WASHINGTON—They think they can, they think they can.
More than a month after a Mars rover on autopilot got stuck in a foot-high dune, space engineers are laboring to guide the six-wheeled vehicle out. Their progress to date totals just over a foot, but it's been steady, and that's heartening to those who've discovered how tricky the task is.
"We're trying to be SO careful," Jim Erickson, the manager of the $900 million Mars rover project, said in an interview.
Never before has any space vehicle been trapped for so long.
Erickson called the miring "a headache," but added: "If we didn't find anything on Mars except what we'd already seen, we wouldn't be learning very much."
You can see the mired exploration vehicle Opportunity on NASA's Web site in a 10-second videotape loop. Its front wheel is churning away like a snow blower chomping into a drift. Note, however, that the clip compresses 11 days of effort.
Before you start kibitzing, consider the situation:
_ Command center engineers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., can't just let the air out of the vehicle's tires. Opportunity's 10-inch wheels are made from solid aluminum blocks.
_ It can't gun its way out. The solar-powered 380-pound rover has only one very low forward gear and a top speed of one-third of a mile per hour.
_ Rocking the rover out of the dune by shifting gears forward and back repeatedly isn't an option either. That's because it takes 10 minutes to transmit a command from Earth to Mars and another 10 to get back video images of the command's effects.
"We could preprogram it to rock back and forth, but we wouldn't know when to stop," said Patrick Whelley, a graduate student in geology at Arizona State University in Tempe. He's one of about 220 NASA personnel, contractors and students who've been working to free the rover since it got stuck April 26. Knowing when to stop matters, because another dune, perhaps more treacherous, lies 10 to 15 feet from Opportunity.
"We don't want to go too far too fast," Erickson said.
Instead, project engineers did what mired Earthly motorists never do: two weeks of intense reconnaissance without once hitting the accelerator.
Their focus was on the vehicle's wheel treads. They're stubby blades that run at right angles to the tire's edges and across its 6-inch surface, making the tires look like paddle wheels.
Opportunity's high-resolution cameras showed a dust-like substance compacted so tightly between the blades that the rover's wheels were, in effect, left bald and spinning. Analysts also realized that while the dune looked like many others, it was a little steeper—maybe 14 degrees. The rover had broken through its crust into a never-before-encountered substance that's as fine as talcum powder and flecked with sand-sized grains.
That made it a case for Robert Sullivan, a planetary geologist at Cornell University in Ithaca, N.Y., and a specialist in simulating Martian conditions. Sullivan took command of the Jet Propulsion Laboratory's test bed, an enclosed sandbox the size of a big indoor swimming pool. The idea was to create soil like that in the dune and run simulations using test vehicles that are clones of the Martian rover.
"Guys in pickup trucks hit every Home Depot in the L.A. basin," recounted Steve Squyres, a Cornell astronomer who is the principal scientific investigator on the project. The quest: to buy up Home Depot's stocks of sand and clay and a very fine substance used in swimming pool filters called diatomaceous earth.
To simulate Martian gravity, which is a third of Earth's, experimenters stripped one of the test rovers of two-thirds of its weight. One problem they couldn't solve was humidity. There's none on Mars and sometimes lots in Pasadena, which affected how Sullivan's soil compounds caked.
Soon, the Opportunity team was ready for action. Experimenters had run countless simulations in their sandbox. They had computed the likely sideways slippage if they rotated the wheels. They had estimated how deeply the rover could sink into the dune and survive.
On May 11, Pasadena commanded the rover to straighten its wheels. Two days later, Pasadena ordered those wheels to rotate 2.5 times, or about 80 inches.
The results: movement of 1.1 inches forward, 0.19 inch sideways and 0.18 inch downward.
The crucial dimension was the downward one, Erickson said. "If it had been any more, we would have stopped and rethought our plan."
Since then, Opportunity has moved forward an average of 0.5 percent of the total distance that its wheels have rotated. That comes to 1.1 feet ahead out of 213 feet spun.
Test-bed simulations produced the same results, according to Squyres, "and the rover eventually got out every time."
He won't estimate how long it will take for Opportunity, however.
What will NASA do if Opportunity gets free of the dune?
"We'll head back into it," Erickson said, because "when we know how to deal with this type of material, we can use our knowledge to develop a new capability."
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A video of the mired Mars rover Opportunity is available online. To see the video, go to www.nasa.gov/vision/universe/solarsystem/mer(UNDERSCORE)main.html and click on "Movie." The page also offers a day-by-day narrative of the recovery effort.
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(c) 2005, Knight Ridder/Tribune Information Services.
PHOTO (from KRT Photo Service, 202-383-6099): SCI-MARS
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