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1

NASA Astrophysics Data System (ADS)

This paper presents an approach to characterize the uncertainty associated with the state vector obtained from the Herrick-Gibbs orbit determination approach using transformation of variables. The approach is applied to estimate the state vector and its probability density function for objects in low Earth orbit using sparse observations. The state vector and associated uncertainty estimates are computed in Cartesian coordinates and Keplerian elements. The approach is then extended to accommodate the J_2 perturbation where the state vector is written in terms of mean orbital elements. The results obtained from the analytical approach presented in this paper are validated using Monte Carlo simulations and compared with the often utilized similarity transformation for Kepler, mean, and nonsingular elements. The measurement uncertainty characterization obtained is used to initialize conventional nonlinear filters as well as operate a Bayesian approach for orbit determination and object tracking.

Weisman, R. M.; Majji, M.; Alfriend, K. T.

2014-01-01

2

Performance Evaluation of Orbit Determination System during Initial Phase of INSAT-3 Mission

NASA Astrophysics Data System (ADS)

INSAT-3C is the second in the third generation of ISRO's INSAT series of satellites that was launched by ARIANE-SPACE on 23 January 2002 at 23 h 46 m 57 s (lift off time in U.T). The ARIANE-4 Flight Nr.147 took off from Kourou in French Guyana and injected the 2750-kg communications satellite in a geostationary transfer orbit of (571 X 35935) km with an inclination of 4.007 deg at 00 h 07 m 48 s U.T on 24 January 2002 (1252 s after lift off). The satellite was successfully guided into its intended geostationary position of 74 deg E longitude by 09 February 2002 after a series of four firings of its Liquid Apogee Motor (LAM) and four station acquisition (STAQ) maneuvers. Six distinct phases of the mission were categorized based on the orbit characteristics of the INSAT- 3C mission, namely, the pre-launch phase, the launch phase, transfer orbit phase, intermediate orbit phase, drift orbit phase and synchronous orbit phase. The orbit with a perigee height of 571 km at injection of the satellite, was gradually raised to higher orbits with perigee height increasing to 9346 km after Apogee Motor Firing #1 (AMF #1), 18335 km after AMF #2, 32448 km after AMF #3 and 35493 km after AMF #4. The North and South solar panels and the reflectors were deployed at this stage of the mission and the attitude of the satellite with respect to the three axes was stabilized. The Orbit Determination System (ODS) that was used in the initial phase of the mission played a crucial role in realizing the objectives of the mission. This system which consisted of Tracking Data Pre-Processing (TDPP) software, Ephemeris Generation (EPHGEN) software and the Orbit Determination (OD) software, performed rigorously and its results were used for planning the AMF and STAQ strategies with a greater degree of accuracy. This paper reports the results of evaluation of the performance of the apogee-motor firings employed to place the satellite in its intended position where it is collocated with INSAT-1D satellite. The orbit of the satellite had to be determined continuously at each stage of the initial phase of the mission at a brisk pace and this study shows that the ODS provided consistent results to meet the stringent requirements of the mission operations. At each stage of the mission the orbit was determined using tracking data obtained over varying periods of time. The orbit solutions obtained from short arc OD's are compared with that obtained using the longest arc OD of each stage of the initial phase of the mission. The results of this study have been tabled in this paper. The performance of the ODS in calibrating the ARIANE-4 launch vehicle has been analyzed. A comparison of the orbit elements obtained from the mission operational ODS with the injection parameters provided by CNES, Centre Spatial Guyanais has been made in this paper which shows that the satellite was injected well within the 1 dispersions quoted by ARIANE-SPACE. A comparison has also been shown between the determined transfer orbit elements with pre-launch nominal orbit elements. For the initial phase of this mission ranging support was provided by Hassan earth station at India and INMARSAT network of stations at LakeCowichan (Canada), Fucino (Italy) and Beijing (China). The performance of the tracking systems employed by these stations has been studied. The quality of tracking data obtained from these stations has also been assessed.

Subramanian, B.; Vighnesam, N. V.

3

Orbit determination for near real time monitoring of satellite movement based on limited observations is discussed. For geostationary satellites this early orbit determination requirement arises after injection into geostationary transfer orbit, apogee motor firing, and larger orbit maneuvers during the on-station phase. Early orbit determination is hampered by the limited amount of data caused by nonavailability of the tracking system.

S. Pallaschke

1986-01-01

4

Initial results of precise orbit and clock determination for COMPASS navigation satellite system

NASA Astrophysics Data System (ADS)

The development of the COMPASS satellite system is introduced, and the regional tracking network and data availability are described. The precise orbit determination strategy of COMPASS satellites is presented. Data of June 2012 are processed. The obtained orbits are evaluated by analysis of post-fit residuals, orbit overlap comparison and SLR (satellite laser ranging) validation. The RMS (root mean square) values of post-fit residuals for one month's data are smaller than 2.0 cm for ionosphere-free phase measurements and 2.6 m for ionosphere-free code observations. The 48-h orbit overlap comparison shows that the RMS values of differences in the radial component are much smaller than 10 cm and those of the cross-track component are smaller than 20 cm. The SLR validation shows that the overall RMS of observed minus computed residuals is 68.5 cm for G01 and 10.8 cm for I03. The static and kinematic PPP solutions are produced to further evaluate the accuracy of COMPASS orbit and clock products. The static daily COMPASS PPP solutions achieve an accuracy of better than 1 cm in horizontal and 3 cm in vertical. The accuracy of the COMPASS kinematic PPP solutions is within 1-2 cm in the horizontal and 4-7 cm in the vertical. In addition, we find that the COMPASS kinematic solutions are generally better than the GPS ones for the selected location. Furthermore, the COMPASS/GPS combinations significantly improve the accuracy of GPS only PPP solutions. The RMS values are basically smaller than 1 cm in the horizontal components and 3-4 cm in the vertical component.

Zhao, Qile; Guo, Jing; Li, Min; Qu, Lizhong; Hu, Zhigang; Shi, Chuang; Liu, Jingnan

2013-05-01

5

In-Orbit Initialization Phase.

National Technical Information Service (NTIS)

The initialization of the onboard real time attitude determination loop of the Hipparcos satellite is presented. It initializes the autonomous onboard operation of the payload functions. The normal mode real time attitude determination processing is summa...

J. Vanderha

1989-01-01

6

ICESat Precision Orbit Determination

NASA Astrophysics Data System (ADS)

Following the successful launch of the Ice, Cloud and land Elevation Satellite (ICESat) on January 13, 2003, 00:45 UTC, the GPS receiver on ICESat was turned on successfully on Jan. 17, 2003. High quality GPS data were collected since then to support Precision Orbit Determination (POD) activities. ICESat carries Geoscience Laser Altimeter System (GLAS) to measure ice-sheet topography and associated temporal changes, as well as cloud and atmospheric properties. To accomplish the ICESat science objectives, the position of the GLAS instrument in space should be determined with an accuracy of 5 cm and 20 cm in radial and horizontal components, respectively. This knowledge is acquired by the POD activities using the data collected by the GPS receiver on ICESat and the ground-based satellite laser ranging (SLR) data. It has been shown from pre-launch POD studies that the gravity model error is the dominant source of ICESat orbit errors. The predicted radial orbit errors at the ICESat orbit (600 km altitude) based on pre-launch gravity models, such as TEG-4 and EGM-96, are 7-15 cm. Performance of these gravity models and the recent gravity models from GRACE on ICESat POD were evaluated. The radial orbit accuracy is approaching 1-2 cm level with the GRACE gravity model. This paper also summarizes POD activities at Center for Space Research (CSR), which is responsible to generate ICESat POD products.

Rim, H.; Yoon, S.; Webb, C. E.; Kim, Y.; Schutz, B. E.

2003-12-01

7

Lunar Reconnaissance Orbiter Orbit Determination Accuracy Analysis

NASA Technical Reports Server (NTRS)

Results from operational OD produced by the NASA Goddard Flight Dynamics Facility for the LRO nominal and extended mission are presented. During the LRO nominal mission, when LRO flew in a low circular orbit, orbit determination requirements were met nearly 100% of the time. When the extended mission began, LRO returned to a more elliptical frozen orbit where gravity and other modeling errors caused numerous violations of mission accuracy requirements. Prediction accuracy is particularly challenged during periods when LRO is in full-Sun. A series of improvements to LRO orbit determination are presented, including implementation of new lunar gravity models, improved spacecraft solar radiation pressure modeling using a dynamic multi-plate area model, a shorter orbit determination arc length, and a constrained plane method for estimation. The analysis presented in this paper shows that updated lunar gravity models improved accuracy in the frozen orbit, and a multiplate dynamic area model improves prediction accuracy during full-Sun orbit periods. Implementation of a 36-hour tracking data arc and plane constraints during edge-on orbit geometry also provide benefits. A comparison of the operational solutions to precision orbit determination solutions shows agreement on a 100- to 250-meter level in definitive accuracy.

Slojkowski, Steven E.

2014-01-01

8

Interplanetary orbit determination

NASA Technical Reports Server (NTRS)

The logistical aspects of orbit determination (OD) in the interplanetary phase of the Mariner Mars 1971 mission are described and the working arrangements for the OD personnel, both within the Navigation Team and with outside groups are given. Various types of data used in the OD process are presented along with sources of the data. Functional descriptions of the individual elements of the OD software and brief sketches of their modes of operation are provided.

Zielenbach, J. W.; Acton, C. H.; Born, G. H.; Breckenridge, W. G.; Chao, C. C.; Duxbury, T. C.; Green, D. W.; Jerath, N.; Jordan, J. F.; Mottinger, N. A.

1973-01-01

9

Voyager orbit determination at Jupiter

This paper summarizes the Voyager 1 and Voyager 2 orbit determination activity extending from encounter minus 60 days to the Jupiter encounter, and includes quantitative results and conclusions derived from mission experiences. The major topics covered include an identification and quantification of the major orbit determination error sources and a review of salient orbit determination results from encounter, with emphasis

J. K. Campbell; S. P. Synnott; G. J. Bierman

1983-01-01

10

Voyager orbit determination at Jupiter

This paper summarizes the Voyager 1 and Voyager 2 orbit determination activity extending from encounter minus 60 days to the Jupiter encounter, and includes quantitative results and conclusions derived from mission experience. The major topics covered include an identifica- tion and quantification of the major orbit determination error sources and a review of salient orbit determination results from encounter, with

JAMES K. CAMPBELL; STEPHEN P. SYNNOTT; GERALD J. BIERMAN

1983-01-01

11

Voyager orbit determination at Jupiter

NASA Technical Reports Server (NTRS)

This paper summarizes the Voyager 1 and Voyager 2 orbit determination activity extending from encounter minus 60 days to the Jupiter encounter, and includes quantitative results and conclusions derived from mission experiences. The major topics covered include an identification and quantification of the major orbit determination error sources and a review of salient orbit determination results from encounter, with emphasis on the Jupiter approach phase orbit determination. Special attention is paid to the use of combined spacecraft-based optical observations and earth-based radiometric observations to achieve accurate orbit determination during the Jupiter encounter approach phase.

Campbell, J. K.; Synnott, S. P.; Bierman, G. J.

1983-01-01

12

Orbit Determination of the Lunar Reconnaissance Orbiter

NASA Technical Reports Server (NTRS)

We present the results on precision orbit determination from the radio science investigation of the Lunar Reconnaissance Orbiter (LRO) spacecraft. We describe the data, modeling and methods used to achieve position knowledge several times better than the required 50-100m (in total position), over the period from 13 July 2009 to 31 January 2011. In addition to the near-continuous radiometric tracking data, we include altimetric data from the Lunar Orbiter Laser Altimeter (LOLA) in the form of crossover measurements, and show that they strongly improve the accuracy of the orbit reconstruction (total position overlap differences decrease from approx.70m to approx.23 m). To refine the spacecraft trajectory further, we develop a lunar gravity field by combining the newly acquired LRO data with the historical data. The reprocessing of the spacecraft trajectory with that model shows significantly increased accuracy (approx.20m with only the radiometric data, and approx.14m with the addition of the altimetric crossovers). LOLA topographic maps and calibration data from the Lunar Reconnaissance Orbiter Camera were used to supplement the results of the overlap analysis and demonstrate the trajectory accuracy.

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

2011-01-01

13

NASA Astrophysics Data System (ADS)

Precise orbit determination (POD) is a key factor to enable phase referencing observations with Astro-G. A POD accuracy of 30 cm is required for efficient X-band phase referencing observations, accuracy of 6 cm for K-band observations, and accuracy of 3 cm for Q-band observations. For the POD, Astro-G will be equipped with a GPS/Galileo receiver and a SLR (Satellite Laser Ranging) retroreflector array. Four POD antennas will be equipped on four sides of the satellite body, to cover all directions. The SLR will be used as a complement to the GPS at middle-to-high altitude. Because the refroreflector array should always face to the Earth direction, it will be set up on the Ka-link antenna gimbal. The most significant perturbing force for the Astro-G is solar radiation pressure (SRP). The reflectivity of each surface component should be preliminary measured in detail to model the SRP. The estimated achievable POD accuracy at apogee is 10 ˜ 30 cm in nominal case. Phase referencing observations in K- or Q-band can be performed if the enough amount of SLR tracking data can be obtained at high altitudes.

Takeuchi, H.; VSOP-2 Orbit Determination Sub-Working Group

2009-08-01

14

Spitzer Orbit Determination During In-orbit Checkout Phase

NASA Technical Reports Server (NTRS)

The Spitzer Space Telescope was injected into heliocentric orbit on August 25, 2003 to observe and study astrophysical phenomena in the infrared range of frequencies. The initial 60 days was dedicated to Spitzer's "In-Orbit Checkout (IOC)" efforts. During this time high levels of Helium venting were used to cool down the telescope. Attitude control was done using reaction wheels, which in turn were de-saturated using cold gas Nitrogen thrusting. Dense tracking data (nearly continuous) by the Deep Space network (DSN) were used to perform orbit determination and to assess any possible venting imbalance. Only Doppler data were available for navigation. This paper deals with navigation efforts during the IOC phase. It includes Dust Cover Ejection (DCE) monitoring, orbit determination strategy validation and results and assessment of non-gravitational accelerations acting on Spitzer including that due to possible imbalance in Helium venting.

Menon, Premkumar R.

2004-01-01

15

Orbit Determination Issues for Libration Point Orbits

NASA Technical Reports Server (NTRS)

Libration point mission designers require knowledge of orbital accuracy for a variety of analyses including station keeping control strategies, transfer trajectory design, and formation and constellation control. Past publications have detailed orbit determination (OD) results from individual libration point missions. This paper collects both published and unpublished results from four previous libration point missions (ISEE (International Sun-Earth Explorer) -3, SOHO (Solar and Heliospheric Observatory), ACE (Advanced Composition Explorer) and MAP (Microwave Anisotropy Probe)) supported by Goddard Space Flight Center's Guidance, Navigation & Control Center. The results of those missions are presented along with OD issues specific to each mission. All past missions have been limited to ground based tracking through NASA ground sites using standard range and Doppler measurement types. Advanced technology is enabling other OD options including onboard navigation using seaboard attitude sensors and the use of the Very Long Baseline Interferometry (VLBI) measurement Delta Differenced One-Way Range (DDOR). Both options potentially enable missions to reduce coherent dedicated tracking passes while maintaining orbital accuracy. With the increased projected loading of the DSN (Deep Space Network), missions must find alternatives to the standard OD scenario.

Beckman, Mark; Bauer, Frank (Technical Monitor)

2002-01-01

16

Orbit Determination Issues for Libration Point Orbits

NASA Technical Reports Server (NTRS)

Libration point mission designers require knowledge of orbital accuracy for a variety of analyses including station keeping control strategies, transfer trajectory design, and formation and constellation control. Past publications have detailed orbit determination (OD) results from individual notation point missions. This paper collects both published and unpublished results from four previous notation point missions (ISEE-3, SOHO, ACE and MAP) supported by Goddard Space Flight Center's Guidance, Navigation & Control Center. The results of those missions are presented along with OD issues specific to each mission. All past missions have been limited to ground based tracking through NASA ground sites using standard marine and Doppler measurement types. Advanced technology is enabling other OD options including onboard navigation using onboard attitude sensors and the use of the Very Long Baseline Interferometry (VLBI) measurement Delta Differenced One-Way Range (DDOR). Both options potentially enable missions to reduce coherent dedicated tracking passes while maintaining orbital accuracy. With the increased projected loading of the DSN, missions must find alternatives to the standard OD scenario.

Beckman, Mark; Bauer, Frank (Technical Monitor)

2002-01-01

17

Mars Observer orbit determination analysis

NASA Technical Reports Server (NTRS)

Results are presented of a simulated orbit determination analysis for three phases of the Mars Observer mission (interplanetary cruise, orbit insertion, and mapping), together with a summary of orbital accuracies throughout the Mars Observer mission. The plan for achieving the navigation objectives of the Mars Observer mission is described. These objectives are to navigate the Mars Observer spacecraft to Mars and achieve accurate targeting at Mars; to propulsively maneuver the spacecraft into a 3-day period, capture orbit; to navigate the spacecraft into a 1.96-hr period low-altitude, nearly circular mapping orbit; and to maintain Mars Observer in the mapping orbit throughout the 687 days devoted for scientific data acquisition. Factors that will affect the spacecraft during each of the three phases are discussed.

Esposito, Pasquale; Roth, Duane; Demcak, Stuart

1991-01-01

18

Mars Observer orbit determination analysis

NASA Astrophysics Data System (ADS)

Results are presented of a simulated orbit determination analysis for three phases of the Mars Observer mission (interplanetary cruise, orbit insertion, and mapping), together with a summary of orbital accuracies throughout the Mars Observer mission. The plan for achieving the navigation objectives of the Mars Observer mission is described. These objectives are to navigate the Mars Observer spacecraft to Mars and achieve accurate targeting at Mars; to propulsively maneuver the spacecraft into a 3-day period, capture orbit; to navigate the spacecraft into a 1.96-hr period low-altitude, nearly circular mapping orbit; and to maintain Mars Observer in the mapping orbit throughout the 687 days devoted for scientific data acquisition. Factors that will affect the spacecraft during each of the three phases are discussed.

Esposito, Pasquale; Roth, Duane; Demcak, Stuart

1991-10-01

19

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

20

Choosing the Initial LISA Orbital Configuration

NASA Astrophysics Data System (ADS)

The Laser Interferometer Space Antenna (LISA) mission proposes to detect gravitational radiation by synthesizing one or more interferometric gravitational wave detectors from fringe velocity measurements generated by chances in the light travel time between three spacecraft in a special set of drag-free, circumsolar orbits. Once the spacecraft are set in their orbits the orientation of the LISA interferometers at any further time is fixed by the Kepler Laws and the initial orientation of the spacecraft constellation. The initial orientation does not affect those locations on the sky where LISA has greatest sensitivity to gravitational waves; however, it does affect those locations where nulls in the LISA response to gravitational waves fall. By artful choice of the LISA initial orientation we can thus choose to optimize LISA's sensitivity to sources or groups of sources whose location (eg., the galactic center or plane, nearby globular cluster, etc.) may be known in advance. )

Jani, Karan; Finn, Lee Samuel; Benacquista, Mathew

2010-02-01

21

Lunar Reconnaissance Orbiter Orbit Determination Accuracy Analysis

NASA Technical Reports Server (NTRS)

LRO definitive and predictive accuracy requirements were easily met in the nominal mission orbit, using the LP150Q lunar gravity model. center dot Accuracy of the LP150Q model is poorer in the extended mission elliptical orbit. center dot Later lunar gravity models, in particular GSFC-GRAIL-270, improve OD accuracy in the extended mission. center dot Implementation of a constrained plane when the orbit is within 45 degrees of the Earth-Moon line improves cross-track accuracy. center dot Prediction accuracy is still challenged during full-Sun periods due to coarse spacecraft area modeling - Implementation of a multi-plate area model with definitive attitude input can eliminate prediction violations. - The FDF is evaluating using analytic and predicted attitude modeling to improve full-Sun prediction accuracy. center dot Comparison of FDF ephemeris file to high-precision ephemeris files provides gross confirmation that overlap compares properly assess orbit accuracy.

Slojkowski, Steven E.

2014-01-01

22

Low thrust orbit determination program

NASA Technical Reports Server (NTRS)

Logical flow and guidelines are provided for the construction of a low thrust orbit determination computer program. The program, tentatively called FRACAS (filter response analysis for continuously accelerating spacecraft), is capable of generating a reference low thrust trajectory, performing a linear covariance analysis of guidance and navigation processes, and analyzing trajectory nonlinearities in Monte Carlo fashion. The choice of trajectory, guidance and navigation models has been made after extensive literature surveys and investigation of previous software. A key part of program design relied upon experience gained in developing and using Martin Marietta Aerospace programs: TOPSEP (Targeting/Optimization for Solar Electric Propulsion), GODSEP (Guidance and Orbit Determination for SEP) and SIMSEP (Simulation of SEP).

Hong, P. E.; Shults, G. L.; Huling, K. R.; Ratliff, C. W.

1972-01-01

23

Research on orbit determination with sparse data of electronic fence

NASA Astrophysics Data System (ADS)

Based on the comprehension of Lambert function and spacial geometry , the orbit determination method is developed by using sparse data of Electronic Fence. According to the simulation of massive objects, the process of orbit improvement is successfully converged by taking the initial orbit elements provided by the method, and the orbit determination precision is better than 100m. The method is so proved to be effective for the overwhelming majority of objects. At last, it is discussed that the station latitude of the Electronic Fence may effect on orbit determination.

Cao, Z. B.; Xu, J.; Ma, J. B.; Hu, W. D.; Fang, A. L.

2008-10-01

24

Calibration effects on orbit determination

NASA Technical Reports Server (NTRS)

The effects of charged particle and tropospheric calibrations on the orbit determination (OD) process are analyzed. The calibration process consisted of correcting the Doppler observables for the media effects. Calibrated and uncalibrated Doppler data sets were used to obtain OD results for past missions as well as Mariner Mars 1971. Comparisons of these Doppler reductions show the significance of the calibrations. For the MM'71 mission, the media calibrations proved themselves effective in diminishing the overall B-plane error and reducing the Doppler residual signatures.

Madrid, G. A.; Winn, F. B.; Zielenbach, J. W.; Yip, K. B.

1974-01-01

25

Orbit determination for ISRO satellite missions

Indian Space Research Organisation (ISRO) has been successful in using the in-house developed orbit determination and prediction software for satellite missions of Bhaskara, Rohini and APPLE. Considering the requirements of satellite missions, software packages are developed, tested and their accuracies are assessed. Orbit determination packages developed are SOIP, for low earth orbits of Bhaskara and Rohini missions, ORIGIN and ODPM,

Ch. Sreehari Rao; S. K. Sinha

1985-01-01

26

Orbit determination by genetic algorithm and application to GEO observation

NASA Astrophysics Data System (ADS)

This paper demonstrates an initial orbit determination method that solves the problem by a genetic algorithm using two well-known solutions for the Lambert's problem: universal variable method and Battin method. This paper also suggests an intuitive error evaluation method in terms of rotational angle and orbit shape by separating orbit elements into two groups. As reference orbit, mean orbit elements (original two-lines elements) and osculating orbit elements considering the J2 effect are adopted and compared. Our proposed orbit determination method has been tested with actual optical observations of a geosynchronous spacecraft. It should be noted that this demonstration of the orbit determination is limited to one test case. This observation was conducted during approximately 70 min on 2013/05/15 UT. Our method was compared with the orbit elements propagated by SGP4 using the TLE of the spacecraft. The result indicates that our proposed method had a slightly better performance on estimating orbit shape than Gauss's methods and Escobal's method by 120 km. In addition, the result of the rotational angle is closer to the osculating orbit elements than the mean orbit elements by 0.02°, which supports that the estimated orbit is valid.

Hinagawa, Hideaki; Yamaoka, Hitoshi; Hanada, Toshiya

2014-02-01

27

Circular orbits and spin in black-hole initial data

The construction of initial data for black-hole binaries usually involves the choice of free parameters that define the spins of the black holes and essentially the eccentricity of the orbit. Such parameters must be chosen carefully to yield initial data with the desired physical properties. In this paper, we examine these choices in detail for the quasiequilibrium method coupled to apparent-horizon/quasiequilibrium boundary conditions. First, we compare two independent criteria for choosing the orbital frequency, the 'Komar-mass condition' and the 'effective-potential method', and find excellent agreement. Second, we implement quasilocal measures of the spin of the individual holes, calibrate these with corotating binaries, and revisit the construction of nonspinning black-hole binaries. Higher-order effects, beyond those considered in earlier work, turn out to be important. Without those, supposedly nonspinning black holes have appreciable quasilocal spin; furthermore, the Komar-mass condition and effective-potential method agree only when these higher-order effects are taken into account. We compute a new sequence of quasicircular orbits for nonspinning black-hole binaries, and determine the innermost stable circular orbit of this sequence.

Caudill, Matthew; Cook, Gregory B.; Grigsby, Jason D.; Pfeiffer, Harald P. [Department of Physics, Wake Forest University, Winston-Salem, North Carolina 27109 (United States); Theoretical Astrophysics, California Institute of Technology, Pasadena, California 91125 (United States)

2006-09-15

28

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

29

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

30

Determination of GPS orbits to submeter accuracy

NASA Technical Reports Server (NTRS)

Orbits for satellites of the Global Positioning System (GPS) were determined with submeter accuracy. Tests used to assess orbital accuracy include orbit comparisons from independent data sets, orbit prediction, ground baseline determination, and formal errors. One satellite tracked 8 hours each day shows rms error below 1 m even when predicted more than 3 days outside of a 1-week data arc. Differential tracking of the GPS satellites in high Earth orbit provides a powerful relative positioning capability, even when a relatively small continental U.S. fiducial tracking network is used with less than one-third of the full GPS constellation. To demonstrate this capability, baselines of up to 2000 km in North America were also determined with the GPS orbits. The 2000 km baselines show rms daily repeatability of 0.3 to 2 parts in 10 to the 8th power and agree with very long base interferometry (VLBI) solutions at the level of 1.5 parts in 10 to the 8th power. This GPS demonstration provides an opportunity to test different techniques for high-accuracy orbit determination for high Earth orbiters. The best GPS orbit strategies included data arcs of at least 1 week, process noise models for tropospheric fluctuations, estimation of GPS solar pressure coefficients, and combine processing of GPS carrier phase and pseudorange data. For data arc of 2 weeks, constrained process noise models for GPS dynamic parameters significantly improved the situation.

Bertiger, W. I.; Lichten, S. M.; Katsigris, E. C.

1988-01-01

31

Galileo Probe delivery and Orbiter approach orbit determination

NASA Technical Reports Server (NTRS)

The configuration of the Galileo mission, in which the Probe and Orbiter are joined as a single spacecraft (until five months before Jupiter encounter, when the Probe will be released into the atmosphere for the Io flyby) is discussed, together with the major mission objectives, and the aspects of the trajectory. Special attention is given to the descriptions of the orbit determination process, error source assumptions (based on the Voyager experience at Jupiter), and data assumptions. The orbit determination results for the interplanetary and Jupiter approach phases of the mission for the previously planned launch in 1986 are presented, together with the preliminary results of navigation studies of the current mission scheduled for a launch for late 1989.

Kenyon, P. R.; Moultrie, B.; Kechichian, J. A.; Nicholson, F. T.

1987-01-01

32

Reducing orbital eccentricity in initial data of binary neutron stars

We develop a method to compute low-eccentricity initial data of binary neutron stars required to perform realistic simulations in numerical relativity. The orbital eccentricity is controlled by adjusting the orbital angular velocity of a binary and incorporating an approaching relative velocity of the neutron stars. These modifications improve the solution primarily through the hydrostatic equilibrium equation for the binary initial data. The orbital angular velocity and approaching velocity of initial data are updated iteratively by performing time evolutions over ~3 orbits. We find that the eccentricity can be reduced by an order of magnitude compared to standard quasicircular initial data, specifically from ~0.01 to <~0.001, by three successive iterations for equal-mass binaries leaving ~10 orbits before the merger.

Koutarou Kyutoku; Masaru Shibata; Keisuke Taniguchi

2014-05-23

33

Reducing orbital eccentricity in initial data of binary neutron stars

NASA Astrophysics Data System (ADS)

We develop a method to compute low-eccentricity initial data of binary neutron stars required to perform realistic simulations in numerical relativity. The orbital eccentricity is controlled by adjusting the orbital angular velocity of a binary and incorporating an approaching relative velocity of the neutron stars. These modifications improve the solution primarily through the hydrostatic equilibrium equation for the binary initial data. The orbital angular velocity and approaching velocity of initial data are updated iteratively by performing time evolutions over ˜3 orbits. We find that the eccentricity can be reduced by an order of magnitude compared to standard quasicircular initial data, specifically from ˜0.01 to ?0.001, by three successive iterations for equal-mass binaries leaving ˜10 orbits before the merger.

Kyutoku, Koutarou; Shibata, Masaru; Taniguchi, Keisuke

2014-09-01

34

Spacecraft orbit determination using GPS navigation solutions

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

35

Orbit determination using synthetic aperture radar

The use of synthetic aperture radar (SAR) images to estimate orbital parameters is studied. The SAR image formation process which requires the ability to repeatedly transmit identical signals and accurately sense the return echoes from a region of terrain is described. The orbit determination capabilities of the SAR system's observables are investigated. Five SAR observations were collected from a simulated

W. L. Taber; S. P. Synnott; J. E. Riedel

1986-01-01

36

Modeling issues in precision orbit determination for Mars orbiter

NASA Technical Reports Server (NTRS)

This paper examines the accuracy of recent Mars gravity models and the importance of perturbations due to the Mars radiation pressure and the Martian moons, Phobos and Deimos, on the trajectories of Mars orbiters. A linear orbit perturbation theory is used to characterize the patterns of gravity field near resonances for the Viking and Mariner 9 spacecraft. These resonances are shown to have considerable power and their potential for contributing to Mars gravity solutions is emphasized. It is shown that some of the same resonance orders which appear in the Viking orbits, dominate the radial orbit error spectrum for Mars Observer. Results of orbit determination simulations at the Goddard Space Flight Center show that the perturbations caused by the Martian moons and the Mars radiation pressure are larger than 0.1 mm/s, the expected precision of the Mars Observer Doppler tracking data. Tests with the Viking Doppler data indicate that best analysis of these data mandates the inclusion of the Phobos gravitational perturbation in the modeling of Viking spacecraft trajectories.

Lemoine, Frank G.; Rosborough, George W.; Smith, David E.

1990-01-01

37

NASA Technical Reports Server (NTRS)

The Chandra X-ray Observatory (CXO, formerly AXAF) is the third of the four NASA great observatories. It was launched from Kennedy Space Flight Center on 23 July 1999 aboard the Space Shuttle Columbia and was successfully inserted in a 330 x 72,000 km orbit by the Inertial Upper Stage (IUS). Through a series of five Integral Propulsion System burns, CXO was placed in a 10,000 x 139,000 km orbit. After initial on-orbit checkout, Chandra's first light images were unveiled to the public on 26 August, 1999. The CXO Pointing Control and Aspect Determination (PCAD) subsystem is designed to perform attitude control and determination functions in support of transfer orbit operations and on-orbit science mission. After a brief description of the PCAD subsystem, the paper highlights the PCAD activities during the transfer orbit and initial on-orbit operations. These activities include: CXO/IUS separation, attitude and gyro bias estimation with earth sensor and sun sensor, attitude control and disturbance torque estimation for delta-v burns, momentum build-up due to gravity gradient and solar pressure, momentum unloading with thrusters, attitude initialization with star measurements, gyro alignment calibration, maneuvering and transition to normal pointing, and PCAD pointing and stability performance.

Quast, Peter; Tung, Frank; West, Mark; Wider, John

2000-01-01

38

Mars Exploration Rover cruise orbit determination

NASA Technical Reports Server (NTRS)

This paper will describe the results of the orbit determination process for each mission, MER-A and MER-B, during their cruise phase to Mars ending with there final approach to Mars atmospheric entry.

Portock, Brian; Baird, Darren; Graat, Eric; McElrath, Tim; Watkins, Michael; Wawrzyniak, Geoff

2004-01-01

39

Orbit determination for next generation space clocks

NASA Astrophysics Data System (ADS)

We study the requirements on orbit determination compatible with operation of next generation space clocks at their expected uncertainty. Using the ACES (Atomic Clock Ensemble in Space) mission as an example, we develop a relativistic model for time and frequency transfer to investigate the effects of orbit determination errors. For the orbit error models considered we show that the required uncertainty goal can be reached with relatively modest constraints on the orbit determination of the space clock, which are significantly less stringent than expected from “naive” estimates. Our results are generic to all space clocks and represent a significant step towards the generalized use of next generation space clocks in fundamental physics, geodesy, and time/frequency metrology.

Duchayne, L.; Mercier, F.; Wolf, P.

2009-09-01

40

Orbit determination methods in view of the PODET project

NASA Astrophysics Data System (ADS)

We present an orbit determination method based on genetic algorithms. Contrary to usual estimation methods mainly based on least-squares methods, these algorithms do not require any a priori knowledge of the initial state vector to be estimated. These algorithms can be applied when a new satellite is launched or for uncatalogued objects We show in this paper preliminary results obtained from an SLR satellite, for which tracking data acquired by the ILRS network enable to build accurate orbital arcs at a few centimeter level, which can be used as a reference orbit. The method is carried out in several steps: (i) an analytical propagation of the equations of motion, (ii) an estimation kernel based on genetic algorithms, which follows the usual steps of such approaches: initialization and evolution of a selected population, so as to determine the best parameters. Each parameter to be estimated, namely each initial keplerian element, has to be searched among an interval that is preliminary chosen.

Deleflie, F.; Coulot, D.; Decosta, R.; Richard, P.

2013-11-01

41

The GEOS-3 orbit determination investigation

NASA Technical Reports Server (NTRS)

The nature and improvement in satellite orbit determination when precise altimetric height data are used in combination with conventional tracking data was determined. A digital orbit determination program was developed that could singly or jointly use laser ranging, C-band ranging, Doppler range difference, and altimetric height data. Two intervals were selected and used in a preliminary evaluation of the altimeter data. With the data available, it was possible to determine the semimajor axis and eccentricity to within several kilometers, in addition to determining an altimeter height bias. When used jointly with a limited amount of either C-band or laser range data, it was shown that altimeter data can improve the orbit solution.

Pisacane, V. L.; Eisner, A.; Yionoulis, S. M.; Mcconahy, R. J.; Black, H. D.; Pryor, L. L.

1978-01-01

42

Precise Orbit Determination for Altimeter Satellites

Orbit error remains a critical component in the error budget for all radar altimeter missions. This paper describes the ongoing work at GSFC to improve orbits for three radar altimeter satellites: TOPEX\\/POSEIDON (T\\/P), Jason, and Geosat Follow-On (GFO). T\\/P has demonstrated that, the time variation of ocean topography can be determined with an accuracy of a few centimeters, thanks to

N. P. Zelensky; S. B. Luthcke; D. D. Rowlands; F. G. Lemoine; B. B. Beckley; Y. Wang; D. S. Chinn

2002-01-01

43

Precision orbit determination for TOPEX/POSEIDON

NASA Technical Reports Server (NTRS)

The TOPEX/POSEIDON mission objective requires that the radial position of the spacecraft be determined with an accuracy better than 13 cm RMS (root mean square). This stringent requirement is an order of magnitude below the accuracy achieved for any altimeter mission prior to the definition of the TOPEX/POSEIDON mission. To satislfy this objective, the TOPEX Precision Orbit determination (POD) Team was established as a joint effort between the NASA Goddard Space Flight Center and the University of Texas at Austin, with collaboration from the University of Colorado and the Jet Propulsion Laboratory. During the prelaunch development and the post launch verification phases, the POD team improved, calibrated, and validated the precision orbit determination computer software systems. The accomplishments include (1) increased accuracy of the gravity and surface force models and (2) improved peformance of both laser ranging and Doppler tracking systems. The result of these efforts led to orbit accuracies for TOPEX/POSEIDON which are significantly better than the original mission requirement. Tests based on data fits, covariance analysis, and orbit comparisons indicate that the radial component of the TOPEX/POSEIDON spacecraft is determined, relative to the Earth's mass center, with an root mean square (RMS) error in the range of 3 to 4 cm RMS. This orbit accuracy, together with the near continuous dual-frequency altimetry from this mission, provides the means to determine the ocean's dynamic topography with an unprecedented accuracy.

Tapley, B. D.; Ries, J. C.; Davis, G. W.; Eanes, R. J.; Schultz, B. E.; Shum, C. K.; Watkins, M. M.; Marshall, J. A.; Nerem, R. S.; Putney, B. H.

1994-01-01

44

Galilean satellite tour orbit determination assessment

NASA Technical Reports Server (NTRS)

Results are given which demonstrate the ability of the orbit determination system to satisfy accuracy requirements in support of the Galileo Project's planned tour of Jupiter's satellites. The results are derived through the application of mission operation strategies and assumptions. It is shown that the achievement of the requisite orbit determination accuracies is predicated on the availability of optical navigation data. It is further demonstrated that the unavailability of tour optical navigation data yields not only degraded orbit determination accuracies which fail to meet propellant budget and science instrument pointing requirements, but also produces, for the planned 200 km flyby of Europa, an approximate 0.02 risk of having the spacecraft collide with the satellite.

Moultrie, B.; Kenyon, P. R.; Kechichian, J. A.; Davis, R. P.; Nicholson, F. T.

1987-01-01

45

Mars Exploration Rovers orbit determination filter strategy

NASA Technical Reports Server (NTRS)

The successful delivery of the Mars Exploration Rover (MER) landers to well within the boundaries of their surface target areas in January of 2004 was the culmination of years of orbit determination analysis. The process began with a careful consideration of the filter parameters used for pre-launch covariance studies, and continued with the refinement of the filter after launch based on operational experience. At the same time, tools were developed to run a plethora of variations around the nominal filter and analyze the results in ways that had never been previously attempted for an interplanetary mission. In addition to achieving sub-kilometer Mars-relative orbit determination knowledge, the filter strategy and process detected unexpected error sources, while at the same time proving robust by indicating thecorrect solution. Consequently, MER orbit determination set a new standard for interplanetary navigation.

McElrath, Timothy P.; Watkins, Michael M.; Portock, Brian M.; Graat, Eric J; Baird, Darren T; Wawrzyniak, Geoffrey G.; Attiyah, Amy A.; Guinn, Joseph R.; Antreasian, Peter G.; Baalke, Ronald C.; Taber, William L.

