A batch-sequential filter for the bepicolombo radio science experiment

Precise trajectory reconstruction of an orbiting spacecraft is inherently related to the estimation of the gravity field of the central body. Gravity not only allows a good orbit determination, but also provides crucial information on the interior structure of the planet, and therefore constitutes an important scientific objective in many planetary missions such as BepiColombo, the ESA mission to Mercury. One of BepiColombo's investigations is the Mercury Orbiter Radioscience Experiment (MORE), whose main objective is the accurate estimation of Mercury's gravity field. This task will be accomplished by means of range rate measurements accurate to 0.003 mm/s (at 1000 s integration times), enabled by highly stable, multi-frequency radio links in X and Ka band. After an introduction to the mission and the MORE experiment, we report on numerical simulations aiming at a realistic assessment of the attainable accuracy in the determination of Mercury's gravity field. The best results are obtained with a batch-sequential filter, which proves to cope well the complexity of the noise and dynamical models.