By Alan Boyle
Science Editor / NBC News
Imagine a movie where astronauts are one failure away from abandoning the International Space Station, and have to deal with toxic chemicals during a spacewalk while facing the risk of drowning in their spacesuits. Oh, and it's just before Christmas.
A Hollywood producer could spin the three spacewalks that NASA is planning over the coming week as a holiday-season sequel to "Gravity," if Sandra Bullock were available. It's more likely that the replacement of one of the space station's external coolant pumps will be completely routine. But NASA is taking extraordinary measures, such as providing the two spacewalkers with jury-rigged spacesuit snorkels, just in case the fix-up job really does turn into a thriller.
Several factors, including a scary spacewalk in July involving water in a spacesuit helmet, have combined to add some extra drama to the repair operation that begins Saturday.
What went wrong on the space station?
The International Space Station is a 450-ton machine that puts out a lot of heat, and there's a complex cooling system that keeps all of the electronics aboard (not to mention the six-person crew) at their proper operating temperature. Two external ammonia-cooled plumbing loops draw the heat away from the internal water-cooled loops and radiate it out into space. Last week, one of the valves in a pump for one of the ammonia loops malfunctioned, and that caused the loop to go offline.
As a result, NASA had to shut down non-critical systems and shift some equipment, ranging from power voltage converters to the freezers that preserve scientific samples, over to the other loop. Mission managers say the station could "limp along" in that condition — but if the other coolant loop fails, urgent action would have to be taken. In a worst-case scenario, the station would have to be abandoned. . . .
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