Improved Orbit Estimation using GPS Measurements for Conjunction Analysis

Alana R. Muldoon, Gabriel H. Elkaim

Abstract:	Orbital debris is a significant hazard for satellite and manned space flight. With upwards of 12,000 pieces of debris moving at very high speeds, satellites move out of the way rather than risk a catastrophic collision. Analysis of collision probability between space objects is often accomplished by using NORAD’s Two-Line Elements (TLEs). TLEs are time stamped orbit position data, updated periodically, that include neither error estimates nor any guarantee of their accuracy. This uncertainty burdens satellite owner/operators, forcing them to take unnecessary actions to avoid other space objects, using up precious fuel and resources, and shortening satellite lifespan. In this paper we compare TLEs to GPS precise ephemerides to find systematic rotational biases in the TLEs, leading to an improvement in positional accuracy of the GPS TLEs. These rotational biases are remarkably stable, showing improved orbit prediction as far as two years out. The remaining error in the TLEs shows structure, and can be predicted. Future efforts will apply this analysis to LEO objects in order to asses the utility of these improvements to the TLEs.
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	786 - 794
Cite this article:	Muldoon, Alana R., Elkaim, Gabriel H., "Improved Orbit Estimation using GPS Measurements for Conjunction Analysis," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 786-794.
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