Advanced radio science instrumentation for the mission BepiColombo to Mercury

Radio science experiments of BepiColombo will provide a detailed mapping of Mercury's 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 metr ic theories of gravity. The classical tests of the solar gravitational defl ection and the precession of perihelion could improve the measurement of th e post-Newtonian parameters beta and gamma by 2-3 orders of magnitude, to a value in the range 10(-6)-10(-5). At these levels, violations of General R elativity 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 g round equipment is needed. The target two-way accuracy is 20-30 cm. for ran ge and 3 x 10(-4) cm/s for range rate (at 1000-10,000 s integration time). This precision requires the capability of transmitting and receiving at mul tiple frequencies (to reduce plasma noise) and larger modulation bandwidths for improved ranging performances. We propose an architecture of the onboa rd and ground radio frequency subsystems which combines minimization of mas s and power, technological feasibility, and adequate phase stability and ra nging accuracy. (C) 2001 Published by Elsevier Science Ltd.