'Hedgehog' robots will hop, tumble in microgravity

Researchers have developed the prototypes of a 'hedgehog' robot that will explore small bodies, such as an asteroid or a comet, by hopping and tumbling on the surface instead of rolling on wheels.
Hedgehog is a new concept for a robot that is specifically designed to overcome the challenges of traversing small bodies.
The project is being jointly developed by researchers at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California; Stanford University in Stanford, California; and the Massachusetts Institute of Technology in Cambridge.
"Hedgehog is a different kind of robot that would hop and tumble on the surface instead of rolling on wheels. It is shaped like a cube and can operate no matter which side it lands on," said Issa Nesnas, leader of the JPL team.

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.
"The spikes could also house instruments such as thermal probes to take the temperature of the surface as the robot tumbles," Nesnas said.

Two Hedgehog prototypes - one from Stanford and one from JPL - were tested aboard NASA's C-9 aircraft for microgravity research in June 2015.
During 180 parabolas, over the course of four flights, these robots demonstrated several types of manoeuvres that would be useful for getting around on small bodies with reduced gravity.

Researchers tested these manoeuvres on different materials that mimic a wide range of surfaces: sandy, rough and rocky, slippery and icy, and soft and crumbly.
"We demonstrated for the first time our Hedgehog prototypes performing controlled hopping and tumbling in comet-like environments," said Robert Reid, lead engineer on the project at JPL.
The JPL Hedgehog prototype has eight spikes and three flywheels. It weighs about 5 kg by itself, but the researchers envision that it could weigh more than 9 kg with instruments such as cameras and spectrometers. The Stanford prototype is slightly smaller and lighter, and it has shorter spikes.

The researchers are currently working on Hedgehog's autonomy, trying to increase how much the robots can do by themselves without instructions from Earth.
Their idea is that an orbiting mothership would relay signals to and from the robot, similar to how NASA's Mars rovers Curiosity and Opportunity communicate via satellites orbiting Mars. The mothership would also help the robots navigate and determine their positions.
The construction of a Hedgehog robot is relatively low-cost compared to a traditional rover, and several could be packaged together for flight, the researchers said.
The mothership could release many robots at once or in stages, letting them spread out to make discoveries on a world never traversed before.