'Scarab' the robot

Lowell Labaro Oct 1, 2007

The Field Robotics Center at Carnegie Mellon’s Robotics Institute has developed a prototype moon rover, “Scarab.” The robot has the ability to perform the challenging task of lunar prospecting.

The ultimate goal of lunar prospecting is to discover, extract, and utilize resources in the soil of other planets.

David Wettergreen, leader of Scarab’s software and autonomy development, said, “This is a technology development program that is focusing on extracting hydrogen and oxygen from lunar soil.

NASA currently has no plans for a robotic mission to the moon. However, Scarab provides developers and engineers a test bed for potential designs and ideas in order to be better prepared for a lunar mission in the future.

Wettergreen said that Scarab mainly serves as “early concept definition and technology development.”

NASA project manager John Caruso said, “Dark navigation and drilling were the major goals.”

Northern Centre for Advanced Technology Inc. (NORCAT) developed a drill for the robot.

According to a Carnegie Mellon press release, the drill is capable of “obtaining meter-long geological core samples and features a novel rocker-arm suspension that enables the robot to plant its belly on the ground.”

In constructing the robot, researchers had to make sure that the body of the rover was light but still capable of providing the required downward force for surface drilling.

According to John Thornton, a graduate student in mechanical engineering who contributed to the project, a drill-centric design was applied to procure the greatest amount of downward force.

By placing the drill at the center of the body, the robot still applies sufficient downward force while maintaining a slim, energy-efficient weight of 250 kilos.

Performing in dark and frigid environments posed another challenge to Scarab developers. Future moon prospecting rovers will be expected to operate and navigate in the depths of craters.

The lack of light in such environments would inhibit the navigational capabilities of any rover. To counter this obstacle, Scarab’s development team “is developing a low-power laser light striper and a position estimation system that will allow Scarab to model its surroundings,” said Wettergreen.

The light striper projects lines onto the ground, which are then captured by a camera. After analyzing the deformation of the stripes, the navigation system can determine the general layout of the terrain.

Mobility over the rough and uneven surfaces was also addressed in Scarab’s design.

According to Thornton, a technique called “differencing” was applied to the functioning of Scarab’s wheels and axles during transit. Differencing allows each wheel to be raised and lowered individually in order to accommodate turbulent terrain.

This technique allows all four wheels to maintain contact with the ground, while simultaneously allowing the body to stay parallel with the surface.

The design of the rover’s body also took mobility into consideration.

“Because of the way the vehicle raises and lowers, the bottom of the vehicle needed to be curved at certain locations to go over small mounds and inconsistencies and to be able to position for drilling on angles and obstacles,” said Caruso.

Furthermore, to perform its tasks, a lunar prospector must have a reliable and sustainable energy source.

To this end, researchers have utilized an advanced sterling radioisotope generator (ASRG). Wettergreen described an ASRG as “a device that converts the heat of isotope decay into electrical power.”
This generator provides energy at a high capacity of 10 years and low output at 100 watts, which means the rover would move slowly and utilize low power components.

If a rover needed to use more power for the purpose of traversing a slope or transmitting more data, it could store generator power in batteries. The energy could then be consumed faster.
The lifetime of the ASRG is the key to this approach. Caruso said, “It is mission enabling to have this power source.”

Lunar prospecting is to be performed inside a crater as opposed to the lunar surface. Once inside the crater, NASA hopes to find ice, which can be converted to hydrogen and oxygen, or liquid water.

These resources would then be processed by In Situ Resource Utilization Element (ISRU) to support a potential lunar outpost. Although NASA has no official plans in lunar prospecting, Scarab has made a significant contribution to the technology for such a mission in the future.

Caruso said that lunar prospecting has been part of “discussions that have been going on in the scientific literature for years.”