During a field test in the Mojave Desert, the DuAxel robot separates into two single-axled robots so that one can rappel down a slope too steep for conventional rovers. The tether connecting both Axels not only allows the one robot to descend the slope while the other remains anchored in place, it also provides power and a means of communication with the anchoring robot above.

The DuAxel project is a technology demonstration being developed by roboticists at NASA's Jet Propulsion Laboratory in Southern California to see how this unconventional rover might fill a niche in the exploration the Moon, Mars, and beyond.

More information about Axel can be found here: https://www-robotics.jpl.nasa.gov/systems/system.cfm?System=16