Tracking GPS Above GPS Satellite Altitude: Results of the GPS Experiment on the HEO Mission Equator-S

Oliver Balbach, Bernd Eissfeller, Günter W. Hein, T. Zink, Werner Enderle, Michael Schmidhuber, Norbert Lemke

Abstract:	Within the framework of the Small Satellite Mission Equator-S (launched on December 2, 1997 with an Ariane 4 rocket) it could be demonstrated that it is possible to use GPS even in the vicinity of the geostationary orbit. The maximum altitude where the GPS receiver provided measurements was about 61,000 km, which constitutes a world record. The GPS-experiment was developed with funding of the German Aerospace Center (DLR), by the Institute of Geodesy and Navigation (IfEN) of the University of Federal Armed Forces in Munich, the German Space Operations Center (GSOC) of DLR in Oberpfaffenhofen, and by the Munich based aerospace company Kayser-Threde GmbH. The experiment data have significant impact for the future use of GPS receivers on-board geostationary satellites. In the past GPS receivers have only been used well below the orbital altitude of the GPS satellites (20,000 km). The reception of signals at greater altitudes could now be demonstrated within the Equator-S GPS experiment. As part of this, GPS signals have also been received from the antenna side lobes of the GPS satellites. The Motorola GPS receiver has originally been designed for use on low Earth orbits. It employs two antennas, which, in case of Equator-S, are aligned with the spacecraft’s spin axis. In order to allow a signal reception up to the peak altitude of 61,000 km under these conditions, the receiver had to be manually operated from GSOC. For each part of the orbit the trackable GPS satellites were determined using a specially designed software and manually assigned to the various receiver channels. This paper focuses on the results especially in high altitudes and the problems that have been encountered by using a receiver designed for a LEO orbit, and it gives a short description of the experiment as far as it is necessary to interpret the results.
Published in:	Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998) September 15 - 18, 1998 Nashville, TN
Pages:	1555 - 1564
Cite this article:	Balbach, Oliver, Eissfeller, Bernd, Hein, Günter W., Zink, T., Enderle, Werner, Schmidhuber, Michael, Lemke, Norbert, "Tracking GPS Above GPS Satellite Altitude: Results of the GPS Experiment on the HEO Mission Equator-S," Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998), Nashville, TN, September 1998, pp. 1555-1564.
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