Special Reports

NASA engineers are testing out a giant, six-legged robot that could pick up and move a future Moon base thousands of kilometres across the lunar surface, allowing astronauts to explore much more than just the area around their landing site.

In a 2005 report about its exploration plans, NASA said it wanted to set up a base at a fixed location on the Moon after initially returning humans there in 2020.

But a gargantuan robotic vehicle called ATHLETE (All-Terrain Hex-Legged Extra-Terrestrial Explorer) could change that. Measuring about 7.5 metres wide, with legs more than 6 metres long, the robot could act essentially like a turtle, carrying the astronauts' living quarters around on its back.

It was designed by engineers at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, US, who are now testing two small-scale prototypes of the robot.

The astronauts' 15-tonne living quarters, or habitat, could be mounted on ATHLETE before sending it to the Moon in a lunar lander. That would solve one major problem for NASA – how to lift the habitat off the lander, whose cargo area may sit up to 6 metres above the ground, and set it down at a desired location.

ATHLETE's wheel-tipped legs are so long, "it just steps right off and carries the payload anywhere you want," says JPL's Brian Wilcox, who heads the ATHLETE project.

'Tiptoe out'

The habitat's solar arrays would power the robot, which could also store power in fuel cells. In Wilcox's scenario, the habitat would stay permanently attached to ATHLETE, which could roam from place to place and simply squat down to bring the habitat door close enough to the ground for astronauts to get in and out (watch a video of ATHLETE lowering itself).

ATHLETE would normally drive around the lunar surface, since that is much more energy-efficient than walking. But whenever the robot encountered very bumpy ground, or its wheels got mired in deep soil, it could switch to walking.

"If we get into ankle-deep dust, we'll lock the wheels, use them as feet, and just tiptoe out, effectively," Wilcox told New Scientist. Watch a video of ATHLETE walking and driving.

Even in driving mode, ATHLETE could handle pretty difficult terrain, keeping itself level by extending some legs and contracting others. This would let it handle slopes of up to 35° where traction was good, and up to 25° where it was slippery.

Since the robot could walk over the most difficult terrain, it could use smaller wheels – as well as smaller motors and gears to drive them – than it could if it simply had to drive. As a result, ATHLETE is 25% lighter than a non-walking vehicle capable of traversing the same terrain would be – a precious savings given how expensive it is to send each kilogram of cargo to the Moon.

Lifting power

ATHLETE could move autonomously if needed, using software based on what is used in the Mars rovers Spirit and Opportunity.

But Wilcox thinks astronauts would probably control the vehicle most of the time. Ground controllers on Earth could also operate the robot, since radio signals can make a round trip between Earth and the Moon in just about 2.5 seconds, and the vehicle moves relatively slowly, with a top speed of 10 kilometres per hour.

Stereo cameras mounted at six places on ATHLETE's frame would provide the operator with a 3D view of the vehicle's surroundings in all directions.

As a bonus to ATHLETE's use as a vehicle, its legs have special mounts on them that allow the robot to use various tools to grasp things, drill into the ground, scoop up soil, or do other tasks (watch a video of it using tools). The legs can also be used as arms to lift heavy objects (watch a video of two ATHLETE robots lifting a mock lunar module off its mount).

Nomadic life

NASA is taking the robot seriously. ATHLETE was discussed in the second and most recent round of planning for operations by the agency's Lunar Architecture Team, which was completed in 2007.

The study, called LAT-2, points out that with ATHLETE-type robots, astronauts would no longer be tied down to a fixed base. Instead, they could live a nomadic life, driving across the lunar surface, setting up camp temporarily at an interesting spot, and using another NASA vehicle called Chariot to explore the surroundings before picking up and moving to the next interesting place.

Several ATHLETEs could be used on the Moon to move around various base components, such as the habitat and laboratory.

Even with its turtle-like pace of less than 10 km/h, ATHLETE could traverse huge swaths of the Moon's surface. At an average speed of 5 km/h, it could travel 1000 kilometres in eight days, which is a significant fraction of the Moon's circumference of about 11,000 kilometres.

'Pole to pole'

"We proposed basically pole to pole exploration, where you'd land at one pole and explore sites down through the equatorial region and end up at the other pole," Wilcox says. "We're working on designs for wheel drives and so on – motors, bearings, gears – that have 10,000 kilometres of life."

NASA is planning to test the mobile base scenario in a desert location in the southwestern US starting in late 2008. The tests would include people in spacesuits and ATHLETE robots moving mock lunar habitats across the desert's surface. Over the next few years, the team hopes to test drive the vehicle over long distances of more than 500 kilometres.

Wilcox presented videos of the ATHLETE prototypes in March at the Lunar and Planetary Science Conference in Houston, Texas, US.

Robots - Learn more about the robotics revolution in our continually updated special report.