Contribution of VLBI for the Orbit Determination to Chinese Lunar Exploration Project

The S/X-band radiometric range/Doppler and very long baseline interferometry（VLBI）techniques are used in Chinese lunar exploration to track the probe. Measurement accuracy is improved for the application of new equipment and techniques. VLBI data plays a very important role in the orbit determination（OD）and lander positioning. VLBI data can improve short arc OD accuracy comparing with the range/Doppler data only. For the lunar orbit, Combining VLBI data helps to improve orbit accuracy especially in along-track and normal directions. Results also indicate that VLBI data contribute more to the OD when the probe is at the edge-on view than at the face-on view. Overlap analysis shows that the position consistency is about 20 m and better than 3 m in the radial direction for CE-3/CE-4 lunar orbit. The statistical positioning method is applied to determine the position for the CE-3 lander combined with 1 h range and VLBI data, and the accuracy is better than 50 m compared to the result of LRO camera.