A Survey of GPS Satellite Selection Algorithms for Space Shuttle Autolanding

Scott P. Cryan, Moises N. Montez

Abstract:	This paper evaluates several GPS satellite selection algorithms for use by candidate Space Shuttle GPS receivers during the autoland phase. The evaluation will concentrate on improving the navigation performance in the vertical direction at landing without large degradations in the horizontal channel. The vertical channel has been shown to be the weakest channel when using GPS in the absolute mode. Improvement of the vertical channel navigation performance is important for landings at contingency sites where no differential GPS capability is expected. A satellite selection algorithm which uses the GDOP optimization criteria will he compared to algorithms which optimize PDOP or VDOP. In addition, two satellite selection algorithms developed by Dr. W. M. Lear, CSDL will be investigated. The first algorithm first selects the satellite nearest the vertical, the second nearest the perpendicular to the first, the third nearest the perpendicular to the plane determined by the first two, the fourth optimizes GDOP, and the fiih optimizes PDOP The second algorithm selects the first sateliite along the velocity vector, the second at 109.47 degrees away from the first, the third to maximize the trihedral volume, and the fourth to minimize GDOP. To perform this evaluation, a receiver simulation was incorporated into an in-house Space Shuttle simulation. The receiver simulation includes a Kalman filter algorithm similar to the Rockwell Collins RCVRSA receiver. The receiver simulation operated in the PVA mode for this analysis.
Published in:	Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992) September 16 - 18, 1992 Albuquerque, NM
Pages:	1165 - 1171
Cite this article:	Cryan, Scott P., Montez, Moises N., "A Survey of GPS Satellite Selection Algorithms for Space Shuttle Autolanding," Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992), Albuquerque, NM, September 1992, pp. 1165-1171.
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