93-160
A Demonstration of TDRS Orbit Determination Using Differential Tracking Observables From GPS Ground Receivers,
Stephen M. Lichten, Charles D. Edwards, Lawrence E. Young, Sumita Nandi, Charles Dunn and Bruce J. Haines*
Abstract
A Global Positioning System (GPS) flight receiver provides a means of precisely determining orbits for satellites in low to moderate altitude orbits. Above 5000 km altitude, however, relatively few GPS satellites are visible. We present a new approach to orbit determination for satellites at higher altitudes. Modification of GPS ground receivers enables a beacon from the orbiter to tracked simultaneously with GPS data. The orbit accuracy expected from this GPS-like tracking (GLT) tecnique in principle could be comparable to accuracies of GPS orbits. Present-day GPS orbit quality from a daily semi-automated analysis system at the Jet Propulsion Laboratory is at the 30-50 cm level: expected accuracies for orbiters with GLT are calculated to be in the few-meter range for altitudes up to 100000 km. For geosynchronous satellites, however, there are unique challenges due to geometrical limitations and the lack of stong dyanmical signature in tracking data. We examine two approaches for tracking TDRS geostationary orbiters, One uses GLT with a global network: the other relies on a small "connected element" ground network with a distributed clock for short baseline differential carrier phase (SBDf). In Principle, both could meet 50-m TDRS operational requirements. However there are practical difficulties with either pure GLT or SBDf tracking schemes for the present-day TDRS satellites, We describe an experiment planned for 1993 which will combine aspects of both GLT and SBDf to demonstrate a new approach for tracking TDRS which offers a number of operationally convenient and attractive features. The TDRS demo will in effect be a proof of concept experiment for both the GLT and SBDf approaches to tracking spacecraft.
* Drs. Lichten, Ewards, and Young are Technical Group Supervisors and Drs. Nandi, Dunn and Haines are Members of the Technical Staff: all are in the Tracking Systems and Applications Section at the Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 238-600, 4800 Oak Grove Drive, Pasadena, California 91109.