Swarm Navigation in Lunar Caves: The First Proof-of-Concept Mission on Lanzarote

Exploring lunar lava caves is currently under research spotlight. These caves could serve as ideal shelters for astronauts and instruments, protecting them from dramatic temperature variations and space radiation. However, so far, humans have only limited knowledge about these lunar caves. Robotic swarms are an emerging technology suitable for rapidly exploring large lunar caves. With the ability to optimize trajectories, the swarm can gather spatial-temporal information most efficiently. However the swarm will face persistent challenges in positioning, navigation, timing (PNT), communication and sensing once entering the lava cave. These challenges stem from the lack of infrastructure, the complexity of underground environments and the unpredictable radio propagation conditions.We propose a self-organized radio network, providing multi-hop communications as well as precise time and position references without requiring additional infrastructure such as global navigation satellite systems (GNSSs) or base stations. In addition, the swarm can utilize either extra sensors or communication signals propagating through the network for environmental sensing. At the German Aerospace Center (DLR), we design compact and portable nodes with ultra-wide band (UWB) technology, which can be easily carried and deployed by robots and are thus suitable for proof-of-concept in space-analog missions. In this paper, we provide a comprehensive overview on the design of our UWB swarm navigation system, according to the development steps, namely, designing mission concepts, establishing a self-organized network, conducting measurements, localizing the nodes, and performing radio-based environmental sensing. We also share insights from the first lunar-analog swarm cave navigation mission conducted in the lava cave Cueva de los Naturalistas, Lanzarote, in 2023, where we collected a massive amount of high-quality data, and showcase the plausibility of swarm navigation and sensing in lava caves with preliminary results.