Testing theories of relativity with ranging via dual Radio links

The BepiColombo mission to Mercury has Radio Science objectives that explore planetary gravity and interior structure as well as tests of aspects of the general theory of relativity. Both classes of science objectives rely on high precision Doppler and ranging at dual wavelengths, X-band and Ka-band. In particular, the relativistic tests require ranging between a ground station and the spacecraft to 15 cm (+/- 5 cm), which is approximately one order of magnitude better than current capabilities at X-band. A new scheme has been developed to reach this accuracy via three techniques: (1) utilizing the simultaneous propagation of two links modulated with ranging codes in order to calibrate the dispersive media, (2) recording the uplink reference tone in the downlink data stream to provide accurate calibration, and (3) employing open-loop receivers with user-developed post-processing algorithms to produce the final data products. This paper¹² will present the proposed instrumentation being prototyped, the encountered challenges and their solutions, as well as the expected results and their implications to the scientific investigations of BepiColombo and future missions.