A new frequency synthesis approach to precisely track the spacecrafts using Same-Beam Interferometry

This article describes a new frequency synthesis approach to realize extremely accurate relative position determination for two spacecrafts with phase measurements at a variety of frequency separations. Both of the spacecrafts transmit one carrier wave phase modulated by two DOR sine tones at X-band, and one wave at S-band. These frequencies are set to resolve the cycle ambiguity of carrier wave at X-band from two group delays corresponding to the four DOR sub-carriers and one phase delay of the carrier wave at S-band. The procedure to resolve the cycle ambiguity is analysed and discussed in detail, and the corresponding conditions, such as prediction of light time, the transmission media, are also clarified based on mathematical analysis and the same-beam tracking data from SELENE mission. The results show that all the conditions to resolve the cycle ambiguity can be satisfied in Same-Beam Interferometry. Thus, the accuracy of the differential phase delay could be achieved within several picoseconds. This method can be used in the missions with challenging navigation requirements, such as planet-relative targeting, as well as rendezvous and docking around Moon and planets beyond.