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One of NASA's Mars rovers named Opportunity has been stuck in a martian sand dune for more than two weeks. Scientists are trying to figure out how to get it going again. And to do that, they've built a fake martian sand dune in a laboratory in California. NPR's Patricia Neighmond reports.
PATRICIA NEIGHMOND reporting:
Steve Squyres is the lead scientist for the rover missions. He says he was a little surprised when Opportunity got stuck in the first place, because it had been driving over what he thought was similar sandy terrain for months.
Mr. STEVE SQUYRES (Lead Scientist, Mars Rover Missions): There are these ripples out on the plains, and we've been driving happily up one side of one and down the other side for quite some time, and then for reasons that we're still grappling with, we just plowed right into this one, and so there was something different about this particular ripple than the other ones.
NEIGHMOND: Squyres says this ripple is higher than usual. It's about a foot tall and steeper, and the sand, he says, is more powdery and sticky. It caked on to the rover's wheels, making it all the more tricky to move. Squyres says the ground rule here is do no harm. Bad directions sent to the robot could dig it in more deeply. To prevent that, NASA decided to replicate the martian sand dune on Earth and then run an exact replica of the Mars rover through it.
(Soundbite of rover)
NEIGHMOND: That's the rover humming this week at the Jet Propulsion Laboratory in Pasadena.
Mr. RICK WELCH (Space Engineer): You can hear the wheels moving, but there's no--very little resistance from the soil, so basically you just hear the hum, the very faint hum of the motors turning.
NEIGHMOND: Rick Welch is a space engineer. He says re-creating an alien environment with just the right ingredients was an enormous challenge. Researchers used trial and error to come up with a recipe that seemed to match with the scant data they had from Mars, and as it turns out, the ingredients they finally arrived at were easily purchased at local home supply and hardware stores.
Mr. WELCH: We looked at what terrestrial materials we could drive around and pick up in the local area, and using a very fine powdered clay, also diatomaceous earth, which is what's used in pool filters, readily available, but it's a very fine powder, and also just using plain sand and mixing that together in about equal amounts, came up with this very nice, soft, powdery material that the rover would easily slip into and give some of the other features that we saw from Mars.
NEIGHMOND: Then they mixed up a batch of more than two tons of simulated martian sand. They dumped it into a giant indoor sandbox, which was first used to test-drive the rovers when they were being designed. Engineers then drove the rover replica into the sand. But it didn't sink like it did on Mars. Welch says they're not sure why. One reason may be that Mars has less gravity than Earth, and so martian sand doesn't get packed down the way it does here.
Mr. WELCH: Here on Earth, we mix it up and get it all fluffy. You can come back five minutes later, and it's started to actually self-compact under its own weight. And that will be less on Mars. That's something we can't replicate, because we don't have an anti-gravity chamber here at JPL.
NEIGHMOND: So Welch says they compensated for the greater gravity on Earth by digging the rover more deeply into the sand with their own hands, and for over a week, they tested different computer commands to try to move the rover's six wheels out of the sand. Yesterday the ground testing produced the first command actually sent to the rover on Mars. It was to straighten the wheels. After that, the big challenge will be to actually move the wheels out of the sand. Steve Squyres says he's confident they'll succeed, but it could take weeks. And once the rover gets out, he says, they will drive it differently.
Mr. SQUYRES: We're going to do it much more cautiously. We're going to try to thread our way through these drifts, staying down in the troughs between them rather than driving up over the crests, which was what got us into trouble here. We're fortunate in that these ripples that we got hung up in run north-south, and it turns out south is the direction that we're going. So we're sort of going with the grain. And rather than having to drive across the crest of all these ripples, we think we can pretty much stay in the troughs and proceed south that way.
NEIGHMOND: If all goes well, rover will head south toward the Erebus Crater. It's currently stuck right on the edge of an area called the etched terrain. Scientists have seen it from orbit--big, big parallel drifts of sand and fine debris--and they hope they'll steer clear of any more sand traps, but just in case, they're keeping their recipe for a martian sand dune. Patricia Neighmond, NPR News.
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