WASHINGTON — Students at the Massachusetts Institute of Technology (MIT) in Cambridge are testing a prototype planetary explorer that would cover large swaths of alien terrain by hopping from one landing site to another. The testing of the second-generation lunar hopper is being carried out under the supervision of engineers from the nearby Draper Laboratory with an eye toward competing for the Google Lunar X Prize in 2012.
Draper and MIT have been working with Sparks, Nev.-based Sierra Nevada Space Systems and Manassas, Va.-based Aurora Flight Sciences Corp. as part of the Next Giant Leap team, one of 20 vying for the Google Lunar X Prize, a $20 million purse that will be awarded to the first privately funded group to send a robot to the Moon. To qualify for the prize, the robot must travel 500 meters across the lunar surface and transmit video, images and other data back to Earth.
The team’s Moon hopper design is based on existing spacecraft built by Sierra Nevada, while Aurora Flight Sciences is contributing experience gleaned from developing small vertical-takeoff-and-landing aircraft. Draper Lab is offering navigation and control expertise, and the students, led by former NASA astronaut Jeff Hoffman, built the prototype vehicle.
Dubbed the Terrestrial Artificial Lunar and Reduced Gravity Simulator, or Talaris, the Moon hopper prototype uses two propulsion systems, including a primary system using an air-breathing electric ducted fan propulsion system that counters the effects of Earth’s gravity. A second cold-gas propulsion system uses impulsive, self-contained propellant to simulate operations in the space environment and will verify Draper Lab’s guidance, navigation and control algorithm in reduced gravity.
The four large fans attached to the corners of the hopper counteract five-sixths of the Earth’s gravity “such that the cold-gas control system feels like it’s operating in a lower-gravity environment like the Moon,” said Seamus Tuohy, director of space systems at Draper Lab.
MIT expects to complete initial test flights of the Talaris hopper this summer with the hope that the Earth-bound prototype could lead to a new class of robotic precursors capable of traversing long distances in short periods of time, gathering scientific data and even collecting samples at multiple sites.
Rather than competing with traditional orbiters, landers and rovers, hoppers could complement these vehicles, quickly covering long distances while carrying scientific payloads.
“It provides an alternate way of doing what I’ll call regional science, as opposed to very local science,” Tuohy said, using Spirit — the NASA Mars rover that is now bogged down in sand after six years of traversing the red planet — as an example.
“If you look at the rover that just got stuck on Mars after years of operation, one thing I think that’s not commonly known is just how little distance it covered. What an achievement it was … but it only covered kilometers,” he said, adding that hopping vehicles are able to traverse much larger areas.
A hopping vehicle also does not require a complex navigation system, because unlike a surface-bound rover, the hopper has no need to navigate over and around craters, boulders or valleys.
“You could go into a crater on the Moon,” Tuohy said. “So the places where we’re thinking of being able to find and trap water ice on the Moon, among the many other challenges is [the fact] that these craters are very deep. And sending a rover from the crater edge down into the crater to try to touch the ice is pretty challenging, whereas in a hopper it’s just a new landing site.”
Moreover, sophisticated navigation and control systems used to negotiate a lander’s descent and pick up landmarks at or near the touchdown zone add “a lot of power and a lot of mass” to a spacecraft, Tuohy said. Although a hopper would land in the same manner as a traditional lander or rover, the accuracy of the landing is not as critical, Tuohy says.
“Once you land you can use the navigation systems you have on Earth to locate yourself very precisely,” he said, adding that even if the hopper arrives a kilometer or more off target, it would be only “a hop or two” away from reaching that target.
However, the hopper concept does have at least one drawback: The distance it can cover depends on the amount of propellant it can carry.
“The bigger the tank, the bigger the hop, so there is a trade there,” he said, adding that the amount of propellant required to fuel the hopper would likely affect the cost to launch it.
Tuohy said Draper and MIT evolved the hopper concept while searching for technical and engineering challenges that could spark student interest in space. Talaris, he said, combines students from a variety of engineering and science backgrounds to study “essentially cool things that haven’t been done before.”
Although planetary rovers are not new, the hopper concept could add a new dimension to robotic planetary exploration, one that Tuohy said could inspire a new generation of engineers, technologists and scientists.
“Not that it’s getting boring, but there is an established level of technology that is accepted and is mature,” he said.
The hopper concept also has the potential to maximize science experiments and observations in a single mission. Because the hopping vehicle is designed to operate in a “very controlled hover-hop” in which it ascends a short distance above the surface and hovers at a consistent altitude to its next landing site, it could conduct experiments or make observations and measurements en route.
“The reason we went this way is you can actually do science along the way,” Tuohy said, adding that Draper and MIT have demonstrated Talaris in various stages of completion to officials at NASA’s Goddard Space Flight Center in Greenbelt, Md.
“They’ve given us some kind of hints … it’d really be neat if you can do science along the way,” he said, adding that the hopper concept “actually opened up what we think may be a new operational way of doing science that you couldn’t do before, or that you wanted to do before but didn’t have the mechanisms to do.”
Tuohy said he hopes Talaris and the Next Giant Leap effort will breed confidence in the emerging technology and that “at some point in the near future there would be a funded mission that would incorporate this operational approach of hopping.”
