Tether Management and Docking System for Multi-Robot Rappeling into Lunar Lava Tubes

Zusammenfassung (Abstract) :

Subsurface lava tubes have been detected from orbit on both the Moon and Mars. These natural voids are potentially the best place for long-term human habitations, because they offer shelter against radiation and meteorites. Skylights, formed by partial cave ceiling collapse, provide an entrance to several of the previously discovered lava tubes. Multi-robot collaboration may allow us to reach and explore these unknown cavities, where sending astronauts without prior knowledge is an evitable risk. This work presents the development and implementation of a novel Tether Management and Docking System (TMDS) designed to support the vertical rappel of a rover through a skylight into a lunar lava tube. The TMDS connects two rovers via a tether, enabling them to cooperate and communicate during such an operation. Its hardware comprises an active winch and two interfaces, a passive HOT- DOCK and a passive EMI. Although particular robotic systems are used to demonstrate the feasibility of the task, the device can link any robots equipped with the active counterparts of these standard interfaces. The height of the TMDS platform can be adjusted by two linear actuators in order to fa- cilitate docking and transport. A framework independent interface provides control over the platform height and the velocity at which the winch releases the tether. The winch speed gets synchronized with the wheel speed of the rappeling rover to allow a controlled descent. The development of hardware and software components is part of the Cooperative Robots for Extreme Environments (CoRob-X) project. In January and February 2023, the approach was thoroughly tested in a three-week lunar analogue mission on Lanzarote, Canary Islands. The tests were divided into four mission phases (MP1-4): At first, the three rovers LUVMI-X, SherpaTT and Coyote3 collaboratively explore and map the area around the skylight (MP1). Subsequently, LUVMI-X ejects a sensor cube into the skylight to gather information about rock formations along the vertical walls and from the landing site (MP2). In the third phase, Coyote3 rappels down into the skylight assisted by movements of SherpaTT’s manipula- tor (MP3). Once Coyote3 has reached the ground, it undocks from the TMDS and explores the lava tunnel (MP4). In this paper, we will discuss the results of our work, focusing on the successful rappel, sharing our experiences and lessons learned from the field test campaign.