Highlights of GPS II-R Autonomous Navigation

John A. Rajan

Abstract:	ITT developed GPS IIR Payloads provide self-navigation capability to the GPS constellation. Each satellite navigates using the rest of the satellites in the constellation. The satellites perform two-way cross-link ranging using pseudo random codes. The cross-link ranges are incorporated in a unique Kalman filter setup in Keplerian coordinates to perform the self-navigation. The Kalman filter uses a reference trajectory that is uploaded from the control segment and estimates corrections to this trajectory. (Refer to Figure 1) This paper discusses this unique Kalman filter setup. The paper highlights the unique challenges encountered in this application and ways in which they were handled. One of the challenges in this Kalman filter design is to reduce the error growth that looks like a constellation rotation. Algorithms have been developed, implemented, and tested for constraining the constellation rotation. Two way ranging enables reduction of the Atomic clock induced errors. A dual frequency ranging technique is used to reduce plasma induced errors. The satellites exchange the data necessary to enable these corrections. This Kalman filter is designed to provide full accuracy for up to 210 days following a reference trajectory upload. On-orbit results are also discussed.
Published in:	Proceedings of the 58th Annual Meeting of The Institute of Navigation and CIGTF 21st Guidance Test Symposium (2002) June 24 - 26, 2002 Hyatt Regency Hotel Albuquerque, NM
Pages:	354 - 363
Cite this article:	Rajan, John A., "Highlights of GPS II-R Autonomous Navigation," Proceedings of the 58th Annual Meeting of The Institute of Navigation and CIGTF 21st Guidance Test Symposium (2002), Albuquerque, NM, June 2002, pp. 354-363.
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