Optimized Network of Ground Stations for LEO Orbit Determination

Tae-Suk Bae

Abstract:	While the kinematic approach of precise Orbit Determination (OD) of Low Earth Orbiter (LEO) satellites has its advantages, it may not produce a good result (even no solution) in case of bad satellite geometry or data gaps. As a way to overcome this limitation, pseudolite transceivers are proposed to improve the geometry of the satellites. For the maximum use of the pseudolites, they should be located optimally on the ground worldwide. Since an optimal network should be homogeneous and isotropic such that the errors are distributed uniformly over the network, therefore, the dispersion matrix of the estimated point coordinates will possess the Taylor-Karman structure. A Second Order Design (SOD) is used here for the network configuration, which approximates the ideal cofactor matrix by varying weights of the baselines. Total of 63 IGS stations are used to test the optimal network design, and distances between the stations are used as measurements. An algorithm designed to find a new network station at each step is described and applied successfully in this paper. The trace of the cofactor matrix can be used as an overall measure of precision in the optimal sense. Since the trace of the cofactor matrix does not change significantly beyond 40 stations, therefore, this would be the optimal number of stations for the network. However, more than 40 stations are needed, in spite of not increasing the optimality of the network itself, because the LEO altitude is low, thus, the 40 optimal pseudolite locations will not provide sufficient data coverage.
Published in:	Proceedings of the 2005 National Technical Meeting of The Institute of Navigation January 24 - 26, 2005 The Catamaran Resort Hotel San Diego, CA
Pages:	515 - 522
Cite this article:	Bae, Tae-Suk, "Optimized Network of Ground Stations for LEO Orbit Determination," Proceedings of the 2005 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2005, pp. 515-522.
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