Flying a spacecraft on a planet with little or no atmosphere presents a definite technical challenge. Wings and propellers are useless, so NASA is practicing the art of flying by thruster on a prototype lander to touch down on an air-less moon.

"It's quite an engineering problem to solve. With our test bed, we're showing we can do it successfully," said engineer Brian Mulac at NASA's Marshall Space Flight Center in Huntsville, Ala. "All it takes is practice, practice, practice. And of course, thrusters."

This week, several teams of private individuals are competing for NASA prize money by test-flying their own mock moon landers as part of the Northrop Grumman Lunar Lander Challenge. About $1.65 million of a $2 million purse offered by NASA for the best mock moon lander in two different challenges is up for grabs. Some of the award money has already been won, with two teams — Texas-based Armadillo Aerospace and California's Masten Space Systems — competing for the $1 million first prize.

Armadillo Aerospace has already qualified for the top prize and won first place in a smaller competition last year. Masten Space Systems has qualified for second prize in the smaller contest and is hoping to snare the $1 million top prize during a series of flight tests slated for today and Thursday.

Floating on air

That competition, however, is separate from the work Mulac and his team are doing. The NASA researchers are conducting the tests in collaboration with other engineers from NASA, the John Hopkins University Applied Physics Laboratory, and the Von Braun Center for Science and Innovation in Huntsville.

They have outfitted their lunar lander with four nozzles that release compressed air, acting as a force against the ground to push the vehicle up. The thrusters release a flow of air that appears electric-blue as it shoots out of the lander.

"They look blue in this photo because the cold air coming out of the thrusters is interacting with our 'nice' Alabama humidity," Mulac explained. "The plumes are like miniature clouds. They contain ice crystals that scatter blue light."

To simulate what it will be like for a lander on the moon, where the gravity is much weaker — about one-sixth that on Earth — the team built in a fifth, large thruster. The force from this nozzle effectively cancels out most of Earth's gravity, making it easier for the mock lunar lander to push off against the ground, as it would be on the moon.

The mock-up allows engineers to test not just lunar locomotion, but also the systems humans will use to remotely operate a lander once it reaches our celestial satellite.

"We're validating the guidance, navigation, and control system needed for a successful lunar landing," said engineer Danny Harris.

Though the lander is pretty tame, the engineers have installed a net around its practice playground - visible in the background of the picture - just in case it got out of control.

"That never happens," Mulac said.

The team hopes the work they do could lend itself not just to future moon trips, but perhaps to landers on other planets as well.

"By conducting these tests, we gain an appreciation for the design of missions that land on airless bodies," said NASA planetary scientist Barbara Cohen. "Many scientifically interesting places in the solar system are airless. Besides the moon, we'd like to visit Mercury, asteroids, Europa and other airless destinations. What we learn here could have a broad application."

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