Hopping, tumbling, and flipping over are not typical maneuvers to be expected from a spacecraft exploring other planets. Traditional Mars rovers roll around on wheels and they can't operate upside-down. But on a small body like an asteroid or a comet, the low-gravity conditions and rough surfaces make traditional driving all the more hazardous. Hedgehog is a new concept for a robot that is specifically designed to overcome the challenges of traversing small bodies. The project is being developed by researchers at NASA's Jet Propulsion Laboratory, Stanford University, and MIT. The basic concept is a cube with spikes that moves by spinning and braking internal flywheels. The spikes protect the robot's body from the terrain and act as feet while hopping and tumbling. There are two Hedgehog prototypes - one from Stanford and one from JPL - and both maneuver by spinning and stopping three internal flywheels using motors and brakes. The braking mechanisms differ between the two prototypes. JPL's version uses disc brakes, and Stanford's prototype uses friction belts to stop the flywheels abruptly.