hechler P. Kristiansen A. Sukhanov

1986-01-01

173

Frontier Molecular Orbital determination of the active sites on dispersed metal catalysts.  

National Technical Information Service (NTIS)

An angular overlap calculation has been used to determine the s, p and d orbital energy levels of the different types of surface sites present on a dispersed metal catalysts. The basis for these calculations is the reported finding that a large number of ...

R. L. Augustine K. M. Lahanas

1992-01-01

174

Global Ultaviolet Imager (GUVI): on-Orbit Performance and Initial Results  

Microsoft Academic Search

The Global Ultraviolet Imager (GUVI) is one of four scientific instruments aboard the NASA TIMED (Thermosphere Ionosphere Mesosphere Energy and Dynamics) satellite launched Dec.6, 2001 into a 630 km circular polar orbit inclined at 74 degrees. The GUVI investigation is to provide geophysical variables derived from the far ultraviolet (FUV) dayglow and auroral emissions emanating from the Earth's thermosphere. The

A. B. Christensen; D. Strickland; L. Paxton; D. Morrison; G. Crowley; R. Meier; J. Craven; C. Meng; C. Swenson; R. Walterscheid; S. Avery; P. Straus

2002-01-01

175

Impact of GPS satellite antenna offsets on GPS-based precise orbit determination  

NASA Astrophysics Data System (ADS)

Since the successful demonstration of GPS-based Precise Orbit Determination (POD) on TOPEX/Poseidon in 1992, GPS-based POD for Low-Earth Orbiters (LEO) such as the CHAMP and GRACE satellites has become a popular method. The orbit accuracy of GPS-based POD has been improved from 3 cm to 1 cm in the radial direction. In order to achieve higher-accuracy results, it is necessary to understand and try to reduce the impact of various error sources on the orbits. One of them is the GPS satellite antenna offset. Currently, most GPS data processing institutions are using relative GPS satellite antenna offsets, and there are big differences (meter level) between the antenna offsets. In addition, accurate antenna offset values can be only estimated from processing GPS data currently with an accuracy of cm to dm levels. In this paper, we studied the impact of GPS satellite antenna offsets on GPS-based POD using the different offsets. The results show that the antenna offsets have large effects (a few cm) on the GPS onboard receiver antenna estimation and relatively small effects (about one cm) on the satellite orbit accuracy.

Kang, Z.; Tapley, B.; Ries, J.; Bettadpur, S.; Nagel, P.

176

Orbit determination and analysis for 1970-97B at 14th-order resonance  

NASA Astrophysics Data System (ADS)

The orbit of the satellite 1970-97B, the rocket of Cosmos 378, at inclination 74 deg, has been determined at 18 epochs between April and August 1971, when the effects of 14th-order resonance with the Earth's gravitational field were appreciable. The orbits were determined with the PROP 6 program from Hewitt camera, kinetheodolite, US Navy and visual observations, and an average accuracy of 90 m in perigee distance was achieved, despite the low perigee height (near 230 km) and the consequent high drag. The orbits, together with 13 previously evaluated, have been analysed to reveal the effects of the 14th-order resonance and to evaluate six lumped geopotential harmonics of order 14. Because the orbit passed through resonance rapidly, the values are not as accurate as those from slow resonances; but they are more accurate than any others available for an inclination near 74 deg, and have proved their worth in a recent determination of individual 14th-order coefficients.

Winterbottom, A. N.; King-Hele, D. G.

1985-06-01

177

Orbit determination and analysis for 1970-97B at 14th-order resonance  

NASA Astrophysics Data System (ADS)

The orbit of the satellite 1970-97B, the rocket of Cosmos 378, at inclination 74 deg, has been determined at 18 epochs between April and August 1971, when the effects of 14th-order resonance with the earth's gravitational field were appreciable. The orbits were determined with the PROP 6 program from Hewitt camera, kinetheodolite, U.S. Navy, and visual observations, and an average accuracy of 90 m in perigee distance was achieved, despite the low perigee height (near 230 km) and the consequent high drag. The orbits, together with 13 previously evaluated, have been analyzed to reveal the effects of the 14th-order resonance and to evaluate six lumped geopotential harmonics of order 14. Because the orbit passed through resonance rapidly, the values are not as accurate as those from slow resonances; but they are more accurate than any others available for an inclination near 74 deg and have proved their worth in a recent determination of individual 14th-order coefficients.

Winterbottom, A. N.; King-Hele, D. G.

1986-01-01

178

A multi-satellite orbit determination problem in a parallel processing environment  

NASA Astrophysics Data System (ADS)

The Engineering Orbit Analysis Unit at GE Valley Forge used an Intel Hypercube Parallel Processor to investigate the performance and gain experience of parallel processors with a multi-satellite orbit determination problem. A general study was selected in which major blocks of computation for the multi-satellite orbit computations were used as units to be assigned to the various processors on the Hypercube. Problems encountered or successes achieved in addressing the orbit determination problem would be more likely to be transferable to other parallel processors. The prime objective was to study the algorithm to allow processing of observations later in time than those employed in the state update. Expertise in ephemeris determination was exploited in addressing these problems and the facility used to bring a realism to the study which would highlight the problems which may not otherwise be anticipated. Secondary objectives were to gain experience of a non-trivial problem in a parallel processor environment, to explore the necessary interplay of serial and parallel sections of the algorithm in terms of timing studies, to explore the granularity (coarse vs. fine grain) to discover the granularity limit above which there would be a risk of starvation where the majority of nodes would be idle or under the limit where the overhead associated with splitting the problem may require more work and communication time than is useful.

Deakyne, M. S.; Anderle, R. J.

1988-09-01

179

TOPAS a new GPS adjustment system for multistation positioning and orbit determination  

Microsoft Academic Search

A new software package is presented for positioning with the Global Positioning System in a multistation\\/multisession network approach. The program allows the determination of satellite orbits, clock and atmospheric parameters and terrestrial positions by using raw undifferenced carrier phase and code measurements in a sequential approach. All parameters are modelled and determined in an optimal filtering\\/smoothing technique based on U-D

Herbert Landau

1988-01-01

180

TerraSAR-X precise orbit determination with real-time GPS ephemerides  

NASA Astrophysics Data System (ADS)

TerraSAR-X is a German Synthetic Aperture Radar (SAR) satellite, which was launched in June 2007 from Baikonour. Its task is to acquire radar images of the Earth's surface. In order to locate the radar data takes precisely, the satellite is equipped with a high-quality dual-frequency GPS receiver -the Integrated Geodetic and Occultation Receiver (IGOR) provided by the GeoForschungsZentrum Potsdam (GFZ). Using GPS observations from the IGOR instrument in a reduced dynamic precise orbit determination (POD), the German Space Operations Center (DLR/GSOC) is computing rapid and science orbit products on a routine basis. The rapid orbit products arrive with a latency of about one hour after data reception with an accuracy of 10-20 cm. Science orbit products are computed with a latency of five days achieving an accuracy of about 5cm (3D-RMS). For active and future Earth observation missions, the availability of near real-time precise orbit information is becoming more and more important. Other applications of near real-time orbit products include the processing of GNSS radio occulation measurements for atmospheric sounding as well as altimeter measurements of ocean surface heights, which are nowadays employed in global weather and ocean circulation models with short latencies. For example after natural disasters it is necessary to evaluate the damage by satellite images as soon as possible. The latency and quality of POD results is mainly driven by the availability of precise GPS ephemerides. In order to have high-quality GPS ephemerides available at real-time, GSOC has developed the real-time clock estimation system RETICLE. The system receives NTRIP-data streams with GNSS observations from the global tracking network of IGS in real-time. Using the known station position, RETICLE estimates precise GPS satellite clock offsets and drifts based on the most recent available IGU predicted orbits. The clock offset estimates have an accuracy of better than 0.3 ns and are globally valid. The latency of the estimated clocks is approximately 7 seconds. Another limiting factor is the frequency of satellite downlinks and the latency of the data transfer from the ground station to the computation center. Therefore a near real-time scenario is examined in which the satellite has about one ground station contact per orbit or respectively one contact in 90 minutes. The results of the near real-time POD are evaluated in an internal consistency check and compared against the science orbit solution and laser ranging observations.

Wermuth, Martin; Hauschild, Andre; Montenbruck, Oliver; Kahle, Ralph

181

Two-site orbit determination: The 2003 GEO observation campaign from Collepardo and Mallorca  

NASA Astrophysics Data System (ADS)

In September 2003 the Group of Astrodynamics of the University of Rome "La Sapienza" (GAUSS) carried out a two-site optical observation campaign addressed to the orbit determination of objects in the geosynchronous region without a priori information. Two 40 cm aperture Ritchey-Chrétien telescopes were employed: the f/7.5 "Collepardo Automatic Telescope" (CAT, located in Collepardo, Italy) and an f/5 tube of the "Observatori Astronòmic de Mallorca" (OAM, located in Mallorca, Spain). The baseline between the sites is about 1000 km. Three second long, 1 min apart exposures were simultaneously taken in sidereal tracking mode, looking at the same arcs of the geosynchronous ring. The size of the fields of view allowed to see a few satellites in two successive frames from both sites. The Lambert theorem has been exploited to determine the orbits, averaging the data with the least square method in the case that more than 2 points were available. Of course, the longer the time interval between the positions, the lower the effect of measuring errors. Nevertheless, the only way to have quite distant points would be tracking the satellite, but following-up is typically time demanding thus not suitable for a surveillance campaign, hence not very interesting from a practical standpoint. In the paper the results of the orbit determination from the September 2003 campaign are reported. More in detail, the outcomes of some classical methods for solving the Lambert theorem, are compared with solutions based on the measurements fitted with the least squares method, with the circular orbit assumption results, with the one-site complete orbit determination and with the TLEs.

Porfilio, Manfredi; Piergentili, Fabrizio; Graziani, Filippo

2006-01-01

182

Initial Mars Upper Atmospheric Structure Results from the Accelerometer Science Experiment aboard Mars Reconnaissance Orbiter  

NASA Astrophysics Data System (ADS)

Designed for aerobraking, Mars Reconnaissance Orbiter (MRO) launched on August 12, 2005, achieved Mars Orbital Insertion (MOI), March 10, 2006, and successfully completed aerobraking on August 30, 2006. Atmospheric density decreases exponentially with increasing height. By small propulsive adjustments of the apoapsis orbital velocity, periapsis altitude was fine tuned to the density surface that safely used the atmosphere of Mars to aerobrake over 445 orbits, providing 890 vertical structures. MRO periapsis precesses from near the South Pole at 6pm LST to near the equator at 3am LST. Meanwhile, apoapsis is brought dramatically from 40,000km at MOI to 480 km at aerobraking completion (ABX). Without aerobraking this would have required an additional 400kg of fuel. After ABX, two small propulsive orbital adjustment maneuvers September 5, 2006 and September 11, 2006 established the final Primary Science Orbit (PSO). Each of the 445 aerobraking orbits provides, a pair of vertical structures inbound toward periapsis and outbound from periapsis, with a distribution of density, scale heights, temperatures, and pressures along the orbital path, providing key in situ insight into various upper atmosphere (> 100 km) processes. One of the major questions for scientists studying Mars is: Where did the water go? Honeywell's substantially improved electronics package for its IMU (QA-2000 accelerometer, gyro, electronics) maximized accelerometer sensitivities at the requests of The George Washington University, JPL, and Lockheed Martin. The improved accelerometer sensitivities allowed density measurements to exceed 200km, at least 40 km higher than with Mars Odyssey (MO). This extends vertical structures from MRO into the neutral lower exosphere, a region where various processes may allow atmospheric gasses to escape. Over the eons, water may have been lost in both the lower atmosphere and the upper atmosphere, thus the water balance throughout the entire atmosphere from subsurface to exosphere may be equally critical. Comparisons of accelerometer data from Mars Global Surveyor (MGS), MO and MRO will help characterize key temporal and spatial cycles. During the Odyssey Aerobraking we discovered a very strong winter polar warming near 100km, where temperatures were found to be up to 100K higher than expected near the North Pole. However, with MRO we detected only a very weak winter polar warming at the South Pole. It is expected that the polar warming results from cross equatorial meridional flow from the summer hemisphere into the winter hemisphere with adiabatic heating near the winter pole. The discovery from MRO of a very weak winter warming near aphelion in the southern winter polar region compared to the very strong winter warming near perihelion in the northern winter polar region is apparently due to a weaker input of solar energy into the meridional circulation resulting in less adiabatic heating near aphelion in the winter polar region. Results are also shown of global scale measurements of non- migrating tides and of global density and temperature distributions.

Keating, G. M.; Bougher, S. W.; Theriot, M. E.; Tolson, R. H.; Blanchard, R. C.; Zurek, R. W.; Forbes, J. M.; Murphy, J.

2006-12-01

183

Initial attitude acquisition result of the Alsat-1 first Algerian microsatellite in orbit  

Microsoft Academic Search

On the November 28th, 2002 at 06:07 am GMT, the first Algerian microsatellite AIsat-1 was launched from the cosmodrome of Plesetsk in Russia into a 700 km sun synchronous orbit. Alsat-1 is an enhanced microsatellite (90 Kg), stabilised in 3 axis for image acquisition mode. It was designed for disaster monitoring and is a part of the international constellation dedicated

A. M. S. Mohammed; M. Benyettou; M. N. Sweeting; J. R. Cooksley

2005-01-01

184

Initial effects of nuclear weapon x-radiation on the LAMPSHADE orbital debris satellite shield  

Microsoft Academic Search

One-dimensional thermal-hydrodynamic calculations have been carried out to estimate the response of the lead bumper plate and tantalum liquidation screen of the LAMPSHADE orbital debris satellite shield. The mass loss fraction in the solid, liquid, and vapor phases as a function of time after irradiation for several typical incident x-ray spectra fluences were calculated using the PUFF-TFT code. The material

M. S. Smith; R. T. Santoro

1989-01-01

185

Two-site autonomous orbit determination: the 2003 GEO observation campaign from Collepardo and Mallorca  

NASA Astrophysics Data System (ADS)

In September 2003 the Group of Astrodynamics of the University of Rome ``La Sapienza'' (GAUSS) carried out a two-site observation campaign devoted to the autonomous orbit determination of objects in the geosynchronous region. Two 40 cm aperture Ritchey-Chrétien devices were employed: the f/7.5 ``Collepardo Automatic Telescope'' (CAT, located in Collepardo, Italy) and a f/5 tube of the ``Observatori Astronòmic de Mallorca'' (OAM, located in Mallorca, Spain). The baseline between the sites is 916 km. 3 s long, 1 minute apart exposures were simultaneously taken in sidereal tracking mode, looking at the same arcs of the GEO ring; the fields of view allowed to see a few satellites in two successive frames from both sites, thus providing two positions: the Lambert theorem has been exploited to determining the orbits. A first order approximation of the targets angular motion has been used to fix synchronism errors. Of course, the longer the time interval between positions, the lower the effect of measurements errors. Nevertheless, the only way to have quite distant points would be tracking the satellite, which is typically not suitable for a surveillance campaign, thus not interesting from a practical standpoint. Currently, in the Measurement Working Group of the Inter-Agency Space Debris Co-ordination Committee (IADC), the orbits of the objects detected during GEO optical observation campaigns, are estimated under the assumption of null eccentricity. This is the only way, if one telescope is used and if only a few observations are available. Obviously, the hypothesis of circular orbit provides excellent results for actually geostationary satellites and definitely incorrect estimates for high eccentricity objects. The systematic cooperation of couples of observatories, would provide good orbit determination, for instance, for GTO debris. In the paper the results of the orbit determination from the September 2003 campaign are reported. More in detail, the outcomes of some classical methods for solving the Lambert theorem, are compared with the least squares improved solutions, with the circular orbit assumption results and with the TLEs.

Porfilio, M.; Piergentili, F.; Graziani, F.

186

A CHAMP-only gravity field model from kinematic orbit determination using the energy balance approach  

NASA Astrophysics Data System (ADS)

A gravity field model has been computed based solely on CHAMP GPS orbit tracking and accelerometry, without any prior gravity information entering the computation. The basic characteristics of our approach are (1) the use of purely kinematic orbits, (2) a translation of velocities to gravity potential employing the principle of energy conservation and (3) correction for non-gravitational forces either derived from measured accelerations or from models. The method of gravity field recovery using energy considerations has recently been tested successfully by various groups, making use of CHAMP data. Thereby the satellite's position and velocity came from a reduced dynamic orbit determination which contains a priori gravity field information. It can be shown, that the derived gravity field is correlated with this a priori information. In order to derive an independent solution, the presented gravity field was derived from a purely kinematic CHAMP orbit. In this case the satellite velocities have to be determined from the kinematic positions separately. Several month of CHAMP data have been used to derive the gravity field model. The quality of the field has been tested by comparing the model to other state-of-the-art models as well as to terrestrial data.

Gerlach, Ch.; Iapg Gravity Team

2003-04-01

187

New technique for determining the shock initiation sensitivity of explosives  

Microsoft Academic Search

A new technique for determining the shock initiation sensitivity of explosives is described. It involves a flyer plate impinging upon the test explosive to induce initiation of detonation. An electrically exploded foil propels the flyer plate, which is a thin disk of polyimide (Kapton) 1 mm in dia; the charging voltage applied to the capacitor discharge fireset is used to

1977-01-01

188

The status of YOHKOH in orbit - an introduction to the initial scientific results  

NASA Astrophysics Data System (ADS)

The design and in-orbit function of the Yohkoh spacecraft and its four scientific instruments are described. The instruments include the Hard X-ray Telescope (HXT), the Soft X-ray Telescope (SXT), the Wide-Band Spectrometer (WBS), and the Bragg Crystal Spectrometers (BCS). The key feature of the Yohkoh is the combined use of the coaligned telescopes (HRT and SXT) and spectrometers (WBS and BCS) operating simultaneously, thus constituting a spaceborne solar observatory. The SXT has already taken hundreds of thousands of excellent pictures of active regions and of flares, and the HXT has obtained data concerning more than 200 major flares.

Ogawara, Yoshiaki; Acton, Loren W.; Bentley, Robert D.; Bruner, Marilyn E.; Culhane, J. Leonard; Hiei, Eijiro; Hirayama, Tadashi; Hudson, Hugh S.; Kosugi, Takeo; Lemen, James R.; Strong, Keith T.; Tsuneta, Saku; Uchida, Yutaka; Watanabe, Tetsuya; Yoshimori, Masato

1992-10-01

189

CBERS-2 LEOP Orbit Analysis  

Microsoft Academic Search

This work presents an analysis of CBERS-2 orbit during LEOP (Launching and Early Orbit Phase), including the main aspects related to the INPE´s pass to pass improvement of the initial orbit determination process application. This is the second of four sun-synchronous earth observation satellites foreseen to be developed and manufactured within a cooperation program between Brazil and China. A short

V. Orlando; H. K. Kuga; J. Tominaga

2004-01-01

190

Chang’E-1 precision orbit determination and lunar gravity field solution  

NASA Astrophysics Data System (ADS)

In this paper we present results assessing the role of Very Long Baseline Interferometry (VLBI) tracking data through precision orbit determination (POD) during the check-out phase for Chang’E-1, and the lunar gravity field solution CEGM-01 based on the orbital tracking data acquired during the nominal phase of the mission. The POD of Chang’E-1 is performed using S-band two-way Range and Range Rate (R&RR) data, together with VLBI delay and delay rate observations. The role of the VLBI data in the POD of Chang’E-1 is analyzed, and the resulting orbital accuracies are estimated for different solution strategies. The final orbital accuracies proved that the VLBI tracking data can improve the Chang’E-1 POD significantly. Consequently, CEGM-01 based on six-month tracking data during Chang’E-1 nominal mission phase is presented, and the accuracy of the model is assessed by means of the gravity field power spectrum, admittance and coherence between gravity and topography, lunar surface gravity anomaly and POD for both Chang’E-1 and Lunar Prospector (LP). Our analysis indicates that CEGM-01 has significant improvements over a prior model (i.e. GLGM-2), and shows the potential of Chang’E-1 tracking data in high resolution lunar gravity field model solution by combining with SELENE and LP tracking data.

Jianguo, Yan; Jinsong, Ping; Fei, Li; Jianfeng, Cao; Qian, Huang; Lihe, Fung

2010-07-01

191

Precise orbit determination of GIOVE-B based on the CONGO network  

NASA Astrophysics Data System (ADS)

GIOVE-B is one of two test satellites for the future European Global Navigation Satellite System Galileo. The Cooperative Network for GIOVE Observation (CONGO) is a global tracking network of GIOVE-capable receivers established by Deutsches Zentrum für Luft- und Raumfahrt (DLR) and Bundesamt für Kartographie und Geodäsie (BKG). This network provides the basis for the precise orbit determination of the GIOVE-B satellite for the time period 29 June till 27 October 2009 with a modified version of the Bernese GPS Software. Different arc lengths and sets of orbit parameters were tested. These tests showed that the full set of nine radiation pressure parameters resulted in a better performance than the reduced set of five parameters. An internal precision of about one to two decimeters could be demonstrated for the central day of 5-day solutions. The orbit predictions have a precision of about 1 m for a prediction period of 24 h. External validations with Satellite Laser Ranging (SLR) show residuals on the level of 12 cm. The accuracy of the final orbits is expected to be on the few decimeter level.

Steigenberger, P.; Hugentobler, U.; Montenbruck, O.; Hauschild, A.

2011-06-01

192

Differential algebraic determination of high-order off-energy closed orbits, chromaticities, and momentum compactions  

NASA Astrophysics Data System (ADS)

For some modern particle accelerators, including the planned muon collider, the accurate analysis of non-linear time-of-flight effects in the form of momentum compactions is critical for the preservation of bunch structure. A Differential Algebra-based (DA) method is presented that allows the determination of off-energy closed orbits and chromaticities to any order. By performing a coordinate transformation to the off-energy closed orbit, it is possible to compute momentum compactions analytically. This method has been implemented in the code COSY INFINITY and is tested for two cases where analytical solutions can be obtained by hand; agreement to machine precision is found. By contrast, comparisons are made with several codes that use conventional numerical methods for the determination of momentum compaction, and it is found that these approaches sometimes yield rather inaccurate results, especially for higher orders.

Berz, M.; Erdélyi, B.; Wan, W.; Ng, K.-Y.

1999-05-01

193

Upper-atmosphere zonal winds determined from orbital analysis of Cosmos 482, 1972-23A  

NASA Astrophysics Data System (ADS)

Atmospheric rotation produces a change in orbital inclination which decreases under the effect of zonal winds. Inclination values obtained for Cosmos 482 are analyzed to determine the atmospheric rotation rate of the zonal wind (East-West) at a height near 235 km. Orbital parameters of Cosmos 482 at 55 epochs from August 1975 to October 1977 were determined by the PROP 6 program, and calculations reveal a diurnal and seasonal dependence. The atmospheric rotation rate has a low average value of 0.9 in summer and a high evening value of 1.4 during the winter months. Resultant wind velocities vary between 48 m/s east to west and 193 m/s west to east, with an average of 48 m/s west to east.

Moore, P.

1981-05-01

194

Differential algebraic determination of high-order off-energy closed orbits, chromaticities, and momentum compactions  

Microsoft Academic Search

For some modern particle accelerators, including the planned muon collider, the accurate analysis of non-linear time-of-flight effects in the form of momentum compactions is critical for the preservation of bunch structure. A Differential Algebra-based (DA) method is presented that allows the determination of off-energy closed orbits and chromaticities to any order. By performing a coordinate transformation to the off-energy closed

Martin Berz; Béla Erdélyi; Weishi Wan; King-Yuen Ng

1999-01-01

195

Mars Express tracking and orbit determination trials with Chinese VLBI network  

Microsoft Academic Search

With strong support from European Space Agency (ESA), Shanghai Astronomical Observatory (SHAO) organized a tracking and orbit\\u000a determination trails using Chinese VLBI Network (CVN) to track Mars Express, the first Mars probe launched by ESA. Using a\\u000a high-resolution VLBI software correlator and Doppler measurement system developed in-house, two sets of tracking data, VLBI\\u000a and Doppler, were acquired. The trials represent

JianFeng Cao; Yong Huang; XiaoGong Hu; MaoLi Ma; WeiMin Zheng

2010-01-01

196

Orbit Determination for Comet C/2011 W3 (Lovejoy) Using a New Technique  

NASA Astrophysics Data System (ADS)

On Nov. 27, 2011, a bright, new member of the Kreutz system of sungrazing comets was discovered, designated C/2011 W3 (Lovejoy). During the 18 days remaining before perihelion, 116 ground-based astrometric observations were made, along with a several dozen from spacecraft observing the Sun. Unfortunately, pre-perihelion data alone was not sufficient for an accurate determination of the orbital period, and the spaceborne astrometric observations were not sufficiently accurate to help. Surprisingly, the comet survived perihelion, but it clearly underwent major changes: the nuclear condensation completely disappeared within days, and a narrow spine tail formed. Post-perihelion ground-based astrometry from Rob McNaught was referenced to the sunward tip of the spine tail, but it could not be used successfully in orbit solutions. We show that the spine tail was a synchronic feature which originated from the terminal disintegration of the nucleus, on Dec. 17.6 ± 0.2 UT (Sekanina & Chodas, submitted). In a new technique, we derive astrometric positions of the missing nucleus via two constraints: first, that it would lie on the extrapolated spine tail, and second, that it would lie on a line of orbital-period variation, obtained by forcing a range or orbital periods to sets of elements based on pre-perihelion astrometry. The resulting osculating orbital period is 698 ± 2 years, which shows that C/2011 W3 cannot be a fragment of any sungrazer observed since the 17th century, and must be a member of the expected new 21st-century cluster of bright Kreutz-system sungrazers, predicted by Sekanina & Chodas (2007).

Chodas, Paul; Sekanina, Z.

2012-10-01

197

DPOD2005: An extension of ITRF2005 for Precise Orbit Determination  

NASA Astrophysics Data System (ADS)

For Precise Orbit Determination of altimetry missions, we have computed a data set of DORIS station coordinates defined for specific time intervals called DPOD2005. This terrestrial reference set is an extension of ITRF2005. However, it includes all new DORIS stations and is more reliable, as we disregard stations with large velocity formal errors as they could contaminate POD computations in the near future. About 1/4 of the station coordinates need to be defined as they do not appear in the original ITRF2005 realization. These results were verified with available DORIS and GPS results, as the integrity of DPOD2005 is almost as critical as its accuracy. Besides station coordinates and velocities, we also provide additional information such as periods for which DORIS data should be disregarded for specific DORIS stations, and epochs of coordinate and velocity discontinuities (related to either geophysical events, equipment problem or human intervention). The DPOD model was tested for orbit determination for TOPEX/Poseidon (T/P), Jason-1 and Jason-2. Test results show DPOD2005 offers improvement over the original ITRF2005, improvement that rapidly and significantly increases after 2005. Improvement is also significant for the early T/P cycles indicating improved station velocities in the DPOD2005 model and a more complete station set. Following 2005 the radial accuracy and centering of the ITRF2005-original orbits rapidly degrades due to station loss.

Willis, P.; Ries, J. C.; Zelensky, N. P.; Soudarin, L.; Fagard, H.; Pavlis, E. C.; Lemoine, F. G.

2009-09-01

198

Kinematic Precise Orbit Determination for LEO Satellites Using Space-borne Dual-frequency GPS Measurements  

NASA Astrophysics Data System (ADS)

Kinematic precise orbit determination (POD) is independent of satellite dynamics (e.g., Earth gravity field, atmospheric drag, solar radiation pressure, etc.). It is the distinctive approach of space-borne GPS technique, and well suited for orbit determination of Low Earth orbiting (LEO) satellites which are strongly perturbed by atmosphere. Firstly, an algorithm of kinematic POD is developed by using the zero-difference space-borne dual-frequency GPS measurements in this paper. And then, how to pre-process the space-borne dual-frequency GPS data and how to set the estimated parameters of kinematic POD are discussed in detail. Finally, the observational data from GRACE (Gravity Recovery And Climate Experiment) satellites covering the whole month of February 2008 are employed to validate the effectiveness and reliability of the method introduced in this paper. It is demonstrated that kinematic POD reaches an accuracy of about 5 cm (with respect to satellite laser ranging), which is at the same level of accuracy as dynamic and reduced-dynamic POD.

Peng, D. J.; Wu, B.

2011-11-01

199

Precise Orbit Determination of LEO Satellite Using Dual-Frequency GPS Data  

NASA Astrophysics Data System (ADS)

KOrea Multi-purpose SATellite (KOMPSAT)-5 will be launched at 550km altitude in 2010. Accurate satellite position (20 cm) and velocity (0.03 cm/s) are required to treat highly precise Synthetic Aperture Radar (SAR) image processing. Ionosphere delay was eliminated using dual frequency GPS data and double differenced GPS measurement removed common clock errors of both GPS satellites and receiver. SAC-C carrier phase data with 0.1 Hz sampling rate was used to achieve precise orbit determination (POD) with ETRI GNSS Precise Orbit Determination (EGPOD) software, which was developed by ETRI. Dynamic model approach was used and satellite's position, velocity, and the coefficients of solar radiation pressure and drag were adjusted once per arc using Batch Least Square Estimator (BLSE) filter. Empirical accelerations for sinusoidal radial, along-track, and cross track terms were also estimated once per revolution for unmodeled dynamics. Additionally piece-wise constant acceleration for cross-track direction was estimated once per arc. The performance of POD was validated by comparing with JPL's Precise Orbit Ephemeris (POE).

