Relative State Estimation Using GPS Flight Data from Co-Orbiting Spacecraft

Dolan Highsmith and Penina Axelrad

Abstract:	The objective of this research is to use flight data to develop and demonstrate the most accurate and robust GPS-based methods for relative navigation for two cooperative, co-orbiting vehicles in LEO. A Kalman filter that directly estimates the relative state between two co-orbiting vehicles using single difference pseudorange observations has been developed. This filter is used in conjunction with an existing GPS absolute orbit determination utility, which provides an estimate of the absolute orbit of the passive vehicle to the relative filter. The Clohessy-Wiltshire equations are used for state and error propagation. This filter has been designed using flight data from the STS-80/ORFEUSSPAS flight experiment performed in December 1996.The root-mean-square (RMS) relative position errors are 6.4 m radial, 5.3 m in-track, and 1.3 m cross-track. The RMS velocity errors are 0.022 m/s radial, 0.018 m/s in-track, and 0.013 m/s cross-track. Though the relative positions are not better than NASA/JSC results, this fairly simple filter achieved an overall improvement of more than 70% in relative velocity. This is an excellent beginning upon which to build future adaptations, which may include relative J2, relative drag, and carrier phase processing.
Published in:	Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999) September 14 - 17, 1999 Nashville, TN
Pages:	401 - 409
Cite this article:	Highsmith, Dolan, Axelrad, Penina, "Relative State Estimation Using GPS Flight Data from Co-Orbiting Spacecraft," Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999), Nashville, TN, September 1999, pp. 401-409.
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