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  • ASTRODYNAMICS  (10)
  • EARTH RESOURCES AND REMOTE SENSING  (3)
  • SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING  (3)
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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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  • 2
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    Precision orbit determination software validation experiment (1980)
    In:  Other Sources
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    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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  • 3
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    Evaluation of the Seasat altimeter time tag bias (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Two methods were used in analyses of Seasat altimeter data, aimed at the corroboration of an inherent altimeter microprocessor delay compensation value of -79.4 msec, which benefited from a global data distribution in the oceanic areas: (1) the crossover method, using altimeter data differenced at points where the Seasat ground track intersected with itself, and (2) the direct use of the altimeter data. Because the former method is independent of errors in the geoid model, it is considered the more reliable. For all crossover method results, the adopted value of -79.4 msec is within the bounds of the standard deviation associated with the estimates, of which -78.1 + or - 2.0 msec is considered the best representative.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Journal of Geophysical Research; 87; Apr. 30
    Format: text
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  • 4
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    Autonomous satellite navigation methods using the Global Positioning Satellite System (1982)
    In:  Other Sources
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    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
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  • 5
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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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  • 6
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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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  • 7
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    Sequential filtering applied to the determination of tracking station locations (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The extended sequential filter has been applied to the problem of dynamically determining the geocentric coordinates of two laser satellite tracking stations. This filter provides significant advantages over the classical batch methods through (1) fewer iterations required for convergence, (2) wider radius of convergence, and (3) availability of the parameter estimate evolution. Processing the data sequentially readily identifies the data arcs required to minimize the effects of geopotential model errors. By means of the Smithsonian standard earth 2 and the Goddard earth model 1 geopotentials to reduce laser range observations of the Beacon Explorer-C satellite, it is demonstrated that a two-pass arc is optimal for estimating the height of one station and all coordinates of the second station while minimizing the effect of geopotential model error. These two-pass estimates are in good agreement with other determinations that utilize considerably more data as well as different satellites.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Journal of Geophysical Research; 80; Feb. 10
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  • 8
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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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  • 9
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    Sensitivity analysis of short-arc station coordinate determinations from range data (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The accurate determination of the geocentric coordinates of a tracking station is essential for most geodetic and geophysical satellite applications. Since most of these satellites are close to the earth, the geopotential model is a dominant source of error which significantly influences station coordinate determinations. Other sources, such as GM error and drag, also influence the accuracy of the station coordinate determination. One technique for reducing the effect of these errors is to use short-arcs consisting of a few passes of the satellite over the tracking station. This paper analyzes the sensitivity of short-arc station coordinate estimates to various errors in the physical model, to the number of observations, and to the station-satellite geometry using simulated as well as real data.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Journal of the Astronautical Sciences; 24; Apr
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  • 10
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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
    Format: application/pdf
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