Hwang, Yoola; Lee, Byoung-Sun; Kim, Jaehoon; Yoon, Jae-Cheol

2009-06-01

200

Experimental determination of orbital and spin orientation of (Ar{sup +}){asterisk} formed in collisions  

SciTech Connect

We have experimentally obtained the state multipoles up to rank two for {ital J}-resolved {sup 2}{ital F}{sub 7/2,5/2} states of Ar{sup +} for the two-electron process He{sup +}+Ar{r_arrow}He(1{ital s}{sup 2})+Ar{sup +}(3{ital p}{sup 4}[{sup 1}{ital D}]4{ital p}{sup 2}{ital F}{sup {ital o}}{sub 7/2,5/2}) by measuring the Stokes parameters of the fluorescence light from (Ar{sup +}){asterisk} in coincidence with the scattered He. By expanding the state multipoles of each {ital J} state in terms of total orbital and total spin multipole moments, we have determined the contributions to the experimentally determined state multipoles of each {ital J} state due to total orbital and total spin angular momenta. When the process is spin dependent, it is possible to extract magnetic octupole moments of the excited state due to the orbital charge circulation. {copyright} {ital 1996 The American Physical Society.}

Moudry, B.W.; Yenen, O.; Jaecks, D.H. [Behlen Laboratory of Physics, University of Nebraska, Lincoln, Nebraska 68588-0111 (United States); Macek, J.H. [Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996-1501 (United States)]|[Oak Ridge National Laboratory, Post Office Box 2009, Oak Ridge, Tennessee 37831 (United States)

1996-11-01

201

Determination of the Orbit of the Planetary Companion to the Metal-Rich Star HD 45350  

NASA Astrophysics Data System (ADS)

We present precise radial velocity data for the metal-rich star HD 45350 collected with the Harlan J. Smith (HJS) 2.7 m telescope and the Hobby-Eberly Telescope (HET) at McDonald Observatory. This star was noticed by us as a candidate for having a giant planetary companion in a highly eccentric orbit, but the lack of data close to periastron left the amplitude and thus the mass of the planet poorly constrained. Marcy et al. (2005) announced the presence of the planet based on their Keck HIRES data, but those authors also cautioned that the remaining uncertainties in the orbital solution might be large due to insufficient data near periastron passage. In order to close this phase gap we exploited the flexible queue-scheduled observing mode of the HET to obtain intensive coverage of the most recent periastron passage of the planet. In combination with the long-term data from the HJS 2.7 m telescope we determine a Keplerian orbital solution for this system with a period of 962 days, an eccentricity of e=0.76, and a velocity semiamplitude K of 57.4 m s-1. The planet has a minimum mass of msini=1.82MJ+/-0.14MJ and an orbital semimajor axis of a=1.92+/-0.07 AU. Based on observations obtained with the Harlan J. Smith Telescope and the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.

Endl, Michael; Cochran, William D.; Wittenmyer, Robert A.; Hatzes, Artie P.

2006-06-01

202

20 CFR 416.1404 - Notice of the initial determination.  

Code of Federal Regulations, 2013 CFR

...notice will explain in simple and clear language what we have determined and the reasons...notice also will contain in understandable language a statement of the case setting forth...benefits has ended because of his or her death. (b) If our initial...

2013-04-01

203

Comparison analyses on the 150 × 150 lunar gravity field models by gravity/topography admittance, correlation and precision orbit determination  

NASA Astrophysics Data System (ADS)

Three high degree lunar gravity field models are compared using various methods.SGM150 is better for geophysical parameters inversion and orbit determination.Localized spectrum can be used to judge the magnitude and depth of mascon.

Yan, Jianguo; Zhong, Zhen; Li, Fei; Dohm, James M.; Ping, Jinsong; Cao, Jianfeng; Li, Xie

2013-08-01

204

Orbit determination and analysis of Meteor 3 (1970-19A) at 15th-order resonance  

NASA Astrophysics Data System (ADS)

The orbit of Meteor 3 (1970-19 A) has been determined at 52 epochs between August, 1978 and January, 1980, during which the orbit was perturbed by 15th-order resonance with the geopotential. The variations in the inclination and eccentricity have been analyzed to determine six lumped harmonics of order 15 and two of order 30. In the analysis of the eccentricity an air drag model incorporating an oblate atmosphere with a diurnal density variation was used. The variations in the inclination and eccentricity have previously been analyzed by King-Hele and Walker (1982) using orbits determined by the USNRL. The aim of this work is to find improved values of the lumped harmonics by using more accurately determined orbits.

Harwood, N. M.; Swinerd, G. G.

1991-07-01

205

Precision Time Transfer and Obit Determination Using Laser Ranging to Lunar Reconnaissance Orbiter  

NASA Astrophysics Data System (ADS)

Since the commissioning of LRO in June, 2009, one-way laser ranging (LR) to Lunar Reconnaissance Orbiter (LRO) has been conducted successfully from NASA's Next Generation Satellite Laser Ranging System (NGSLR) at Goddard Geophysical and Astronomical observatory (GGAO) in Greenbelt, Maryland. With the support of the International Laser Ranging Service (ILRS), ten international satellite laser ranging (SLR) ground stations have participated in this experiment and over 1200 hours of ranging data have been collected. In addition to supplementing the precision orbit determination (POD) of LRO, LR is able to perform time transfer between the ground station and the spacecraft clocks. The LRO clock oscillator is stable to 1 part in 10^{12} over several hours, and as stable for much longer periods after correcting for a long-term drift rate and an aging rate. With a precisely-determined LRO ephemeris, the oscillator-determined laser pulse receive time can be differenced with ground station clock transmit times using H-maser and GPS-steered Rb oscillators as references. Simultaneous ranging to LRO among 2, 3, or 4 ground stations has made it possible for relative time transfer among the participating LR stations. Results have shown about 100 ns difference between some LR stations and the primary NGSLR station. At present, the time transfer accuracy is limited to 100 ns at NGSLR. However, an All-View GPS receiver has been installed, which, in combination with a H-maser, is expected to improve the accuracy to 1 ns r.m.s. at NGSLR. Results of new ranging and time transfer experiments using the new time base will be reported. The ability to use LR for time transfer validates the selection of a commercially-supplied, oven-controlled crystal oscillator on board LRO for one-way laser ranging.The increased clock accuracy also provides stronger orbit constraints for LRO POD. The improvements due to including LR data in the LRO POD will be presented.

Mao, D.; Barker, M. K.; Clarke, C. B.; Golder, J. E.; Hoffman, E.; Horvath, J. E.; Mazarico, E.; Mcgarry, J.; Neumann, G. A.; Torrence, M. H.; Rowlands, D. D.; Skillman, D.; Smith, D. E.; Sun, X.; Zuber, M. T.

2011-12-01

206

The effect of absolute proper motion determinations of the globular cluster M3 on calculations of its orbit.  

NASA Astrophysics Data System (ADS)

Two different determinations of M3's absolute proper motion are used, one of which is based on the new determination of reference stars from the Hipparcos Catalogue. Using the reduced galactocentric space - and velocity - components of the M3, the orbit is calculated with the galactic mass distribution model of Dauphole and Colin. The effect of the different absolute proper motions on the orbit of M3 is investigated too.

Wu, Zhenyu; Wu, Jiaji

207

11 CFR 9033.10 - Procedures for initial and final determinations.  

Code of Federal Regulations, 2012 CFR

...candidate of its initial determination...the Commission's initial determination is...candidate will be given an opportunity to...the results of any investigation upon which the determination...Commission makes an initial determination...

2012-01-01

208

Investigations to Determine the Origin of the Solar Wind with the SPICE EUV Imaging Spectrograph and the Solar Orbiter Mission  

NASA Astrophysics Data System (ADS)

At large spatial scales, the structure of the solar wind and it's mapping back to the solar corona, is thought to be reasonably well understood. However, the detailed structure of the various source regions at chromospheric and transition region heights is extremely complex, and less well understood. Determining this connection between heliospheric structures and their source regions at the Sun is one of the overarching objective of the Solar Orbiter mission. During perihelion segments of its orbit, when the spacecraft is in quasi-corotation with the Sun, Solar Orbiter will determine the plasma parameters and compositional signatures of the solar wind, which can be compared directly with the spectroscopic signatures of coronal ions with differing charge-to-mass ratios and FIP. One of the key instruments on the Solar Orbiter mission to make these remote sensing measurements is the SPICE (Spectral Imaging of the Coronal Environment) imaging spectrograph. SPICE will provide the images and plasma diagnostics needed to characterize the plasma state in different source regions, from active regions to quiet Sun to coronal holes. By comparing composition, plasma parameters, and low/high FIP ratios of structures remotely, with those measured directly at the Solar Orbiter spacecraft, Solar Orbiter will provide the first direct link between solar wind structures and their source regions at the Sun. This talk will provide a background of previous compositional correlation measurements and an outline of the method to be used for comparing the spectroscopic and in-situ plasma parameters to be measured with Solar Orbiter.

Hassler, D. M.; Deforest, C.; Spice Team

2011-12-01

209

Skylab 1 Rocket, 1973-27B: Orbit Determination and Analysis.  

National Technical Information Service (NTIS)

Contents: Introduction; The Observations; The Orbits; Analysis of the Observations; Revision of the Orbits; The 31:2 Resonance; Upper-Atmosphere Rotation; Analysis of Variations in Eccentricity due to Air Drag; Conclusions; Appendix: Correction of Eccentr...

D. G. King-Hele

1979-01-01

210

De Vergelijkingen van Hill voor de Bepaling van een Satellietbaan (Hill Equations for Satellite Orbit Determination).  

National Technical Information Service (NTIS)

Equations of motion using a periodical circular orbit are addressed. The orbital perturbations are given with respect to this moving triad. This set of equations, called the Hill equations, exists of three second order linear differential equations. They ...

R. G. Vancoevorden

1992-01-01

211

Ab Initio determination of Cu 3d orbital energies in layered copper oxides  

PubMed Central

It has long been argued that the minimal model to describe the low-energy physics of the high Tc superconducting cuprates must include copper states of other symmetries besides the canonical one, in particular the orbital. Experimental and theoretical estimates of the energy splitting of these states vary widely. With a novel ab initio quantum chemical computational scheme we determine these energies for a range of copper-oxides and -oxychlorides, determine trends with the apical Cu–ligand distances and find excellent agreement with recent Resonant Inelastic X-ray Scattering measurements, available for La2CuO4, Sr2CuO2Cl2, and CaCuO2.

Hozoi, Liviu; Siurakshina, Liudmila; Fulde, Peter; van den Brink, Jeroen

2011-01-01

212

Orbit determination of the SELENE satellites using multi-satellite data types and evaluation of SELENE gravity field models  

Microsoft Academic Search

The SELENE mission, consisting of three separate satellites that use different terrestrial-based tracking systems, presents\\u000a a unique opportunity to evaluate the contribution of these tracking systems to orbit determination precision. The tracking\\u000a data consist of four-way Doppler between the main orbiter and one of the two sub-satellites while the former is over the far\\u000a side, and of same-beam differential VLBI

S. Goossens; K. Matsumoto; D. D. Rowlands; F. G. Lemoine; H. Noda; H. Araki

2011-01-01

213

Combined processing and orbit determination of Galileo and GPS satellites by estimating phase clocks  

NASA Astrophysics Data System (ADS)

As a first step we introduced Galileo observables in the Bernese GPS software to study the combined processing of Galileo and GPS measurements based on the estimation of phase clocks for both GNSS systems We then simulated measurements for both the Galileo and the GPS constellation and estimated all relevant IGS parameters like Galileo GPS orbits high-rate Galileo GPS satellite clocks Earth orientation parameters EOPs station coordinates troposphere zenith delays etc In this contribution we show how Galileo helps to de-correlate troposphere zenith delay receiver clock and horizontal station coordinates from the station height and improves the overall IGS processing performance and precise point positioning quality We study ambiguity resolution strategies for such a combination of navigation satellite systems and discuss the improvements that the Galileo system might bring The method of phase clocks was originally developed for the orbit determination of LEO satellites and is based on the estimation of GNSS satellite clocks and ground receiver clocks using only zero-difference phase measurements from about 30 ground IGS stations In this way any influence coming from the noisy pseudo-range measurements or systematic code effects like inter-channel code biases or large code multipath is avoided Phase clocks found very nice application in precise point positioning and frequency transfer By making differences between the receiver clocks estimated in such way one can immediately obtain information on the frequency comparison between them Therefore we

Svehla, D.

214

Precise Orbit Determination of LAGEOS satellites: results on fundamental physics and perspectives  

NASA Astrophysics Data System (ADS)

The LAGEOS satellites, launched for geodynamics and geophysics purposes, are offering also an outstanding test bench to fundamental physics. Indeed, their physical characteristics, as well as those of their orbits, and the availability of high--quality tracking data provided by the International Laser Ranging Service, allow for precise tests of gravitational theories. In this talk recent work on data analysis will be presented. A fairly large amount of LAGEOS and LAGEOS II Satellite Laser Ranging data has been analyzed with NASA/GSFC Geodyn II software, using a set of dedicated models for satellite dynamics, and the related post--fit residuals have been analyzed. In particular, general relativistic effects leave peculiar imprint on nodal longitude, argument of perigee and inclination behaviour, which have been used to obtain precise estimates of the related parameters. The most precise --- as today --- estimate of the effects on argument of perigee has been obtained, providing a direct measurement of the relativistic ``Schwarzschild'' precession in the field of the Earth. At the same time the constraints on a non--Newtonian (i.e. Yukawa--type) gravitational dynamics have been improved. The measurement error budget will be discussed, emphasizing the role of gravitational and, especially, of non--gravitational forces modeling on the overall precise orbit determination quality, as well as on future new measurements and constraints of the gravitational interaction.

Peron, Roberto; Lucchesi, David

2012-07-01

215

Designing Delta-DOR acquisition strategies to determine highly elliptical earth orbits  

NASA Astrophysics Data System (ADS)

Delta-DOR acquisition strategies are designed for use in determining highly elliptical earth orbits. The requirements for a possible flight demonstration are evaluated for the Charged Composition Explorer spacecraft of the Active Magnetospheric Particle Tracer Explorers. The best-performing strategy uses data spanning the view periods of two orthogonal baselines near the same orbit periapse. The rapidly changing viewing geometry yields both angular position and velocity information, but each observation may require a different reference quasar. The Delta-DOR data noise is highly dependent on acquisition geometry, varying several orders of magnitude across the baseline view periods. Strategies are selected to minimize the measurement noise predicted by a theoretical model. Although the CCE transponder is limited by S-band and a small bandwidth, the addition of Delta-DOR to coherent Doppler and range improves the one-sigma apogee position accuracy by more than an order of magnitude. Additional Delta-DOR accuracy improvements possible using dual-frequency (S/X) calibration, increased spanned bandwidth, and water-vapor radiometry are presented for comparison. With these benefits, the residual Delta-DOR data noise is primarily due to quasar position uncertainties.

Frauenholz, R. B.

1986-08-01

216

20 CFR 636.8 - Initial and final determination; request for hearing at the Federal level.  

Code of Federal Regulations, 2012 CFR

...HEARINGS § 636.8 Initial and final determination...Federal level. (a) Initial determination. Upon...administrative record of an investigation conducted pursuant to...Grant Officer shall make an initial determination...

2012-04-01

217

Meter-level orbit determination of geosynchronous satellites by an economical tracking system  

NASA Astrophysics Data System (ADS)

Covariance analyses to study the performance of a proposed high precision and low cost geosynchronous satellites tracking system are presented. The tracking systems main components are one TDRS, a near-by geosynchronous satellite, 4-5 automatic ground stations, and a Very Long Baseline Interferometric (VLBI) system. The automated ground station provides doubly differenced ranging measurements without precision clock. The VLBI system consists of 4 one meter antennas positioned on orthogonal 6000 km baselines and uses a GPS signal for clock synchronization. Based on the anticipated characteristics of the 1990 era VLBI system, doubly differenced ranging and dynamic model, a factor of 20 or better improvement can be expected in the TDRSS orbit determination accuracy. This would make the satellite-based delta-VLBI deep space navigation system more attractive than the other systems which have been proposed.

Culp, R. D.; Wang, T.-H.

218

An improved adaptive Sage filter with applications in GEO orbit determination and GPS kinematic positioning  

NASA Astrophysics Data System (ADS)

The shortcomings of an adaptive Sage filter are analyzed in this paper. An improved adaptive Sage filter is developed by using a weighted average quadratic form of the historical residuals of observations and predicted states to evaluate the covariance matrices of observations and dynamic model errors at the present epoch. The weight function is constructed based on the variances of observational residuals or predicted state residuals and the space distance between the previous and the present epoch. In order to balance the contributions of the measurements and the dynamic model information, an adaptive factor is applied by using a two-segment function and predicted state discrepancy statistics. Two applications, orbit determination of a maneuvered GEO satellite and GPS kinematic positioning, are conducted to verify the performance of the proposed method.

Xu, TianHe; Jiang, Nan; Sun, ZhangZhen

2012-05-01

219

Comparison Between Monteiro DA Rocha and Wilhelm Olbers' Methods for the Determination of the Orbits of Comets  

NASA Astrophysics Data System (ADS)

In 1797, under von Zach sponsoring, Wilhelm Olbers published his work on the determination of the parabolic orbits of the comets - "Abhandlung tiber die leichteste und bequemste Methode, die Bahn eines Cometen aus einigen Beobachtungen zu berechnen von Wilhelm Olbers". Over the next century, this method would become the main tool to determine comets' parabolic orbits. Two years later, in 1799, an article of Monteiro da Rocha entitled "Determinação das Orbitas dos Cometas" is published in Memórias da Academia Real das Ciências de Lisboa. This study publishes a method to solve the problem of the determination of comets' orbits very similar with the one proposed by Olbers. In the current article we intend to provide some information about the method of Monteiro da Rocha, which in fact was formerly formulated circa 16-17 years in advance to Olbers method, and to present the results of the quantitative side-by-side comparison of methods.

Figueiredo, Fernando B.; Fernandes, João

2006-08-01

220

Methodology for determining an endoatmospheric thrust termination to achieve a low-earth-orbit  

Microsoft Academic Search

During the launch of a winged spacecraft propelled by an airbreathing\\/rocket engine system into a prescribed orbit, the powered boost phase inevitably terminates in the atmosphere. For this craft, a portion of the coasting-along-an-orbit transfer ellipse occurs in the atmosphere. The resulting aerodynamic drag penalty that depresses the orbit must be compensated at the time of the thrust termination. However,

Hideo Ikawa

1991-01-01

221

Determination of the orbital lineup at reactive organic semiconductor interfaces using photoemission spectroscopy  

SciTech Connect

We determined the orbital lineup of the tris (8-hydroxyquinolinato) gallium (Gaq{sub 3})/Mg interface using combined x-ray and ultraviolet photoemission spectroscopy (XPS and UPS) measurements. The Gaq{sub 3}/Mg system is a prototypical model structure for organic electron/low work function electrode transporting materials interfaces found in organic light emitting diodes (OLED). A Gaq{sub 3} thin film was grown in 15 steps on a previously sputter-cleaned Mg substrate starting at a 1 Aa nominal thickness up to a final thickness of 512 Aa. Before, and in between the growth steps, the sample surface was characterized by XPS and UPS. The results indicate the formation of a reaction layer of about 12 Aa thickness at the Mg interface, which resulted in a 0.96 V interface dipole potential. At Gaq{sub 3} coverages higher than 256 Aa, a strong charging shift occurred in the overlayer related UPS-emission lines, which was identified by measuring the high binding energy cutoff (secondary edge) of both the XP and UP spectra. The several magnitudes different x-ray and ultraviolet source photon intensities allow pinpointing charging shifts with high sensitivity. Due to the low work function of the reacted interface layer, the Gaq{sub 3} electronic states are aligned at a binding energy below the substrate Fermi edge that exceeds the magnitude of the optical gap between the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO). This allowed the conclusion that the ground state exciton binding energy of Gaq{sub 3} needs to be larger than 0.43 eV. Based on these considerations, the lowest possible electron injection barrier matching the experimental data was estimated to be 0.15 eV. {copyright} 2001 American Institute of Physics.

Schlaf, R.; Merritt, C. D.; Picciolo, L. C.; Kafafi, Z. H.

2001-08-15

222

Quality assessment of DORIS/Jason-2 data for orbit determination and geodesy  

NASA Astrophysics Data System (ADS)

We describe our analysis of DORIS/Jason-2 data collected between mid 2008 and early 2010 using the GIPSY/OASIS software package. We demonstrate first that the Jason-2/DORIS data, unlike those from Jason-1, show no signs that the on-board clock is adversely affected by radiation over the South Atlantic Anomaly. Post-processed Jason-2 orbit solutions based on DORIS data alone yield daily (internal) overlaps of 10 mm (RMS) for the radial compo-nent. External comparisons with Jason-2/GPS-only orbits still yield 15 mm RMS consistency in the radial component, for both the reduced-dynamic and dynamic approaches. Prelimi-nary tests show that an empirical correction may be needed to estimate an additional offset between the DORIS antenna center of phase and the satellite center of mass (relative to the pre-flight measured values). However, this empirical correction is sensitive to the tropospheric mapping function used (GMF or VMF-1), as a large number of DORIS/Jason-2 data are avail-able using the new DGXX multi-channel receiver. We also describe early results obtained for weekly station position determination, as well as terrestrial reference parameters (geocenter and scale). Finally, multi-satellite DORIS results for station positions are also considered to check the importance of adding these new DORIS/Jason-2 data to the latest DORIS/IGN solutions (ignwd08 time series). In particular, the importance of adding an additional satellite plane (66 instead of 98 inclination) is also discussed.

Willis, Pascal; Haines, Bruce; Gobinddass, Marie-Line; Bertiger, Willy

223

Ephemeris calculation and orbit determination of geostationary satellites, using Taylor series integration  

NASA Astrophysics Data System (ADS)

It is shown that Taylor series integration allows problems of celestial mechanics for interplanetary orbits to be solved with relatively simple orbit models. The method is adapted to the computation of satellite orbits. A new implementation concept is included, which allows a programmation of the equations of motion. It offers simultaneously extension possibilities, which are necessary for the computation of special terms of the power function. The linking of Sun and Moon ephemeris for the treatment of gavitational disturbances of the satellite orbit is used as an example. This concept is represented with the principles of Taylor series integration, and compared with variants of the process. The power spectrum of the method is examined for disturbed and undisturbed Kepler orbits.

Montenbruck, Oliver

1991-02-01

224

A new determination of lunar orbital parameters, precession constant and tidal acceleration from LLR measurements  

NASA Astrophysics Data System (ADS)

An analysis of Lunar Laser Ranging (LLR) observations from January 1972 until April 2001 has been performed, and a new solution for the lunar orbital motion and librations has been constructed that has been named S2001. With respect to prior solutions, improvements in the statistical treatment of the data, new nutation and libration models and the addition of the positions of the observing stations to the list of fitted parameters have been introduced. Globally, for recent observations, our rms (root mean square error) is within 2 to 3 centimeters in the lunar distance. Special attention has been paid to the determination of the correction to the IAU76 luni-solar constant of precession, and the value of the secular acceleration of the Moon's longitude due to the tidal forces. The main results are: - correction to the constant of precession: Delta p = -0.302 +/- 0.003 ''/cy, - tidal acceleration of the lunar longitude: Gamma = -25.858 +/- 0.003 ''/cy2. The positions and velocities of the stations have also been determined. The results are consistent with the ITRF2000 determinations from SLR observations. The lunar theory ELP is referred to a dynamical system and introduces the inertial mean ecliptic of J2000.0. The positioning of the reference system of the theory with respect to ICRS is performed (and also with respect to some useful JPL numerical integrations). Finally the orientation of the celestial axes with respect to the ICRS reference system has been derived as well as the offsets of the Celestial Ephemeris Pole.

Chapront, J.; Chapront-Touzé, M.; Francou, G.

2002-05-01

225

ERS orbit control  

Microsoft Academic Search

The European remote sensing mission orbit control is addressed. For the commissioning phase, the orbit is defined by the following requirements: Sun synchronous, local time of descending node 10:30; three days repeat cycle with 43 orbital revolutions; overhead Venice tower (12.508206 deg east, 45.314222 deg north). The launch, maneuvers for the initial acquisition of the operational orbit, orbit maintenance maneuvers,

Mats Rosengren

1991-01-01

226

A generalized harmonic function perturbation method for determining limit cycles and homoclinic orbits of Helmholtz—Duffing oscillator  

NASA Astrophysics Data System (ADS)

In this paper, a novel description of periodic solution and homoclinic orbit of undamped Helmholtz—Duffing oscillator is proposed via nonlinear time transformation. Based on this novel description, a generalized harmonic function perturbation method is presented to determine the limit cycles and homoclinic orbits of Helmholtz—Duffing oscillator with nonlinear damping. The amplitude of limit cycle and critical value of the homoclinic bifurcation parameter can be also predicted. To illustrate the accuracy of the present method, the solutions obtained in this paper are compared with those of Runge—Kutta method, which shows the method proposed in this paper is effective and feasible.

Li, Zhenbo; Tang, Jiashi; Cai, Ping

2013-10-01

227

Determination of orbits and colors for two new binaries in the Koronis asteroid family  

NASA Astrophysics Data System (ADS)

We propose to measure color and orbital properties of two asteroid binaries in the Koronis family discovered in our SNAP-9747 survey. The best previously studied asteroid binary system, Ida/Dactyl, is also in the Koronis family. Differential space weathering measured on the Ida and Dactyl surfaces has been a powerful constraint on models of satellite formation mechanisms and satellite survivability. HST offers the unique opportunity for similar measurements of these much smaller, main-belt binaries. The new satellites are believed to have formed through different collisional mechanisms than Ida/Dactyl. Further, with a set of 4 relative position measurements for each of the two systems, added to the discovery snapshots, we will determine and compare the densities of the primaries with Ida {a large, 31.5 km, asteroid with density 2.6+-0.5 g/cm^3, measured by the Galileo flyby}. In contrast, {17246} and {22899} are 4.5 km bodies that are likely to have been restructured since the family-forming event by subsequent collisions. As all are members of the same family, differences in density would constrain bulk composition and internal structure {e.g. shard vs. rubble-pile}. Hence, these measurements are likely to further elucidate the mechanisms for formation of satellites.

Merline, William

2004-07-01

228

Short-arc orbit determination using coherent X-band ranging data  

NASA Astrophysics Data System (ADS)

The use of X-band frequencies in ground-spacecraft and spacecraft-ground telecommunication links for current and future robotic interplanetary missions makes it possible to perform ranging measurements of greater accuracy than previously obtained. It is shown that ranging data of sufficient accuracy, when acquired from multiple stations, can sense the geocentric angular position of a distant spacecraft. The application of high-accuracy S/X-band and X-band ranging to orbit determination with relatively short data arcs is investigated in planetary approach and encounter scenarios. Actual trajectory solutions for the Ulysses spacecraft constructed from S/X-band ranging and Doppler data are presented; error covariance calculations are used to predict the performance of X-band ranging and Doppler data. The Ulysses trajectory solutions indicate that the aim point for the spacecraft's February 1992 Jupiter encounter was predicted to a geocentric accuracy of 0.20 to 0.23/microrad. Explicit modeling of range bias parameters for each station pass is shown to largely remove systematic ground system calibration errors and transmission media effects from the Ulysses range measurements, which would otherwise corrupt the angle finding capabilities of the data. The Ulysses solutions were found to be reasonably consistent with the theoretical results, which suggest that angular accuracies of 0.08 to 0.1/microrad are achievable with X-band ranging.

Thurman, S. W.; McElrath, T. P.; Pollmeier, V. M.

229

45 CFR 233.26 - Retrospective budgeting; determining eligibility after the initial one or two months.  

Code of Federal Regulations, 2012 CFR

...determining eligibility after the initial one or two months...DEPARTMENT OF HEALTH AND HUMAN SERVICES COVERAGE AND CONDITIONS OF ELIGIBILITY IN FINANCIAL...determining eligibility after the initial one or two months...determining eligibility. The State plan shall...

2012-10-01

230

45 CFR 233.26 - Retrospective budgeting; determining eligibility after the initial one or two months.  

Code of Federal Regulations, 2011 CFR

...determining eligibility after the initial one or two months...DEPARTMENT OF HEALTH AND HUMAN SERVICES COVERAGE AND CONDITIONS OF ELIGIBILITY IN FINANCIAL...determining eligibility after the initial one or two months...determining eligibility. The State plan shall...

2011-10-01

231

The Cooling Rate of an Active Aa Lava Flow Determined Using an Orbital Imaging Spectrometer  

NASA Astrophysics Data System (ADS)

The surface temperature of an active lava flow is an important physical property to measure. Through its influence on lava crystallinity, cooling exerts a fundamental control on lava rheology. Remotely sensed thermal radiance data acquired by multispectral sensors such as Landsat Thematic Mapper and the Terra Advanced Spaceborne Thermal Emission and Reflection Radiometer, are of insufficient spectral and radiometric fidelity to allow for realistic determination of lava surface temperatures from Earth orbit. This paper presents results obtained from the analysis of active lava flows using hyperspectral data acquired by NASA's Earth Observing-1 Hyperion imaging spectrometer. The contiguous nature of the measured radiance spectrum in the 0.4-2.5 micron region means that, although sensor saturation most certainly occurs, unsaturated radiance data are always available from even the hottest, and most radiant, active lava flow surfaces. The increased number of wavebands available allows for the assumption of more complex flow surface temperature distributions in the radiance-to-temperature inversion processes. The technique is illustrated by using a hyperspectral image of the active lava lake at Erta Ale volcano, Ethiopia, a well characterized calibration target. We then go on to demonstrate how this approach can be used to constrain the surface cooling rate of an active lava flow at Mount Etna, Sicily, using three images acquired during a four day period in September 2004. The cooling rate of the active channel as determined from space falls within the limits commonly assumed in numerical lava flow models. The results provide insights into the temperature-radiance mixture modeling problem that will aid in the analysis of data acquired by future hyperspectral remote sensing missions, such as NASA's proposed HyspIRI mission.

