Determination of the Orbit of Chang’E-4 Relay Satellite Under Sparse Observation

Chang’E-4 relay satellite successfully entered the Earth-Moon L2 Halo orbit on June 14, 2018, and assumed the data transmission function between the ground-based measurement and control station and Chang’E-4 lander. At present, Chang’E-4 relay satellite is in sparse observation mode, with an average of 4~5 days for each observation. This paper analyzes the orbit determination accuracy of Chang’E-4 relay satellite circling the Earth-Moon L2 in January 2021. The orbit accuracy of the relay satellite around the L2 point is better than 2km, and the arc including the VLBI delay and delay rate reaches the level of 100 meters. Under the premise of VLBI observation, reasonable allocation of the coverage period of the ranging and velocity measurement arcs can effectively improve the orbit accuracy under the same data coverage.