Dual Differential I-SBI Method for Investigating the Lunar Interior

Using several widely separated microwave transponders, fixed to the lunar surface, to measure differential range could be a helpful method in the investigating of the lunar interior. Compared to the LLR (Lunar Laser Ranging) method, it can potentially produce more accurate results. In this paper, a new method named dual differential I-SBI is proposed. The method does not need Ka-band digital transponders or CDMA (Code Division Multiple Access) signal structure, which allow for easier utilization. The key components for this method are coherent-mode transponders, two geographically close ground stations and numerically close operational frequencies for the transponders. It can be verified that the observables of this method contains the information related to the variation of the baseline which is constituted by the landers. An expected experiment will be performed to verify this method after the launch of Chang'e-5 mission, which is a Chinese lunar sample return mission. The error budget shows that the measurement accuracy could be approximately 1mm.