Bepicolombo gravity and rotation experiment in a pseudo drag-free system

The Mercury Orbiter Radioscience Experiment (MORE) on-board the BepiColombo mission was designed to provide an accurate estimation of the gravity field and the rotational state of Mercury. The Mercury Planetary Orbiter (MPO) is equipped with on-board instrumentation that allows highly stable, multi-frequency radio links in X and Ka band in order to achieve range rate and range coherent two-way measurements accurate to 0.003 mm/s (at 1000 s integration time) and 20 cm, respectively. Precise trajectory reconstruction allows us to estimate accurately the spherical harmonic coefficients of the Hermean gravity field, at least up to degree 35, the tide and the rotational parameters (right ascension and declination of the pole and physical librations in longitude). The determination these parameters provides crucial information on the interior structure of the planet. A full numerical simulation of the radioscience orbit determination process has been carried out taking into account the data provided by the on-board Italian Spring Accelerometer (ISA). This allows us to realize a software version of a drag-free system. In this paper, we report on the results of these numerical simulations aiming at a realistic assessment of the attainable accuracy in the determination of the gravity field and the rotation of Mercury with the implementation of a pseudo drag-free orbit determination process.