Study on differential phase delay of same-beam VLBI in rendezvous and docking of Chang'E-5

The Chang'E-5 (CE5) ascender achieved lunar orbit autonomous rendezvous and docking with orbiter-returner successfully on 5 December 2020. Same-beam Very Long Baseline Interferometry (VLBI) (SBI) observations were performed for the first time for autonomous rendezvous and docking in lunar orbit. In this paper, by studying the CE5 rendezvous and docking data observed by the Chinese VLBI network and analyzing the residual differential phase delay of the autonomous control phase, we successfully captured the maneuver of the 5 km holding of the orbiter-returner. The differential phase delay (DPD) data of the far-range guidance phase were used to perform orbit determination of the ascender and orbiter-returner successfully. The results of orbit determination show that the DPD data can improve the relative position accuracy between the ascender and the orbiter-returner, and the residual root mean square of the DPD data is 5 ps. Furthermore, when one of the probes has only DPD data, its orbit can also be determined.