2004-01-01

46

Mars Exploration Rovers orbit determination filter strategy

NASA Technical Reports Server (NTRS)

The successful delivery of the Mars Exploration Rover (MER) landers to well with in the boundaries of their surface target areas in January of 2004 was the culmination of years of orbit determination analysis. The process began with a careful consideration of the filter parameters used for pre-launch covariance studies, and continued with the refinement of the filter after launch based on operational experience. At the same time, tools were developed to run a plethora of variations around the nominal filter and anlyze the results in ways that had never been previously attempted for an interplanetary mission. In addition to the achieved sub-kilometer Mars B plane orbit determination knowledge, the filter strategy and process responded to unexpected error sources by both detecting them and proving robust. All these facets of the MER orbit determination filter strategy are described in this paper.

McElrath, Tim; Watkins, Michael L.; Portock, Brian; Graat, Eric; Baird, Darren; Wawrzyniak, Geoffrey; Guinn, Joseph; Antreasian, Peter; Attiyah, Amy; Baalke, Ronald; Taber, William

2004-01-01

47

Real time orbit determination during apogee maneuvers

NASA Astrophysics Data System (ADS)

The use of bi-propellant thrusters, of low thrust level, for apogee boost maneuvers to determine, in real time during the thrust, the instantaneously obtained orbits is described. The accuracy of the orbit determination is sufficient to predict the optimum date of the cut off of the thruster, in order to minimize errors due to the thrust inaccuracy. The expected accuracy of such a procedure could simplify greatly the station acquisition phase, by shorter station acquisition duration; and all the maneuvers could be achieved in sight of the same stations, so the number of necessary stations could be reduced.

Belon, B.

48

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

49

Preliminary orbit determination for lunar satellites.

NASA Technical Reports Server (NTRS)

Methods for the determination of orbits of artificial lunar satellites from earth-based range rate measurements developed by Koskela (1964) and Bateman et al. (1966) are simplified and extended to include range measurements along with range rate measurements. For illustration, a numerical example is presented.

Lancaster, E. R.

1973-01-01

50

Precision Orbit Determination for the Lunar Reconnaissance Orbiter

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

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

2010-01-01

51

James Webb Space Telescope Orbit Determination Analysis

NASA Technical Reports Server (NTRS)

The James Webb Space Telescope (JWST) is designed to study and answer fundamental astrophysical questions from an orbit about the Sun-EarthMoon L2 libration point, 1.5 million km away from Earth. Three mid-course correction (MCC) maneuvers during launch and early orbit phase and transfer orbit phase are required for the spacecraft to reach L2. These three MCC maneuvers are MCC-1a at Launch+12 hours, MCC-1b at L+2.5 days and MCC-2 at L+30 days. Accurate orbit determination (OD) solutions are needed to support MCC maneuver planning. A preliminary analysis shows that OD performance with the given assumptions is adequate to support MCC maneuver planning. During the nominal science operations phase, the mission requires better than 2 cmsec velocity estimation performance to support stationkeeping maneuver planning. The major challenge to accurate JWST OD during the nominal science phase results from the unusually large solar radiation pressure force acting on the huge sunshield. Other challenges are stationkeeping maneuvers at 21-day intervals to keep JWST in orbit around L2, frequent attitude reorientations to align the JWST telescope with its targets and frequent maneuvers to unload momentum accumulated in the reaction wheels. Monte Carlo analysis shows that the proposed OD approach can produce solutions that meet the mission requirements.

Yoon, Sungpil; Rosales, Jose; Richon, Karen

2014-01-01

52

Tethered body problems and relative motion orbit determination

NASA Technical Reports Server (NTRS)

Selected problems dealing with orbiting tethered body systems have been studied. In addition, a relative motion orbit determination program was developed. Results from these tasks are described and discussed. The expected tethered body motions were examined, analytically, to ascertain what influence would be played by the physical parameters of the tether, the gravity gradient and orbit eccentricity. After separating the motion modes these influences were determined; and, subsequently, the effects of oscillations and/or rotations, on tether force, were described. A study was undertaken, by examining tether motions, to see what type of control actions would be needed to accurately place a mass particle at a prescribed position relative to a main vehicle. Other applications for tethers were studied. Principally these were concerned with the producing of low-level gee forces by means of stabilized tether configurations; and, the initiation of free transfer trajectories from tether supported vehicle relative positions.

Eades, J. B., Jr.; Wolf, H.

1972-01-01

53

Formation Flying In Highly Elliptical Orbits Initializing the Formation

NASA Technical Reports Server (NTRS)

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 Multiscale (MMS), Auroral Multiscale Midex (AMM), and Cluster is used as a test bed Such a formation provides full three degrees-of-freedom in the relative motion about the reference orbit and is germane to several missions. The type of maneuver strategy that can be employed depends on the specific initial conditions of each member of the formation. Single-impulse maneuvers based on a Gaussian variation-of-parameters (VOP) approach, while operationally simple and intuitively-based, work only in a limited sense for a special class of initial conditions. These 'tailored' initial conditions are characterized as having only a few of the Keplerian elements different from the reference orbit. Attempts to achieve more generic initial conditions exceed the capabilities of the single impulse VOP. For these cases, multiple-impulse implementations are always possible but are generally less intuitive than the single-impulse case. The four-impulse VOP formalism discussed by Schaub is examined but smaller delta-V costs are achieved in our test problem by optimizing a Lambert solution.

Mailhe, Laurie; Schiff, Conrad; Hughes, Steven

2000-01-01

54

On the atmospheric drag in orbit determination for low Earth orbit

NASA Astrophysics Data System (ADS)

The atmosphere model is always a major limitation for low Earth orbit (LEO) in orbit prediction and determination. The accelerometer can work around the non-gravitational perturbations in orbit determination, but it helps little to improve the atmosphere model or to predict the orbit. For certain satellites, there may be some specific software to handle the orbit problem. This solution can improve the orbit accuracy for both prediction and determination, yet it always contains empirical terms and is exclusive for certain satellites. This report introduces a simple way to handle the atmosphere drag for LEO, which does not depend on instantaneous atmosphere conditions and improves accuracy of predicted orbit. This approach, which is based on mean atmospheric density, is supported by two reasons. One is that although instantaneous atmospheric density is very complicated with time and height, the major pattern is determined by the exponential variation caused by hydrostatic equilibrium and periodic variation caused by solar radiation. The mean density can include the major variations while neglect other minor details. The other reason is that the predicted orbit is mathematically the result from integral and the really determinant factor is the mean density instead of instantaneous density for every time and spot. Using the mean atmospheric density, which is mainly determined by F10.7 solar flux and geomagnetic index, can be combined into an overall parameter B^{*} = C_{D}(S/m)?_{p_{0}}. The combined parameter contains several less accurate parameters and can be corrected during orbit determination. This approach has been confirmed in various LEO computations and an example is given below using Tiangong-1 spacecraft. Precise orbit determination (POD) is done using one-day GPS positioning data without any accurate a-priori knowledge on spacecraft or atmosphere conditions. Using the corrected initial state vector of the spacecraft and the parameter B^* from POD, the orbit is propagated to the end of the 11th day (including the first day for POD). It is found that this approach provides reasonable results that match the analytical accuracy. At the end of the 11th day, the along-track error increases to 20km following an approximate time-square law, while the radial error a few hundred meters, the normal error below 50 meters and both follow a mild linear law. The results show that with accurate observation, the mean atmospheric density processed with appropriate approach is sufficient to provide reasonably precise orbit in prediction and determination without having to acquire accurate atmosphere conditions. Once long arc becomes available, the parameter B^* can also be used to study its long-term variation (monthly or seasonal). This can be expected as an alternative way to improve orbit accuracy in prediction and determination for LEO.

Tang, Jingshi; Liu, Lin; Miao, Manqian

2012-07-01

55

Jason2 Precise Orbit Determination : current status and future improvements

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

Luca Cerri

2010-01-01

56

The JPL orbit determination software system

NASA Technical Reports Server (NTRS)

The Jet Propulsion Laboratory (JPL) orbit determination software system is described. Consisting of a set of computer programs, this system has been developed at JPL for the primary purpose of determining the flight path of deep-space mission spacecraft in NASA's planetary program. Secondary uses include science studies in celestial mechanics and extraterrestrial atmospherics. Attention is given to such features as the capability for processing 30 data types from up to 15 tracking stations, and for precise navigation to natural satellites of outer planets. In addition, the system contains models for such conditions as mascons, atmospheric drag, attitude control, and finite motor burns, to provide for extensive solve-on capabilities.

Ekelund, J. E.

1979-01-01

57

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

58

Mars Exploration Rover Cruise Orbit Determination

NASA Technical Reports Server (NTRS)

The Mars Exploration Rover project consisted of two missions (MER-A: spirit rover and MER-B: opportunity rover) that launched spacecraft on June 10, 2003, and July 8, 2003, respectively. The spacecraft arrived at Mars approximately seven months later on January 4, 2004, and January 24, 2004. These spacecraft needed to be precisely navigated to a Mars atmospheric entry flight path angle of -11.5 deg +/-0.12 deg (3(sigma)) for MER-A and +/-0.14 deg (3(sigma)) for MER-B in order to satisfy the landing site delivery requirements. The orbit determination task of the navigation team needed to accurately determine the trajectory of the spacecraft, predict the trajectory to Mars atmospheric entry, and account for all possible errors sources so that the each spacecraft could be correctly targeted using five trajectory corrections along the way. This paper describes the orbit determination analysis which allowed MER-A to be targeted using only four trajectory correction maneuvers to an entry flight path angle of -11.49 deg +/-O.010 deg (3(sigma)) and MER-B to be targeted using only three trajectory correction maneuvers to an entry flight path angle of -11.47 +/-0.021 deg(3(sigma)).

Portock, Brian; Baird, Darren; Graat, Eric; Guinn, Joseph; McElrath, Tim; Watkins, Michael

2004-01-01

59

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

60

Application of two special orbits in the orbit determination of lunar satellites

NASA Astrophysics Data System (ADS)

Using inter-satellite range data, the combined autonomous orbit determination problem of a lunar satellite and a probe on some special orbits is studied in this paper. The problem is firstly studied in the circular restricted three-body problem, and then generalized to the real force model of the Earth-Moon system. Two kinds of special orbits are discussed: collinear libration point orbits and distant retrograde orbits. Studies show that the orbit determination accuracy in both cases can reach that of the observations. Some important properties of the system are carefully studied. These findings should be useful in the future engineering implementation of this conceptual study.

Liu, Peng; Hou, Xi-Yun; Tang, Jing-Shi; Liu, Lin

2014-10-01

61

Orbit determination singularities in the Doppler tracking of a planetary orbiter

NASA Technical Reports Server (NTRS)

On a number of occasions, spacecraft launched by the U.S. have been placed into orbit about the moon, Venus, or Mars. It is pointed out that, in particular, in planetary orbiter missions two-way coherent Doppler data have provided the principal data type for orbit determination applications. The present investigation is concerned with the problem of orbit determination on the basis of Doppler tracking data in the case of a spacecraft in orbit about a natural body other than the earth or the sun. Attention is given to Doppler shift associated with a planetary orbiter, orbit determination using a zeroth-order model for the Doppler shift, and orbit determination using a first-order model for the Doppler shift.

Wood, L. J.

1985-01-01

62

Study on reduced-dynamic orbit determination of low Earth orbiters

NASA Astrophysics Data System (ADS)

Some orbit determination methods using onboard GPS Observations were discussed firstly in this paper, especially the principle and mathematical model of reduced-dynamic Precise Orbit Determination (POD) of Low Earth Satellite (LEO) based on undifferenced spaceborne dual-frequency GPS data. Then a weeklong (from July 28, 2003 to August 3,2003) dual-frequency onboard GPS observation from CHAMP satellite was computed using reduced-dynamic POD. Compared with TUM solutions, our CHAMP orbiting results of one week using reduced dynamic POD method are within 8 centimeters, which can meet the requirements of some higher precision orbit satellite orbits. In order to obtain high precision orbiting results, the impact of different gravity models and proper interval of pseudo-stochastic-pulses on the orbit determination accuracy were analyzed as well.

Han, Bao-min

2007-11-01

63

Initial Results from the Lunar Reconnaissance Orbiter Laser Ranging Investigation

NASA Astrophysics Data System (ADS)

The Lunar Reconnaissance Orbiter (LRO) Laser Ranging (LR) system is enabling the spacecraft to achieve its precision orbit determination requirement. The LR is routinely making one-way range measurements via laser pulse time-of-flight from the Earth to LRO. The LR consists of a receiver telescope mounted on LRO’s high-gain antenna that captures the uplinked laser signal, and a fiber optic cable that routes the signal to the Lunar Orbiter Laser Altimeter (LOLA) on LRO. The LOLA receiver electronics record the time of the laser signal and provide it to LRO’s data system. The LR ground system consists of laser ranging stations that times and transmits the laser pulse, a data facility, and the LOLA Science Operations Center. The primary ground station is NASA’s Next Generation Satellite Laser Ranging System (NGSLR) in Greenbelt, MD, and successful ranging has also been accomplished by MOBLAS-7 at Greenbelt, MLRS at Fort Davis, Texas, Herstmonceux in England, and Zimmerwald in Switzerland. Other approved stations in the International Laser Ranging Service (ILRS) will participate in the future. LR measurements permit improvement in the geodetic positioning of LRO to the sub-meter level with respect to the Moon’s center of mass. Positioning by the LR will enable the determination of a three-dimensional geodetic grid for the Moon based on the precise seleno-location of ground spots from LOLA. Current performance indicates 48-cm single-shot range error, or 24 cm with refined calibration. Up to an order of magnitude improvement can be expected from shot averaging.

Torrence, M. H.; Zuber, M. T.; Smith, D. E.; Mazarico, E.; Lemoine, F. G.; Cavanaugh, J. F.; Sun, X.; Zagwodzki, T.; Liiva, P.

2009-12-01

64

Ulysses orbit determination at high declinations

NASA Technical Reports Server (NTRS)

The trajectory of the Ulysses spacecraft caused its geocentric declination to exceed 60 deg South for over two months during the Fall of 1994, permitting continuous tracking from a single site. During this time, spacecraft operations constraints allowed only Doppler tracking data to be collected, and imposed a high radial acceleration uncertainty on the orbit determination process. The unusual aspects of this situation have motivated a re-examination of the Hamilton-Melbourne results, which have been used before to estimate the information content of Doppler tracking for trajectories closer to the ecliptic. The addition of an acceleration term to this equation is found to significantly increase the declination uncertainty for symmetric passes. In addition, a simple means is described to transform the symmetric results when the tracking pass is non-symmetric. The analytical results are then compared against numerical studies of this tracking geometry and found to be in good agreement for the angular uncertainties. The results of this analysis are applicable to the Near Earth Asteroid Rendezvous (NEAR) mission and to any other missions with high declination trajectories, as well as to missions using short tracking passes and/or one-way Doppler data.

Mcelrath, Timothy P.; Lewis, George D.

1995-01-01

65

Initial observations from the Lunar Orbiter Laser Altimeter (LOLA)

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 ...

Smith, David Edmund

66

NASA Astrophysics Data System (ADS)

Gauss method for the initial orbit determination was tested using angle-only data obtained by orbit propagation using TLE and SGP4/SDP4 orbit propagation model. As the analysis of this simulation, a feasible time span between observation time of satellite resulting the minimum error to the true orbit was found. Initial orbit determination is performed using observational data of GPS 26 and Koreasat 2 from 0.6m telescope of KAO(Korea Astronomy Observatory) and precise orbit determination is also performed using simulated data. The result of precise orbit determination shows that the accuracy of resulting orbit is related to the accuracy of the observations and the number of data.

Lee, Woo-Kyoung; Lim, Hyung-Chul; Park, Pil-Ho; Youn, Jae-Hyuk; Yim, Hong-Suh; Moon, Hong-Kyu

2004-09-01

67

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

68

Two Line Element Aided Orbit Determination Using Single Station SLR Data

NASA Astrophysics Data System (ADS)

It is difficult to use the single-station satellite laser ranging (SLR) data for orbit determination, due to the singular geometrical distribution of the observations. The single-station data generated by performing diffuse-reflection SLR to the orbital space debris are therefore ineffective for orbit improvement. We propose a method to resolve the singularity in the observation distribution. Since the initial orbits of space debris such as the two line elements (TLE) exist prior to the SLR tracking, we use it to simulate observations from other SLR sites. We combine the simulated and actual observations with a proper weight to fit an orbit, thus resolving the singularity in the observation distribution. We then propagate the fitted orbit forward in time to validate against the precision ephemeris derived from the international laser ranging service (ILRS). The method is implemented and applied to the satellite Ajisai. Using the single-station SLR data of five passes in one day and corresponding TLE as the initial orbit, we fit the orbit and the generated predictions. The predicted position error is less than 40 meter in five-day span, significantly improved over the initial SGP4 propagated orbit. The method's potential application to space debris orbit improvement is also discussed.

Liang, Z. P.; Liu, C. Z.; Fan, C. B.; Sun, M. G.

2012-03-01

69

Orbit determination and prediction study for Dynamic Explorer 2

NASA Technical Reports Server (NTRS)

Definitive orbit determination accuracy and orbit prediction accuracy for the Dynamic Explorer-2 (DE-2) are studied using the trajectory determination system for the period within six weeks of spacecraft reentry. Baseline accuracies using standard orbit determination models and methods are established. A promising general technique for improving the orbit determination accuracy of high drag orbits, estimation of random drag variations at perigee passages, is investigated. This technique improved the fit to the tracking data by a factor of five and improved the solution overlap consistency by a factor of two during a period in which the spacecraft perigee altitude was below 200 kilometers. The results of the DE-2 orbit predictions showed that improvement in short term prediction accuracy reduces to the problem of predicting future drag scale factors: the smoothness of the solar 10.7 centimeter flux density suggests that this may be feasible.

Smith, R. L.; Nakai, Y.; Doll, C. E.

1983-01-01

70

Benefits Derived From Laser Ranging Measurements for Orbit Determination of the GPS Satellite Orbit

NASA Technical Reports Server (NTRS)

While navigation systems for the determination of the orbit of the Global Position System (GPS) have proven to be very effective, the current research is examining methods to lower the error in the GPS satellite ephemerides below their current level. Two GPS satellites that are currently in orbit carry retro-reflectors onboard. One notion to reduce the error in the satellite ephemerides is to utilize the retro-reflectors via laser ranging measurements taken from multiple Earth ground stations. Analysis has been performed to determine the level of reduction in the semi-major axis covariance of the GPS satellites, when laser ranging measurements are supplemented to the radiometric station keeping, which the satellites undergo. Six ground tracking systems are studied to estimate the performance of the satellite. The first system is the baseline current system approach which provides pseudo-range and integrated Doppler measurements from six ground stations. The remaining five ground tracking systems utilize all measurements from the current system and laser ranging measurements from the additional ground stations utilized within those systems. Station locations for the additional ground sites were taken from a listing of laser ranging ground stations from the International Laser Ranging Service. Results show reductions in state covariance estimates when utilizing laser ranging measurements to solve for the satellite s position component of the state vector. Results also show dependency on the number of ground stations providing laser ranging measurements, orientation of the satellite to the ground stations, and the initial covariance of the satellite's state vector.

Welch, Bryan W.

2007-01-01

71

NASA Astrophysics Data System (ADS)

In the age of intensive exploring of the solar system, many professionals and non-professionals become interested in calculating the basic data regarding the solar system planets. We have considered some concepts of the physical ephemeris calculation for the natural and artificial solar system bodies. As an effective result, during a conference session, we presented an oral explanation of an interactive program for practical calculation of the physical ephemeris of the planets as a problem of general interest. As a specific example, in this article the readers can find the theoretical and practical elements and procedure explanation for two useful methods of the satellite orbit determination: LSQOD and EKF.

Segan, S.; Marceta, D.

2009-09-01

72

Semi-Major Axis Knowledge and GPS Orbit Determination

NASA Technical Reports Server (NTRS)

In recent years spacecraft designers have increasingly sought to use onboard Global Positioning System receivers for orbit determination. The superb positioning accuracy of GPS has tended to focus more attention on the system's capability to determine the spacecraft's location at a particular epoch than on accurate orbit determination, per se. The determination of orbit plane orientation and orbit shape to acceptable levels is less challenging than the determination of orbital period or semi-major axis. It is necessary to address semi-major axis mission requirements and the GPS receiver capability for orbital maneuver targeting and other operations that require trajectory prediction. Failure to determine semi-major axis accurately can result in a solution that may not be usable for targeting the execution of orbit adjustment and rendezvous maneuvers. Simple formulas, charts, and rules of thumb relating position, velocity, and semi-major axis are useful in design and analysis of GPS receivers for near circular orbit operations, including rendezvous and formation flying missions. Space Shuttle flights of a number of different GPS receivers, including a mix of unfiltered and filtered solution data and Standard and Precise Positioning, Service modes, have been accomplished. These results indicate that semi-major axis is often not determined very accurately, due to a poor velocity solution and a lack of proper filtering to provide good radial and speed error correlation.

Carpenter, J. Russell; Schiesser, Emil R.; Bauer, F. (Technical Monitor)

2000-01-01

73

Astrodynamics. Volume 1 - Orbit determination, space navigation, celestial mechanics.

NASA Technical Reports Server (NTRS)

Essential navigational, physical, and mathematical problems of space exploration are covered. The introductory chapters dealing with conic sections, orientation, and the integration of the two-body problem are followed by an introduction to orbit determination and design. Systems of units and constants, as well as ephemerides, representations, reference systems, and data are then dealt with. A detailed attention is given to rendezvous problems and to differential processes in observational orbit correction, and in rendezvous or guidance correction. Finally, the Laplacian methods for determining preliminary orbits, and the orbit methods of Lagrange, Gauss, and Gibbs are reviewed.

Herrick, S.

1971-01-01

74

Precise orbit determination for CAPS project

The Chinese Area Positioning System (CAPS) is a new type of satellite navigation systems. The geostationary satellites for normal communication with 2 or 3 sets of inclined geostationary orbit (GEO) satellites are employed to construct a satellite navigation system. The navigation signals are constructed and disseminated on the ground, and the satellites only transfer the signals to the ground by

Wu Wenjun; Li Zhigang; Chen Xuan; Lei Hui; Yang Xuhai; Feng Chugang

2010-01-01

75

NASA Astrophysics Data System (ADS)

Autonomous satellite orbit determination is a key technique in autonomous satellite navigation. Many kinds of technologies have been proposed to realize the autonomous satellite navigation, such as the star sensor, the Earth magnetometer, the occultation time survey, and the phase measurement of X-ray pulsar signals. This dissertation studies a method of autonomous satellite orbit determination using star sensor. Moreover, the method is extended to the autonomous navigation of satellite constellation and the space-based surveillance. In chapters 1 and 2, some usual time and reference systems are introduced. Then the principles of several typical autonomous navigation methods, and their merits and shortcomings are analyzed. In chapter 3, the autonomous satellite orbit determination using star sensor and infrared Earth sensor (IRES) is specifically studied, which is based on the status movement simulation, the stellar background observation from star sensor, and the Earth center direction survey from IRES. By simulating the low Earth orbit satellites and pseudo Geostationary Earth orbit (PGEO) satellites, the precision of position and speed with autonomous orbit determination using star sensor is obtained. Besides, the autonomous orbit determination using star sensor with double detectors is studied. According to the observation equation's characters, an optimized type of star sensor and IRES initial assembly model is proposed. In the study of the PGEO autonomous orbit determination, an efficient sampling frequency of measurements is promoted. The simulation results confirm that the autonomous satellite orbit determination using star sensor is feasible for satellites with all kinds of altitudes. In chapter 4, the method of autonomous satellite orbit determination using star sensor is extended to the autonomous navigation of mini-satellite constellation. Combining with the high-accuracy inter satellite links data, the precision of the determined orbit and constellation configuration is higher than that ever expected. In chapter 5, two related pre-project researches are developed with respect to the space-based satellite surveillance. One solves the un-convergence question in the preliminary orbit determination and finds an advantageous preliminary orbit determination using inter satellite angle measurement. In the other pre-project research, a creative space-based satellite surveillance model is proposed, which is based on the autonomous surveillance platform navigation. Using the star sensor's navigation data associated with the inter satellite angle measurement, the orbit parameters of the tracking space objects and the surveillance platform are determined. Compared to the available experiment results overseas, the preliminary orbit determination method and the autonomous navigation surveillance platform model are found to be feasible. The research will significantly contribute to the new conception of ``space awareness'', as well as our country's space security construction.

Gan, Q. B.

2012-07-01

76

Application of the GPS system for preliminary satellite orbit determination

In this paper, we discuss a method of preliminary orbit determination for an artificial satellite based on the navigation message of the GPS constellation. Orbital elements are considered as state variables and a simple dynamic model, based on the classic two-body problem, is used. The observations are formed by range and range and range-rate with respect to four visible GPS.

A. P. M Chiaradia; S da Silva Fernandes; R. Vilhena de Moraes

1997-01-01

77

Evaluation of the IMP-16 microprocessor orbit determination system filter

NASA Technical Reports Server (NTRS)

The results of the numerical tests performed in evaluating the interplanetary monitoring platform-16 orbit determination system are presented. The system is capable of performing orbit determination from satellite to satellite tracking data in applications technology satellite range and range rate format. The estimation scheme used is a Kalman filter, sequential (recursive) estimator. Descriptions of the tests performed and tabulations of the numerical results are included.

Shenitz, C. M.; Tasaki, K. K.

1979-01-01

78

Real - Time Orbit Determination of Low Earth Orbit Satellites Using Radar System and SGP4 Model

NASA Astrophysics Data System (ADS)

In case that we independently obtain orbital informations about the low earth satellites of foreign countries using radar systems, we develop the orbit determination algorithm for this purpose using a SGP4 model with an analytical orbit model and the extended Kalman filter with a real-time processing method. When the state vector is Keplerian orbital elements, singularity problems happen to compute partial derivative with respect to inclination and eccentricity orbit elements. To cope with this problem, we set state vector osculating to mean equinox and true equator cartesian elements with coordinate transformation. The state transition matrix and the covariance matrix are numerically computed using a SGP4 model. Observational measurements are the type of azimuth, elevation and range, filter process to each measurement in a lump. After analyzing performance of the developed orbit determination algorithm using TOPEX/POSEIDON POE(Precision Orbit Ephemeris), its position error has about 1 km. To be similar to performance of NORAD system that has up to 3km position accuracy during 7 days need to radar system performance that have accuracy within 0.1 degree for azimuth and elevation and 50m for range.

Lee, Jae-Kwang; Lee, Sung-Seub; Yoon, Jae-Cheol; Choi, Kyu-Hong

2003-03-01

79

Autonomous orbit determination and its effects on geolocation

NASA Astrophysics Data System (ADS)

Geolocation is the problem of finding where on earth a spacecraft sensor is pointing. It is a problem of orbit determination, attitude determination, and the actual geolocation algorithm. The effects of autonomous orbit determination errors on geolocation accuracy for a range of altitudes were examined. The orbit determination was performed using the reduced dynamic technique (RDT) with simulated GPS flight receiver data using the GIPSY-OASIS II software package. The RDT sigma's for minimizing orbit error in the radial, cross track, and along track directions, and for minimizing the three dimensional position error are presented for a variety of low altitude, sun synchronous orbits. In addition, the study examined the ability of RDT to remove drag error. Perturbing the drag coefficient simulated the drag error. In an autonomous application, the RDT technique removes drag as a significant error source at altitudes above about 350 kilometers. Also, for this altitude regime, the optimum sigma is nearly the same whether or not drag error is included in the solution. The geolocation error caused by a given orbit error is independent of altitude. However, orbit error decreases as the altitude increases because gravity and drag force model errors have a lower effect at higher altitudes. Consequently, the effects of orbit error on geolocation error decrease with altitude. Conversely, a given attitude error causes a greater geolocation error at a higher altitude. Above 400 kilometers the attitude error rapidly starts to dominate the total geolocation error even for precise attitude determination systems. However, for extremely low altitude systems the orbit error may dominate if the attitude errors are low. This is particularly true in the regime where RDT cannot compensate for drag model errors.

McLaughlin, Craig Alan

80

Orbit Determination Accuracy for Comets on Earth-Impacting Trajectories

NASA Technical Reports Server (NTRS)

The results presented show the level of orbit determination accuracy obtainable for long-period comets discovered approximately one year before collision with Earth. Preliminary orbits are determined from simulated observations using Gauss' method. Additional measurements are incorporated to improve the solution through the use of a Kalman filter, and include non-gravitational perturbations due to outgassing. Comparisons between observatories in several different circular heliocentric orbits show that observatories in orbits with radii less than 1 AU result in increased orbit determination accuracy for short tracking durations due to increased parallax per unit time. However, an observatory at 1 AU will perform similarly if the tracking duration is increased, and accuracy is significantly improved if additional observatories are positioned at the Sun-Earth Lagrange points L3, L4, or L5. A single observatory at 1 AU capable of both optical and range measurements yields the highest orbit determination accuracy in the shortest amount of time when compared to other systems of observatories.

Kay-Bunnell, Linda

2004-01-01

81

Benefits of a Geosynchronous Orbit (GEO) Observation Point for Orbit Determination

NASA Astrophysics Data System (ADS)

Determining orbits of unknown objects is a fundamental space situational awareness activity. The U.S. Space Surveillance Network (SSN) currently relies on ground-based radars, optical telescopes, and the Space Based Space Surveillance (SBSS) System. The SBSS system overcomes many of the pitfalls of optical ground-based systems like limited observation times (e.g. weather and time of day) and measurement uncertainty from atmospheric effects. However, the SBSS satellite is in a low earth orbit (630 km, sun synchronous), and must look “up” for GEO objects. This paper analyzes the potential benefits of a GEO observation point for performing metric observations that are combined with ground-based data. Several different scenarios are considered to quantify the reduction in orbit uncertainty from these types of observations. All results are derived using an Extended Kalman filter (EKF) to process the observations. Orbital uncertainties are expressed in terms of the error covariance.

Byrne, R.; Griesmeyer, M.; Schmidt, R.; Shaddix, J.; Bodette, D.

2011-09-01

82

Application of Encke's method for low-earth orbit determination

An analysis is made to study the application of Encke's method for low-earth orbit propagation and determination. The numerical results, based on a comparison to Cowell's method using a single-step integration algorithm, have shown that for a typical low-earth orbit the integration step size can be increased by a factor of three while maintaining the same accuracy when the reference

R. L. Alford; J. J. F. Liu

1986-01-01

83

Precision orbit determination using TOPEX\\/Poseidon TDRSS observations

The TOPEX\\/Poseidon (T\\/P) Mission carries a variety of packages to support experimental, precision and operational orbit determination. Included are a GPS transponder, laser retro-reflectors, the French-developed Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) Doppler tracking system and a Tracking Data Relay Satellite System (TDRSS) transponder. Presently, TDRSS tracking is used for operational orbit support and is processed with force

Jerome Teles; B. Putney; J. Phelps; J. McCarthy; W. Eddy; S. Klosko

1993-01-01

84

NASA Astrophysics Data System (ADS)

The main part of this work dealt with the development and evaluation of efficient methods for precise orbit determination of LEOs. A kinematic approach using GPS zero-difference observations was developed (program LEOKIN) and a procedure for generation of dynamic and reduced-dynamic orbits was presented (program SATORB). The procedures have been tested using long GPS data series gathered by two LEO satellites, namely CHAMP and SAC-C. An external comparison was available for the time interval of the eleven days of the IGS CHAMP test campaign (May 20 to 30, 2001). The orbit solution generated at the Technical University of Munich (TUM), Germany, using the Bernese GPS Software was used for this purpose. The TUM-solution is believed to be one of the best solutions contributing to the IGS test campaign. Comparisons with this solution showed that both our best kinematic trajectory and a post-fit reduced-dynamic orbit based on this kinematic solution compare within an RMS error per coordinate (of a Helmert transformation) of about 10 cm with the TUM-solutions. This indicates that LEO orbits with a quality of about 10 cm result from our analyses. The goal of developing efficient methods for precise orbit determination of LEOs is therefore achieved with the zero-difference kinematic point positioning procedure in LEOKIN and the program SATORB to generate reduced-dynamic orbits. It is worth mentioning that the procedure, when using only code observations as input, results in reduced-dynamic orbits with a qualitiy of already 30 cm RMS.

Bock, Heike

85

One year of Galileo IOV orbit and clock determination

NASA Astrophysics Data System (ADS)

With activation of the fourth Galileo satellite, the Galileo In-Orbit Validation (IOV) phase was achieved in December 2012. The Galileo IOV constellation consists of Proto Flight Model (PFM) and Flight Model 2 (FM2) launched in October 2011 and FM3 and FM4 launched in October 2012. Although the satellites are transmitting navigation signals on all designated frequencies, transmission of the navigation message has not yet started. However, the availability of an orbit product is a prerequisite for most user applications. To support early applications of Galileo, IOV orbit and clock parameters are estimated from observations of the Cooperative Network for GNSS Observation (CONGO) and the Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS). The quality of these GNSS-only orbits as evaluated by internal consistency tests and Satellite Laser Ranging (SLR) residuals is in general on the one decimeter level. However, the orbits suffer from systematic errors depending on the elevation of the Sun above the orbital plane. These errors show up, e.g., as a bump in the Allan deviation of the estimated clock parameters at the orbital frequency. We started with the Galileo orbit and clock determination in January 2012 and 2013 for PFM/FM2 and FM3/FM4, respectively. The time period of more than one year for PFM/FM2 allows for a proper analysis of the systematic errors. The impact of including SLR observations for a combined GNSS+SLR orbit determination, namely a reduction of the systematic errors, is demonstrated. Finally, the performance of the different clocks on board the IOV satellites (Rubidium clocks and Hydrogen masers) is evaluated and compared with other state-of-the-art GNSS satellite clocks.

Steigenberger, Peter; Hackel, Stefan; Hugentobler, Urs; Montenbruck, Oliver

2013-04-01

86

GOCE: precise orbit determination for the entire mission

NASA Astrophysics Data System (ADS)

The Gravity field and steady-state Ocean Circulation Explorer (GOCE) was the first Earth explorer core mission of the European Space Agency. It was launched on March 17, 2009 into a Sun-synchronous dusk-dawn orbit and re-entered into the Earth's atmosphere on November 11, 2013. The satellite altitude was between 255 and 225 km for the measurement phases. The European GOCE Gravity consortium is responsible for the Level 1b to Level 2 data processing in the frame of the GOCE High-level processing facility (HPF). The Precise Science Orbit (PSO) is one Level 2 product, which was produced under the responsibility of the Astronomical Institute of the University of Bern within the HPF. This PSO product has been continuously delivered during the entire mission. Regular checks guaranteed a high consistency and quality of the orbits. A correlation between solar activity, GPS data availability and quality of the orbits was found. The accuracy of the kinematic orbit primarily suffers from this. Improvements in modeling the range corrections at the retro-reflector array for the SLR measurements were made and implemented in the independent SLR validation for the GOCE PSO products. The satellite laser ranging (SLR) validation finally states an orbit accuracy of 2.42 cm for the kinematic and 1.84 cm for the reduced-dynamic orbits over the entire mission. The common-mode accelerations from the GOCE gradiometer were not used for the official PSO product, but in addition to the operational HPF work a study was performed to investigate to which extent common-mode accelerations improve the reduced-dynamic orbit determination results. The accelerometer data may be used to derive realistic constraints for the empirical accelerations estimated for the reduced-dynamic orbit determination, which already improves the orbit quality. On top of that the accelerometer data may further improve the orbit quality if realistic constraints and state-of-the-art background models such as gravity field and ocean tide models are used for the reduced-dynamic orbit determination.

Bock, Heike; Jäggi, Adrian; Beutler, Gerhard; Meyer, Ulrich

2014-07-01

87

Application of GPS tracking techniques to orbit determination for TDRS

NASA Technical Reports Server (NTRS)

In this paper, we evaluate two fundamentally different approaches to TDRS orbit determination utilizing Global Positioning System (GPS) technology and GPS-related techniques. In the first, a GPS flight receiver is deployed on the TDRSS spacecraft. The TDRS ephemerides are determined using direct ranging to the GPS spacecraft, and no ground network is required. In the second approach, the TDRSS spacecraft broadcast a suitable beacon signal, permitting the simultaneous tracking of GPS and TDRSS satellites from a small ground network. Both strategies can be designed to meet future operational requirements for TDRS-2 orbit determination.

Haines, B. J.; Lichten, S. M.; Malla, R. P.; Wu, S. C.

1993-01-01

88

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

NASA Technical Reports Server (NTRS)

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

89

Evaluation of semiempirical atmospheric density models for orbit determination applications

NASA Technical Reports Server (NTRS)

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.

1994-01-01

90

Autonomous satellite orbital navigation and attitude determination

NASA Technical Reports Server (NTRS)

A known linear landmark navigation system is described. It involves the use of an electro-optical sensor to provide sightings to linear earth features such as highways and coast lines. The sensor concept and the navigation system mechanization are described. Performance analysis results show that landmark sightings provide accurate navigation update and that this accuracy can be preserved using radar altimeter measurements. Description of a stellar inertial attitude determination system is also presented. Attitude reference performance consistent with the requirement of the navigation system is shown to be achievable by this method.

Kau, S. P.

1978-01-01

91

Application of Encke's method for low-earth orbit determination

NASA Astrophysics Data System (ADS)

An analysis is made to study the application of Encke's method for low-earth orbit propagation and determination. The numerical results, based on a comparison to Cowell's method using a single-step integration algorithm, have shown that for a typical low-earth orbit the integration step size can be increased by a factor of three while maintaining the same accuracy when the reference orbit is reinitialized frequently. The paper also addresses the integration of Encke's method using a multi-step algorithm such as the eighth-order Gauss-Jackson and exposes a numerical difficulty which is caused by frequency rectification of the reference orbit using a common starting method for the algorithm.

Alford, R. L.; Liu, J. J. F.

1986-08-01

92

28 CFR 301.305 - Initial determination.

Code of Federal Regulations, 2011 CFR

...FEDERAL PRISON INDUSTRIES, INC., DEPARTMENT OF JUSTICE INMATE ACCIDENT COMPENSATION Compensation for Work-Related Physical Impairment or Death § 301.305 Initial determination. A claim for inmate accident compensation shall be...

2011-07-01

93

28 CFR 301.305 - Initial determination.

Code of Federal Regulations, 2012 CFR

...FEDERAL PRISON INDUSTRIES, INC., DEPARTMENT OF JUSTICE INMATE ACCIDENT COMPENSATION Compensation for Work-Related Physical Impairment or Death § 301.305 Initial determination. A claim for inmate accident compensation shall be...

2012-07-01

94

95

28 CFR 301.305 - Initial determination.

Code of Federal Regulations, 2013 CFR

...FEDERAL PRISON INDUSTRIES, INC., DEPARTMENT OF JUSTICE INMATE ACCIDENT COMPENSATION Compensation for Work-Related Physical Impairment or Death § 301.305 Initial determination. A claim for inmate accident compensation shall be...

