Analysis and Test Results of GPS and Geostationary Satellite Orbit Determination for WAAS

Scott Pogorelc, Tim Cashin, Marie Lage

Abstract:	The FAA’s Wide Area Augmentation System (WAAS) is being designed to compute and broadcast GPS differential correction information to airborne users operating inside the National Airspace System (NAS). The National Satellite Testbed (NSTB) is a precursor to the WAAS and is being used extensively by the FAA as a research and development environment to test and evaluate WAAS capabilities and performance. Like the WAAS, the NSTB’s primary function is to supply satellite correction data, ionospheric grid information and satellite integrity information to the user in real-time over a geostationary satellite (GEO) link. In addition to using the GE0 as a communications link, the NSTB will validate an independent GE0 ranging capability as a means of improving satellite availability for navigation. In order to supply satellite corrections which are applicable over a wide-area and to provide the GE0 ranging capability, the NSTB must be capable of determining accurate GPS and GE0 orbits. To help meet a key NSTB goal of verifying that WAAS navigation accuracy requirements can be achieved, Stanford Telecom (STel) developed orbit estimation software which accurately separates clock and ephemeris errors for both GPS and GE0 satellites in real-time. The algorithms include high fidelity force models as well as precise earth orientation models to estimate and predict both satellite and ancillary states (e.g. solar radiation model parameters). Extensive analysis of test data has demonstrated that GPS orbits can be determined in real- time to < 1.5 meters (3-D RSS) using a global tracking network, and c 3 meters (3-D RSS) using a North America-only tracking network. Additionally, initial tests of the GE0 ranging capability using the AOR West Inmarsat-II geostationary satellite have been completed and the results clearly demonstrate the ability to use the GE0 satellite as an additional ranging source.
Published in:	Proceedings of the 1997 National Technical Meeting of The Institute of Navigation January 14 - 16, 1997 Loews Santa Monica Hotel Santa Monica, CA
Pages:	429 - 439
Cite this article:	Pogorelc, Scott, Cashin, Tim, Lage, Marie, "Analysis and Test Results of GPS and Geostationary Satellite Orbit Determination for WAAS," Proceedings of the 1997 National Technical Meeting of The Institute of Navigation, Santa Monica, CA, January 1997, pp. 429-439.
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