Down in Antarctica, there are some big, mysterious lakes. They're locked away under thick permanent sheets of ice. Scientists would love to know more about them, and later this year, they plan to explore one large Antarctic lake with the help of a swimming robot. First, they have to make sure it can withstand the cold, so a team recently ventured to Lake Mendota in Wisconsin to put their robot to the test.

NPR's Nell Greenfieldboyce was there.

(Soundbite of chain saw)

Professor PETER DORAN (Earth and Environmental Science, University of Illinois; Lead Investigator): Initially we were talking about a 30-by-30 hole and once they started getting here and cutting, that seems a little unrealistic, so we're cutting back our expectations.

NELL GREENFIELDBOYCE: Peter Doran is from the University of Illinois in Chicago. He is standing on a vast expanse of white ice next to a couple of guys with chain saws. They're carving out thick blocks of ice to open up a rectangle of blue water. It looks like a swimming pool.

Prof. DORAN: Yeah, that's the other thing we could do is the polar swim.

GREENFIELDBOYCE: But this is where a crane is going to drop a round robot the size of a VW Bug. The robot has sensors, and it can carry science equipment and swim around by itself to map a body of water.

Prof DORAN: So far, this thing has had a very cushy life swimming around in Mexican caves that are about 25 degrees Celsius.

GREENFIELDBOYCE: That's 77 degrees Fahrenheit.

Prof. DORAN: So we want to put it to the test in the cold.

GREENFIELDBOYCE: The robot is sitting inside a nearby building. The machine looks like some kind of mechanical fruit.

Ms. VICKIE SIEGEL (Stone Aerospace): Oh, I don't know, I usually say that it looks like a big tangerine.

GREENFIELDBOYCE: Vickie Siegel works with Stone Aerospace, the company that built this bot. She says it's named ENDURANCE after the ship that Ernest Shackleton took to Antarctica. But some people call the robot the clementine.

Ms. SIEGEL: It's bright orange. It's definitely bright orange.

GREENFIELDBOYCE: The color is on the special foam that helps it float. She says the foam is her favorite part, and not just because it looks cheerful.

Ms. SIEGEL: There's nothing that can go wrong with the foam, really. Everything else is a potential problem.

GREENFIELDBOYCE: The whole point of today is to find those problems. A forklift takes the robot out of its garage. The researchers hook it to a cable, and a crane lifts it up. It looks like a UFO flying over the ice.

(Soundbite of communication)

GREENFIELDBOYCE: What do you do?

Ms. SIEGEL: Be prepared to pull the robot out if we need to.

GREENFIELDBOYCE: The robot sinks gently into the water with a small burble. A bright green cable runs from the robot up to the second floor of a building on shore. That's the control room.

On a computer screen, you can see what the robot sees: the underside of the ice. But something's wrong.

Mr. BILL STONE (Head, Stone Aerospace): It's dead in the water as far as mobility. Everything else is up and running but it's like telling your feet to move and it don't want to move. You know, they're talking to you saying, I can't move, I got an error signal (unintelligible) you're going, well, why.

GREENFIELDBOYCE: Bill Stone, the head of Stone Aerospace, says it's possible that the cold has knocked out electrical connectors, but who knows.

Mr. STONE: We're going to just go down one by one the things that we think we can debug, and if we have to tonight, we're going to tear the vehicle apart.

GREENFIELDBOYCE: That's just what they do. The next morning, the robot is in the garage. Its cheerful orange foam has been taken off, and its guts are spilling out. Then the team puts the whole thing back together and sends it out again. First, they have to hack out the ice that froze over their swimming pool.

Folks in the control room try firing the robot's thrusters. There's just a small ripple in the water as it starts to rotate, still attached to the crane's cable.

Ms. SIEGEL: That's a good sign. The thrusters are working.

GREENFIELDBOYCE: So they unhook the robot. Bill Stone radios up to the control room.

Mr. STONE: I guess you didn't copy the last - you're free; you're clear. You are drifting a little bit on to the left-hand side of the ice, about a quarter of the vehicle is under the ice.

GREENFIELDBOYCE: And soon the orange robot is gone, somewhere beneath our feet.

Over the next couple of days, the team troubleshoots more glitches. Everything has to be working before the robot goes to Antarctica this fall. It's headed for Lake Bonney, a big body of water that's perpetually under 12 to 15 feet of ice.

And if that effort goes well - who knows? Someday a robot like this could be sent off to Europa, that's a moon of Jupiter. It has a thick icy crust and maybe, inside, a secret ocean.

Nell Greenfieldboyce, NPR News.

NORRIS: We've put photos of ENDURANCE taking it's experimental plunge on our Web site,

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