2013-07-01

96

28 CFR 301.305 - Initial determination.

Code of Federal Regulations, 2010 CFR

2010-07-01

97

Interplanetary orbit determination. [for Viking 1 and 2 spacecraft

NASA Technical Reports Server (NTRS)

A general description of the Viking interplanetary orbit determination activity extending from launch to Mars encounter is given. The emphasis is on the technical fundamentals of the problem, basic strategies and data types used, quantitative results, and specific conclusions derived from the inflight experience. Special attention is given to the use of the spacecraft-based optical measurements and their first application as a principal navigational data type for an interplanetary mission. The optical-based orbit determination, in fact, was the primary contributor to the exceptional interplanetary navigation accuracy experienced by both Viking missions. The Viking application of optical orbit determination relied in large part on the technology developed and demonstrated by the Mariner 9 Optical Navigation Demonstration.

Rourke, K. H.; Jerath, N.; Acton, C. H.; Breckenridge, W. G.; Campbell, J. K.; Christensen, C. S.; Donegan, A. J.; Koble, H. M.; Mottinger, N. A.; Rinker, G. C.

1979-01-01

98

Evaluation of orbit determination using dual-TDRS tracking

NASA Technical Reports Server (NTRS)

This paper describes the results of a study to evaluate the orbit determinatioin of Tracking and Data Relay Satellite System (TDRSS) user spacecraft within the dual-Tracking and Data Relay Satellite (TDRS) environment. Dense TDRSS tracking of the Earth Radiation Budget Satellite (ERBS) was acquired for the period August 16 through 22, 1989. This tracking information was processed to evaluate the orbit determination consistency achieved using the Goddard Trajectory Determination System batch least-squares estimator. The effects of the use of the second operational relay spacecraft, of refinements in orbit determination models (geopotentials, polar motion, solid earth tidal gravitational perturbations, ionospheric refraction corrections), and of methods for providing relay spacecraft spacecraft position information were also studied.

Oza, D. H.; Hodjatzadeh, M.; Radomski, M. S.; Doll, C. E.; Gramling, C. J.

1990-01-01

99

Use of the VLBI delay observable for orbit determination of Earth-orbiting VLBI satellites

NASA Technical Reports Server (NTRS)

Very long-baseline interferometry (VLBI) observations using a radio telescope in Earth orbit were performed first in the 1980s. Two spacecraft dedicated to VLBI are scheduled for launch in 1995; the primary scientific goals of these missions will be astrophysical in nature. This article addresses the use of space VLBI delay data for the additional purpose of improving the orbit determination of the Earth-orbiting spacecraft. In an idealized case of quasi-simultaneous observations of three radio sources in orthogonal directions, analytical expressions are found for the instantaneous spacecraft position and its error. The typical position error is at least as large as the distance corresponding to the delay measurement accuracy but can be much greater for some geometries. A number of practical considerations, such as system noise and imperfect calibrations, set bounds on the orbit-determination accuracy realistically achievable using space VLBI delay data. These effects limit the spacecraft position accuracy to at least 35 cm (and probably 3 m or more) for the first generation of dedicated space VLBI experiments. Even a 35-cm orbital accuracy would fail to provide global VLBI astrometry as accurate as ground-only VLBI. Recommended charges in future space VLBI missions are unlikely to make space VLBI competitive with ground-only VLBI in global astrometric measurements.

Ulvestad, J. S.

1992-01-01

100

Using Crossover Data from Satellite Altimeter for Orbit Determination

NASA Astrophysics Data System (ADS)

Beginning from the development status of oceanic altimeter satellites, the significance of orbit determination using altimeter data is introduced. Then, the error correcting model of altimeter data and the calculation method of crossover data are analyzed. The error correcting parameters and the adopted models which are concerned in the altimeter data files of JASON-1 are also introduced in detail. Finally, through the calculations of the simulated data and observational data, the orbit determination accuracies which can be reached by using the altimeter data and crossover data are analyzed. This work provides a valuable reference to the practical applications in future.

Zhang, R. Z.; Zhou, F. Q.; Xiong, J.

2010-07-01

101

Evaluation of advanced geopotential models for operational orbit determination

NASA Technical Reports Server (NTRS)

To meet future orbit determination accuracy requirements for different NASA projects, analyses are performed using Tracking and Data Relay Satellite System (TDRSS) tracking measurements and orbit determination improvements in areas such as the modeling of the Earth's gravitational field. Current operational requirements are satisfied using the Goddard Earth Model-9 (GEM-9) geopotential model with the harmonic expansion truncated at order and degree 21 (21-by-21). This study evaluates the performance of 36-by-36 geopotential models, such as the GEM-10B and Preliminary Goddard Solution-3117 (PGS-3117) models. The Earth Radiation Budget Satellite (ERBS) and LANDSAT-5 are the spacecraft considered in this study.

Radomski, M. S.; Davis, B. E.; Samii, M. V.; Engel, C. J.; Doll, C. E.

1988-01-01

102

The role of laser determined orbits in geodesy and geophysics

NASA Technical Reports Server (NTRS)

Some of the results of orbit analysis from the NASA SLR analysis group are presented. The earth's orientation was determined for 5-day intervals to 1.9 mas for the pole and 0.09 msec for length of day. The 3d center of mass station positions was determined to 33 mm over a period of 3 months, and geodesic rates of SLR tracking sites were determined to 5 mm/yr.

Kolenkiewicz, R.; Smith, D. E.; Dunn, P. J.; Torrence, M. H.; Robbins, J. W.

1991-01-01

103

Initial spare parts supply of an orbital system

This article presents a method of management of the initial spare parts supply. This generic problem is of particular interest in certain systems in which the difficulty of accessibility or the life cycle duration constitute risks tied to the possible depletion of the spare parts stock. In this paper we consider the spatial context. After having commented on the particularities

François Pérès; Jean-Christophe Grenouilleau

2002-01-01

104

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

105

Modeling GPS satellite attitude variation for precise orbit determination

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

106

Simplified solution to determination of a binary orbit

We present a simplified solution to orbit determination of a binary system from astrometric observations. An exact solution was found by Asada, Akasaka and Kasai by assuming no observational errors. We extend the solution considering observational data. The generalized solution is expressed in terms of elementary functions, and therefore requires neither iterative nor numerical methods.

Hideki Asada; Toshio Akasaka; Kazuya Kudoh

2006-09-28

107

NASA Astrophysics Data System (ADS)

It has been over half a century since the launch of the first artificial satellite Sputnik in 1957, which marks the beginning of the Space Age. During the past 50 years, with the development and innovations in various fields and technologies, satellite application has grown more and more intensive and extensive. This thesis is based on three major research projects which the author joined in. These representative projects cover main aspects of satellite orbit theory and application of precise orbit determination (POD), and also show major research methods and important applications in orbit dynamics. Chapter 1 is an in-depth research on analytical theory of satellite orbits. This research utilizes general transformation theory to acquire high-order analytical solutions when mean-element method is not applicable. These solutions can be used in guidance and control or rapid orbit forecast within the accuracy of 10-6. We also discuss other major perturbations, each of which is considered with improved models, in pursuit of both convenience and accuracy especially when old models are hardly applicable. Chapter 2 is POD research based on observations. Assuming a priori force model and estimation algorithm have reached their accuracy limits, we introduce empirical forces to Shenzhou-type orbit in order to compensate possible unmodeled or mismodeled perturbations. Residuals are analyzed first and only empirical force models with actual physical background are considered. This not only enhances a posteriori POD accuracy, but also considerably improves the accuracy of orbit forecast. This chapter also contains theoretical discussions on modeling of empirical forces, computation of partial derivatives and propagation of various errors. Error propagation helps to better evaluate orbital accuracy in future missions. Chapter 3 is an application of POD in space geodesy. GRACE satellites are used to obtain Antarctic temporal gravity field between 2004 and 2007. Various changes from traditional methods are implemented to better represent the regional temporal gravity field in this work. As a thesis in astrodynamics, this chapter will concentrate on orbit problems and estimation approaches. Although most details in geophysics are skipped, gravity field solutions will be displayed and the preliminary images of Antarctic mass flux will be revealed. These researches are summarized but not concluded in this thesis. Many problems have been left in all the aspects mentioned in this thesis and need to be studied in future researches, not to mention that the fast developing space technology keeps redefining our traditional knowledge with new concepts and elements. So future work and directions will be discussed at the end of the thesis, expecting further progress upon the present achievements.

Tang, J. S.

2011-03-01

108

This paper reports on our effort in modeling realistic astrophysical neutron star binaries in general relativity. We analyze under what conditions the conformally flat quasiequilibrium (CFQE) approach can generate ``astrophysically relevant'' initial data, by developing an analysis that determines the violation of the CFQE approximation in the evolution of the binary described by the full Einstein theory. We show that the CFQE assumptions significantly violate the Einstein field equations for corotating neutron stars at orbital separations nearly double that of the innermost stable circular orbit (ISCO) separation, thus calling into question the astrophysical relevance of the ISCO determined in the CFQE approach. With the need to start numerical simulations at large orbital separation in mind, we push for stable and long term integrations of the full Einstein equations for the binary neutron star system. We demonstrate the stability of our numerical treatment and analyze the stringent requirements on resolution and size of the computational domain for an accurate simulation of the system.

Mark Miller; Philip Gressman; Wai-Mo Suen

2003-12-04

109

NASA Astrophysics Data System (ADS)

Clock error estimation has been the focus of a great deal of research because of the extensive usage of clocks in GPS positioning applications. The receiver clock error in the spacecraft orbit determination is commonly estimated on an epoch-by-epoch basis, along with the spacecraft’s position. However, due to the high correlation between the spacecraft orbit altitude and the receiver clock parameters, estimates of the radial component are degraded in the kinematic approach. Using clocks with high stability, the predictable behaviour of the receiver oscillator can be exploited to improve the positioning accuracy, especially for the radial component. This paper introduces two GPS receiver clock models to describe the deterministic and stochastic property of the receiver clock, both of which can improve the accuracy of kinematic orbit determination for spacecraft in low earth orbit. In particular, the clock parameters are estimated as time offset and frequency offset in the two-state model. The frequency drift is also estimated as an unknown parameter in the three-state model. Additionally, residual non-deterministic random errors such as frequency white noise, frequency random walk noise and frequency random run noise are modelled. Test results indicate that the positioning accuracy could be improved significantly using one day of GRACE flight data. In particular, the error of the radial component was reduced by over 40.0% in the real-time scenario.

Yang, Yang; Yue, Xiaokui; Yuan, Jianping; Rizos, Chris

2014-11-01

110

Application of the GPS system for preliminary satellite orbit determination

NASA Astrophysics Data System (ADS)

In this paper, we discuss a method of preliminary orbit determination for an artificial satellite based on the navigation message of the GPS constellation. Orbital elements are considered as state variables and a simple dynamic model, based on the classic two-body problem, is used. The observations are formed by range and range and range-rate with respect to four visible GPS. A discrete Kalman filter with simulated data is used as filtering technique. The data are obtained through numerical propagation (Cowell's method), which considers special perturbations for the GPS satellite constellation and a user satellite.

Chiaradia, A. P. M.; da Silva Fernandes, S.; de Moraes, R. Vilhena

111

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

112

Automated Orbit Determination System (AODS) requirements definition and analysis

NASA Technical Reports Server (NTRS)

The requirements definition for the prototype version of the automated orbit determination system (AODS) is presented including the AODS requirements at all levels, the functional model as determined through the structured analysis performed during requirements definition, and the results of the requirements analysis. Also specified are the implementation strategy for AODS and the AODS-required external support software system (ADEPT), input and output message formats, and procedures for modifying the requirements.

Waligora, S. R.; Goorevich, C. E.; Teles, J.; Pajerski, R. S.

1980-01-01

113

Orbit Determination Support for the Microwave Anisotropy Probe (MAP)

NASA Technical Reports Server (NTRS)

NASA's Microwave Anisotropy Probe (MAP) was launched from the Cape Canaveral Air Force Station Complex 17 aboard a Delta II 7425-10 expendable launch vehicle on June 30, 2001. The spacecraft received a nominal direct insertion by the Delta expendable launch vehicle into a 185-km circular orbit with a 28.7deg inclination. MAP was then maneuvered into a sequence of phasing loops designed to set up a lunar swingby (gravity-assisted acceleration) of the spacecraft onto a transfer trajectory to a lissajous orbit about the Earth-Sun L2 Lagrange point, about 1.5 million km from Earth. Because of its complex orbital characteristics, the mission provided a unique challenge for orbit determination (OD) support in many orbital regimes. This paper summarizes the premission trajectory covariance error analysis, as well as actual OD results. The use and impact of the various tracking stations, systems, and measurements will be also discussed. Important lessons learned from the MAP OD support team will be presented. There will be a discussion of the challenges presented to OD support including the effects of delta-Vs at apogee as well as perigee, and the impact of the spacecraft attitude mode on the OD accuracy and covariance analysis.

Bauer, Frank (Technical Monitor); Truong, Son H.; Cuevas, Osvaldo O.; Slojkowski, Steven

2003-01-01

114

NASA Astrophysics Data System (ADS)

NORAD Two Line Element (TLE) is very useful to simplify the ground station antenna pointing and mission operations. When a satellite operations facility has the capability to determine NORAD type TLE which is independent of NORAD, it is important to analyze the applicable tracking data arcs for obtaining the best possible orbit. The applicable tracking data arcs for NORAD independent TLE orbit determination of the KOMPSAT-1 using GPS navigation solutions was analyzed for the best possible orbit determination and propagation results. Data spans of the GPS navi gation solutions from 1 day to 5 days were used for TLE orbit determination and the results were used as initial orbit for SGP4 orbit propagation. The operational orbit determination results using KOMPSAT-1 Mission Analysis and Planning System (MAPS) were used as references for the comparisons. The best-matched orbit determination was obtained when 3 days of GPS navigation solutions were used. The resulting 4 days of orbit propagation results were within 2 km of the KOMPSAT-1 MAPS results.

Lee, Byoung-Sun

2005-09-01

115

Orbit determination and orbit control for the Earth Observing System (EOS) AM spacecraft

NASA Technical Reports Server (NTRS)

Future NASA Earth Observing System (EOS) Spacecraft will make measurements of the earth's clouds, oceans, atmosphere, land and radiation balance. These EOS Spacecraft will be part of the NASA Mission to Planet Earth. This paper specifically addresses the EOS AM Spacecraft, referred to as 'AM' because it has a sun-synchronous orbit with a 10:30 AM descending node. This paper describes the EOS AM Spacecraft mission orbit requirements, orbit determination, orbit control, and navigation system impact on earth based pointing. The EOS AM Spacecraft will be the first spacecraft to use the TDRSS Onboard Navigation System (TONS) as the primary means of navigation. TONS flight software will process one-way forward Doppler measurements taken during scheduled TDRSS contacts. An extended Kalman filter will estimate spacecraft position, velocity, drag coefficient correction, and ultrastable master oscillator frequency bias and drift. The TONS baseline algorithms, software, and hardware implementation are described in this paper. TONS integration into the EOS AM Spacecraft Guidance, Navigation, and Control (GN&C) System; TONS assisted onboard time maintenance; and the TONS Ground Support System (TGSS) are also addressed.

Herberg, Joseph R.; Folta, David C.

1993-01-01

116

Meteoroid and Orbital Debris Threats to NASA's Docking Seals: Initial Assessment and Methodology

NASA Technical Reports Server (NTRS)

The Crew Exploration Vehicle (CEV) will be exposed to the Micrometeoroid Orbital Debris (MMOD) environment in Low Earth Orbit (LEO) during missions to the International Space Station (ISS) and to the micrometeoroid environment during lunar missions. The CEV will be equipped with a docking system which enables it to connect to ISS and the lunar module known as Altair; this docking system includes a hatch that opens so crew and supplies can pass between the spacecrafts. This docking system is known as the Low Impact Docking System (LIDS) and uses a silicone rubber seal to seal in cabin air. The rubber seal on LIDS presses against a metal flange on ISS (or Altair). All of these mating surfaces are exposed to the space environment prior to docking. The effects of atomic oxygen, ultraviolet and ionizing radiation, and MMOD have been estimated using ground based facilities. This work presents an initial methodology to predict meteoroid and orbital debris threats to candidate docking seals being considered for LIDS. The methodology integrates the results of ground based hypervelocity impacts on silicone rubber seals and aluminum sheets, risk assessments of the MMOD environment for a variety of mission scenarios, and candidate failure criteria. The experimental effort that addressed the effects of projectile incidence angle, speed, mass, and density, relations between projectile size and resulting crater size, and relations between crater size and the leak rate of candidate seals has culminated in a definition of the seal/flange failure criteria. The risk assessment performed with the BUMPER code used the failure criteria to determine the probability of failure of the seal/flange system and compared the risk to the allotted risk dictated by NASA's program requirements.

deGroh, Henry C., III; Nahra, Henry K.

2009-01-01

117

Meteoroid and Orbital Debris Threats to NASA's Docking Seals: Initial Assessment and Methodology

NASA Technical Reports Server (NTRS)

The Crew Exploration Vehicle (CEV) will be exposed to the Micrometeoroid Orbital Debris (MMOD) environment in Low Earth Orbit (LEO) during missions to the International Space Station (ISS) and to the micrometeoroid environment during lunar missions. The CEV will be equipped with a docking system which enables it to connect to ISS and the lunar module known as Altair; this docking system includes a hatch that opens so crew and supplies can pass between the spacecrafts. This docking system is known as the Low Impact Docking System (LIDS) and uses a silicone rubber seal to seal in cabin air. The rubber seal on LIDS presses against a metal flange on ISS (or Altair). All of these mating surfaces are exposed to the space environment prior to docking. The effects of atomic oxygen, ultraviolet and ionizing radiation, and MMOD have been estimated using ground based facilities. This work presents an initial methodology to predict meteoroid and orbital debris threats to candidate docking seals being considered for LIDS. The methodology integrates the results of ground based hypervelocity impacts on silicone rubber seals and aluminum sheets, risk assessments of the MMOD environment for a variety of mission scenarios, and candidate failure criteria. The experimental effort that addressed the effects of projectile incidence angle, speed, mass, and density, relations between projectile size and resulting crater size, and relations between crater size and the leak rate of candidate seals has culminated in a definition of the seal/flange failure criteria. The risk assessment performed with the BUMPER code used the failure criteria to determine the probability of failure of the seal/flange system and compared the risk to the allotted risk dictated by NASA s program requirements.

deGroh, Henry C., III; Gallo, Christopher A.; Nahra, Henry K.

2009-01-01

118

Tests of Magnetometer/Sun-Sensor Orbit Determination Using Flight Data and Mark L. Psiaki

Tests of Magnetometer/Sun-Sensor Orbit Determination Using Flight Data Hee Jung* and Mark L. Psiaki Cornell University, Ithaca, N.Y. 14853-7501 Abstract A magnetometer-based orbit determination batch filter the performance of a low-cost autonomous orbit determination system. The spacecraft's orbit, magnetometer biases

Psiaki, Mark L.

119

Magnetospheric Multiscale (MMS) Mission Commissioning Phase Orbit Determination Error Analysis

NASA Technical Reports Server (NTRS)

The Magnetospheric MultiScale (MMS) mission commissioning phase starts in a 185 km altitude x 12 Earth radii (RE) injection orbit and lasts until the Phase 1 mission orbits and orientation to the Earth-Sun li ne are achieved. During a limited time period in the early part of co mmissioning, five maneuvers are performed to raise the perigee radius to 1.2 R E, with a maneuver every other apogee. The current baseline is for the Goddard Space Flight Center Flight Dynamics Facility to p rovide MMS orbit determination support during the early commissioning phase using all available two-way range and Doppler tracking from bo th the Deep Space Network and Space Network. This paper summarizes th e results from a linear covariance analysis to determine the type and amount of tracking data required to accurately estimate the spacecraf t state, plan each perigee raising maneuver, and support thruster cal ibration during this phase. The primary focus of this study is the na vigation accuracy required to plan the first and the final perigee ra ising maneuvers. Absolute and relative position and velocity error hi stories are generated for all cases and summarized in terms of the ma ximum root-sum-square consider and measurement noise error contributi ons over the definitive and predictive arcs and at discrete times inc luding the maneuver planning and execution times. Details of the meth odology, orbital characteristics, maneuver timeline, error models, and error sensitivities are provided.

Chung, Lauren R.; Novak, Stefan; Long, Anne; Gramling, Cheryl

2009-01-01

120

How to Determine an Exomoon's Sense of Orbital Motion

NASA Astrophysics Data System (ADS)

We present two methods to determine an exomoon's sense of orbital motion (SOM), one with respect to the planet's circumstellar orbit and one with respect to the planetary rotation. Our simulations show that the required measurements will be possible with the European Extremely Large Telescope (E-ELT). The first method relies on mutual planet-moon events during stellar transits. Eclipses with the moon passing behind (in front of) the planet will be late (early) with regard to the moon's mean orbital period due to the finite speed of light. This "transit timing dichotomy" (TTD) determines an exomoon's SOM with respect to the circumstellar motion. For the 10 largest moons in the solar system, TTDs range between 2 and 12 s. The E-ELT will enable such measurements for Earth-sized moons around nearby Sun-like stars. The second method measures distortions in the IR spectrum of the rotating giant planet when it is transited by its moon. This Rossiter-McLaughlin effect (RME) in the planetary spectrum reveals the angle between the planetary equator and the moon's circumplanetary orbital plane, and therefore unveils the moon's SOM with respect to the planet's rotation. A reasonably large moon transiting a directly imaged planet like ? Pic b causes an RME amplitude of almost 100 m s–1, about twice the stellar RME amplitude of the transiting exoplanet HD209458 b. Both new methods can be used to probe the origin of exomoons, that is, whether they are regular or irregular in nature.

Heller, René; Albrecht, Simon

2014-11-01

121

We present an algorithm for solving the general relativistic initial value equations for a corotating polytropic star in quasicircular orbit with a nonspinning black hole. The algorithm is used to obtain initial data for cases where the black hole mass is 1, 3, and 10 times larger than the mass of the star. By analyzing sequences of constant baryon mass, constant black hole mass initial data sets and carefully monitoring the numerical error, we find innermost stable circular orbit (ISCO) configuration for these cases. While these quasiequilibrium, conformally flat sequences of initial data sets are not true solutions of the Einstein equations (each set, however, solves the full initial value problem), and thus, we do not expect the ISCO configurations found here to be completely consistent with the Einstein equations, they will be used as convenient starting points for future numerical evolutions of the full 3+1 Einstein equations.

Mark Miller

2001-06-06

122

Enhanced orbit determination filter sensitivity analysis: Error budget development

NASA Technical Reports Server (NTRS)

An error budget analysis is presented which quantifies the effects of different error sources in the orbit determination process when the enhanced orbit determination filter, recently developed, is used to reduce radio metric data. The enhanced filter strategy differs from more traditional filtering methods in that nearly all of the principal ground system calibration errors affecting the data are represented as filter parameters. Error budget computations were performed for a Mars Observer interplanetary cruise scenario for cases in which only X-band (8.4-GHz) Doppler data were used to determine the spacecraft's orbit, X-band ranging data were used exclusively, and a combined set in which the ranging data were used in addition to the Doppler data. In all three cases, the filter model was assumed to be a correct representation of the physical world. Random nongravitational accelerations were found to be the largest source of error contributing to the individual error budgets. Other significant contributors, depending on the data strategy used, were solar-radiation pressure coefficient uncertainty, random earth-orientation calibration errors, and Deep Space Network (DSN) station location uncertainty.

Estefan, J. A.; Burkhart, P. D.

1994-01-01

123

Position determination systems. [using orbital antenna scan of celestial bodies

NASA Technical Reports Server (NTRS)

A system for an orbital antenna, operated at a synchronous altitude, to scan an area of a celestial body is disclosed. The antenna means comprises modules which are operated by a steering signal in a repetitive function for providing a scanning beam over the area. The scanning covers the entire area in a pattern and the azimuth of the scanning beam is transmitted to a control station on the celestial body simultaneous with signals from an activated ground beacon on the celestial body. The azimuth of the control station relative to the antenna is known and the location of the ground beacon is readily determined from the azimuth determinations.

Shores, P. W. (inventor)

1976-01-01

124

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

125

Precise Orbit Determination for a New Horizons KBO

NASA Astrophysics Data System (ADS)

The New Horizons (NH) spacecraft will flyby the Pluto system next summer, after this the spacecraft will be retargeted to one or more Kuiper Belt Objects (KBOs) to learn about the remnant material from our outer solar system's formation. We are actively carrying out dedicated ground-based observations to identify a target for NH to flyby and continue to improve our analysis algorithms. To date, we have 52 discoveries including five objects that are long-range reconnaissance candidates, and two that current orbit predictions require about a factor of 2 more propellant than is available for the encounter maneuver. Our searches are continuing in to 2014 and we anticipate as many as 2 objects that will require high precision HST imaging. Unfortunately, NH's trajectory line of site is within the galactic center (Sagittarius) making stellar confusion a major problem in recovering these objects from the ground to obtain precise astrometry and high precision orbits. HST's sensitivity, resolution and PSF stability are crucial components for the success of the NH Kuiper belt mission component. We are requesting 4 TOO orbits to be triggered when a candidate object is found within the targetable region. These observations will provide the required high precision astrometry required for targeting, will evaluate if the NH candidate is binary (~30%) and will make a preliminary color determination to assist in long or short range encounter planning.

Benecchi, Susan

2014-10-01

126

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

127

Orbital period determination in an eclipsing dwarf nova HT Cas

NASA Astrophysics Data System (ADS)

HT Cassiopeiae was discovered over seventy years ago (Hoffmeister 1943). Unfortunately, for 35 years this object did not receive any attention, until the eclipses of HT Cas were observed by Bond. After a first analysis, Patterson (1981) called HT Cas "a Rosetta stone among dwarf novae". Since then, the literature on this star is still growing, reaching several dozens of publications. We present an orbital period determination of HT Cas during the November 2010 super-outburst, but also during a longer time span, to check its stability.

B?kowska, Karolina; Olech, Arkadiusz

2014-09-01

128

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

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 > or approx. 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 ratio 1 and vanishing spin, the eccentricity reaches e=0.004. For mass ratio 1 ratio 1 and aligned spins of size 0.85M{sup 2} the eccentricity is about e=0.07 for the Taylor method and e=0.014 for the effective-one-body method.

Walther, Benny; Bruegmann, Bernd; Mueller, Doreen [Theoretical Physics Institute, University of Jena, 07743 Jena (Germany)

2009-06-15

129

NASA Astrophysics Data System (ADS)

The value of the initial velocity of the stream meteoroids from the parent bodies is given by the physics of the outgassing of the cometary nuclei and by modeling the collisions between asteroids. In both cases the outflow speed of the meteoroid particles are small (Whipple 1951, Hughes 1977, 2000, Gustafson 1989, Jones 1995, Ma et al. 2002) and as result, the most meteoroid streams have similar orbits to either comets or asteroids. The formulae relating the changes of the orbital elements due to the small increment of the velocity were developed, among others by Plavec (1955), Pecina and Simek(1997), Williams (1996, 2001), Ma et al. (2001), Ma and Williams (2002). Assuming that the members of the observed meteor stream evolved dynamically under the influence of gravitational perturbations only, Pittich (1988), Harris and Hughes (1995), Williams (1996, 2001) estimated the initial velocity of the stream meteoroids. In their approach, Harris and Hughes have used the dispersion of the semimajor axes of the stream meteoroids. Williams proposed the method were used the mean orbit of the stream and the orbit of the identified parent body of the stream. The obtained results are not free from the discrepancy, explained partly by the particular orbital structure of the stream. However Kresak (1992) has strongly criticized the attempts to determine the initial velocities of the stream using the statistics of the meteor orbits. He argued that this is essentially impossible, because the dispersion of the initial velocities are masked by much larger measuring errors and also by the accumulated effects of planetary perturbations. In our paper, we decided to verify the reliability of the methods proposed by Harris and Hughes (1995), and by Williams (1996,2001). We made an numerical experiment consisting of the simulation of formation of several meteor streams and their dynamical evolution over 5000 years. We ejected meteoroids particles from the comets: Halley, Swift-Tuttle, Tempel-Tuttle. During the integration, the initial velocities of the stream members were estimated using the methods proposed by Hughes and Harris, and that by Williams. The results which we calculated till present, shows that the velocities obtained by the Williams method are to high when compared with the known velocities of the stream formation. On the other hand, the velocities obtained using Harris and Hughes method are to small. This work was supported by the KBN Project 2-P03-D-007-22.

Jopek, T. J.; Rudawska, R.; Dybczynski, P. A.

2005-08-01

130

The atmospheric mass density of the upper atmosphere from the spherical Starlette satellite's Precise Orbit Determination is first derived with Satellite Laser Ranging measurements at 815 to 1115 km during strong solar and geomagnetic activities. Starlette's orbit is determined using the improved orbit determination techniques combining optimum parameters with a precise empirical drag application to a gravity field. MSIS-86 and

H. S. Jeon; S. Cho; Y. S. Kwak; J. K. Chung; J. U. Park; D. K. Lee; M. Kuzmicz-Cieslak

2011-01-01

131

Filter parameter tuning analysis for operational orbit determination support

NASA Technical Reports Server (NTRS)

The use of an extended Kalman filter (EKF) for operational orbit determination support is being considered by the Goddard Space Flight Center (GSFC) Flight Dynamics Division (FDD). To support that investigation, analysis was performed to determine how an EKF can be tuned for operational support of a set of earth-orbiting spacecraft. The objectives of this analysis were to design and test a general purpose scheme for filter tuning, evaluate the solution accuracies, and develop practical methods to test the consistency of the EKF solutions in an operational environment. The filter was found to be easily tuned to produce estimates that were consistent, agreed with results from batch estimation, and compared well among the common parameters estimated for several spacecraft. The analysis indicates that there is not a sharply defined 'best' tunable parameter set, especially when considering only the position estimates over the data arc. The comparison of the EKF estimates for the user spacecraft showed that the filter is capable of high-accuracy results and can easily meet the current accuracy requirements for the spacecraft included in the investigation. The conclusion is that the EKF is a viable option for FDD operational support.

Dunham, J.; Cox, C.; Niklewski, D.; Mistretta, G.; Hart, R.

1994-01-01

132

The Cramer-Rao bound for initial conditions estimation of chaotic orbits

We derive the Cramer-Rao Lower Bound (CRLB) for the estimation of initial conditions of noise-embedded orbits produced by general one-dimensional maps. We relate this bound's asymptotic behavior to the attractor's Lyapunov number and show numerical examples. These results pave the way for more suitable choices for the chaotic signal gen- erator in some chaotic digital communication systems. 2006 Published by

Marcio Eisencraft; Luiz Antonio Baccalab

2007-01-01

133

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

134

Analysis of filter tuning techniques for sequential orbit determination

NASA Technical Reports Server (NTRS)

This paper examines filter tuning techniques for a sequential orbit determination (OD) covariance analysis. Recently, there has been a renewed interest in sequential OD, primarily due to the successful flight qualification of the Tracking and Data Relay Satellite System (TDRSS) Onboard Navigation System (TONS) using Doppler data extracted onboard the Extreme Ultraviolet Explorer (EUVE) spacecraft. TONS computes highly accurate orbit solutions onboard the spacecraft in realtime using a sequential filter. As the result of the successful TONS-EUVE flight qualification experiment, the Earth Observing System (EOS) AM-1 Project has selected TONS as the prime navigation system. In addition, sequential OD methods can be used successfully for ground OD. Whether data are processed onboard or on the ground, a sequential OD procedure is generally favored over a batch technique when a realtime automated OD system is desired. Recently, OD covariance analyses were performed for the TONS-EUVE and TONS-EOS missions using the sequential processing options of the Orbit Determination Error Analysis System (ODEAS). ODEAS is the primary covariance analysis system used by the Goddard Space Flight Center (GSFC) Flight Dynamics Division (FDD). The results of these analyses revealed a high sensitivity of the OD solutions to the state process noise filter tuning parameters. The covariance analysis results show that the state estimate error contributions from measurement-related error sources, especially those due to the random noise and satellite-to-satellite ionospheric refraction correction errors, increase rapidly as the state process noise increases. These results prompted an in-depth investigation of the role of the filter tuning parameters in sequential OD covariance analysis. This paper analyzes how the spacecraft state estimate errors due to dynamic and measurement-related error sources are affected by the process noise level used. This information is then used to establish guidelines for determining optimal filter tuning parameters in a given sequential OD scenario for both covariance analysis and actual OD. Comparisons are also made with corresponding definitive OD results available from the TONS-EUVE analysis.

Lee, T.; Yee, C.; Oza, D.

1995-01-01

135

Cassini Orbit Determination Performance (July 2008 - December 2011)

NASA Technical Reports Server (NTRS)

This paper reports on the orbit determination performance for the Cassini spacecraft from July 2008 to December 2011. During this period, Cassini made 85 revolutions around Saturn and had 52 close satellite encounters. 35 of those were with the massive Titan, 13 with the small, yet interesting, Enceladus as well as 2 with Rhea and 2 with Dione. The period also includes 4 double encounters, where engineers had to plan the trajectory for two close satellite encounters within days of each other at once. Navigation performance is characterized by ephemeris errors relative to in-flight predictions. Most Titan encounters 3-dimensional results are within a 1.5 formal sigma, with a few exceptions, mostly attributable to larger maneuver execution errors. Results for almost all other satellite encounter reconstructions are less than 3 sigma from their predictions. The errors are attributable to satellite ephemerides errors and in some cases to maneuver execution errors.

Pelletier, Frederic J.; Antreasian, Peter; Ardalan, Shadan; Buffington, Brent; Criddle, Kevin; Ionasescu, Rodica; Jacobson, Robert; Jones, Jeremy; Nandi, Sumita; Nolet, Simon; Parcher, Daniel; Roth, Duane; Smith, Jonathon; Thompson, Paul

2012-01-01

136

NASA Technical Reports Server (NTRS)

Launched in the summer of 1992, TOPEX/POSEIDON (T/P) was a joint mission between NASA and the Centre National d Etudes Spatiales (CNES), the French Space Agency, to make precise radar altimeter measurements of the ocean surface. After the remarkably successful 13-years of mapping the ocean surface T/P lost its ability to maneuver and was de-commissioned January 2006. T/P revolutionized the study of the Earth s oceans by vastly exceeding pre-launch estimates of surface height accuracy recoverable from radar altimeter measurements. The precision orbit lies at the heart of the altimeter measurement providing the reference frame from which the radar altimeter measurements are made. The expected quality of orbit knowledge had limited the measurement accuracy expectations of past altimeter missions, and still remains a major component in the error budget of all altimeter missions. This paper describes critical improvements made to the T/P orbit time series over the 13-years of precise orbit determination (POD) provided by the GSFC Space Geodesy Laboratory. The POD improvements from the pre-launch T/P expectation of radial orbit accuracy and Mission requirement of 13-cm to an expected accuracy of about 1.5-cm with today s latest orbits will be discussed. The latest orbits with 1.5 cm RMS radial accuracy represent a significant improvement to the 2.0-cm accuracy orbits currently available on the T/P Geophysical Data Record (GDR) altimeter product.

Lemoine, F. G.; Zelensky, N. P.; Luthcke, S. B.; Rowlands, D. D.; Beckley, B. D.; Klosko, S. M.

2006-01-01

137

NASA Technical Reports Server (NTRS)

The Geostationary Operational Environmental Satellite (GOES)-8 experienced a series of orbital perturbations from autonomous attitude control thrusting before perigee raising maneuvers. These perturbations influenced differential correction orbital state solutions determined by the Goddard Space Flight Center (GSFC) Goddard Trajectory Determination System (GTDS). The maneuvers induced significant variations in the converged state vector for solutions using increasingly longer tracking data spans. These solutions were used for planning perigee maneuvers as well as initial estimates for orbit solutions used to evaluate the effectiveness of the perigee raising maneuvers. This paper discusses models for the incorporation of attitude thrust effects into the orbit determination process. Results from definitive attitude solutions are modeled as impulsive thrusts in orbit determination solutions created for GOES-8 mission support. Due to the attitude orientation of GOES-8, analysis results are presented that attempt to absorb the effects of attitude thrusting by including a solution for the coefficient of reflectivity, C(R). Models to represent the attitude maneuvers are tested against orbit determination solutions generated during real-time support of the GOES-8 mission. The modeling techniques discussed in this investigation offer benefits to the remaining missions in the GOES NEXT series. Similar missions with large autonomous attitude control thrusting, such as the Solar and Heliospheric Observatory (SOHO) spacecraft and the INTELSAT series, may also benefit from these results.

Forcey, W.; Minnie, C. R.; Defazio, R. L.

1995-01-01

138

Initial elementary processes in tetrafluoroethylene plasma: An ab initio molecular orbital study

NASA Astrophysics Data System (ADS)

Initial elementary processes in tetrafluoroethylene plasma are studied by using an ab initio molecular orbital method. The energy-surfaces at excited states are obtained by the Hartree-Fock method with a double zeta basis set, plus Rydberg orbitals. A ?-?* transition is low-lying both at singlet and triplet excited states. Vinyl-polymerization-type reactions are expected in the presence of some radical species via these transitions. The C=C bond cleaves via a triplet ?-?* transition to form CF2. The predicted elementary processes via these states are compatible with experimental results that C2F4* and CF2 are primary precursors. No excited states that bring about a C—F bond cleavage are obtained within 10 eV of the ground state. As a path for a C—F bond cleavage, a dissociative electron attachment process is found in a low energy region. This process is considered to be important for producing fluorine anions.

Sato, Kota; Komatsu, Toru; Iwabuchi, Susumu

1993-12-01

139

Initial On-Orbit Radiometric Calibration of the Suomi NPP VIIRS Reflective Solar Bands

NASA Technical Reports Server (NTRS)

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, Vincent; Xiong, Jack

2012-01-01

140

Precise Orbit Determination for Altimetric Missions: Past trends, Current issues and IGGOS

Satellite positioning, as computed within Precise Orbit Determination software, is a fundamental component of Geophysical Data Records (GDR) for altimetric missions. In particular, orbital analysts compute the normal height above a reference ellipsoid providing the essential link between the height recorded by the altimeter and the Earth's surface. Orbital accuracies are sought at a level commensurate with that of the

P. Moore

2002-01-01

141

20 CFR 416.203 - Initial determinations of SSI eligibility.

Code of Federal Regulations, 2010 CFR

...2010-04-01 false Initial determinations of SSI eligibility. 416.203 Section 416.203...General § 416.203 Initial determinations of SSI eligibility. (a) What happens when you apply for SSI benefits. When you apply for...

