GNSS-based orbit determination method and flight performance for geostationary satellites

The utilization of Global Navigation Satellite System (GNSS) is becoming an attractive approach for the orbit determination of geostationary orbit (GEO) satellites. As a flight test for the feasibility of GNSS-based orbit determination at high orbit altitude, a GEO satellite named TJS-2 is launched. This satellite is equipped with a high-gain antenna, a pre-amplifier, and a high-sensitivity receiver. This study investigates the methods of high-sensitivity processing for the GNSS side lobe signals and the onboard orbit determination filter to improve navigation performance. In accordance with flight data, the GNSS signal characteristics, including availability, position dilution of precision (PDOP), carrier-to-noise ratio density (C/N₀), and quality of observations, are analyzed. The mean number of GPS, GLONASS, and BDS satellites tracked is 7.6, 4.6, and 0.3, respectively. The mean PDOP of GPS, GPS + GLONASS, and GPS + BDS satellites tracked is 10.8, 8.4, and 8.9, respectively. The distribution of C/N₀ and the number of observations with respect to the nadir angles are illustrated. For GPS, GLONASS, and BDS, the corresponding standard deviation of the pseudorange noise is 7.7, 16.1, and 5.2 m, and that of the carrier-phase noise is 37.6, 41.8, and 53.7 mm, respectively, in terms of C/N₀ < 30. We give the navigation performance through comparisons with two reference orbits. The root mean square (RMS) of position accuracy of the onboard solutions in radial, along-track, and cross-track directions is 20.90, 3.34, and 2.68 m, respectively. The RMS of position accuracy in radial direction is reduced to 4.13 m after the optimization of the orbit determination filter parameters. For the single-epoch least squares solution, the velocity accuracy can improve from 0.25 to 0.16 m/s when GPS and GLONASS observations are combined. We discuss the performance of single-epoch least squares solutions combined with BDS observations. A remarkable improvement in the vertical dilution of precision is obtained when BDS inclined geostationary orbit observation is involved. The RMS of position and velocity accuracy is reduced from 39.30 to 16.90 m and from 0.26 to 0.09 m/s, respectively.