First Results from PoSAT-1 GPS Experiment

Martin J. Unwin and Martin N. Sweeting

Abstract:	The PoSAT-1 microsatellite was designed and constructed in the University of Surrey in the UK by Surrey Satellite Technology Ltd. and the PoSAT Portuguese Academic and Industrial Consortium. The microsatellite was successfully launched by Arianespace as an auxiliary satellite alongside the French SPOT-3 remote sensing satellite into an 800 km polar orbit on September 26th 1993. On-board the microsatellite there is a GPS Navigation Unit, an experiment consisting of GPS receiver, antenna and processing hardware. The GPS receiver provides an accurate real-time position and velocity to other satellite sub-systems. Using the Navigation Unit, the satellite will be able to directly generate new mean orbital elements for distribution to all users. The supporting software also enables the logging of experimental data, the synchronisation of the satellite and ground station clocks, and has the potential for payload switching and direct on-board orbit determination through data filtering. The implementation of this experiment represents a significant step forward in autonomous satellite operations. The expected 3-D accuracies from a single frequency GPS receiver are around 150 metres. This level of uncertainty of position surpasses any other tracking techniques previously used for UoSATclass microsatellites, and is more than adequate for existing microsatellite operations, However the availability of such accuracy will enable new capabilities and scientific payloads to be flown even on such small low- cost satellites, and so there is motivation for the filtering of the GPS data to provide higher accuracies. This paper describes the architecture of the PoSAT- 1 navigation unit and present the first results from initial operations. A comparison between the existing source of tracking data and the new GPS derived tracking data are made. Targets are set for on-board processing tasks of the Navigation Unit, and the results are processed accordingly. The continuing developments to the Navigation Unit are listed and the applications to future UoSAT-class microsatellites are described.
Published in:	Proceedings of the 1994 National Technical Meeting of The Institute of Navigation January 24 - 26, 1994 Catamaran Resort Hotel San Diego, CA
Pages:	413 - 420
Cite this article:	Unwin, Martin J., Sweeting, Martin N., "First Results from PoSAT-1 GPS Experiment," Proceedings of the 1994 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 1994, pp. 413-420.
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