February 28, 2008
In a car commercial, it would sound odd: active suspension, six-wheel drive with independent steering for each wheel, no doors, no windows, no seats and the only color available is gold.
But NASA's latest concept vehicle is meant to go way off-road, as in 240,000 miles from the nearest pavement, and drive on the Moon. NASA is working to send astronauts to the Moon by 2020 to set up a lunar outpost, where they will do scientific research and prepare for journeys to more distant destinations.
Built at NASA's Johnson Space Center in Houston, the new design is one concept for a future lunar truck. The vehicle provides an idea of what the transportation possibilities may be when astronauts start exploring the Moon. Other than a few basic requirements, the primary instruction given to the designers was to throw away assumptions made on NASA's previous rovers and come up with new ideas.
"To be honest with you, it was scary when we started," says Lucien Junkin, a Johnson robotics engineer and the design lead for the prototype rover. "They tasked us last October to build the next generation rover and challenge the conventional wisdom. The idea is that, in the future, NASA can put this side-by-side with alternate designs and start to pick their features."
One of the first standards to go was the traditional expectation that a vehicle should have four wheels. Mars rovers Spirit and Opportunity, still cruising around the Red Planet, have already proved the value of a couple of extra wheels. When one of the six wheels became inoperable, the rovers had no problem rolling on using the remaining five.
With the number of wheels decided, the next question was how those wheels should turn. On a car, the front wheels turn a few inches in either direction, and both wheels point in the same direction. On this rover, all six wheels can pivot individually in any direction, regardless of where any other wheel points. To parallel park, a driver could pull up next to the parking place, turn all the wheels to the right and slide right in.
Of course, astronauts will not have trouble finding a parking space on the Moon. But the feature, called crab steering, has advantages for a vehicle designed to drive into the craters of the Moon. If a slope is too steep to drive down safely, the vehicle could drive sideways instead, no backing up or three-point turns required. The all-wheels, all-ways steering also could come in handy when unloading and docking payloads or plugging into a habitat for recharging.
Introducing crab steering drove the concept in several other ways. If the rover's wheels turn to drive in a different direction, the driver needs to be able to do the same. The driver stands at the steering mechanism because sitting in a spacesuit is not comfortable or practical. The astronaut's perch, steering mechanism, driver and all, can pivot 360 °.
"The Apollo astronauts couldn't back up at all because they couldn't see where they were going in reverse," says Rob Ambrose, assistant chief of the Automation, Robotics and Simulation Division at Johnson. "If you have a payload on the back or are plugging into something, it could be really important to keep your eyes directly on it."
The vehicle also can be the ultimate low-rider. It can lower its belly to the ground, making it easier for astronauts in spacesuits to climb on and off. Individual wheels or sections can be raised and lowered to keep the vehicle level when driving on uneven ground.
Some, all or none of these features may be selected for the design of a rover that eventually goes to the Moon. NASA's lunar architects currently envision pressurized rovers that would travel in pairs, with two astronauts in each rover. The new prototype vehicle is meant to provide ideas as those future designs are developed.
"This rover concept changed the whole paradigm," says Diane Hope, program element manager for NASA's Exploration Technology Development Program at NASA's Langley Research Center, which sponsored the vehicle's development. "It's not something I would have expected. It provides an alternative approach."