[meteorite-list] 'Hedgehog' Robots Hop, Tumble in Microgravity

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?feature=4712

'Hedgehog' Robots Hop, Tumble in Microgravity
Jet Propulsion Laboratory
September 3, 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.

"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.

During one of the experiments on the parabolic flights, the researchers 
confirmed that Hedgehog can also perform a "tornado" maneuver, in which 
the robot aggressively spins to launch itself from the surface. This maneuver 
could be used to escape from a sandy sinkhole or other situations in which 
the robot would otherwise be stuck.

The JPL Hedgehog prototype has eight spikes and three flywheels. It weighs 
about 11 pounds (5 kilograms) by itself, but the researchers envision 
that it could weigh more than 20 pounds (9 kilograms) with instruments 
such as cameras and spectrometers. The Stanford prototype is slightly 
smaller and lighter, and it has shorter spikes.

Both prototypes 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.

"By controlling how you brake the flywheels, you can adjust Hedgehog's 
hopping angle. The idea was to test the two braking systems and understand 
their advantages and disadvantages," said Marco Pavone, leader of the 
Stanford team, who originally proposed Hedgehog with Nesnas in 2011.

"The geometry of the Hedgehog spikes has a great influence on its hopping 
trajectory. We have experimented with several spike configurations and 
found that a cube shape provides the best hopping performance. The cube 
structure is also easier to manufacture and package within a spacecraft," 
said Benjamin Hockman, lead engineer on the project at Stanford.

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 say. The mothership could release many robots at once 
or in stages, letting them spread out to make discoveries on a world never 
traversed before.

Hedgehog is currently in Phase II development through the NASA Innovative 
Advanced Concepts (NIAC) Program, and is led by Pavone. The flight development 
and testing were supported by NASA's Center Innovation Fund (CIF) and 
NASA's Flight Opportunities Program (FOP), which were led by Nesnas. NIAC, 
CIF and FOP are programs in NASA's Space Technology Mission Directorate, 
located at the agency's headquarters in Washington. JPL is managed by 
the California Institute of Technology for NASA. Stanford University, 
MIT and JPL collaborate on the project.

For a complete list of the selected proposals and more information about 
NIAC, visit:

http://www.nasa.gov/niac

For more information about the Space Technology Mission Directorate, visit:

http://www.nasa.gov/spacetech


Media Contact

Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425
elizabeth.landau at jpl.nasa.gov 

2015-292