Tether Management and Docking System for Multi-Robot Rappeling into Lunar Lava Tubes
In EASN Conference Proceedings, (EASN-2023), 5.9.-8.9.2023, Salerno, Campania, IOP Publishing Ltd., Terweidenstraat 28
Belgium, 2023. European Aeronautics Science Network (EASN).
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.