GPS Based Attitude Determination On Nonaligned Antenna Arrays

E. Glenn Lightsey and Bradford W. Parkinson

Abstract:	GPS carrier phase based attitude determination has been traditionally limited to aligned or nearly aligned antenna arrays; that is, arrays where all antenna boresights point in the same direction or are slightly canted. While this arrangement is suitable for most terrestrial applications where the GPS constellation is generally oriented overhead, it does not lead to robust attitude measurement availability for many spacecraft applications. When a spacecraft is inertially pointed, spinning, or tumbling, limiting GPS signal reception to one hemisphere of the vehicle body results in significant outages of attitude data. This paper generalizes previously derived GPS attitude determination algorithms to allow non- aligned antenna arrays. This is a new application of a technique used to account for the phase contribution due to circular polarization of the received GPS carrier signal. The required phase correction is a function of the antenna boresight vector in the vehicle reference frame and the GPS signal line of sight. By enabling non- aligned antenna arrays to be used for attitude determination, the robustness of GPS-based attitude determination is significantly enhanced for many demanding applications, especially on spacecraft. The method is validated through rooftop tests using a Trimble TANS Vector receiver that has been substantially modified for space. This paper presents these results and demonstrates the effects of neglecting the circular polarization correction on nonaligned arrays. The data indicates that a GPS receiver can be successfully employed as the sole attitude determination sensor on a spacecraft from an initial tumbling acquisition to inertial or spinning stabilization.
Published in:	Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996) September 17 - 20, 1996 Kansas City, MO
Pages:	1081 - 1090
Cite this article:	Lightsey, E. Glenn, Parkinson, Bradford W., "GPS Based Attitude Determination On Nonaligned Antenna Arrays," Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996), Kansas City, MO, September 1996, pp. 1081-1090.
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