ARUN RATH, HOST:
This morning, astronauts Michael Hopkins and Richard Mastracchio stepped outside the International Space Station. Their mission: to conduct one of three urgent spacewalks to repair a coolant system. Mission Control seemed happy with today's effort.
(SOUNDBITE OF MISSION CONTROL RECORDING)
UNIDENTIFIED MAN #1: OK. Really nice work, guys. We're about an hour and a half ahead. Let's take some steps beforehand. First, we want to do an ammonia inspection.
UNIDENTIFIED MAN #2: Copy that.
RATH: A little audio note from the astronauts there. Dr. Jonathan McDowell is with the Harvard-Smithsonian Center for Astrophysics. He watched today's spacewalk and says things did go very well.
DR. JONATHAN MCDOWELL: They got ahead of the schedule and did part of the next spacewalk. The only slight snag was when NASA asked lead spacewalker Richard Mastracchio whether they wanted to go on and do even more, he was sort of pretty clear that he wanted to come back inside now, thank you very much. And it seems like he may not have been feeling very well toward the end there. So - but that happens. That's a minor glitch. And I'm sure they'll be fine to go on and complete the repair in two days' time.
RATH: Why was it the repairs to the coolant system on the International Space Station were so urgent?
MCDOWELL: You know, you're out in space. You're running a lot of electricity for all the experiments for the life support. That generates heat and you've got to get rid of that heat somehow. And so they really want to get it back up where they can operate the station at full capacity.
RATH: Is that as big of a job as it sounds?
MCDOWELL: This pump module that they were replacing is the size of a refrigerator. It doesn't weigh anything in space, but it still has the same mass, so it's difficult to move around. And it's full of ammonia. And when you unhook the plumbing, little flakes of ammonia come out, and that's toxic, so you don't want to get it on your spacesuit. It is a pretty big job.
RATH: And there was a bit more attention on this spacewalk because, previously, there had been an issue with water had leaked into an astronaut's helmet and ran the risk of drowning.
MCDOWELL: Absolutely. Luca Parmitano, the Italian astronaut, back in July was out there in the vacuum of space. This is not the safest situation, you know? And suddenly, your helmet is filling with water. That's got to be a very scary thing. They used the same spacesuit today for Mike Hopkins, and it seemed to work just fine. They took a lot of precautions. They took a snorkel with them. Looks like the fix worked well.
RATH: You mentioned the repairs have finished early, but there's still two other scheduled spacewalks that will be happening on Monday and again on Christmas Day. What else needs to happen with these repairs?
MCDOWELL: The next thing they need to do is crawl along the outside of the space station to where they've stored a spare unit, plug it in and then take the old pump unit and put it back in a more permanent storage location. So there's still a lot of work to do before they can even see if they've got a repair.
RATH: Dr. Jonathan McDowell is an astrophysicist at the Harvard-Smithsonian Center for Astrophysics. Dr. McDowell, thank you.
MCDOWELL: You're welcome. Transcript provided by NPR, Copyright NPR.