Over the past two-and-a-half years, a group of students from ETH Zurich have been developing a robot with three spindly legs that was designed to be able to hop like an insect in microgravity. That's right -- the curious little machine was built for space, specifically for the exploration of small celestial bodies like asteroids and moons. SpaceHopper, as the robot is called, could thus provide us more information to advance our understanding of life's origin, of the origin of water on our planet and of asteroids as potential providers of valuable resources. It has no preferred orientation, so it can go in any direction, and it has nine motors that give it the capability to jump long distances in low-gravity environments. The robot can even self-right after landing, ensuring the safety of any scientific payload it may carry. Since SpaceHopper was made for use on asteroids and moons, which have very little gravity compared to Earth, it has to be tested under conditions similar to those environments first.

We present SpaceHopper, a three-legged, small-scale robot designed for future mobile exploration of asteroids and moons. The robot weighs 5.2kg and has a body size of 245mm while using space-qualifiable components. Furthermore, SpaceHopper's design and controls make it well-adapted for investigating dynamic locomotion modes with extended flight-phases. Instead of gyroscopes or fly-wheels, the system uses its three legs to reorient the body during flight in preparation for landing. We control the leg motion for reorientation using Deep Reinforcement Learning policies. In a simulation of Ceres' gravity (0.029g), the robot can reliably jump to commanded positions up to 6m away. Our real-world experiments show that SpaceHopper can successfully reorient to a safe landing orientation within 9.7 degree inside a rotational gimbal and jump in a counterweight setup in Earth's gravity. Overall, we consider SpaceHopper an important step towards controlled jumping locomotion in low-gravity environments.