BepiColombo mission: Estimation of Mercury gravity field and rotation parameters

BepiColombo mission shall answer a number of questions about Mercury. Among them: the rotation state of the planet, the static and dynamic gravitational field. Very precise range and range-rate tracking will be used together with on-board accelerometer data and the observation of landmarks on the surface of Mercury. This paper presents the achievable accuracy for the gravitational field coefficients up to degree and order 20 and the k2k2 Love number. Good knowledge of the accelerometer thermal noise is demonstrated to be required. The determination of the rotation state, in terms of obliquity and libration motion of the planet could be achieved by means of optical measurements and information obtained from the gravitational field. It is shown how the observability of the libration motion depends on the orbital plane orientation due to the 32 resonance of the planet spin motion with respect to the orbital motion around the Sun. An orbital plane with an angle of 0∘0∘ with respect to the Sun–Mercury periapsis line is shown to be the more appropriate. Results are computed by using the Gravity and Rotation State Estimation Software Tool for Solar System Bodies (GREST), a software tool developed by DEIMOS Space under ESA/ESOC contract.