MMX - development of a rover locomotion system for Phobos

The MMX mission (Martian Moons eXploration) is a robotic sample return mission of the JAXA (Japan Aerospace Exploration Agency), CNES (Centre National d'Etudes Spatiales ) and DLR (German Aerospace Center) for launch in 2024. The mission aims to answer the question on the origin of Phobos and Deimos which will also help to understand the material transport in the earliest period of our solar system and the most important question how was the water brought on Earth. Besides the MMX mothership (JAXA) which is responsible for sampling and sample return to Earth a small rover which is built by CNES and DLR shall land on Phobos for in-situ measurements similar to MASCOT (Mobile Asteroid Surface Scout) on Ryugu. The MMX rover is a four wheel driven autonomous system with a size of 41 cm x 37 cm x 30 cm and a weight of approx. 25 kg. Multiple science instruments and cameras are integrated in the rover body. The rover body is basically a rectangular box, attached at the sides are four legs with one wheel per leg. When the rover is detached from the mothership, the legs are folded together at the side of the rover body. When the rover has landed passively (no parachute, braking rockets) on Phobos, the legs are autonomously controlled to bring the rover in an upright orientation. One Phobos day lasts 7 earth hours, which gives for the total mission time of 3 earth months, the number of about 300 extreme temperature cycles. These cycles and the wide span of surface temperature between day and night are main design drivers for the rover. This paper gives a short overview on the MMX mission, the MMX rover and a detailed view on the development of the MMX rover locomotion subsystem