GUY RAZ, host:
We're back with ALL THINGS CONSIDERED from NPR News. I'm Guy Raz.
Tomorrow, two astronauts aboard the International Space Station will put on their space suits and go back outside to finish a repair job. A cooling pump on the station failed two weeks ago. That's left the crew inside without a critical backup system.
The astronauts have already been out twice. One of the spacewalks lasted more than seven hours and occasionally sounded like an episode of "This Old House."
Unidentified Man #1: Okay, I see pocket A. And I think I can get it in here with just releasing the (unintelligible).
Unidentified Man #2: You should be able to release the flap on your left hand there. And down at the right side should be a (unintelligible) that the (unintelligible) will go in.
RAZ: NPR science correspondent Joe Palca has been watching the space station repairs, and he joins me now.
JOE PALCA: Hi.
RAZ: Why is replacing this pump so important?
PALCA: Well, these cooling systems are absolutely essential because there's a lot of equipment on the space station, it - electrical equipment. It makes a lot of heat as it's operating. You've got to get rid of that heat somehow.
This is part of a complicated system where they have like a more like a refrigerator outside, and that cools water inside, which circulates and cools equipment and makes the environment cool. So it has to have it. And right now, they've only got one system working. And when there's only one system out in space, people get nervous.
RAZ: They get nervous because there's no backup.
PALCA: Right. You know, you can't go call the HVAC guy, get him to come around in his truck.
If it failed this has been the question. If it failed, they would not have enough life support in the American part of the station. They would all have to move into the Russian part of the station where they have a separate cooling system and live in there and only venture into the American part when they had a specific task that they wanted to perform. So it's bad if the other one breaks.
RAZ: They've already done two spacewalks to try and fix this. Why has it been so hard to replace?
PALCA: It turns out that it's like any repair job in a 10-year-old home. Things that you thought would be, oh, I'll just snap off this connector, they don't snap off.
PALCA: And so they thought it would be an easy task to unbuckle four lines of coolant, and one of them wouldn't unbuckle, and they spent hours just trying to work at it and pull on it and twist on it. Then they had to wait a couple of days, and they lowered the pressure, you know, all these kinds of things.
But if it's a home repair, no big deal. But if you're out in space, you've got to think all this stuff through. It takes a lot of time.
RAZ: And they actually keep all these replacement parts on the station, right?
RAZ: They've got this huge sort of storage facility.
PALCA: Well, you have to ask yourself, okay, I've got X number, it turns out there's 14 critical components and they figure out how long they think each one's going to last, and then they make sure they have spares for each one.
In this case, they have four spares for a component that's absolutely critical that they think will last about 10 years. So they have to make a guess about how long it's going to last before it breaks.
RAZ: Now, obviously, these astronauts are scientists. They're not there to repair things, but they have to...
RAZ: ...from time to time. Does this repair affect the other experiments that they're doing?
PALCA: Yeah, absolutely. Every other station activity basically stops.
PALCA: There's a couple dozen experiments onboard the station. They're being tended in the absolute minimum way to keep them going if they have to have any kind of attention. But everybody's preparing for and getting ready for and getting equipment ready for and going through procedures for these spacewalks.
RAZ: That's NPR science correspondent Joe Palca.
Joe, thanks so much.
PALCA: You're welcome.
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