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October
15, 2009: How do you fly on a world with no atmosphere?
Wings won't work and neither do propellers. And don't even
try that parachute!
NASA
engineer Brian Mulac has the answer. "All it takes is
practice, practice, practice," he says. "And of
course, thrusters."
The
space agency is perfecting the art using a prototype lunar
lander at the Marshall Space Flight Center:
"What
we've got here is a 'flying testbed' to help us to learn how
to hover1 and land on the Moon," says Mulac. He's 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.
The
electric-blue jets emerging from the lander look like some
kind of futuristic high-tech gas, but in fact they are just
ordinary compressed air.
"They
look blue in this photo because the cold air coming out of
the thrusters is interacting with our 'nice' Alabama humidity,"
explains Mulac. "The plumes are like miniature clouds.
They contain ice crystals that scatter blue light."
The
center of the prototype has one big thruster to cancel 5/6ths
of Earth's gravity. That leaves 1/6 g for the rest of the
thrusters--the same as gravity on the Moon.
"This
prototype's thrusters are in the same configuration as they
would be on the flight robotic lunar lander, so the control
algorithms and dynamics are similar," says project manager
Julie Bassler.
"That's
important," adds engineer Danny Harris, "because
we're validating the guidance, navigation, and control system
needed for a successful lunar landing."
And
if the lander gets out of control? "That never happens,"
says Mulac, "but just in case, we've surrounded the test
chamber with a huge net." The net is visible in the picture
as a background network of criss-crossed ropes and would intercept
the lander if it ever strayed off course.
So
far, the prototype has passed all tests with flying colors:
"Once we start a test, it's all autonomous," Mulac
continues. "An onboard computer directs the thrusters.
The flight profile is pre-programmed. We tell the craft where
to go and it goes there on its own."
"By
conducting these tests, we gain an appreciation for the design
of missions that land on airless bodies," says 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."
"It's
quite an engineering problem to solve," says Mulac. "With
our test bed, we're showing we can do it successfully."
Author: Dauna Coulter
| Editor:
Dr. Tony Phillips | Credit: Science@NASA
| footnotes
and more information |
| 1"This
isn't really a hovercraft, though," explains Mulac.
"Being able to hover is just a side-benefit of
the system that we use to test our stability and orientation
control. We're mainly focused on the ability to demonstrate
landing."
Partners
in this project include Johns Hopkins University Applied
Science Laboratory and the Von Braun Center for Science
and Innovation. Orion Propulsion in Huntsville, subcontracting
to Teledyne Brown Engineering, designed, built, and
tested the test bed's propulsion system.
Robotic
Lunar Lander -- NASA Picture of the Day |
|
