The BepiColombo mission to Mercury: Reaction wheels desaturation manoeuvres and the ISA accelerometer ΔV⇒ measurements

The Mercury Planetary Orbiter will be a three-axis stabilized spacecraft and nadir pointing to Mercury center-of-mass. The pointing accuracy, needed for the very ambitious goals of the ESA space mission to Mercury denominated BepiColombo, is reached thanks to the onboard reaction wheels, and it is also required during the unobserved arcs. The unavoidable manoeuvres of desaturation of the reaction wheels, which are necessary to remove the accumulated angular momentum, represent a clear reduction of the accuracy of the objectives of the ESA space mission. Indeed, these manoeuvres are performed through the spacecraft thrusters and directly impact the accuracy of the propagated state-vector of the satellite at the beginning of the subsequent observed arc. Their impact is quantified by their number, position along the orbit and, especially, in the uncertainty in the linear momentum transferred to the spacecraft. The present paper is devoted to prove the feasibility of the speed variation measurements produced by the thruster thanks to the onboard accelerometer, ISA. Therefore, such measurements may be an essential ingredient in order to preserve the accuracy of the BepiColombo Radio Science Experiments and of other onboard instruments pointing accuracy, as is the case of BELA. This additional capability of ISA strengthens once more the key role of the accelerometer in the BepiColombo mission to Mercury.