Wright, Robert; Garbeil, Harold

2010-05-01

232

The determination and analysis of the orbit of NIMBUS 1 ROCKET, 1964-52B Part 2: Variations in orbital eccentricity  

NASA Astrophysics Data System (ADS)

The influence of aerodynamic drag and the geopotential on the motion of the satellite 1964-52B is considered. A model of the atmosphere is adopted that allows for oblateness, and in which the density behaviour approximates to the observed diurnal variation. A differential equation governing the variation of the eccentricity, e, combining the effects of air drag with those of the Earth's gravitational field is given. This is solved numerically using as initial conditions 310 computed orbits of 1964-52B. The observed values of eccentricity are modified by the removal of perturbations due to luni-solar attraction, solid Earth and ocean tides, solar radiation pressure and low-order long-periodic tesseral harmonic perturbations. The method of removal of these effects is given in some detail. The behaviour of the orbital eccentricity predicted by the numerical solution is compared with the modified observed eccentricity to obtain values of atmospheric parameters at heights between 310 and 430 km. The daytime maximum of air density is found to be at 14.5 hours local time. Analysis of the eccentricity near 15th order resonance with the geopotential yielded values of four lumped geopotential harmonics of order 15, namely: 109 C1,015 = -78.8 +/- 7.0, 109 S1,015 = -69.4 +/- 5.3, 109 C-1,215 = -41.6 +/- 3.5 109 S-1,215 = -26.1 +/- 8.9, at inclination 98.68°. Permanent address: Department of Mathematics, Coventry (Lanchester) Polytechnic, Priory Street, Coventry CV1 5FB, U.K.

Boulton, W. J.

1985-06-01

233

Concepts of orbital mechanics  

Microsoft Academic Search

Parameters determining an orbit, perturbations acting on a satellite and orbital deviations resulting from them, and a study of the particular types of orbits relevant to the use of artificial earth satellites for finding and developing natural resources are presented. The discussion shows the constraints imposed on teledetective search by certain characteristics of the orbits.

A. Alouges

1974-01-01

234

The initiation codon determines the efficiency but not the site of translation initiation in Chlamydomonas chloroplasts.  

PubMed Central

To study translation initiation in Chlamydomonas chloroplasts, we mutated the initiation codon AUG to AUU, ACG, ACC, ACU, and UUC in the chloroplast petA gene, which encodes cytochrome f of the cytochrome b6/f complex. Cytochrome f accumulated to detectable levels in all mutant strains except the one with a UUC codon, but only the mutant with an AUU codon grew well at 24 degrees C under conditions that require photosynthesis. Because no cytochrome f was detectable in the UUC mutant and because each mutant that accumulated cytochrome f did so at a different level, we concluded that any residual translation probably initiates at the mutant codon. As a further demonstration that alternative initiation sites are not used in vivo, we introduced in-frame UAA stop codons immediately downstream or upstream or in place of the initiation codon. Stop codons at or downstream of the initiation codon prevented accumulation of cytochrome f, whereas the one immediately upstream of the initiation codon had no effect on the accumulation of cytochrome f. These results suggest that an AUG codon is not required to specify the site of translation initiation in chloroplasts but that the efficiency of translation initiation depends on the identity of the initiation codon.

Chen, X; Kindle, K L; Stern, D B

1995-01-01

235

Application of satellite laser altimetry in Chang'E-1 precision orbit determination and lunar gravity field solution  

NASA Astrophysics Data System (ADS)

The application of satellite laser altimetry measurement in planetary spacecraft precision or-bit determination (POD) and planetary gravity field recovery has been implemented in Mars Global Surveyor (MGS) and Lunar Reconnaissance Orbiter, and shows improvements both on POD and gravity field solution. During Chang'E-1 nominal mission phase, the satellite laser altimetry provided continuous measurements for about 4 months. In this work we outline Chang'E-1 satellite laser altimetry measurement firstly. Then results of Chang'E-1 precision orbit determination (POD) and lunar gravity field solution are given by combining Chang'E-1 orbital tracking data (including two way range and range rate, as well as Very Long Baseline Interferometry delay and delay rate data) with satellite laser altimetry are given. Analysis and comparison are put forward between POD and gravity field results with and without al-timetry measurement. It indicates that altimetry measurement can improve POD and gravity field solution of Chang'E-1 significantly. The result will be helpful to recomputed Chang'E-1 ephemeris to improve Chang'E-1 topography model.

Jianguo, Yan; Jinsong, Ping

236

Effect of refraction correction of the Weilheim interferometer data on the accuracy of satellite orbit determination and prediction, based on a data sample  

Microsoft Academic Search

The effect of refraction correction on orbit determination accuracy during a 10 day observation interval, and on the accuracy of prediction using an orbit determination program, was investigated for the Symphonie 1 satellite based on a sample taken from tracking data. It is shown that, although the application of refraction correction produces an improvement of the mean error of single

K. Zimmermann

1976-01-01

237

Geomorphic analysis of lobate debris aprons on Mars at Mars Orbiter Camera scale: Evidence for ice sublimation initiated by fractures  

Microsoft Academic Search

Lobate debris aprons, known to be geomorphic landform indicators of the presence of ground ice, are of special interest for future missions devoted to the research of water on Mars. Lobate debris aprons in fretted terrains of Deuteronilus and Protonilus Mensae (35°-50°N) show typical convex shapes interpreted to be the result of viscous deformation. At the scale of Mars Orbiter

N. Mangold

2003-01-01

238

Next Generation of Spaceborne GNSS Receiver for Radio Occultation Science and Precision Orbit Determination  

NASA Astrophysics Data System (ADS)

Several planned NASA and NOAA missions require an advanced science-quality GNSS receiver as mission-critical payloads to meet science objectives (e. g. CLARREO, COSMIC-2, ICESat II and DESDynI). The science measurement and mission navigation needs require that GNSS receivers track signals from GPS, GALILEO, and other new GNSS systems. JPL is developing the next generation multi-antenna GNSS receiver called the TriG (Tri-GNSS) Receiver for spaceborne scientific measurements that will enable both the continued access of NASA missions to precision orbit determination for remote sensing missions and the application of GNSS signals for the technically demanding radio occultation observations. The TriG receiver will track both the legacy L1CA, L2 Codeless, and the new L2C and L5 signals from GPS as well as new GNSS signals from Galileo and GLONASS. The ability to track multiple GNSS satellite signals would allow full capability to operate during the transition to GPS-III and past the 2020 retirement of the legacy signals and also significantly improve the quality and quantity of the radio occultation measurements. In addition, the TriG receiver features several innovations including digital beam steering, wideband open loop tracking, and “Blue Shift” signal processing algorithm that would enable the necessary precision in the atmosphere and to increase the SNR from the lower regions of the atmosphere in order to dramatically improve the percentage of profiles reaching into the lowest regions of the atmosphere. This presentation will describe the TriG architecture and features how those may be beneficial for the next-generation of global network instruments.

Tien, J. Y.; Young, L.; Meehan, T.; Franklin, G.; Hurst, K. J.; Esterhuizen, S.; Trig Gnss Receiver Team

2010-12-01

239

Cooling rate of some active lavas determined using an orbital imaging spectrometer  

NASA Astrophysics Data System (ADS)

The surface temperature of an active lava flow is an important physical property to measure. Through its influence on lava crystallinity, cooling exerts a fundamental control on lava rheology. Remotely sensed thermal radiance data acquired by multispectral sensors such as Landsat Thematic Mapper and the Terra Advanced Spaceborne Thermal Emission and Reflection Radiometer are of insufficient spectral and radiometric fidelity to allow for realistic determination of lava surface temperatures from Earth orbit. This paper presents results obtained from the analysis of active lava flows using hyperspectral data acquired by NASA's Earth Observing-1 Hyperion imaging spectrometer. The contiguous nature of the measured radiance spectrum in the 0.4-2.5 ?m region means that, although sensor saturation most certainly occurs, unsaturated radiance data are always available from even the hottest, and most radiant, active lava flow surfaces. The increased number of wave bands available allows for the assumption of more complex flow surface temperature distributions in the radiance-to-temperature inversion processes. The technique is illustrated by using a hyperspectral image of the active lava lake at Erta Ale volcano, Ethiopia, a well-characterized calibration target, a time series of three Hyperion images of an active lava flow acquired during a 4 day period at Mount Etna, Sicily, as well as a lava flow erupted at Nyamuragira, Democratic Republic of Congo. The results provide insights into the temperature-radiance mixture modeling problem that will aid in the analysis of data acquired by future hyperspectral remote sensing missions, such as NASA's proposed HyspIRI mission.

Wright, Robert; Garbeil, Harold; Davies, Ashley G.

2010-06-01

240

The cooling rate of an aa lava flow determined using an orbital imaging spectrometer  

NASA Astrophysics Data System (ADS)

The surface temperature of an active lava flow is an important property to measure. Through its influence on lava crystallinity, cooling exerts a fundamental control on lava rheology. Remotely sensed thermal radiance data acquired by multispectral sensors such as Landsat Thematic Mapper and the Terra Advanced Spaceborne Thermal Emission and Reflection Radiometer, are of insufficient spectral and radiometric fidelity to allow for realistic determination of lava surface temperatures from Earth orbit. This presentation describes results obtained from the analysis of active lava flows using hyperspectral data acquired by NASA’s Earth Observing-1 Hyperion imaging spectrometer. The contiguous nature of the measured radiance spectrum in the 0.4-2.5 micron region means that, although sensor saturation most certainly occurs, unsaturated radiance data are always available from even the hottest, and most radiant, active lava flow surfaces. The increased number of wavebands available allows for the assumption of more complex flow surface temperature distributions in the radiance-to-temperature inversion processes. The application of such data to the analysis of a time-series of three Hyperion images of an active lava flow, acquired during a four day period at Mount Etna, Sicily, is demonstrated. The results provide insights into the temperature-radiance mixture modeling problem that will aid in the analysis of data acquired by future hyperspectral remote sensing missions, such as NASA’s proposed HyspIRI mission. By also proving radiance data on the opposite limb of the planckian emittance curve (i.e. the MIR and TIR), HyspIRI will allow us to improve upon these antecedent results.

Wright, R.; Garbeil, H.

2009-12-01

241

A comparison of methods to determine phytoplankton bloom initiation  

NASA Astrophysics Data System (ADS)

Phytoplankton bloom phenology has important consequences for marine ecosystems and fisheries. Recent studies have used remotely sensed ocean color data to calculate metrics associated with the phenological cycle, such as the phytoplankton bloom initiation date, on regional and global scales. These metrics are often linked to physical or biological forcings. Most studies choose one of several common methods for calculating bloom initiation, leading to questions about whether bloom initiation dates calculated with different methods yield comparable results. Here we compare three methods for finding the date of phytoplankton bloom initiation in the North Atlantic: a biomass-based threshold method, a rate of change method, and a cumulative biomass-based threshold method. We use these methods to examine whether the onset of positive ocean-atmosphere heat fluxes coincides with subpolar bloom initiation. In several coherent locations, we find differences in the patterns of bloom initiation created by each method and differences in the synchrony between bloom initiation and positive heat fluxes, which likely indicate various physical processes at play in the study region. We also assess the effect of missing data on the chosen methods.

Brody, Sarah R.; Lozier, M. Susan; Dunne, John P.

2013-05-01

242

Determination of the initiation rate in the polymerization of zinc, cobalt and nickel acrylates  

Microsoft Academic Search

Results for the determination of the initiation rate of polymerization reaction of zinc, cobalt and nickel acrylates, initiated by 2,2?-azobisisobutyronitryle in dimethylformamide at different temperatures are reported. The inhibition method involving the stable radical N,N-diphenyl-N?-picryl-hydrazyl has been used. The initiation rate constants 2kdf and activation energy of initiation E2kdf have been determined.

Tadeusz Czerniawski; Zbigniew Wojtczak

1996-01-01

243

42 CFR 405.906 - Parties to the initial determinations, redeterminations, reconsiderations, hearings and reviews.  

Code of Federal Regulations, 2012 CFR

...reconsiderations, hearings and reviews. (a) Parties to the initial determination. The parties to the initial determination are the following...subpart E of this chapter. Payment by a third party payer does not entitle that entity to...

2012-10-01

244

75 FR 56136 - Notice of Commission Decision Not To Review an Initial Determination Terminating the...  

Federal Register 2010, 2011, 2012, 2013

...TRADE COMMISSION [Investigation No. 337-TA-698...Decision Not To Review an Initial Determination Terminating the Investigation; In the Matter...administrative law judge's initial determination...to terminate the investigation as to one...

2010-09-15

245

49 CFR 802.12 - Initial adverse agency determination on correction or amendment.  

Code of Federal Regulations, 2012 CFR

...Transportation 7 2012-10-01 2012-10-01 false Initial adverse agency determination on correction or amendment. 802.12... Correction or Amending the Record § 802.12 Initial adverse agency determination on correction or amendment....

2012-10-01

246

49 CFR 802.12 - Initial adverse agency determination on correction or amendment.  

Code of Federal Regulations, 2011 CFR

...Transportation 7 2011-10-01 2011-10-01 false Initial adverse agency determination on correction or amendment. 802.12... Correction or Amending the Record § 802.12 Initial adverse agency determination on correction or amendment....

2011-10-01

247

7 CFR 1.118 - Appeal of initial adverse agency determination on correction or amendment.  

Code of Federal Regulations, 2012 CFR

...2012-01-01 2012-01-01 false Appeal of initial adverse agency determination on correction or amendment. 1.118...REGULATIONS Privacy Act Regulations § 1.118 Appeal of initial adverse agency determination on correction or amendment....

2012-01-01

248

Orbit determination and analysis for Cosmos 58 at 15th-order resonance, to evaluate geopotential harmonics of order 15 and 30  

Microsoft Academic Search

The orbital parameters of Cosmos 58 have been determined at 65 epochs from some 4500 observations, between March 1982 and September 1983, using the RAE orbit refinement program, PROP. During this time, the satellite passed slowly through 15th-order resonance, and the orbital inclination and eccentricity have been analyzed. Six lumped 15th-order geopotential harmonic coefficients have been evaluated, with an accuracy

Doreen M. C. Walker

1986-01-01

249

Determination of the orbit of a visual binary by the method of parameters of the apparent motion from observations over a short arc  

NASA Astrophysics Data System (ADS)

The problem of determining the orbital elements of a visual binary on the basis of highly accurate observations of a short arc of this orbit is examined. It is shown that in a rigorous statement the problem can be solved by the differential dynamic method, using the observations to determine the vectors of the relative position and relative velocity of the components of the binary. The method of parameters of apparent motion (the PAM) method is used to solve the problem under consideration. The fundamental importance of the radius of curvature of the apparent arc of the orbit of the binary in the problem of determining its orbit is established. The PAM method is applied to determine the orbits of three nearby binaries, ADS 48, ADS 7251, and 61 Cyg.

Kiselev, A. A.; Kiyaeva, O. V.

1980-12-01

250

Determinants of client-initiated and auditor-initiated auditor changes  

Microsoft Academic Search

Purpose – Prior studies include auditor-initiated (AI) and client-initiated (CI) auditor changes together and conduct research as though they were the same. This paper aims to hypothesize that AI and CI changes are driven by different interests and to examine factors that could explain and predict them. Design\\/methodology\\/approach – Based on the prior literature, the authors classified factors into AI

Thomas G. Calderon; Emeka Ofobike

2008-01-01

251

Spectroscopic Analysis and Orbital Determination of the Chromospherically Active Binary BK Psc (2RE J0039+103)  

NASA Astrophysics Data System (ADS)

BK Psc (2REJ 0039 +103) is a recently, X-ray/EUV selected star with strong H? emission above the continuum. Radial velocity variations (Jeffries et al. 1995; Cutispoto 1999)indicate that it is a binary system, but no orbital solution has been determined until now, because there were not enough radial velocity data. Using high resolution echelle spectroscopic observations taken by us during three observing runs (July 1999; August 2000; November 2000) we have determined precise radial velocities by cross correlation with radial velocity standard stars. Only the photospheric lines of the K5V primary are observed in the spectra (it is a SB1 system). However, the chromospheric emission lines from the secondary component are also detected in our spectra and it has been possible to measure the radial velocity of the secondary and obtain the orbital solution of the system as in the case of a SB2 system. We have obtained a near circular orbit with an orbital period of 2.17 days very close to its photometric period of 2.24 days (indicating synchronous rotation). The resulting masses (Msin3i) are compatible with the observed K5V primary and a unseen M3V secondary. These multiwavelength optical observations allow us to study the chromosphere of this active binary system using the information provided for several optical spectroscopic features (from the Ca II H & K to Ca II IRT lines) that are formed at different heights in the chromosphere. The chromospheric contribution in these lines has been determined using the spectral subtraction technique. In addition, we have determined rotational velocities (vsin i). The lithium (Li I ?6707.8 Å) absorption line is not detected in this star.

Montes, D.; Gálvez, M. C.; Fernández-Figueroa, M. J.; López-Santiago, J.; de Castro, E.

252

78 FR 44971 - Certain Robotic Toys and Components Thereof; Commission Determination Not To Review an Initial...  

Federal Register 2010, 2011, 2012, 2013

...INTERNATIONAL TRADE COMMISSION [Investigation No. 337-TA-869] Certain Robotic Toys and Components Thereof; Commission Determination Not To Review an Initial Determination Granting a Joint Motion for...

2013-07-25

253

Combined processing and orbit determination of Galileo and GPS satellites by estimating phase clocks  

Microsoft Academic Search

As a first step we introduced Galileo observables in the Bernese GPS software to study the combined processing of Galileo and GPS measurements based on the estimation of phase clocks for both GNSS systems We then simulated measurements for both the Galileo and the GPS constellation and estimated all relevant IGS parameters like Galileo GPS orbits high-rate Galileo GPS satellite

D. Svehla

2006-01-01

254

A new determination of lunar orbital parameters, precession constant and tidal acceleration from LLR measurements  

Microsoft Academic Search

An analysis of Lunar Laser Ranging (LLR) observations from January 1972 until April 2001 has been performed, and a new solution for the lunar orbital motion and librations has been constructed that has been named S2001. With respect to prior solutions, improvements in the statistical treatment of the data, new nutation and libration models and the addition of the positions

J. Chapront; M. Chapront-Touzé; G. Francou

2002-01-01

255

A new determination of the orbit and masses of the Be binary system delta Scorpii  

Microsoft Academic Search

The binary star delta Sco (HD143275) underwent remarkable brightening in the visible in 2000, and continues to be irregularly variable. The system was observed with the Sydney University Stellar Interferometer (SUSI) in 1999, 2000, 2001, 2006 and 2007. The 1999 observations were consistent with predictions based on the previously published orbital elements. The subsequent observations can only be explained by

W. J. Tango; J. Davis; A. P. Jacob; A. Mendez; J. R. North; J. W. O'Byrne; E. B. Seneta; P. G. Tuthill

2009-01-01

256

Accurate Determination of Comet and Asteroid Orbits Leading to Collision With Earth.  

National Technical Information Service (NTIS)

Movements of the celestial bodies in our solar system inspired Isaac Newton to work out his profound laws of gravitation and motion; with one or two notable exceptions, all of those objects move as Newton said they would. But normally harmonious orbital m...

C. M. Roithmayr L. Kay-Bunnell D. D. Mazanek R. R. Kumar H. Seywald M. A. Hausman

2005-01-01

257

20 CFR 418.3605 - What is an initial determination?  

Code of Federal Regulations, 2013 CFR

...determination? 418.3605 Section 418.3605 Employees' Benefits SOCIAL SECURITY ADMINISTRATION MEDICARE SUBSIDIES Medicare Part D Subsidies Determinations and the Administrative Review Process § 418.3605 What is an...

2013-04-01

258

Determination of initial velocities of enzymic reactions from progress curves.  

PubMed Central

The present communication describes a novel method for estimating initial velocities (v) of enzyme-catalysed reactions. It is based on an approximation of experimental data obtained by the cubic spline function. The initial velocity of a reaction is calculated as a derivative of the approximating function at a time value equal to zero. The proposed method is usable on a computer with a FORTRAN IV program. The method can be successfully used in such cases as substantial extents of substrate conversion, the inactivation of an enzyme in the course of a reaction, the existence of large experimental error or when the reaction mechanism is unknown.

Dagys, R; Pauliukonis, A; Kazlauskas, D; Mankevicius, M; Simutis, R

1986-01-01

259

Precise Orbits for Ground-Based GPS Meteorology: Processing Strategy and Quality Assessment of the Orbits Determined at Geodetic Observatory Pecny  

Microsoft Academic Search

The GPS meteorology has been the driving force behind the near real-time (NRT) GPS analyses during the past few years. High availability of precise near real-time GPS orbits is essential for obtaining reliable solutions in almost all applications. This is especially true when estimating the troposphere parameters. Besides the demand on high accuracy, the orbit products should stand out for

Jan DOUŠA

2004-01-01

260

Determinants of breastfeeding initiation among mothers in Kuwait  

PubMed Central

Background Exclusive breastfeeding is recommended as the optimal way to feed infants for the first six months of life. While overall breastfeeding rates are high, exclusive breastfeeding is relatively uncommon among Middle Eastern women. The objective of this study was to identify the incidence of breastfeeding amongst women in the six governorates of Kuwait and the factors associated with the initiation of breastfeeding. Methods A sample of 373 women (aged 17-47 years), recruited shortly after delivery from four hospitals in Kuwait, completed a structured, interviewer-administered questionnaire. Multivariate logistic regression analysis was used to identify those factors independently associated with the initiation of breastfeeding. Results In total, 92.5% of mothers initiated breastfeeding and at discharge from hospital the majority of mothers were partially breastfeeding (55%), with only 30% of mothers fully breastfeeding. Prelacteal feeding was the norm (81.8%) and less than 1 in 5 infants (18.2%) received colostrum as their first feed. Only 10.5% of infants had been exclusively breastfed since birth, the remainder of the breastfed infants having received either prelacteal or supplementary infant formula feeds at some time during their hospital stay. Of the mothers who attempted to breastfeed, the majority of women (55.4%) delayed their first attempt to breastfeed until 24 hours or more after delivery. Breastfeeding at discharge from hospital was positively associated with paternal support for breastfeeding and negatively associated with delivery by caesarean section and with the infant having spent time in the Special Care Nursery. Conclusions The reasons for the high use of prelacteal and supplementary formula feeding warrant investigation. Hospital policies and staff training are needed to promote the early initiation of breastfeeding and to discourage the unnecessary use of infant formula in hospital, in order to support the establishment of exclusive breastfeeding by mothers in Kuwait.

2010-01-01

261

Research note Yield stress for initial firmness determination on yogurt  

Microsoft Academic Search

Yield stress and apparent residual stress were measured in laboratory-made yogurts containing different gum concentrations and in seven retail yogurts. Yield stress exhibited significant correlation (p < 0.001) with the sensory initial firmness perceived by trained pan- elists in both laboratory-made (r = 0.99) and retail (r > 0.97) yogurts. Apparent residual stress was significantly correlated with sensory viscosity for

F. Harte; S. Clark; G. V. Barbosa-Canovas

262

High-precision onboard orbit determination for small satellites - the GPS-based XNSon X-SAT  

NASA Astrophysics Data System (ADS)

X-SAT is a mini-satellite developed by the Satellite Engineering Centre of the Nanyang Technological University at Singapore. The focus of the technology- driven mission is the high-resolution remote sensing of the Southeast Asian region for environmental monitoring. To achieve the ambitious mission objectives, the GPS-based X-SAT Navigation System (XNS) will provide high-precision onboard orbit determination solutions as well as orbit forecasts. With a targeted real-time position accuracy of about 1-2 m 3D r.m.s., the XNS provides an unprecedented accuracy performance and thus enables the support of any satellite mission which requires precise onboard position knowledge.

Gill, E.; Montenbruck, O.; Arichandran, K.; Tan, S.H.; Bretschneider

2004-11-01

263

Role of heavy-ion nuclear reactions in determining on-orbit single event error rates  

Microsoft Academic Search

Simulations show that neglecting ion-ion interaction processes (both particles having Z>1) results in an underestimation of the total on-orbit single event upset error rate by more than two orders of magnitude for certain technologies. The inclusion of ion-ion nuclear reactions leads to dramatically different SEU error rates for CMOS devices containing high Z materials compared with direct ionization by the

Christina L. Howe; Robert A. Weller; Robert A. Reed; Marcus H. Mendenhall; Ronald D. Schrimpf; Kevin M. Warren; Dennis R. Ball; Lloyd W. Massengill; Kenneth A. LaBel; Nadim F. Haddad

2005-01-01

264

Factorization methods for precision satellite orbit determination foi HC\\/MF  

Microsoft Academic Search

State-of-the-art square root information filtering and smoothing technology that is incorporated into the Aerospace TRACE orbital analysis program are presented. Topics include a pseudo-epoch state batch-sequential filter formulation, techniques for inclusion of Markov process noise models, a variable dimension filter structure that accomodates state vectors of large size, and inclusion of a GPS second-order Markov clock model within the framework

G. J. Bierman; L. A. Campbell; W. A. Feess

1981-01-01

265

A new determination of the orbit and masses of the Be binary system delta Scorpii  

Microsoft Academic Search

The binary star delta Sco (HD143275) underwent remarkable brightening in the\\u000avisible in 2000, and continues to be irregularly variable. The system was\\u000aobserved with the Sydney University Stellar Interferometer (SUSI) in 1999,\\u000a2000, 2001, 2006 and 2007. The 1999 observations were consistent with\\u000apredictions based on the previously published orbital elements. The subsequent\\u000aobservations can only be explained by

W. J. Tango; J. Davis; A. P. Jacob; A. Mendez; J. R. North; J. W. O'Byrne; E. B. Seneta; P. G. Tuthill

2008-01-01

266

40 CFR 63.705 - Performance test methods and procedures to determine initial compliance.  

Code of Federal Regulations, 2010 CFR

...required to conduct an initial performance test... (b) When an initial compliance demonstration...used in determining initial compliance with...applied to the base substrate (i.e., the...determine HAP or VOC concentration of air exhaust...used for sample and velocity traverses....

2009-07-01

267

40 CFR 63.705 - Performance test methods and procedures to determine initial compliance.  

Code of Federal Regulations, 2010 CFR

...required to conduct an initial performance test... (b) When an initial compliance demonstration...used in determining initial compliance with...applied to the base substrate (i.e., the...determine HAP or VOC concentration of air exhaust...used for sample and velocity traverses....

2010-07-01

268

The effect of initial velocity on manually controlled remote docking of an orbital maneuvering vehicle (OMV) to a space station  

Microsoft Academic Search

Simulated docking maneuvers were performed to assess the effect of initial velocity on docking failure rate, mission duration, and total impulse (fuel consumption). The effect of the removal of the range and rate displays was also examined. Since duration and impulse decrease and increase respectively with increases in initial velocity, two parameters were created by subtracting a reference value from

Adam R. Brody

1989-01-01

269

Upper-atmosphere rotation rate determined from the orbit of CHINA 6 rocket /1976-87B/  

NASA Astrophysics Data System (ADS)

The orbit of CHINA 6 rocket, 1976-87B, has been determined at 51 epochs during its 17 month life, using the RAE orbit refinement computer program, PROP 6, with over 4000 radar and optical observations. The rotation rate of the upper atmosphere in lambda rev/day, for the height-band of 200-230 km, was calculated from the decrease in orbital inclination to give the following results: (1) for morning conditions, lambda = 0.9 for May-June and Aug.-Sept. 1977, at 215 km mean height, and it is 0.7 for Oct.-Nov. 1977, at 210 km, (2) for evening conditions, lambda = 1.2 for July and Sept.-Oct. 1977, at 215 km, and (3) for mean (morning plus evening) conditions, lambda = 1.0 plus or minus 0.1 between Oct. 1976 and May 1977, at 230 km, and 0.8 plus or minus 0.1 for Dec. 1977 to Jan. 1978, at 215 km and mean latitude of 57 deg S.

Hiller, H.

1980-05-01

270

Determining olivine composition of basaltic dunes in Gale Crater, Mars, from orbit: Awaiting ground truth from Curiosity  

NASA Astrophysics Data System (ADS)

successful landing of the Mars Science Laboratory Curiosity rover in Gale Crater, Mars, presents a rare opportunity for validation of a spectral index developed for determining olivine chemistry from orbital midinfrared remote-sensing data. Here, a spectral index is developed using laboratory emissivity data of 13 synthetic Mg-Fe olivines. Utilizing this spectral index, a prediction of olivine composition (~Fo55 ± 5) is made from orbital data for a NE-SW trending dune field near the Curiosity rover. This dune field will be crossed during the mission as the rover travels toward a ~5 km-high sediment stack (Mount Sharp) that contains orbitally detected clays and sulfates. Curiosity can use its instrument suite (ChemMin, Alpha Particle X-ray Spectrometer, ChemCam) when it reaches the dunes to verify or refute the olivine-chemistry prediction presented here. The ability to validate the developed spectral index using the rover's ground-truth instruments will strengthen olivine-chemistry mapping across the Martian surface using this spectral index.

