National Satellite Testbed (NSTB) GPS Satellite Clock/Ephemeris Determination Analysis and Results

Scott Pogorelc, Mark Lorenz, Kelly Murdock, Brent Harding, Tim Cashin, and Donna Kraus

Abstract:	The FAA’s National Satellite Testbed (NSTB) is a precursor to the Wide Area Augmentation System (WAAS). The testbed is designed to verify the WAAS concept by computing and broadcasting GPS integrity and differential correction information to a user aircraft. In addition to supplying ionospheric and satellite integrity information, one of the testbed’s primary functions is to provide separate clock and ephemeris corrections. To help meet the goal of the testbed and to satisfy the WAAS navigation accuracy requirements, Stanford Telecom (STel) has performed extensive analysis on the problem of separating the clock and ephemeris errors for GPS satellites in near real-time. As a result of this analysis, STel has developed and implemented algorithms which provide the testbed with GPS satellite clock and ephemeris determination capabilities. The algorithms include accurate force models as well as precise earth orientation models to estimate and predict the GPS satellite states. This paper describes the clock/ephemeris algorithms developed for the NSTB, including initial performance analysis and test results. A description of the tests conducted as well as a description of the algorithms is also presented.
Published in:	Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995) September 12 - 15, 1995 Palm Springs, CA
Pages:	247 - 256
Cite this article:	Pogorelc, Scott, Lorenz, Mark, Murdock, Kelly, Harding, Brent, Cashin, Tim, Kraus, Donna, "National Satellite Testbed (NSTB) GPS Satellite Clock/Ephemeris Determination Analysis and Results," Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995), Palm Springs, CA, September 1995, pp. 247-256.
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