Using L1-Frequency GPS Signals for the Relative Navigation of Space Vehicles

M. Hartrampf, E. Gottzein, A. Konrad, M. Mittnacht

Abstract:	Using a GPS receiver for the orbit determination is state-of-the-art for many space applications and many have been employed in a lot of different orbits from low Earth orbits (LEO) to high eccentric orbits (HEO). Even the use of GPS receivers in geostationary orbits (GEO) was already tested [1] and more missions are scheduled in the near future. State-of-the-art and future scientific missions for Earth and space observation using a space-borne observatory need high accuracy in the determination of the position and velocity of the observing vehicle. In addition, the characteristics of the space environment make special demands on the equipment used on a satellite. High dynamics and radiation are the main factors a space-borne GNSS receiver has to cope with compared to a ground based system. On the other hand, tropospheric influence is of no concern and even the impact of the ionosphere on the signals is limited due to the high altitude of the spacecrafts. While the accuracy of a GPS receiver that uses only the civil coarse acquisition (C/A) code on the L1 frequency of the GPS signal is sufficient for most commercial missions that require an accuracy of absolute position of some meters, many scientific missions have higher demands. Examples are formation flying for interferometric measurements, rendez-vous and in orbit inspection in low Earth orbit (LEO). For these missions a high precision in absolute and relative position and velocity is necessary, whereby the requirements for relative position and velocity between the different spacecrafts of the formation is often more restrict than the absolute one. Typically, a position accuracy in the sub-meter range for absolute position or even sub-centimetre range for relative position is required. In order to meet these requirements with GPS, a receiver, using both the L1 and the L2 frequency is normally used. This paper demonstrates possibilities to increase the accuracy of absolute and relative position determination with a single frequency C/A-code GPS receiver in order to venture into these missions applying Carrier Phase Differential GPS (CDGPS) for relative position and velocity determination and the use of carrier smoothing algorithms as well as SBAS signals for the absolute position.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	2201 - 2211
Cite this article:	Hartrampf, M., Gottzein, E., Konrad, A., Mittnacht, M., "Using L1-Frequency GPS Signals for the Relative Navigation of Space Vehicles," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 2201-2211.
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