Lane, Melissa D.; Christensen, Philip R.

2013-07-01

271

20 CFR 404.904 - Notice of the initial determination.  

Code of Federal Regulations, 2013 CFR

...notice will explain in simple and clear language what we have determined and the reasons...notice also will contain in understandable language a statement of the case setting forth...benefits has ended because of his or her death. [72 FR 51177, Sept. 6,...

2013-04-01

272

Initial determination of the micromechanical properties of oxide scales  

Microsoft Academic Search

A depth-sensing submicron identation technique is being used to characterize the mechanical response of oxide scales. The method has been applied to studies of chromia-rich and alumina scales grown on a stainless steel and an iron aluminide respectively. Results on room temperature micromechanical properties (elastic modulus, hardness, etc.) are presented to provide data for determining scale fracture criteria and to

P. F. Tortorelli; J. R. Keiser; W. C. Oliver; K. R. Willson

1990-01-01

273

Gravity and Orbits: Orbits  

NSDL National Science Digital Library

This Science Object is the third of three Science Objects in the Gravity and Orbits SciPack. It provides an understanding of how gravitational forces influence the motion of an object in orbit. When a force acts toward a single center, an object's forward motion and its motion toward that center can combine to create a curved path around the center. Gravity governs the motion of all objects in the solar system. The Sun's gravitational pull holds the Earth and other planets in their orbits, just as the planets' gravitational pull keeps their moons in orbit around them. Learning Outcomes:� Describe the conditions that would lead an object into orbital motion in terms of the effects of gravitational force.� Explain how an object orbits a planet in terms of trajectories and free fall.� Identify gravity as the force that keeps the planets in their orbits around the Sun and the moons in their orbits around the planets.

National Science Teachers Association (NSTA)

2006-11-01

274

Orbital pseudotumor.  

PubMed

Orbital pseudotumor is a benign condition that accounts for approximately 10% of all orbital mass lesions. Any part of the orbit may be involved. The etiology is unknown. The presentation may be either acute or subacute. Patients may present with a palpable mass, a swollen eyelid, congestion, pain, diminished ocular motility, and/or decreased visual acuity. Approximately, 25% of patients present with bilateral disease. A modest proportion of patients experience resolution of their symptoms without treatment. Biopsy is indicated for those who do not respond to, or relapse after, first-line therapy. Oral corticosteroids are the initial treatment and approximately 80% of patients respond. Roughly half of those who respond to corticosteroids relapse. Second-line therapy consists of either low-dose radiotherapy (20-30 Gy at 2 Gy per fraction), cytotoxic chemotherapy, or immunosuppressive agents. Radiotherapy results in long-term local control rates of 50% or higher. Limited lesions may be successfully resected. A small subset of patients may experience inexorable progression to a fixed, painful, sightless eye and require orbital exenteration. PMID:19738455

Mendenhall, William M; Lessner, Alan M

2010-06-01

275

The effect of initial velocity on manually controlled remote docking of an orbital maneuvering vehicle (OMV) to a space station  

NASA Astrophysics Data System (ADS)

Simulated docking maneuvers were performed to assess the effect of initial velocity on docking failure rate, mission duration, and total impulse (fuel consumption). The effect of the removal of the range and rate displays was also examined. Since duration and impulse decrease and increase respectively with increases in initial velocity, two parameters were created by subtracting a reference value from each. These values were termed 'reserve time' and 'radial impulse'. Naive subjects were capable of achieving a high success rate in performing simulated docking maneuvers without extensive experience, and failure rate did not significantly increase with increased velocity. The amount of time pilots reserved for final approach increased with starting velocity. Piloting of docking maneuvers was not significantly affected in any way by the removal of range and rate displays. Values for reserve time, and radial impulse were lowest for docking maneuvers begun at the lowest initial velocity.

Brody, Adam R.

1989-01-01

276

Orbital geometry determined by orthogonal high-order harmonic polarization components  

SciTech Connect

We study the polarization state of high-order harmonics produced by linearly polarized light interacting with two-center molecules. By generating high-harmonic 'polarization maps' from Radon transformations of excited electronic wave functions, we show that the polarization of the harmonic radiation can be linked to the geometry of the molecular orbital. While in the Radon transformation the plane-wave approximation for the rescattered electron is implicitly assumed, numerical solutions of the two-dimensional time-dependent Schro{center_dot}{center_dot}dinger equation, in which this approximation is not made, confirm the validity of this topological connection. We also find that measuring two orthogonal amplitude components of the harmonics provides a method for quantum tomography that substantially improves the quality of reconstructed molecular states.

Hijano, Eliot [ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, E-08860 Castelldefels (Barcelona) (Spain); Serrat, Carles [ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, E-08860 Castelldefels (Barcelona) (Spain); DTDI, Universitat de Vic, Carrer de la Laura 13, E-08500 Vic (Barcelona) (Spain); Gibson, George N. [Department of Physics, University of Connecticut, Storrs, Connecticut 06269 (United States); Biegert, Jens [ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, E-08860 Castelldefels (Barcelona) (Spain); ICREA-Institucio Catalana de Recerca i Estudis Avancats, E-08010 Barcelona (Spain)

2010-04-15

277

COMET C/2011 W3 (LOVEJOY): ORBIT DETERMINATION, OUTBURSTS, DISINTEGRATION OF NUCLEUS, DUST-TAIL MORPHOLOGY, AND RELATIONSHIP TO NEW CLUSTER OF BRIGHT SUNGRAZERS  

SciTech Connect

We describe the physical and orbital properties of C/2011 W3. After surviving perihelion passage, the comet was observed to undergo major physical changes. The permanent loss of the nuclear condensation and the formation of a narrow spine tail were observed first at Malargue, Argentina, on December 20 and then systematically at Siding Spring, Australia. The process of disintegration culminated with a terminal fragmentation event on December 17.6 UT. The postperihelion dust tail, observed for {approx}3 months, was the product of activity over <2 days. The nucleus' breakup and crumbling were probably caused by thermal stress due to the penetration of the intense heat pulse deep into the nucleus' interior after perihelion. The same mechanism may be responsible for cascading fragmentation of sungrazers at large heliocentric distances. The delayed response to the hostile environment in the solar corona is at odds with the rubble-pile model, since the residual mass of the nucleus, estimated at {approx}10{sup 12} g (equivalent to a sphere 150-200 m across) just before the terminal event, still possessed nontrivial cohesive strength. The high production rates of atomic oxygen, observed shortly after perihelion, are compatible with a subkilometer-sized nucleus. The spine tail-the product of the terminal fragmentation-was a synchronic feature, whose brightest part contained submillimeter-sized dust grains, released at velocities of up to 30 m s{sup -1}. The loss of the nuclear condensation prevented an accurate orbital-period determination by traditional techniques. Since the missing nucleus must have been located on the synchrone, whose orientation and sunward tip have been measured, we compute the astrometric positions of this missing nucleus as the coordinates of the points of intersection of the spine tail's axis with the lines of forced orbital-period variation, derived from the orbital solutions based on high-quality preperihelion astrometry from the ground. The resulting orbit gives 698 {+-} 2 yr for the osculating orbital period, showing that C/2011 W3 is the first member of the expected new, 21st-century cluster of bright Kreutz-system sungrazers, whose existence was predicted by these authors in 2007. From the spine tail's evolution, we determine that its measured tip, populated by dust particles 1-2 mm in diameter, receded antisunward from the computed position of the missing nucleus. The bizarre appearance of the comet's dust tail in images taken only hours after perihelion with the coronagraphs on board the SOHO and STEREO spacecraft is readily understood. The disconnection of the comet's head from the tail released before perihelion and an apparent activity attenuation near perihelion have a common cause-sublimation of all dust at heliocentric distances smaller than about 1.8 solar radii. The tail's brightness is strongly affected by forward scattering of sunlight by dust. From an initially broad range of particle sizes, the grains that were imaged the longest had a radiation-pressure parameter {beta} {approx_equal} 0.6, diagnostic of submicron-sized silicate grains and consistent with the existence of the dust-free zone around the Sun. The role and place of C/2011 W3 in the hierarchy of the Kreutz system and its genealogy via a 14th-century parent suggest that it is indirectly related to the celebrated sungrazer X/1106 C1, which, just as the first-generation parent of C/2011 W3, split from a common predecessor during the previous return to perihelion.

Sekanina, Zdenek; Chodas, Paul W., E-mail: Zdenek.Sekanina@jpl.nasa.gov, E-mail: Paul.W.Chodas@jpl.nasa.gov [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)

2012-10-01

278

Comet C/2011 W3 (Lovejoy): Orbit Determination, Outbursts, Disintegration of Nucleus, Dust-tail Morphology, and Relationship to New Cluster of Bright Sungrazers  

NASA Astrophysics Data System (ADS)

We describe the physical and orbital properties of C/2011 W3. After surviving perihelion passage, the comet was observed to undergo major physical changes. The permanent loss of the nuclear condensation and the formation of a narrow spine tail were observed first at Malargue, Argentina, on December 20 and then systematically at Siding Spring, Australia. The process of disintegration culminated with a terminal fragmentation event on December 17.6 UT. The postperihelion dust tail, observed for ~3 months, was the product of activity over <2 days. The nucleus' breakup and crumbling were probably caused by thermal stress due to the penetration of the intense heat pulse deep into the nucleus' interior after perihelion. The same mechanism may be responsible for cascading fragmentation of sungrazers at large heliocentric distances. The delayed response to the hostile environment in the solar corona is at odds with the rubble-pile model, since the residual mass of the nucleus, estimated at ~1012 g (equivalent to a sphere 150-200 m across) just before the terminal event, still possessed nontrivial cohesive strength. The high production rates of atomic oxygen, observed shortly after perihelion, are compatible with a subkilometer-sized nucleus. The spine tail—the product of the terminal fragmentation—was a synchronic feature, whose brightest part contained submillimeter-sized dust grains, released at velocities of up to 30 m s-1. The loss of the nuclear condensation prevented an accurate orbital-period determination by traditional techniques. Since the missing nucleus must have been located on the synchrone, whose orientation and sunward tip have been measured, we compute the astrometric positions of this missing nucleus as the coordinates of the points of intersection of the spine tail's axis with the lines of forced orbital-period variation, derived from the orbital solutions based on high-quality preperihelion astrometry from the ground. The resulting orbit gives 698 ± 2 yr for the osculating orbital period, showing that C/2011 W3 is the first member of the expected new, 21st-century cluster of bright Kreutz-system sungrazers, whose existence was predicted by these authors in 2007. From the spine tail's evolution, we determine that its measured tip, populated by dust particles 1-2 mm in diameter, receded antisunward from the computed position of the missing nucleus. The bizarre appearance of the comet's dust tail in images taken only hours after perihelion with the coronagraphs on board the SOHO and STEREO spacecraft is readily understood. The disconnection of the comet's head from the tail released before perihelion and an apparent activity attenuation near perihelion have a common cause—sublimation of all dust at heliocentric distances smaller than about 1.8 solar radii. The tail's brightness is strongly affected by forward scattering of sunlight by dust. From an initially broad range of particle sizes, the grains that were imaged the longest had a radiation-pressure parameter ? ~= 0.6, diagnostic of submicron-sized silicate grains and consistent with the existence of the dust-free zone around the Sun. The role and place of C/2011 W3 in the hierarchy of the Kreutz system and its genealogy via a 14th-century parent suggest that it is indirectly related to the celebrated sungrazer X/1106 C1, which, just as the first-generation parent of C/2011 W3, split from a common predecessor during the previous return to perihelion.

Sekanina, Zdenek; Chodas, Paul W.

2012-10-01

279

In Stable Orbit: An Initial Assessment of Dispositional Changes Arising from Learning Using the Citizenship Education Videogame Space Station Leonis  

Microsoft Academic Search

This paper presents an initial analysis of data obtained from an implementation of citizenship education using the videogame Space Station Leonis in two Singapore classrooms. The paper highlights the importance of citizenship education today and describes how game environments can be used to foster identity construction as part of the broader agenda of citizenship education in Singapore. The data presented

Kenneth Y. T. Lim; Yam San Chee

2007-01-01

280

20 CFR 663.515 - What is the process for initial determination of provider eligibility?  

Code of Federal Regulations, 2013 CFR

...2013-04-01 2013-04-01 false What is the process for initial determination...Training Providers § 663.515 What is the process for initial determination...the State; (ii) Providing an opportunity for interested members of the...

2013-04-01

281

Trust in Government Cross-Boundary Information Sharing Initiatives: Identifying the Determinants  

Microsoft Academic Search

This paper identifies a set of determinants of trust in government cross-boundary information sharing (CBI) initiatives. Although there are some studies that identify the antecedents of trust in collaboration, research about trust relationships in government interorganizational initiatives is lacking. Little attention, in particular, has been paid to the determinants of trust in government CBI. To fill this gap in the

José Ramón Gil-García; Ahmet Guler; Theresa A. Pardo; G. Brian Burke

2010-01-01

282

Atomic Orbitals  

NSDL National Science Digital Library

The Atomic Orbitals website is a distribution point for the orbital image generating program "Orbital Viewer" as well as the home of a collection of images generated with the program. Atomic and molecular orbitals are constructed. For atoms, the hydrogenic solution, up to n=30, is generated and for molecules the linear combination of atomic orbitals method is used.

Manthey, David

2009-03-24

283

Periodic orbits around areostationary points in the Martian gravity field  

NASA Astrophysics Data System (ADS)

This study investigates the problem of areostationary orbits around Mars in three-dimensional space. Areostationary orbits are expected to be used to establish a future telecommunication network for the exploration of Mars. However, no artificial satellites have been placed in these orbits thus far. The characteristics of the Martian gravity field are presented, and areostationary points and their linear stability are calculated. By taking linearized solutions in the planar case as the initial guesses and utilizing the Levenberg-Marquardt method, families of periodic orbits around areostationary points are shown to exist. Short-period orbits and long-period orbits are found around linearly stable areostationary points, but only short-period orbits are found around unstable areostationary points. Vertical periodic orbits around both linearly stable and unstable areostationary points are also examined. Satellites in these periodic orbits could depart from areostationary points by a few degrees in longitude, which would facilitate observation of the Martian topography. Based on the eigenvalues of the monodromy matrix, the evolution of the stability index of periodic orbits is determined. Finally, heteroclinic orbits connecting the two unstable areostationary points are found, providing the possibility for orbital transfer with minimal energy consumption.

Liu, Xiao-Dong; Baoyin, Hexi; Ma, Xing-Rui

2012-05-01

284

Near-parabolic comets observed in 2006-2010. The individualized approach to 1/a-determination and the new distribution of original and future orbits  

NASA Astrophysics Data System (ADS)

Dynamics of a complete sample of small perihelion distance near-parabolic comets discovered in the years 2006-2010 are studied (i.e. of 22 comets of qosc < 3.1 au). First, osculating orbits are obtained after a very careful positional data inspection and processing, including where appropriate, the method of data partitioning for determination of pre- and post-perihelion orbit for tracking then its dynamical evolution. The non-gravitational acceleration in the motion is detected for 50 per cent of investigated comets, in a few cases for the first time. Different sets of non-gravitational parameters are determined from pre- and post-perihelion data for some of them. The influence of the positional data structure on the possibility of the detection of non-gravitational effects and the overall precision of orbit determination is widely discussed. Secondly, both original and future orbits were derived by means of numerical integration of swarms of virtual comets obtained using a Monte Carlo cloning method. This method allows us to follow the uncertainties of orbital elements at each step of dynamical evolution. The complete statistics of original and future orbits that includes significantly different uncertainties of 1/a-values is presented, also in the light of our results obtained earlier. Basing on 108 comets examined by us so far, we conclude that only one of them, C/2007 W1 Boattini, seems to be a serious candidate for an interstellar comet. We also found that 53 per cent of 108 near-parabolic comets escaping in the future from the Solar system, and the number of comets leaving the Solar system as so called Oort spike comets (i.e. comets suffering very small planetary perturbations) is 14 per cent. A new method for cometary orbit quality assessment is also proposed by means of modifying the original method, introduced by Marsden, Sekanina & Everhart. This new method leads to a better diversification of orbit quality classes for contemporary comets.

Królikowska, Ma?gorzata; Dybczy?ski, Piotr A.

2013-10-01

285

Comparison of orbit phasing maneuvers  

Microsoft Academic Search

Prussing and Chiu developed a general analysis method for optimizing multiple-impulse, time-fixed rendezvous between circular orbits. Orbit phasing maneuvers, where the maneuvering spacecraft simply changes position within the same orbit, are a subset of these general maneuvers. The present analysis compares the use of simple orbit phasing maneuvers with the optimal maneuvers derived by Prussing and Chiu to determine the

John M. Hanson

1990-01-01

286

Heat Transfer Rate Distribution on North American Rockwell delta Wing Orbiter Determined by Phase Change Paint Technique at a Mach Number of 8, Volume 1.  

National Technical Information Service (NTIS)

The results of a wind tunnel test program to determine aerodynamic heat transfer distributions on an orbiter configuration are presented. Heat-transfer rates were determined by the phase change paint technique on 0.013-scale Stycast models using Tempilaq ...

J. D. Warmbrod R. K. Matthews W. R. Martindale

1972-01-01

287

An analysis of the accuracy of orbit determination for PHOBOS, the Earth, and Mars in project PHOBOS based on solving a modeling problem  

Microsoft Academic Search

The problem was solved of studying the feasibility and accuracy of determining the parameters of the orbits of Phobos, Mars, and the Earth by the method of modeling measurements of the radio signals from an autonomous station on the surface of Phobos. Conclusions are drawn about the dependence of the errors in determining the parameters sought on the length of

S. N. Vashkov'yak; N. V. Emel'Yanov

1990-01-01

288

Determination of an Amazon Hot Reference Target for the On-Orbit Calibration of Microwave Radiometers  

Microsoft Academic Search

A physically based model is developed to determine hot calibration reference brightness temperatures (TBs) over depolarized regions in the Amazon rain forest. The model can be used to evaluate the end-to-end calibration of any satellite microwave radiometer operating at a frequency between 18 and 40 GHz and angle of incidence between nadir and 55°. The model is constrained by Special

Shannon T. Brown; Christopher S. Ruf

2005-01-01

289

Precise Orbit Determination with the DORIS/SPOT2 System: First Results.  

National Technical Information Service (NTIS)

One of the main challenges of the French/U.S. oceanographic mission, TOPEX/Poseidon, is the need to determine the position of the spacecraft with an accuracy of 10 cm in the radial direction after 10 days. In order to reach this level of accuracy, a track...

F. Nouel J. P. Berthias P. Broca A. Comps M. Deleuze

1991-01-01

290

77 FR 69501 - Certain Devices for Mobile Data Communication; Determination Not To Review an Initial...  

Federal Register 2010, 2011, 2012, 2013

...Review an Initial Determination Granting a Motion By Complainant To Terminate the Investigation...administrative law judge (``ALJ'') granting a motion by complainant to terminate the investigation...notice of investigation named Research In Motion Ltd. of Ontario, Canada; Research...

2012-11-19

291

42 CFR 405.904 - Medicare initial determinations, redeterminations and appeals: General description.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 2012-10-01 false Medicare initial determinations, redeterminations...904 Public Health CENTERS FOR MEDICARE & MEDICAID SERVICES, DEPARTMENT OF HEALTH AND HUMAN SERVICES MEDICARE PROGRAM FEDERAL HEALTH...

2012-10-01

292

40 CFR 179.110 - Determination by Administrator to review initial decision.  

Code of Federal Regulations, 2013 CFR

Within 10 days following the expiration of the time for filing exceptions (including any extensions), the Administrator may file with the hearing clerk, and serve on the parties, a notice of the Administrator's determination to review the initial...

2013-07-01

293

15 CFR 930.38 - Consistency determinations for activities initiated prior to management program approval.  

Code of Federal Regulations, 2013 CFR

...determinations for activities initiated prior to management program approval. 930.38 Section...COMMERCE OCEAN AND COASTAL RESOURCE MANAGEMENT FEDERAL CONSISTENCY WITH APPROVED COASTAL MANAGEMENT PROGRAMS Consistency for Federal...

2013-01-01

294

Status of the Precision Orbit Determination solutions for the most recent altimeter missions: focusing on the long-term stability for the analysis of Mean Sea Level trends  

NASA Astrophysics Data System (ADS)

The reference Ocean Surface Topography Mission/Jason-2 satellite (CNES/NASA) has been in orbit for four years (since June 2008). It extends the continuous record of highly accurate sea surface height measurements begun in 1992 by the Topex/Poseidon mission and continued in 2001 by the Jason-1 mission. The complementary missions CryoSat-2 (ESA) and HY-2A (CNSA), with lower altitudes and higher inclinations, were launched in April 2010 and August 2011, respectively. Although the two last satellites fly in different orbits, they contribute to the altimeter constellation while enhancing the global coverage. The CNES Precision Orbit Determination (POD) Group delivers precise and homogeneous orbit solutions for these independent altimeter missions. This talk will address the issues related to the long-term stability of the orbit solutions; in particular, it focuses on the impact of the time-varying gravity field on the geographically correlated errors that are of interest for the altimeter analyst and on the recent modeling improvements that allow to deliver consistent orbit solutions across different missions. We will also give an overview of the performance of the tracking systems, and address some issues (like the use of a geocenter model on DORIS-SLR coordinates) concerning the prospects for improvements in modeling of the tracking data that would allow to improve the accuracy of the POD solutions in the long run.

Couhert, Alexandre; Cerri, Luca

2012-07-01

295

Lorenz Attractor Periodic Orbits  

NSDL National Science Digital Library

The butterfly-like Lorenz attractor is a simplified model of two-dimensional convective fluid flow and is one of the best known images of chaos. Embedded in this attractor are unstable periodic orbits described by Viswanath and this model computes a number of these orbits. Each periodic orbit is classified by the number of times the trajectory orbits the A and B fixed points before it repeats. Note that because the attractor is chaotic and because of numerical errors and the finite precision of the initial conditions, errors accumulate and the trajectory leaves the vicinity of a periodic orbit after a half dozen cycles. The Lorenz Attractor Periodic Orbits Model was created using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_chaos_LorenzAttractor.jar file will run the program if Java is installed.

Christian, Wolfgang

2009-05-20

296

Root cause determination of on-orbit degradation of the VIIRS rotating telescope assembly  

NASA Astrophysics Data System (ADS)

The Visible Infrared Imaging Radiometer Suite (VIIRS) is a sensor onboard the recently launched Suomi NPP spacecraft. Shortly after launch, VIIRS was found to exhibit a pronounced decrease in the optical throughput of several bands, with the near-infrared bands being more affected than those in the visible. The anomaly investigation team performed several experiments that concluded the primary source of degradation was throughput loss in the VIIRS rotating telescope assembly, likely caused by ultraviolet light illumination. This paper will discuss the laboratory investigation that determined the root cause of the telescope degradation to be UV photo-darkening of a tungsten oxide contaminant film that had been inadvertently deposited during the mirror manufacturing process. We will present data from experiments conducted on witness mirrors manufactured along with the telescope, as well as other mirrors of the same type that were not contaminated.

Barrie, J. D.; Fuqua, P. D.; Meshishnek, M. J.; Ciofalo, M. R.; Chu, C. T.; Chaney, J. A.; Moision, R. M.; Graziani, L.

2012-09-01

297

Orbit determination and analysis for Cosmos 58 at 15th-order resonance, to evaluate geopotential harmonics of order 15 and 30  

NASA Astrophysics Data System (ADS)

The orbital parameters of Cosmos 58 have been determined at 65 epochs from some 4500 observations, between March 1982 and September 1983, using the RAE orbit refinement program, PROP. During this time, the satellite passed slowly through 15th-order resonance, and the orbital inclination and eccentricity have been analyzed. Six lumped 15th-order geopotential harmonic coefficients have been evaluated, with an accuracy equivalent to between 0.8 and 2.0 cm in geoid height. Six 30th-order coefficients have also been determined, with accuracies between 2 and 7 cm in geoid height. The coefficients have been compared with those from the GEM 10B and 10C models. There is good agreement for nine of the twelve coefficients.

Walker, Doreen M. C.

1986-12-01

298

Validation of GPS Based Precise Orbits Using SLR Observations  

NASA Astrophysics Data System (ADS)

In this study, the YLPODS (Yonsei Laser-ranging Precision Orbit Determination System) is developed for POD using SLR (Satellite Laser Ranging) NP (Normal Point) observations. The performance of YLPODS is tested using SLR NP observations of TOPEX/POSEIDON and CHAMP satellite. JPL's POE (Precision Orbit Ephemeris) is assumed to be true orbit, the measurement residual RMS (Root Mean Square) and the orbit accuracy (radial, along-track, cross-track) are investigated. The validation of POD using GPS (Global Positioning System) raw data is achieved by YLPODS performance and highly accurate SLR NP observations. YGPODS (Yonsei GPS-based Precision Orbit Determination System) is used for generating GPS based precise orbits for TOPEX/POSEIDON. The initial orbit for YLPODS is derived from the YGPODS results. To validate the YGPODS results the range residual of the first adjustment of YLPODS is investigated. The YLPODS results using SLR NP observations of TOPEX/POSEIDON and CHAMP satellite show that the range residual is less than 10 cm and the orbit accuracy is about 1 m level. The validation results of the YGPODS orbits using SLR NP observations of the TOPEX/POSEIDON satellite show that the range residual is less than 10 cm. This result predicts that the accuracy of this GPS based orbits is about 1m level and it is compared with JPL's POE. Thus this result presents that the YLPODS can be used for POD validation using SLR NP observations such as STSAT-2 and KOMPSAT-5.

Kim, Young-Rok; Park, Eunseo; Park, Sang-Young; Choi, Kyu-Hong; Hwang, Yoola; Kim, Hae-Yeon; Lee, Byoung-Sun; Kim, Jaehoon

2009-03-01

299

Optimal periodic relative orbit and rectilinear relative orbits with eccentric reference orbits  

NASA Astrophysics Data System (ADS)

The problem of two-body linearized periodic relative orbits with eccentric reference orbits is studied in this paper. The periodic relative orbit in the target-orbital coordinate system can be used in fly-around and formation-flying orbit design. Based on the closed-form solutions to the Tschauner-Hempel equations, the initial condition for periodic relative orbits is obtained. Then the minimum-fuel periodic-orbit condition with a single impulse is analytically derived for given initial position and velocity vectors. When considering the initial coasting time, the impulse position of the global minimum-fuel periodic orbit is proved to be near to the perigee of the target and can be obtained by numerical optimization algorithms. Moreover, the condition for a special periodic orbit, i.e., the rectilinear relative orbit in the target-orbital frame, is obtained. Numerical simulations are used to demonstrate the efficacy of the method, and show the geometry of the periodic relative orbit and the rectilinear relative orbit.

Zhang, Gang; Zhou, Di; Sun, Zhaowei; Cao, Xibin

2013-10-01

300

Error localization in RHIC by fitting difference orbits  

SciTech Connect

The presence of realistic errors in an accelerator or in the model used to describe the accelerator are such that a measurement of the beam trajectory may deviate from prediction. Comparison of measurements to model can be used to detect such errors. To do so the initial conditions (phase space parameters at any point) must be determined which can be achieved by fitting the difference orbit compared to model prediction using only a few beam position measurements. Using these initial conditions, the fitted orbit can be propagated along the beam line based on the optics model. Measurement and model will agree up to the point of an error. The error source can be better localized by additionally fitting the difference orbit using downstream BPMs and back-propagating the solution. If one dominating error source exist in the machine, the fitted orbit will deviate from the difference orbit at the same point.

Liu C.; Minty, M.; Ptitsyn, V.

2012-05-20

301

A complex RNA sequence determines the internal initiation of encephalomyocarditis virus RNA translation.  

PubMed Central

Translation initiation on EMCV RNA occurs via binding of ribosomes to an internal sequence within the 5' noncoding region. To investigate the organization of the internal ribosome entry site (IRES) we have determined the translational efficiencies of a series of deletion mutants within the 5' noncoding region of EMCV RNA. Three functional regions have been distinguished: a sequence between nts 315-484 and the upper parts of the double-helical structural domains III (nts 488-647) and IV (nts 701-763). The first one greatly enhances translation, but is not absolutely necessary for internal initiation. The other two regions are indispensable to this process. A sequence within domain IV determines inhibition of in vitro translation of mRNAs with 5'-terminal dependent initiation. It is proposed to interact with a translational factor(s) common to the internal and 5'-terminal dependent initiation. Images

Evstafieva, A G; Ugarova, T Y; Chernov, B K; Shatsky, I N

1991-01-01

302

A comparison of operationally determined atmospheric densities from satellite orbit solutions and the exospheric temperature from the Jacchia-Roberts model  

NASA Astrophysics Data System (ADS)

Operational orbit determination by the Flight Dynamics Division at the Goddard Space Flight Center has yielded a data base of orbit solutions covering the onset of solar cycle 22. Solutions for nine satellites include an estimated drag adjustment parameter (rho sub 1) determined by the Goddard Trajectory Determination System (GTDS). The rho sub 1 is used to evaluate correlations between density variations and changes in the following: 10.7-centimeter wavelength solar flux (F sub 10.7), the geomagnetic index A sub p, and two exospheric temperatures (T sub c and T sub infinity) adapted from the Jacchia-Roberts atmospheric density model in GTDS. T sub c depends on the daily and 81-day centered mean F sub 10.7; T sub infinity depends on T sub c and the geomagnetic index K sub p values. The highest correlations are between density and T sub infinity. Correlations with T sub c and F sub 10.7 are lower by 9 and 10 percent, respectively. For most cases, correlations with A sub p are considerably lower; however, significant correlations with A sub p were found for some high-inclination, moderate-altitude orbits. Results from this analysis enhance the understanding of the drag model and the accommodation of atmospheric density variations in the operational orbit determination support. The degree of correlation demonstrates the sensitivity of the orbit determination process to drag variations and to the input parameters that characterize aspects of the atmospheric density model. To this extent, the degree of correlation provides a measure of performance for methods of selecting or modeling the thermospheric densities using the solar F sub 10.7 and geomagnetic data as input to the process.

