Free Astronomy Magazine November-December 2015

ASTRONAUTICS crogravity environment, would be too light to get a hold on the terrain, and if it did, it may be so speeded up that it will launch it- self off the surface. Effective exploration of small solar system bodies thus requires a new kind of engi- neering approach. The solution to this prob- lem began to emerge in 2011, when Marco Pavone, Stanford University, and Issa Nes- nas, NASA’s Jet Propulsion Laboratory, pro- posed to use small hedgehog-shaped ro- bots (and thus generically known as “Hedge- hogs”), capable of hopping and rolling on any type of surface, while remaining per- fectly operational regardless of their posi- tion with respect to the ground. In recent years, Stanford University and JPL, in collaboration with the Massachu- T he video above sum- marizes the Hedgehog con- cept. Left, close- up of a Hedgehog prototype dis- played in a rock- et garden. [JPL/ NASA, California Institute of Tech- nology] setts Institute of Technology (MIT), have designed several versions of these robots, in order to assess which may be the most suit- able shapes and inter- nal devices for oper- ating on smaller bod- ies. The engineers have come to the conclu- sion that the most suit- able structure for a Hedgehog robot con- sists of a cube with spikes on the corners, capable of moving thanks to the pulses generated by the spin- ning and abrupt brak- ing of three internal flywheels, positioned in three different spa- tial directions. By suitably adjusting the speeds of the fly- wheels and the ac- tion of their respective brakes, the resultant kinetic energy is trans- mitted to the entire ro- bot structure, prompt- ing it to move in the directions associated with the flywheels. Depending on the amount of energy gen- erated and the speed