Effects of Multipath and Signal Blockage on GPS Navigation in the Vicinity of the International Space Station (ISS)

D.E. Gaylor, E.G. Lightsey, K.W. Key

Abstract:	A number of studies have examined GPS relative navigation for spacecraft performing rendezvous and docking with the International Space Station (ISS). However, these studies have not accounted for degradation in GPS navigation performance due to multipath signals being reflected off of the ISS or blockage of GPS signals by the ISS. The objective of this study is to analyze these effects on GPS navigation in the vicinity of the ISS using simple models for GPS signal blockage and multipath. A simulation of a spacecraft GPS receiver operating near the ISS has been developed. This simulation includes orbit models for the GPS constellation, the ISS and the spacecraft. It also includes a GPS signal blockage model and a multipath model. These models can be used to predict the performance obtained by combining various sensors with GPS for navigation or attitude determination for spacecraft operating near the ISS or other large reflecting body. The blockage simulation shows that aiding of GPS is required when the spacecraft approaches within 60 meters the ISS. The multipath simulation results show the expected trends in the range errors as a function of the GPS satellite elevation angle, the distance from the ISS, the number of multipath rays modelled, and the radar cross-sectional area of the ISS. Both effects may significantly degrade GPS navigation near the ISS. The next logical step is to validate these models with actual flight data. If appropriate flight data cannot be found, the results of this paper may be used to justify a future flight experiment.
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:	2238 - 2247
Cite this article:	Updated citation: Published in NAVIGATION: Journal of the Institute of Navigation
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