Space–Ground Joint Support Method in Autonomous Orbit Determination of BeiDou Satellites

When relying exclusively on inter-satellite links for autonomous orbit determination, it cannot suppress or eliminate the constellation overall rotation, rendering it incapable of determining its spatial orientation relative to terrestrial and celestial reference frames. To address these limitations, an autonomous orbit determination method for BeiDou Satellites is proposed by integrating satellite-to-ground, inter-satellite, and space-based orientation observations. This study introduces space-based orientation data between navigation satellites to provide inertial frame orientation references for the BeiDou constellation, while utilizing ground-based anchor stations to establish orientation references in the Earth-fixed frame. The results demonstrate that (1) In a 90-day autonomous operation within the inertial frame, the combined use of inter-satellite links and space-based orientation data achieves a 3D orbit position accuracy of 0.45 m. (2) In semi-autonomous operation, with Earth rotation parameter (ERP) updates every three days from ground stations, the 3D orbit determination accuracy reaches the decimeter level; using long-term predicted ERPs in conjunction with satellite-to-ground data, meter-level accuracy is maintained. (3) When the space-based orientation measurement noise is limited to 5 milliarcseconds, the accuracies of polar motion parameters xp and yp reach 2.23 milliarcseconds and 3.55 milliarcseconds, respectively, while the UT1–UTC parameter achieves an accuracy of 0.42 milliseconds. This work provides critical technical support for flexible autonomous navigation of the BeiDou system when the ground control stations are destroyed in the wartime and contributes to the independent determination of ERP within China.