Daisy Chain Navigation and Communication in Underground Environments

Lava tubes on Moon and Mars are of significant interest as potential sites for human habitats and for finding traces of life in the sheltered environments they provide. Robotic operations in underground environments such as cave systems, tunnel systems, and mines are also of great interest for military operations, search and rescue, and resource prospecting. Navigation in such underground environments is challenging, as the unstructured walls, floors and ceilings make simultaneous location and mapping (SLAM) algorithms perform poorly, and as odometry is complicated by wheel slippage on sandy and slippery floors. At the same time, non-uniform material densities, wave absorption, and irregularly shaped tunnels challenge radio communication. Expanding on the concept of daisy chaining communication breadcrumbs to relay radio signals into and out of an underground environment, the paper explores the concept of using visual navigation beacons to enable a robot of tracking its position and orientation without other references. The navigation beacons feature LEDs arranged in five-point tracking targets commonly used in spacecraft rendezvous and docking sensor systems. Using multi-colored targets, an array of cameras, and the QUEST navigation algorithm, the robot is able to determine its position and orientation relative to the closest beacon. Deploying beacons near obstacles or at bends or forks in the cave, the robot can then daisy chain its location and orientation relative to the mouth of the cave through a simple multiplication of homogenous transformation matrices. The paper details the system design, the beacon design, and the computation algorithms. It also provides the results of verification experiments and discusses lessons learned in the design, implementation and test of the concept.