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  • 1
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    Precision orbit determination software validation experiment (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: This paper presents the results of an experiment which was designed to ascertain the level of agreement between GEODYN and UTOPIA, two completely independent computer programs used for precision orbit determination, and to identify the sources which limit the agreement. For a limited set of models and a seven-day data set arc length, the altitude components of the ephemeris obtained by the two programs agree at the sub-centimeter level throughout the arc.
    Keywords: ASTRODYNAMICS
    Type: Journal of the Astronautical Sciences; 28; Oct
    Format: text
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  • 2
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    Advanced simulation and analysis of a geopotential research mission (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Computer simulations have been performed for an orbital gradiometer mission to assist in the study of high degree and order gravity field recovery. The simulations were conducted for a satellite in near-circular, frozen orbit at a 160-km altitude using a gravitational field complete to degree and order 360. The mission duration is taken to be 32 days. The simulation provides a set of measurements to assist in the evaluation of techniques developed for the determination of the gravity field. Also, the simulation provides an ephemeris to study available tracking systems to satisfy the orbit determination requirements of the mission.
    Keywords: ASTRODYNAMICS
    Type: NASA-CR-182355 , NAS 1.26:182355
    Format: application/pdf
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  • 3
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    Orbit accuracy assessment for Seasat (1980)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Laser range measurements are used to determine the orbit of Seasat during the period from July 28, 1978, to Aug. 14, 1978, and the influence of the gravity field, atmospheric drag, and solar radiation pressure on the orbit accuracy is investigated. It is noted that for the orbits of three-day duration, little distinction can be made between the influence of different atmospheric models. It is found that the special Seasat gravity field PGS-S3 is most consistent with the data for three-day orbits, but an unmodeled systematic effect in radiation pressure is noted. For orbits of 18-day duration, little distinction can be made between the results derived from the PGS gravity fields. It is also found that the geomagnetic field is an influential factor in the atmospheric modeling during this time period. Seasat altimeter measurements are used to determine the accuracy of the altimeter measurement time tag and to evaluate the orbital accuracy.
    Keywords: ASTRODYNAMICS
    Type: Journal of the Astronautical Sciences; 28; Oct
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  • 4
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    A comparison of filtering algorithms for GPS satellite navigation application (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A comparison of three square root filter formulations with the standard extended Kalman filter is described. The characteristics of the algorithms were compared by simulating the application of a phase one GPS system to the determination of a LANDSAT-D Satellite.
    Keywords: ASTRODYNAMICS
    Type: NASA. Goddard Space Flight Center Flight Mech.(Estimation Theory Symp.; p 253-2279
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  • 5
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    Geophysical parameters from the analysis of laser ranging to starlette (1987)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Starlette Satellite Laser Ranging (SLR) data were used, along with several other satellite data sets, for the solution of a preliminary gravity field model for TOPEX, PTGF1. A further improvement in the earth gravity model was accomplished using data collected by 12 satellites to solve another preliminary gravity model for TOPEX, designated PTGF2. The solution for the Earth Rotation Parameter (ERP) was derived from the analysis of SLR data to Starlette during the MERIT Campaign. Starlette orbits in 1976 and 1983 were analyzed for the mapping of the tidal response of the earth. Publications and conference presentations pertinent to research are listed.
    Keywords: ASTRODYNAMICS
    Type: NASA-CR-180596 , NAS 1.26:180596
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  • 6
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    Accuracy assessment of GPS satellite orbits (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: GPS orbit accuracy is examined using several evaluation procedures. The existence is shown of unmodeled effects which correlate with the eclipsing of the sun. The ability to obtain geodetic results that show an accuracy of 1-2 parts in 10 to the 8th or better has not diminished.
    Keywords: ASTRODYNAMICS
    Type: of the COSPAR 28th Plenary Meeting, The Hague, Netherlands, June 25-July 6, 1990. A91-47626 20-12) Advances in Space Research (ISSN 0273-1177); 189-192
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  • 7
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    Application of Encke's method to long arc orbit determination solutions (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Keywords: ASTRODYNAMICS
    Type: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 14; 683-686
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  • 8
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    Precision orbit determination for Topex (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The ability of radar altimeters to measure the distance from a satellite to the ocean surface with a precision of the order of 2 cm imposes unique requirements for the orbit determination accuracy. The orbit accuracy requirements will be especially demanding for the joint NASA/CNES Ocean Topography Experiment (Topex/Poseidon). For this mission, a radial orbit accuracy of 13 centimeters will be required for a mission period of three to five years. This is an order of magnitude improvement in the accuracy achieved during any previous satellite mission. This investigation considers the factors which limit the orbit accuracy for the Topex mission. Particular error sources which are considered include the geopotential, the radiation pressure and the atmospheric drag model.
    Keywords: ASTRODYNAMICS
    Type: Advances in Space Research (ISSN 0273-1177); 10; 4-Mar
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  • 9
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    Precision orbit determination for the Geosat Exact Repeat Mission (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Precise ephemerides have been determined for the U.S. Navy Geosat Exact Repeat Mission (ERM) using an improved gravity-field model, PTGF-4A (Shum et al. 1989). The Geosat orbits were computed in a terrestrial reference system which is tied to the reference system defined by satellite laser ranging (SLR) to Lageos through a survey between the Tranet Doppler receiver and the SLR system located at Wettzell, FRG. The remaining Doppler tracking station coordinates were estimated simultaneously with the geopotential in the PTGF-4A solution. In this analysis, three continuous 17-day Geosat orbits, which were computed using the 46-station Tranet data and global altimeter crossover data, have a crossover residual rms of 20 cm, indicating that the Geosat radial orbit error is of the order of 20 cm. The orbits computed based on data collected by a 7-station OPNET tracking network and crossover data have the same level of accuracy.
    Keywords: ASTRODYNAMICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 2887-289
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  • 10
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    Altimeter crossover methods for precision orbit determination and the mapping of geophysical parameters (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Accurate orbit determination and the recovery of geophysical parameters are presently attempted via methodologies which use differenced height measurements at the points where the ground tracks of the altimetric satellite orbits intersect. Such 'crossover measurements' could significantly improve the earth's gravity field model. Attention is given to a novel technique employing crossover measurements from two satellites carrying altimeter instruments; this method can observe zonal harmonics of the earth's geopotential which are weakly observed through single-satellite crossovers. This dual-satellite crossover technique will be applicable to data from such future oceanographic satellites as ERS-1.
    Keywords: ASTRODYNAMICS
    Type: Journal of the Astronautical Sciences (ISSN 0021-9142); 38; 355-368
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