Initial Results of Precise Orbit Determination Using Satellite-Ground and Inter-Satellite Link Observations for BDS-3 Satellites

By the end of 2018, China has successfully launched 19 BDS-3 satellites into orbit. These BDS-3 satellites are equipped with high-precision inter-satellite link (ISL) payloads and have successfully realized inter-satellite two-way pseudorange measurements. We introduce the ISL observation model and carry out precise orbit determination (POD) for eight BDS-3 satellites using L-band satellite-ground and Ka-band ISL observations. The L-band satellite-ground data is collected from six international GNSS monitoring and assessment system (iGMAS) stations located in China's territory. The results show that the root mean square (RMS) value of POD residual for the ISL observations is better than 6 cm, and the estimations of ISL equipment time delays vary within ±0.15 ns for these BDS-3 satellites. When the ground L-band tracking station is confined to the territory, the addition of ISL observations can significantly improve the orbit determination accuracy. By the orbit overlap comparison, the errors of satellite orbits obtained by combined POD are about 13 cm in 3D and about 3 cm in radial direction, yielding an improvement of 85% compared to ground-only POD using 6 stations in China.