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Monday, August 16th, 2010
Associated Press

by Marcia Dunn, AP Aerospace Writer

In this image taken from video and made available by NASA, astronauts Douglas Wheelock, right, and Tracy Caldwell Dyson, bottom center, work on the International Space Station attempting urgent repairs to restore a crucial cooling system on Wednesday Aug. 11, 2010. The International Space Station has been operating with only half its usual cooling capability ever since an ammonia pump failed one-and-a-half weeks ago. Science research is on hold and unnecessary equipment is off until the pump can be replaced. The cooling system is crucial for keeping electronics from overheating. (AP Photo/NASA)

CAPE CANAVERAL, Fla. (AP) — A pair of space station astronauts had to hammer loose a stuck connector Saturday during an urgent spacewalk to restore a crucial cooling system, one of the most challenging repairs ever attempted at the orbiting lab.

Douglas Wheelock and Tracy Caldwell Dyson went into the spacewalk hoping to remove a broken ammonia coolant pump on the outside of the International Space Station. But they fell behind because of the stiff connector and were forced to leave the pump in place. What's more, a fair amount of ammonia leaked out, forcing them to set aside time to get the toxic substance off their spacesuits. The job was considered so difficult that two spacewalks were ordered up by NASA. Saturday was part one.

Halfway through the spacewalk, Wheelock and Caldwell Dyson had trouble disconnecting the hoses from the disabled pump. They could not get one of the four pressurized lines to come off.

"Wow. That thing is not budging," he told Mission Control. Caldwell Dyson floated by his side, unable to offer much assistance because of the tight quarters. They were so close their helmets kept bumping against each other.

A bit of ammonia coolant leaked out as the two struggled with the connections. Wheelock said the escaping ammonia resembled tiny snowflakes.

Running well behind by this point, the spacewalkers managed to remove three of the four hoses. Wheelock tried once more to disconnect the balky line, banging a jammed button with a special tool. It worked.

In a photo made from NASA television, Expedition 24 astronauts Tracy Caldwell Dyson and Douglas Wheelock work outside the space station Monday Aug. 16, 2010 as they prepare to install a cooling pump module, replacing the one that failed. (AP Photo/NASA)

Mission Control erupted in applause. "Awesome," Mission Control radioed up. But the exuberance was dampened by a stream of escaping ammonia. "It's got a pretty good snowstorm there," Wheelock reported.

The astronauts managed to stop the leak when they plugged the troublesome connector back in. There was time for little else as the spacewalk neared the seven-hour mark.

The ammonia pump shut down last weekend and knocked out half of the space station's cooling system. The pump is supposed to push ammonia coolant through the lines on the right side of the complex and prevent equipment from overheating. To cope with the failure, the six-person crew had to turn off all unnecessary equipment and halt science experiments.

The cooling line on the left side — unaffected by the trouble — has had to manage everything.

Engineers worked nonstop over the past week to come up with the emergency repair plan, which involved replacing the pump. In addition, astronauts in Houston rehearsed every step of the spacewalk while submerged in NASA's huge training pool.

Although space station managers knew an ammonia pump would fail one day, they did not expect it to happen so soon in the 12-year life of the complex. The pump was launched in 2002, but did not start operating fully until 2006.

Wheelock could find nothing wrong with the pump, and he saw no signs it had been hit by micrometeorites or other debris.

Each pump is a boxy 5½ feet by 4 feet by 3 feet and has a mass of 780 pounds. Several cooling lines will have to be connected to the new pump, an on-board spare, at least some of which will be done on the second spacewalk planned for Wednesday.

NASA said the breakdown is serious but has not endangered the crew, and the one functional cooling loop has kept the space station stable. Additional breakdowns could leave the station in a precarious situation, however, and that's why managers wanted to get the broken line working again as soon as possible. Saturday's spacewalk was the first by Americans, without a shuttle present, since 2008.

The crew includes three Americans and three Russians. Caldwell Dyson has been on board since April, and Wheelock since June.

Written by Marcia Dunn, AP Aerospace Writer
Copyright 2003 Associated Press. All rights reserved.This material may not be published, broadcast, rewritten , or redistributed.

Photos courtesy of AP Photo/NASA
Last changed on: 8/16/2010

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