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  • SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING  (3)
  • 1
    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
    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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  • 3
    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
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