Qualification of the MMX Rover Locomotion Subsystem for the Martian Moon Phobos

Planetary rovers have proven their function and value for the Earth moon as well as Mars in the past decades. While these celestial bodies have a gravity of the same order of magnitude as the Earth, wheeled locomotion has never been performed on a body with much lower gravity. Within the Japanese Martian Moon eXploration (MMX) mission, a wheeled rover will land on the Martian Moon Phobos with a gravity of about 1/2000 of the Earth gravity. The Robotic and Mechatronics Center of the German Aerospace Center (DLR-RMC) has designed and built the locomotion subsystem (LSS) for this rover. As the first ever driving gear for milli-gravity, the LSS needed to undergo a comprehensive qualification campaign. Due to the very challenging timeline of this project, the extent of the campaign needed to be carefully tailored to the needs of the mission. This work describes the concept of the verification including some crucial tailoring choices that have been made. The individual domains of verification are then described in detail with their scope, setup, procedure and results. The goal of this publication is to give a good overview and a detailed insight into the verification of the LSS for milli-gravity. Besides follow-up missions to Phobos, this work is also a good foundation for the qualification of future driving gears for low gravity environments or small rovers in general.