The Global Positioning System (GPS) Autonomous User System

M. P. Ananda, H. Bernstein, W. A. Feess, T. C. Paugstat

Abstract:	A GPS autonomous navigation system, transparent to the user, will be operational with the GPS Block IIR satellites in the first decade of the 21st century. This system will be capable of providing the user with full navigational accuracy for a period of 180 days even if the GPS Operational Control Segment (OCS) ls inoperable. However, until such a system is operational, the GPS navigation accuracy depends on continued operation of the control segment. If the control segment falls. the navigation accuracy degrades rapidly. To provide interim full system accuracy In the event of the loss of the OCS, an Autonomous User System (AUS) has been designed, implemented, and field tested. Autonomy ls achieved with modifications to the GPS user segment only. In this paper, the AUS ls described and test results are presented. The test results indicate that, In the 180-day period, the autonomous user can achieve a navigation accuracy of the same order of magnitude as ls obtained when the OCS is functioning properly. An autonomous user has a GPS user equipment set augmented with an atomic clock, an autonomous user algorithm and a pre-stored data base which consists of 6 months of ephemeris (reference trajectory) and clock parameters for each GPS satellite. The AUS utilizes satellite-to-user pseudorange and delta pseudorange measurements (while stationary from a pre-surveyed location) to estimate differences of the true satellite ephemeris and clock from the pre-stored reference. The corrected reference can then be utilized for navigation by the autonomous or other (survivable) users. The successful field test program has demonstrated that the AUS implementation will enhance force effectiveness of several critical users. While the AUS was designed and demonstrated for the GPS, the concepts have wide universal applications to all satellite programs where autonomy is an issue.
Published in:	Proceedings of the 1988 National Technical Meeting of The Institute of Navigation January 26 - 29, 1988 Santa Barbara, CA
Pages:	174 - 186
Cite this article:	Ananda, M. P., Bernstein, H., Feess, W. A., Paugstat, T. C., "The Global Positioning System (GPS) Autonomous User System," Proceedings of the 1988 National Technical Meeting of The Institute of Navigation, Santa Barbara, CA, January 1988, pp. 174-186.
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