Precise Orbit Determination of Combined GNSS and LEO Constellations with Regional Ground Stations

Abstract

The distinctive high orbits, regional coverage and stationary characteristics of BeiDou Geostationary Earth Orbit (GEO) satellites result in the poor geometric diversity with respect to ground stations and the difficulty for Precise Orbit Determination (POD). Considering that BeiDou is a regional system currently, the global ground stations cannot effectively ameliorate POD geometry, especially for GEO and IGSO satellites. Integrating the LEO-onboard GNSS data would be an effective way to improve the estimation of BeiDou orbits since LEO’s faster motion can significantly enhance geometric diversity. In this paper, we study the POD of combined GNSS and LEO constellation with regional ground stations in China, where the LEO constellation plays the role of moving tracking stations to ameliorate the poor POD geometry resulting from regional ground stations. The Iridium system is used as the LEO constellation and the LEO-onboard and ground tracking GNSS data are all simulated. The POD of combined GPS, BeiDou and LEO constellation is conducted with 8 ground stations in mainland of China. To balance the computation burden and POD accuracy, the different LEO satellites are selected for combined POD while the orbits of remained LEO satellites are computed with solved GPS and BeiDou orbits. With the LEO satellites increasing, the orbits of all GPS and BeiDou satellites are significantly improved, especially for along-track direction of GEO satellites. With the regional ground stations, the sub-decimeter-level orbit accuracies are achievable for BeiDou GEO and IGSO satellites, and centimeter accuracies for BeiDou MEO and GPS satellites. Furthermore, the impact of code precision on combined POD is numerically analyzed.