Consistent On-Board Multipath Calibration for GPS-Based Spacecraft Attitude Determination

Roberto V. F. Lopes and Paulo G. Milani

Abstract:	Aspects of the on-board calibration of spacecraft three- axis attitude determination systems employing the GPS phase-observable signal are examined. More specifically, a new consistent on-board estimation algorithm is proposed that uses a special set of calibration coefficients for multipath mitigation. A two-dimensional Taylor series in a convenient planar-projection coordinate system is used to model the global distortion effect of the GPS line of sight due to multipath. This selected projection avoids distortion and singularities close to the antenna zenith. Based on a previous solution to the similar problem of on- board star-sensor calibration, the model is purged of all misalignment-like components to cope with the inherent lack of observability. The algorithm was tested in the presence of a strong multipath effect using an empirical model based on a ground experiment data set. The test considered an inertially-stabilized satellite in a low-Earth orbit with low inclination. The data span covered 24 hours of continuous simulation with no a priori attitude information. The results were compared with those obtained when exact a priori attitude knowledge was included using a ground calibration algorithm. Both algorithms present the same significant gain in accuracy. The simulation results show that this methodology should be employed in order to assure precise autonomous on- board attitude determination using the GPS.
Published in:	Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000) September 19 - 22, 2000 Salt Palace Convention Center Salt Lake City, UT
Pages:	2216 - 2226
Cite this article:	Lopes, Roberto V. F., Milani, Paulo G., "Consistent On-Board Multipath Calibration for GPS-Based Spacecraft Attitude Determination," Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000), Salt Lake City, UT, September 2000, pp. 2216-2226.
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