High-Precision VLBI Orbit Measurement Technology in the Chang'E-4 Mission

Chang'E-4（CE-4）achieved the soft landing and patrol survey on the far side of the Moon for the first time in the world. The S-band ΔDOR measurement technology is used in the relay satellite mission, and the new S-band ΔDOR observation data processing system is developed. During the prober mission, the VLBI system realized fast time-sharing observations for the relay satellite and lander-rover combination prober for the first time; and the Tianma radio telescope is used to calibrate the relay satellite antenna in orbit. Considering the characteristics of CE-4, the key technical issues to be solved by the VLBI technology are analyzed, and specific measures are proposed. The analysis of the measurement results during the real-time mission of the two spacecraft show that these technical measures play important roles in the accomplishment of mission goals.