2010-04-01

142

TLE-Aided Orbit Determination Using Single-Station SLR Data

NASA Astrophysics Data System (ADS)

It is difficult to use the single-station satellite laser ranging (SLR) data for orbit determination, due to the singular geometrical distribution of the observations. The single-station data produced by performing the diffuse- reflection SLR on the earth-orbiting space debris are therefore ineffective for orbit improvement. To solve this problem, we propose an orbit determination method by using single-station SLR data in aid of the two-line element set (TLE). For verifying its feasibility, this method is implemented and applied to the orbit determination of the satellite Ajisai, using the single-station SLR data of five passes in one day and the corresponding TLE. And on this basis, the five-day orbit prediction is generated, the result indicates that the errors of predicted positions are less than 40 m. In addition, the potential application of this method in the orbit improvement of space debris is discussed.

Liang, Zhi-peng; Liu, Cheng-zhi; Fan, Cun-bo; Sun, Ming-guo

2012-10-01

143

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

Prior to the invention of the telescope many astronomers worked out a theory of the motion of the Moon. The purpose of such theories was to be able to predict the position of the Moon in the sky. These geometrical models implied a certain range of distance of the Moon. Ptolemy's model, in fact, 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 pre-telescopic astronomers. These could have helped refine the models of the motion of the Moon, but hardly anyone seems to have made any measurements. Using a piece of cardboard with a small hole punched in it which slides up and down a yardstick, we show that it is possible to determine an approximate value of the eccentricity of the Moon's orbit. We find epsilon ~ 0.039 +/- 0.006. A typical measurement uncertainty of the Moon's angular size is +/- 0.8 arcmin. Since the Moon's angular size ranges from 29.4 to 33.5 arcmin, carefully taken naked eye data are accura...

Krisciunas, Kevin

2010-01-01

144

TERRASAR-X RAPID AND PRECISE ORBIT DETERMINATION

TerraSAR-X is a German Synthetic Aperture Radar (SAR) satellite that has been placed into orbit in mid 2007 and is since then collecting SAR imagery on a routine basis. To support the TerraSAR-X navigation needs, the satellite is equipped with two independent GPS receiver systems. The German Space Operation Center is providing several orbit products with different latencies and accuracy

M. Wermuth; A. Hauschild; O. Montenbruck; A. Jäggi

145

Orbit determination of the Comet Rendezvous/Asteroid Flyby mission - Post-rendezvous phases

NASA Technical Reports Server (NTRS)

Orbit determination during the post-rendezvous phases of the Comet Rendezvous/Asteroid Flyby mission is described. The orbit determination process is discussed, with emphasis placed on optical imaging of landmarks and Doppler tracking. Rotational dynamics are introduced for the cometary nucleus. State estimation errors are given for spacecraft trajectory prediction and cometary nucleus attitude prediction. Estimation errors are also given for parameters that describe the cometary nucleus such as moments of inertia and gravity harmonics. The orbit determination performance in support of science observations while in orbit about the nucleus is described.

Miller, James K.; Wood, Lincoln J.; Weeks, Connie J.

1989-01-01

146

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

147

Orbit determination and prediction of GEO satellite of BeiDou during repositioning maneuver

NASA Astrophysics Data System (ADS)

In order to establish a continuous GEO satellite orbit during repositioning maneuvers, a suitable maneuver force model has been established associated with an optimal orbit determination method and strategy. A continuous increasing acceleration is established by constructing a constant force that is equivalent to the pulse force, with the mass of the satellite decreasing throughout maneuver. This acceleration can be added to other accelerations, such as solar radiation, to obtain the continuous acceleration of the satellite. The orbit determination method and strategy are illuminated, with subsequent assessment of the orbit being determined and predicted accordingly. The orbit of the GEO satellite during repositioning maneuver can be determined and predicted by using C-Band pseudo-range observations of the BeiDou GEO satellite with COSPAR ID 2010-001A in 2011 and 2012. The results indicate that observations before maneuver do affect orbit determination and prediction, and should therefore be selected appropriately. A more precise orbit and prediction can be obtained compared to common short arc methods when observations starting 1 day prior the maneuver and 2 h after the maneuver are adopted in POD (Precise Orbit Determination). The achieved URE (User Range Error) under non-consideration of satellite clock errors is better than 2 m within the first 2 h after maneuver, and less than 3 m for further 2 h of orbit prediction.

Cao, Fen; Yang, XuHai; Li, ZhiGang; Sun, BaoQi; Kong, Yao; Chen, Liang; Feng, Chugang

2014-11-01

148

The iterative solution of the problem of orbit determination using Chebyshev series

NASA Technical Reports Server (NTRS)

A method of orbit determination is investigated which employs Picard iteration and Chebyshev series. The method is applied to the problem of determining the orbit of an earth satellite from range and range-rate observations contaminated by noise. It is shown to be readily applicable and to possess linear convergence.

Feagin, T.

1975-01-01

149

A study of orbit determination accuracies for future earth observatory missions

It is anticipated that global orbital accuracies of 10 meters will be required for future earth observatory missions. Results are presented of a study of the LANDSAT-1 orbit to determine position accuracies obtainable today so as to assess what future advancements are necessary to meet a 10-meter goal. Accuracies of 50 meters were determined to be achievable now from two-day

W. C. Bryant Jr.; C. C. Goad

1975-01-01

150

NASA Technical Reports Server (NTRS)

Onboard and real time image processing to enhance geometric correction of the data is discussed with application to autonomous navigation and attitude and orbit determination. Specific topics covered include: (1) LANDSAT landmark data; (2) star sensing and pattern recognition; (3) filtering algorithms for Global Positioning System; and (4) determining orbital elements for geostationary satellites.

Fuchs, A. J. (editor)

1979-01-01

151

Analytical determination of unstable periodic orbits in area preserving maps

NASA Astrophysics Data System (ADS)

The Birkhoff normal form, for the neighbourhood of an unstable fixed point of an analytical area preserving map, was proved by Moser to converge. We here show that the region of convergence in fact stretches along a narrow strip surrounding the stable and the unstable manifolds. Consequently the normal form can be used to compute homoclinic points and unstable periodic orbit families that accumulate on them. This is verified for quadratic maps: we find unstable orbits which return to themselves within an accuracy of twenty-one significant figures. A pair of linear equations is derived, which supply approximately all the periodic orbits accumulating on a given homoclinic point. This explicit formula is asymptotically valid in the limit of large periods.

Da Silva Ritter, G. L.; Ozorio De Almeida, A. M.; Douady, R.

1987-11-01

152

Orbit Determination Error Analysis Results for the Triana Sun-Earth L2 Libration Point Mission

NASA Technical Reports Server (NTRS)

Using the NASA Goddard Space Flight Center's Orbit Determination Error Analysis System (ODEAS), orbit determination error analysis results are presented for all phases of the Triana Sun-Earth L1 libration point mission and for the science data collection phase of a future Sun-Earth L2 libration point mission. The Triana spacecraft was nominally to be released by the Space Shuttle in a low Earth orbit, and this analysis focuses on that scenario. From the release orbit a transfer trajectory insertion (TTI) maneuver performed using a solid stage would increase the velocity be approximately 3.1 km/sec sending Triana on a direct trajectory to its mission orbit. The Triana mission orbit is a Sun-Earth L1 Lissajous orbit with a Sun-Earth-vehicle (SEV) angle between 4.0 and 15.0 degrees, which would be achieved after a Lissajous orbit insertion (LOI) maneuver at approximately launch plus 6 months. Because Triana was to be launched by the Space Shuttle, TTI could potentially occur over a 16 orbit range from low Earth orbit. This analysis was performed assuming TTI was performed from a low Earth orbit with an inclination of 28.5 degrees and assuming support from a combination of three Deep Space Network (DSN) stations, Goldstone, Canberra, and Madrid and four commercial Universal Space Network (USN) stations, Alaska, Hawaii, Perth, and Santiago. These ground stations would provide coherent two-way range and range rate tracking data usable for orbit determination. Larger range and range rate errors were assumed for the USN stations. Nominally, DSN support would end at TTI+144 hours assuming there were no USN problems. Post-TTI coverage for a range of TTI longitudes for a given nominal trajectory case were analyzed. The orbit determination error analysis after the first correction maneuver would be generally applicable to any libration point mission utilizing a direct trajectory.

Marr, G.

2003-01-01

153

Orbit determination of highly elliptical Earth orbiters using improved Doppler data-processing modes

NASA Technical Reports Server (NTRS)

A navigation error covariance analysis of four highly elliptical Earth orbits is described, with apogee heights ranging from 20,000 to 76,800 km and perigee heights ranging from 1,000 to 5,000 km. This analysis differs from earlier studies in that improved navigation data-processing modes were used to reduce the radio metric data. For this study, X-band (8.4-GHz) Doppler data were assumed to be acquired from two Deep Space Network radio antennas and reconstructed orbit errors propagated over a single day. Doppler measurements were formulated as total-count phase measurements and compared to the traditional formulation of differenced-count frequency measurements. In addition, an enhanced data-filtering strategy was used, which treated the principal ground system calibration errors affecting the data as filter parameters. Results suggest that a 40- to 60-percent accuracy improvement may be achievable over traditional data-processing modes in reconstructed orbit errors, with a substantial reduction in reconstructed velocity errors at perigee. Historically, this has been a regime in which stringent navigation requirements have been difficult to meet by conventional methods.

Estefan, J. A.

1995-01-01

154

NASA Technical Reports Server (NTRS)

Orbit determination results are obtained by the Goddard Space Flight Center (GSFC) Flight Dynamics Division (FDD) using the Goddard Trajectory Determination System (GTDS) and a real-time extended Kalman filter estimation system to process Tracking Data and Relay Satellite (TDRS) System (TDRSS) measurements in support of the Ocean Topography Experiment (TOPEX)/Poseidon spacecraft navigation and health and safety operations. GTDS is the operational orbit determination system used by the FDD, and the extended Kalman fliter was implemented in an analysis prototype system, the Real-Time Orbit Determination System/Enhanced (RTOD/E). The Precision Orbit Determination (POD) team within the GSFC Space Geodesy Branch generates an independent set of high-accuracy trajectories to support the TOPEX/Poseidon scientific data. These latter solutions use the Geodynamics (GEODYN) orbit determination system with laser ranging tracking data. The TOPEX/Poseidon trajectories were estimated for the October 22 - November 1, 1992, timeframe, for which the latest preliminary POD results were available. Independent assessments were made of the consistencies of solutions produced by the batch and sequential methods. The batch cases were assessed using overlap comparisons, while the sequential cases were assessed with covariances and the first measurement residuals. The batch least-squares and forward-filtered RTOD/E orbit solutions were compared with the definitive POD orbit solutions. The solution differences were generally less than 10 meters (m) for the batch least squares and less than 18 m for the sequential estimation solutions. The differences among the POD, GTDS, and RTOD/E solutions can be traced to differences in modeling and tracking data types, which are being analyzed in detail.

Doll, C.; Mistretta, G.; Hart, R.; Oza, D.; Cox, C.; Nemesure, M.; Bolvin, D.; Samii, Mina V.

1993-01-01

155

Orbit determination support for Hiten's aerobraking in the Earth's atmosphere

Two passes of the ISAS (Japan's Institute of Space and Astronautical Science) Hiten spacecraft through the Earth's atmosphere, at perigee altitudes of 125 km and 120 km, during Mar. 1991 marked the first aerobraking technology demonstrations for an object in cis-lunar orbit traveling at near Earth escape velocity. Prediction and control of perigee altitude to better than 1 km was

L. Efron; J. Ellis; P. R. Menon; B. Tucker

1991-01-01

156

Determination of SBUV\\/2 Sensor Electronic Offset in Orbital Measurements

A series of Solar Backscatter Ultraviolet Mod 2 instruments (SBUV\\/2) have flown on NOAA polar orbiting satellites for more than 18 years. They have continuously provided valuable long-term data records to monitor the global trends of the total ozone column density and the ozone profile in the upper atmosphere. In order to provide accurate ozone retrievals, many aspects of the

L. K. Huang; M. T. DeLand; C. A. McKay

2002-01-01

157

Validation of individual GOCE accelerometers by precise orbit determination

NASA Astrophysics Data System (ADS)

The European Space Agency (ESA) Gravity field and steady-state Ocean Circular Explorer (GOCE) carries a gradiometer consisting of three pairs of accelerometers in an orthogonal triad. Precise GOCE science orbit solutions (PSO), which are based on Satellite-to-Satellite Tracking (SST) observations by the Global Positioning System (GPS) and which are claimed to be at the few cm precision level, can be used to validate the observations taken by the accelerometers. This has been done for each individual accelerometer by a dynamic orbit fit of the time series of position coordinates from the PSOs, where the accelerometer observations represent the non-gravitational accelerations. Since the accelerometers do not coincide with the center of mass of the GOCE satellite, the observations have to be corrected for rotational and gravity gradient terms. This is opposed to using the so-called common-mode accelerations, provided the center of the gradiometer coincides with the center of mass. Dynamic orbit fits based on these common-mode accelerations therefore served as reference. It will be shown that for all individual accelerometers similar dynamic orbit fits can be obtained, provided the above mentioned corrections are made. When using the common-mode accelerations, similar fits are obtained. In addition, attention will be paid to the possibility of estimating accelerometer calibration parameters, such as biases and scale factors.

Visser, Pieter N. A. M.

2012-07-01

158

NASA Technical Reports Server (NTRS)

The development of the Real-Time Orbit Determination/Enhanced (RTOD/E) system as a prototype system for sequential orbit determination on a Disk Operating System (DOS) based Personal Computer (PC) is addressed. The results of a study to compare the orbit determination accuracy of a Tracking and Data Relay Satellite System (TDRSS) user spacecraft obtained using RTOD/E with the accuracy of an established batch least squares system, the Goddard Trajectory Determination System (GTDS), is addressed. Independent assessments were made to examine the consistencies of results obtained by the batch and sequential methods. Comparisons were made between the forward filtered RTOD/E orbit solutions and definitive GTDS orbit solutions for the Earth Radiation Budget Satellite (ERBS); the maximum solution differences were less than 25 m after the filter had reached steady state.

Oza, D. H.; Jones, T. L.; Hodjatzadeh, M.; Samii, M. V.; Doll, C. E.; Hart, R. C.; Mistretta, G. D.

1991-01-01

159

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

NASA Technical Reports Server (NTRS)

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.

1988-01-01

160

NASA Technical Reports Server (NTRS)

The Memory Test Experiment is a space test of a ferroelectric memory device on a low Earth orbit satellite that launched in November 2010. The memory device being tested is a commercial Ramtron Inc. 512K memory device. The circuit was designed into the satellite avionics and is not used to control the satellite. The test consists of writing and reading data with the ferroelectric based memory device. Any errors are detected and are stored on board the satellite. The data is sent to the ground through telemetry once a day. Analysis of the data can determine the kind of error that was found and will lead to a better understanding of the effects of space radiation on memory systems. The test is one of the first flight demonstrations of ferroelectric memory in a near polar orbit which allows testing in a varied radiation environment. The initial data from the test is presented. This paper details the goals and purpose of this experiment as well as the development process. The process for analyzing the data to gain the maximum understanding of the performance of the ferroelectric memory device is detailed.

MacLeond, Todd C.; Sims, W. Herb; Varnavas,Kosta A.; Ho, Fat D.

2011-01-01

161

NASA Technical Reports Server (NTRS)

The Goddard Space Flight Center (GSFC) Flight Dynamics Division (FDD) commissioned Applied Technology Associates, Incorporated, to develop the Real-Time Orbit Determination/Enhanced (RTOD/E) system on a Disk Operating System (DOS)-based personal computer (PC) as a prototype system for sequential orbit determination of spacecraft. This paper presents the results of a study to compare the orbit determination accuracy for a Tracking and Data Relay Satellite (TDRS) System (TDRSS) user spacecraft, Landsat-4, obtained using RTOD/E, operating on a PC, with the accuracy of an established batch least-squares system, the Goddard Trajectory Determination System (GTDS), operating on a mainframe computer. The results of Landsat-4 orbit determination will provide useful experience for the Earth Observing System (EOS) series of satellites. The Landsat-4 ephemerides were estimated for the May 18-24, 1992, timeframe, during which intensive TDRSS tracking data for Landsat-4 were available. During this period, there were two separate orbit-adjust maneuvers on one of the TDRSS spacecraft (TDRS-East) and one small orbit-adjust maneuver for Landsat-4. Independent assessments were made of the consistencies (overlap comparisons for the batch case and covariances and the first measurement residuals for the sequential case) of solutions produced by the batch and sequential methods. The forward-filtered RTOD/E orbit solutions were compared with the definitive GTDS orbit solutions for Landsat-4; the solution differences were generally less than 30 meters after the filter had reached steady state.

Oza, D. H.; Jones, T. L.; Feiertag, R.; Samii, M. V.; Doll, C. E.; Mistretta, G. D.; Hart, R. C.

1993-01-01

162

Calibration of GOCE Accelerometers by Precise Orbit Determination

NASA Astrophysics Data System (ADS)

The European Space Agency (ESA) Gravity field and steady-state Ocean Circular Explorer (GOCE) carries a gradiometer consisting of three pairs of accelerometers in an orthogonal triad. Precise GOCE science orbit solutions (PSO), which are based on Satellite-to-Satellite Tracking (SST) observations by the Global Positioning System (GPS) and which are claimed to be at the few cm precision level, have been used to calibrate the observations taken by the accelerometers. This has been done for each individual accelerometer by a dynamic orbit fit of the time series of position coordinates from the PSOs, where the accelerometer observations represent the non-gravitational accelerations. Since the individual accelerometers do not coincide with the center of mass of the GOCE satellite, the observations have to be corrected for rotational and gravity gradient terms. This is opposed to using the so-called common-mode accelerations, provided the center of the gradiometer coincides with the center of mass. Dynamic orbit fits based on these common-mode accelerations therefore served as reference. It will be shown that for all individual accelerometers similar dynamic orbit fits can be obtained comparable to the fits achieved using the common-mode accelerations, provided the above mentioned corrections are made. In addition, attention will be paid to the possibility of estimating accelerometer calibration parameters, such as biases and scale factors. Furthermore, an assessment was made of remaining gravity field modeling errors on the estimates of the calibration parameters. Acknowledgment. The European Space Agency is acknowledged for supporting this study and providing the GOCE observations.

Visser, P. N.

2012-12-01

163

Comparison of ERBS orbit determination accuracy using batch least-squares and sequential methods

NASA Technical Reports Server (NTRS)

The Flight Dynamics Div. (FDD) at NASA-Goddard commissioned a study to develop the Real Time Orbit Determination/Enhanced (RTOD/E) system as a prototype system for sequential orbit determination of spacecraft on a DOS based personal computer (PC). An overview is presented of RTOD/E capabilities and the results are presented of a study to compare the orbit determination accuracy for a Tracking and Data Relay Satellite System (TDRSS) user spacecraft obtained using RTOS/E on a PC with the accuracy of an established batch least squares system, the Goddard Trajectory Determination System (GTDS), operating on a mainframe computer. RTOD/E was used to perform sequential orbit determination for the Earth Radiation Budget Satellite (ERBS), and the Goddard Trajectory Determination System (GTDS) was used to perform the batch least squares orbit determination. The estimated ERBS ephemerides were obtained for the Aug. 16 to 22, 1989, timeframe, during which intensive TDRSS tracking data for ERBS were available. Independent assessments were made to examine the consistencies of results obtained by the batch and sequential methods. Comparisons were made between the forward filtered RTOD/E orbit solutions and definitive GTDS orbit solutions for ERBS; the solution differences were less than 40 meters after the filter had reached steady state.

Oza, D. H.; Jones, T. L.; Fabien, S. M.; Mistretta, G. D.; Hart, R. C.; Doll, C. E.

1991-01-01

164

GPS orbit determination at the National Geodetic Survey

NASA Technical Reports Server (NTRS)

The National Geodetic Survey (NGS) independently generates precise ephemerides for all available Global Positioning System (GPS) satellites. Beginning in 1991, these ephemerides were produced from double-differenced phase observations solely from the Cooperative International GPS Network (CIGNET) tracking sites. The double-difference technique combines simultaneous observations of two satellites from two ground stations effectively eliminating satellite and ground receiver clock errors, and the Selective Availability (S/A) signal degradation currently in effect. CIGNET is a global GPS tracking network whose primary purpose is to provide data for orbit production. The CIGNET data are collected daily at NGS and are available to the public. Each ephemeris covers a single week and is available within one month after the data were taken. Verification is by baseline repeatability and direct comparison with other ephemerides. Typically, an ephemeris is accurate at a few parts in 10(exp 7). This corresponds to a 10 meter error in the reported satellite positions. NGS is actively investigating methods to improve the accuracy of its orbits, the ultimate goal being one part in 10(exp 8) or better. The ephemerides are generally available to the public through the Coast Guard GPS Information Center or directly from NGS through the Geodetic Information Service. An overview of the techniques and software used in orbit generation will be given, the current status of CIGNET will be described, and a summary of the ephemeris verification results will be presented.

Schenewerk, Mark S.

1992-01-01

165

Orbit Determination and Navigation of the Solar Terrestrial Relations Observatory (STEREO)

NASA Technical Reports Server (NTRS)

This paper provides an overview of the required upgrades necessary for navigation of NASA's twin heliocentric science missions, Solar TErestrial RElations Observatory (STEREO) Ahead and Behind. The orbit determination of the STEREO spacecraft was provided by the NASA Goddard Space Flight Center's (GSFC) Flight Dynamics Facility (FDF) in support of the mission operations activities performed by the Johns Hopkins University Applied Physics Laboratory (APL). The changes to FDF's orbit determination software included modeling upgrades as well as modifications required to process the Deep Space Network X-band tracking data used for STEREO. Orbit results as well as comparisons to independently computed solutions are also included. The successful orbit determination support aided in maneuvering the STEREO spacecraft, launched on October 26, 2006 (00:52 Z), to target the lunar gravity assists required to place the spacecraft into their final heliocentric drift-away orbits where they are providing stereo imaging of the Sun.

Mesarch, Michael A.; Robertson, Mika; Ottenstein, Neil; Nicholson, Ann; Nicholson, Mark; Ward, Douglas T.; Cosgrove, Jennifer; German, Darla; Hendry, Stephen; Shaw, James

2007-01-01

166

Laser ranging network performance and routine orbit determination at D-PAF

NASA Technical Reports Server (NTRS)

ERS-1 is now about 8 months in orbit and has been tracked by the global laser network from the very beginning of the mission. The German processing and archiving facility for ERS-1 (D-PAF) is coordinating and supporting the network and performing the different routine orbit determination tasks. This paper presents details about the global network status, the communication to D-PAF and the tracking data and orbit processing system at D-PAF. The quality of the preliminary and precise orbits are shown and some problem areas are identified.

Massmann, Franz-Heinrich; Reigber, C.; Li, H.; Koenig, Rolf; Raimondo, J. C.; Rajasenan, C.; Vei, M.

1993-01-01

167

AIAA-98-4308 Autonomous LEO Orbit Determination From Magnetometer and Sun Sensor Data

AIAA-98-4308 Autonomous LEO Orbit Determination From Magnetometer and Sun Sensor Data Mark L to autonomously estimate the orbit of a LEO spacecraft using data only from a magnetometer and a sun sensor parameters, a drag parameter, magnetometer biases, and corrections to the Earth's magnetic field. It does

Psiaki, Mark L.

168

Precise orbit determination and gravity field improvement for the ERS satellites

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

169

Aleksandar KOSTADINOV: Expected performance of Orbit Determination of the GALILEO Satellites

Aleksandar KOSTADINOV: Expected performance of Orbit Determination of the GALILEO Satellites (completed JÃ¤nner 2003) In March 2002 the European Union decided to finance the GALILEO orbits (MEOs) at 23600 km altitude. The launch of the first GALILEO satellites can be expected

Schuh, Harald

170

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

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

George M. Levin

1996-01-01

171

NASA Astrophysics Data System (ADS)

A new method is proposed for computing the preliminary orbit of a small celestial body from three pairs of range and range rate observations. The method is based on using the intermediate orbit that we previously constructed from two position vectors and the corresponding time instants. This intermediate orbit allows for most of the perturbations in the motion of the body under study. The methodical error of orbit determination by the proposed method is two orders smaller than the corresponding error of the commonly used approach based on the construction of the unperturbed Keplerian orbit. Using the examples of finding the orbits of artificial Earth satellites, the results obtained by the procedure implementing the traditional approach and the new method are compared. The comparison shows that the new method is a highly efficient means for studying perturbed motion.

Shefer, V. A.

2012-12-01

172

Present status and future trends in near-Earth satellite orbit determination

NASA Technical Reports Server (NTRS)

The major components of an orbit determination system and the evolution of the elements making up each component are reviewed. Typical accuracies presently achievable in the orbit determination process, the factors limiting the accuracies, and improvements in the dynamic models used in the process are summarized. Models are developed for orbit determination programs which include: (1) time varying area for solar radiation pressure; (2) a time varying model for albedo radiation pressure; (3) Earth tides which account for the distortions in the Earth's body due to Sun and Moon attraction; and (4) ocean tides which affect satellite altimeter data.

Fuchs, A. J.

1981-01-01

173

NASA Technical Reports Server (NTRS)

A covariance analysis is presented for satellite tracking and gravity recovery with a differential Global Positioning System-based technique to be demonstrated on TOPEX in the early 1990s. The technique employs data from an ensemble of repeat ground tracks to recover a unique satellite epoch state for each track and a set of invariant positional parameters common to all tracks. The positional parameters represent the effect of mismodeled gravitational field on the satellite orbit. At an altitude of 1336 km, where gravity modeling is the dominant systematic error, averaging of random error over many arcs and adjustment of the gravity model reduce the final satellite position error. The positional parameters can then be used to produce a refined global gravity model. The analysis indicates that errors ranging from 5 to 8 cm in TOPEX altitude and 0.05 to 0.2 mGal for the gravity field can be achieved, depending on the number of repeat arcs used.

Wu, Jiun-Tsong; Yunck, Thomas P.

1992-01-01

174

Determining Mars parking orbits which ensure tangential periapsis burns at arrival and departure

NASA Technical Reports Server (NTRS)

A method is presented which finds Mars parking orbits which allow tangential periapsis burns at both arrival and departure. This method accounts for the actual geometry at both arrival and departure between the hyperbolic asymptotes and the orbital plane, along with the precession effects caused by the oblateness of Mars. Thus, realistic Delta-V values (and hence initial low-earth orbit masses) are obtained for these orbits. The results obtained from the present method compare very well with a trajectory integration program while only requiring CPU times of about one minute. Therefore, due to the computational efficiency and accuracy, the present method would be an ideal tool to use in preliminary mission design, since it provides the opportunity to incorporate realistic Mars parking orbits effects.

Desai, Prasun N.; Buglia, James J.

1992-01-01

175

NASA Technical Reports Server (NTRS)

Refinements of the orbital elements for 24 minor planets that will be observed with the Fine Guidance Sensors (FGSs) on the Hubble Space Telescope (HST) are presented. The accuracy of these orbits is discussed in the context of the ephemeris requirements for target acquisition with the FGSs. Comparisons with standard catalog orbits are made to evaluate the suitability of the use of the catalog orbits for HST pointing. It is found that the orbits published in the most recent Minor Planet Circulars are capable of positional predictions that are accurate at the 1-arcsec level. However, there are still many orbits that have not been revised in the last 10 yr and these should not be used for critical pointing ephemerides. In many cases, the orbital elements will have to be refined using recent ground-based observations before a minor planet can be reliably observed by HST.

Whipple, Arthur L.; Hemenway, Paul D.; Ingram, Doug

1991-01-01

176

NASA Astrophysics Data System (ADS)

Satellite Laser Ranging (SLR) measurements contain information about the spin parameters of the fully passive, geodetic satellites. In this paper we spectrally analyze the SLR data of 5 geodetic satellites placed on the Low Earth Orbits: GFZ-1, WESTPAC, Larets, Starlette, Stella, and successfully retrieve the frequency signal from Larets and Stella only. The obtained signals indicate an exponential increase of the spin period of Larets: T = 0.860499·exp(0.0197066·D) [s], and Stella: T = 13.5582·exp(0.00431232·D) [s], where D is in days since launch. The initial spin periods calculated from the first month of the SLR observations are: Larets: Tinitial = 0.8239 s, Stella: Tinitial = 13.2048 s. Analysis of the apparent effects indicates the counter-clockwise spin direction of the satellites. The twice more heavy Stella lost its rotational energy more than four times slower than Larets. Fitting the spin model to the observed spin trends allows determination of the spin axis orientation evolution for Larets and Stella before their rotational period becomes equal to the orbital period.

Kucharski, D.; Lim, H.-C.; Kirchner, G.; Koidl, F.

2014-01-01

177

On precise orbit determination of HY-2 with space geodetic techniques

NASA Astrophysics Data System (ADS)

As the first radar altimetric satellite of China, HY-2 requires the precise orbit determination with a higher accuracy than that of other satellites. In order to achieve the designed radial orbit with the accuracy better than 10 cm for HY-2, the methods of precise orbit determination for HY-2 with the centimeter-level accuracy based on space geodetic techniques (DORIS, SLR, and satellite-borne GPS) are studied in this paper. Perturbations on HY-2 orbit are analyzed, in particular those due to the non-spherical gravitation of the earth, ocean tide, solid earth tide, solar and earth radiation, and atmospheric drag. Space geodetic data of HY-2 are simulated with the designed HY-2 orbit parameters based on the orbit dynamics theory to optimize the approaches and strategies of precise orbit determination of HY-2 with the dynamic and reduced-dynamic methods, respectively. Different methods based on different techniques are analyzed and compared. The experiment results show that the nonspherical perturbation modeled by GGM02C causes a maximum perturbation, and errors caused by the imperfect modeling of atmospheric drag have an increasing trend on T direction, but errors are relatively stable on the other two directions; besides, the methods with three space geodetic techniques achieve the radial orbit with the precision better than 10 cm.

Guo, Jinyun; Kong, Qiaoli; Qin, Jian; Sun, Yu

2013-06-01

178

Improved solution accuracy for TDRSS-based TOPEX/Poseidon orbit determination

NASA Technical Reports Server (NTRS)

Orbit determination results are obtained by the Goddard Space Flight Center (GSFC) Flight Dynamics Division (FDD) using a batch-least-squares estimator available in the Goddard Trajectory Determination System (GTDS) and an extended Kalman filter estimation system to process Tracking and Data Relay Satellite (TDRS) System (TDRSS) measurements. GTDS is the operational orbit determination system used by the FDD in support of the Ocean Topography Experiment (TOPEX)/Poseidon spacecraft navigation and health and safety operations. The extended Kalman filter was implemented in an orbit determination analysis prototype system, closely related to the Real-Time Orbit Determination System/Enhanced (RTOD/E) system. In addition, the Precision Orbit Determination (POD) team within the GSFC Space Geodesy Branch generated an independent set of high-accuracy trajectories to support the TOPEX/Poseidon scientific data. These latter solutions use the geodynamics (GEODYN) orbit determination system with laser ranging and Doppler Orbitography and Radiopositioning integrated by satellite (DORIS) tracking measurements. The TOPEX/Poseidon trajectories were estimated for November 7 through November 11, 1992, the timeframe under study. Independent assessments were made of the consistencies of solutions produced by the batch and sequential methods. The batch-least-squares solutions were assessed based on the solution residuals, while the sequential solutions were assessed based on primarily the estimated covariances. The batch-least-squares and sequential orbit solutions were compared with the definitive POD orbit solutions. The solution differences were generally less than 2 meters for the batch-least-squares and less than 13 meters for the sequential estimation solutions. After the sequential estimation solutions were processed with a smoother algorithm, position differences with POD orbit solutions of less than 7 meters were obtained. The differences among the POD, GTDS, and filter/smoother solutions can be traced to differences in modeling and tracking data types, which are being analyzed in detail.

Doll, C. E.; Mistretta, G. D.; Hart, R. C.; Oza, D. H.; Bolvin, D. T.; Cox, C. M.; Nemesure, M.; Niklewski, D. J.; Samii, M. V.

1994-01-01

179

Precise orbit determination of Smart-1 and Chang'E-1

NASA Astrophysics Data System (ADS)

The Smart-1 was tracked by Chinese VLBI network and USB stations from 28 May, 2006 to 2 June, 2006 as a test for Chinese deep space network tracking ability, precise orbit determination was processed combining VLBI delay, delay rate and Doppler data. The reaction wheel unloadings were considered in long arc orbit determination, it showed good consistency with reconstructed orbit provided by ESA, the strategy used in smart-1 was used in Chang'E-1 precise orbit determination. Chang'E-1 was launched at 24 Oct, 2007, one of the main scientific objections is to map the lunar surface and get 3-D lunar topography model by satellite laser altimetry. The precise orbit determination of Chang'E-1 was realized by combining VLBI and USB data using GEODYNII/SOVLE software of GSFC/NASA/USA (Rowland,1997; Ullman,1994),, the frequently reaction wheel unloadings are considered in order to get high accuracy and continuous orbit, which can attribute to the laser altimetry data process and possible lunar gravity field recovery. Keywords: smart-1, Chang'E-1, precise orbit determination, reaction wheel unloading

Jianguo, Yan; Ping, Jing-Song; Li, Fei

180

Orbit determination for Magellan and Pioneer 12 using same-beam interferometry

NASA Technical Reports Server (NTRS)

Simultaneous tracking of two spacecraft in orbit about a distant planet, by two widely-separated earth-based radio antennas, provides more accurate positioning information than can be obtained by tracking each spacecraft separately. A demonstration of this tracking technique, referred to as Same-Beam Interferometry (SBI), is in progress using the Magellan and Pioneer 12 orbiters at Venus. Signals from both spacecraft fall within the same beamwidth of the earth-based tracking antennas. The plane-of-sky position difference between spacecraft is precisely determined by double-differenced phase measurements. This data type complements line-of-sight Doppler. Data were collected from Magellan and Pioneer 12 on Aug. 11-12, 1990, shortly after Magellan was inserted into Venus orbit. Orbits for both spacecraft were fit with one day data arc using Doppler and SBI data and compared to orbits fit to only Doppler data. The Doppler plus SBI orbits show improved orbit-to-orbit consistency over the Doppler-only orbits.

Folkner, W. M.; Engelhardt, D. B.; Border, J. S.; Mottinger, N. A.

1992-01-01

181

IRS-P6 orbit determination and achieved accuracy during early phase

The IRS-P6 satellite launched by the Indian Space Research Organization (ISRO) is envisaged as a continuity mission of ISRO's earlier spacecraft IRS-1C and IRS-1D, with enhanced capabilities both in the platform and payloads. The orbit determination results for all the Indian Remote Sensing (IRS) satellites of ISRO are obtained by the operational orbit determination software “ISRO-ODP” developed at ISRO Satellite

N. V. Vighnesam; Anatta Sonney; Boominathan Subramanian; Pramod Kumar Soni

2007-01-01

182

A high order method for orbital conjunctions analysis: Sensitivity to initial uncertainties

NASA Astrophysics Data System (ADS)

A high order method to quickly assess the effect that uncertainties produce on orbital conjunctions through a numerical high-fidelity propagator is presented. In particular, the dependency of time and distance of closest approach to initial uncertainties on position and velocity of both objects involved in a conjunction is studied. The approach relies on a numerical integration based on differential algebraic techniques and a high-order algorithm that expands the time and distance of closest approach in Taylor series with respect to relevant uncertainties. The modeled perturbations are atmospheric drag, using NRLMSISE-00 air density model, solar radiation pressure with shadow, third body perturbation using JPL's DE405 ephemeris, and EGM2008 gravity model. The polynomial approximation of the final position is used as an input to compute analytically the expansion of time and distance of closest approach. As a result, the analysis of a close encounter can be performed through fast, multiple evaluations of Taylor polynomials. Test cases with objects ranging from LEO to GEO regimes are considered to assess the performances and the accuracy of the proposed method.

Morselli, Alessandro; Armellin, Roberto; Di Lizia, Pierluigi; Bernelli Zazzera, Franco

2014-02-01

183

NASA Astrophysics Data System (ADS)

As a special approach to orbit determination for satellites with spaceborne GPS receivers, the kinematic Precise Orbit Determination (POD) is independent of any mechanical model (e.g., the Earth gravity ?eld, atmospheric drag, solar radiation pressure, etc.), and thus especially suitable for the orbit determination of Low Earth Orbiting (LEO)satellites perturbed strongly bythe atmosphere. In this paper, based on the space-borne dual-frequency GPS data, we study the kinematic POD, discuss the pre-processing of the data, and construct an algorithm of zero-difference kinematic POD. Using the observational data from GRACE (Gravity Recovery And Climate Experiment) satellites covering the whole month of February 2008, we verify the effectiveness and reliability of this algorithm. The results show that the kinematic POD may attain an accuracy of about 5 cm (with respect to satellite laser ranging data), which is at the same level as the dynamic and reduced-dynamic PODs

Peng, Dong-ju; Wu, Bin

2012-07-01

184

Improved solution accuracy for Landsat-4 (TDRSS-user) orbit determination

NASA Technical Reports Server (NTRS)

This paper presents the results of a study to compare the orbit determination accuracy for a Tracking and Data Relay Satellite System (TDRSS) user spacecraft, Landsat-4, obtained using a Prototype Filter Smoother (PFS), with the accuracy of an established batch-least-squares system, the Goddard Trajectory Determination System (GTDS). The results of Landsat-4 orbit determination will provide useful experience for the Earth Observing System (EOS) series of satellites. The Landsat-4 ephemerides were estimated for the January 17-23, 1991, timeframe, during which intensive TDRSS tracking data for Landsat-4 were available. Independent assessments were made of the consistencies (overlap comparisons for the batch case and convariances for the sequential case) of solutions produced by the batch and sequential methods. The filtered and smoothed PFS orbit solutions were compared with the definitive GTDS orbit solutions for Landsat-4; the solution differences were generally less than 15 meters.

Oza, D. H.; Niklewski, D. J.; Doll, C. E.; Mistretta, G. D.; Hart, R. C.

1994-01-01

185

Precise orbit determination of Compass-M1: a primary result

NASA Astrophysics Data System (ADS)

On April 13, 2007, the first experiment satellite, Compass-M1, of China's the second generation Compass Navigation system was successfully launched. Unlike previous Compass satellites, Compass-M1 is the first satellite in medium earth orbit (MEO), and broadcast navigation signals in multi-frequencies in L-band. If signals were received from more than four satellites, users can determine their locations in a passive manner like using GPS. A primary result of precise orbit determination of Compass-M1 is presented in this paper. Five tracking stations, all located in China, are used. Double-frequency code and carrier phase observations are processed in zero-difference mode. Receiver and satellite clocks are modeled by linear or quadratic polynomial. The radiation pressure model is the so-called extended CODE orbit model, and an a priori model is introduced according to the size and physical attribute of Compass-M1. The solution is based on 3-day arc dynamical precise orbit determination. Estimated parameters include six keplerian orbit elements, two radiation pressure model parameters and clock polynomial coefficients. Orbit overlap difference and validating with SLR indicate that the accuracy of the precise orbit is quite exciting and exceeds our expectation.

