Astronauts remove cooling pump from space station

U.S. astronauts removed a failed cooling pump from the International Space Station on Wednesday, taking a big step toward restoring the laboratory to full health. Spacewalkers Doug Wheelock and Tracy Caldwell Dyson found success after their first attempt to unbolt the large 780-pound pumping system on Saturday was frustrated by a balky ammonia line. "Today was a very successful day for us," said Mike Suffredini, manager of the space station program. "The hardware cooperated with us."

On Saturday, Wheelock had difficulty removing one of the four ammonia coolant lines connected to the failed pump. When he finally got it loose, it sprayed flakes of ammonia into space. To relieve pressure on the ammonia line Wednesday, NASA designed several work-around solutions, but when Wheelock tried disconnecting the line, he found it leaked far less ammonia. This allowed him to fully disconnect the line, and then he and Caldwell Dyson removed five electrical lines and four bolts. With that done, they were able to remove and store the old pump.

NASA now can turn its attention toward installing one of the four spares that have been delivered to the space station in recent years by space shuttle supply missions. The space agency has tentatively chosen Monday as the day to conduct a third spacewalk during which the new pump will be installed. For redundancy, the space station has two cooling loops to keep its critical systems cool when the laboratory is in direct sunlight. 

Although there's no signal that failure of the backup cooling system is imminent, like the failed system it's also eight years old. Both cooling loops have an expected lifetime of about 10 years.  Although there's no signal that failure of the backup cooling system is imminent, like the failed system it's also eight years old. Both cooling loops have an expected lifetime of about 10 years. Were the second loop also to fail, the majority of the football field-size lab would have to be shut down, and the six astronauts in orbit would have to evacuate into the Russian module.