On the Use of the Global Positioning System for Orbit Determination of Low Flying Satellites

Isabel V. P. Osorio

Abstract:	The main purpose of this paper is to study the feasibility of precise orbit determination for low altitude satellites, by using on board phase measurements of the NAVSTAR/GPS satellite signals, and to use such methods for the evaluation of the total electron content in different directions of the upper ionosphere. To deal with the motion of the station satellite it is adopted a mathematical model based on the use of modified Poincare variables. The idea is to avoid the problems of small eccentricities and small inclinations. From the large amount of information received from NAVSTAWGPS satellites, it is proposed to use phase data only, due to the precision and stability of such measurements. For that purpose, the effects of clock errors and signal propagation in the atmosphere are adequately modelled. The rapid change of geometric configurations defined by the NAVSTAR/GPS satellites and the station satellite allows to have on board two types of signals: those passing outside the ionosphere and those coming through the ionosphere. By using phase measurements belonging to the first type of signals, the satellite position is obtained as well as the phase ambiguity and clock error parameters. For that purpose, a mathematical model was developed, based on a Kalman filtering technique. The initial solution is derived through a preliminary orbit determination procedure, where pseudorange measurements are also taken into account for a few seconds. When a GPS satellite goes low enough in the horizon of the station satellite, in such a way that the signals cross the ionosphere before reaching the receiver, the phase measurements and the results of the first computations are used for the evaluation of the total electron content along the signal path within the ionosphere. Computer programs were written based on the theory developed along this work. The results obtained show the feasibility of the use of the Global Positioning System for the orbit determination of low altitude satellites and for the evaluation of the total electron content in the upper ionosphere.
Published in:	Proceedings of the 1994 National Technical Meeting of The Institute of Navigation January 24 - 26, 1994 Catamaran Resort Hotel San Diego, CA
Pages:	403 - 412
Cite this article:	Osorio, Isabel V. P., "On the Use of the Global Positioning System for Orbit Determination of Low Flying Satellites," Proceedings of the 1994 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 1994, pp. 403-412.
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