GPS-based precise tracking of Earth satellites from very low to geosynchronous orbits

Various GPS (Global Positioning System)-based tracking strategies for Earth orbiting satellites are reviewed. Three different categories of user satellites are studied: low circular orbits with altitudes between a few hundred and a few thousand kilometers, highly elliptical orbits with perigees as low as a few hundred and apogees as high as tens of thousands of kilometers, and high circular orbits up to the geosynchronous altitude. Results of covariance analyses which assess the orbit determination performance in all three categories are presented. Low circular orbits can be determined to subdecimeter or even a few-centimeters accuracy using up-looking differential GPS. Highly elliptical orbits, because of wide altitude range, require both up-looking and down-looking observing scenarios for optimum tracking. Among high circular orbits, geosynchronous satellites present the most difficult tracking challenge: the information content of ground-based observations is weak due to lack of temporal change in geometry; and the users are well beyond the GPS altitude and can hardly receive GPS signals. Inverted differential GPS, which requires the user to transmit signal ground GPS receivers can observe, appears ideal for tracking geosynchronous satellites.>