The crew aboard the International Space Station is struggling to fix one of the biggest problems yet to afflict the orbiting outpost. A critical pump in one of the station's cooling systems failed 10 days ago, and two crew members are scheduled to perform a spacewalk Wednesday to replace it.
The failed pump circulated ammonia through one of two cooling systems aboard the ISS, and without it, the cooling system is inoperable. Cooling is essential because like all electronic equipment, the space station equipment generates a lot of excess heat.
"All of the systems other than some of the components out on the truss where the power modules are, get their cooling from this system," Michael Suffredini, the ISS manager, told reporters last week.
There is, however, another completely independent cooling system that is working just fine, but the failed pump means there's no margin for another failure.
"If we lose the next cooling system, then we don't have the ability to cool most of the components aboard ISS, and so that would be a significant challenge to the team to work through that," Suffredini said.
"Significant challenge" might be an understatement. The Russian modules that make up ISS have their own cooling systems, so the entire crew of six would have to live in those modules until one of the systems could be repaired, and that would be a tight squeeze.
"This is an anomaly we knew someday would happen," Suffredini said. "It's an anomaly we have trained for; it's an anomaly we have planned for. So we're in a good position to solve this problem. It is a significant failure though, and it's one that we have to get after."
NASA managers were hoping that two spacewalks would be sufficient to replace the pumps with one of the four spares at the station, but the astronauts performing the first walk last Saturday ran into a problem disconnecting one of the four ammonia lines on the pump. When they finally did manage to disconnect it, they discovered an ammonia leak, so the spacewalkers ended their excursion with one of the four ammonia lines still attached.
The plan now is to try again Wednesday. Spacewalk officer David Beaver says there's still several things to disconnect before the failed pump can be removed, including one fluid connection, five electrical connections and four bolts.
Then the new pump has to be bolted into place, all the lines connected and the old pump stowed away. Suffredini says it will take a third spacewalk, and possibly more, to complete the repairs.
"We will get through this problem," he said. "The challenge is to get through this problem before the next problem hits the other cooling system."
Losing the existing system isn't an idle concern: The pump on that system is the same age as the one that failed.