August 3, 2010

NASA Plans Emergency Spacewalk To Fix Cooling System

NASA teams raced Monday to try and get ready for two spacewalks to fix a pump module on the International Space Station's (ISS) cooling system, which failed last week.

NASA said the ISS astronauts will need at least two spacewalks to remove the failed ammonia pump and replace it with a new one.  The first spacewalk will take place on Friday.

Two astronauts held dry-runs for the spacewalks at the Neutral Buoyancy Laboratory (NBL) in Houston, where they choreographed what needed to be done.

NASA gave the green light to ISS astronauts Doug Wheelock and Tracy Caldwell Dyson after practicing the steps needed to remove and place the failed unit.

"Mission managers, program managers, flight controllers, engineers, astronauts and spacewalk experts made the decision Monday evening after continuing to analyze and refine engineering requirements, and reviewing the results of an underwater practice session," NASA said on its website.

Courtenay McMillan, the spacewalk flight director for the expedition, told reporters earlier that the first spacewalk could take place on Thursday.

The first spacewalk will focus on the failed unit out of the starboard truss on the ISS.  McMillan said this unit poses a few technical challenges including releasing lines that are pressurized with ammonia, which is usually pumped into the cooling system.

Once the failed unit has been removed, the astronauts will move a 780-pound spare unit around 30 feet from the opposite side of the truss for insertion into the gap that was left by the defective pump module.

"This is a big, unwieldy object, so maneuvering it around and handing it off to crewmembers... could take some time and a lot of focus," said McMillan.

Mike Suffredini, manager of the ISS program, said the cooling pump going down was a "Big 14 failure," but NASA was prepared for it.

"This is an anomaly we knew someday would happen. It's an anomaly we've trained for, it's an anomaly we've planned for, it's obviously one we've spared for. So we're in a good position to solve this problem," Suffredini told AFP.

"But it is a significant failure, in terms of systems on board ISS. So it's one that we have to get after."

If the second of the two ISS cooling units failed, then the astronauts on board the ISS would no longer be able to cool most of the components on board.

The crew would not be in immediate danger because they could move to the Russian segment of the ISS, which has its own cooling system.

Astronauts tried to reactivate the pump module after Saturday's failure, but the circuit breaker tripped, said Suffredini.

"The data suggest that the motor is not frozen. In fact, it did start to pump some of the ammonia when we tried to start it the second time. So this tells us that there's a short somewhere in the powerfeed of the motor."


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