Sun, Baoqi

186

TDRSS-user orbit determination using batch least-squares and sequential methods

NASA Technical Reports Server (NTRS)

The Goddard Space Flight Center (GSFC) Flight Dynamics Division (FDD) commissioned Applied Technology Associates, Incorporated, to develop the Real-Time Orbit Determination/Enhanced (RTOD/E) system on a Disk Operating System (DOS)-based personal computer (PC) as a prototype system for sequential orbit determination of spacecraft. This paper presents the results of a study to compare the orbit determination accuracy for a Tracking and Data Relay Satellite System (TDRSS) user spacecraft, Landsat-4, obtained using RTOD/E, operating on a PC, with the accuracy of an established batch least-squares system, the Goddard Trajectory Determination System (GTDS), and operating on a mainframe computer. The results of Landsat-4 orbit determination will provide useful experience for the Earth Observing System (EOS) series of satellites. The Landsat-4 ephemerides were estimated for the January 17-23, 1991, timeframe, during which intensive TDRSS tracking data for Landsat-4 were available. Independent assessments were made of the consistencies (overlap comparisons for the batch case and covariances and the first measurement residuals for the sequential case) of solutions produced by the batch and sequential methods. The forward-filtered RTOD/E orbit solutions were compared with the definitive GTDS orbit solutions for Landsat-4; the solution differences were less than 40 meters after the filter had reached steady state.

Oza, D. H.; Jones, T. L.; Hakimi, M.; Samii, Mina V.; Doll, C. E.; Mistretta, G. D.; Hart, R. C.

1993-01-01

187

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

188

Radial orbit error reduction and sea surface topography determination using satellite altimetry

NASA Technical Reports Server (NTRS)

A method is presented in satellite altimetry that attempts to simultaneously determine the geoid and sea surface topography with minimum wavelengths of about 500 km and to reduce the radial orbit error caused by geopotential errors. The modeling of the radial orbit error is made using the linearized Lagrangian perturbation theory. Secular and second order effects are also included. After a rather extensive validation of the linearized equations, alternative expressions of the radial orbit error are derived. Numerical estimates for the radial orbit error and geoid undulation error are computed using the differences of two geopotential models as potential coefficient errors, for a SEASAT orbit. To provide statistical estimates of the radial distances and the geoid, a covariance propagation is made based on the full geopotential covariance. Accuracy estimates for the SEASAT orbits are given which agree quite well with already published results. Observation equations are develped using sea surface heights and crossover discrepancies as observables. A minimum variance solution with prior information provides estimates of parameters representing the sea surface topography and corrections to the gravity field that is used for the orbit generation. The simulation results show that the method can be used to effectively reduce the radial orbit error and recover the sea surface topography.

Engelis, Theodossios

1987-01-01

189

OREMUS: Prototype of an orbit determination center dedicated to mini-satellite control

NASA Astrophysics Data System (ADS)

The OREMUS project aims to achieve at moderate cost a ground segment prototype for the purposes of orbiting satellite operations. In order to demonstrate the feasibility of a general system capable of satisfying the requirements of various users, main functions to be improved are data acquisition, orbit restitution, orbital maneuver calculations, and orbit linked expected operations. MERCATOR system architecture, components, capabilities, interest, and performance are recalled as well as the OOC (Operational Orbit determination Center) needs as regards the software. Characteristics and advantages of a new man machine interface called SISSI are presented. The OREMUS general system is based on MERCATOR and SISSI functions, and on the recovery of former modulus used in spatial mechanics. Descriptor files are documented by the users. Prototype main functions, data acquisition, orbit restitution, attitude restitution, orbital maneuver calculations, orbit linked expected operations, file management, and parameters graphic visualization are available in a control ground segment. These functions are performed by means of modulus; the linking and interfaces of which are managed by the man machine interface.

Laporte, Francois; Campan, Genevieve; Conessa, Huguette

1993-01-01

190

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

191

A demonstration of high precision GPS orbit determination for geodetic applications

NASA Technical Reports Server (NTRS)

High precision orbit determination of Global Positioning System (GPS) satellites is a key requirement for GPS-based precise geodetic measurements and precise low-earth orbiter tracking, currently under study at JPL. Different strategies for orbit determination have been explored at JPL with data from a 1985 GPS field experiment. The most successful strategy uses multi-day arcs for orbit determination and includes fine tuning of spacecraft solar pressure coefficients and station zenith tropospheric delays using the GPS data. Average rms orbit repeatability values for 5 of the GPS satellites are 1.0, 1.2, and 1.7 m in altitude, cross-track, and down-track componenets when two independent 5-day fits are compared. Orbit predictions up to 24 hours outside the multi-day arcs agree within 4 m of independent solutions obtained with well tracked satellites in the prediction interval. Baseline repeatability improves with multi-day as compared to single-day arc orbit solutions. When tropospheric delay fluctuations are modeled with process noise, significant additional improvement in baseline repeatability is achieved. For a 246-km baseline, with 6-day arc solutions for GPS orbits, baseline repeatability is 2 parts in 100 million (0.4-0.6 cm) for east, north, and length components and 8 parts in 100 million for the vertical component. For 1314 and 1509 km baselines with the same orbits, baseline repeatability is 2 parts in 100 million for the north components (2-3 cm) and 4 parts in 100 million or better for east, length, and vertical components.

Lichten, S. M.; Border, J. S.

1987-01-01

192

Onboard orbit determination using GPS observations based on the unscented Kalman filter

NASA Astrophysics Data System (ADS)

Spaceborne GPS receivers are used for real-time navigation by most low Earth orbit (LEO) satellites. In general, the position and velocity accuracy of GPS navigation solutions without a dynamic filter are 25 m (1 ?) and 0.5 m/s (1 ?), respectively. However, GPS navigation solutions, which consist of position, velocity, and GPS receiver clock bias, have many abnormal excursions from the normal error range for space operation. These excursions lessen the accuracy of attitude control and onboard time synchronization. In this research, a new onboard orbit determination algorithm designed with the unscented Kalman filter (UKF) was developed to improve the performance. Because the UKF is able to obtain the posterior mean and covariance accurately by using the second-order Taylor series expansion through the sampled sigma points that are propagated by using the true nonlinear system, its performance can be better than that of the extended Kalman filter (EKF), which uses the linearized state transition matrix to predict the covariance. The dynamic models for orbit propagation applied perturbations due to the 40 × 40 geo-potential, the gravity of the Sun and Moon, solar radiation pressure, and atmospheric drag. The 7(8)th-order Runge-Kutta numerical integration was applied for orbit propagation. Two types of observations, navigation solutions and C/A code pseudorange, can be used at the user's discretion. The performances of the onboard orbit determination were verified using real GPS data of the CHAMP and KOMPSAT-2 satellites. The results of the orbit determination were compared with the precision orbit ephemeris (POE) of the CHAMP and KOMPSAT-2 satellites. The comparison of the orbit determination results using EKF and UKF shows that orbit determination using the UKF yields better results than that using the EKF. In addition, the estimation of the accuracy using the C/A code pseudorange is better than that using the navigation solutions. The absolute position and velocity accuracies of the UKF using GPS C/A code pseudorange were 12.098 m and 0.0159 m/s in the case of the CHAMP satellite, and 8.172 m and 0.0085 m/s in the case of the KOMPSAT-2 satellite. Moreover, the abnormal excursions of navigation solutions can be eliminated. These results verify that onboard orbit determination using GPS C/A code pseudorange, which is based on the UKF can provide more stable and accurate orbit information in the spaceborne GPS receiver.

Choi, Eun-Jung; Yoon, Jae-Cheol; Lee, Byoung-Sun; Park, Sang-Young; Choi, Kyu-Hong

2010-12-01

193

RESEARCH ARTICLE Open Access Determinants of smoking initiation among

RESEARCH ARTICLE Open Access Determinants of smoking initiation among women in five European Gritz11 , Mia Hashibe1,12* Abstract 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

Paris-Sud XI, UniversitÃ© de

194

FEDS - An experiment with a microprocessor-based orbit determination system using TDRS data

NASA Technical Reports Server (NTRS)

An experiment in microprocessor-based onboard orbit determination has been conducted at NASA's Goddard Space Flight Center. The experiment collected forward-link observation data in real time from a prototype transponder and performed orbit estimation on a typical low-earth scientific satellite. This paper discusses the hardware and organizational configurations of the experiment, the structure of the onboard software, the mathematical models, and the experiment results.

Shank, D.; Pajerski, R.

1986-01-01

195

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

196

Orbit and attitude determination results during launch support operations for SBS-5

NASA Technical Reports Server (NTRS)

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 low inclination transfer orbit. Apogee motor firing (AMF) attitude was achieved with trim maneuvers. An apogee kick motor placed the spacecraft into drift orbit. Postburn, reorientation and spindown maneuvers were performed during the next 25 hours. The spacecraft was on-station 19 days later. The orbit and attitude were determined by both an extended Kalman filter and a weighted least squares batch processor. Although the orbit inclination was low and the launch was near equinox, post-AMF analysis indicated an attitude declination error of 0.034 deg., resulting in a saving of 8.5 pounds of fuel. The AMF velocity error was 0.4 percent below nominal. The post-AMF drift rate was determined with the filter only 2.5 hours after motor firing. The filter was used to monitor and retarget the reorientation to orbit normal in real time.

Hartman, K. R.; Iano, P. J.

1989-01-01

197

Low-cost autonomous orbit control about Mars: Initial simulation results

Interest in studying the possibility of extraterrestrial life has led to the re-emergence of the Red Planet as a major target of planetary exploration. Currently proposed missions in the post-2000 period are routinely calling for rendezvous with ascent craft, long-term orbiting of, and sample-return from Mars. Such missions would benefit greatly from autonomous orbit control as a means to reduce

S. D Dawson; L. W Early; C. W Potterveld; H. J Königsmann

1999-01-01

198

A review of GPS-based tracking techniques for TDRS orbit determination

NASA Technical Reports Server (NTRS)

This article evaluates two fundamentally different approaches to the Tracking and Data Relay Satellite (TDRS) orbit determination utilizing Global Positioning System (GPS) technology and GPS-related techniques. In the first, a GPS flight receiver is deployed on the TDRS. The TDRS ephemerides are determined using direct ranging to the GPS spacecraft, and no ground network is required. In the second approach, the TDRS's broadcast a suitable beacon signal, permitting the simultaneous tracking of GPS and Tracking and Data Relay Satellite System satellites by ground receivers. Both strategies can be designed to meet future operational requirements for TDRS-II orbit determination.

Haines, B. J.; Lichten, S. M.; Malla, R. P.; Wu, S.-C.

1993-01-01

199

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

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

2013-01-01

200

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

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

2013-01-01

201

NASA Technical Reports Server (NTRS)

The tracking of space objects requires frequent and accurate monitoring for collision avoidance. As even collision events with very low probability are important, accurate prediction of collisions require the representation of the full probability density function (PDF) of the random orbit state. Through representing the full PDF of the orbit state for orbit maintenance and collision avoidance, we can take advantage of the statistical information present in the heavy tailed distributions, more accurately representing the orbit states with low probability. The classical methods of orbit determination (i.e. Kalman Filter and its derivatives) provide state estimates based on only the second moments of the state and measurement errors that are captured by assuming a Gaussian distribution. Although the measurement errors can be accurately assumed to have a Gaussian distribution, errors with a non-Gaussian distribution could arise during propagation between observations. Moreover, unmodeled dynamics in the orbit model could introduce non-Gaussian errors into the process noise. A Particle Filter (PF) is proposed as a nonlinear filtering technique that is capable of propagating and estimating a more complete representation of the state distribution as an accurate approximation of a full PDF. The PF uses Monte Carlo runs to generate particles that approximate the full PDF representation. The PF is applied in the estimation and propagation of a highly eccentric orbit and the results are compared to the Extended Kalman Filter and Splitting Gaussian Mixture algorithms to demonstrate its proficiency.

Mashiku, Alinda; Garrison, James L.; Carpenter, J. Russell

2012-01-01

202

A Multiple GNSS-based Orbit Determination Algorithm for Geostationary Satellites

The application of Global Positioning System (GPS) technology to the Geostationary Earth Orbit (GEO) determination has been constrained by the poor satellite visibility and weak signal power. This situation is expected to improve when multi-constellation Global Navigation Satellite Systems (GNSS) are available in the future. This paper aims to investigate a navigation algorithm to determine the GEO state vector in

Li Qiao; Samsung Lim; Chris Rizos; Jianye Liu

2009-01-01

203

Orbit determination accuracies using satellite-to-satellite tracking

NASA Technical Reports Server (NTRS)

The uncertainty in relay satellite sate is a significant error source which cannot be ignored in the reduction of satellite-to-satellite tracking data. Based on simulations and real data reductions, it is numerically impractical to use simultaneous unconstrained solutions to determine both relay and user satellite epoch states. A Bayesian or least squares estimation technique with an a priori procedure is presented which permits the adjustment of relay satellite epoch state in the reduction of satellite-to-satellite tracking data without the numerical difficulties introduced by an ill-conditioned normal matrix.

Vonbun, F. O.; Argentiero, P. D.; Schmid, P. E.

1977-01-01

204

NASA Technical Reports Server (NTRS)

Images produced by pinhole cameras using film sensitive to atomic oxygen provide information on the ratio of spacecraft orbital velocity to the most probable thermal speed of oxygen atoms, provided the spacecraft orientation is maintained stable relative to the orbital direction. Alternatively, information on the spacecraft attitude relative to the orbital velocity can be obtained, provided that corrections are properly made for thermal spreading and a corotating atmosphere. The Long Duration Exposure Facility (LDEF) orientation, uncorrected for a corotating atmosphere, was determined to be yawed 8.0 +/- 0.4 degrees from its nominal attitude, with an estimated +/- 0.35 degree oscillation in yaw. The integrated effect of inclined orbit and corotating atmosphere produces an apparent oscillation in the observed yaw direction, suggesting that the LDEF attitude measurement will indicate even better stability when corrected for a corotating atmosphere. The measured thermal spreading is consistent with major exposure occurring during high solar activity, which occurred late during the LDEF mission.

Peters, Palmer N.; Gregory, John C.

1992-01-01

205

Radio metric orbit determination for the Giotto mission to Comet Halley

NASA Technical Reports Server (NTRS)

An international fleet of five spacecraft will fly past Comet Halley as it travels through the inner solar system in early 1986. This paper discusses orbit determination problems associated with the Giotto spacecraft, sponsored by the European Space Agency. The large number of spin axis precession maneuvers required to maintain the desired spacecraft attitude creates a new kind of radio metric orbit determination problem for this mission. This paper investigates the accuracy with which the Giotto spacecraft orbit can be determined relative to the earth or the sun, and establishes the sensitivity of this accuracy to the selection of the parameters to be estimated, the form of estimator used, the number of tracking stations employed, the length of the data arc, the selection of data types processed, and the levels of various error sources.

Wood, L. J.; Mottinger, N. A.; Jordan, J. F.

1983-01-01

206

Determination of binary asteroid orbits with a genetic-based algorithm

NASA Astrophysics Data System (ADS)

Aims: Over the past decade, discoveries of multiple and binary 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. Methods: We implemented a new approach 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. This statistical method is fast enough to permit the search for an orbital solution across a large parameter space and without a priori information about the mutual orbit. Results: 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.

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

2012-07-01

207

Phase Function Determination in Support of Orbital Debris Size Estimation

NASA Technical Reports Server (NTRS)

To recover the size of a space debris object from photometric measurements, it is necessary to determine its albedo and basic shape: if the albedo is known, the reflective area can be calculated; and if the shape is known, the shape and area taken together can be used to estimate a characteristic dimension. Albedo is typically determined by inferring the object s material type from filter photometry or spectroscopy and is not the subject of the present study. Object shape, on the other hand, can be revealed from a time-history of the object s brightness response. The most data-rich presentation is a continuous light-curve that records the object s brightness for an entire sensor pass, which could last for tens of minutes to several hours: from this one can see both short-term periodic behavior as well as brightness variations with phase angle. Light-curve interpretation, however, is more art than science and does not lend itself easily to automation; and the collection method, which requires single-object telescope dedication for long periods of time, is not well suited to debris survey conditions. So one is led to investigate how easily an object s brightness phase function, which can be constructed from the more survey-friendly point photometry, can be used to recover object shape. Such a recovery is usually attempted by comparing a phase-function curve constructed from an object s empirical brightness measurements to analytically-derived curves for basic shapes or shape combinations. There are two ways to accomplish this: a simple averaged brightness-versus phase curve assembled from the empirical data, or a more elaborate approach in which one is essentially calculating a brightness PDF for each phase angle bin (a technique explored in unpublished AFRL/RV research and in Ojakangas 2011); in each case the empirical curve is compared to analytical results for shapes of interest. The latter technique promises more discrimination power but requires more data; the former can be assembled in its essentials from fewer measurements but will be less definitive in its assignments. The goal of the present study is to evaluate both techniques under debris survey conditions to determine their relative performance and, additionally, to learn precisely how a survey should be conducted in order to maximize their performance. Because the distendedness of objects has more of an effect than their precise shape in calculating a characteristic dimension, one is interested in the techniques discrimination ability to distinguish between an elongated rectangular prism and a short rectangular prism or cube, or an elongated cylinder from a squat cylinder or sphere. Sensitivity studies using simulated data will be conducted to determine discrimination power for both techniques as a function of amount of data collected and range (and specific region) of phase angles sampled. Empirical GEODSS photometry data for distended objects (dead payloads with solar panels, rocket bodies) and compact objects (cubesats, calibration spheres, squat payloads) will also be used to test this discrimination ability. The result will be a recommended technique and data collection paradigm for debris surveys in order to maximize this type of discrimination.

Hejduk, M. D.; Cowardin, H. M.; Stansbery, Eugene G.

2012-01-01

208

Investigating On-Orbit Attitude Determination Anomalies for the Solar Dynamics Observatory Mission

NASA Technical Reports Server (NTRS)

The Solar Dynamics Observatory (SDO) was launched on February 11, 2010 from Kennedy Space Center on an Atlas V launch vehicle into a geosynchronous transfer orbit. SDO carries a suite of three scientific instruments, whose observations are intended to promote a more complete understanding of the Sun and its effects on the Earth's environment. After a successful launch, separation, and initial Sun acquisition, the launch and flight operations teams dove into a commissioning campaign that included, among other things, checkout and calibration of the fine attitude sensors and checkout of the Kalman filter (KF) and the spacecraft s inertial pointing and science control modes. In addition, initial calibration of the science instruments was also accomplished. During that process of KF and controller checkout, several interesting observations were noticed and investigated. The SDO fine attitude sensors consist of one Adcole Digital Sun Sensor (DSS), two Galileo Avionica (GA) quaternion-output Star Trackers (STs), and three Kearfott Two-Axis Rate Assemblies (hereafter called inertial reference units, or IRUs). Initial checkout of the fine attitude sensors indicated that all sensors appeared to be functioning properly. Initial calibration maneuvers were planned and executed to update scale factors, drift rate biases, and alignments of the IRUs. After updating the IRU parameters, the KF was initialized and quickly reached convergence. Over the next few hours, it became apparent that there was an oscillation in the sensor residuals and the KF estimation of the IRU bias. A concentrated investigation ensued to determine the cause of the oscillations, their effect on mission requirements, and how to mitigate them. The ensuing analysis determined that the oscillations seen were, in fact, due to an oscillation in the IRU biases. The low frequencies of the oscillations passed through the KF, were well within the controller bandwidth, and therefore the spacecraft was actually following the oscillating biases, resulting in movement of the spacecraft on the order of plus or minus 20 arcsec. Though this level of error met the ACS attitude knowledge requirement of [35, 70, 70] arcsec, 3 sigma, the desire of the ACS and instrument teams was to remove as much of the oscillation as possible. The Kearfott IRUs have an internal temperature controller, designed to maintain the IRU temperature at a constant temperature of approximately 70 C, thus minimizing the change in the bias drift and scale factors of the mechanical gyros. During ground testing of the observatory, it was discovered that the 83-Hz control cycle of the IRU heaters put a tremendous amount of stress on the spacecraft battery. Analysis by the power systems team indicated that the constant charge/discharge on the battery due to the IRU thermal control cycle could potentially limit the life of the battery. After much analysis, the decision was made not to run the internal IRU heaters. Analysis of on orbit data revealed that the oscillations in the IRU bias had a connection to the temperature of the IRU; changes in IRU temperature resulted in changes in the amplitude and period of the IRU biases. Several mitigating solutions were investigated, the result of which was to tune the KF with larger IRU noise assumptions which allows the KF to follow and correct for the time-varying IRU biases.

Vess, Melissa F.; Starin, Scott R.; Chia-Kuo, Alice Liu

2011-01-01

209

Landsat-4 (TDRSS-user) orbit determination using batch least-squares and sequential methods

NASA Technical Reports Server (NTRS)

TDRSS user orbit determination is analyzed using a batch least-squares method and a sequential estimation method. It was found that in the batch least-squares method analysis, the orbit determination consistency for Landsat-4, which was heavily tracked by TDRSS during January 1991, was about 4 meters in the rms overlap comparisons and about 6 meters in the maximum position differences in overlap comparisons. The consistency was about 10 to 30 meters in the 3 sigma state error covariance function in the sequential method analysis. As a measure of consistency, the first residual of each pass was within the 3 sigma bound in the residual space.

Oza, D. H.; Jones, T. L.; Hakimi, M.; Samii, M. V.; Doll, C. E.; Mistretta, G. D.; Hart, R. C.

1992-01-01

210

A study of orbit determination accuracies for future earth observatory missions

NASA Technical Reports Server (NTRS)

It is anticipated that global orbital accuracies of 10 meters will be required for future earth observatory missions. Results are presented of a study of the LANDSAT-1 orbit to determine position accuracies obtainable today so as to assess what future advancements are necessary to meet a 10-meter goal. Accuracies of 50 meters were determined to be achievable now from two-day tracking arcs. One-half-day arcs yield accuracies of about 30 meters. The dominant error source was found to be geopotential model uncertainty. All other systematic errors produced less than 10 meters total position error.

Bryant, W. C., Jr.; Goad, C. C.

1975-01-01

211

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

212

Accurate orbit determination strategies for the tracking and data relay satellites

NASA Technical Reports Server (NTRS)

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.

1995-01-01

213

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

214

Precise orbit determination of BeiDou constellation based on BETS and MGEX network

NASA Astrophysics Data System (ADS)

Chinese BeiDou Navigation Satellite System is officially operational as a regional constellation with five Geostationary Earth Orbit (GEO) satellites, five Inclined Geosynchronous Satellite Orbit (IGSO) satellites and four Medium Earth Orbit (MEO) satellites. Observations from the BeiDou Experimental Tracking Stations (BETS) and the IGS Multi-GNSS Experiment (MGEX) network from 1 January to 31 March 2013 are processed for orbit determination of the BeiDou constellation. Various arc lengths and solar radiation pressure parameters are investigated. The reduced set of ECOM five-parameter model produces better performance than the full set of ECOM nine-parameter model for BeiDou IGSO and MEO. The orbit overlap for the middle days of 3-day arc solutions is better than 20 cm and 14 cm for IGSO and MEO in RMS, respectively. Satellite laser ranging residuals are better than 10 cm for both IGSO and MEO. For BeiDou GEO, the orbit overlap of several meters and satellite laser ranging residuals of several decimetres can be achieved.

Lou, Yidong; Liu, Yang; Shi, Chuang; Yao, Xiuguang; Zheng, Fu

2014-04-01

215

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

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

216

NASA Technical Reports Server (NTRS)

A method to determine satellite orbits using tracking data and a priori gravitational field is described. The a priori constraint on the orbit dynamics is determined by the covariance matrix of the spherical harmonic coefficients for the gravity model, so that the optimal combination of the measurements and gravitational field is achieved. A set of bin parameters is introduced to represent the perturbation of the gravitational field on the position of the satellite orbit. The covariance matrix of a conventional gravity model is transformed into that for the bin parameters by the variational partial derivatives. The covariance matrices of the bin parameters and the epoch state are combined to form the covariance matrix of the satellite positions at the measurement times. The combined matrix is used as the a priori information to estimate the satellite positions with measurements.

Wu, Jiun-Tsong; Wu, Sien-Chong

1992-01-01

217

NASA Astrophysics Data System (ADS)

In view of the present technology of autonomous orbit determination for navigation satellite constellation (NSC) and the geographical conditions of China, we propose a long-term semi-autonomous orbit determination scheme supported by a few ground stations for NSC in this paper. Since the effect of rotation and translation of the entire constellation relative to the inertial reference frame can bring large errors to the autonomous orbit determination using only cross-link range measurement, a few ground stations (such as 1-3) are supposed to construct the connection between the NSC and the ground. Supported by such a few ground stations, the NSC can realize long-term orbit determination called semi-autonomous orbit determination. The simulation results based on the IGS ephemeris indicate that, for a certain degree of measurement errors, the NSC can maintain its semi-autonomous orbit determination in a period of 240 days within 5 meters of URE.

Yi, Hang; Xu, Bo; Gao, YouTao; Wang, JiaSong

2011-07-01

218

NASA Astrophysics Data System (ADS)

A satellite tracking campaign was organized, with 4 S-band stations, for 1 wk. The relative geometry of the network with respect to the satellites was an opportunity to show how the most precise orbit can be computed with the operational software. This precise orbit served as a reference to evaluate what can be achieved with one station with range and angular measurements, a typical configuration used for stationkeeping of geostationary satellites. Orbit computation implied numerical integration with gravitational (Earth, Moon, and Sun) and solar radiation pressure forces acting on the satellite. Arc lengths of 2 days gave initial state vectors which were compared every day. Precision of 10 m is achieved. However, an analysis of the influence of parameters in the orbit computations reveals that the absolute accuracy is of the order of 100 m, since modeling perturbations were neglected in the operational software (e.g., polar motion). In a relative sense, the reference orbit allows estimation of systematic errors for other tracking antennas.

Guitart, A.; Mesnard, B.

1986-05-01

219

NASA Technical Reports Server (NTRS)

The Flight Dynamics Facility (FDF) at Goddard Space Flight Center (GSFC) provides spacecraft trajectory determination for a wide variety of National Aeronautics and Space Administration (NASA)-supported satellite missions, using the Tracking Data Relay Satellite System (TDRSS) and Ground Spaceflight and Tracking Data Network (GSTDN). To take advantage of computerized decision making processes that can be used in spacecraft navigation, the Orbit Determination Automation System (ODAS) was designed, developed, and implemented as a prototype system to automate orbit determination (OD) and orbit quality assurance (QA) functions performed by orbit operations. Based on a machine-resident generic schedule and predetermined mission-dependent QA criteria, ODAS autonomously activates an interface with the existing trajectory determination system using a batch least-squares differential correction algorithm to perform the basic OD functions. The computational parameters determined during the OD are processed to make computerized decisions regarding QA, and a controlled recovery process is activated when the criteria are not satisfied. The complete cycle is autonomous and continuous. ODAS was extensively tested for performance under conditions resembling actual operational conditions and found to be effective and reliable for extended autonomous OD. Details of the system structure and function are discussed, and test results are presented.

Mardirossian, H.; Beri, A. C.; Doll, C. E.

1990-01-01

220

NASA Technical Reports Server (NTRS)

The Flight Dynamics Facility (FDF) at Goddard Space Flight Center (GSFC) provides spacecraft trajectory determination for a wide variety of National Aeronautics and Space Administration (NASA)-supported satellite missions, using the Tracking Data Relay Satellite System (TDRSS) and Ground Spaceflight and Tracking Data Network (GSTDN). To take advantage of computerized decision making processes that can be used in spacecraft navigation, the Orbit Determination Automation System (ODAS) was designed, developed, and implemented as a prototype system to automate orbit determination (OD) and orbit quality assurance (QA) functions performed by orbit operations. Based on a machine-resident generic schedule and predetermined mission-dependent QA criteria, ODAS autonomously activates an interface with the existing trajectory determination system using a batch least-squares differential correction algorithm to perform the basic OD functions. The computational parameters determined during the OD are processed to make computerized decisions regarding QA, and a controlled recovery process isactivated when the criteria are not satisfied. The complete cycle is autonomous and continuous. ODAS was extensively tested for performance under conditions resembling actual operational conditions and found to be effective and reliable for extended autonomous OD. Details of the system structure and function are discussed, and test results are presented.

Mardirossian, H.; Heuerman, K.; Beri, A.; Samii, M. V.; Doll, C. E.

1989-01-01

221

A method for determining the orbital parameters of interacting pairs of galaxies is presented and evaluated using artificial data. The method consists of a genetic algorithm which can search efficiently through the very large space of possible orbits. It is found that, in most cases, orbital parameters close to the actual orbital parameters of the pair can be found. The method does not require information about the velocity field of the interacting system, and is able to cope with noisy data. The inner regions of the galaxies, which are difficult to model, can be neglected, and the orbital parameters can be determined using the remaining information.

M. Wahde

1997-10-24

222

The atmospheric mass density of the upper atmosphere from the spherical Starlette satellite’s Precise Orbit Determination\\u000a is first derived with Satellite Laser Ranging measurements at 815 to 1115 km during strong solar and geomagnetic activities.\\u000a Starlette’s orbit is determined using the improved orbit determination techniques combining optimum parameters with a precise\\u000a empirical drag application to a gravity field. MSIS-86 and

H. S. Jeon; S. Cho; Y. S. Kwak; J. K. Chung; J. U. Park; D. K. Lee; M. Kuzmicz-Cieslak

2011-01-01

223

Arrival and departure impulsive Delta V determination for precessing Mars parking orbits

NASA Technical Reports Server (NTRS)

An attempt is made to develop a method for realistic estimation of the initial LEO mass. The method takes into account the actual geometry between the inbound and outbound hyperbolic asymptotes and the parking orbit, along with precession effects caused by the oblateness of Mars, in calculating the arrival and departure Delta V values. Three mission scenarios alternative to the arbitrarily assumed two tangential periapsis burns are described: a tangential periapsis arrival and an in-plane departure; an in-plane arrival and in-plane departure; and a tangential periapsis arrival and a 3D departure. Results obtained by the method under consideration compared well with a trajectory integration code, where the differences in the initial LEO orbit mass were within one percent, for all three cases. The method is considered to be an ideal tool for preliminary mission design, since it reduces the analysis computation time with minimal loss in accuracy.

Desai, Prasun N.; Buglia, James J.

1992-01-01

224

Satellite Orbit Determination Using a Single-Channel Global Positioning System Receiver by Mark L system has been analyzed, one that uses measurements from a single-channel Global Positioning System (GPS. Introduction The Global Positioning System (GPS) offers an attractive alternative to ground-based tracking

Psiaki, Mark L.

225

NASA Technical Reports Server (NTRS)

The programming techniques used to implement the equations and mathematical techniques of the Houston Operations Predictor/Estimator (HOPE) orbit determination program on the UNIVAC 1108 computer are described. Detailed descriptions are given of the program structure, the internal program structure, the internal program tables and program COMMON, modification and maintainence techniques, and individual subroutine documentation.

Daly, J. K.

1974-01-01

226

A system for autonomous navigation and attitude determination in geostationary orbit

The results of a joint CNES-Aerospatiale study leading to an autonomous navigation and three-axis attitude determination system are presented. The principles, software architecture, preprocessing, navigator, orbit control, and hardware configuration of the system are described. The optimization process is described as well with attention given to sensor architecture and operational modes. It is found that the presence of an additional

P. Maute; O. Defonte

1990-01-01

227

An analytical theory for determining accurately the coordinates of a satellite at any time during its movement around the earth was developed using a power series of regularized time and a spheroidal coordinate system. The theory is used to design a computer program for determining orbits of geodynamical satellites. The results of determining the orbit of Lageos with this program

Nikola Georgiev; Iavor Chapanov

1990-01-01

228

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

229

An initial comparative assessment of orbital and terrestrial central power systems

NASA Technical Reports Server (NTRS)

A silicon photovoltaic orbital power system, which is constructed from an earth source of materials, is compared to likely terrestrial (fossil, nuclear, and solar) approaches to central power generation around the year 2000. A total social framework is used that considers not only the projection of commercial economics (direct or in internal costs), but also considers external impacts such as research and development investment, health impacts, resource requirements, environment effects, and other social costs.

Caputo, R.

1977-01-01

230

NASA Technical Reports Server (NTRS)

Data collected from a worldwide 1992 experiment were processed at JPL to determine precise orbits for the satellites of the Global Positioning System (GPS). A filtering technique was tested to improve modeling of solar-radiation pressure force parameters for GPS satellites. The new approach improves orbit quality for eclipsing satellites by a factor of two, with typical results in the 25- to 50-cm range. The resultant GPS-based estimates for geocentric coordinates of the tracking sites, which include the three DSN sites, are accurate to 2 to 8 cm, roughly equivalent to 3 to 10 nrad of angular measure.

Vigue, Y.; Lichten, S. M.; Muellerschoen, R. J.; Blewitt, G.; Heflin, M. B.

1993-01-01

231

NASA Astrophysics Data System (ADS)

The reference Ocean Surface Topography Mission/Jason-2 satellite (CNES/NASA) has been in orbit for six 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), HY-2A (CNSA) and SARAL/AltiKa (CNES/ISRO), with lower altitudes and higher inclinations, were launched in April 2010, August 2011 and February 2013, respectively. Although the three 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. The focus of this talk will be on the long-term stability of the orbit time series for mean sea level applications on a regional scale. We discuss various issues related to the assessment of radial orbit error trends; in particular orbit errors dependant on the tracking technique, the reference frame accuracy and stability, the modeling of the temporal variations of the geopotential. Strategies are then explored to meet a 1 mm/y radial orbit stability over decadal periods at regional scales, and the challenge of evaluating such an improvement is discussed.

Couhert, Alexandre

232

Determining Mars parking orbits which ensure in-plane arrival and departure burns

NASA Technical Reports Server (NTRS)

A numerical method to find suitable Mars parking orbits is developed which takes into account geometries associated with the asymptotes, along with the nodal precession caused by the oblateness of Mars. A selected orbital plane which contains the arrival asymptote precesses through the stay time to the plane also containing the departure asymptote. The parking orbit is co-planar with both the arrival and departure asymptotes and only in-plane burns are required at both Mars arrival and departure. The need for a plane change at Mars departure to achieve the proper velocity vector for earth return is eliminated. The method requires very little computation time to determine a set of all possible inclinations and right ascensions of the ascending nodes.

Desai, Prasun N.; Buglia, James J.

1992-01-01

233

The determination of maximum deep space station slew rates for a high Earth orbiter

NASA Technical Reports Server (NTRS)

As developing national and international space ventures, which seek to employ NASA's Deep Space Network (DSN) for tracking and data acquisition, evolve, it is essential for navigation and tracking system analysts to evaluate the operational capability of Deep Space Station antennas. To commission the DSN for use in tracking a highly eccentric Earth orbiter could quite possibly yield the greatest challenges in terms of slewing capability; certainly more so than with a deep-space probe. The focus here is on the determination of the maximum slew rates needed to track a specific high Earth orbiter, namely the Japanese MUSES-B spacecraft of the Very Long Baseline Interferometry Space Observatory Program. The results suggest that DSN 34-m antennas are capable of meeting the slew rate requirements for the nominal MUSES-B orbital geometries currently being considered.

Estefan, J. A.

1990-01-01

234

NORAD TLE Type Orbit Determination of LEO Satellites Using GPS Navigation Solutions

NASA Astrophysics Data System (ADS)

NORAD Two Line Elements (TLE) are widely used for the increasing number of small satellite mission operations and analysis. However, due to the irregular periodicity of generation of the NORAD TLE, a new TLE that is independent of NORAD is required. A TLE type Orbit Determination (TLEOD) has been developed for the generation of a new TLE. Thus, the TLEOD system can provide an Antenna Control Unit (ACU) with the orbit determination result in the type of a TLE, which provides a simple interface for the commercialized ACU system. For the TLEOD system, NORAD SGP4 was used to make a new orbit determination system. In addition, a least squares method was implemented for the TLEOD system with the GPS navigation solutions of the KOMPSAT-1. Considering both the Orbit Propagation (OP) difference and the tendency of B* value, the preferable span of the day in the observation data was selected to be 3 days. Through the OD with 3 days observation data, the OP difference was derived and compared with that of Mission Analysis and Planning (MAPS) for the KOMPSAT-1. It has the extent from 2 km after six days to 4 km after seven days. This is qualified enough for the efficiency of an ACU in image reception and processing center of the KOMPSAT-2.

Cho, Chang-Hwa; Lee, Byoung-Sun; Lee, Jeong-Sook; Kim, Jae-Hoon; Choi, Kyu-Hong

2002-09-01

235

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

NASA Technical Reports Server (NTRS)

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.

1988-01-01

236

Tracking and orbit determination of deep-space probes in ISAS mission

NASA Astrophysics Data System (ADS)

The Institute of Space and Astronautical Science (ISAS) has launched three deep-space probes. They are Sakigake and Suisei for observation of Halley's comet, and Hiten for the lunar swing-by mission. Sakigake, which was launched on January 8, 1985, came back to the neighborhood of the Earth, after the successful encounter with the Halley's comet in March 1986 and several revolutions around the Sun. It approached to 90,000 km from the Earth on January 8, 1992. The communication link with this probe has been reestablished since July 1991 and the tracking and orbit determination have been successfully carried out using two-way range and range-rate data. Hiten, on the other hand, was launched on January, 1990 and lunar swing-by operations have been conducted, which was supported by the precise orbit determination (OD) using both S and X band signals. The integrated operations covering the Usuda Deep-Space Center (UDSC), having a 64 m antenna as well as the Sagamihara Space Operation Center (SSOC) will be described in this paper and numerical results of orbit determination of these probes will be presented in detail. Finally, the strategy leading to the injection of Hiten into an elliptical orbit around the Moon in February, 1992 and the requirement of OD precision in achieving this goal, as well as tracking results after injection, will be discussed.

Nishimura, T.; Ichikawa, T.; Katoh, T.; Kosaka, H.; Ushikoshi, A.; Shimizu, T.

237

NASA Astrophysics Data System (ADS)

A universal method of determining the orbits of newly discovered small bodies in the Solar System using their positional observations has been developed. The proposed method suggests determining geocentric distances of a small body by means of an exhaustive search for heliocentric orbital planes and subsequent determination of the distance between the observer and the points at which the chosen plane intersects with the vectors pointing to the object. Further, the remaining orbital elements are determined using the classical Gauss method after eliminating those heliocentric distances that have a fortiori low probabilities. The obtained sets of elements are used to determine the rms between the observed and calculated positions. The sets of elements with the least rms are considered to be most probable for newly discovered small bodies. Afterwards, these elements are improved using the differential method.