Ward, D. T.; Smith, E. A.; Phenneger, M. C.

1990-12-01

303

Metal-sulfur valence orbital interaction energies in metal-dithiolene complexes: determination of charge and overlap interaction energies by comparison of core and valence ionization energy shifts.  

PubMed

The electronic interactions between metals and dithiolenes are important in the biological processes of many metalloenzymes as well as in diverse chemical and material applications. Of special note is the ability of the dithiolene ligand to support metal centers in multiple coordination environments and oxidation states. To better understand the nature of metal-dithiolene electronic interactions, new capabilities in gas-phase core photoelectron spectroscopy for molecules with high sublimation temperatures have been developed and applied to a series of molecules of the type Cp(2)M(bdt) (Cp = ?(5)-cyclopentadienyl, M = Ti, V, Mo, and bdt = benzenedithiolato). Comparison of the gas-phase core and valence ionization energy shifts provides a unique quantitative energy measure of valence orbital overlap interactions between the metal and the sulfur orbitals that is separated from the effects of charge redistribution. The results explain the large amount of sulfur character in the redox-active orbitals and the 'leveling' of oxidation state energies in metal-dithiolene systems. The experimentally determined orbital interaction energies reveal a previously unidentified overlap interaction of the predominantly sulfur HOMO of the bdt ligand with filled ? orbitals of the Cp ligands, suggesting that direct dithiolene interactions with other ligands bound to the metal could be significant for other metal-dithiolene systems in chemistry and biology. PMID:21988484

Wiebelhaus, Nicholas J; Cranswick, Matthew A; Klein, Eric L; Lockett, L Tori; Lichtenberger, Dennis L; Enemark, John H

2011-10-11

304

12 CFR 192.460 - How do I determine the initial balances of liquidation sub-accounts?  

Code of Federal Regulations, 2013 CFR

...initial balances of liquidation sub-accounts? 192.460 Section 192.460...Standard Conversions Liquidation Account § 192.460 How do I determine...initial balances of liquidation sub-accounts? (a)(1) You determine...

2013-01-01

305

12 CFR 563b.460 - How do I determine the initial balances of liquidation sub-accounts?  

Code of Federal Regulations, 2013 CFR

...initial balances of liquidation sub-accounts? 563b.460 Section 563b...Standard Conversions Liquidation Account § 563b.460 How do I determine...initial balances of liquidation sub-accounts? (a)(1) You determine...

2013-01-01

306

Social determinants of health in Canada: Are healthy living initiatives there yet? A policy analysis  

PubMed Central

Introduction Preventative strategies that focus on addressing the social determinants of health to improve healthy eating and physical activity have become an important strategy in British Columbia and Ontario for combating chronic diseases. What has not yet been examined is the extent to which healthy living initiatives implemented under these new policy frameworks successfully engage with and change the social determinants of health. Methods Initiatives active between January 1, 2006 and September 1, 2011 were found using provincial policy documents, web searches, health organization and government websites, and databases of initiatives that attempted to influence to nutrition and physical activity in order to prevent chronic diseases or improve overall health. Initiatives were reviewed, analyzed and grouped using the descriptive codes: lifestyle-based, environment-based or structure-based. Initiatives were also classified according to the mechanism by which they were administered: as direct programs (e.g. directly delivered), blueprints (or frameworks to tailor developed programs), and building blocks (resources to develop programs). Results 60 initiatives were identified in Ontario and 61 were identified in British Columbia. In British Columbia, 11.5% of initiatives were structure-based. In Ontario, of 60 provincial initiatives identified, 15% were structure-based. Ontario had a higher proportion of direct interventions than British Columbia for all intervention types. However, in both provinces, as the intervention became more upstream and attempted to target the social determinants of health more directly, the level of direct support for the intervention lessened. Conclusions The paucity of initiatives in British Columbia and Ontario that address healthy eating and active living through action on the social determinants of health is problematic. In the context of Canada's increasingly neoliberal political and economic policy, the public health sector may face significant barriers to addressing upstream determinants in a meaningful way. If public health cannot directly affect broader societal conditions, interventions should be focused around advocacy and education about the social determinants of health. It is necessary that health be seen for what it is: a political matter. As such, the health sector needs to take a more political approach in finding solutions for health inequities.

2012-01-01

307

Determinants of smoking initiation among women in five European countries: a cross-sectional survey  

PubMed Central

Background The rate of smoking and lung cancer among women is rising in Europe. The primary aim of this study was to determine why women begin smoking in five different European countries at different stages of the tobacco epidemic and to determine if smoking is associated with certain characteristics and/or beliefs about smoking. Methods A cross-sectional telephone survey on knowledge and beliefs about tobacco was conducted as part of the Women in Europe Against Lung Cancer and Smoking (WELAS) Project. A total of 5 000 adult women from France, Ireland, Italy, Czech Republic, and Sweden were interviewed, with 1 000 from each participating country. All participants were asked questions about demographics, knowledge and beliefs about smoking, and their tobacco use background. Current and former smokers also were asked questions about smoking initiation. Basic statistics on the cross-sectional data was reported with chi-squared and ANOVA p-values. Logistic regression was used to analyze ever versus never smokers. Linear regression analyses were used to analyze age of smoking initiation. Results Being older, being divorced, having friends/family who smoke, and having parents who smoke were all significantly associated with ever smoking, though the strength of the associations varied by country. The most frequently reported reason for initiation smoking was friend smoking, with 62.3% of ever smokers reporting friends as one of the reasons why they began smoking. Mean age of smoking initiation was 18.2 years and over 80% of participants started smoking by the age of 20. The highest levels of young initiators were in Sweden with 29.3% of women initiating smoking at age 14-15 and 12.0% initiating smoking younger than age 14. The lowest level of young initiators was in the Czech Republic with 13.7% of women initiating smoking at age 14-15 and 1.4% of women initiating smoking younger than age 14. Women who started smoking because their friends smoked or to look 'cool' were more likely to start smoking at a younger age. Women who started smoking to manage stress or to feel less depressed were more likely to start smoking at an older age. Conclusions In all five participating countries, friends were the primary factor influencing ever smoking, especially among younger women. The majority of participants began smoking in adolescence and the average reported age of smoking initiation was youngest in Sweden and oldest in the Czech Republic.

2010-01-01

308

Clinical and Genetic Determinants of Warfarin Pharmacokinetics and Pharmacodynamics during Treatment Initiation  

PubMed Central

Variable warfarin response during treatment initiation poses a significant challenge to providing optimal anticoagulation therapy. We investigated the determinants of initial warfarin response in a cohort of 167 patients. During the first nine days of treatment with pharmacogenetics-guided dosing, S-warfarin plasma levels and international normalized ratio were obtained to serve as inputs to a pharmacokinetic-pharmacodynamic (PK-PD) model. Individual PK (S-warfarin clearance) and PD (Imax) parameter values were estimated. Regression analysis demonstrated that CYP2C9 genotype, kidney function, and gender were independent determinants of S-warfarin clearance. The values for Imax were dependent on VKORC1 and CYP4F2 genotypes, vitamin K status (as measured by plasma concentrations of proteins induced by vitamin K absence, PIVKA-II) and weight. Importantly, indication for warfarin was a major independent determinant of Imax during initiation, where PD sensitivity was greater in atrial fibrillation than venous thromboembolism. To demonstrate the utility of the global PK-PD model, we compared the predicted initial anticoagulation responses with previously established warfarin dosing algorithms. These insights and modeling approaches have application to personalized warfarin therapy.

Gong, Inna Y.; Schwarz, Ute I.; Crown, Natalie; Dresser, George K.; Lazo-Langner, Alejandro; Zou, GuangYong; Roden, Dan M.; Stein, C. Michael; Rodger, Marc; Wells, Philip S.; Kim, Richard B.; Tirona, Rommel G.

2011-01-01

309

Determination of laser damage initiation probability and growth on fused silica scratches  

SciTech Connect

Current methods for the manufacture of optical components inevitably leaves a variety of sub-surface imperfections including scratches of varying lengths and widths on even the finest finishes. It has recently been determined that these finishing imperfections are responsible for the majority of laser-induced damage for fluences typically used in ICF class lasers. We have developed methods of engineering subscale parts with a distribution of scratches mimicking those found on full scale fused silica parts. This much higher density of scratches provides a platform to measure low damage initiation probabilities sufficient to describe damage on large scale optics. In this work, damage probability per unit scratch length was characterized as a function of initial scratch width and post fabrication processing including acid-based etch mitigation processes. The susceptibility of damage initiation density along scratches was found to be strongly affected by the post etching material removal and initial scratch width. We have developed an automated processing procedure to document the damage initiations per width and per length of theses scratches. We show here how these tools can be employed to provide predictions of the performance of full size optics in laser systems operating at 351 nm. In addition we use these tools to measure the growth rate of a damage site initiated along a scratch and compare this to the growth measured on an isolated damage site.

Norton, M A; Carr, C W; Cross, D A; Negres, R A; Bude, J D; Steele, W A; Monticelli, M V; Suratwala, T I

2010-10-26

310

Laser preparation and probing of initial and final orbital alignment in collision-induced energy transfer Ca(4s5p, 1P1) +He?Ca(4s5p, 3P2)+He  

Microsoft Academic Search

In a crossed beam atomic energy transfer experiment, relative cross sections are measured between initial and final magnetic substates of atomic orbitals in a three vector correlation experiment. A pulsed laser beam prepares Ca(4s5p 1P1) in a single magnetic sublevel ‖j1mi? with respect to the laser polarization vector. Subsequent collision with He at a well-defined relative velocity yields Ca(4s5p 3P2).

Christopher J. Smith; Jan P. J. Driessen; Larry Eno; Stephen R. Leone

1992-01-01

311

Definitive orbit of minor planet (29) Amphitrite from 91 oppositions 1825-1985 and a new determination of the mass of Jupiter  

Microsoft Academic Search

A definitive orbit of minor planet (29) Amphitrite based on 1,577 observations from 91 apparitions covering the time span 1825 to 1985 is evaluated. (29) Amphitrite moves near to the 3:1 resonance to Jupiter and seems particularly suited for a new determination of the mass of the Jupiter system. A most probable mass value of 1\\/(1047.369±0.029) solar masses is obtained

L. D. Schmadel

1986-01-01

312

42 CFR 476.85 - Conclusive effect of QIO initial denial determinations and changes as a result of DRG validations.  

Code of Federal Regulations, 2012 CFR

...determinations and changes as a result of DRG validations. 476.85 Section 476...determinations and changes as a result of DRG validations. A QIO initial denial determination or change as a result of DRG validation is final and binding...

2012-10-01

313

Determination of the Primary Specular Point in the Sunglint Pattern of a Polar-Orbiting Satellite Image.  

National Technical Information Service (NTIS)

A mathematical procedure for calculating the location of the primary specular point (PSP) in polar-orbiting satellite data is described in step-by-step detail. For purposes of this discussion, the PSP is defined as 'that point on the great circle arc perp...

R. W. Fett T. L. Tsui

1980-01-01

314

Determining the Orbit Locations of Turkish Airborne Early Warning and Control Aircraft Over the Turkish Air Space.  

National Technical Information Service (NTIS)

This research provides optimal orbit locations that can be updated according to the threats, for Turkish AEW&C aircraft in the combat arena. Three combat scenarios Turkey might encounter are examined. Turkey can expect threats from everywhere. The worst c...

N. Sarikaya

2009-01-01

315

Atomic Orbitals  

NSDL National Science Digital Library

The Atomic Orbitals Web site "was established as part of an (ongoing) project at Purdue University to develop 'visualization modules' for general chemistry students." Using the Chime plug-in, which allows unique and stunning visualizations, visitors can learn what an atomic orbital is; what the 1s, 2s, 3s, 2p, 3p, and 3d orbitals are; what hybrid orbitals are; and more. The combination of easy-to-read descriptions and educational graphics make the site a great learning resource for high school and even college level chemistry students.

2007-06-05

316

Predisposing, Enabling and Pregnancy-Related Determinants of Late Initiation of Prenatal Care  

Microsoft Academic Search

Prenatal care is important for the health and wellbeing of women and their babies. There is international consensus that prenatal\\u000a care should begin in the first trimester. This study aims to analyze the effects of predisposing, enabling and pregnancy-related\\u000a determinants of late prenatal care initiation. In this prospective observational study, 333 women were recruited consecutively\\u000a at the beginning of their

Katrien Beeckman; Fred Louckx; Koen Putman

317

Asthma Severity According to Global Initiative for Asthma and Its Determinants: An International Study  

Microsoft Academic Search

Background: The identification of the factors associated with severe asthma may shed some light on its etiology and on the mechanisms of its development. We aimed to describe asthma severity using the Global Initiative for Asthma (GINA) classification and to investigate its determinants in a cross-sectional, population-based sample in Europe. Methods: In the European Community Respiratory Health Survey II (1999–2002),

Lucia Cazzoletti; Alessandro Marcon; Angelo Corsico; Christer Janson; Deborah Jarvis; Isabelle Pin; Simone Accordini; Massimiliano Bugiani; Isa Cerveri; David Gislason; Amund Gulsvik; Roberto de Marco

2010-01-01

318

Determinants of Late Prenatal Care Initiation by African American Women in Washington, DC  

Microsoft Academic Search

Objectives: The objective of this study was to identify the determinants of late prenatal care (PNC) initiation among minority women in Washington, DC. Methods: DC-resident, African American women (n = 303) were recruited at 14 PNC facilities, representing the various types of PNC facilities located in DC: 4 hospital-based clinics, 5 community-based clinics, and 5 private practices. The women were

Allan A. Johnson; M. Nabil El-Khorazaty; Barbara J. Hatcher; Barbara K. Wingrove; Renee Milligan; Cynthia Harris; Leslie Richards

2003-01-01

319

New experimental approach to determine initial fatigue quality with fastener holes  

SciTech Connect

A new experimental approach to determine Initial Fatigue Quality (IFQ) with fastener holes is presented. Theoretical analysis and experiments show the IFQs for each fastener hole on multi-pin joints are in mutual independence during the life test. When small cracks appear on the hole edges, the load distribution for each hole does not change significantly. It is found that replacing traditional dog-bone specimens by specimens with multi-pin joints increases the efficiency more than 10 times. 2 refs.

Yi, W.Z. [Univ. of Nanjing Aeronautics and Astronautics, Nanjing (China)

1994-07-01

320

12 CFR 1403.9 - Appeal of an initial adverse determination of a request to amend a record.  

Code of Federal Regulations, 2012 CFR

...2012-01-01 false Appeal of an initial adverse determination of a request to amend a...REGULATIONS § 1403.9 Appeal of an initial adverse determination of a request to amend a...after receipt by an individual of an adverse determination on the...

2012-01-01

321

Determination of the initial beam parameters in Monte Carlo linac simulation  

SciTech Connect

For Monte Carlo linac simulations and patient dose calculations, it is important to accurately determine the phase space parameters of the initial electron beam incident on the target. These parameters, such as mean energy and radial intensity distribution, have traditionally been determined by matching the calculated dose distributions with the measured dose distributions through a trial and error process. This process is very time consuming and requires a lot of Monte Carlo simulation experience and computational resources. In this paper, we propose an easy, efficient, and accurate method for the determination of the initial beam parameters. We hypothesize that (1) for one type of linacs, the geometry and material of major components of the treatment head are the same; the only difference is the phase space parameters of the initial electron beam incident on the target, and (2) most linacs belong to a limited number of linac types. For each type of linacs, Monte Carlo treatment planning system (MC-TPS) vendors simulate the treatment head and calculate the three-dimensional (3D) dose distribution in water phantom for a grid of initial beam energies and radii. The simulation results (phase space files and dose distribution files) are then stored in a data library. When a MC-TPS user tries to model their linac which belongs to the same type, a standard set of measured dose data is submitted and compared with the calculated dose distributions to determine the optimal combination of initial beam energy and radius. We have applied this method to the 6 MV beam of a Varian 21EX linac. The linac was simulated using EGSNRC/BEAM code and the dose in water phantom was calculated using EGSNRC/DOSXYZ. We have also studied issues related to the proposed method. Several common cost functions were tested for comparing measured and calculated dose distributions, including {chi}{sup 2}, mean absolute error, dose difference at the penumbra edge point, slope of the dose difference of the lateral profile, and the newly proposed {kappa}{sub {alpha}} factor (defined as the fraction of the voxels with absolute dose difference less than {alpha}%). It was found that the use of the slope of the lateral profile difference or the difference of the penumbra edge points may lead to inaccurate determination of the initial beam parameters. We also found that in general the cost function value is very sensitive to the simulation statistical uncertainty, and there is a tradeoff between uncertainty and specificity. Due to the existence of statistical uncertainty in simulated dose distributions, it is practically impossible to determine the best energy/radius combination; we have to accept a group of energy/radius combinations. We have also investigated the minimum required data set for accurate determination of the initial beam parameters. We found that the percent depth dose curves along or only a lateral profile at certain depth for a large field size is not sufficient and the minimum data set should include several lateral profiles at various depths as well as the central axis percent depth dose curve for a large field size.

Aljarrah, Khaled; Sharp, Greg C.; Neicu, Toni; Jiang, Steve B. [Department of Physics, University of Massachusetts Lowell, Lowell, Massachusetts (United States); Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts (United States)

2006-04-15

322

Application of Transit Timing Variations to the Detection of Exoplanets and the Determination of their Orbital and Structural Properties  

NASA Astrophysics Data System (ADS)

We expand upon the results of Veras at el. (2010) and investigate the practical utility of exo-planet transit timing variations (TTVs) in a number of different scenarios: (i) We introduce significant non-coplanarity into our TTV investigations. This is because an increasing number of (Rossiter-McLaughlin) observations of transiting planets suggest that at least 10% of transiting planets are in retrograde orbits. We demonstrate that planets in retrograde orbits can frequently have significantly reduced TTVs, allowing the possibility that relatively massive, closely spaced systems of planets could escape detection via the TTV method (ii) We apply the TTV method to the expected flood of Kepler detections, and ask whether the planets that are directly detected first by Kepler (hot-Jupiters and hot-Neptunes ) can be employed to indirectly detect Earth-mass planets in the habitable zone via the TTVs they induce in the inner planet. We show that this is indeed the case for certain systems, illustrating the dependencies on mass, inclination, eccentricity, etc , but place particular emphasis on the importance of long data streams (iii) Finally, we turn to the specific example of the HAT-P-13 system, the first system in which a transiting planet is known to be accompanied by another planet in a well constrained orbit. We illustrate how observing TTVs in the inner planet can potentially constrain not only the eccentricity and the relative inclination of the (probably non-transiting) outer planet to the orbit of the inner planet , but potentially also the internal structure of the inner planet.

Payne, Matthew J.; Veras, D.; Ford, E. B.

2010-05-01

323

Orbital myositis: Diagnosis and management  

Microsoft Academic Search

Orbital myositis is an inflammatory process that primarily involves the extraocular muscles and most commonly affects young\\u000a adults in the third decade of life, with a female predilection. Clinical characteristics of orbital myositis include orbital\\u000a and periorbital pain, ocular movement impairment, diplopia, proptosis, swollen eyelids, and conjunctival hyperemia. The most\\u000a common presentation is acute and unilateral, which initially responds to

Roberta M. S. Costa; Oana M. Dumitrascu; Lynn K. Gordon

2009-01-01

324

Determination of dynamic fracture-initiation toughness using a novel impact bend test procedure  

SciTech Connect

A novel impact bend test procedure is described for determining the dynamic fracture-initiation toughness, K[sub Id], at a loading rate (stress intensity factor rate), K[sub I], of the order of 10[sup 6] MPa [radical]m/s. A special arrangement of the split Hopkinson pressure bar is adopted to measure accurately dynamic loads applied to a fatigue-precracked bend specimen. The dynamic stress intensity factor history for the bend specimen is evaluated by means of a dynamic finite element technique. The onset of crack initiation is detected using a string gage attached on the side of the specimen near a crack tip. The value of K[sub Id] is determined from the critical dynamic stress intensity factor at crack initiation. A series of dynamic fracture tests is carried out on a 7075-T6 aluminum alloy, a Ti-6246 alloy and an AISI 4340 steel. The K[sub Id] values obtained for the three structural materials are compared with the corresponding values obtained under quasi-static loading conditions.

Yokoyama, T. (Osaka Univ. (Japan). Faculty of Engineering Okayama Univ. of Science (Japan). Dept. of Mechanical Engineering)

1993-11-01

325

Automatic determination of focal mechanism solutions using initial motion polarities of P and S waves  

NASA Astrophysics Data System (ADS)

This study proposes an automatic method of determining a focal mechanism solution. This method includes picking initial motion polarities of P and S waves and judging reliability of the solution. The method of picking the polarities is as follows. Displacement waveform data are calculated only for S waves. A Bessel band-pass filter is then applied. Finally, arrival times of the P and S wave initial motions are detected by using an autoregressive (AR) model and an AR filter is applied. A grid search method is used to determine the focal mechanism solution. The reliability of the solution is evaluated synthetically from the stability of the solution and by comparing it with focal mechanism solutions of earthquakes that occurred near the event. About 71% of the polarities of P waves picked manually by the Japan Meteorological Agency (JMA) can be picked automatically by applying this method. Moreover, the ratio of inconsistent polarities between those picked in this study and by JMA is less than 4.0%. This proves that automatic picking of the polarities of P waves is sufficiently accurate. About 85% of the polarities of S waves satisfy focal mechanism solutions that are determined with acceptable reliability. This also demonstrates that automatic picking of the polarities of S waves is sufficiently accurate. Furthermore, 2.8 times the solutions obtained by JMA are determined with sufficient reliability by applying the method. We can occasionally determine the stable solutions of inland shallow earthquakes that are less than 2.0 in magnitude, or of deep earthquakes whose magnitudes cannot be calculated because of their small sizes. Applying this method, we can effectively determine focal mechanism solutions with sufficient reliability.

Nakamura, Masaki

2004-09-01

326

GPS single frequency precise orbit determination of LEO satellites with the cm-level accuracy and comparison with the precise point positioning  

NASA Astrophysics Data System (ADS)

Using single frequency GPS measurements from the CHAMP satellite it was demonstrated before that during the solar maximum the LEO orbit can be determined with an accuracy below 10 cm RMS (1D). The first order ionosphere effect is removed by linear combination of pseudorange and carrier phase measurements using the so-called LP linear combination. The main limitation of this POD approach is the high noise of the pseudorange measurements. By forming the LP linear combination, noise in the pseudorange measurements is reduced by 50%, and by estimating half-cycle phase ambiguities an additional reduction can be expected in all systematic effects (e.g. multipath, group delay variations, etc.). Furthermore, thanks to the high quality GPS measurements from the GRACE mission, it was demonstrated that the orbit of a LEO satellite can be determined using single frequency measurements with an accuracy of 5 cm RMS (1D). This is very close to the cm-level accuracy of the LEO orbits based on dual-frequency carrier phase measurements. Here we show that based on the latest gravity field models short term perturbations can very accurately be modelled in the numerical integration, considerably reducing the number of empirical parameters. This allows to average errors in the pseudorange measurements over a longer period of time and further increase the accuracy of GRACE orbit down to 3 cm RMS (1D) and beyond. However, at this level of accuracy systematic errors in the code to carrier coherence play a crucial role, especially in terms of signal group delay variations of GPS satellite and LEO antenna. Here we demonstrate a novel approach in the code to carrier calibration based on a geometry and ionosphere free linear combination. We show that it is possible to separate the group delay variations of the GPS satellite antenna from the group delay variations of a LEO or a ground antenna. This leads to very accurate mean group delay maps of the GPS satellite antennas. Validation of the code to carrier coherence calibration is carried out with the independent measurements from a high-gain steerable ground antenna. Here we show how code to phase coherence calibration improves LEO orbit determination based on single frequency measurements and compare our results with the ground precise point positioning based on single-frequency GPS measurements. A typical performance curve relating convergence time and accuracy is derived for PPP, as well as POD of the GRACE satellites during the solar minimum and maximum.

Svehla, Drazen; Escobar, Diego A.; Dow, John M.

327

42 CFR 476.94 - Notice of QIO initial denial determination and changes as a result of a DRG validation.  

Code of Federal Regulations, 2010 CFR

...determination and changes as a result of a DRG validation. 476.94 Section 476...determination and changes as a result of a DRG validation. (a) Notice of initial denial...For retrospective review, (excluding DRG validation and post procedure...

2010-10-01

328

42 CFR 476.94 - Notice of QIO initial denial determination and changes as a result of a DRG validation.  

Code of Federal Regulations, 2010 CFR

...determination and changes as a result of a DRG validation. 476.94 Section 476...determination and changes as a result of a DRG validation. (a) Notice of initial denial...For retrospective review, (excluding DRG validation and post procedure...

2009-10-01

329

Fe L-edge XAS Determination of Differential Orbital Covalency of Siderophore Model Compounds: Electronic Structure Contributions to High Stability Constants  

PubMed Central

Most bacteria and fungi produce low-molecular weight iron-chelators called siderophores. Although different siderophore structures have been characterized, the iron binding moieties often contain catecholate or hydroxamate groups. Siderophores function because of their extraordinarily high stability constants (KSTAB = 1030-1049) and selectivity for Fe(III), yet the origin of these high stability constants has been difficult to quantify experimentally. Herein, we utilise Fe L-edge X-ray absorption spectroscopy to determine the differential orbital covalency (i.e. the differences in the mixing of the metal d orbitals with ligand valence orbitals) of a series of siderophore model compounds. The results enable evaluation of the electronic structure contributions to their high stability constants in terms of ?– and ?–donor covalent bonding, ionic bonding and solvent effects. The results indicate substantial differences in the covalent contributions to stability constants of hydroxamate and catecholate complexes and that an increased ? as well as ? bonding contributes to the high stability constants of catecholate complexes

Hocking, Rosalie K.; DeBeer George, Serena; Raymond, Kenneth N.; Hodgson, Keith O.; Hedman, Britt; Solomon, Edward I.

2010-01-01

330

Two Body Orbits Model  

NSDL National Science Digital Library

The Two Body Orbits model for teachers shows the motion of two objects (binary star or moon-planet system) interacting via Newton's law of universal gravitation. It is designed to teach physics, Earth science, and environmental science topics by showing the spatial path of objects around their common center of mass (barycenter). An optional 3D view shows the celestial sphere and and the orbital plane (ecliptic). Default units are chosen for Earth obit about our Sun so that the distance unit is one astronomical unit and the time unit is one year.   An important feature of the ready-to-run Two Body Orbits simulation is that it can be customized by teachers to meet various learning objectives. The teacher sets the ratio of the two masses, their initial positions and velocities, and various visualization and scale parameters. Documentation, such as an exercise or lesson, can be added to the simulation by entering a filename into the Customization dialog. Selecting the âstudentâ checkbox creates a ready-to-run package with the new configuration without the Customization dialog. The Two Body Orbits model was created using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run Java archive. Double clicking the ejs_mech_orbits_TwoBodyOrbits.jar file will run the program if Java is installed. EJS is a part of the Open Source Physics Project and is available in the OSP Collection.

Christian, Wolfgang

2012-07-18

331

Advanced Space System Concepts and Their Orbital Support Needs (1980 - 2000). Volume 3: Detailed Data. Part 1: Catalog of Initiatives, Functional Options, and Future Environments and Goals.  

National Technical Information Service (NTIS)

The following areas were discussed in relation to a study of the commonality of space vehicle applications to future national needs: (1) index of initiatives (civilian observation, communication, support), brief illustrated description of each initiative,...

H. L. Mayer I. Bekey M. G. Wolfe

1976-01-01

332

Orbital Dynamics  

NSDL National Science Digital Library

This video from SpaceTEC National Aerospace Technical Education Center explains the mechanics of orbital dynamics and Newton's first law of motion. This three minute video is one of the aerospace certification readiness courses.

2011-07-27

333

Study of quick orbital transfer technology for improving viability of remote sensing satellites  

NASA Astrophysics Data System (ADS)

Non-coplanar circular orbital transfers based on the invariability of descending nodical local time is studied in this paper. Based on minimum principle, both of the thrust direction and magnitude are optimized, regarding minimum total impulse and final position and velocity constraints as the performance index on the assumption of fixed transfer time and continuous thrust. The optimal transfer orbit is then obtained using conjugate gradient method. As transfer time is given, a special initial condition for orbital transfers is determined, which ensures the invariability of descending nodical local time. The validity of orbital transfer strategy adopted has been verified by simulation results.

