Precisely Relative Positioning of Chang'E 3 Rover with SBI Delta VLBI Delay Measurements

Based on Chinese VLBI Network, the Chang'E 3 lander and rover are traced with the same beam interferometry (SBI) method. The SBI delta group delay and phase delay measurements are obtained respectively from the digital signal and telemetry signals of the onboard detectors. The two detectors are close to each other in the flat region of Mare Imbrium on the moon. We present the kinematically combined or statistical relative positioning of the rover with respect to the lander in two dimensions with lunar height constrained to the lander. Relative position accuracy was better than 100m with SBI delta group observations, while the accuracy reached 1m with SBI delta phase delay measurements. Our positioning method will play an important role in relative positioning during the course of separation and locking of spacecrafts in the future Phase III of Chinese lunar project and other future deep space projects.