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  • SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING  (3)
  • ASTRODYNAMICS  (2)
  • 1980-1984  (5)
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  • 1
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    Relative performance of algorithms for autonomous satellite orbit determination (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Limited word size in contemporary microprocessors causes numerical problems in autonomous satellite navigation applications. Numerical error introduced in navigation computations performed on small wordlength machines can cause divergence of sequential estimation algorithms. To insure filter reliability, square root algorithms have been adopted in many applications. The optimal navigation algorithm requires a careful match of the estimation algorithm, dynamic model, and numerical integrator. In this investigation, the relationship of several square root filters and numerical integration methods is evaluated to determine their relative performance for satellite navigation applications. The numerical simulations are conducted using the Phase I GPS constellation to determine the orbit of a LANDSAT-D type satellite. The primary comparison is based on computation time and relative estimation accuracy.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: Journal of the Astronautical Sciences; 29; Jan
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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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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    NASA TECHNICAL REPORTS
  • 3
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    Autonomous satellite navigation methods using the Global Positioning Satellite System (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: This investigation considers the problem of autonomous satellite navigation using the NAVSTAR Global Positioning System (GPS). The major topics covered include the design, implementation, and validation of onboard navigation filter algorithms by means of computer simulations. The primary errors that the navigation filter design must minimize are computational effects and modeling inaccuracies due to limited capability of the onboard computer. The minimization of the effect of these errors is attained by applying the sequential extended Kalman filter using a factored covariance implementation with Q-matrix or dynamical model compensations. Peformance evaluation of the navigation filter design is carried out using both the CDC Cyber 170/750 computer and the PDP-11/60 computer. The results are obtained assuming the Phase I GPS constellation, consisting of six satellites, and a Landsat-D type spacecraft as the model for the user satellite orbit.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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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
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Orbit determination requirements for TOPEX (1981)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The error sensitivity of orbit calculations in support of the NASA Ocean Surface Topography Mapping Experiment (TOPEX), which require an accuracy on the order of 5 cm, is investigated. The contributions of errors in the gravitational, atmospheric drag and solar radiation pressure models to the computed orbit are analyzed for the cases of an ideal data distribution and realistic laser ranging data coverage. It is found that the major contributor to radial orbital error is the error in the geopotential model, accounting for orbital errors of 30 to 70 cm, with the effects of solar radiation pressure, drag modeling, tracking station coordinate errors making lesser contributions. It is concluded that TOPEX accuracy goals cannot be met using ground-based laser ranging data without improving the geopotential model.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AAS PAPER 81-158 , Astrodynamics Specialist Conference; Aug 03, 1981 - Aug 05, 1981; Lake Tahoe, NV; US
    Format: text
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    NASA TECHNICAL REPORTS
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