Lu, Qisheng; Wang, Zhigang

2007-11-01

334

SPONTANEOUS INITIATION OF DETONATIONS IN WHITE DWARF ENVIRONMENTS: DETERMINATION OF CRITICAL SIZES  

SciTech Connect

Some explosion models for Type Ia supernovae (SNe Ia), such as the gravitationally confined detonation (GCD) or the double detonation sub-Chandrasekhar (DDSC) models, rely on the spontaneous initiation of a detonation in the degenerate {sup 12}C/{sup 16}O material of a white dwarf (WD). The length scales pertinent to the initiation of the detonation are notoriously unresolved in multidimensional stellar simulations, prompting the use of results of one-dimensional simulations at higher resolution, such as those performed for this work, as guidelines for deciding whether or not conditions reached in the higher dimensional full star simulations successfully would lead to the onset of a detonation. Spontaneous initiation relies on the existence of a suitable gradient in self-ignition (induction) times of the fuel, which we set up with a spatially localized nonuniformity of temperature-a hot spot. We determine the critical (smallest) sizes of such hot spots that still marginally result in a detonation in WD matter by integrating the reactive Euler equations with the hydrodynamics code FLASH. We quantify the dependences of the critical sizes of such hot spots on composition, background temperature, peak temperature, geometry, and functional form of the temperature disturbance, many of which were hitherto largely unexplored in the literature. We discuss the implications of our results in the context of modeling of SNe Ia.

Seitenzahl, Ivo R. [Department of Physics, University of Chicago, Chicago, IL 60637 (United States); Meakin, Casey A.; Townsley, Dean M.; Truran, James W. [Joint Institute for Nuclear Astrophysics, University of Chicago, Chicago, IL 60637 (United States); Lamb, Don Q. [The Center for Astrophysical Thermonuclear Flashes, The University of Chicago, Chicago, IL 60637 (United States)

2009-05-01

335

36 CFR 1121.8 - Appeal of an initial adverse agency determination on correction or amendment of the record.  

Code of Federal Regulations, 2011 CFR

...2011-07-01 2011-07-01 false Appeal of an initial adverse agency determination on correction or amendment of the record...PRIVACY ACT IMPLEMENTATION § 1121.8 Appeal of an initial adverse agency determination on correction or amendment of the...

2011-07-01

336

1 CFR 455.8 - Appeal of an initial adverse agency determination on correction or amendment of the record.  

Code of Federal Regulations, 2012 CFR

...2012-01-01 2012-01-01 false Appeal of an initial adverse agency determination on correction or amendment of the record...PRIVACY ACT REGULATIONS) § 455.8 Appeal of an initial adverse agency determination on correction or amendment of the...

2012-01-01

337

36 CFR 1121.8 - Appeal of an initial adverse agency determination on correction or amendment of the record.  

Code of Federal Regulations, 2012 CFR

...2012-07-01 2012-07-01 false Appeal of an initial adverse agency determination on correction or amendment of the record...PRIVACY ACT IMPLEMENTATION § 1121.8 Appeal of an initial adverse agency determination on correction or amendment of the...

2012-07-01

338

On-Orbit-Servicing Spacecraft Flyaround Orbit Design and LQR Keep Control in Eccentric Orbits  

Microsoft Academic Search

The paper presents the initialization condition for chaser flying around target and optimal keeping control algorithm to satisfy the requirement of on-orbit-servicing in eccentric orbits. The necessary condition for chaser fly around is presented by detailed analyzing with the time variant linear relative motion formula and resolution. Then, the condition for target to locate at the center of fly around

Wang Feng; Cao Xibin; Chen Xueqin

2007-01-01

339

Detector positioning for the initial subcriticality level determination in accelerator-driven systems  

SciTech Connect

Within the GUINEVERE project (Generation of Uninterrupted Intense Neutrons at the lead Venus Reactor) carried out at SCK-CEN in Mol, the continuous deuteron accelerator GENEPI-3C was coupled to the VENUS-F fast simulated lead-cooled reactor. Today the FREYA project (Fast Reactor Experiments for hYbrid Applications) is ongoing to study the neutronic behavior of this Accelerator Driven System (ADS) during different phases of operation. In particular the set-up of a monitoring system for the subcriticality of an ADS is envisaged to guarantee safe operation of the installation. The methodology for subcriticality monitoring in ADS takes into account the determination of the initial subcriticality level, the monitoring of reactivity variations, and interim cross-checking. At start-up, the Pulsed Neutron Source (PNS) technique is envisaged to determine the initial subcriticality level. Thanks to its reference critical state, the PNS technique can be validated on the VENUS-F core. A detector positioning methodology for the PNS technique is set up in this paper for the subcritical VENUS-F core, based on the reduction of higher harmonics in a static evaluation of the Sjoestrand area method. A first case study is provided on the VENUS-F core. This method can be generalised in order to create general rules for detector positions and types for full-scale ADS. (authors)

Uyttenhove, W.; Van Den Eynde, G.; Baeten, P.; Kochetkov, A.; Vittiglio, G.; Wagemans, J. [SCKCEN, Belgian Nuclear Research Centre, Boeretang 200, BE-2400 Mol (Belgium); Lathouwers, D.; Kloosterman, J. L.; Van Der Hagen, T. J. H. H.; Wols, F. [Delft Univ. of Technology, Mekelweg 15, NL-2629 JB Delft (Netherlands); Billebaud, A.; Chabod, S.; Thybault, H. E. [LPSC-CNRS-IN2P3/UJF/INPG, 53, Avenue des Martyrs, 38026 Grenoble Cedex (France); Lecouey, J. L.; Ban, G.; Lecolley, F. R.; Marie, N.; Steckmeyer, J. C. [LPC Caen, ENSICAEN/Unicersit de Caen/CNRS-IN2P3, Caen (France); Dessagne, P.; Kerveno, M. [IPHC-DRS/UdS/CNRS-IN2P3, Strasbourg (France); Mellier, F. [CEA/DEN/DER/SPEX/LPE, Cadarache 13108 Saint-Paul-les-Durance (France)

2012-07-01

340

Ganymede's Thermal and Orbital Evolution  

NASA Astrophysics Data System (ADS)

The heating mechanism that created the melting and global expansion necessary to form Ganymede's ubiquitous grooved terrains remains unclear. While the current Laplace resonance does not pump Ganymede's eccentricity, Malhotra (1991) and Showman and Malhotra (1997) showed that the Galilean satellites may have passed through Laplace-like resonances that did force Ganymede's eccentricity, leading to internal heating of the satellite. Showman et al. (1997) explored the effects of such tidal heating on Ganymede and found that it can lead to thermal runaway and melting, helping to explain the extensive resurfacing of the satellite. While the likelihood of thermal runaway appeared small, improved understanding of the internal structure of Ganymede and the nature of stagnant lid convection warrants a new study. Here we present simulations of Ganymede's coupled thermal and orbital evolution. The orbital model allows a dynamical investigation of the orbital histories of the Galilean satellites near the observed 2:1 mean motion resonance. The thermal model simultaneously solves the energy balance in Ganymede's ice shell, silicate mantle, and Fe/FeS core. Stagnant lid convection, radiogenic heating, ocean formation, and inner core growth are included in the model. Coupling between the orbital and thermal models occurs via tidal dissipation, which uses the model of Tobie et al. 2005 to determine how tidal heating is distributed throughout the satellite interior. These simulations reveal that passage through the Laplace-like resonance can lead to melting under a much broader range of initial conditions than suggested by Showman et al. (1997). Such melting requires that the grain sizes in Ganymede's icy mantle be 1 mm or less, and that the Galilean satellites passed through one of the stronger Laplace-like resonances. The generation of melt would not only lead to satellite expansion and extensional stress, but would also provide a source of near surface melt, permitting cryovolcanic activity.

Bland, Michael T.; Showman, A. P.; Tobie, G.

2007-10-01

341

15 CFR 930.38 - Consistency determinations for activities initiated prior to management program approval.  

Code of Federal Regulations, 2010 CFR

...activities initiated prior to management program approval. (a...projects initiated prior to management program approval, which...at the earliest practicable time following management program approval, and...

2009-01-01

342

The Exoplanet Orbit Database  

NASA Astrophysics Data System (ADS)

We present a database of well-determined orbital parameters of exoplanets, and their host stars' properties. This database comprises spectroscopic orbital elements measured for 427 planets orbiting 363 stars from radial velocity and transit measurements as reported in the literature. We have also compiled fundamental transit parameters, stellar parameters, and the method used for the planets discovery. This Exoplanet Orbit Database includes all planets with robust, well measured orbital parameters reported in peer-reviewed articles. The database is available in a searchable, filterable, and sortable form online through the Exoplanets Data Explorer table, and the data can be plotted and explored through the Exoplanet Data Explorer plotter. We use the Data Explorer to generate publication-ready plots, giving three examples of the signatures of exoplanet migration and dynamical evolution: We illustrate the character of the apparent correlation between mass and period in exoplanet orbits, the different selection biases between radial velocity and transit surveys, and that the multiplanet systems show a distinct semimajor-axis distribution from apparently singleton systems.

Wright, J. T.; Fakhouri, O.; Marcy, G. W.; Han, E.; Feng, Y.; Johnson, John Asher; Howard, A. W.; Fischer, D. A.; Valenti, J. A.; Anderson, J.; Piskunov, N.

2011-04-01

343

Bridge-mediated excitation energy transfer pathways through protein media: a Slater determinant-based electronic coupling calculation combined with localized molecular orbitals.  

PubMed

A computational method for calculating electronic coupling and pathway of electron transfer (ET) has been extended to that for excitation energy transfer (EET). A molecular orbital (MO)-based description has been generalized to one based on Slater determinants. This approach reduces the approximations used for the Green's function method from the perturbation of chemical-bond interactions to the perturbation of the configuration interactions. It is, therefore, reasonable to apply this method to EET, which involves the transfer of an electron-hole pair. To represent EET donor, acceptor, and bridge states, we adopted recently developed localized molecular orbitals (LMOs) for constructing locally excited determinants. The LMO approach provides a chemically meaningful interpretation of how each local excitation on the bridge contributes to the total electronic coupling of the EET. We applied the method to six model peptides and calculated their electronic couplings as well as the direct and through-peptide terms. Although the through-peptide term is usually negligibly small compared with the direct term, it can dominate the EET reaction in appropriate situations. The direct term dominates in long-range interactions because the indirect term decays in shorter distances. PMID:21861486

Kawatsu, Tsutomu; Matsuda, Kenji; Hasegawa, Jun-ya

2011-09-12

344

Analysis of the orbit of 1966-63A near 15th-order resonance  

NASA Astrophysics Data System (ADS)

Data from U.S. Navy and the RAE orbit refinement program PROP are employed to calculate orbits of the 1966-63A (OV1-8) satellite which circled the earth from 1966-1978. Initial orbit predictions for the OV1-8 spacecraft, particularly for 15th and higher orbit harmonics were found to be unsatisfactory. Weekly orbit determinations from each of 32 epochs were investigated using the standard deviation of 0.003 deg for inclinations. An analysis performed with the THROE program, which removed perturbations caused by atmospheric rotation and lunisolar precession of the earth's axis, in addition to a later accounting for solar radiation pressure, was determined to be 1% more accurate than previous calculations. Account was taken for eccentricity due to zonal harmonics and atmospheric drag. Resonance was determined to have little effect on eccentricity, and lumped values were found which yielded improved results for the 15th order harmonics.

Walker, D. M. C.; Winterbottom, A. N.

1982-08-01

345

Dynamical modelling of stars and gas in NGC 2974: determination of mass-to-light ratio, inclination and orbital structure using the Schwarzschild method  

NASA Astrophysics Data System (ADS)

We study the large-scale stellar and gaseous kinematics of the E4 galaxy NGC 2974, based on panoramic integral-field data obtained with SAURON. We quantify the velocity maps with Fourier methods (kinemetry), and show that the large-scale kinematics is largely consistent with axisymmetry. We construct general axisymmetric dynamical models for the stellar motions using the Schwarzschild orbit-superposition method, and compare the inferred inclination and mass-to-light ratio with the values obtained by modelling the gas kinematics. Both approaches give consistent results. However, we find that the stellar models provide fairly weak constraints on the inclination. The intrinsic orbital distribution of NGC 2974, which we infer from our model, is characterized by a large-scale stellar component of high angular momentum. We create semi-analytical test models, resembling NGC 2974, to study the ability of the Schwarzschild modelling technique to recover the given input parameters (mass-to-light ratio and inclination) and the distribution function. We also test the influence of a limited spatial coverage on the recovery of the distribution function (i.e. the orbital structure). We find that the models can accurately recover the input mass-to-light ratio, but we confirm that even with perfect input kinematics the inclination is only marginally constrained. This suggests a possible degeneracy in the determination of the inclination, but further investigations are needed to clarify this issue. For a given potential, we find that the analytical distribution function of our test model is well recovered by the three-integral model within the spatial region constrained by integral-field kinematics.

Krajnovi?, Davor; Cappellari, Michele; Emsellem, Eric; McDermid, Richard M.; de Zeeuw, P. Tim

2005-03-01

346

Magnitude determination using initial P waves for Cascadia Subduction Zone in Canada's west cost  

NASA Astrophysics Data System (ADS)

The critical goal of earthquake early warning (EEW) is determining the overall size of an earthquake and the expected strong ground motion from the first few seconds of the P wave. We explore a practical approach to earthquake early warning in the Cascadia subduction zone in Canada's west coast by determining earthquake early warning parameter ?c from the initial 3 s of the P waveforms recorded at the National Resource Canada (NRCan) seismic network stations for earthquakes with M > 4.0 We selected 75 earthquakes with that has been recorded during 1986-2010 by Seismic Network stations in the region operated by NRCan. The vertical components of earthquakes signals were converted to ground velocity and displacement. The displacements are filtered with a one-way Butterworth high-pass filter with a cut-off frequency of 0.075 Hz. From the vertical components, ?c is computed. We found the relationship between ?c and magnitude (M) for this region, therefore earthquake size, can be estimated using only with 3 of seconds of signal from the P wave while the rupture itself is still propagating and final dimension of rupture is far from complete.

Eshaghi, A.; Tiampo, K. F.

2010-12-01

347

Orbital Elements  

NSDL National Science Digital Library

Coordinates for tracking the International Space Station and the Mir Space Station are available here from NASA's Johnson Space Center Flight Design and Dynamics Division. The Orbital Elements page offers real-time data for use in ground track plotting programs. The site cautions the data are for ground track plotting programs only and "should not be used for precise applications or analysis!"

348

Nuclear orbiting  

SciTech Connect

Nuclear orbiting following collisions between sd and p shell nuclei is discussed. The dependence of this process on the real and imaginary parts of the nucleus-nucleus potential is discussed, as well as the evolution of the dinucleus toward a fully equilibrated fused system. 26 refs., 15 figs.

Shapira, D.

1988-01-01

349

Elliptical Orbits  

NSDL National Science Digital Library

Although not inquiry, this activity is important for students to understand what an ellipse is and what a focus is, and to break misconceptions about Earth's orbit being highly elliptical. This is the perfect place to check to see if students have the mis

Horton, Michael

2009-05-30

350

GOCE Precise Science Orbits  

NASA Astrophysics Data System (ADS)

GOCE (Gravity field and steady-state Ocean Circulation Explorer), as the first ESA (European Space Agency) Earth Explorer Core Mission, is dedicated for gravity field recovery of unprece-dented accuracy using data from the gradiometer, its primary science instrument. Data from the secondary instrument, the 12-channel dual-frequency GPS (Global Positioning System) receiver, is used for precise orbit determination of the satellite. These orbits are used to accu-rately geolocate the gradiometer observations and to provide complementary information for the long-wavelength part of the gravity field. A precise science orbit (PSO) product is provided by the GOCE High-Level Processing Facility (HPF) with a precision of about 2 cm and a 1-week latency. The reduced-dynamic and kinematic orbit determination strategies for the PSO product are presented together with results of about one year of data. The focus is on the improvement achieved by the use of empirically derived azimuth-and elevation-dependent variations of the phase center of the GOCE GPS antenna. The orbits are validated with satellite laser ranging (SLR) measurements.

Bock, Heike; Jäggi, Adrian; Meyer, Ulrich; Beutler, Gerhard; Heinze, Markus; Hugentobler, Urs

351

Elements of a Chemical Orbital Theory  

NASA Astrophysics Data System (ADS)

Interaction is important in chemistry. Interactions of atoms form chemical bonds. Bonds interact with each other in molecules to determine the molecular properties. Interactions of molecules give rise to chemical reactions. Electrons control atoms, bonds, and molecules. The behavior of electrons is simply and effectively represented by orbitals, which contain wave properties, i.e., phase and amplitude. In our chemical orbital theory we consider the interactions of the orbitals of atoms, bonds and molecules. The elements of the chemical orbital theory are separated into three groups: (1) interactions of two orbitals, (2) interactions of three orbitals, and (3) cyclic interactions of more than two orbitals. Here, general aspects of the interactions of two orbitals are summarized to show the background of this volume and assist nonspecialists to read the following chapters. Among the keywords are: phase and amplitude of orbitals, strength of orbital interactions, electron delocalization, electron localization, exchange repulsion, ionization energy, electronic spectrum, frontier orbitals, reactivity, selectivity, orbital symmetry, and so on. The remaining elements of the chemical orbital theory, i.e., an orbital mixing rule for the three-orbital interactions and an orbital phase theory for the cyclic interactions, are introduced briefly.

Inagaki, Satoshi

352

42 CFR 476.96 - Review period and reopening of initial denial determinations and changes as a result of DRG...  

Code of Federal Regulations, 2012 CFR

...Health 4 2012-10-01 2012-10-01 false Review period and reopening of initial denial determinations...IMPROVEMENT ORGANIZATIONS UTILIZATION AND QUALITY CONTROL REVIEW Review Responsibilities of Utilization and Quality...

2012-10-01

353

Integrable approximation of J 2-perturbed relative orbits  

NASA Astrophysics Data System (ADS)

Most existing satellite relative motion theories utilize mean elements, and therefore cannot be used for calculating long-term bounded perturbed relative orbits. The goal of the current paper is to find an integrable approximation for the relative motion problem under the J 2 perturbation, which is adequate for long-term prediction of bounded relative orbits with arbitrary inclinations. To that end, a radial intermediary Hamiltonian is utilized. The intermediary Hamiltonian retains the original structure of the full J 2 Hamiltonian, excluding the latitude dependence. This formalism provides integrability via separation, a fact that is utilized for finding periodic relative orbits in a local-vertical local-horizontal frame and determine an initialization scheme that yields long-term boundedness of the relative distance. Numerical experiments show that the intermediary-based computation of orbits provides long-term bounded orbits in the full J 2 problem for various inclinations. In addition, a test case is shown in which the radial intermediary-based initial conditions of the chief and deputy satellites yield bounded relative distance in a high-precision orbit propagator.

Lara, M.; Gurfil, P.

2012-11-01

354

Effect of determining initial conditions by four-dimensional variational data assimilation on storm surge forecasting  

NASA Astrophysics Data System (ADS)

A tangent linear model and an adjoint model of the three-dimensional, time-dependent, nonlinear Princeton Ocean Model (POM) are developed to construct a four-dimensional variational data assimilation (4D-Var) algorithm for coastal ocean prediction. To verify and evaluate the performance of this 4D-Var method, a suite of numerical experiments are conducted for a storm surge case using model-generated “pseudo-observations”. The pseudo-observations are generated by a nested-grid high-resolution numerical model which is coupled to an inundation/drying scheme that is not included in the original POM. The 4D-Var algorithm based on POM is tested thoroughly for both code accuracy and the potential application in storm surge forecasting. The assimilation cycles lead to effective convergence between the forecasts and the “observations”. Assimilating water level alone or together with surface currents both lead to significant improvements in storm surge forecasts within and several hours beyond the data assimilation window. It is worth noting that, assimilating water level alone produces improvements in storm surge forecasts that are comparable to those by assimilating both water level and surface currents, suggesting that optimizations of water level and surface currents are linked through the 4D-Var assimilation cycles. However, it is also worth noting that, the benefit resulting from the reduction of initial error in water level and/or surface currents through data assimilation decreases rapidly in time outside the assimilation window. This suggests that determining initial conditions of water level and/or surface currents via data assimilation is only effective within and a few hours beyond the assimilation window for storm surge forecasting. Thus, alternative data assimilation approaches are needed to improve the accuracy and lead time in operational storm surge forecasting.

Peng, S.-Q.; Xie, L.

355

Orbiter Servicer Rendezvous Simulation (ORSIM)  

NASA Astrophysics Data System (ADS)

Orbiter Servicer Rendezvous Simulation (ORSIM) is an automated tool that simulates sequential transfer maneuvers of an orbital maneuvering vehicle (OMV) transporting orbital replaceable units from a space-based depot, or logistics platform, to higher altitude SDI sdatellites. ORSIM calculates OMV energy expenditures (velocity changes) and event histories for various combinations of user-selected orbital transfer maneuvers. Additionally, ORSIM determines the optimal configuration/quantities of logistics platforms and OMVs which conform to the dynamics of differential nodal precession, given user-prescribed values of the scheduled maintenance cycle and required servicing times. ORSIM is coded in FORTRAN-77 and is resident on an IBM PC/AT.

Amato, Amiel; Hoffman, Mickie D.

356

The homogeneous/ Heterogeneous data weighting method of LEO combined orbit determination based on BI-satellite positioning system with its application  

NASA Astrophysics Data System (ADS)

Aiming at combined orbit determination (COD) multi-source data fusion for low earth orbit (LEO) based on bi-satellite positioning system (BPS), an improved variance component estimation (VCE) optimal weighting method of homogeneous data is established with two-step system errors correction. And then an integrated optimal weighting method based on model structure characteristics analysis and VCE estimation of heterogeneous data is put forward by analyzing the essence of multi-source fusion measure model which is a multi-structural, multi-parametric, non-linear regression model. Then the algorithm of optimal weighting and COD parameters estimation is designed, and two kinds of COD simulation experiments are carried out by processing homogeneous data of bi-satellite range sum and its back-up satellite data, heterogeneous data of bi-satellite range sum data and star sensor angle data. Theoretical analysis and simulation computations show that improved VCE method based on two-step system errors correction can gain higher precision than that of traditional experience weighting method for COD of homogeneous data weighting. At the same time, by introducing weighting factor which denotes model structure characteristics and proves the designed optimal weighting algorithm, the amelioration of COD precision of LEO and bi-satellite gain to some extent is feasible from practical application.

Zhao, D. Y.; Pan, X. G.; Wang, J. Q.; Wang, Z. M.

2008-01-01

357

22 CFR 215.9 - Appeal of initial adverse agency determination.  

Code of Federal Regulations, 2013 CFR

... 2013-04-01 false Appeal of initial adverse agency...Foreign Relations AGENCY FOR INTERNATIONAL DEVELOPMENT REGULATIONS...ACT OF 1974 § 215.9 Appeal of initial adverse agency...by mail to: Director, International Development Cooperation...

2013-04-01

358

Environmental dynamics at orbital altitudes  

Microsoft Academic Search

The influence of real satellite aerodynamics on the determination of upper atmospheric density was investigated. A method of analysis of satellite drag data is presented which includes the effect of satellite lift and the variation in aerodynamic properties around the orbit. The studies indicate that satellite lift may be responsible for the observed orbit precession rather than a super rotation

G. R. Karr

1976-01-01

359

Choice of Initial Combination Antiretroviral Therapy in Individuals With HIV Infection: Determinants and Outcomes.  

PubMed

BACKGROUND Current guidelines give recommendations for preferred combination antiretroviral therapy (cART). We investigated factors influencing the choice of initial cART in clinical practice and its outcome. METHODS We analyzed treatment-naive adults with human immunodeficiency virus (HIV) infection participating in the Swiss HIV Cohort Study and starting cART from January 1, 2005, through December 31, 2009. The primary end point was the choice of the initial antiretroviral regimen. Secondary end points were virologic suppression, the increase in CD4 cell counts from baseline, and treatment modification within 12 months after starting treatment. RESULTS A total of 1957 patients were analyzed. Tenofovir-emtricitabine (TDF-FTC)-efavirenz was the most frequently prescribed cART (29.9%), followed by TDF-FTC-lopinavir/r (16.9%), TDF-FTC-atazanavir/r (12.9%), zidovudine-lamivudine (ZDV-3TC)-lopinavir/r (12.8%), and abacavir/lamivudine (ABC-3TC)-efavirenz (5.7%). Differences in prescription were noted among different Swiss HIV Cohort Study sites (P < .001). In multivariate analysis, compared with TDF-FTC-efavirenz, starting TDF-FTC-lopinavir/r was associated with prior AIDS (relative risk ratio, 2.78; 95% CI, 1.78-4.35), HIV-RNA greater than 100 000 copies/mL (1.53; 1.07-2.18), and CD4 greater than 350 cells/?L (1.67; 1.04-2.70); TDF-FTC-atazanavir/r with a depressive disorder (1.77; 1.04-3.01), HIV-RNA greater than 100 000 copies/mL (1.54; 1.05-2.25), and an opiate substitution program (2.76; 1.09-7.00); and ZDV-3TC-lopinavir/r with female sex (3.89; 2.39-6.31) and CD4 cell counts greater than 350 cells/?L (4.50; 2.58-7.86). At 12 months, 1715 patients (87.6%) achieved viral load less than 50 copies/mL and CD4 cell counts increased by a median (interquartile range) of 173 (89-269) cells/?L. Virologic suppression was more likely with TDF-FTC-efavirenz, and CD4 increase was higher with ZDV-3TC-lopinavir/r. No differences in outcome were observed among Swiss HIV Cohort Study sites. CONCLUSIONS Large differences in prescription but not in outcome were observed among study sites. A trend toward individualized cART was noted suggesting that initial cART is significantly influenced by physician's preference and patient characteristics. Our study highlights the need for evidence-based data for determining the best initial regimen for different HIV-infected persons. PMID:22892835

Elzi, Luigia; Erb, Stefan; Furrer, Hansjakob; Ledergerber, Bruno; Cavassini, Matthias; Hirschel, Bernard; Vernazza, Pietro; Bernasconi, Enos; Weber, Rainer; Battegay, Manuel

2012-09-24

360

New method to determine initial surface water displacement at tsunami source  

NASA Astrophysics Data System (ADS)

Friday, March 11, 2011 at 05:46:23 UTC, Japan was struck by an 8.9-magnitude earthquake near its Northeastern coast. This is one of the largest earthquakes that Japan has ever experienced. Tsunami waves swept away houses and cars and caused massive human losses. To predict tsunami wave parameters better and faster, we propose to improve data inversion scheme and achieve the performance gain of data processing. One of the reasons of inaccurate predictions of tsunami parameters is that very little information is available about the initial disturbance of the sea bed at tsunami source. In this paper, we suggest a new way of improving the quality of tsunami source parameters prediction. Modern computational technologies can accurately calculate tsunami wave propagation over the deep ocean provided that the initial displacement (perturbation of the sea bed at tsunami source) is known [4]. Direct geophysical measurements provide the location of an earthquake hypocenter and its magnitude (the released energy evaluation). Among the methods of determination of initial displacement the following ones should be considered. Calculation through the known fault structure and available seismic information. This method is widely used and provides useful information. However, even if the exact knowledge about rock blocks shifts is given, recalculation in terms of sea bed displacement is needed. This results in a certain number of errors. GPS data analysis. This method was developed after the December 2004 event in the Indian Ocean. A good correlation between dry land based GPS sensors and tsunami wave parameters was observed in the particular case of the West coast of Sumatra, Indonesia. This approach is very unique and can hardly been used in other geo locations. Satellite image analysis. The resolution of modern satellite images has dramatically improved. In the future, correct data of sea surface displacement will probably be available in real time, right after a tsunamigenic earthquake. However, today it is not yet possible. Ground-based sea radars. This is an effective tool for direct measurement of tsunami wave. At the same time, the wave is measured at a rather narrow area in front of the radar and does not include information about neighboring parts of the wave. Direct measurement of tsunami wave at deep water [2]. Today, this technology is certainly among the most useful and promising. The DART II® system consists of a seafloor bottom pressure recording (BPR) system, capable of detecting tsunamis as small as 1 cm, and a moored surface buoy for real-time communications. We focus our research on improving the later method, direct measurement of tsunami wave at deep water. We suggest the new way to analyze DART data, modifying the methodology originally proposed by V. Titov. Smaller system of unit sources [3] should be considered to approximate all typical shapes of initial disturbance by several suitable basis functions. To successfully implement it, performance of data analysis should be dramatically improved. This could be done by using a signal orthogonalization procedure for considered system of unit sources and calculation of Fourier coefficients of the measured time series with respect to orthogonal basis. The approach suggested was used as a part of computerized workstation for tsunami hazard monitoring [5-6]. National Oceanic and Atmospheric Administration Center for Tsunami Research. URL: http://nctr.pmel.noaa.gov/honshu20110311/ National Data Buoy Center. URL: http://www.ndbc.noaa.gov/dart.shtml National Oceanic and Atmospheric Administration Center for Tsunami Research. URL: http://sift.pmel.noaa.gov/thredds/dodsC/uncompressed/ National Oceanic and Atmospheric Administration Center for Tsunami Research. URL: http://nctr.pmel.noaa.gov/model.html Alexey Romanenko, Mikhail Lavrentiev-jr, Vasily Titov, "Modern Architecture for Tsunami Hazard Mitigation" // Asia Oceania Geosciences Society (AOGS-2012), ISBN 978-981-07-2049-0 Mikhail Lavrentiev-jr, Andrey Marchuk, Alexey Romanenko, Konstantin Simonov, and Vasiliy T

Lavrentyev, Mikhail; Romanenko, Alexey; Tatarintsev, Pavel

2013-04-01

361

A comprehensive method for determination of fatty acids in the initial oral biofilm (pellicle)  

PubMed Central

The acquired pellicle is a tenacious organic layer covering the surface of teeth, protecting the underlying dental hard tissues. Lipids account for about one quarter of the pellicle's dry weight and are assumed to be of considerable importance for their protective properties. Nevertheless, only preliminary information is available about the nature of lipids in the pellicle. Gas chromatography coupled with electron impact ionization mass spectrometry was used to establish a convenient analytical protocol in order to obtain a qualitative and quantitative characterization of a wide range of FAs (C12–C22). In situ biofilm formation was performed on bovine enamel slabs mounted on individual splints carried by 10 subjects. A modified Folch extraction procedure was adopted to extract the lipids from the detached pellicle, followed by transesterification to fatty acid methyl esters using methanol and concentrated hydrochloric acid. Tridecanoic and nonadecanoic acid were used as internal standards suitable and reliable for robust, precise and accurate measurements. The present study demonstrates, for the first time, a procedure based on a combination of innovative specimen generation and convenient sample preparation with sensitive GC-MS analysis for the determination of the fatty acid profile of the initial oral biofilm.

