High-Precision Orbit Determination of the Small TJU-1 Satellite Using GPS, GLONASS, and BDS

Tianjin University-1 (TJU-1) is a small low-Earth-orbiting (LEO) meteorological satellite equipped with a multi-global navigation satellite system (GNSS) receiver that provides the dual-frequency pseudorange and carrier-phase measurements from Global Positioning System (GPS), Global Navigation Satellite System (GLONASS), and BeiDou Navigation Satellite System (BDS), including BDS-2 and BDS-3. In this contribution, the quality of GNSS data during the period of 2022/31–2022/37 is assessed, and the precise orbit determination (POD) based on the onboard GNSS data is conducted. Assessing the pseudorange measurement accuracy, it reveals that the GPS and BDS-3 are comparable, followed by BDS-2, and GLONASS the worst. The POD experiments demonstrate that the orbit precision of all single-GNSS solutions is almost at an equivalent level of 2.2–3.4 cm, in terms of the overlapped orbit consistency, and the GPS-based solution is slightly worse than the BDS-based one and the GLONASS-based one is worse than other two. According to the orbit differences between different solutions, the orbit accuracy of single-GNSS solutions is inferred to be at the level of about 4.7–6.2 cm. With the multi-GNSS fusion, the precision and inferred accuracy of orbits could be improved significantly to 1.7–2.1 cm and about 1.7–3.7 cm, respectively. Furthermore, the root mean square (RMS) of posteriori carrier-phase residuals for all the IGSO/MEO satellites is at the level of 7–15 mm in different single-GNSS and multi-GNSS fusion solutions. These performances have fully demonstrated that the centimeter-level POD is easily achievable for small LEO satellites by using the multi-GNSS receiver.