high above the earth, two american astronauts are making a dramatic christmas eve spacewalk, to wrap up work on the international space station. Their urgent mission, to fix a critical cooling system.... See More
high above the earth, two american astronauts are making a dramatic christmas eve spacewalk, to wrap up work on the international space station. Their urgent mission, to fix a critical cooling system. And ryan owens has the latest from the johnson space center in houston. Good morning, ryan. Reporter: Good morning, lara. What a unique opportunity this is. We're inside the airlock. This is where these astronauts train. They come to this room to depressurize, just before they enter the darkness of space. One final check of the spacesuits this morning before american astronauts rick mashracchio and mike hopkins open the airlock and enter the vacuum of space. They gave the suits a close inspection monday, too. And who could blame them? One leak, one tear, and they are dead in an instant. I know you train for it. But is it scary when you're up there and there's nothing else? It is scary. It's a matter of just managing that fear. Reporter: Recent problems with those 35-year-old spacesuits have added to that fear. In july, an italian astronaut nearly drowned when water leaks into his helmet. I experienced what it was like to be a goldfish in a fish bowl, from the point of view of the goldfish. Reporter: From part one on the spacewalk on saturday, a different problem with water in the suit. We want to dry that suit out overnight. It's very, very cold. Reporter: The american duo is hoping to finish their mission today, replacing this massive cooling pump on the space station. Doug did the same spacewalk three years ago. He'll be talking them through it this morning. How much does it help that fear to have someone in their ear when you've been there? It's the difference between night and day. When you hear a calm, reassuring voice. Reporter: And we are already hearing doug's voice this morning. This is a live look, more than 200 miles above earth. The spacewalk is expected to last 6, maybe 6 1/2 hours. As one astronaut told us yesterday, they hope on the end of the international space station, they will find a new cooling pump under the christmas tree, just in time for christmas morning. Lara? I hope they do. We will be following it all morning. George? Thanks, lara.
This transcript has been automatically generated and may not be 100% accurate.