September 5, 2015

'Hedgehog' Robots Hop, Tumble in Microgravity

While a Mars rover can't operate upside down, the Hedgehog robot can function
regardless of which side lands up. Credit: NASA/JPL-Caltech/Stanford

(September 5, 2015)  Hopping, tumbling and flipping over are not typical maneuvers you would expect from a spacecraft exploring other worlds. Traditional Mars rovers, for example, roll around on wheels, and they can't operate upside-down. But on a small body, such as an asteroid or a comet, the low-gravity conditions and rough surfaces make traditional driving all the more hazardous.

Enter Hedgehog: 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 in Pasadena, California; Stanford University in Stanford, California; and the Massachusetts Institute of Technology in Cambridge.

NASA's C-9 aircraft for microgravity research gave two Hedgehog prototypes
a ride in June 2015 to test their maneuvers. Credit: NASA

"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 maneuvers that would be useful for getting around on small bodies with reduced gravity. Researchers tested these maneuvers 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.

Hedgehog's simplest maneuver is a "yaw," or a turn in place. After pointing itself in the right direction, Hedgehog can either hop long distances using one or two spikes or tumble short distances by rotating from one face to another. Hedgehog typically takes large hops toward a target of interest, followed by smaller tumbles as it gets closer.

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