Nightly News   |  December 21, 2013

Day one of spacewalk is a success

American astronauts began a dramatic emergency repair outside the International Space Station. NBC’s Tom Costello reports.

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>>> most unforgiving environment known to man, two american astronauts spent part of this day performing a dramatic emergency repair job outside the international space station . the pictures of a space walk were stunning. the task itself, critical. replacing a piece of hardware that could prove vital to keeping the space station livable. all with people around the planet looking over their shoulders via a live nasa video stream . the job isn't finished yet and there are more space walks to come. meantime adding more drama to the day was the fact that this was the first space walk since a pretty close call for another astronaut last july. nbc's tom costello reports.

>> go to egress.

>> reporter: 230 miles above the earth today a high stakes space walk at 17,000 miles per hour.

>> safety cover and i see mike hanging out and i've got a good visual on you.

>> reporter: almost immediately the walk went better than anyone had hoped.

>> i don't know if you guys believe in miracles but i got the hitch pin on the first try.

>> that's awesome, rick.

>> reporter: the job, disconnect and remove a cooling pump that failed ten days ago, leaving just one cooling pump for the entire space station .

>> that makes me nervous. see how loose it is.

>> reporter: without that cooling pump the space station crew has been forced to turn off nonessential systems.

>> we powered down things. we tried to preserve a lot of our science. equipment, life support systems that the crew has to operate of course to keep oxygen in the cabin and pressurization.

>> reporter: if all goes well, astronauts will slip a spare pump into position. the pump is massive and difficult to maneuver, 780 pounds, about the size of a double door refrigerator, with internal plumbing that is full of toxic ammonia.

>> reporter: the space walk is considered risky because an astronaut almost drowned. they feel they fixed the problem with homemade snorkels just in case but today there was no need.

>> good news from both crew members. everything is still dry.

>> reporter: the water never returned.

>> you have a go for gca to remove the pump.

>> the astronauts worked quickly to remove the pump on the side placing it on a storage platform and leaving behind the empty slot for its replacement in all wrapping up the walk a full hour early.

>> a good stopping point and you will be well rested to come out monday and finish with the spare and get it connected.

>> reporter: space walks have become so routine the public rarely notices anymore when astronauts step outside the station, but last july nasa came very close to losing an astronaut. for many it drove home the message that stakes on space walks are very high. lester.

>> tom costello, the next space walk will happen on christmas eve . we have a veteran from three space walks who retired last year from nasa after 36 years. thanks so much for being here. help me understand the urgency of this mission. if you lose all of your cooling on the space station , what happens?

>> it's not good at all to lose the cooling an a space station because everything on the space station runs with electrical power . electricity running in an engine or computer generates heat. one of the critical elements is the ability to get rid of the heat. if you can't get rid of the heat you have to stop generating heat which means you have to turn everything off which means you have to go home.

>> take me up there. you're doing this highly technical mission. you're going through a lot of physical stress. you have the earth spinning right below you and you have people watching you on video. tell me what that's like.

>> that last part is the hardest part to get used to. everybody is looking at your hands as you do it. every little boo boo you do people see and all the wonderful things you do, of course they don't notice, but it's a tremendous amount of training to get ready. after you go outside after years of training, you put on your space suit , go outside, and you work harder than you ever have in your life. it's like going to the gym all day long at the same time you're in a chess tournament.

>> that's why only a few of you do this for a living. stephen robinson , thanks