Collaborative Multi-Rover Crater Exploration: Concept and Results from the ARCHES Analog Mission

Access to extreme terrain, like caves or craters, is a key challenge for future planetary exploration robots. Many experimental robotic systems either use innovative locomotion concepts or elaborate mission designs to explore more challenging terrain. However, this requires a highly-specialized task-specific robot design, limiting the scope of the robot's general application. We investigate an alternative approach, by enabling an existing team of rover systems to crater exploration as an additional opportunistic mission task. The rovers collaborate in a tethered abseiling operation, enhancing the locomotion capabilities of one member of the robotic team. We use our two planetary rover prototypes for crater exploration within the scope of a general multi-purpose multi-robot Moon analog mission. In this paper, we first outline the design of and the modifications to our rover systems and describe the general partial-autonomous setup of the experiment, including the robot collaboration for hooking the tether and the abseiling into the crater. Second, we showcase the feasibility of this concept during a Moon analog campaign on the volcano Mt. Etna, Italy, in 2022. At the site, the rovers successfully access the Cisternazza crater, a crater of approximately 150 m in width and 30 m in depth, featuring steep flanks of partially compacted and partially loose volcanic soil. The experiment showed the feasibility of collaborative manipulation for tethering the two rovers. It additionally demonstrated enhanced rover locomotion capabilities due to the winch, enabling safe crater exploration. We finally discuss the lessons learned from this experiment and the remaining implementation steps to achieve full locally autonomous crater exploration.