Accuracy assessment of GPS satellite orbits

Abstract

Global Positioning System (GPS) orbit determination using data collected by the civilian tracking network CIGNET have been used in a variety of experiments, along with data collected from special campaigns to augment the global tracking data. These experiments have been used to investigate the fidelity of the satellite force and kinematic models with the goal of improving the GPS ephemeris accuracy. Software has been developed for the preprocessing of GPS pseudo-range and phase measurements, including procedures for cycle slip correction. A multi-satellite orbit determination program, MSODP, allows for satellite-dependent force models, including high-low satellite constellations. Assessments of orbit accuracies derived from measurements collected in campaigns with nearly global networks have been performed with a variety of techniques, including determination of baselines known from SLR or VLBI, the computation of long, multi-week arcs and the comparison of predicted ephemerides with determined ephemerides. These results have provided indications of inadequacies in the force models, especially with the nongravitational forces, particularly those aspects associated with eclipsing.