Bondarenko, Yu. S.; Vavilov, D. E.; Medvedev, Yu. D.

2014-05-01

238

NASA Technical Reports Server (NTRS)

The results of a study to analyze the dependence of TDRSS user spacecraft orbit determination consistencies on varying tracking schedules are presented. In this study, the TDRS-East orbit determination results obtained utilizing Bilateration Ranging Transponder System data were evaluated. Six state parameters, three position and three velocity components and the solar radiation pressure coefficient, are estimated for TDRS-East. It is concluded that, in order to achieve high-precision orbit determination, the tracking coverage should not fall below 10 minutes every two orbits as decreasing it to every four orbits will significantly degrade the accuracy; present state-of-the-art consistency in orbit determination using TDRSS tracking is approximately 15 to 20 meters.

Doll, C. E.; Gramling, C. J.; Oza, D. H.; Radomski, M. S.

1990-01-01

239

The GLAS Algorithm Theoretical Basis Document for Precision Orbit Determination (POD)

NASA Technical Reports Server (NTRS)

The Geoscience Laser Altimeter System (GLAS) was the sole instrument for NASA's Ice, Cloud and land Elevation Satellite (ICESat) laser altimetry mission. The primary purpose of the ICESat mission was to make ice sheet elevation measurements of the polar regions. Additional goals were to measure the global distribution of clouds and aerosols and to map sea ice, land topography and vegetation. ICESat was the benchmark Earth Observing System (EOS) mission to be used to determine the mass balance of the ice sheets, as well as for providing cloud property information, especially for stratospheric clouds common over polar areas. The GLAS instrument operated from 2003 to 2009 and provided multi-year elevation data needed to determine changes in sea ice freeboard, land topography and vegetation around the globe, in addition to elevation changes of the Greenland and Antarctic ice sheets. This document describes the Precision Orbit Determination (POD) algorithm for the ICESat mission. The problem of determining an accurate ephemeris for an orbiting satellite involves estimating the position and velocity of the satellite from a sequence of observations. The ICESatGLAS elevation measurements must be very accurately geolocated, combining precise orbit information with precision pointing information. The ICESat mission POD requirement states that the position of the instrument should be determined with an accuracy of 5 and 20 cm (1-s) in radial and horizontal components, respectively, to meet the science requirements for determining elevation change.

Rim, Hyung Jin; Yoon, S. P.; Schultz, Bob E.

2013-01-01

240

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

241

NASA Astrophysics Data System (ADS)

The Kaguya spacecraft were launched from Tanegashima Space Center on September 14, 2007. Kaguya consists of three orbiters: a main orbiter in a low-altitude (100 km) circular polar orbit, and two sub-satellites (Rstar and Vstar) in elliptical orbits. The satellites were tracked by a variety of terrestrial based tracking systems: in addition to standard two-way Doppler and range tracking, there was 4-way Doppler tracking between Rstar and the main orbiter, providing the first tracking data of a satellite over the lunar far side, and there was same-beam differential VLBI tracking between the two sub-satellites, providing precise orbits for these satellites. The main orbiter was also equipped with a laser altimeter (LALT) to measure the topography of the Moon. At points where the ground tracks of different orbits intersect, these data can provide further constraints on the orbit of the main satellite in the form of crossovers, as essentially the same topography should be measured. This comprehensive data set between the satellites allows for a unique opportunity to evaluate the contribution of these tracking systems to orbit and gravity field determination. Precise orbits are important for geolocation of the topography and camera data, whereas the gravity field can be used for studies of the lunar interior. Here, we present the analysis of the combinations of these tracking data. The use of 4-way and same-beam differential VLBI data leads to large improvements in orbit precision of all satellites involved, where especially peaks in orbit overlap differences during edge-on periods are reduced. The use of the altimetry crossovers improves the orbit of the main satellite further, resulting in an orbit precision of in general less than 20 m. We have also used the full set of SELENE tracking data (including all 4-way and all S-band same-beam differential VLBI data), together with historical data, for gravity field determination. We show a lunar gravity field model with an improved orbit determination performance, especially for orbits over the deep far side. Finally, we use the improved gravity field model to investigate the determination of the lower degrees of the spherical harmonics expansion. These results thus show the benefits from having multiple spacecraft tracking for orbit and gravity field determination.

Goossens, S. J.; Matsumoto, K.; Kikuchi, F.; Liu, Q.; Hanada, H.; Lemoine, F. G.; Rowlands, D. D.; Ishihara, Y.; Jianguo, Y.; Araki, H.; Noda, H.; Namiki, N.; Iwata, T.

2010-12-01

242

Flight dynamics facility operational orbit determination support for the ocean topography experiment

NASA Technical Reports Server (NTRS)

The Ocean Topography Experiment (TOPEX/POSEIDON) mission is designed to determine the topography of the Earth's sea surface across a 3 yr period, beginning with launch in June 1992. The Goddard Space Flight Center Dynamics Facility has the capability to operationally receive and process Tracking and Data Relay Satellite System (TDRSS) tracking data. Because these data will be used to support orbit determination (OD) aspects of the TOPEX mission, the Dynamics Facility was designated to perform TOPEX operational OD. The scientific data require stringent OD accuracy in navigating the TOPEX spacecraft. The OD accuracy requirements fall into two categories: (1) on orbit free flight; and (2) maneuver. The maneuver OD accuracy requirements are of two types; premaneuver planning and postmaneuver evaluation. Analysis using the Orbit Determination Error Analysis System (ODEAS) covariance software has shown that, during the first postlaunch mission phase of the TOPEX mission, some postmaneuver evaluation OD accuracy requirements cannot be met. ODEAS results also show that the most difficult requirements to meet are those that determine the change in the components of velocity for postmaneuver evaluation.

Bolvin, D. T.; Schanzle, A. F.; Samii, M. V.; Doll, C. E.

1991-01-01

243

NASA Astrophysics Data System (ADS)

The Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the Suomi National Polar-orbiting Partnership (SNPP) satellite carries out radiometric calibration of its reflective solar bands primarily through observing a sunlit onboard solar diffuser (SD). The SD bidirectional reflectance distribution function (BRDF) degrades over time. The degradation factor is determined by an onboard solar diffuser stability monitor (SDSM) which observes the Sun through a pinhole screen and the sunlit SD. The transmittance of the SDSM pinhole screen over a range of solar angles was determined prelaunch and used initially to determine the BRDF degradation factor. The degradation factor versus time curves were found to have a number of very large unphysical undulations likely due to the inaccuracies in the prelaunch determined SDSM screen transmittance. To validate and if necessary to refine both the SD and the SDSM screen transmittances, satellite yaw maneuvers were carried out. With the yaw maneuver data determined SDSM screen transmittance, the computed BRDF degradation factor curves still have large unphysical ripples, indicating that the projected solar horizontal angular step size in the yaw maneuver data is too large to resolve the transmittance at a fine angular scale. We develop a methodology to use both the yaw maneuver and regular on-orbit data to determine the SDSM screen transmittance at a fine angular scale with a relative error standard deviation from 0.00029 (672 nm; detector 5) to 0.00074 (926 nm; detector 8). With the newly determined SDSM screen transmittance, the computed BRDF degradation factor behaves much more smoothly over time.

Lei, Ning; Chen, Xuexia; Xiong, Xiaoxiong

2014-09-01

244

31 CFR 29.404 - Initial benefit determinations and reconsideration by the Benefits Administrator.

Code of Federal Regulations, 2010 CFR

...2010-07-01 false Initial benefit determinations and reconsideration by the Benefits Administrator. 29...reconsideration by the Benefits Administrator. (a) Initial benefit determinations. The Benefits Administrator will...

2010-07-01

245

On-orbit determination and adjustment of electrostatic accelerometer lever arm

NASA Astrophysics Data System (ADS)

In order to ensure the proof mass center of electrostatic accelerometer (EA) is fixed at the center of gravity of satellite as precisely as possible, an on-orbit determination and adjustment strategy of EA lever arm is presented in this paper. The EA lever arm is determined using the observations of EA, gyro and magnetometer first. Then it is adjusted by screw slider mechanism. The simulation results demonstrate that the proposed strategy can be carried out several times to yield better accuracy. Meanwhile, the optimal geographic location for EA lever arm determination along each axis is found.

Benli, Wang; He, Liao; Dahao, Yang

2011-04-01

246

Assessing attitude error of FORMOSAT-3/COSMIC satellites and its impact on orbit determination

NASA Astrophysics Data System (ADS)

An attitude determination and control system (ADCS) is critical to satellite attitude maneuvers and to the coordinate transformation from the inertial frame to the spacecraft frame. This paper shows specific sensors in the ADCS of the satellite mission FORMOSAT-3/COSMIC (F3/C) and the impact of the ADCS quality on orbit accuracy. The selection of main POD antenna depends on the beta angles of the different F3/C satellites (for FM2 and FM4) during the inflight phase. In particular, under the eclipse, alternative attitude sensors are activated to replace the Sun sensors, and such a sensor change leads to anomalous GPS phase residuals and a degraded orbit accuracy. Since the nominal attitude serves as a reference for ADCS, the 3-dimensional attitude-induced errors in reduced dynamic orbits over selected days in 2010 show 9.35, 10.78, 4.97, 5.48, 7.18, and 6.89 cm for FM1-FM6. Besides, the 3-dimensional velocity errors induced by the attitude effect are 0.10, 0.10, 0.07, 0.08, 0.09, and 0.10 for FM1-FM6. We analyze the quality of the observed attitude transformation matrix of F3/C and its impact on kinematic orbit determination. With 249 days of GPS in 2008, the analysis leads to the following averaged 3-dimensional attitude-induced orbit errors: 2.72, 2.62, 2.37, 1.90, 1.70, and 1.99 cm for satellites FM1-FM6. Critical suggestions of geodetic payloads for the follow-on mission of F3/C are presented based on the current result.

Tseng, Tzu-Pang; Hwang, Cheinway; Yang, Shan Kuo

2012-05-01

247

A Study on Orbit Determination by Using the Data of Crossovers from Satellite-borne Altimeter

NASA Astrophysics Data System (ADS)

Starting with the status of the developments of oceanic altimetry satellites, the significance of orbit determination by using altimeter data is introduced. Then the error correction model of the altimeter data and the calculational method of the data of crossovers are analyzed. The modification quantities of the errors and the adopted model concerned in the files of the altimeter data from the aircraft JASON-1 are also introduced in detail. Finally, through the calculations of the simulated data and the data of actual measurements, the highest accuracies of the orbit determination reached by solely using the altimeter data and the data of crossovers are analyzed, respectively. And this work provides a valuable reference to the practical applications in future.

Zhang, Rong-Zhi; Zhou, Feng-Qi; Xiong, Jing

2011-01-01

248

Orbit Determination for the Be/X-Ray Transient EXO 2030+375

NASA Technical Reports Server (NTRS)

The Be/X-ray binary transient pulsar EXO 2030+375 has been observed during twenty-two outbursts over four years (1991-1994) using the large area detectors (LADs) of the Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory (CGRO). Thirteen outbursts between 1992 February and 1993 August occurred regularly at -46 day intervals, close to the orbital period determined using EXOSAT data. EXOSAT discovered this pulsar during, a "giant" outburst in 1985 May. All BATSE outbursts were "normal" type. Pulse phases derived from the thirteen consecutive outbursts were fit to two different models to determine a binary orbit. A summary of the results are presented here.

Stollberg, Mark T.; Finger, Mark H.; Wilson, Robert B.; Scott, Matthew; Crary, David J.; Paciesas, William S.

1999-01-01

249

Precise orbit determination of Multi-GNSS constellation including GPS GLONASS BDS and GALIEO

NASA Astrophysics Data System (ADS)

In addition to the existing American global positioning system (GPS) and the Russian global navigation satellite system (GLONASS), the new generation of GNSS is emerging and developing, such as the Chinese BeiDou satellite navigation system (BDS) and the European GALILEO system. Multi-constellation is expected to contribute to more accurate and reliable positioning and navigation service. However, the application of multi-constellation challenges the traditional precise orbit determination (POD) strategy that was designed usually for single constellation. In this contribution, we exploit a more rigorous multi-constellation POD strategy for the ongoing IGS multi-GNSS experiment (MGEX) where the common parameters are identical for each system, and the frequency- and system-specified parameters are employed to account for the inter-frequency and inter-system biases. Since the authorized BDS attitude model is not yet released, different BDS attitude model are implemented and their impact on orbit accuracy are studied. The proposed POD strategy was implemented in the PANDA (Position and Navigation Data Analyst) software and can process observations from GPS, GLONASS, BDS and GALILEO together. The strategy is evaluated with the multi-constellation observations from about 90 MGEX stations and BDS observations from the BeiDou experimental tracking network (BETN) of Wuhan University (WHU). Of all the MGEX stations, 28 stations record BDS observation, and about 80 stations record GALILEO observations. All these data were processed together in our software, resulting in the multi-constellation POD solutions. We assessed the orbit accuracy for GPS and GLONASS by comparing our solutions with the IGS final orbit, and for BDS and GALILEO by overlapping our daily orbit solution. The stability of inter-frequency bias of GLONASS and inter-system biases w.r.t. GPS for GLONASS, BDS and GALILEO were investigated. At last, we carried out precise point positioning (PPP) using the multi-constellation POD orbit and clock products, and analyzed the contribution of these POD products to PPP. Keywords: Multi-GNSS, Precise Orbit Determination, Inter-frequency bias, Inter-system bias, Precise Point Positioning

Dai, Xiaolei

2014-05-01

250

Application of the total least squares method to the determination of preliminary orbit

NASA Astrophysics Data System (ADS)

Based on the analysis of the characteristics of the equations of condition in the UVM2 (Unit Vector Method 2), the total least squares method (TLS) is introduced into the orbital determination and the linearization of the vis-viva formula in the original algorithm is thereby avoided. The calculated results from simulation and observation data show that the application of TLS to UVM2 is effective.

Chen, Wu-shen; Zhang, Jing; Ma, Jing-yuan; Lu, Ben-kui

2006-10-01

251

Single frequency GPS measurements in real-time artificial satellite orbit determination

A simplified and compact algorithm with low computational cost providing an accuracy around tens of meters for artificial satellite orbit determination in real-time and on-board is developed in this work. The state estimation method is the extended Kalman filter. The Cowell's method is used to propagate the state vector, through a simple Runge–Kutta numerical integrator of fourth order with fixed

A. P. M. Chiaradia; H. K. Kuga; A. F. B. A. Prado

2003-01-01

252

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

253

NASA Technical Reports Server (NTRS)

This paper presents the technique and results of maximum likelihood estimation used to determine lift and drag characteristics of the Space Shuttle Orbiter. Maximum likelihood estimation uses measurable parameters to estimate nonmeasurable parameters. The nonmeasurable parameters for this case are elements of a nonlinear, dynamic model of the orbiter. The estimated parameters are used to evaluate a cost function that computes the differences between the measured and estimated longitudinal parameters. The case presented is a dynamic analysis. This places less restriction on pitching motion and can provide additional information about the orbiter such as lift and drag characteristics at conditions other than trim, instrument biases, and pitching moment characteristics. In addition, an output of the analysis is an estimate of the values for the individual components of lift and drag that contribute to the total lift and drag. The results show that maximum likelihood estimation is a useful tool for analysis of Space Shuttle Orbiter performance and is also applicable to parameter analysis of other types of aircraft.

Trujillo, B. M.

1986-01-01

254

NASA Technical Reports Server (NTRS)

Images produced by pinhole cameras using film sensitive to atomic oxygen provide information on the ratio of spacecraft orbital velocity to the most probable thermal speed of oxygen atoms, provided the spacecraft orientation is maintained stable relative to the orbital direction. Alternatively, as it is described, information on the spacecraft attitude relative to the orbital velocity can be obtained, provided that corrections are properly made for thermal spreading and a co-rotating atmosphere. The LDEF orientation, uncorrected for a co-rotating atmosphere, was determined to be yawed 8.0 minus/plus 0.4 deg from its nominal attitude, with an estimated minus/plus 0.35 deg oscillation in yaw. The integrated effect of inclined orbit and co-rotating atmosphere produces an apparent oscillation in the observed yaw direction, suggesting that the LDEF attitude measurement will indicate even better stability when corrected for a co-rotating atmosphere. The measured thermal spreading is consistent with major exposure occurring during high solar activity, which occurred late during the LDEF mission.

Peters, Palmer N.; Gregory, John C.

1991-01-01

255

NASA Astrophysics Data System (ADS)

The spin-orbit interaction plays a crucial role in diverse fields of condensed matter, including the investigation of Majorana fermions, topological insulators, quantum information and spintronics. In III-V zinc-blende semiconductor heterostructures, two types of spin-orbit interaction—Rashba and Dresselhaus—act on the electron spin as effective magnetic fields with different directions. They are characterized by coefficients ? and ?, respectively. When ? is equal to ?, the so-called persistent spin helix symmetry is realized. In this condition, invariance with respect to spin rotations is achieved even?in the presence of the spin-orbit interaction, implying strongly enhanced spin lifetimes for spatially periodic spin modes. Existing methods to evaluate ?/? require fitting analyses that often include ambiguity in the parameters used. Here, we experimentally demonstrate a simple and fitting parameter-free technique to determine ?/? and to deduce the absolute values of ? and ?. The method is based on the detection of the effective magnetic field direction and the strength induced by the two spin-orbit interactions. Moreover, we observe the persistent spin helix symmetry by gate tuning.

Sasaki, A.; Nonaka, S.; Kunihashi, Y.; Kohda, M.; Bauernfeind, T.; Dollinger, T.; Richter, K.; Nitta, J.

2014-09-01

256

NASA Technical Reports Server (NTRS)

The NASA Earth-to-Orbit (ETO) Propulsion Technology Program is dedicated to advancing rocket engine technologies for the development of fully reusable engine systems that will enable space transportation systems to achieve low cost, routine access to space. The program addresses technology advancements in the areas of engine life extension/prediction, performance enhancements, reduced ground operations costs, and in-flight fault tolerant engine operations. The primary objective is to acquire increased knowledge and understanding of rocket engine chemical and physical processes in order to evolve more realistic analytical simulations of engine internal environments, to derive more accurate predictions of steady and unsteady loads, and using improved structural analyses, to more accurately predict component life and performance, and finally to identify and verify more durable advanced design concepts. In addition, efforts were focused on engine diagnostic needs and advances that would allow integrated health monitoring systems to be developed for enhanced maintainability, automated servicing, inspection, and checkout, and ultimately, in-flight fault tolerant engine operations.

Stephenson, Frank W., Jr.

1988-01-01

257

NASA Technical Reports Server (NTRS)

The Triana spacecraft was designed to be launched by the Space Shuttle. The nominal Triana mission orbit will be a Sun-Earth L1 libration point orbit. Using the NASA Goddard Space Flight Center's Orbit Determination Error Analysis System (ODEAS), orbit determination (OD) error analysis results are presented for all phases of the Triana mission from the first correction maneuver through approximately launch plus 6 months. Results are also presented for the science data collection phase of the Fourier Kelvin Stellar Interferometer Sun-Earth L2 libration point mission concept with momentum unloading thrust perturbations during the tracking arc. The Triana analysis includes extensive analysis of an initial short arc orbit determination solution and results using both Deep Space Network (DSN) and commercial Universal Space Network (USN) statistics. These results could be utilized in support of future Sun-Earth libration point missions.

Marr, Greg C.

2003-01-01

258

NASA Technical Reports Server (NTRS)

The results are presented of a series of no-vent fill experiments conducted on a 175 cu ft flightweight hydrogen tank. The experiments consisted of the nonvented fill of the tankage with liquid hydrogen using two different inlet systems (top spray, and bottom spray) at different tank initial conditions and inflow rates. Nine tests were completed of which six filled in excess of 94 percent. The experiments demonstrated a consistent and repeatable ability to fill the tank in excess of 94 percent using the nonvented fill technique. Ninety-four percent was established as the high level cutoff due to requirements for some tank ullage to prevent rapid tank pressure rise which occurs in a tank filled entirely with liquid. The best fill was terminated at 94 percent full with a tank internal pressure less than 26 psia. Although the baseline initial tank wall temperature criteria was that all portions of the tank wall be less than 40 R, fills were achieved with initial wall temperatures as high as 227 R.

Chato, David J.

1991-01-01

259

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

260

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

261

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

262

The application of Encke's method to long arc orbit determination solutions

NASA Technical Reports Server (NTRS)

The Laser Geodynamics Satellite (LAGEOS) was launched on May 4, 1976 to provide geophysical measurements by means of laser ranging techniques. To date, over twelve years of laser range measurements have been collected from various tracking stations located around the world. Laser range measurements to LAGEOS have contributed to studies of earth rotation, plate tectonics, global baseline, and the gravity field as well as many other areas. Some of these studies are based upon the determination of a single, continuous orbit for LAGEOS for time spans on the order of several years. Current studies at the University of Texas Center for Space Research include the precision orbit determination of LAGEOS for arc lengths of up to 12.8 years which represents over 31,000 orbital revolutions. These long arc studies have led to the implementation of Encke's method to improve the convergence of the batch filter while reducing numerical integration errors. While the technique has been successfully applied to arc lengths of up to 12.8 years, the results presented focus on the solution of a six-year arc.

Lundberg, J. B.; Schutz, B. E.; Fields, R. K.; Watkins, M. M.

1990-01-01

263

Desaturation Maneuvers and Precise Orbit Determination for the BepiColombo Mission

The purpose of this work is the analysis of the consequences that desaturation maneuvers can have in the precise orbit determination corresponding to the Radio Science Experiment (MORE) of the BepiColombo mission to Mercury. This mission is an ESA/JAXA joint project with very challenging objectives regarding geodesy, geophysics and fundamental physics. In the neighborhood of Mercury, the s/c will experience strong solar radiation pressure torques; the s/c attitude is controlled by inertial wheels that after some time reach their maximum rotation state. Then they have to be slowed down by means of thruster pulses, inducing a residual acceleration on the s/c, with a desaturation (or off-loading) maneuver. In this paper, we will show how such maneuvers affect the orbit of the s/c and the radio science measurements and, also, how to include them in the orbit determination and parameter estimation procedure. The non linear least squares fit we consider is applied on a set of observational arcs separated by interva...

Alessi, Elisa Maria; Milani, Andrea; Tommei, Giacomo

2012-01-01

264

NASA Astrophysics Data System (ADS)

A new method is proposed for computing the preliminary orbit of a small celestial body from three pairs of range and range rate observations. The method is based on using the superosculating intermediate orbit with a fourth-order tangency that we previously constructed. This intermediate orbit allows for most of the perturbations in the motion of the body under study. The methodical error of orbit determination by the proposed method is three orders smaller than the corresponding error of the commonly used approach based on the construction of the unperturbed Keplerian orbit. Using the examples of finding the orbits of artificial Earth satellites, the results obtained by the procedure implementing the traditional approach and the new method are compared. The comparison shows that the new method is a highly efficient means for studying perturbed motion.

Shefer, V. A.

2013-12-01

265

Representation of Probability Density Functions from Orbit Determination using the Particle Filter

NASA Technical Reports Server (NTRS)

Statistical orbit determination enables us to obtain estimates of the state and the statistical information of its region of uncertainty. In order to obtain an accurate representation of the probability density function (PDF) that incorporates higher order statistical information, we propose the use of nonlinear estimation methods such as the Particle Filter. The Particle Filter (PF) is capable of providing a PDF representation of the state estimates whose accuracy is dependent on the number of particles or samples used. For this method to be applicable to real case scenarios, we need a way of accurately representing the PDF in a compressed manner with little information loss. Hence we propose using the Independent Component Analysis (ICA) as a non-Gaussian dimensional reduction method that is capable of maintaining higher order statistical information obtained using the PF. Methods such as the Principal Component Analysis (PCA) are based on utilizing up to second order statistics, hence will not suffice in maintaining maximum information content. Both the PCA and the ICA are applied to two scenarios that involve a highly eccentric orbit with a lower apriori uncertainty covariance and a less eccentric orbit with a higher a priori uncertainty covariance, to illustrate the capability of the ICA in relation to the PCA.

Mashiku, Alinda K.; Garrison, James; Carpenter, J. Russell

2012-01-01

266

NASA Technical Reports Server (NTRS)

A new orbital debris environment model (ORDEM 3.0) defines the density distribution of the debris environment in terms of the fraction of debris that are low-density (plastic), medium-density (aluminum) or high-density (steel) particles. This hypervelocity impact (HVI) program focused on assessing ballistic limits (BLs) for steel projectiles impacting the enhanced Soyuz Orbital Module (OM) micrometeoroid and orbital debris (MMOD) shield configuration. The ballistic limit was defined as the projectile size on the threshold of failure of the OM pressure shell as a function of impact speeds and angle. The enhanced OM shield configuration was first introduced with Soyuz 30S (launched in May 2012) to improve the MMOD protection of Soyuz vehicles docked to the International Space Station (ISS). This test program provides HVI data on U.S. materials similar in composition and density to the Russian materials for the enhanced Soyuz OM shield configuration of the vehicle. Data from this test program was used to update ballistic limit equations used in Soyuz OM penetration risk assessments. The objective of this hypervelocity impact test program was to determine the ballistic limit particle size for 440C stainless steel spherical projectiles on the Soyuz OM shielding at several impact conditions (velocity and angle combinations). This test report was prepared by NASA-JSC/ HVIT, upon completion of tests.

Lyons, Frankel

2013-01-01

267

Single Step to Orbit; a First Step in a Cooperative Space Exploration Initiative

NASA Technical Reports Server (NTRS)

At the end of the Cold War, disarmament planners included a recommendation to ease reduction of the U.S. and Russian aerospace industries by creating cooperative scientific pursuits. The idea was not new, having earlier been suggested by Eisenhower and Khrushchev to reduce the pressure of the "Military Industrial Complex" by undertaking joint space exploration. The Space Exploration Initiative (SEI) proposed at the end of the Cold War by President Bush and Premier Gorbachev was another attempt to ease the disarmament process by giving the bloated war industries something better to do. The engineering talent and the space rockets could be used for peaceful pursuits, notably for going back to the Moon and then on to Mars with human exploration and settlement. At the beginning of this process in 1992 staff of the Stanford Center for International Cooperation in Space attended the International Space University in Canada, met with Russian participants and invited a Russian team to work with us on a joint Stanford-Russian Mars Exploration Study. A CIA student and Airforce and Navy students just happened to join the Stanford course the next year and all students were aware that the leader of the four Russian engineers was well versed in Russian security. But, as long as they did their homework, they were welcome to participate with other students in defining the Mars mission and the three engineers they sent were excellent. At the end of this study we were invited to give a briefing to Dr. Edward Teller at Stanford's Hoover Institution of War and Peace. We were also encouraged to hold a press conference on Capitol Hill to introduce the study to the world. At a pre-conference briefing at the Space Council, we were asked to please remind the press that President Bush had asked for a cooperative exploration proposal not a U.S. alone initiative. The Stanford-Russian study used Russia's Energia launchers, priced at $300 Million each. The mission totaled out to $71.5 Billion, to send a six-person crew to establish a Mars base and return. It was an on going international venture with plans for new crews, base expansion, and extended exploration at every two year opportunity. The $71.5 Billion international approach contrasted with NASA's own 90-day U.S. - alone study that proposed a package topping $500 Billion by some admissions. NASA's approach was also challenged by an internal D.O.E. proposal at much lower cost, described to the Mars Society last year by Lowell Wood and, of course, by Bob Zubrin's "Mars Direct" proposal.

Lusignan, Bruce; Sivalingam, Shivan

1999-01-01

268

NSDL National Science Digital Library

The Orbit program displays the dynamics of multiple massive objects interacting gravitationally. The default scenario shows the figure-eight orbit of three particles first discovered by Montgomery. Additional particles and their initial positions and velocities can be specified using the Display | Switch GUI menu item. Orbit is an Open Source Physics program written for the teaching of classical orbits. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the mech_orbit.jar file will run the program if Java is installed. Other classical mechanics programs are also available. They can be found by searching ComPADRE for Open Source Physics, OSP, or mechanics.

Christian, Wolfgang

2008-05-20

269

BATSE Observations and Orbit Determination of the Be/X-Ray Transient EXO 2030+375

NASA Technical Reports Server (NTRS)

The Be/X-ray binary transient pulsar EXO 2030+375 (P(sub s) approx equal 42 s) has been observed with the large area detectors (LADs) of the Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory (CGRO). Beginning in May 1991, twenty-two outbursts were observed over four years. Thirteen outbursts between February 1992 and August 1993 occurred consecutively at intervals of approx equal 46 days, close to the orbital period determined by Parmar et al. (1989) using EXOSAT data. The pulse profiles from the BATSE data are double-peaked and show no significant energy or luminosity dependence, unlike the EXOSAT observations of May-August 1985. An exponential model was used to fit the observed hard X-ray energy spectra from the thirteen consecutive outbursts. When EXOSAT discovered this pulsar during a giant outburst in May 1985, the X-ray luminosity peaked at L(sub x) = 1.0 x 10(esp 38) erg/ s (1-20 keV), assuming a 5 kpc distance to the source. The BATSE outbursts are found to be weaker 0.3 x 10(exp 37) less than or equal to L(sub x)(I-20 keV) less than or equal to 3.0 x 10(exp 37) erg/ s after extrapolating the observed flux (20-50 keV) to the EXOSAT energy band. Pulse phases derived from the thirteen outbursts were fit to two different models to determine a binary orbit. The new orbit is used to estimate 95% confidence limits for the mean peak spin frequency change during the out- bursts observed with BATSE. This, and the mean peak flux, are compared to the spin-up rates and fluxes determined by EXOSAT from the 1985 giant outburst, where disk accretion was thought to have occurred. It is unclear if these normal outbursts were driven by wind or disk accretion.

Strollberg, Mark T.; Finger, Mark H.; Wilson, Robert B.; Scott, D. Matthew; Crary, David J.; Paciesas, William S.

1998-01-01

270

Abstract In previous studies of saccadic eye movement reaction time, the manipulation of initial eye position re-vealed a behavioral bias that facilitates the initiation of movements towards of positions that the eyes can take in the orbits delimits the extent of visual exploration by head

Munoz, Douglas Perry

271

NASA Astrophysics Data System (ADS)

Solar sail propulsion systems enable a wide range of space missions that are not feasible with current propulsion technology. Hardware concepts and analytical methods have matured through ground development to the point that a flight validation mission is now realizable. Astronomical observations may play an important role in the flight validation of solar sail propulsion systems. Astrometric data and visual magnitude estimation has great potential for contributing to orbit determination, thrust performance verification, and optical model validation. This paper presents an overview of solar sail technology and proposes a collaboration between astronomical imagers and mission analysts for a flight validation mission.

Whorton, M. S.

2005-05-01

272

A new semi-analytical method is presented for solving the calculation of the perturbed orbits of Global Positioning System (GPS) satellites. Preliminary notions concerning coordinates, Keplerian orbits, and the perturbed orbit are established. The basic principles of the analytical and numerical method are introduced along with the models of the principal perturbations affecting the GPS satellites. Different methods of orbit calculation

Caroline Huot

1993-01-01

273

Frozen Orbital Plane Solutions for Satellites in Nearly Circular Orbit

NASA Astrophysics Data System (ADS)

This paper deals with the determination of the initial conditions (right ascension of the ascending node and inclination) that minimize the orbital plane variation for nearly circular orbits with a semimajor axis between 3 and 10 Earth radii. An analysis of two-line elements over the last 40 years for mid-, geostationary-, and high-Earth orbits has shown, for initially quasi-circular orbits, low eccentricity variations up to the geostationary altitude. This result makes the application of mathematical models based on satellite circular orbits advantageous for a fast prediction of long-term temporal evolution of the orbital plane. To this purpose, a previous model considering the combined effect due to the Earth's oblateness, moon, and sun (both in circular orbit) has been improved in terms of required computational time and accuracy. The eccentricity of the sun and moon and the equinoctial precession have been taken into account. Resonance phenomena with the lunar plane motion have been found in mid-Earth orbit. Dynamical properties concerning the precession motions of the orbital pole have been investigated, and frozen solutions for geosynchronous and navigation satellites have been proposed. Finally, an accurate model validation has also been carried out by comparing the obtained results with two-line elements of abandoned geostationary-Earth orbit and mid-Earth orbit satellites.

Ulivieri, Carlo; Circi, Christian; Ortore, Emiliano; Bunkheila, Federico; Todino, Francesco

2013-08-01

274

Orbit determination accuracy assessment for an asteroid flyby - A Galileo case study

NASA Technical Reports Server (NTRS)

The Galileo spacecraft may be targeted for a close flyby of an asteroid on its way to an encounter with Jupiter. An orbit determination accuracy analysis was carried out for the case of the asteroid 29 Amphitrite based on the use of radio metric and optical data types. Prior to encounter, the uncertainty in the asteroid's position, based on astrometric observations from earth, amounts to several hundred kilometers. This ephemeris uncertainty constitutes the dominant error in the determination of the spacecraft orbit with respect to Amphitrite. It is shown that the spacecraft-asteroid relative position can be improved by imaging asteroid-star pairs with the Galileo charge-coupled device (CCD) camera, enabling an accurate flyby of the asteroid. The main benefit of optical navigation is to enable the instrument pointing updates necessary for closeup viewing of the asteroid. A discussion of the evolution of the target error ellipse parameters as a function of data coverage and various combinations of radiometric and optical data types is also presented.

Kechichian, Jean A.; Kenyon, Paul R.; Moultrie, Benjamin

1987-01-01

275

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

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. PMID:22355584

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

2011-01-01

276

GPS-Based Precision Orbit Determination for a New Era of Altimeter Satellites: Jason-1 and ICESat

NASA Technical Reports Server (NTRS)

Accurate positioning of the satellite center of mass is necessary in meeting an altimeter mission's science goals. The fundamental science observation is an altimetric derived topographic height. Errors in positioning the satellite's center of mass directly impact this fundamental observation. Therefore, orbit error is a critical Component in the error budget of altimeter satellites. With the launch of the Jason-1 radar altimeter (Dec. 2001) and the ICESat laser altimeter (Jan. 2003) a new era of satellite altimetry has begun. Both missions pose several challenges for precision orbit determination (POD). The Jason-1 radial orbit accuracy goal is 1 cm, while ICESat (600 km) at a much lower altitude than Jason-1 (1300 km), has a radial orbit accuracy requirement of less than 5 cm. Fortunately, Jason-1 and ICESat POD can rely on near continuous tracking data from the dual frequency codeless BlackJack GPS receiver and Satellite Laser Ranging. Analysis of current GPS-based solution performance indicates the l-cm radial orbit accuracy goal is being met for Jason-1, while radial orbit accuracy for ICESat is well below the 54x1 mission requirement. A brief overview of the GPS precision orbit determination methodology and results for both Jason-1 and ICESat are presented.

Luthcke, Scott B.; Rowlands, David D.; Lemoine, Frank G.; Zelensky, Nikita P.; Williams, Teresa A.

2003-01-01

277

Single frequency GPS measurements in real-time artificial satellite orbit determination

NASA Astrophysics Data System (ADS)

A simplified and compact algorithm with low computational cost providing an accuracy around tens of meters for artificial satellite orbit determination in real-time and on-board is developed in this work. The state estimation method is the extended Kalman filter. The Cowell's method is used to propagate the state vector, through a simple Runge-Kutta numerical integrator of fourth order with fixed step size. The modeled forces are due to the geopotential up to 50th order and degree of JGM-2 model. To time-update the state error covariance matrix, it is considered a simplified force model. In other words, in computing the state transition matrix, the effect of J 2 (Earth flattening) is analytically considered, which unloads dramatically the processing time. In the measurement model, the single frequency GPS pseudorange is used, considering the effects of the ionospheric delay, clock offsets of the GPS and user satellites, and relativistic effects. To validate this model, real live data are used from Topex/Poseidon satellite and the results are compared with the Topex/Poseidon Precision Orbit Ephemeris (POE) generated by NASA/JPL, for several test cases. It is concluded that this compact algorithm enables accuracies of tens of meters with such simplified force model, analytical approach for computing the transition matrix, and a cheap GPS receiver providing single frequency pseudorange measurements.

Chiaradia, orbit determination A. P. M.; Kuga, H. K.; Prado, A. F. B. A.

2003-07-01

278

Effect of Ocean Tide Models on the Precise Orbit Determination of Geodetic Satellites

NASA Astrophysics Data System (ADS)

Several ocean tide models are tested with precise observation data of satellite laser ranging to geodetic satellites, Starlette and Stella. Four ocean models, NAO.99b, CSR 3.0 (standard model in IERS Conventions 2003), CSR 4.0, and GOT99.2b were implemented in our orbit analysis software "concerto ver. 4". NAO.99b model was developed by assimilating tidal solutions from TOPEX/POSEIDON altimeter data into hydrodynamical model. Eight constituents (M2, S2, K1, O1, N2, P1, K2, Q1) were taken into account in each ocean tide model. Moreover, eight additional constituents (M1, J1, OO1, 2N2, Mu2, Nu2, L2, T2) can be included in NAO.99b model. Effect of ocean tides on geopotential coefficients were computed to 20th order. SLR data to Starlette and Stella were divided into arcs of 7 days length and 52 arcs (Jan. 2 - Dec. 30, 2004) were analyzed. Using different ocean tide model, orbits of these satellites were determined and weighted rms of postfit residuals are compared. We found that the NAO.99b model with 16 constituents can reduce weighted rms of postfit residuals using to the level of about 6.0 cm (Starlette) and 9.6 cm (Stella). These values are about 3-5 % smaller compared to other ocean tide models.

Kubo-Oka, T.; Matsumoto, K.; Otsubo, T.; Gotoh, T.

2005-12-01

279

Determination of the chemical potential and HOMO\\/LUMO orbitals in density purification methods

Several density purification methods have been proposed to achieve linear scaling in Hartree–Fock and Kohn–Sham calculations. However, only the density is found, while in the traditional diagonalization method the orbitals are also obtained. This could be seen as a drawback as in many cases one would like at least the HOMO and LUMO orbitals and their orbital energies. In this

Emanuel H. Rubensson; Hans Jørgen Aa. Jensen

2006-01-01

280

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

281

NASA Technical Reports Server (NTRS)

Jason-1, launched on December 7,2001, is continuing the time series of centimeter level ocean topography observations as the follow-on to the highly successful TOPEX/POSEIDON (T/P) radar altimeter satellite. The precision orbit determination (POD) is a critical component to meeting the ocean topography goals of the mission. T P has demonstrated that the time variation of ocean topography can be determined with an accuracy of a few centimeters, thanks to the availability of highly accurate orbits based primarily on SLR+DORIS tracking. The Jason-1 mission is intended to continue measurement of the ocean surface with the same, if not better accuracy. Fortunately, Jason- 1 POD can rely on four independent tracking data types available including near continuous tracking data from the dual frequency codeless BlackJack GPS receiver. Orbit solutions computed using individual and various combinations of GPS, SLR, DORIS and altimeter crossover data types have been determined from over 100 days of Jason-1 tracking data, The performance of the orbit solutions and tracking data has been evaluated. Orbit solution evaluation and comparison has provided insight into possible areas of refinement. Several aspects of the POD process are examined to obtain orbit improvements including measurement modeling, force modeling and solution strategy. The results of these analyses will be presented.

