Applications of same-beam VLBI in the orbit determination of multi-spacecrafts in a lunar sample-return mission

Abstract

Same-beam VLBI means that two spacecrafts with small separation angles that transmit multi-frequency signals specially designed are observed simultaneously through the main beam of receiving antennas. In same-beam VLBI, the differential phase delay between the two spacecrafts and the two receiving antennas can be obtained within a small error of several picoseconds. As a successful application, the short-arc orbit determination of several hours for Rstar and Vstar, which are two small sub-spacecrafts of SELENE, has been much improved by using the same-beam VLBI data together with the Doppler and range data. The long-arc orbit determination of several days has also been accomplished within an error of about 10 m with the same-beam VLBI data incorporated. These results show the value of the same-beam VLBI for the orbit determination of multi-spacecrafts. This paper introduces the same-beam VLBI and Doppler observations of SELENE and the orbit determination results. In addition, this paper introduces how to use the same-beam VLBI for a lunar sample-return mission, which usually consists of an orbiter, a lander and a return unit. The paper also offers the design for the onboard radio sources in the lunar sample-return mission, and introduces applications of S-band multi-frequency same-beam VLBI in lunar gravity exploration and applications during all stages in the position/orbit determinations such as orbiting, landing, sampling, ascending, and docking.