Disturbance torque compensation of the BepiColombo spacecraft during interplanetary cruise flight using solar sailing effect

This paper addresses disturbance torque compensation of the interplanetary cruise flight to Mercury of the BepiColombo spacecraft. During the cruise flight, the spacecraft is nominally driven by the onboard solar electrical propulsion system, consisting of four ion thrusters, either one or two being used at any time, depending on available solar array power. Each thruster features a thruster vectoring capability which allows a compensation of the disturbance torques and possible motion of the centre of mass location. While operating a single ion thruster, the disturbance torques projected to the direction of the thrust force can not be compensated solely by the single thruster. It is common practice to use reaction wheels to allow the spacecraft attitude to be kept constant and to use continuous adjustment of the electric propulsion thrusters to provide continuous offloading of the wheels. However, when only one electric propulsion thruster is used, the wheel-offloading procedure needs to be periodically invoked by firing the attitude chemical thrusters what will lead to undesirable fuel losses during the cruise. This paper proposes a new method that avoids unnecessary fuel consumption when a single thruster is being operated. The new method is based on a solar sailing effect that can be generated by the solar arrays. Through an appropriate selection of the sun aspect angle of the solar arrays the uncompensated projection of the solar pressure torque can be fully eliminated. This paper gives details on this new approach.