Luthcke, Scott B.; Zelensky, N. P.; Rowlands, D. D.; Lemoine, F. G.; Chinn, D. S.; Williams, T. A.

2002-01-01

282

NASA Technical Reports Server (NTRS)

Jason-1, launched on December 7, 2001, is continuing the time series of centimeter level ocean topography observations as the follow-on to the highly successful TOPEX/POSEIDON (T/P) radar altimeter satellite. The precision orbit determination (POD) is a critical component to meeting the ocean topography goals of the mission. T/P has demonstrated that the time variation of ocean topography can be determined with an accuracy of a few centimeters, thanks to the availability of highly accurate orbits based primarily on SLR+DORIS tracking. The Jason-1 mission is intended to continue measurement of the ocean surface with the same, if not better accuracy. Fortunately, Jason-1 POD can rely on four independent tracking data types available including near continuous tracking data from the dual frequency codeless BlackJack GPS receiver. Orbit solutions computed using individual and various combinations of GPS, SLR, DORIS and altimeter crossover data types have been determined from over 100 days of Jason-1 tracking data. The performance of the orbit solutions and tracking data has been evaluated. Orbit solution evaluation and comparison has provided insight into possible areas of refinement. Several aspects of the POD process are examined to obtain orbit improvements including measurement modeling, force modeling and solution strategy. The results of these analyses will be presented.

Luthcke, S. B.; Zelensky, N. P.; Lemoine, Frank G.; Chinn, D. S.; Williams, T. A.

2002-01-01

283

Complete determination of molecular orbitals by measurement of phase symmetry and electron density.

Several experimental methods allow measuring the spatial probability density of electrons in atoms, molecules and solids, that is, the absolute square of the respective single-particle wave function. But it is an intrinsic problem of the measurement process that the information about the phase is generally lost during the experiment. The symmetry of this phase, however, is a crucial parameter for the knowledge of the full orbital information in real space. Here, we report on a key experiment that demonstrates that the phase symmetry can be derived from a strictly experimental approach from the circular dichroism in the angular distribution of photoelectrons. In combination with the electron density derived from the same experiment, the full quantum mechanical wave function can thus be determined experimentally. PMID:24910256

Wießner, M; Hauschild, D; Sauer, C; Feyer, V; Schöll, A; Reinert, F

2014-01-01

284

20 CFR 405.115 - Notice of the initial determination.

Code of Federal Regulations, 2010 CFR

... 405.115 Section 405.115 Employees' Benefits SOCIAL SECURITY ADMINISTRATION ADMINISTRATIVE REVIEW PROCESS FOR...in simple and clear language what we have determined and the reasons for and the effect of our determination. If our...

2010-04-01

285

NASA Astrophysics Data System (ADS)

An analytical theory for determining accurately the coordinates of a satellite at any time during its movement around the earth was developed using a power series of regularized time and a spheroidal coordinate system. The theory is used to design a computer program for determining orbits of geodynamical satellites. The results of determining the orbit of Lageos with this program are compared with those obtained by means of a numerical integration, showing a coincidence greater than 1 cm for a six-day period and greater than 3 mm for a two-week period.

Georgiev, Nikola; Chapanov, Iavor

286

Climatic determinants of Holocene peatland initiation in South Florida

NASA Astrophysics Data System (ADS)

An overview of basal ages of peatlands in Southern Florida shows two episodes of peatland initiation, the first between 4.5-6.5 kiloyear before present (ka) and a second between 2.0-3.5 ka. Here we test three hypotheses that may explain these two episodes of peatland initiation: (1) a gradual increase in precipitation throughout the Holocene, (2) decreased drainage due to Holocene sea level rise and, (3) increased climate variability from the mid to the late Holocene. The three hypotheses were tested by means of specific forcings in a model of peat accumulation and decomposition in Southern Florida. The magnitudes of these forcings were based upon climatic conditions for this region as derived from multiple independent proxy datasets. The model results suggest that long-term average precipitation was sufficient for peat development throughout the Holocene. Hence, the onset of peatland development at 6.5 ka cannot be explained by increased precipitation alone. Although sea level rise could explain this first period of peatland initiation, it could not account for the decline in peatland initiation after 4.5 ka. Instead, this period of reduced peatland initiation between 3.5-4.5 ka may be explained by an increase of multidecadal variability in precipitation. Multidecadal droughts may decrease the hydroperiod and make peatlands vulnerable to erosion and fires. The results further suggest that ample precipitation and the relatively high sea level of the late Holocene began to alleviate the impact of these multidecadal droughts after 3.5 ka, explaining the second episode of peatland initiation in Southern Florida. We conclude that the role of multidecadal climate variability is crucial to understand peatland development in Southern Florida.

Dekker, S. C.; Boer, De, H. J.; Eppinga, M. B.

2011-12-01

287

NASA Astrophysics Data System (ADS)

We survey the methods proposed in the literature for detecting moons of extrasolar planets in terms of their ability to distinguish between prograde and retrograde moon orbits, an important tracer of the moon formation channel. We find that most moon detection methods, in particular, sensitive methods for detecting moons of transiting planets, cannot observationally distinguishing prograde and retrograde moon orbits. The prograde and retrograde cases can only be distinguished where the dynamical evolution of the orbit due to, e.g., three body effects is detectable, where one of the two cases is dynamically unstable, or where new observational facilities, which can implement a technique capable of differentiating the two cases, come online. In particular, directly imaged planets are promising targets because repeated spectral and photometric measurements, which are required to determine moon orbit direction, could also be conducted with the primary interest of characterizing the planet itself.

Lewis, Karen M.; Fujii, Yuka

2014-08-01

288

We survey the methods proposed in the literature for detecting moons of extrasolar planets in terms of their ability to distinguish between prograde and retrograde moon orbits, an important tracer of moon formation channel. We find that most moon detection methods, in particular, sensitive methods for detecting moons of transiting planets, cannot observationally distinguishing prograde and retrograde moon orbits. The prograde and retrograde cases can only be distinguished where dynamical evolution of the orbit due to e.g. three body effects is detectable, where one of the two cases is dynamically unstable or where new observational facilities which can implement a technique capable of differentiating the two cases, come on line. In particular, directly imaged planets are promising targets as repeated spectral and photometric measurements, required to determine moon orbit direction, could also be conducted with the primary interest of characterising the planet itself.

Lewis, Karen M

2014-01-01

289

NASA Technical Reports Server (NTRS)

Temperatures measured at the aerodynamic surface of the Orbiter's thermal protection system (TPS), and calorimeter measurements, are used to determine heating rates to the TPS surface during atmospheric entry. On the Orbiter leeside, where convective heating rates are low, it is possible that a significant portion of the total energy input may result from solar radiation, and for the wing, cross radiation from the hot (relatively) Orbiter fuselage. In order to account for the potential impact of these sources, values of solar- and cross-radiation heat transfer are computed, based upon vehicle trajectory and attitude information and measured surface temperatures. Leeside heat-transfer data from the STS-2 mission are presented, and the significance of solar radiation and fuselage-to-wing cross-radiation contributions to total energy input to Orbiter leeside surfaces is assessed.

Throckmorton, D. A.

1982-01-01

290

NASA Astrophysics Data System (ADS)

In this paper, a brief but essential development strategy for the lunar orbit determination system is discussed to prepare for the future Korea's lunar missions. Prior to the discussion of this preliminary development strategy, technical models of foreign agencies for the lunar orbit determination system, tracking networks to measure the orbit, and collaborative efforts to verify system performance are reviewed in detail with a short summary of their lunar mission history. Covered foreign agencies are European Space Agency, Japan Aerospace Exploration Agency, Indian Space Research Organization and China National Space Administration. Based on the lessons from their experiences, the preliminary development strategy for Korea's future lunar orbit determination system is discussed with regard to the core technical issues of dynamic modeling, numerical integration, measurement modeling, estimation method, measurement system as well as appropriate data formatting for the interoperability among foreign agencies. Although only the preliminary development strategy has been discussed through this work, the proposed strategy will aid the Korean astronautical society while on the development phase of the future Korea's own lunar orbit determination system. Also, it is expected that further detailed system requirements or technical development strategies could be designed or established based on the current discussions.

Song, Young-Joo; Ahn, Sang-il; Sim, Eun-Sup

2014-09-01

291

NASA Astrophysics Data System (ADS)

We determined the orbital lineup of the tris (8-hydroxyquinolinato) gallium (Gaq3)/Mg interface using combined x-ray and ultraviolet photoemission spectroscopy (XPS and UPS) measurements. The Gaq3/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 Gaq3 thin film was grown in 15 steps on a previously sputter-cleaned Mg substrate starting at a 1 Å nominal thickness up to a final thickness of 512 Å. 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 Å thickness at the Mg interface, which resulted in a 0.96 V interface dipole potential. At Gaq3 coverages higher than 256 Å, 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 Gaq3 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 Gaq3 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.

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

2001-08-01

292

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

293

Determinants of breastfeeding initiation among mothers in Kuwait

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. PMID:20667112

2010-01-01

294

Research note Yield stress for initial firmness determination on yogurt

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

295

Yield stress for initial firmness determination on yogurt

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 panelists in both laboratory-made (r=0.99) and retail (r>0.97) yogurts. Apparent residual stress was significantly correlated with sensory viscosity for retail yogurts (r>0.90). The yield stress had

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

2007-01-01

296

Radiation Pressure Modelling for Precise Orbit Determination of the Galileo IOV Satellites

NASA Astrophysics Data System (ADS)

Four Galileo satellites are currently in orbit for In Orbit Validation (IOV) of the European Global Navigation Satellite System and are providing navigation signals. Precise orbits for these satellites are computed by several groups in the context of the Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS). MGEX currently makes available tracking data of a global network of more than 90 multi-GNSS receivers. Satellite Laser Ranging (SLR) tracking data indicate orbit modelling issues for the Galileo IOV satellites. Once-per-rev orbit errors depending on the Sun elevation above the orbital plane are also evidenced from apparent clock offset variations of the highly stable on-board hydrogen masers. Based on the analysis of clock corrections a variety of radiation pressure models for the Galileo IOV satellites are assessed and models with a significantly improved performance as compared to the standard models currently used in the community are highlighted.

Hugentobler, Urs; Montenbruck, Oliver; Steigenberger, -Peter

297

Initial visual information determines endpoint precision for rapid pointing.

We investigated how visual noise in the initial estimate of target location affects precision for rapid pointing. Visual localization thresholds (an error measure) rise systematically with eccentricity, doubling at eccentricities of a degree or less. Previous work, which we confirmed, has shown that the precision of pointing, measured by the standard deviation, to a single isolated target is relatively constant over small lateral extents near the midline, and that pointing error is substantially larger than visual error. We used target uncertainty (randomly chosen locations) to greatly increase visual noise so that we could explore the influence of visual noise on pointing error. We compared precision for comparable visual and pointing tasks as a function of target eccentricity. The target was presented for 110 ms at one of eight isoeccentric locations, chosen at random. Under these conditions, pointing error increased significantly with increasing target eccentricity. Beyond 4 degrees eccentricity, visual thresholds and pointing error were identical. Even when the target remained visible until the movement was completed, initial target eccentricity affected pointing error. The quality of visual information varies with task demands, and therefore so does its influence on endpoint precision. Our results demonstrate that the initial visual information about target location can limit endpoint precision, even over as small a range as 12 degrees in the central visual field (a lateral extent of +/-8.5 cm at the midline). PMID:17070889

Ma-Wyatt, Anna; McKee, Suzanne P

2006-12-01

298

A computerized survey of a selected subset of initial orbit determination methods

1 3 2 5 (7up ? 3upq ? up)dt + 8 o o 0 0 0 0 0 i (121) and 1 3 1 4 g = bt. ? ? u 4t. + ? u p 4t. + i 6 o i 4 o o i 1 (9uq -45up +u)dt + 2 2 5 0 0 0 0 0 (122) 29 and where u 0 3 r 0 (123) r ~ r po = r (124 ) 2 2 v -ru 0 qo 2 r (125... 0 0 0 5 3 2 4 + ? (7 up ? 3upq -up)bt 8 onooooo 1 1 2 2 3 2 4 + (630upq ? 24 uq -u ? 45 uq ? 945 p 120 o 0 o 0 0 0 0 0 o + 210 u p )btl + . 2 2 5 0 0 (132) and = 1 ? ? u bt + u p bt + ? (9 u q, ? 45 u p + u )bt 1 2 3 5 2 2 4 1 2 o 1 oo 1 120 o...

Cleveland, Durand Ennis

2012-06-07

299

A Comprehensive Comparison Between Angles-Only Initial Orbit Determination Techniques

in LEO by Varying Observation Interval : : : : : : : : : 60 13 IOD Errors in LEO Varying Semi-Major Axis : : : : : : : : : : : : : 61 14 IOD Errors in LEO Varying Inclination (1 min Observation Interval) 62 15 IOD Errors in LEO Varying Inclination (3... min observation interval) : 63 16 IOD Errors in LEO Varying Inclination from 20 Latitude (1 min time interval) : : : : : : : : : : : : : : : : : : : : : : : : : : : : 63 17 IOD Errors in LEO Varying Inclination from 20 Latitude (3 min time interval...

Schaeperkoetter, Andrew Vernon

2012-02-14

300

Near-Real Time Satellite Orbit Determination for GPS Radio Occultation with CHAMP and GRACE

\\u000a Precise and rapidly available orbits of GPS and Low-Earth-Orbiting (LEO) satellites are the prerequisite for processing of\\u000a the radio occultation data from CHAMP, GRACE and other LEOs performing occultation measurements. For efficient occultation\\u000a data assimilation by the weather prediction systems a 3 h timeline is required. In 2002 GFZ has started to generate orbits\\u000a at fixed 3 h intervals with a mean

Grzegorz Michalak; Rolf König

301

Federal Register 2010, 2011, 2012, 2013

...Commission has determined not to review initial determinations (``IDs'') (Order Nos. 69, 70, and 71) granting joint motions...received. The Commission has determined not to review the subject IDs. The investigation is terminated in its entirety. This...

2012-07-31

302

20 CFR 408.1003 - Which administrative actions are initial determinations?

Code of Federal Regulations, 2010 CFR

...determinations? Initial determinations regarding SVB include, but are not limited to, determinations about— (a) Whether you qualify for SVB; (b) Whether you are entitled to receive SVB payments on the basis of your residence...

2010-04-01

303

20 CFR 404.904 - Notice of the initial determination.

Code of Federal Regulations, 2013 CFR

...SECURITY ADMINISTRATION FEDERAL OLD-AGE, SURVIVORS AND DISABILITY INSURANCE...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...

2013-04-01

304

305

20 CFR 404.904 - Notice of the initial determination.

Code of Federal Regulations, 2011 CFR

...SECURITY ADMINISTRATION FEDERAL OLD-AGE, SURVIVORS AND DISABILITY INSURANCE...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...

2011-04-01

306

20 CFR 404.904 - Notice of the initial determination.

Code of Federal Regulations, 2010 CFR

...SECURITY ADMINISTRATION FEDERAL OLD-AGE, SURVIVORS AND DISABILITY INSURANCE...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...

2010-04-01

307

20 CFR 404.904 - Notice of the initial determination.

Code of Federal Regulations, 2012 CFR

2012-04-01

308

14 CFR 1206.603 - Procedures and time limits for initial determinations.

Code of Federal Regulations, 2010 CFR

14 Aeronautics and Space 5 2010-01-01...false Procedures and time limits for initial determinations...603 Aeronautics and Space NATIONAL AERONAUTICS AND SPACE ADMINISTRATION AVAILABILITY...603 Procedures and time limits for initial...

2010-01-01

310

14 CFR 1206.603 - Procedures and time limits for initial determinations.

Code of Federal Regulations, 2012 CFR

14 Aeronautics and Space 5 2012-01-01...false Procedures and time limits for initial determinations...603 Aeronautics and Space NATIONAL AERONAUTICS AND SPACE ADMINISTRATION AVAILABILITY...603 Procedures and time limits for initial...

2012-01-01

311

14 CFR 1206.603 - Procedures and time limits for initial determinations.

Code of Federal Regulations, 2011 CFR

14 Aeronautics and Space 5 2011-01-01...true Procedures and time limits for initial determinations...603 Aeronautics and Space NATIONAL AERONAUTICS AND SPACE ADMINISTRATION AVAILABILITY...603 Procedures and time limits for initial...

2011-01-01

312

14 CFR 1206.603 - Procedures and time limits for initial determinations.

Code of Federal Regulations, 2013 CFR

14 Aeronautics and Space 5 2013-01-01...false Procedures and time limits for initial determinations...603 Aeronautics and Space NATIONAL AERONAUTICS AND SPACE ADMINISTRATION AVAILABILITY...603 Procedures and time limits for initial...

2013-01-01

313

Seasat orbit determination experiments in preparation for the ERS-1 altimetry mission

NASA Astrophysics Data System (ADS)

Techniques to generate highly accurate orbits for ERS-1, and to process the satellite's radar altimeter measurements were investigated. To test numerical techniques, the orbit of Seasat was recomputed using state-of-the-art dynamic models. It is demonstrated that the Seasat rms radial orbit error is 0.9 to 1.1 m for 3-day arcs computed from laser tracking data and applying the PGS-S4 Seasat-tailored gravity and station coordinates models. With the GEM-T1 gravity model in combination with the UT/CSR LSC 8402 laser station coordinates an improvement is observed: rms radial orbit error decreases to 0.6 m for the same arc length and tracking network. It is expected that through further improvement of gravity and other dynamic models the radial component of the Seasat orbit may be computed with an rms accuracy of 0.4 m. It is also demonstrated that the radial accuracy of orbits computed from laser range observations acquired by only one laser station in combination with altimeter cross-over height differences may be just as good as the accuracy of orbits computed from laser range observations acquired by a global network of laser stations. For many oceanographic applications of the altimeter data the indicated orbit accuracy levels are, however, still too low, but improvement is possible.

Wakker, K. F.; Zandbergen, R. C. A.; Ambrosius, B. A. C.

1987-06-01

314

The purpose of this study is to locate critical inclinations in long term high eccentricity orbits about Mars using numerical methods. A critical inclination is defined as the inclination at orbit insertion which produces a local maximum in the amplitude of the variation of eccentricity or inclination. The perturbation model consists of the first non-zero zonal harmonic of the Mars

Denis F. Durand

1989-01-01

315

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

316

NASA Astrophysics Data System (ADS)

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, evaluation of the orbit control, and the drift of the inclination are summarized.

Rosengren, Mats

1991-12-01

317

GPS interferometric attitude and heading determination - Initial flight test results

NASA Technical Reports Server (NTRS)

Attitude and heading determination using GPS interferometry is a well-understood concept. However, efforts have been concentrated mainly in the development of robust algorithms and applications for low-dynamic, rigid platforms (e.g., shipboard). This paper presents results of what is believed to be the first real-time flight test of a GPS attitude and heading determination system. Signals from four antennas are processed by a 24-channel GPS receiver. Data from the receiver are sent to a microcomputer for storage and further computations. Attitude and heading data are sent to a second computer for display on a software-generated artificial horizon. Demonstration of this technique proves its candidacy for augmentation of aircraft state estimation for flight control and navigation, as well as for numerous other applications.

Van Graas, Frank; Braasch, Michael

1992-01-01

318

The beverage intake questionnaire: determining initial validity and reliability.

Consuming energy-containing beverages may lead to weight gain, yet research investigating this issue is limited. An easily administered beverage intake assessment tool could facilitate research on this topic. The purpose of this cross-sectional investigation was to determine the validity and reliability of a self-administered beverage intake questionnaire (BEVQ) that estimates mean daily intake of beverages consumed across 19 beverage categories. Participants (N=105; aged 39+/-2 years) underwent assessments of height, weight, body mass index, and dietary intake using 4-day food intake records from June 2008 to June 2009. The BEVQ was completed at two additional visits (BEVQ1, BEVQ2). Urine samples were collected to objectively determine total fluid intake and encourage accurate self-reporting. Validity was assessed by comparing BEVQ1 with food intake record results; reliability was assessed by comparing BEVQ1 and BEVQ2. Analyses included descriptive statistics, bivariate correlations, paired samples t tests, and independent samples t tests. Self-reported water and total beverage intake (in grams) were not different between the BEVQ1 and food intake records (mean difference 129+/-77 g [P=0.096] and 61+/-106 g [P=0.567], respectively). Total beverage and sugar-sweetened beverage energy intake were significantly different, although mean differences were small (63 and 44 kcal, respectively). Daily consumption (in grams) of water (r=0.53), total beverages (r=0.46), and sugar-sweetened beverages (r=0.49) determined by the BEVQ1 were correlated with reported intake determined by the food intake record, as was energy from total beverages (r=0.61) and sugar-sweetened beverages (r=0.59) (all P values <0.001). Reliability was demonstrated, with correlations (P<0.001) detected between BEVQ1 and BEVQ2 results. The BEVQ is a valid, reliable, and rapid self-administered dietary assessment tool. PMID:20656099

Hedrick, Valisa E; Comber, Dana L; Estabrooks, Paul A; Savla, Jyoti; Davy, Brenda M

2010-08-01

319

NASA Astrophysics Data System (ADS)

The formation of biofilms by water microorganisms such as Pseudomonas aeruginosa in spacecraft water systems has been a matter of concern for long-duration space flight. Crewed spacecraft plumbing includes internal surfaces made of 316L stainless steel. Experiments were therefore undertaken to compare the ability of P. aeruginosa to grow in suspension, attach to stainless steel and to grow on stainless steel in low gravity on the space shuttle. Four categories of cultures were studied during two space shuttle flights (STS-69 and STS-77). Cultures on the ground were held in static horizontal or vertical cylindrical containers or were tumbled on a clinostat and activated under conditions identical to those for the flown cultures. The containers used on the ground and in flight were BioServe Space Technologies’ Fluid Processing Apparatus (FPA), an open-ended test tube with rubber septa that allows robotic addition of bacteria to culture media to initiate experiments and the addition of fixative to conclude experiments. Planktonic growth was monitored by spectrophotometry, and biofilms were characterized quantitatively by epifluorescence and scanning electron microscopy. In these experiments it was found that: (1) Planktonic growth in flown cultures was more extensive than in static cultures, as seen repeatedly in the history of space microbiology, and closely resembled the growth of tumbled cultures. (2) Conversely, the attachment of cells in flown cultures was as much as 8 times that in tumbled cultures but not significantly different from that in static horizontal and vertical cultures, consistent with the notion that flowing fluid reduces microbial attachment. (3) The final surface coverage in 8 days was the same for flown and static cultures but less by a factor of 15 in tumbled cultures, where coverage declined during the preceding 4 days. It is concluded that cell attachment to 316L stainless steel in the low gravity of orbital space flight is similar to that found in stagnant cultures at 1 x g. Research was supported by NASA contract NAGW-1197 to the University of Colorado.

Todd, Paul; Pierson, Duane L.; Allen, Britt; Silverstein, JoAnn

320

NASA Astrophysics Data System (ADS)

A detailed analysis of the passage through the atmosphere of a very bright meteor that exploded in the air near Chelyabinsk, Russia on February 15, 2013 is presented. A number of videos and photographs were examined thoroughly to determine the meteor trajectory beginning from the recorded atmospheric entry height of about 62.5 km until its disappearance at about 9.8 km. The calculated velocity changes as a function time revealed an unusual behavior: during the first 10 seconds the meteor velocity increased from 16.6 km/s up to about 20.6 km/s in the main air burst at the altitude of 26.5 km. Afterwards it decreased rapidly. The light curves derived from videos enabled the total radiant energy and mass loss variations to be calculated. The heliocentric orbit of the meteoroid and possible parent bodies were computed. We proposed an additional 'close approaches' method to the existing method of checking meteoroid/bolide parent bodies based on different D-criteria.

W?odarczyk, K.; W?odarczyk, I.

2014-07-01

321

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

322

323

Code of Federal Regulations, 2010 CFR

...reconsideration of an initial determination on your application for SVB? 408.1014 Section 408.1014 Employees' Benefits ...reconsideration of an initial determination on your application for SVB? When you appeal an initial determination on your...

2010-04-01

324

NASA Astrophysics Data System (ADS)

The present work describes our investigation of the navigation anomaly of the Pioneer 10 and 11 probes which became known as the Pioneer Anomaly. It appeared as a linear drift in the Doppler data received by the spacecraft, which has been ascribed to an approximately constant Sunward acceleration of about 8.5×10-13 km/s2. Since then, the existence of the anomaly has been confirmed independently by several groups and a large effort was devoted to find its origin. Recently, different analyses were published where the authors claimed the acceleration due to anisotropic thermal emission to be the most likely cause of the unexplained acceleration. Here we report the methodology and the results of an independent study carried out in the last years, aimed at supporting the thermal origin of the anomaly. This work consists of two main parts: thermal modeling of the spacecraft throughout its trajectory, and orbit determination analysis. Based on existing documentation and published telemetry data, we built a thermal finite element model of the spacecraft, whose complexity has been constrained to a degree allowing for sensitivity analysis, leading to the computation of its formal uncertainty. The trajectory analysis and orbit determination were carried out using NASA/JPL's Orbit Determination Program, and our results show that orbital solutions are achieved that do not require the addition of any "unknown" acceleration other than that of thermal origin.

Modenini, D.; Tortora, P.

2014-07-01

325

The present work describes the investigation of the navigation anomaly of Pioneer 10 and 11 probes which became known as the Pioneer Anomaly. It appeared as a linear drift in the Doppler data received by the spacecraft, which has been ascribed to an approximately constant sunward acceleration of about $8.5 \\times 10^{-13} km/s^2$. Since then, the existence of the anomaly has been confirmed independently by several groups and a large effort was devoted to find its origin. The present study consists of two main parts: thermal modeling of the spacecraft throughout its trajectory, and orbit determination analysis. Based on existing documentation and published telemetry data we built a thermal finite element model of the spacecraft, whose complexity has been constrained to a degree allowing for sensitivity analysis, leading to the computation of its formal uncertainty. The trajectory analysis and orbit determination was carried out using NASA/JPL's ODP (Orbit Determination Program) and our results show that orbital solutions may be achieved that do not require the addition of any "unknown" acceleration other than the one of thermal origin.

Dario Modenini; Paolo Tortora

2013-11-20

326

Orbit determination results and trajectory reconstruction for the Cassini/Huygens Mission

NASA Technical Reports Server (NTRS)

During Cassini's third orbit around Saturn, the Huygens Probe was successfully released on a trajectory that resulted in the probe entering Titan's atmosphere on January 14, 2005, making it both the most distant spacecraft landing and the first spacecraft to successfully land on the moon of another planet. This paper documents the reconstruction of both the orbiter and probe trajectoriespanning the Titan-B and Titan-C encounters.

Bordi, John J.; Antreasian, Pete; Jones, Jerry; Meek, Cameron; Ionasescu, Rodica; Roundhill, Ian; Roth, Duane

2005-01-01

327

Composition of the Moon as Determined from Orbit by Gamma-Ray Spectroscopy

NASA Technical Reports Server (NTRS)

A spacecraft placed in a planetary orbit of suitably high inclination will pass over all or most of the planet's surface in a matter of several weeks to months. The quite prodigious scientific potential of planetary orbiters lies in coupling this comprehensive coverage with observing systems capable of gathering data on properties that include elemental and mineralogic composition, exogenic and endogenic surface alterations, thermal balance, gravity, topography, stratigraphy, albedo and magnetism.

Metzger, A. E.

1994-01-01

329

20 CFR 418.3615 - Will we mail you a notice of the initial determination?

Code of Federal Regulations, 2010 CFR

... 418.3615 Section 418.3615 Employees' Benefits SOCIAL SECURITY ADMINISTRATION MEDICARE SUBSIDIES Medicare Part...you: (1) What our initial determination is; (2) The reasons for our determination; and (3) The effect of our...

2010-04-01

330

Code of Federal Regulations, 2010 CFR

...2010-10-01 false Retrospective budgeting; determining eligibility after the...PROGRAMS § 233.26 Retrospective budgeting; determining eligibility after the initial...months. (a) Under retrospective budgeting, there are three options for...

2010-10-01

331

20 CFR 408.1005 - Will we mail you a notice of the initial determination?

Code of Federal Regulations, 2010 CFR

...reconsideration of the determination. (c) If our initial determination is that we must suspend, reduce your SVB payments or terminate your SVB entitlement, the notice will also tell you that you have a right to a reconsideration before the...

2010-04-01

332

18 CFR 701.204 - Time limits for WRC initial determinations regarding requests for information.

Code of Federal Regulations, 2011 CFR

(1) In those instances where the initial determination by the Public Information Officer is to grant the request and the information is immediately supplied such action will serve as both notice of determination and compliance with the...

2011-04-01

333

Determining the nature of orbits in disk galaxies with non spherical nuclei

We investigate the regular or chaotic nature of orbits of stars moving in the meridional plane $(R,z)$ of an axially symmetric galactic model with a flat disk and a central, non spherical and massive nucleus. In particular, we study the influence of the flattening parameter of the central nucleus on the nature of orbits, by computing in each case the percentage of chaotic orbits, as well as the percentages of orbits of the main regular families. In an attempt to maximize the accuracy of our results upon distinguishing between regular and chaotic motion, we use both the Fast Lyapunov Indicator (FLI) and the Smaller ALingment Index (SALI) methods to extensive samples of orbits obtained by integrating numerically the equations of motion as well as the variational equations. Moreover, a technique which is based mainly on the field of spectral dynamics that utilizes the Fourier transform of the time series of each coordinate is used for identifying the various families of regular orbits and also to recognize the s...

Zotos, Euaggelos E

2014-01-01

334

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

335

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

336

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

337

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

338

NASA Astrophysics Data System (ADS)

A new semi-analytical method is presented for solving the calculation of the perturbed orbits of Global Positioning System (GPS) satellites. Preliminary notions concerning coordinates, Keplerian orbits, and the perturbed orbit are established. The basic principles of the analytical and numerical method are introduced along with the models of the principal perturbations affecting the GPS satellites. Different methods of orbit calculation are reviewed to demonstrate the main advantages and drawbacks of each. A comparison proves that the method of extended Lagrange series has many advantages. Contrary to Cowell's method, the extended Lagrange series method does not require any starting algorithm. The proposed method is distinguished from other techniques of integration by its simple formulation and for its facility in analyzing one or many perturbations. Results obtained using the MicroCosm program are presented which indicate that calculation of the orbit by the extended Lagrange series method is accurate to within 4 cm and 70 cm for short arcs of 6 and 10 hours respectively.

Huot, Caroline

1993-09-01

339

Determining the nature of orbits in disk galaxies with non spherical nuclei

We investigate the regular or chaotic nature of orbits of stars moving in the meridional plane $(R,z)$ of an axially symmetric galactic model with a flat disk and a central, non spherical and massive nucleus. In particular, we study the influence of the flattening parameter of the central nucleus on the nature of orbits, by computing in each case the percentage of chaotic orbits, as well as the percentages of orbits of the main regular families. In an attempt to maximize the accuracy of our results upon distinguishing between regular and chaotic motion, we use both the Fast Lyapunov Indicator (FLI) and the Smaller ALingment Index (SALI) methods to extensive samples of orbits obtained by integrating numerically the equations of motion as well as the variational equations. Moreover, a technique which is based mainly on the field of spectral dynamics that utilizes the Fourier transform of the time series of each coordinate is used for identifying the various families of regular orbits and also to recognize the secondary resonances that bifurcate from them. Varying the value of the flattening parameter, we study three different cases: (i) the case where we have a prolate nucleus (ii) the case where the central nucleus is spherical and (iii) the case where an oblate massive nucleus is present. Furthermore, we present some additional findings regarding the reliability of short time (fast) chaos indicators, as well as a new method to define the threshold between chaos and regularity for both FLI and SALI, by using them simultaneously. Comparison with early related work is also made.

Euaggelos E. Zotos; Nicolaos D. Caranicolas

2014-04-15

340

The Use of Laser Altimetry in the Orbit and Attitude Determination of Mars Global Surveyor

NASA Technical Reports Server (NTRS)

Altimetry from the Mars Observer Laser Altimeter (MOLA) which is carried on board Mars Global Surveyor (MGS) has been analyzed for the period of the MOS mission known as Science Phasing Orbit 1 (SPO-1). We have used these altimeter ranges to improve orbit and attitude knowledge for MGS. This has been accomplished by writing crossover constraint equations that have been derived from short passes of MOLA data. These constraint equations differ from traditional Crossover constraints and exploit the small foot print associated with laser altimetry.

Rowlands, D. D.; Pavlis, D. E.; Lemoine, F. G.; Neumann, G. A.; Luthcke, S. B.

1999-01-01

341

342

NASA Technical Reports Server (NTRS)

A plasma diagnostic package is deployed on the International Space Station (ISS). The system - a Floating Potential Measurement Unit (FPMU) - is used by NASA to monitor the electrical floating potential of the vehicle to assure astronaut safety during extravehicular activity. However, data from the unit also reflects the ionosphere state and seems to represent an unutilized scientific resource in the form of an archive of scientific plasma state data. The unit comprises a Floating Potential probe and two Langmuir probes. There is also an unused but active plasma impedance probe. The data, at one second cadence, are collected, typically for a two week period surrounding extravehicular activity events. Data is also collected any time a visiting vehicle docks with ISS and also when any large solar events occur. The telemetry system is unusual because the package is mounted on a television camera stanchion and its data is impressed on a video signal that is transmitted to the ground and streamed by internet to two off center laboratory locations. The data quality has in the past been challenged by weaknesses in the integrated ground station and distribution systems. These issues, since mid-2010, have been largely resolved and the ground stations have been upgraded. Downstream data reduction has been developed using physics based modeling of the electron and ion collecting character in the plasma. Recursive algorithms determine plasma density and temperature from the raw Langmuir probe current voltage sweeps and this is made available in real time for situational awareness. The purpose of this paper is to describe and record the algorithm for data reduction and to show that the Floating probe and Langmuir probes are capable of providing long term plasma state measurement in the ionosphere. Geophysical features such as the Appleton anomaly and high latitude modulation at the edge of the Auroral zones are regularly observed in the nearly circular, 51 deg inclined, 400 km altitude ISS orbit. Evidence of waves in the ion collection current data is seen in geographic zones known to exhibit the spread-F phenomenon. An anomaly in the current collection characteristic of the cylindrical probe appears also too be organized by the geomagnetic field.

Kramer, Leonard

2014-01-01

343

Real-time, autonomous precise satellite orbit determination using the global positioning system

NASA Astrophysics Data System (ADS)

The desire for autonomously generated, rapidly available, and highly accurate satellite ephemeris is growing with the proliferation of constellations of satellites and the cost and overhead of ground tracking resources. Autonomous Orbit Determination (OD) may be done on the ground in a post-processing mode or in real-time on board a satellite and may be accomplished days, hours or immediately after observations are processed. The Global Positioning System (GPS) is now widely used as an alternative to ground tracking resources to supply observation data for satellite positioning and navigation. GPS is accurate, inexpensive, provides continuous coverage, and is an excellent choice for autonomous systems. In an effort to estimate precise satellite ephemeris in real-time on board a satellite, the Goddard Space Flight Center (GSFC) created the GPS Enhanced OD Experiment (GEODE) flight navigation software. This dissertation offers alternative methods and improvements to GEODE to increase on board autonomy and real-time total position accuracy and precision without increasing computational burden. First, GEODE is modified to include a Gravity Acceleration Approximation Function (GAAF) to replace the traditional spherical harmonic representation of the gravity field. Next, an ionospheric correction method called Differenced Range Versus Integrated Doppler (DRVID) is applied to correct for ionospheric errors in the GPS measurements used in GEODE. Then, Dynamic Model Compensation (DMC) is added to estimate unmodeled and/or mismodeled forces in the dynamic model and to provide an alternative process noise variance-covariance formulation. Finally, a Genetic Algorithm (GA) is implemented in the form of Genetic Model Compensation (GMC) to optimize DMC forcing noise parameters. Application of GAAF, DRVID and DMC improved GEODE's position estimates by 28.3% when applied to GPS/MET data collected in the presence of Selective Availability (SA), 17.5% when SA is removed from the GPS/MET data and 10.8% on SA free TOPEX data. Position estimates with RSS errors below I meter are now achieved using SA free TOPEX data. DRVID causes an increase in computational burden while GAAF and DMC reduce computational burden. The net effect of applying GAAF, DRVID and DMC is an improvement in GEODE's accuracy/precision without an increase in computational burden.

Goldstein, David Ben

2000-10-01

344

Orbit determination results and trajectory reconstruction for the Cassini/Huygens mission

NASA Technical Reports Server (NTRS)

During Cassini's third orbit around Saturn, the Huygens Probe was successfully released on a trjectory that resulted in the probe entering Titan's atmosphere on 14-January-2005, making it both the most distant spacecraft landing and the first spacecraft to successfully land on the moon of another planet.

Bordi, J.; Antreasian, P.; Jones, J.; Meek, C.; Ionasescu, R.; Roundhill, I.; Roth, D.

2005-01-01

345

Small satellites for earth observation are an important ongoing development in space research. Small satellites are usually powered from a solar energy system. In order to maximize the solar energy captured on small satellites, orbit path selection becomes an important parameter. In this work, we have conducted some numerical studies for future small satellites (nanosatellites) developed within the PERSEUS project.

Bogdan Mocanu; Maria-Mihaela Burlacu; Josephine Kohlenberg; Mahendiran Prathaban; Pascal Lorenz; Ruxandra Tapu

2009-01-01

346

Modeling radiation forces acting on TOPEX/Poseidon for precision orbit determination

NASA Technical Reports Server (NTRS)

Geodetic satellites such as GEOSAT, SPOT, ERS-1, and TOPEX/Poseidon require accurate orbital computations to support the scientific data they collect. Until recently, gravity field mismodeling was the major source of error in precise orbit definition. However, albedo and infrared re-radiation, and spacecraft thermal imbalances produce in combination no more than a 6-cm radial root-mean-square (RMS) error over a 10-day period. This requires the development of nonconservative force models that take the satellite's complex geometry, attitude, and surface properties into account. For TOPEX/Poseidon, a 'box-wing' satellite form was investigated that models the satellite as a combination of flat plates arranged in a box shape with a connected solar array. The nonconservative forces acting on each of the eight surfaces are computed independently, yielding vector accelerations which are summed to compute the total aggregate effect on the satellite center-of-mass. In order to test the validity of this concept, 'micro-models' based on finite element analysis of TOPEX/Poseidon were used to generate acceleration histories in a wide variety of orbit orientations. These profiles are then compared to the box-wing model. The results of these simulations and their implication on the ability to precisely model the TOPEX/Poseidon orbit are discussed.

