Transcript for This day in history: Dec. 12, 2013

Six people including two Americans floating more than 200 miles above the earth. They are on board the International Space Station while down below engineers are scrambling to find answers and solutions to a critical breakdown. And ABC's Clayton send Dell is right there where the decisions are being mate. Tonight engineering a tricky repair job 230. Miles above the ground what is actually going wrong mission control today troubleshooting 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 but now there's no backup if not one fails to this is a position we don't want Ambien. NASA says for now the two Americans three Russians and one Japanese astronaut living on the station are not in danger and get a good stable configuration cruising Puget. Engineers say they have two options first upload new software to reboot that stopped well but if that doesn't work the hop to swap it for spare during a risky emergency spacewalk. Astronaut Doug wheelock replace this very same park in 2010 during his own space walk. How dangerous is this if they decide they do have to go. Well I'd like to how that don't we say that whenever we open that hatch and send people outside it's always dangerous. Another problem NASA suspended space walks in July after water that was supposed to keep Italian astronaut Luke apartments auto cool leaked into his suit. He nearly drowned. And we hand Luke Donald worst case scenario the crew would have to evacuate hitching a ride home on a Russian Soyuz capsule attached to the station. Now take a look at this Diane this is where the astronauts actually trained to live and work on the station it's the light of a football field. Now we're told that a decision on whether or not that's spacewalk is a go or no go is coming on Monday the bottom line here 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.