Four-wheeled robotic rovers may be a good choice for the exploration of other planets, but they could conceivably get stuck at the bottom of deep craters. NASA's DuAxel rover is designed with that in mind, as it splits in two for steep descents.
Designed via a partnership between the NASA Jet Propulsion Laboratory and the California Institute of Technology, DuAxel takes its name from the fact that it's actually made up of two of NASA's existing Axel robots. Each one of these is designed to move around on two wheels, dragging a multi-purpose link shaft behind it. For the DuAxel, the two Axels' links are plugged into either side of a central module, creating a single four-wheeled vehicle.
The rover stays in that configuration while traversing relatively flat expanses of the Moon, Mars or wherever. Once it reaches the edge of a crater or other steep-walled geological feature, the Axel on that side disengages, rolling down the wall.
It's not totally on its own as it does so, though, since it's still joined to the rest of the rover by a tether that extends out of its link. That tether provides power to the rappelling Axel, and allows it to remain in communication with the topside section of the rover, which is now serving as an anchor and base station.
As the Axel makes its way down, it utilizes onboard sensors to analyze the soil, while mapping its surroundings and steering around obstacles via an integrated camera system. Once the crater-exploring mission is complete, the main rover simply reels it back up. The Axel then links back into that rover, transforming it into a four-wheeled vehicle again.
You can see the DuAxel taking part in field tests in the Mojave Desert, in the video below.
Source: NASA via IEEE Spectrum
