Advanced radio science instrumentation for the mission BepiColombo to Mercury

Radio science experiments of BepiColombo will provide a detailed mapping of Mercuryʹs gravity field and important information about its deep internal structure. The global orbital solutions, obtained from precise radio metric data, entail also very accurate tests of General Relativity and other metric theories of gravity. The classical tests of the solar gravitational deflection and the precession of perihelion could improve the measurement of the post-Newtonian parameters β and γ by 2–3 orders of magnitude, to a value in the range 10−6–10−5. At these levels, violations of General Relativity due to scalar fields, remnant of the inflation age, could occur. In order to achieve the scientific objectives in geophysics and fundamental physics, a suitable radio frequency instrumentation both for onboard and ground equipment is needed. The target two-way accuracy is 20–30 cm for range and 3×10−4 cm/s for range rate (at 1000–10,000 s integration time). This precision requires the capability of transmitting and receiving at multiple frequencies (to reduce plasma noise) and larger modulation bandwidths for improved ranging performances. We propose an architecture of the onboard and ground radio frequency subsystems which combines minimization of mass and power, technological feasibility, and adequate phase stability and ranging accuracy.