  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.
