Comparison of Space Shuttle GPS Flight Data to Geometric Theory of Diffraction Predictions

Susan F. Gomez, Shian U. Hwu

Abstract:	Multipath is a concern of the International Space Station (ISS) GPS subsystem. The ISS GPS subsystem must provide navigation, attitude, and a time reference. Multipath is the main error source for the attitude determination accuracy. In order to predict the effects of multipath on the ISS, the Uniform Geometric Theory of Diffraction (GTD) technique is being used. This paper compares the results of using that technique to actual data collected on a Space Shuttle flight experiment. Differential carrier phase measurements using a Trimble Advanced Navigation System (TANS) Vector were taken during the 1996 Space Shuttle flight experiment called GPS Attitude and Navigation Experiment (GANE). The GANE used four Micropulse choke ring antennas mounted to a rigid structure which was mounted in the Shuttle payload bay on a HitchHiker platform. A Honeywell inertial reference unit was also mounted to the GANE structure to provide an attitude reference in combination with the Shuttle inertial measurement units and star trackers. The differential carrier phase measurements made during GANE are compared to predicted differential carrier phase measurements using GTD. GTD is a rigorous computational technique that provides a high frequency approximate solution to the electromagnetic fields including incident, reflected, and diffracted fields and their interactions. In general, good agreement was seen between the measured data and the predicted data, but some areas of discrepancy are seen and investigated.
Published in:	Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997) September 16 - 19, 1997 Kansas City, MO
Pages:	605 - 614
Cite this article:	Gomez, Susan F., Hwu, Shian U., "Comparison of Space Shuttle GPS Flight Data to Geometric Theory of Diffraction Predictions," Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997), Kansas City, MO, September 1997, pp. 605-614.
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