We begin with that drama, six people including two americans floating more than 200 miles above the earth. They're on board the international space station while down below engineers are scrambling to... See More
We begin with that drama, six people including two americans floating more than 200 miles above the earth. They're on board the international space station while down below engineers are scrambling to find critical solutions to a breakdown. We're right there where the decisions are being made. Houston station -- Reporter: Tonight engineering a tricky repair job, 230 miles above the ground. What is actually going wrong -- Reporter: Mission control today trouble shooting how to fix a faulty critical component, one of two cooling loops that keep the station from dangerously overheating, a valve in one of them is stuck, forcing the six astronauts on board to rely on the duplicate. Now there's no back-up if that fails, too. This is a position we don't want to be in long term. Reporter: Nasa says for that you the two americans, three russians and one japanese astronaut living on the station are not in danger. The crew is in good shape. Reporter: Engineers say they have two options, first upload new software to reboot that stuck valve. If that doesn't work they'll have to swap it for a spare during a risky emergency space walk. Astronaut doug wheelock replaced this same part in 2010 during his space walk. How dangerous is it if they do have to go and do it? Whenever we open that hatch and send people outside it's dangerous. Reporter: Nasa suspended space walks in july after water that was supposed to keep an italian astronaut cool leaked into his suit. He nearly drowned. In a worst case scenario, the crew would have to evacuate on a soyuz capsule. This is where the astronauts train to live and work on the station. It's the length of a football field. We're told whether that space walk is a go or no go is coming on monday. The bottom line is that houston has a problem but it's one they're confident they can fix.
This transcript has been automatically generated and may not be 100% accurate.