Reich, Marco; Hannig, Christian; Al-Ahmad, Ali; Bolek, Richard; Kummerer, Klaus

2012-01-01

362

Neptune Orbiter Mission Scenario Based on Nuclear Electric Propulsion and Aerocapture Orbital Insertion  

NASA Astrophysics Data System (ADS)

insertion of spacecraft into elliptical orbit around target planet is proposed for Neptune orbiter mission. The primary goal of combining nuclear electric propulsion (NEP) and aerocapture orbital insertion is a reduction of a trip time comparing to that of similar mission, which would use nuclear electric propulsion only. One of the limitations of the all NEP orbiter is that at the planetary approach it must match its arrival velocity with Neptune's orbital speed in order to initiate slow capture into the desired orbit using low thrust electric propulsion. Use of aerocapture for insertion into closed elliptical orbit around Neptune through a single aerodynamically controlled atmospheric pass gives advantage of having higher entry velocities than it would be possible in case of all NEP scenario, thus reducing trip time required for interplanetary transfer. propulsion and thermal protection systems. Moreover, because faster interplanetary trip times for combined NEP/Aerocapture orbiter result in a higher entry velocities into the Neptune's atmosphere, they will also drive the increase in aerobrake mass fraction. In addition, aerocapture at Neptune also presents a challenge for aerobrake's guidance system which must target vehicle to the desired atmospheric exit conditions in the presence of significant uncertainties in Neptune's atmospheric density. Hence, there is a need to design a robust nominal aerocapture trajectory capable of accommodating density dispersions and also optimized for minimum thermal protection mass, thus contributing to overall reduction of aerobrake mass fraction. determine the optimal combination between reduction of the trip time and increase in aerobrake mass fraction was undertaken. The initial assumptions on aerobrake thermal protection materials and NEP system characteristics were based on near term state of the art technology, corresponding to 2007-2010 time frame, when such a mission to Neptune could be launched. interplanetary trajectory simulation including capture into orbit around Neptune. In these low thrust trajectory simulations the trust level and the specific impulse of a single electric rocket engine were fixed, thus allowing to optimize number of engines and their thrust time history for a rapid transfer to Neptune. Therefore, for combined NEP/Aerocapture mission use of this approach made possible to determine the change in NEP mass fraction, comparing to that one of all NEP mission scenario where spacecraft velocity at its arrival would have to be matched with Neptune's orbital speed. atmosphere, where vehicle was captured into a highly elliptical orbit, which insures periodical close fly-by of the biggest Neptune's moon Triton, thus allowing its scientific observation. Nominal trajectories found in the process of aerocapture simulations were optimized for minimum mass of aerobrake's thermal protection system and were also shown to withstand significant density variations which are likely to be encountered in Neptune's atmosphere. These nominal trajectories were used to determine sensitivity of aerobrake's thermal protection system mass fraction to the variation of atmospheric entry velocity resulted from shorter trip times to Neptune. that for the same initial mass at the low earth orbit, all NEP mission flight time is 11-12 years, when as for the mission scenario which combines NEP and aerocapture flight time can be reduced to 5-6 years. Such a reduction in mission flight time represents much faster scientific return and it also translates into a higher chance of mission success and significant operational cost savings due to much shorter mission time.

Jits, R.

2002-01-01

363

Bacillus subtilis YabA is involved in determining the timing and synchrony of replication initiation  

Microsoft Academic Search

It is shown here by flow cytometry that Bacillus subtilis YabA negatively regulates the timing of replication initiation. When the level of YabA was reduced, replication began at a decreased cell mass and when the level was increased, initiation was delayed. Synchrony of replication initiation was also disrupted at low levels of YabA. Yfp-YabA localized as foci in cells. Since

Miho Hayashi; Yoshitoshi Ogura; Elizabeth J. Harry; Naotake Ogasawara; Shigeki Moriya

2005-01-01

364

Dynamic and thermal analyses of flexible structures in orbit  

NASA Astrophysics Data System (ADS)

Due to the launch cost and functional requirements, space structures, such as satellite antenna, deployable structures, solar sails, the space station, and solar panels, are necessarily built lightweight, large, and very flexible. These space structures undergo large orbital rigid body motions as well as large structural deformations caused by gravitational force and other disturbances, such as shuttle jet impingement loading, deployment factor, thermal effects, and debris impact. It is of utmost importance to study thoroughly the dynamic behavior of flexible structures in orbit under various external forces. In this study, first a finite element methodology program based on the absolute nodal coordinate formulation is developed to determine the coupled structural and orbital response of the flexible structure under gravitational and external loading, i.e., gravitational force, impact force, and jet impingement, and thermal loading. It is found from the simulation results that pitch and structural response of the flexible structures are greatly impacted by the initial and loading conditions, such as orbit eccentricity, initial misalignment, etc. The absolute nodal coordinate formulation may lead to inaccurate results due to the fact that the orbit radius is used for element coordinate, which is much greater than the amplitude of the pitch (attitude) motion and deformations of the orbiting structures. Therefore, to improve the accuracy of structural response in the simulation, a floating (moving) frame that is attached with the orbiting structure's center of mass and that moves parallel to the inertia frame fixed at the Earth's center is introduced to separate the attitude motion and structural deformation from the orbit radius. The finite element formulation is developed in this parallel reference frame system for two and three dimensional beam structures. It is then used to study dynamic response of flexible structures in two and three dimensional orbits. In some cases the structure is subjected to both the Earth's gravitational force and jet impingement loading and in other only the gravitational force. Numerical examples showed that the parallel reference frame formulation gives more accurate results than the absolute nodal coordinate formulation when they are both used to study the orbital structure dynamics. A simplified beam model is presented for investigation of flexible beam structure in three dimensional orbits to greatly reduce the computational time. The parallel reference frame formulation is also applied to investigate coupled thermal-structural response of orbiting beam structure. It is seen that the flexible structure is experiencing rapid temperature changes when it enters and exits the earth shadow in a short period of time. A non-uniform temperature distribution across the cross section is developed due to the temperature change. The flexible beam structure is bent due to the uneven temperature distribution.

Lin, Chijie

365

Orbiting space debris: Dangers, measurement, and mitigation  

NASA Astrophysics Data System (ADS)

Space debris is a growing environmental problem. Accumulation of objects in Earth orbit threatens space systems through the possibility of collisions and runaway debris multiplication. The amount of debris in orbit is uncertain due to the lack of information on the population of debris between 1 and 10 centimeters diameter. Collisions with debris even smaller than 1 cm can be catastrophic due to the high orbital velocities involved. Research efforts are under way at NASA, Unites States Space Command and the Air Force Phillips Laboratory to detect and catalog the debris population in near-Earth space. Current international and national laws are inadequate to control the proliferation of space debris. Space debris is a serious problem with large economic, military, technical, and diplomatic components. Actions need to be taken now for the following reasons: determine the full extent of the orbital debris problem; accurately predict the future evolution of the debris population; decide the extent of the debris mitigation procedures required; implement these policies on a global basis via an international treaty. Action must be initiated now, before the the loss of critical space systems such as the Space Shuttle or the Space Station.

McNutt, Ross T.

1992-01-01

366

Orbiting space debris: Dangers, measurement and mitigation  

NASA Astrophysics Data System (ADS)

Space debris is a growing environmental problem. Accumulation of objects in earth orbit threatens space systems through the possibility of collisions and runaway debris multiplication. The amount of debris in orbit is uncertain due to the lack of information on the population of debris between 1 and 10 centimeters diameter. Collisions with debris even smaller than 1 cm can be catastrophic due to the high orbital velocities involved. Research efforts are under way at NASA, United States Space Command and the Air Force Phillips Laboratory to detect and catalog the debris population in near-earth space. Current international and national laws are inadequate to control the proliferation of space debris. Space debris is a serious problem with large economic, military, technical and diplomatic components. Actions need to be taken now to: determine the full extent of the orbital debris problem; accurately predict the future evolution of the debris population; decide the extent of the debris mitigation procedures required; implement these policies on a global basis via an international treaty. Action must be initiated now, before the loss of critical space systems such as the space shuttle or the space station.

McNutt, Ross T.

1992-06-01

367

Kilometer-scale slopes on Mars and their correlation with geologic units: Initial results from Mars Orbiter Laser Altimeter (MOLA) data  

NASA Astrophysics Data System (ADS)

Martian surface slopes were calculated at baselines from 0.4 to 25 km using profiles obtained by the Mars Orbiter Laser Altimeter (MOLA) instrument during the aerobraking phase of the Mars Global Surveyor mission. Median slope is proposed as a characteristic measurement of the typical surface roughness at each corresponding scale. Median slope is favored over RMS slope because it is not influenced by the small number of higher slopes at the upper end of the slope-frequency distribution tail. Median slope complements interquartile scale roughness characterization in that it is more sensitive to smaller baseline slopes. A map of the median slope of the northern hemisphere is presented. Median slopes and their scale dependences are used to characterize typical kilometer-scale roughness for a set of geologic units mapped in the northern hemisphere. This analysis demonstrates that many individual units and groups of units are characterized by distinctive surface slopes and that these characteristics are sufficiently different that they hold promise for use in the definition and characterization of units. Characterization of the slope properties of geologic units provides information useful in the interpretation of their origin and evolution. For example, the generally smooth topography of the diverse Vastitas Borealis Formation subunits is dominated by about 3 km, 0.3° steep features almost indistinguishable in Viking images. The roughness characteristics of this unit differ from those of other geologic units on Mars and suggest some distinctive process(es) of formation and/or modification of kilometer-scale topography common for all subunits. The similarity of roughness characteristics of the several highland plateau units suggests that kilometer-scale topography was largely inherited from the period of heavy bombardment. The northern polar cap and layered terrains are largely very smooth at small scale. The long, steep-sloped tails of the slope-frequency distributions are compared for the dominant terrain types in the northern hemisphere of Mars and are compared with Earth continents. The Vastitas Borealis Formation found in the northern lowlands differs significantly from both cratered uplands and volcanic plains, and these latter two units can be distinguished from each other on the basis of median slope. Terrestrial continents are smoother than cratered highlands but rougher than the Vastitas Borealis Formation and most volcanic plains. An inventory of all observed slopes much steeper than the angle of repose is presented. Steep slopes occur in the upper parts of tectonic scarps, most likely representing bedrock exposures. The presence of extremely steep slopes in the presumably ductile polar cap provides evidence for geologically recent and/or ongoing formation of these slopes.

Kreslavsky, M. A.; Head, J. W.

1999-09-01

368

An orbit fit program for localizing errors in RHIC  

SciTech Connect

Many errors in an accelerator are evidenced as transverse kicks to the beam which distort the beam trajectory. Therefore, the information of the errors are imprinted in the distorted orbits, which are different from what would be predicted by the optics model. In this note, we introduce an algorithm for fitting the orbit based on an on-line optics model. By comparing the measured and fitted orbits, we first present results validating the algorithm. We then apply the algorithm and localize the location of the elusive source of vertical diurnal variations observed in RHIC. The difference of two trajectories (linear accelerator) or closed orbits (storage ring) should match exactly a betatron oscillation, which is predictable by the optics model, in an ideal machine. However, in the presence of errors, the measured trajectory deviates from prediction since the model is imperfect. Comparison of measurement to model can be used to detect such errors. To do so the initial conditions (phase space parameters at any point) must be determined which can be done by comparing the difference orbit to prediction using only a few beam position monitors (BPMs). The fitted orbit can be propagated along the beam line based on the optics model. Measurement and model will agree up to the point of an error. The error source can be better localized by additionally fitting the difference orbit using downstream BPMs and back-propagating the solution. If one dominating error source exist in the machine, the fitted orbit will deviate from the difference orbit at the same point.

Liu, C.; Minty, M.; Ptitsyn, V.

2011-11-01

369

Determinants of meditation practice inventory: development, content validation, and initial psychometric testing.  

PubMed

Background Meditation health benefits have been difficult to document, as many efficacy studies are marred by lack of statistical power secondary to small sample size and/or threats to validity from high attrition. To date, no published studies have examined barriers to meditation that are likely responsible for low enrollment and high attrition. Objective To develop an instrument to capture barriers to meditation use, namely, the Determinants of Meditation Practice Inventory (DMPI). Design A five-step, mixed-methods approach was used, including literature review, qualitative interviews, content validation, reliability testing, and construct validation. Participants/Setting Four distinct participant groups contributed. Four meditation teachers participated in qualitative interviews. Five expert panelists conducted the content validation. Ten nonmeditators participated in the pilot test. For reliability testing and construct validation, 150 cancer family caregivers participated. Outcome Measures Big Five Inventory (BFI) and Caregiver Reactions Assessment (CRA) were used to test convergent construct validity. Results The three content domains are perceptions and misconceptions, pragmatic concerns, and sociocultural beliefs. Initially, 53 items were generated. Three reviews by the expert panel concluded with a 22-item survey. After pilot testing, a 17-item survey was created. Data from 150 caregivers showed Cronbach's coefficient alpha of 0.87. The intraclass correlation for baseline and retest was 0.86 (confidence interval 0.82-0.90). BFI and CRA were significantly and positively correlated with DMPI. Conclusion Preliminary results indicate the DMPI is psychometrically sound. By identifying barriers to meditation, the DMPI will enable researchers to address the needs and concerns of the target population when designing recruitment and intervention procedures, potentially maximizing recruitment, minimizing attrition, and optimizing interpretation of results. PMID:22314672

Williams, Anna-Leila; Dixon, Jane; McCorkle, Ruth; Van Ness, Peter H

370

BIASES ON INITIAL MASS FUNCTION DETERMINATIONS. III. CLUSTER MASSES DERIVED FROM UNRESOLVED PHOTOMETRY  

SciTech Connect

It is currently common to use spatially unresolved multifilter broadband photometry to determine the masses of individual stellar clusters (and hence the cluster mass function, CMF). I analyze the stochastic effects introduced by the sampling of the stellar initial mass function (SIMF) in the derivation of the individual masses and the CMF, and I establish that such effects are the largest contributor to the observational uncertainties. An analytical solution, valid in the limit where uncertainties are small, is provided to establish the range of cluster masses over which the CMF slope can be obtained with a given accuracy. The validity of the analytical solution is extended to higher mass uncertainties using Monte Carlo simulations and the Gamma approximation. The value of the Poisson mass is calculated for a large range of ages and a variety of filters for solar-metallicity clusters measured with single-filter photometry. A method that uses the code CHORIZOS is presented to simultaneously derive masses, ages, and extinctions. The classical method of using unweighted UBV photometry to simultaneously establish ages and extinctions of stellar clusters is found to be unreliable for clusters older than {approx}30 Ma, even for relatively large cluster masses. On the other hand, augmenting the filter set to include longer-wavelength filters and using weights for each filter increases the range of masses and ages that can be accurately measured with unresolved photometry. Nevertheless, a relatively large range of masses and ages is found to be dominated by SIMF sampling effects that render the observed masses useless, even when using UBVRIJHK photometry. A revision of some literature results affected by these effects is presented and possible solutions for future observations and analyses are suggested.

Maiz Apellaniz, J., E-mail: jmaiz@iaa.es

2009-07-10

371

Determination of the step duration of gait initiation using a mechanical energy analysis  

Microsoft Academic Search

The analysis of gait initiation (the transient state between standing and walking) is an important diagnostic tool in the study of pathologic gait and the evaluation of prosthetic devices. Therefore it is important to know the step duration of gait initiation. However, there is little agreement in the literature regarding this step duration, since each author has based their conclusion

Christopher A. Miller; Mary C. Verstraete

1996-01-01

372

Orbit analysis  

SciTech Connect

The past fifteen years have witnessed a remarkable development of methods for analyzing single particle orbit dynamics in accelerators. Unlike their more classic counterparts, which act upon differential equations, these methods proceed by manipulating Poincare maps directly. This attribute makes them well matched for studying accelerators whose physics is most naturally modelled in terms of maps, an observation that has been championed most vigorously by Forest. In the following sections the author sketchs a little background, explains some of the physics underlying these techniques, and discusses the best computing strategy for implementing them in conjunction with modeling accelerators.

Michelotti, L.

1995-01-01

373

Frozen orbit analysis in the Martian system  

Microsoft Academic Search

A frozen orbit is an orbit whose time rate of change of the argument of the periapsis, the eccentricity, the semi major axis, or the angle of inclination (i) is approximately equal to zero. Martian frozen orbits are known to exist for polar trajectories with altitudes from 300 km to 1000 km. The objective of this study was to determine

James W. Foister III

1987-01-01

374

Management of preseptal and orbital cellulitis  

PubMed Central

Orbital cellulitis describes an infection involving the soft tissues posterior to the orbital septum, including the fat and muscle within the bony orbit. This condition may be associated with severe sight and life-threatening complications. Despite significant advances in antimicrobial therapies and diagnostic technologies, the management of orbital cellulitis often remains challenging, and rapid diagnosis and prompt initiation of therapy are important in minimizing complications and optimizing outcomes. This review summarizes the distinctive characteristics of preseptal and orbital cellulitis, with a focus on anatomic considerations, predisposing conditions, approaches to evaluation, and management strategies.

Lee, Seongmu; Yen, Michael T.

2010-01-01

375

The determination by microdensitometry of the initial maximum velocity rate of rat ovarian 3 ? hydroxysteroid dehydrogenase activity  

Microsoft Academic Search

The determination of the initial maximum velocity rate of 3ß hydroxysteroid dehydrogenase activity (3ß HSD) of the newest generation of corpora lutea of the adult dioestrous rat ovary is described. Under conditions where the substrate and co-factor concentrations are not rate limiting (4×10-4 M epiandrosterone; 3×10-3 M NAD+ respectively) the initial maximum reaction rate was maintained for approximately 6 min.

W. R. Robertson; R. J. Earnshaw; A. Lambert

1982-01-01

376

Socioeconomic Determinants of Fertility Behavior in Developing Nations: Theory and Initial Results.  

National Technical Information Service (NTIS)

This comparative study presents the initial theoretical and empirical results of the Michigan Comparative Fertility Project which is devoted to comparative research on reproductive behavior. The report has two chapters. Chapter 1 develops a microlevel spe...

B. Entwisle A. I. Hermalin W. M. Mason

1982-01-01

377

Co-orbital Asteroids of Earth as Candidates for Asymmetric Impactors on the Moon  

NASA Astrophysics Data System (ADS)

The observed leading/trailing asymmetry of rayed lunar craters may be owed to impactors having lower average encounter velocity than that of the current model of Near Earth Objects [NEOs] (Ito and Malhotra 2010). We are investigating the possibility that currently undetected co-orbital asteroids of Earth may partially account for the missing low velocity impactors. First, we obtain the dynamical lifetimes of asteroids in the co-orbital region of Earth's orbit. We adopt the realistic model of the eight major planets of the solar system and examine a wide range of initial orbital parameters of Earth co-orbital asteroids: semi-major axis, eccentricity, inclination, and relative longitude; we compare our results with those of a previous study (Tabachnik and Evans 2000, Evans and Tabachnik 2002). Then, we trace the escaping objects from the co-orbital region and determine their impact velocity with the Moon. We confirm that these objects have typical impact velocities much lower than the average impact velocity of NEOs. We estimate the current co-orbital population that may account for the leading/trailing asymmetry of lunar rayed craters. We discuss mechanisms for the possible origin and re-supply of co-orbital asteroids and the role of hypothetical primordial co-orbitals on the lunar crater asymmetry. This research is supported by NSF grant AST-0806828.

JeongAhn, Youngmin; Malhotra, R.

2010-10-01

378

Determination of the Point-spread Function for the Fermi Large Area Telescope from On-orbit Data and Limits on Pair Halos of Active Galactic Nuclei  

NASA Astrophysics Data System (ADS)

The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to detect photons with energies from ?20 MeV to >300 GeV. The pre-launch response functions of the LAT were determined through extensive Monte Carlo simulations and beam tests. The point-spread function (PSF) characterizing the angular distribution of reconstructed photons as a function of energy and geometry in the detector is determined here from two years of on-orbit data by examining the distributions of ? rays from pulsars and active galactic nuclei (AGNs). Above 3 GeV, the PSF is found to be broader than the pre-launch PSF. We checked for dependence of the PSF on the class of ?-ray source and observation epoch and found none. We also investigated several possible spatial models for pair-halo emission around BL Lac AGNs. We found no evidence for a component with spatial extension larger than the PSF and set upper limits on the amplitude of halo emission in stacked images of low- and high-redshift BL Lac AGNs and the TeV blazars 1ES0229+200 and 1ES0347-121.

Ackermann, M.; Ajello, M.; Allafort, A.; Asano, K.; Atwood, W. B.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bottacini, E.; Brandt, T. J.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Burnett, T. H.; Busetto, G.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Casandjian, J. M.; Cecchi, C.; Charles, E.; Chaty, S.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Cillis, A. N.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Colafrancesco, S.; Conrad, J.; Cutini, S.; D'Ammando, F.; de Palma, F.; Dermer, C. D.; Silva, E. do Couto e.; Drell, P. S.; Drlica-Wagner, A.; Dubois, R.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fortin, P.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giglietto, N.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grandi, P.; Grenier, I. A.; Grove, J. E.; Guiriec, S.; Hadasch, D.; Hayashida, M.; Hays, E.; Horan, D.; Hou, X.; Hughes, R. E.; Jackson, M. S.; Jogler, T.; Jóhannesson, G.; Johnson, R. P.; Johnson, A. S.; Kamae, T.; Kataoka, J.; Kerr, M.; Knödlseder, J.; Kuss, M.; Lande, J.; Larsson, S.; Latronico, L.; Lavalley, C.; Lee, S.-H.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Mazziotta, M. N.; McConville, W.; McEnery, J. E.; Mehault, J.; Michelson, P. F.; Mignani, R. P.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Naumann-Godo, M.; Nemmen, R.; Nishino, S.; Norris, J. P.; Nuss, E.; Ohsugi, T.; Omodei, N.; Orienti, M.; Orlando, E.; Ormes, J. F.; Paneque, D.; Panetta, J. H.; Pelassa, V.; Perkins, J. S.; Pesce-Rollins, M.; Pierbattista, M.; Piron, F.; Pivato, G.; Poon, H.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Reyes, L. C.; Ritz, S.; Rochester, L. S.; Romoli, C.; Roth, M.; Sanchez, D. A.; Saz Parkinson, P. M.; Scargle, J. D.; Sgrò, C.; Siskind, E. J.; Snyder, A.; Spandre, G.; Spinelli, P.; Stephens, T. E.; Suson, D. J.; Tajima, H.; Takahashi, H.; Tanaka, T.; Thayer, J. G.; Thayer, J. B.; Thompson, D. J.; Tibaldo, L.; Tibolla, O.; Tinivella, M.; Tosti, G.; Troja, E.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vianello, G.; Vitale, V.; von Kienlin, A.; Waite, A. P.; Wallace, E.; Weltevrede, P.; Winer, B. L.; Wood, K. S.; Wood, M.; Yang, Z.; Zimmer, S.

2013-03-01

379

Determinants of awareness, initiation and maintenance of physical activity among the over-fifties: a Delphi study.  

PubMed

To develop effective interventions to stimulate physical activity (PA), insight into its underlying variables is needed. The aim of this study was to obtain an overview of the most relevant determinants of awareness, initiation and maintenance of PA among the over-fifties by means of a three-round Delphi study. In the first round, 17 key-experts outlined possible relevant determinants into an open-ended electronic questionnaire. In the second round, 118 experts completed a structured electronic questionnaire that was based on the first round results, in which they scored each determinant on its relevance. In the third round, experts were asked to re-rate the relevance of each determinant, after feedback was given about the group median relevance score. After three rounds, the experts agreed on 30 relevant determinants of the three phases of PA. When compared with longitudinal studies, the Delphi study pointed out new concepts, such as several post-motivational and social and environmental determinants as possible relevant determinants, suggesting that this method has the potential to trace new and promising determinants. The results further showed that next to similarities, much dissimilarity in relevant determinants of awareness, initiation and maintenance of PA was found, suggesting that most determinants could be phase specific. PMID:18927443

van Stralen, M M; Lechner, L; Mudde, A N; de Vries, H; Bolman, C

2008-10-16

380

Determinants of Mortality among HIV Positives after Initiating Antiretroviral Therapy in Western Ethiopia: A Hospital-Based Retrospective Cohort Study  

PubMed Central

Studies revealed that there are various determinants of mortality among HIV positives after ART initiation. These determinants are so variable with context and dynamic across time with the advancement of cares and treatments. In this study we tried to identify determinants of mortality among HIV positives after initiating ART. A retrospective cohort study was conducted among 416 ART attendees enrolled between July 2005 to January 2012 in Nekemte Referral Hospital, Western Ethiopia. Actuarial table was used to estimate survival of patients after ART initiation and log rank test was used to compare the survival curves. Cox proportional-hazard regression was applied to determine the independent determinants of time to death. The estimated mortality was 4%, 5%, 6%, 7%, and 7% at 6, 12, 24, 36 and 48 months respectively with mortality incidence density of 1.89 deaths per 100 person years (95% CI 1.74, 3.62). Forty years and above AHR = 3.055 (95% CI 1.292, 7.223), low baseline hemoglobin level (AHR = 0.523 (95% CI .335, 0.816)), and poor ART adherence (AHR 27.848 (95% CI 8.928, 86.8)) were found to be an independent determinants of mortality. These determinants of mortality have to be taken into account to enhance better clinical outcomes of ART attendees.

Hambisa, Mitiku Teshome; Ali, Ahmed; Dessie, Yadeta

2013-01-01

381

20 CFR 418.3620 - What is the effect of an initial determination?  

Code of Federal Regulations, 2013 CFR

...determination? 418.3620 Section 418.3620 Employees' Benefits SOCIAL SECURITY ADMINISTRATION MEDICARE SUBSIDIES Medicare Part D Subsidies Determinations and the Administrative Review Process § 418.3620 What is the...

2013-04-01

382

20 CFR 418.3615 - Will we mail you a notice of the initial determination?  

Code of Federal Regulations, 2013 CFR

...determination? 418.3615 Section 418.3615 Employees' Benefits SOCIAL SECURITY ADMINISTRATION MEDICARE SUBSIDIES Medicare Part D Subsidies Determinations and the Administrative Review Process § 418.3615 Will we mail...

2013-04-01

383

Satellite Orbital Interpolation Comparison Methods  

NASA Astrophysics Data System (ADS)

A satellite or artificial probe orbit is made of time series of orbital elements such as state vectors (position and velocities, keplerian orbital elements) given at regular or irregular time intervals. These time series are fitted to observations, so that differences between observations (distance, radial velocity) and the theoretical quantity be minimal, according to a statistical criterion, mostly based on the least-squared algorithm. These computations are carried out using dedicated software, such as the GINS used by GRGS, mainly at CNES Toulouse and Paris Observatory. From an operational point of view, time series of orbital elements are 7-day long. Depending on the dynamical configurations, more generally, they can typically vary from a couple of days to some weeks. One of the fundamental parameters to be adjusted is the initial state vector. This can lead to time gaps, at the level of a few dozen of centimeters between the last point of a time series to the first one of the following data set. The objective of this presentation consists in the improvement of an interpolation method freed itself of such possible "discontinuities" resulting between satellite's orbit arcs when a new initial bulletin is adjusted. We show the principles of interpolation for these time series and compare solutions coming from different interpolation methods such as Lagrange polynomial, spline cubic, Chebyshev orthogonal polynomial and cubic Hermite polynomial. These polynomial coefficients are used to reconstruct and interpolate the satellite orbits without time gaps and discontinuities and requiring a weak memory size.

Richard, J.-Y.; Deleflie, F.; Gambis, D.

2012-04-01

384

Aggressive Multilateralism: The Determinants of GATT\\/WTO Dispute Initiation, 1948-1998  

Microsoft Academic Search

Abstract Why do states initiate trade disputes under the General Agreement on Tariffs and Trade (GATT) or its successor, the World Trade Organization (WTO)? Existing studies suggest that democracies,should either experience fewer trade conflicts or at least resolve them more cooperatively. Other works contend that the filing of complaints itself constitutes proof of the efficacy of the trade dispute settlement

Eric Reinhardt

2000-01-01

385

76 FR 61384 - Notice of Initial Determination Revising the List of Products Requiring Federal Contractor...  

Federal Register 2010, 2011, 2012, 2013

...visits and reviewing local media sources. For this initial...of forced or indentured child labor that [[Page 61385...as forced or indentured child labor. Institutions or...such as independent news media, trade unions and NGOs...of forced or indentured child labor; the source...

