The terrain on rocky planets and moons is a far cry from a smooth, paved road. Robotic explorers have to be versatile when it comes to the terrain; if they get stuck, that’s it for them. Nobody can give them a shove to help. The Resource Prospector 15 (RP15) is a prototype robotic lunar rover developed to tackle such terrains.

The RP15 is an exciting project, but there are uncertainties about its full capabilities. To gather more information, researchers have created a smaller 3D-printed prototype that can not only wheel around, but also lift its wheels and crawl. Once stuck in granular material, it can start paddling through it. It can literally “swim” up and down hills made of soil where normally the wheels wouldn’t be able to rotate. The design and description of the rover are published in Science Robotics. It has been tested on a variety of simulated terrains, truly pushing the limits of what a rover can do. 

“The rover was developed with a modular mechatronic architecture, commercially available components, and a minimal number of parts,” lead author Siddharth Shrivastava, from the Georgia Institute of Technology, said in a statement. “This enabled our team to use our robot as a robust laboratory tool and focus our efforts on exploring creative and interesting experiments without worrying about damaging the rover, service downtime, or hitting performance limitations.”

NASA lost the Spirit rover to this kind of snag when the robotic explorer got stuck on a sand dune in 2009. This led to the rover not getting enough sunlight to recharge its battery. The RP15 is designed to make sure this won’t happen again.

“In our previous studies of pure legged robots, modeled on animals, we had kind of figured out that the secret was to not make a mess,” senior author Dan Goldman explained. “If you end up making too much of a mess with most robots, you end up just paddling and digging into the granular material. If you want fast locomotion, we found that you should try to keep the material as solid as possible by tweaking the parameters of motion.”

“This combination of lifting and wheeling and paddling, if used properly, provides the ability to maintain some forward progress even if it is slow,” Dan Goldman explained. “Through our laboratory experiments, we have shown principles that could lead to improved robustness in planetary exploration – and even in challenging surfaces on our own planet.”