When they explore other planets, probes enjoy a perk many of us on Earth take for granted: gravity. But when it comes to investigating smaller celestial bodies up close, rovers don't have much to keep them on the ground. Space agencies aren't exactly keen on losing multimillion-dollar robots to the endless vacuum of space, which means it's up to engineers to develop bots that can independently overcome the challenges inherent to zero-gravity environments. SpaceHopper could be one such bot.
Conceived initially as an undergraduate student research project at ETH Zurich two and a half years ago, SpaceHopper is now the focus of five master's degree students and one doctoral student. The 11.4-pound robot features a triangle-shaped aluminum body measuring roughly 9.6 inches from point to point. Inside the body are a custom power distribution board, a microcontroller, an internal temperature sensor, three time-of-flight laser range sensors, an Nvidia Jetson Nano, and three Maxon motor controllers. These controllers connect with a leg at each tip of the triangle.
Zero-gravity environments technically aren't entirely devoid of gravity—instead, they have so little that it's virtually equivalent to zero when compared with Earth and other large terrestrial bodies. This means even small bodies have just enough gravity to help SpaceHopper return to the ground it's hopping on, even if it has to do some silly-looking leg movements to get there. When SpaceHopper moves, it uses its laser range sensors to determine its distance from solid ground, then swings its legs until it makes contact again. The result is successful, if slightly chaotic, "zero-gravity" locomotion.
The SpaceHopper team tested their robot in an artificial zero-gravity environment produced by the European Space Agency (ESA). Their parabolic flight mimicked the gravity found on Ceres, a dwarf planet in the middle main asteroid belt that divides Mars and Jupiter. Ceres' gravity (0.029 g) is minute compared with Earth's (1 g), but SpaceHopper managed to scramble from place to place for up to 15 jumps, after which a human operator had to intervene.
SpaceHopper isn't quite space-ready, however. In a preprint paper shared to the arXiv, the team notes that the robot isn't radiation-shielded and would require the addition of thermal insulation to survive in space. SpaceHopper also currently relies on an external motion capture system. This means it couldn't embark on its first mission before receiving an internal state estimation that could constantly estimate the robot's position and velocity as it moves. Still, SpaceHopper is a step toward the concrete exploration of small celestial bodies that remain nearly inaccessible.
