Lessons Learned from the use of GPS in Space: Application to the Orbital use of GALILEO

J-L. Issler, A. de Latour, L. Ries, L. Lestarquit, M. Grondin, J. Dantepal

Abstract:	Most applications of GNSS receivers in space need to have a real time on-board positioning and timing information. This paper presents the positioning and timing accuracy that we can get using GPS radio navigation signals on-board space vehicle in orbit. First of all, the paper presents our contribution to positioning and timing of spacecrafts thanks to GPS, using the TOPSTAR 3000 family of spaceborne GNSS receivers specified by CNES and ESA. A dozen of these equipments already flew in orbit or even on board the Atmospheric Re-entry Demonstrating capsule (ARD) launched by ARIANE 503 in 1998. Moreover, about one hundred and fifty of these equipments have been ordered. New flight results are provided, including the performances of the CNES-made on board DIOGENE Kalman filter, with single frequency or dual frequency GPS measurements. The DIOGENE Kalman filter allows an accuracy of 30 cm in real time without any external data message have been obtained using the TOPEX-POSEIDON downloaded dual frequency raw measurements, associated to broadcasted ephemeris less accurate than today. The Kalman filter flight results are also provided, as observed on board the HETE2 ( NASA and MIT ) and DEMETER ( CNES ) missions. These missions use single frequency TOPSTAR receivers, and robust navigations with a radial accuracy of 3 meters. A specific attention is given to the in orbit validation of the low C/No tracking capability of the TOPSTAR GPS receiver, not only on board ARD, but also on board DEMETER. Moreover, DEMETER used successfully Autonomous Orbit Control (AOC) thanks to GPS, and the main AOC results are also presented. All this experiences allows to better predict future space navigation system accuracies using GALILEO in orbit. The positioning and timing solutions have been estimated with two types of navigation algorithms which deliver the well-known single-point solution and the Kalman filtered solution. The analysis shows that Galileo signals enables very good positioning and timing accuracy for LEO and that tracking Galileo signals in HEO and GEO can be achieved. Moreover, since GPS and GALILEO has two common frequencies and signals, this allows to increase the accuracy and the robustness of GNSS navigation thanks to a simple equipment.
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	719 - 735
Cite this article:	Issler, J-L., de Latour, A., Ries, L., Lestarquit, L., Grondin, M., Dantepal, J., "Lessons Learned from the use of GPS in Space: Application to the Orbital use of GALILEO," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 719-735.
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