Orbit Determination of IGSO/GEO Spacecraft Using BeiDou Inter-Satellite Link

Objectives: Inter-satellite link (ISL) technology can realize autonomous orbit determination of navigation satellites and improve accuracy of orbit determination. It can also support orbit determination of user spacecrafts, and the performance of orbit determination for user spacecraft with BeiDou inter-satellite link has not been validated. Methods: BeiDou medium earth orbit (MEO) satellites serve as reference satellites, BeiDou inclined geosynchronous orbit (IGSO) and geostationary earth orbit (GEO) satellites are used as user spacecrafts, and real inter-satellite link data between them are used to study orbit determination method of user spacecraft. Orbit determination experiments of IGSO and GEO satellites under different orbital plane distribution, number of satellites, link time distribution and duration of MEO satellites are carried out, and the orbit accuracy of IGSO and GEO satellites are analyzed in detail. Results: Results show that MEO satellites with established links are distributed across more orbital planes, the orbit determination accuracy of IGSO/GEO satellites is better. When 6 linked MEO satellites are distributed across three orbital planes, three-dimensional root mean square (3D RMS) of IGSO and GEO orbit errors are 45.3 cm and 55.0 cm, respectively. Compared to MEO satellites distributed in one or two orbital planes, orbit determination accuracies of IGSO/MEO are improved by 11.4%, 62.3% and 6.0%, 17.0%. When MEO satellites are evenly distributed across three orbital planes, the orbit accuracy of IGSO/GEO satellites improves as the number of the linked MEO satellites increases. When the number of satellites is increased from 3 to 9, the 3D RMS of IGSO and GEO orbit errors are improved from 79.4 cm and 150.8 cm to 34.6 cm and 38.3 cm, respectively. When the number of MEO satellites is increased to 24, the orbit determination accuracy of IGSO and GEO satellites are improved by 80.1% and 87.3% with 3D RMS reaching 15.8 cm and 19.1 cm, respectively. When using all 24 MEO satellites, the more uniform time distribution of satellite links and the longer linked time, the higher orbit determination accuracy. When 4-hour link duration is evenly distributed, orbit determination accuracy of IGSO and GEO satellites are 31.5 cm and 89.1 cm, respectively. When the linked duration is increased from 4 h to 12 h, the 3D RMS of IGSO and GEO orbit errors reach 16.5 cm and 26.2 cm with an improvement of 47.6% and 70.6%, respectively. The accuracy improvement is not significant when the linked duration is further increased. Conclusions: This study demonstrates that the BDS-3 inter-satellite link can provide orbit determination services for user spacecrafts with decimeter-level accuracy.