GPS Operations on the PCsat Microsatellite

Oliver Montenbruck, Sunny Leung and Robert Bruninga

Abstract:	While spaceborne GPS receivers can in general be consid- ered as a well established tracking tool for low Earth orbit (LEO) satellites, their use on micro- or nano-satellites poses multiple problems from a systems engineering point of view. Representative examples include the mass budget, the lack of a suitable attitude stabilization, antenna alloca- tion problems, restricted command and telemetry links as well as limited onboard power resources. The recent flight of a small GPS receiver onboard the PCsat Prototype Communications satellite provides an illustrative example of GPS operations on a 10 kg class of micro-satellites. PCsat was built by the United States Naval Academy (USNA), Annapolis, and carries a 12 channel C/A GPS receiver for C/A code tracking developed at the German Space Operations Center (GSOC). It was launched into an 800 km/67° orbit on 30 Sept. 2001 by an Athena 1 rocket from Kodiak, Alaska. During a period of full Sun orbits in January 2002, the receiver could be operated almost con- tinuously for more than ten days with telemetry data col- lected by a world wide net of radio amateurs. Using an analytical orbit model for Doppler and visibility prediction, the receiver was able to acquire tracking autonomously within a few minutes after power up and hot starts were always performed within less than 60 s. On average the receiver tracked 10-11 out of 13-15 GPS satellites visible above the Earth’s rim using a simple monopole antenna. In a ground based postprocessing an rms pseudorange accu- racy of 2.5m has been determined, which includes the effect of uncorrected ionospheric path delays. However, a notable number of outliers with errors of 10-100m exists that restrict the real-time navigation accuracy to about 10 - 15m rms in each axis. These outliers are typically encoun- tered at the acquisition of GPS signals, which occur rather frequently due to the tumbling motion of PCsat and its constantly changing antenna orientation.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	77 - 84
Cite this article:	Montenbruck, Oliver, Leung, Sunny, Bruninga, Robert, "GPS Operations on the PCsat Microsatellite," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 77-84.
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