GPS Attitude Determination From Double Difference Differential Phase Measurements

R. Fuller, S. Gomez, L. Marradi and J. Rodden

Abstract:	Use of GPS for attitude determination on spacecraft nominally require a time consuming pre-flight self survey calibration procedure for establishing the antenna baselines and line biases as system parameters. A method for eliminating uncompensated baseline phase changes from affecting attitude determination accuracy involves double differencing of carrier phase measurements in the attitude algorithm. The method involves the algebraic combination of the Master Equations relating the differences of phase difference from two GPS SVs across each antenna baseline. The technique effectively uses some of the SV data to calibrate out the baseline phase and eliminates those phase variations as an error source. The algorithm uses the same terms, although rearranged, as the single difference algorithm developed previously. The solution path is unchanged for attitude and rate determination. The integer ambiguity is solved separately as before and does require an initial estimate of the line bias. The use of an attitude algorithm using double differencing of the differential phase measurement can reduce the requirements for a self survey process. The need for line bias determination is eliminated with the double difference attitude determination algorithm. The integer resolution can also be established without line bias information. An integer resolution scheme using double differencing will be presented. A modification of an integer search algorithm to resolve integer ambiguity involving double differencing of phase measurements during the attitude determination process will be shown. Attitude performance results with live GPS satellites from a static roof top array and also orbital GPS Simulator tests will be shown.
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:	1073 - 1080
Cite this article:	Fuller, R., Gomez, S., Marradi, L., Rodden, J., "GPS Attitude Determination From Double Difference Differential Phase Measurements," 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. 1073-1080.
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