Transforming Rover Image
The DuAxel rover in field tests in the Mojave Desert. The four-wheeled rover is composed of two Axel robots. (Credit: NASA/JPL-Caltech/J.D. Gammell)

NASA’s DuAxel, a pair of two-wheeled rovers each called Axel, can split in half with each half connected only by a tether that unspools as the lead axle approaches a hazard.

The idea behind creating two single-axle rovers that can combine into one is to maximize versatility: The four-wheeled configuration lends itself to driving great distances across rugged landscapes and the two-wheeled version offers a nimbleness that larger rovers cannot achieve.