Exoskeleton shows running best on Moon

NewScientist.com news service
David Shiga, Cambridge

Video Available

Future astronauts should run, not walk, across the lunar surface to conserve energy, new laboratory tests suggest. The tests were done using an MIT-built exoskeleton that mimics the experience of moving around in a spacesuit.

Astronauts move differently on the Moon than on Earth because of the Moon's weaker gravity and the constricting properties of spacesuits. So Christopher Carr and Dava Newman of MIT in Cambridge, US, have devised a way to simulate that motion in the hopes of designing better spacesuits and planning future lunar activities.

They reasoned that walking inside a pressurised spacesuit is like wearing an air-filled balloon. Like balloons, the suits resist bending and tend to want to return to their original shape, making it harder for Moon-walking astronauts to bend their legs at the knee.

So the researchers built an exoskeleton to simulate this, based on a design by another MIT scientist, Hugh Herr, who creates devices to aid people with disabilities. The exoskeleton consists of fibreglass rods that run the length of the wearer's legs and clip into modified cycling shoes.

Like a pressurised spacesuit, the exoskeleton resists bending at the knee, applying a force that tends to straighten the leg again. Intriguingly, this spring-like property makes running more efficient than walking for an exoskeleton-clad person. That's because the extra springiness helps to recover a higher percentage of the energy put into each stride while running.

The researchers believe that the same effect makes running the more efficient choice for space-suited astronauts on the Moon, something they had already suspected from watching videos of Apollo lunar missions. "The spacesuit is storing energy," Carr says, explaining that the air-filled spacesuit legs act like springs.

Less restrictive

Indeed, Apollo astronauts have reported such experiences. "It seems like I could run forever on the Moon and my legs would not get tired," wrote Alan Bean in a book describing his 1969 visit to the lunar surface. And Harrison Schmitt, the last Apollo astronaut to set foot on the Moon, said he skied across the surface, becoming "the fastest man on the Moon."

Knowing that running is more efficient than walking could help future astronauts explore the Moon or Mars, Carr says. "If you're out somewhere stuck in your spacesuit, running low on oxygen, and you have to get back to base, you should run, not walk, because the energy per unit distance is lower for running," he told New Scientist.

It is also an important consideration for mission planners designing safety rules for astronauts, he says. In the Apollo missions, NASA had rules about how far astronauts could venture from the safe haven of their lunar lander, based on how far they could safely walk before their spacesuit oxygen would run out.

"It turns out that walking is not the most efficient way," Carr says. "If you knew that you could run back, then potentially you could be less restrictive in your mission."

For the full effect of Moon walking, the laboratory Carr and Newman used for their research can also simulate lunar gravity. By tying the exoskeleton-clad person to a cord that runs up to the ceiling and is attached to a spring, the researchers can adjust the downward force to match the Moon's surface gravity, which is one-sixth that of Earth.

Exoskeleton Study