12. A Simulation Study of Orbit Determination for Lunar Probe via Relay Satellite

Chang’E-4 will be the first to achieve a soft landing on the far-side of the moon. The tracking and data transmission for Chang’E-4 will depend on a relay satellite on a Lissajous orbit around the Earth–Moon L2 point, and the four-way ranging measurement is expected to be obtained. The capability of orbit determination for Chang’E-4 is studied by simulation. The results show that the relay satellite can realize a near full time tracking for lunar probe. In terms of the orbit determination capability, the orbital accuracy of relay satellite is an important constraint. Once the tracking arc reaches 5 h, the orbit solution for lunar probe tends to be stable. However, the orbital accuracy is still one order of magnitude lower than that of relay satellite. For inter-satellite tracking, the stability of the satellite clock is another constraint. With 1 h auxiliary ground station tracking every day, an orbital accuracy of 100 m can be achieved.