ESA GNC Conference Papers Repository

The Martian Moons eXploration (MMX) mission led by the Japan Aerospace Exploration Agency (JAXA) aims at studying Phobos and Deimos, with a launch planned mid-2024. It includes a small rover (about 30kg) carried out jointly by the French Space Agency (CNES, Centre National des Etudes Spatiales) and the German Aerospace Center (DLR, Deutsches Zentrum für Luft- und Raumfahrt), released from the main spacecraft to explore the surface of Phobos. The MMX rover survival depends on its ability to charge its battery, powered by a solar array (SA) fixed with respect to the rover body. For that purpose, the attitude control system? (SKA, System für die Kontrolle of the Attitude) manages the orientation of the rover, using the locomotion system? (its "legs") and based on a sun sensor measurements. Conceptually, the system stems from a classic Attitude Determination and Control System?? (ADCS), but the specifics are due to the dynamic interaction between the wheels and the regolith: mouvements limitation to avoid sinkage, delays in the control loop. This paper presents the SKA architecture, through the various challenges encountered: limited design flexibility with major changes during the development, small knowledge of Phobos' expected soil, "nanosatellite philosophy" constraints and in particular very tight schedule to meet the JAXA delivery date (mid-2023). The design drivers were to create the most simple, robust and efficient system to orient the rover in order to maximize the battery charge, while ensuring the rover stability and addressing all of the above issues. A particular focus is made on the preliminary simulation results. Finally, the way forward is outlined with the development and validation steps.