Spacecraft Attitude Estimation Using GPS: Methodology and Results for RADCAL

Lisa Ward and Penina Axelrad

Abstract:	This paper presents attitude solutions for the gravity gradient stabilized RADCAL satellite, determined using GPS data collected onboard. The methodology, which is based on a sequence of algorithms including an initialization step, baseline estimator, and attitude Kalman filter is described. Results from five data sets collected on-orbit are presented and their implications are discussed. We observed that RADCAL is exhibiting periods of regular pitch and roll oscillations accompanied by a slow yaw rotation with occasional spin-up and spin- down intervals. As there is no external attitude sensor for comparison, the accuracy of the estimates is assessed based on consistency of results between data sets. The maximum contribution of baseline errors is estimated to be at the 1 degree level. Large multipath errors of up to 2 centimeters, which appear to be associated with reflections from the gravity gradient tip mass, are illustrated in the measurement residuals.
Published in:	Proceedings of the 1995 National Technical Meeting of The Institute of Navigation January 18 - 20, 1995 Disneyland Hotel Anaheim, CA
Pages:	813 - 825
Cite this article:	Ward, Lisa, Axelrad, Penina, "Spacecraft Attitude Estimation Using GPS: Methodology and Results for RADCAL," Proceedings of the 1995 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 1995, pp. 813-825.
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