MELISSA BLOCK, host:

Today, mission managers at NASA announced how they plan to extricate the Mars rover called Spirit from a predicament. Last April, the rover drove into some soft soil and got stuck.

As NPRs Joe Palca reports, even if the plan fails, the Rover missions have already been successful beyond anybodys wildest dreams.

JOE PALCA: Its hard to blame mission scientist Jim Bell of Cornell University for sounding a bit celebratory when he greets caller.

Professor JIM BELL (Astronomy, Cornell University; Mission Scientist, Mars Pathfinder Mission): Happy sol 2082 of our 90-day mission.

(Soundbite of laughter)

PALCA: Sol is what scientists call a Martian day, slightly longer than an Earth day. Actually, I spoke with him earlier in the week. Today is sol 2084, nearly six Earth years on Mars for what was originally designed to be a three-month mission. Bell is the scientist in charge of the panoramic cameras, or pancams. Theyve been sending back remarkable pictures, just take a look on our Web site, npr.org.

Prof. BELL: We never imagined, of course, that they would be doing this well. But for the pancams, we passed our quarter-million image mark.

PALCA: Did you so crazily over-designed these that they just, you know, they were built for 90 days, but they could last a decade or have you been lucky or either can you see any signs of wear?

Prof. BELL: Its a little bit of both. I mean you cant really talk about over-designing for something that youve never built before. Sony can tell you exactly how long any of its TVs are going to last because they build millions of them. But with space vehicles, theyre one-offs, theyre one-shot deals.

PALCA: Or in this case two-shot deals, because there are two pancams working on Mars: one on the rover Opportunity, the other on the rover Spirit. And its Spirit thats gone and got itself into trouble. Last April, as it was driving south, it broke through a thin layer of crusty soil. What was underneath was extremely fine-grain soil, and Spirits wheels quickly got stuck.

Mr. JOHN CALLAS (Manager, Rover Project): We havent found a clear solution to how to get Spirit out of its predicament.

PALCA: John Callas is the rover project manager. He says the situation is challenging. One wheel on the rover stopped working years ago, now another may be in trouble. And the rovers underbelly, what Callas calls the belly pan, is perilously close to some rocks. And perhaps worst of all, every time theyve tried to move the rover, it sunk a little deeper. Sinking much further would be disastrous.

Mr. CALLAS: Because if you put the belly pan of the rover on the ground, thats pretty much game over in terms of trying to get the rover out, because then you would be bearing the weight of the rover on the belly pan and not on the wheels, where you need the traction.

PALCA: So after months of working on the problem, on Monday, the team will send the rover instructions to try backing out the way it came in. Managers sound hopeful, but not optimistic. Cornells Jim Bell says even if the rescue plan fails, there is still science that Spirit can do. In addition to taking pictures, its robotic arm still works. So Bells says it can do things like

Prof. BELL: analysis of these salty deposits that the rover is stuck in. I mean, its a great place to get stuck if you have to be stuck somewhere.

PALCA: On the other side of Mars, Opportunity is still rolling along. Its on a 12-mile trek across a sandy plain to a crater scientists want to explore. Bell says Opportunity is still making cool discoveries. Just the other day, it came across a large rock.

Prof. BELL: The hope is that this is a piece of Mars that comes from somewhere else. It was thrown out by a big impact crater, and it just happens to have landed in our path. And this is kind of a free way to sample more of Mars than we have been sampling where we are.

PALCA: Possibly one more feather in the rovers already well-decorated cap.

Joe Palca, NPR News, Washington.

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