Marshall, J. A.; Luthcke, S. B.; Antreasian, P. G.; Rosborough, G. W.

1992-01-01

347

Path and phase determination for an interfering photon with orbital angular momentum.

A polarized photon with well-defined orbital angular momentum that emerges from a Mach-Zehnder interferometer (MZI) is shown to seemingly circumvent wave-particle duality constraints. For certain phase differences between the MZI arms, this pattern yields both reliable which-path information and high phase sensitivity. PMID:18157260

Kolá, Michal; Opatrný, Tomás; Kurizki, Gershon

2008-01-01

348

The analyzation of satellite orbits using a modified-Gauss determination method

OF FIGURES INERTIAL COORDINATE SYSTEM ELLIPTICAL CROSS SECTION OF EARTH . ALTITUDE VARIATION OF EARIH FOR GEODETIC LATITUDE ORIENTATION OF SATELLITE IN SPACE . ORIENTATION OF THE ORBIT PLANE ERROR IN SEMI~OR AXIS ERROR IN ECCENTRICITY . ERROR... IN INCLINATION ERROR IN PARAMETER P ERROR IN SEMI~OR AXIS . . . . . . . ~ ERROR IN ECCENTRICITY . ERROR IN INCLINATION ERROR IN PARAMFKR P Page 35 43 44 45 48 LIST OF SYMBOLS re radius of earth at equator radius of earth at pole flattening...

Rupley, James Allen

2012-06-07

349

Determination of the Spin-Orbit Interaction for Neutron-Nucleus Scattering

Accurate analyzing power data have been obtained for scattering of 10- and 14-MeV neutrons from 54Fe and 65Cu, with use of a new combination of techniques to produce pulsed, polarized neutron beams. Parametrization with the conventional optical model yields a spin-orbit interaction which is consistent with that observed for proton-nucleus scattering. This combined experimental and theoretical study represents the most

C. E. Floyd; P. P. Guss; K. Murphy; R. C. Byrd; G. Tungate; S. A. Wender; R. L. Walter; T. B. Clegg

1981-01-01

350

Determination of the area and mass distribution of orbital debris fragments

An important factor in modeling the orbital debris environment is the loss rate of debris due to atmospheric drag and luni\\/solar perturbations. An accurate knowledge of the area-to-mass ratio of debris fragments is required for the calculation of the effect of atmospheric drag. In general, this factor is unknown and assumed values are used. However, this ratio can be calculated

Gautam D. Badhwar; Phillip D. Anz-Meador

1989-01-01

351

Determination of the Area and Mass Distribution of Orbital Debris Fragments

An important factor in modeling the orbital debris environment is the loss rate of debris due to atmospheric drag and luni\\/solar perturbations. An accurate knowledge of the area-to-mass ratio of debris fragments is required for the calculation of the effect of atmospheric drag. In general, this factor is unknown and assumed values are used. However, this ratio can be calculated

Gautam D. Badhwar; Phillip D. Anz-Meador

1989-01-01

352

AN ANALYTIC METHOD TO DETERMINE HABITABLE ZONES FOR S-TYPE PLANETARY ORBITS IN BINARY STAR SYSTEMS

With more and more extrasolar planets discovered in and around binary star systems, questions concerning the determination of the classical habitable zone have arisen. Do the radiative and gravitational perturbations of the second star influence the extent of the habitable zone significantly, or is it sufficient to consider the host star only? In this article, we investigate the implications of stellar companions with different spectral types on the insolation a terrestrial planet receives orbiting a Sun-like primary. We present time-independent analytical estimates and compare them to insolation statistics gained via high precision numerical orbit calculations. Results suggest a strong dependence of permanent habitability on the binary's eccentricity, as well as a possible extension of habitable zones toward the secondary in close binary systems.

Eggl, Siegfried; Pilat-Lohinger, Elke; Gyergyovits, Markus; Funk, Barbara [Institute for Astronomy, University of Vienna, Tuerkenschanzstr. 17, A-1180 Vienna (Austria); Georgakarakos, Nikolaos, E-mail: siegfried.eggl@univie.ac.at, E-mail: elke.pilat-lohinger@univie.ac.at [128 V. Olgas str., Thessaloniki 546 45 (Greece)

2012-06-10

353

THE SYNERGY OF DIRECT IMAGING AND ASTROMETRY FOR ORBIT DETERMINATION OF EXO-EARTHS

The holy grail of exoplanet searches is an exo-Earth, an Earth mass planet in the habitable zone (HZ) around a nearby star. Mass is one of the most important characteristics of a planet and can only be measured by observing the motion of the star around the planet-star center of gravity. The planet's orbit can be measured either by imaging the planet at multiple epochs or by measuring the position of the star at multiple epochs by space-based astrometry. The measurement of an exoplanet's orbit by direct imaging is complicated by a number of factors. One is the inner working angle (IWA). A space coronagraph or interferometer imaging an exo-Earth can separate the light from the planet from the light from the star only when the star-planet separation is larger than the IWA. Second, the apparent brightness of a planet depends on the orbital phase. A single image of a planet cannot tell us whether the planet is in the HZ or distinguish whether it is an exo-Earth or a Neptune-mass planet. Third is the confusion that may arise from the presence of multiple planets. With two images of a multiple planet system, it is not possible to assign a dot to a planet based only on the photometry and color of the planet. Finally, the planet-star contrast must exceed a certain minimum value in order for the planet to be detected. The planet may be unobservable even when it is outside the IWA, such as when the bright side of the planet is facing away from us in a 'crescent' phase. In this paper we address the question: 'Can a prior astrometric mission that can identify which stars have Earth-like planets significantly improve the science yield of a mission to image exo-Earths?' In the case of the Occulting Ozone Observatory, a small external occulter mission that cannot measure spectra, we find that the occulter mission could confirm the orbits of {approx}4 to {approx}5 times as many exo-Earths if an astrometric mission preceded it to identify which stars had such planets. In the case of an internal coronagraph we find that a survey of the nearest {approx}60 stars could be done with a telescope half the size if an astrometric mission had first identified the presence of Earth-like planets in the HZ and measured their orbital parameters.

Shao, Michael; Catanzarite, Joseph; Pan Xiaopei, E-mail: michael.shao@jpl.nasa.go, E-mail: joseph.catanzarite@jpl.nasa.go, E-mail: xiaopei.pan@jpl.nasa.go [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr, Pasadena, CA 91109 (United States)

2010-09-01

354

NASA Technical Reports Server (NTRS)

In order to validate the operational and computational capabilities of the Preliminary Orbit Determination System (PODS), tests were performed using tracking measurements for several systems including the ERB satellite, the SMM, the STS and Landsat-4. POD procedures are utilized to generate a state vector following an unplanned orbital perturbation or spacecraft maneuver, when an estimation process such as a differential correction orbit determination cannot obtain a solution. Results are presented to demonstrate POD for several situations involving different qualities of a priori target state vectors, data type combinations, data arc lengths, and mixtures of single-TDRS, dual-TDRS, and GSTDN measurements. The system's ability to determine accurately the state vector for the spacecraft and the effectiveness of the solution screening process are discussed. It is shown that PODS is capable of determining a spacecraft vector when differential correction orbit determination processes fail.

Kirschner, S. M.; Beri, A. C.; Broaddus, S. R.; Doll, C. E.

1990-01-01

355

NASA Technical Reports Server (NTRS)

The destruction rates of a perfluoropolyether (PFPE) lubricant, Krytox 143AC, subjected to rolling contact with 440C steel in a spiral orbit tribometer at room temperature have been evaluated as a function of test environment. The rates in ultrahigh vacuum, 0.213 kPa (1.6 torr) oxygen and one atmosphere of dry nitrogen were about the same. Water vapor in the test environment-a few ppm in one atmosphere of nitrogen-reduced the destruction rate by up to an order of magnitude. A similar effect of water vapor was found for the destruction rate of Pennzane 2001A, an unformulated multiply alkylated cyclopentane (MAC) hydrocarbon oil.

Pepper, Stephen V.

2011-01-01

356

NASA Technical Reports Server (NTRS)

In the spring of 1993, the MOMS-02 (modular Optoelectronic Multispectral Scanner) camera, as part of the second German Spacelab mission aboard STS-55, successfully took digital threefold stereo images of the surface of the Earth. While the mission is experimental in nature, its primary goals are to produce high quality maps and three-dimensional digital terrain models of the Earth's surface. Considerable improvement in the quality of the terrain model can be attained if information about the position and attitude of the camera is included during the adjustment of the image data. One of the primary sources of error in the Shuttle's position is due to the significant attitude maneuvers conducted during the course of the mission. Various arcs, using actual Tracking and Data Relay Satellite (TDRSS) Doppler data of STS-55, were processed to determine how effectively empirical force modeling could be used to solve for the radial, transverse, and normal components of the orbit perturbations caused by these routine maneuvers. Results are presented in terms of overlap-orbit differences in the three components. Comparisons of these differences, before and after the maneuvers are estimated, show that the quality of an orbit can be greatly enhanced with this technique, even if several maneuvers are present. Finally, a discussion is made of some of the difficulties encountered with this approach, and some ideas for future studies are presented.

Vonbraun, C.; Reigber, Christoph

1994-01-01

357

Federal Register 2010, 2011, 2012, 2013

Notice is hereby given that the U.S. International Trade Commission has determined not to review the presiding administrative law judge's (``ALJ'') initial determination (``ID'') (Order No. 9) granting in part complainant's motion for leave to amend the complaint and notice of investigation as to removing respondent Jie Sheng Technology of Tainan City, Taiwan (``Jie Sheng Taiwan'') from the......

2013-05-30

358

Federal Register 2010, 2011, 2012, 2013

...Investigation No. 337-TA-880 Certain Linear Actuators; Commission Determination Not...telephone (202) 205-3041. Copies of non- confidential documents filed in connection...United States after importation of certain linear actuators by reason of infringement...

2013-08-07

359

NASA Technical Reports Server (NTRS)

The TOPEX/Poseidon spacecraft was launched on August 10, 1992 to study the Earth's oceans. To achieve maximum benefit from the altimetric data it is to collect, mission requirements dictate that TOPEX/Poseidon's orbit must be computed at an unprecedented level of accuracy. To reach our pre-launch radial orbit accuracy goals, the mismodeling of the radiative nonconservative forces of solar radiation, Earth albedo an infrared re-radiation, and spacecraft thermal imbalances cannot produce in combination more than a 6 cm rms error over a 10 day period. Similarly, the 10-day drag modeling error cannot exceed 3 cm rms. In order to satisfy these requirements, a 'box-wing' representation of the satellite has been developed in which, the satellite is modelled as the combination of flat plates arranged in the shape of a box and a connected solar array. The radiative/thermal nonconservative forces acting on each of the eight surfaces are computed independently, yielding vector accelerations which are summed to compute the total aggregate effect on the satellite center-of-mass. Select parameters associated with the flat plates are adjusted to obtain a better representation of the satellite acceleration history. This study analyzes the estimation of these parameters from simulated TOPEX/Poseidon laser data in the presence of both nonconservative and gravity model errors. A 'best choice' of estimated parameters is derived and the ability to meet mission requirements with the 'box-wing' model evaluated.

Luthcke, S. B.; Marshall, J. A.

1992-01-01

360

GOCE Gravity Gradients in an Orbital Aspect

NASA Astrophysics Data System (ADS)

This work includes a study of the possibility of the Gravity Field and Steady-State Ocean Circulation Explorer Mission (GOCE) satellite orbit improvement using gravity gradient observations. The orbit improvement is performed by a dedicated software package, called Orbital Computation System (OCS), which is based on the classical least squares method. In an iterative process, the corrections to the initial state vector components of the satellite are estimated, using dynamical models describing gravitational perturbations. An important component implemented in the OCS package is the Cowell 8th order numerical integration procedure, which directly generates the satellite orbit. Taking into account the GOCE real and simulated gravity gradients, different variants of solution of the orbit improvement process were obtained. The improved orbits were compared to the GOCE reference orbits (Precise Science Orbits of the GOCE satellite delivered by the European Space Agency) using the root mean squares (RMS) of the differences between the satellite positions on the improved orbits and on the reference ones. The comparison between the improved orbits and the reference ones was performed with respect to the inertial reference frame (IRF) at J2000.0 epoch. RMS values for the solutions based on the real gravity gradients measurements are at a level of hundreds of kilometers and more. This means that the orbit improvement using the real gravity gradients is ineffective. However, all solutions using the simulated gravity gradients, have RMS values below the threshold determined by RMS values for the computed orbits (without the improvement). The most promising results have been achieved here in the case of improving of short orbital arcs with the lengths from a few to tens of minutes. For these short arcs, RMS values reach the level of centimeters, which is close to the accuracy of Precise Science Orbit of GOCE satellite. Additional research have provided requirements for the effective orbit improvement in terms of the accuracy and spectral content of measured gravity gradients.

Bobojc, Andrzej; Drozyner, Andrzej

2014-05-01

361

Patient: Male, 17 Final Diagnosis: Burkitt lymphoma Symptoms: Anisocoria, ipsilateral ptosis, opthalmoparesis, paresis Medication: — Clinical Procedure: — Specialty: Oncology Objective: Unusual clinical course Background: Burkitt lymphoma rarely affects the central nervous system and ocular region. Under these conditions, computed tomography and (particularly) magnetic resonance imaging of the skull increase the diagnostic accuracy, as they objectively show the topography of lesions and the effect of neoplasia on structures. Case Report: We report here the case of a 17-year-old male whose initial clinical manifestations were related to neurological impairment and to the ocular musculature and ocular innervation. The diagnosis of Burkitt lymphoma with leukemization and infiltration of the central nervous system was confirmed. Conclusions: In this case, it is important to recognize that the neuroimaging findings were fundamentally important in indicating the initial form of the disease and in directing the appropriate clinical management. PMID:25243420

Camilo, Gustavo Bittencourt; Machado, Dequitier Carvalho; de Oliveira, Celso Estevao; Lacerda, Leticia da Silva; de Oliveira, Romulo Varella; de Franca Silva, Monique; Lopes, Agnaldo Jose

2014-01-01

362

Orbit Design of Earth-Observation Satellite

NASA Astrophysics Data System (ADS)

The purpose of this study is to design a reliable orbit for a medium-resolution scientific satellite to observe Earth for developmental issues such as water resources, agricultural, and industrial. To meet this objective this study firstly, defines the mission, secondly, determines mission constraints, thirdly, design the attitude and orbit control system. As for the observation requirements, and the revisit time are provided as a function of the orbital parameters. Initial orbital parameters are obtained by optimal analysis between observation characteristics and attitude and orbit maintenance costs. Long term station-keeping strategies will be provided for the proposed solutions. Impulsive control will be investigated to provide a reliable and affordable attitude and orbit control system.

Owis, Ashraf

363

Conversion of Osculating Orbital Elements to Mean Orbital Elements

NASA Technical Reports Server (NTRS)

Orbit determination and ephemeris generation or prediction over relatively long elapsed times can be accomplished with mean elements. The most simple and efficient method for orbit determination, which is also known as epoch point conversion, performs the conversion of osculating elements to mean elements by iterative procedures. Previous epoch point conversion methods are restricted to shorter elapsed times with linear convergence. The new method presented in this paper calculates an analytic initial guess of the unknown mean elements from a first order theory of secular perturbations and computes a transition matrix with accurate numerical partials. It thereby eliminates the problem of an inaccurate initial guess and an identity transition matrix employed by previous methods. With a good initial guess of the unknown mean elements and an accurate transition matrix, converging osculating elements to mean elements can be accomplished over long elapsed times with quadratic convergence.

Der, Gim J.; Danchick, Roy

1996-01-01

364

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

365

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

Code of Federal Regulations, 2010 CFR

...false How do I determine the initial balances of liquidation sub-accounts? 563b...460 How do I determine the initial balances of liquidation sub-accounts? ...You determine the initial sub-account balance for a savings account held by an...

2010-01-01

366

Appropriate distribution of time and energy between work and personal life poses a challenge to many working people. Unfortunately, many professionally active people experience work-family conflict. In order to minimize it, employees are offered various solutions aimed at reconciling professional and private spheres (work-life balance (WLB) initiatives). The authors attempt to answer what makes employees use WLB initiatives and what influences the decision to reject the available options. The review is based on the articles published after 2000, searched by Google Scholar and Web of Knowledge with use of the key words: work-life balance, work-family conflict, work-life balance initiatives, work-life balance initiatives use, use of WLB solutions. We focused on organizational and individual determinants of WLB initiatives use, such as organizational culture, stereotypes and values prevailing in the work environment that may result in stigmatization of workers - flexibility stigma. We discuss the reasons why supervisors and co-workers stigmatize their colleagues, and what are the consequences of experiencing such stigmatization. Among the individual determinants of WLB initiatives use, we have inter alia focused on the preference for integration vs. separation of the spheres of life. The presented material shows that social factors - cultural norms prevailing in a society, relationships in the workplace and individual factors, such as the level of self-control - are of equal importance for decisions of using WLB initiatives as their existence. Our conclusion is that little attention has been paid to the research on determinants of WLB initiatives use, especially to individual ones. PMID:24834699

Andysz, Aleksandra; Najder, Anna; Merecz-Kot, Dorota

2014-01-01

367

Determination of Spin-Orbit Coefficients and Phase Coherence Times in InGaAs/InAlAs Quantum Wells

NASA Astrophysics Data System (ADS)

We report the determination of the intrinsic spin-orbit interaction (SOI) parameters and phase coherence times for In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As quantum wells (QWs) from the analysis of the weak antilocalization (WAL) measurements at dilution temperatures. We find that the Dresselhaus SOI is mostly negligible in this system and that the intrinsic parameters for the Rashba effect, aSO??/

Koga, Takaaki; Faniel, Sebastien; Matsuura, Toru; Mineshige, Shunsuke; Sekine, Yoshiaki; Sugiyama, H.

2011-12-01

368

Orbit Determination of Close Binary Systems using Lucky F. M. Rica1,2*

and multiple stars are prime targets for determining and calibrating basic stellar physics in general. The main importance in its study resides in stellar mass determination and in the mass-luminosity calibration recognized as a basic key to the understanding of stellar structure, formation and evolution. Binary

369

Aerobraking for capture into Martian orbit

A summary is given of several studies into problems associated with aerobraking a manned vehicle into a Martian capture orbit. The problems investigated are the establishment of entry flight path angle windows that allow aerocapture; the determination of the sensitivity of the entry trajectory to initial flight path angle; the determination of the effect on aerocapture of the assumed Martian

William T. Suit; Mary C. Lee; Paul V. Tartbini; Barbara S. Tomlinson

1990-01-01

370

The fertilizing value of livestock waste is hardly determined considering its initial variability-products in Thai Binh The various observed states Livestock farmers' practices with regard to effluents management to transport. Manure is often used in this form by fish farmers, but it can also be treated. When

Paris-Sud XI, UniversitÃ© de

371

The effect of stellar brightness and temperature calibration on calculation of the initial mass function was studied. Data luminosity and effective temperature for each star were calculated. Only B star associations were investigated. The geometric similarity of the theoretical evolutionary track of stars of different masses facilitated the of determination star mass and age. It is found that the different

V. I. Myakutin

1983-01-01

372

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:ï¿½ Describe the conditions that would lead an object into orbital motion in terms of the effects of gravitational force.ï¿½ Explain how an object orbits a planet in terms of trajectories and free fall.ï¿½ 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

373

Long range orbital error estimation for applications satellites

NASA Technical Reports Server (NTRS)

A method of optimum orbital averaging was employed to study the long range accuracy potential of polar orbiting applications satellites. This approach involved the determination of the boundary conditions of one set of differential equations of motion by adjusting the initial conditions in a least square sense with the use of data generated by another set of differential equations of motion.

Bonavito, N. L.; Foreman, J. C.

1978-01-01

374

The Kaguya spacecraft were launched from Tanegashima Space Center on September 14, 2007. Kaguya consists of three orbiters: a main orbiter in a low-altitude (100 km) circular polar orbit, and two sub-satellites (Rstar and Vstar) in elliptical orbits. The satellites were tracked by a variety of terrestrial based tracking systems: in addition to standard two-way Doppler and range tracking, there

S. J. Goossens; K. Matsumoto; F. Kikuchi; Q. Liu; H. Hanada; F. G. Lemoine; D. D. Rowlands; Y. Ishihara; Y. Jianguo; H. Araki; H. Noda; N. Namiki; T. Iwata

2010-01-01

375

minor planets are located inside the orbit of Mercury? Venus? Earth? Mars? Answer: Students should count planets inside the orbit of Venus. Between Earth and Venus there are about 280 for a total of 412 minor planets inside Earth's orbit. Between Mars and Earth, a careful student may be able to count about 833

376

A study to explore the use of orbital remote sensing to determine native arid plant distribution

NASA Technical Reports Server (NTRS)

The author has identified the following significant results. A theory has been developed of a method for determining the reflectivities of natural areas from ERTS-1 data. This method requires the following measurements: (1) ground truth reflectivity data from two different calibration areas; (2) radiance data from ERTS-1 MSS imagery for the same two calibration areas; and (3) radiance data from ERTS-1 MSS imagery for the area(s) in which reflectivity is to be determined. The method takes into account sun angle effects and atmospheric effects on the radiance seen by the space sensor. If certain assumptions are made, the ground truth data collection need not be simultaneous with the ERTS-1 overflight. The method allows the calculation of a conversion factor for converting ERTS-1 MSS radiance measurements of a given overflight to reflectivity values. This conversion factor can be used to determine the reflectivity of any area in the general vicinity of the calibration areas which has a relatively similar overlying atmosphere. This method, or some modification of it, may be useful in ERTS investigations which require the determination of spectral signatures of areas from spacecraft data.

Mcginnies, W. G. (principal investigator); Haase, E. F.; Musick, H. B. (compiler)

1973-01-01

377

NASA Technical Reports Server (NTRS)

Measurements of Mars-orbit perturbations have been conducted in order to estimate the masses of the Ceres, Pallas, and Vesta asteroids. A full, least-squares adjustment of all ephemeris parameters, including the relevant asteroid masses, is compiled on the basis of observational data encompassing the highly accurate Viking Lander ranging data. The mass for Ceres, of 5.0 + or - 0.2 x 10 to the -10th solar masses, that for Pallas, of 1.4 + or - 0.2 x 10 to the -10th solar masses, and that for Vesta, of 1.5 + or - 0.3 x 10 to the -10th solar masses, respectively represent 15, 30, and 9 percent increases over Schubart's (1970, 1974, 1975) previous determinations.

Standish, E. Myles, Jr.; Hellings, Ronald W.

1989-01-01

378

Using Data to Determine the Initial Conditions in Heavy Ion Collisions

NASA Astrophysics Data System (ADS)

We have developed a framework, the Comprehensive Heavy Ion Model Evaluation Reporting Algorithm (CHIMERA) to determine the optimal model and initial conditions of heavy ion collisions by comparing to data from a variety of observables. We have used this framework to study simple participant and binary collisions scaling in the presence of pre-equilibrium flow in the context of the VH2 2D+1 viscous hydrodynamic model with UrQMD afterburner for data from RHIC. We have also used this framework to explore the significance of variations in the equation of state. We have recently begun to apply this framework to a new hydro-solver tools known as CHOMBO, which incorporates adaptive mesh refinement techniques that are well suited to the study of initial state fluctuations. We will review results from using CHIMERA with VH2, and discuss future plans for using CHOMBO to study initial state fluctuations.

Soltz, Ron; Garishvili, Irakli; Abelev, Betty

2012-10-01

379

Preliminary orbital parallax catalog

NASA Technical Reports Server (NTRS)

The study is undertaken to calibrate the more reliable parallaxes derived from a comparison of visual and spectroscopic orbits and to encourage observational studies of other promising binaries. The methodological techniques used in computing orbital parallaxes are analyzed. Tables summarizing orbital data and derived system properties are then given. Also given is a series of detailed discussions of the 71 individual systems included in the tables. Data are listed for 57 other systems which are considered promising candidates for eventual orbital parallax determination.

Halliwell, M.

1981-01-01

380

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

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

381

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

382

Code of Federal Regulations, 2010 CFR

...initial denial determination and changes as a result of a DRG validation. 476.94 Section...initial denial determination and changes as a result of a DRG validation. (a) Notice of...determination. (b) Notice of changes as a result of a DRG validation. The QIO...

2010-10-01

383

In 1994, a collaborative programme was set up between the University of Surrey and the Chilean Air Force to design and build a low-cost 50 kg microsatellite with instrumentation capable of monitoring the distribution and concentration of stratospheric ozone, particularly over Chilean territory. This resulted in the joint design and development of the ozone-layer monitoring experiment (OLME), which was flown on board the resultant FASat-Bravo microsatellite, launched in July 1998 into an 820 km altitude Sun-synchronous orbit. The nadir-pointing OLME measures the solar ultraviolet light backscattered from the atmosphere in four spectral bands. From these raw radiometric data, total column ozone concentrations can be deduced. Since the launch, a series of high-spatial-resolution measurements have been made over Chilean scientific stations, while continuous low-spatial-resolution measurements have been used to provide global coverage. To date, the University of Surrey has concentrated on these global measurements, and has used a simplified ozone retrieval algorithm to check the results qualitatively against ozone maps produced by NASA's Earth Probe Total Ozone Mapping Spectrometer (TOMS) payload. These initial results look promising, with apparently good correlation between the two datasets. A novel, more-complex retrieval algorithm has been applied to the high-resolution data, and early results have shown agreement with the TOMS. PMID:12626242

Underwood, Craig I; Valenzuela, Alvaro; Schoenherr, Marcelo; Arancibia, Mario; Fouquet, Marc

2003-01-15

384

GRACE Orbit Deterimation for Gravity Field Recovery at CSR

NASA Astrophysics Data System (ADS)

Determining the orbits of the GRACE satellites is an important aspect of the operational data processing for gravity field recovery. Precise orbits are required for data quality assessment and verification and finally as reference for the gravity field estimation step. Several stages are needed as part of the preparation for the gravity field solution. Using GPS tracking data, initial orbits are computed to produce model accelerometer and attitude data, edited tracking data and improved initial conditions. The model data are used to assess the performance of the accelerometer and star tracker as well as the quality of the measurements from these instruments. The tracking data are further edited to remove anomalous data. A final converged orbit is determined using the on-board accelerometer and attitude data along with the edited tracking data. Results of initial and final orbit fits for a period of data from April and May 2002 will be presented. Orbit quality metrics including GPS data residuals and SLR residuals will be presented. Improvement of the orbit fits due to an improved gravity field will be demonstrated. Using an initial GRACE derived gravity solution, an orbit accuracy at the few cm level is achieved.

Nagel, P. B.; Kang, Z.; Cheng, M.; Pastor, R.

2002-12-01

385

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

386

Variability in neonatal vancomycin pharmacokinetics and the lack of consensus for optimal trough concentrations in neonatal intensive care units pose challenges to dosing vancomycin in neonates. Our objective was to determine vancomycin pharmacokinetics in neonates and evaluate dosing regimens to identify whether practical initial recommendations that targeted trough concentrations most commonly used in neonatal intensive care units could be determined. Fifty neonates who received vancomycin with at least one set of steady-state levels were evaluated retrospectively. Mean pharmacokinetic values were determined using first-order pharmacokinetic equations, and Monte Carlo simulation was used to evaluate initial dosing recommendations for target trough concentrations of 15 to 20 mg/liter, 5 to 20 mg/liter, and ?20 mg/liter. Monte Carlo simulation revealed that dosing by mg/kg of body weight was optimal where intermittent dosing of 9 to 12 mg/kg intravenously (i.v.) every 8 h (q8h) had the highest probability of attaining a target trough concentration of 15 to 20 mg/liter. However, continuous infusion with a loading dose of 10 mg/kg followed by 25 to 30 mg/kg per day infused over 24 h had the best overall probability of target attainment. Initial intermittent dosing of 9 to 15 mg/kg i.v. q12h was optimal for target trough concentrations of 5 to 20 mg/liter and ?20 mg/liter. In conclusion, we determined that the practical initial vancomycin dose of 10 mg/kg vancomycin i.v. q12h was optimal for vancomycin trough concentrations of either 5 to 20 mg/liter or ?20 mg/liter and that the same initial dose q8h was optimal for target trough concentrations of 15 to 20 mg/liter. However, due to large interpatient vancomycin pharmacokinetic variability in neonates, monitoring of serum concentrations is recommended when trough concentrations between 15 and 20 mg/liter or 5 and 20 mg/liter are desired. PMID:24614381

Kim, Julianne; Iaboni, Dolores C.; Walker, Scott E.; Elligsen, Marion; Dunn, Michael S.; Allen, Vanessa G.; Simor, Andrew

2014-01-01

387

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

388

NASA Technical Reports Server (NTRS)

Wind tunnel pressure measurements were acquired from orifices on a 0.1 scale forebody model of the space shuttle orbiter that were arranged in a preliminary configuration of the shuttle entry air data system (SEADS). Pressures from those and auxiliary orifices were evaluated for their ability to provide air data at subsonic and transonic speeds. The orifices were on the vehicle's nose cap and on the sides of the forebody forward of the cabin. The investigation covered a Mach number range of 0.25 to 1.40 and an angle of attack range from 4 deg. to 18 deg. An air data system consisting of nose cap and forebody fuselage orifices constitutes a complete and accurate air data system at subsonic and transonic speeds. For Mach numbers less than 0.80 orifices confined to the nose cap can be used as a complete and accurate air data system. Air data systems that use only flush pressure orifices can be used to determine basic air data on other aircraft at subsonic and transonic speeds.

Larson, T. J.; Siemers, P. M., III

1980-01-01

389

Code of Federal Regulations, 2010 CFR

...2010-07-01 2010-07-01 false Initiation of proceedings to hear and determine jurisdictional disputes under section 10(k...k) of the Act § 101.31 Initiation of proceedings to hear and determine jurisdictional disputes under section...

2010-07-01

390

Determinants of Early Initiation, Exclusiveness, and Duration of Breastfeeding in Uganda

ABSTRACT Breastfeeding practices in Uganda are contrary to the best practice recommended by World Health Organization (WHO). Only six in 10 Ugandan children below the age of six months are exclusively breastfed. This paper investigated the determinants of breastfeeding practices in Uganda. Using the Uganda Demographic and Health Survey (UDHS) of 2006, we employed probit and Cox's regression techniques as well as the Kaplan-Meier survival functions during the analysis. On average, 56% and 46% initiated breastfeeding in the first hour and practised exclusive breastfeeding respectively while 25%, 50%, and 75% terminated breastfeeding at 18, 24, and 26 months respectively. The mean number of months of breastfeeding was 14.1, and the maximum was 40. Hospital delivery increased the probability of early initiation and exclusive breastfeeding by 4-5% (p<0.01) and 7-8% (p<0.01) respectively. Prenatal care increased the probability of early initiation and exclusive breastfeeding by 6-7% (p<0.05) and 5-7% (p<0.05) respectively. Birth intervals less than 24 months increased the risk of early termination of breastfeeding by 19% (p<0.01). Hospital delivery and prenatal care should be made a priority, and mothers should be encouraged to adopt higher birth intervals. PMID:25076662

2014-01-01

391

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

392

The Hubble Space Telescope has demonstrated that on-orbit servicing can provide significant benefits for scientific space programs. Specifically, servicing missions can replace failed components to keep spacecraft operational, ...

Baldesarra, Mark

2007-01-01

393

First-principles determination of charge and orbital interactions in Fe[subscript 3]O[subscript]4

The interactions between charge and orbitally ordered d electrons are important in many transition-metal oxides. We propose an effective energy model for such interactions, parameterized with density-functional theory ...

Zhou, Fei

394

Background: Tobacco smoking is the leading cause of preventable mortality. The prevalence of smoking in adolescents in high schools ranges from 23.5% to 41%, respectively. In Colombia, these figures are similar and students entering the University are exposed to initiate smoking. The purpose of this study was to establish the determinants associated with the initiation of tobacco smoking among university students. Methods: A case–control paired by sex and age study design was used. The study population was the students of a private university of Bucaramanga, Santander, Colombia. The final sample consisted of 167 cases and 314 controls randomly select undergraduate university students. Data analysis was performed using a Logistic regression model adjusted by gender and age; using the initiation of tobacco smoking as the dependent variable, and as independent variables relationship with parents, history of parental smoking, university social environment, being away from hometown, steady girlfriend/boyfriend who smokes, alcohol consumption, physical activity, and Francis Score. Results: The social environment (odds ratio [OR]: 32.70, 7.40-144.55), being away from hometown (OR: 3.06, 1.55-6.07), history of steady girlfriend/boyfriend who smoke (OR: 2.87, 1.43-5.76), a bad relationship with the father (OR: 8.01, 2.01-31.83), history of tobacco consumption of the mother (OR: 2.66, 1.37-5.17) and alcohol consumption (OR: 4.79, 1.91-12.00) appeared as determinants of initiation of tobacco smoking. As protector factors we found media advertisement (OR: 0.19, 0.05-0.71), light physical activity 2-3 times a week (OR: 0.33, 0.12-0.88), and a high result in Francis score (OR: 0.95, 0.919-0.99). Conclusions: University efforts for tobacco-free policies should focus on preventive advertisement, promoting physical activity and awareness among young students of social environmental factors that could influence their decision to start smoking tobacco. PMID:25317292

Afanador, Laura del Pilar Cadena; Radi, Daniel Sebastián Salazar; Pinto, Luis Enrique Vásquez; Pinzón, Cristian Eduardo Pérez; Carreño, Manuel Felipe Castro

2014-01-01

395

Background In Mozambique, tuberculosis (TB) is thought to be the most common cause of death among antiretroviral therapy (ART) enrollees. Monitoring proportions of enrollees screened for TB, and incidence and determinants of TB during ART can help clinicians and program managers identify program improvement opportunities. Methodology/Principal Findings We conducted a retrospective cohort study among a nationally representative sample of the 79,500 adults (>14 years old) initiating ART during 2004–2007 to estimate clinician compliance with TB screening guidelines, factors associated with active TB at ART initiation, and incidence and predictors of documented TB during ART follow-up. Of 94 sites enrolling >50 adults on ART, 30 were selected using probability-proportional-to-size sampling; 2,596 medical records at these sites were randomly selected for abstraction and analysis. At ART initiation, median age of patients was 34, 62% were female, median baseline CD4+ T-cell count was 153/µL, and 11% were taking TB treatment. Proportions of records with TB screening documentation before ART initiation improved from 31% to 66% during 2004–2007 (p<0.001). TB screening compliance varied widely by ART clinic [n?=?30, 2%–98% (p<0.001)] and supporting non-Governmental Organization (NGO) [n?=?7, 27%–83% (p<0.001)]. Receiving TB treatment at ART enrollment was associated with male sex (p<0.001), weight <45 kg (p<0.001) and CD4<50/µL (p?=?0.001). Isoniazid preventive therapy (IPT) was prescribed to <1% of ART enrollees not taking TB treatment. TB incidence during ART was 2.32 cases per 100 person-years. Factors associated with TB incidence included adherence to ART <95% (AHR 2.06; 95% CI, 1.32–3.21). Conclusion Variations in TB screening by clinic and NGO may reflect differing investments in TB screening activities. Future scale-up should target under-performing clinics. Scale-up of TB screening at ART initiation, IPT, and ART adherence interventions could significantly reduce incident TB during ART. PMID:23349948

Auld, Andrew F.; Mbofana, Francisco; Shiraishi, Ray W.; Alfredo, Charity; Sanchez, Mauro; Ellerbrock, Tedd V.; Nelson, Lisa J.

2013-01-01

396

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

397

NASA Astrophysics Data System (ADS)

Reservoir releases on large regulated rivers are increasingly being used to rejuvenate riverine habitat downstream of dams. Determining the effective flow level is complicated by the trade-off between mobilizing bed particles and retaining coarse sediment in rivers with low sediment supply. This study determined mobilization and transport distance of bed particles using motion-sensing radio transmitting particles that approximated the reach-average D84 grain size. The distribution of shear stress at initial motion varied substantially between flood events, and suggests that the sequence of flood events and the history of underthreshold flows may be an important determinant of bed strength and thus particle mobility. In addition, particle activity was greatest on the rising limb of each flood and was maximized at near bank-full flow. Travel distances did not vary between floods when scaled by transport event duration, and a negative exponential distribution was a good fit to the data. Results of this study provide important insight into individual particle movement, which can be used to inform flow releases and understand the effects of flood magnitude on particle mobility and transport.

May, C. L.; Smith Pryor, B.; Lisle, T. E.

2012-12-01

398

Code of Federal Regulations, 2010 CFR

...denial determinations and changes as a result of DRG validations. 476.85 Section...denial 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...

2010-10-01

399

Multidisciplinary Management of Orbital Rhabdomyosarcoma

\\u000a Rhabdomyosarcoma (RMS) is the most common orbital malignancy in childhood. Embryonal RMS and alveolar RMS are the two most\\u000a common histologic subtypes of RMS, and embryonal RMS is the most common subtype of orbital RMS. The clinical presentation\\u000a of orbital RMS depends on the tumor location in the orbit. Diagnosis is chiefly made through open biopsy, and complete initial\\u000a tumor

Winston W. Huh; Anita Mahajan

400

Phase identity of the maize leaf is determined after leaf initiation

The vegetative development of the maize shoot can be divided into juvenile and adult phases based on the types of leaves produced at different times in shoot development. Models for the regulation of phase change make explicit predictions about when the identity of these types of leaves is determined. To test these models, we examined the timing of leaf type determination in maize. Clones induced in transition leaf primordia demonstrated that the juvenile and adult regions of these leaves do not become clonally distinct until after the primordium is 700 ?m in length, implying that these cell fates were undetermined at this stage of leaf development. Adult shoot apices were cultured in vitro to induce rejuvenation. We found that leaf primordia as large as 3 mm in length can be at least partially rejuvenated by this treatment, and the location of rejuvenated tissue is correlated with the maturation pattern of the leaf. The amount and distribution of juvenile tissue in rejuvenated leaves suggests that rejuvenation occurs nearly simultaneously in all leaf primordia. In vitro culture rejuvenated existing leaf primordia and the P0 primordium, but did not change the identity of subsequent primordia or the total number of leaves produced by the shoot. This result suggests that leaf identity can be regulated independently of the identity of the shoot apical meristem, and it implies that vegetative phase change is not initiated by a change in the identity of the shoot apical meristem. PMID:10973480

Orkwiszewski, Joseph A. J.; Poethig, R. Scott

2000-01-01