GPS Inertial Attitude Estimation via Carrier Accumulated Phase Measurements And Statistical Filtering Of Phase Cycle Count Ambiguity

Haywood S. Satz, Duncan B. Cox Jr., Ronald L. Beard and G. Paul Landis

Abstract:	This paper describes the design and simulation performance of an integrated GPS/INS system which accomplishes space vehicle navigation and attitude estimation. The simulation contains models of a strapped-down inertial measurement unit (IMU), a GPS receiver processing signals received from an array of antennas placed on the spacecraft structure, and an integrated navigation filter. A nonlinear statistical filter is used to optimize the performance of the system. GPS carrier accumulated-phase measurements are made from precise antenna phase-center locations in +he user vehicle structure. The vehicle orientation in inertial space is obtained by interpreting baseline-difference phase measurements as orientations of antenna baselines relative to well known satellite line-of-sight vectors. The method of attitude estimation described herein is distinguished from other methods in that it does not employ search algorithms to resolve carrier phase cycle ambiguities. Instead, each ambiguity is modeled as a random process and is included as an error state of the statistical filter. Estimation of ambiguity states is augmented by the imposition of integer constraints on these states. The imposition of each constraint is accomplished automatically and is guided by monitors of thresholds of associated residuals and variances. As a result, the attitude estimation time history evolves directly for any dynamic enviroment. The ability of the filter to estimate vehicle attitude has been demonstrated fro a wide range of body rotation rates and initial attitude errors.
Published in:	Proceedings of the 1991 National Technical Meeting of The Institute of Navigation January 22 - 24, 1991 Sheraton San Marcos Hotel Phoenix, AZ
Pages:	289 - 294
Cite this article:	Updated citation: Published in NAVIGATION: Journal of the Institute of Navigation
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