2011-10-04

386

77 FR 59418 - Notice of Initial Determination Revising the List of Products Requiring Federal Contractor...  

Federal Register 2010, 2011, 2012, 2013

...visits and reviewing local media sources. For this initial...of forced or indentured child labor that was available...as forced or indentured child labor. Institutions or...such as independent news media, trade unions and NGOs...of forced or indentured child labor; the source...

2012-09-27

387

Transnasal endoscopic surgery for benign orbital tumors.  

PubMed

Two cases of orbital tumor are presented, and the surgical technique by means of an endoscopic transnasal approach is discussed. In Case 1, a non-vascular, benign tumor was located inside the orbit, and it was able to be completely removed, without any complications. The tumor in Case 2 was also located inside the orbit, but it was determined to be a hemangioma based on the intraoperative pathology. To avoid eye complications arising from performance of the surgery in the presence of bleeding, it was decided to widely open the orbital lamina papyracea and periosteum, and perform only orbital decompression. The eye symptoms disappeared in both patients. Endoscopic transnasal surgery is indicated for benign orbital tumors that are medially located in the orbit. It can be thought that the eye symptoms can be alleviated by avoiding orbital pressure, regardless of whether-based on the intraoperative pathology-the tumor is completely removed or not. PMID:22595376

Haruna, Shinichi; Tukidate, Toshiharu; Konno, Wataru; Fukami, Satoshi; Nakajima, Itsuo

2012-05-15

388

18 CFR 292.211 - Petition for initial determination on whether a project has a substantial adverse effect on the...  

Code of Federal Regulations, 2010 CFR

(a) An applicant that has filed a petition under § 292.210 may also file an AEE petition with the Commission for an initial determination on whether the project satisfies the requirement that it has no substantial adverse effect on the environment as specified in §...

2013-04-01

389

Determinants of smoking initiation among women in five European countries: a cross-sectional survey  

Microsoft Academic Search

BACKGROUND: The rate of smoking and lung cancer among women is rising in Europe. The primary aim of this study was to determine why women begin smoking in five different European countries at different stages of the tobacco epidemic and to determine if smoking is associated with certain characteristics and\\/or beliefs about smoking. METHODS: A cross-sectional telephone survey on knowledge

Debora L Oh; Julia E Heck; Carolyn Dresler; Shane Allwright; Margaretha Haglund; Sara S Del Mazo; Eva Kralikova; Isabelle Stucker; Elizabeth Tamang; Ellen R Gritz; Mia Hashibe

2010-01-01

390

Initiating oncogenic event determines gene-expression patterns of human breast cancer models  

Microsoft Academic Search

Molecular expression profiling of tumors initiated by transgenic overexpression of c-myc, c-neu, c-ha-ras, polyoma middle T antigen (PyMT) or simian virus 40 T\\/t antigen (T-ag) targeted to the mouse mammary gland have identified both common and oncogene-specific events associated with tumor formation and progression. The tumors shared great similarities in their gene-expression profiles as compared with the normal mammary gland

Kartiki V. Desai; Nianqing Xiao; Weili Wang; Lisa Gangi; John Greene; John I. Powell; Robert Dickson; Priscilla Furth; Kent Hunter; Raju Kucherlapati; Richard Simon; Edison T. Liu; Jeffrey E. Green

2002-01-01

391

Molecular determinants of origin discrimination by Orc1 initiators in archaea  

PubMed Central

Unlike bacteria, many eukaryotes initiate DNA replication from genomic sites that lack apparent sequence conservation. These loci are identified and bound by the origin recognition complex (ORC), and subsequently activated by a cascade of events that includes recruitment of an additional factor, Cdc6. Archaeal organisms generally possess one or more Orc1/Cdc6 homologs, belonging to the Initiator clade of ATPases associated with various cellular activities (AAA+) superfamily; however, these proteins recognize specific sequences within replication origins. Atomic resolution studies have shown that archaeal Orc1 proteins contact double-stranded DNA through an N-terminal AAA+ domain and a C-terminal winged-helix domain (WHD), but use remarkably few base-specific contacts. To investigate the biochemical effects of these associations, we mutated the DNA-interacting elements of the Orc1-1 and Orc1-3 paralogs from the archaeon Sulfolobus solfataricus, and tested their effect on origin binding and deformation. We find that the AAA+ domain has an unpredicted role in controlling the sequence selectivity of DNA binding, despite an absence of base-specific contacts to this region. Our results show that both the WHD and ATPase region influence origin recognition by Orc1/Cdc6, and suggest that not only DNA sequence, but also local DNA structure help define archaeal initiator binding sites.

Dueber, Erin C.; Costa, Alessandro; Corn, Jacob E.; Bell, Stephen D.; Berger, James M.

2011-01-01

392

Reducing orbital eccentricity in binary black hole simulations  

Microsoft Academic Search

Binary black hole simulations starting from quasi-circular (i.e., zero radial velocity) initial data have orbits with small but nonzero orbital eccentricities. In this paper, the quasi-equilibrium initial-data method is extended to allow nonzero radial velocities to be specified in binary black hole initial data. New low-eccentricity initial data are obtained by adjusting the orbital frequency and radial velocities to minimize

Harald P Pfeiffer; Duncan A Brown; Lawrence E Kidder; Lee Lindblom; Geoffrey Lovelace; Mark A Scheel

2007-01-01

393

ERS Orbit Control.  

National Technical Information Service (NTIS)

The European remote sensing mission orbit control is addressed. For the commissioning phase, the orbit is defined by the following requirements: Sun synchronous, local time of descending node 10:30; three days repeat cycle with 43 orbital revolutions; ove...

M. Rosengren

1991-01-01

394

Magnetorquer Control for Orbital Manoeuvre of Low Earth Orbit Microsatellite  

Microsoft Academic Search

A propulsion system is required in order for the spacecraft to be able to operate as a part of the constellation, and is used to carry out initial launcher injection corrections, spacecraft separation into their respective orbital slots, altitude maintenance and finally an end of life manoeuvre to remove the spacecraft from the operational system also these manoeuvres allow the

A. M. SI MOHAMMED; A. BOUDJEMAI; S. CHOURAQUI; M. BENYETTOU

395

BINARY STAR ORBITS. IV. ORBITS OF 18 SOUTHERN INTERFEROMETRIC PAIRS  

SciTech Connect

First orbits are presented for 3 interferometric pairs and revised solutions for 15 others, based in part on first results from a recently initiated program of speckle interferometric observations of neglected southern binaries. Eight of these systems contain additional components, with multiplicity ranging up to 6.

Mason, Brian D.; Hartkopf, William I. [U.S. Naval Observatory, 3450 Massachusetts Avenue, NW, Washington, DC 20392-5420 (United States); Tokovinin, Andrei, E-mail: bdm@usno.navy.mi, E-mail: wih@usno.navy.mi, E-mail: atokovinin@ctio.noao.ed [Cerro Tololo Inter-American Observatory, Casilla 603, La Serena (Chile)

2010-09-15

396

Orbital overlap and chemical bonding.  

PubMed

The chemical bonds in the diatomic molecules Li(2)-F(2) and Na(2)-Cl(2) at different bond lengths have been analyzed by the energy decomposition analysis (EDA) method using DFT calculations at the BP86/TZ2P level. The interatomic interactions are discussed in terms of quasiclassical electrostatic interactions DeltaE(elstat), Pauli repulsion DeltaE(Pauli) and attractive orbital interactions DeltaE(orb). The energy terms are compared with the orbital overlaps at different interatomic distances. The quasiclassical electrostatic interactions between two electrons occupying 1s, 2s, 2p(sigma), and 2p(pi) orbitals have been calculated and the results are analyzed and discussed. It is shown that the equilibrium distances of the covalent bonds are not determined by the maximum overlap of the sigma valence orbitals, which nearly always has its largest value at clearly shorter distances than the equilibrium bond length. The crucial interaction that prevents shorter bonds is not the loss of attractive interactions, but a sharp increase in the Pauli repulsion between electrons in valence orbitals. The attractive interactions of DeltaE(orb) and the repulsive interactions of DeltaE(Pauli) are both determined by the orbital overlap. The net effect of the two terms depends on the occupation of the valence orbitals, but the onset of attractive orbital interactions occurs at longer distances than Pauli repulsion, because overlap of occupied orbitals with vacant orbitals starts earlier than overlap between occupied orbitals. The contribution of DeltaE(elstat) in most nonpolar covalent bonds is strongly attractive. This comes from the deviation of quasiclassical electron-electron repulsion and nuclear-electron attraction from Coulomb's law for point charges. The actual strength of DeltaE(elstat) depends on the size and shape of the occupied valence orbitals. The attractive electrostatic contributions in the diatomic molecules Li(2)-F(2) come from the s and p(sigma) electrons, while the p(pi) electrons do not compensate for nuclear-nuclear repulsion. It is the interplay of the three terms DeltaE(orb), DeltaE(Pauli), and DeltaE(elstat) that determines the bond energies and equilibrium distances of covalently bonded molecules. Molecules like N(2) and O(2), which are usually considered as covalently bonded, would not be bonded without the quasiclassical attraction DeltaE(elstat). PMID:17024702

Krapp, Andreas; Bickelhaupt, F Matthias; Frenking, Gernot

2006-12-13

397

20 CFR 408.1004 - Which administrative actions are not initial determinations?  

Code of Federal Regulations, 2013 CFR

...SOCIAL SECURITY ADMINISTRATION SPECIAL BENEFITS FOR CERTAIN WORLD WAR II VETERANS Determinations and the Administrative Review...claim for benefits based on alleged misinformation because one or more of the conditions specified in §...

2013-04-01

398

20 CFR 418.2320 - What is the effect of an initial determination?  

Code of Federal Regulations, 2013 CFR

...418.2320 Section 418.2320 Employees' Benefits SOCIAL SECURITY ADMINISTRATION MEDICARE SUBSIDIES Income-Related Monthly Adjustments to Medicare Prescription Drug Coverage Premiums Determinations and the Administrative Review...

2013-04-01

399

15 CFR 4.10 - Appeals from initial determinations or untimely delays.  

Code of Federal Regulations, 2013 CFR

...file a written appeal or an electronic appeal, which must be received...General Counsel during normal business hours (8:30 a.m...determination. Written or electronic appeals arriving after normal business hours will be deemed...

2013-01-01

400

Enzymatic fluorometric method for the determination of D-arabinitol in serum by initial rate analysis.  

PubMed

We describe a new, simple, fluorometric assay for D-arabinitol in serum. The method is based on oxidation of D-arabinitol by D-arabinitol dehydrogenase (EC 1.1.1.11), with the concomitant reduction of NAD. The initial rate of NAD reduction, which is proportional to the D-arabinitol content of serum, can be measured with a recording spectrofluorometer. Sensitivity, specificity, recovery and reproducibility experiments gave satisfactory results. The proposed method is suitable for clinical use, and may be helpful in the diagnosis of invasive candidiasis. PMID:4028438

Soyama, K; Ono, E

1985-07-15

401

Orbital forcing of the inception of the Laurentide ice sheet?  

Microsoft Academic Search

A low-resolution spectral atmospheric general-circulation model is used to simulate two annual cycles under the orbitally determined insolation conditions of 125,000 and 115,000 years ago, corresponding to the beginning and end of the last interglacial optimum. The theoretical bases and numerical-computation techniques of the model are discussed. Initial boundary conditions other than insolation were the same for each simulation and

J. F. Royer; Michel Deque; Pierre Pestiaux

1983-01-01

402

Precise determination of orbital parameters in system with slowly drifting phases: application to the case of XTE J1807-294  

NASA Astrophysics Data System (ADS)

We describe a timing technique that allows obtaining precise orbital parameters of an accreting millisecond pulsar in those cases in which intrinsic variations of the phase delays (caused, for example, by proper variation of the spin frequency) with characteristic time-scale longer than the orbital period do not allow to fit the orbital parameters over a long observation (tens of days). We show under which conditions this method can be applied along with the results obtained applying this method to the 2003 outburst observed by RXTE of the accreting millisecond pulsar XTE J1807-294 which shows in its phase delays a non-negligible erratic behaviour. We refined the orbital parameters of XTE J1807-294 using all the 90 days in which the pulsation is strongly detected and the method applicable. In this way, we obtain the orbital parameters of the source with a precision more than one order of magnitude better than the previous available orbital solution, a precision obtained to date, on accreting millisecond pulsars, only for SAX J1808.4-3658 analysing several outbursts spanning over seven years and with much better statistics.

Riggio, A.; di Salvo, T.; Burderi, L.; Iaria, R.; Papitto, A.; Menna, M. T.; Lavagetto, G.

2007-12-01

403

Horseshoe periodic orbits in the restricted problem of three bodies for a sun-Jupiter mass ratio  

NASA Astrophysics Data System (ADS)

Segments of seven families of symmetric horseshoe periodic orbits of the restricted three body problem for a sun-Jupiter mass ratio have been numerically determined. Each family is found to have a region consisting of smooth horseshoe shaped orbits with the family evolving to orbits acquiring loops on both sides of the smooth horseshoes. The general evolution of these families is discussed and one in particular (Rabe's horseshoe is a member of this family) is described in more detail with the aid of computer plots of orbits in this family. The smooth horseshoes do not continuously evolve along one family but are members of many distinct families. The change in shape of the smooth horseshoe orbits is examined as they have closer approaches to Jupiter. Each family has a bifurcation with an asymmetric family of periodic orbits. The initial conditions and other quantities describing these bifurcation orbits are given. Starting from these orbits the initial segments of the asymmetric families has been determined.

Taylor, D. B.

1981-11-01

404

African American and Latino patient versus provider perceptions of determinants of prenatal care initiation.  

PubMed

Few studies have compared provider and patient perceptions of barriers, motivators and facilitators of prenatal care (PNC) initiation. The current study compared these perceptions in providers and patients in Washington, DC, a city characterized by infant mortality and low birth weight rates that are among the highest in the nation, and poor utilization of PNC, particularly among minority groups. The results reported here were part of a larger study of barriers, motivators and facilitators influencing PNC utilization in Washington, DC. A convenience sample of 331 African American and Latino patients and 61 providers were interviewed to identify which of 63 motivators, facilitators, and barriers significantly influenced PNC initiation. Both sample groups were recruited at 14 PNC facilities, selected to represent all sites in DC known to serve high-risk, low-income minority women, including hospital-based clinics, community-based clinics, and private practices. Data were analyzed using Fisher exact tests and Kendall's concordance tests. Results indicated that there was good agreement between patients and providers about the relative importance of the various barriers (especially psychosocial), motivators, and facilitators. However, differences were found between patients and providers in the response frequencies. Providers were more likely to report barriers while patients were more likely to report certain motivators (especially learning better health habits and how to protect health). These results indicate that despite widespread agreement on most issues, especially psychosocial barriers, patients rated health education higher than providers. PMID:21842248

Johnson, Allan A; Wesley, Barbara D; El-Khorazaty, M Nabil; Utter, Julie M; Bhaskar, Brinda; Hatcher, Barbara J; Milligan, Renee; Wingrove, Barbara K; Richards, Leslie; Rodan, Margaret F; Laryea, Haziel A

2011-12-01

405

Admissible orbits in the Oort cloud and velocities on such orbits  

Microsoft Academic Search

In this paper we deal with determinations of: admissible orbits and ranges of orbital velocity in the cloud, extremal velocities at the distance r from the Sun. Moreover, in velocity space we consider the Or region in which there are located tips of velocity vectors for comets moving on admissible orbits.

Richard A. Serafin; A. Mickiewicz

1987-01-01

406

The orbit of Proton 4 redetermined, with geophysical implications  

Microsoft Academic Search

The orbit of Proton 4, 1968-103A, has been redetermined, in greater detail and with better accuracy, in order to clarify previously puzzling features in the variation of orbital inclination. Orbital parameters have been determined at 25 epochs between December 1968 and July 1969, using about 1600 optical and radar observations with the RAE orbit refinement program PROP6. During January 1969

H. Hiller; D. G. King-Hele

1976-01-01

407

[Procedure for determining the initiation of tube feeding in children in an intensive care unit].  

PubMed

A procedure is proposed to determine the timing of tube feeding in children treated in an intensive care unit, which records the hypertonia of the pyloric sphincter and consists in the determination the time of gastric administration of distilled water before its evacuation into the duodenal lumen (water evacuation test) visualized in the real-time mode through abdominal ultrasonography. The proposed procedure was successfully applied to 42 children aged 3 months to 14 years who had severe brain injury, appendicular peritonitis, polytrauma, and polysegmental pneumonias. This determining procedure makes it possible to exclude radiation exposure in patients treated in intensive care units and to improve the outcomes of treatment, by prescribing the artificial feeding, that is adequate to the patients' status, in the periods optimal for each specific clinical case. PMID:16613047

Uglitskikh, A K; Dibrivny?, G S; Pykov, M I; Kon', I Ia; Ostre?kov, I F; Nikitin, V V; Bagaev, V G

408

Orbit mechanics of deep space probes  

Microsoft Academic Search

Emphasized are orbits with high inclinations from the earth-moon orbital plane, with initial major axes oriented perpendicularly or inclined to the axis of syzygies and with period near that of the moon. The relation of this problem to the restricted problem of three and four bodies is discussed, showing the effects of luni-solar ephemerides versus the 'circular problem'. Various modifications

J. J. F. Liu; J. Segrest; V. Szebehely

1986-01-01

409

78 FR 32442 - Certain Cases for Portable Electronic Devices; Determination Not To Review an Initial...  

Federal Register 2010, 2011, 2012, 2013

...Determination Granting in Part Complainant's Motion for Leave To Amend the Complaint and Notice...9) granting in part complainant's motion for leave to amend the complaint and notice...attorney filed a response in support of the motion. No other responses to the motion...

2013-05-30

410

An Initial Analysis of the Solar Storming Effects on the Determination of Coordinates Using GNSS  

Microsoft Academic Search

The present work aims to investigate Solar Storming effects on the determination of geodetic coordinates. Preliminary results of an analysis of satellite and ground - based measurements during extremely strong geomagnetic storm on 11th September 2005 are presented. A similar situation was also observed on 30th October 2003 and 8th November 2004. The disturbance of the Sun, solar wind, and

Vilma Zubinaite; George Preiss

2010-01-01

411

Determining the value of simulation in nurse education: study design and initial results  

Microsoft Academic Search

Nowadays simulation is taking an important place in training and education of healthcare professionals. The University of Hertfordshire is carrying out a study which aims to determine the effect of realistic scenario-based simulation on nursing students' competence and confidence. This project is sponsored by the British Heart Foundation and takes place in the Hertfordshire Intensive Care and Emergency Simulation Centre

Guillaume Alinier; William B. Hunt; Ray Gordon

2004-01-01

412

Determination of the first anisotropy constant of uniaxial anisotropic material from initial susceptibility of magnetization hard direction  

Microsoft Academic Search

A method to calculate the first anisotropy constant of a uniaxial anisotropy system from the initial susceptibility of magnetization hard direction have been studied. The formulas for single crystal and magnetically aligned powder based on rigid coupled magnetization model or two sublattice magnetization model have been derived and applied to determine the anisotropy constant of RE2Fe14B (RE=Ce, Pr, Gd, Tb,

Y. B Kim; Han-Min Jin

1998-01-01

413

Experimental Determination of Dynamic Crack Initiation and Propagation Fracture Toughness in Thin Aluminum Sheets  

Microsoft Academic Search

An experimental investigation was undertaken to characterize the dynamic fracture characteristics of 2024-T3 aluminum thin sheets ranging in thickness from 1.63–2.54 mm. Specifically, the critical dynamic stress intensity factor Kdc was determined over a wide range of loading rates ( expressed as the time rate of change of the stress intensity factor KdI ) using both a servo- hydraulic loading

D. M. Owen; S. Zhuang; A. J. Rosakis; G. Ravichandran

1998-01-01

414

Development and initial validation of the determinants of physical activity questionnaire  

PubMed Central

Background Physical activity interventions are more likely to be effective if they target causal determinants of behaviour change. Targeting requires accurate identification of specific theoretical determinants of physical activity. Two studies were undertaken to develop and validate the Determinants of Physical Activity Questionnaire. Methods In Study 1, 832 male and female university staff and students were recruited from 49 universities across the UK and completed the 66-item measure, which is based on the Theoretical Domains Framework. Confirmatory factor analysis was undertaken on a calibration sample to generate the model, which resulted in a loss of 31 items. A validation sample was used to cross-validate the model. 20 new items were added and Study 2 tested the revised model in a sample of 466 male and female university students together with a physical activity measure. Results The final model consisted of 11 factors and 34 items, and CFA produced a reasonable fit ?2 (472)?=?852.3, p?determinants of physical activity has been developed with reasonable reliability and validity. Further work is required to test the measure amongst a more representative sample. This study provides an innovative approach to identifying potential barriers to physical activity. This approach illustrates a method for moving from diagnosing implementation difficulties to designing and evaluating interventions.

2013-01-01

415

Reduced domestic satellite orbit spacing  

NASA Astrophysics Data System (ADS)

The demand for services provided by communications satellites in geostationary orbit is growing, and problems arise with respect to the required increase in capacity. One approach for providing such an increase involves the employment of more satellites operating at smaller orbital spacings. The present investigation is concerned with the results of technical studies conducted by the Federal Communications Commission (FCC) to determine the feasibility of reducing orbital spacings between U.S. 'domestic fixed satellites' (domsats). Attention is given to details regarding the usable orbital arc, an adjacent satellite interference model, antenna sidelobe patterns, a single entry analysis, a 4/6 GHz aggregate analysis, results for the 4/6 GHz bands, results for the 12/14 GHz bands, data services, voice services, video reception, and high power spot beams.

Sharp, G. L.

416

Low Earth orbit communications satellite  

NASA Astrophysics Data System (ADS)

A current thrust in satellite communication systems considers a low-Earth orbiting constellations of satellites for continuous global coverage. Conceptual design studies have been done at the time of this design project by LORAL Aerospace Corporation under the program name GLOBALSTAR and by Motorola under their IRIDIUM program. This design project concentrates on the spacecraft design of the GLOBALSTAR low-Earth orbiting communication system. Overview information on the program was gained through the Federal Communications Commission licensing request. The GLOBALSTAR system consists of 48 operational satellites positioned in a Walker Delta pattern providing global coverage and redundancy. The operational orbit is 1389 km (750 nmi) altitude with eight planes of six satellites each. The orbital planes are spaced 45 deg., and the spacecraft are separated by 60 deg. within the plane. A Delta 2 launch vehicle is used to carry six spacecraft for orbit establishment. Once in orbit, the spacecraft will utilize code-division multiple access (spread spectrum modulation) for digital relay, voice, and radio determination satellite services (RDSS) yielding position determination with accuracy up to 200 meters.

Moroney, D.; Lashbrook, D.; McKibben, B.; Gardener, N.; Rivers, T.; Nottingham, G.; Golden, B.; Barfield, B.; Bruening, J.; Wood, D.

417

Determination of the Fermi velocity by angle-dependent periodic orbit resonance measurements in the organic conductor ?-(BEDT-TTF)2KHg(SCN)4  

NASA Astrophysics Data System (ADS)

We report on detailed angle-dependent studies of the microwave (?=50-90 GHz) interlayer magnetoelectrodynamics of a single crystal sample of the organic charge-density-wave (CDW) conductor ?-(BEDT-TTF)2KHg(SCN)4. Recently developed instrumentation enables both magnetic-field (B) sweeps for a fixed sample orientation and angle sweeps at fixed ?/B. We observe series' of resonant absorptions, which we attribute to periodic orbit resonances (POR)-a phenomenon closely related to cyclotron resonance. The angle dependence of the POR indicates that they are associated with the low-temperature quasi-one-dimensional (Q1D) Fermi surface (FS) of the title compound; indeed, all of the resonance peaks collapse onto a single set of ?/B versus angle curves, generated using a semiclassical magnetotransport theory for a single Q1D FS. We show that Q1D POR measurements provide one of the most direct methods for determining the Fermi velocity, without any detailed assumptions concerning the band structure; our analysis yields an average value of vF=6.5×104 m/s. Quantitative analysis of the POR harmonic content indicates that the Q1D FS is strongly corrugated. This is consistent with the assumption that the low-temperature FS derives from a reconstruction of the high-temperature quasi-two-dimensional FS, caused by the CDW instability. Detailed analysis of the angle dependence of the POR yields parameters associated with the CDW superstructure, which are consistent with published results. Finally, we address the issue as to whether or not the interlayer electrodynamics are coherent in the title compound. We obtain a relaxation time from the POR linewidths, which is considerably longer than the interlayer hopping time, indicating that the transport in this direction is coherent.

Kovalev, A. E.; Hill, S.; Qualls, J. S.

2002-10-01

418

A Southern Hemisphere radar meteor orbit survey  

NASA Astrophysics Data System (ADS)

A meteor radar system has been operated on a routine basis near Christchurch, New Zealand, to determine the orbits of Earth-impacting interplanetary dust and meteoroids. The system sensitivity is +13 visual magnitude, corresponding to approximately 100 micron sized meteoroids. With an orbital precision of 2 degrees in angular elements and 10 percent in orbital energy (1/a), the operation yields an average of 1500 orbits daily with a total to date in excess of 105. The use of pc's and automated data reduction permit the large orbital data sets we collect to be routinely reduced. Some illustrative examples are presented of the signal formats/processing and the results of data reduction, giving the individual orbital elements and hence the overall distributions. Current studies include the distribution of dust in the inner solar system; the influx of meteoroids associated with near-Earth asteroids; and the orbital structure existing in comet-produced streams.

Baggaley, W. Jack; Steel, Duncan I.; Taylor, Andrew D.

419

Unilateral orbital pain and eyelid swelling in a 46-year-old woman: orbital metastasis of occult invasive lobular carcinoma of breast masquerading orbital pseudotumour  

PubMed Central

Orbital metastasis is very infrequent in breast cancer; more so as an initial and sole presenting feature. The authors report a case of orbital metastasis of occult breast carcinoma in a 46-year-old woman, who presented with unilateral orbital pain and eyelid swelling. This was initially diagnosed as orbital pseudotumour and treated with steroids. The development of breast symptoms and finding of breast nodule, 3 months later, led to the diagnosis of invasive lobular carcinoma of the breast with orbital metastases, confirmed on biopsy.

Gupta, Shilpi; Bhatt, Vijaya Raj; Varma, Seema

2011-01-01

420

Unilateral orbital pain and eyelid swelling in a 46-year-old woman: orbital metastasis of occult invasive lobular carcinoma of breast masquerading orbital pseudotumour.  

PubMed

Orbital metastasis is very infrequent in breast cancer; more so as an initial and sole presenting feature. The authors report a case of orbital metastasis of occult breast carcinoma in a 46-year-old woman, who presented with unilateral orbital pain and eyelid swelling. This was initially diagnosed as orbital pseudotumour and treated with steroids. The development of breast symptoms and finding of breast nodule, 3 months later, led to the diagnosis of invasive lobular carcinoma of the breast with orbital metastases, confirmed on biopsy. PMID:22698907

Gupta, Shilpi; Bhatt, Vijaya Raj; Varma, Seema

2011-03-15

421

Initiating oncogenic event determines gene-expression patterns of human breast cancer models  

PubMed Central

Molecular expression profiling of tumors initiated by transgenic overexpression of c-myc, c-neu, c-ha-ras, polyoma middle T antigen (PyMT) or simian virus 40 T/t antigen (T-ag) targeted to the mouse mammary gland have identified both common and oncogene-specific events associated with tumor formation and progression. The tumors shared great similarities in their gene-expression profiles as compared with the normal mammary gland with an induction of cell-cycle regulators, metabolic regulators, zinc finger proteins, and protein tyrosine phosphatases, along with the suppression of some protein tyrosine kinases. Selection and hierarchical clustering of the most variant genes, however, resulted in separating the mouse models into three groups with distinct oncogene-specific patterns of gene expression. Such an identification of targets specified by particular oncogenes may facilitate development of lesion-specific therapeutics and preclinical testing. Moreover, similarities in gene expression between human breast cancers and the mouse models have been identified, thus providing an important component for the validation of transgenic mammary cancer models.

Desai, Kartiki V.; Xiao, Nianqing; Wang, Weili; Gangi, Lisa; Greene, John; Powell, John I.; Dickson, Robert; Furth, Priscilla; Hunter, Kent; Kucherlapati, Raju; Simon, Richard; Liu, Edison T.; Green, Jeffrey E.

2002-01-01

422

Molecular determinants of the substrate specificity of the complement-initiating protease, C1r.  

PubMed

The serine protease, C1r, initiates activation of the classical pathway of complement, which is a crucial innate defense mechanism against pathogens and altered-self cells. C1r both autoactivates and subsequently cleaves and activates C1s. Because complement is implicated in many inflammatory diseases, an understanding of the interaction between C1r and its target substrates is required for the design of effective inhibitors of complement activation. Examination of the active site specificity of C1r using phage library technology revealed clear specificity for Gln at P2 and Ile at P1', which are found in these positions in physiological substrates of C1r. Removal of one or both of the Gln at P2 and Ile at P1' in the C1s substrate reduced the rate of C1r activation. Substituting a Gln residue into the P2 of the activation site of MASP-3, a protein with similar domain structure to C1s that is not normally cleav