August 11, 2010

Coolant System Repairs Focus Of Wednesday Spacewalk

A second spacewalk to help repair a failed ammonia coolant Pump Module onboard the International Space Station (ISS) will take place on Wednesday morning, according to NASA reports.

"Expedition 24 Flight Engineers Doug Wheelock and Tracy Caldwell Dyson spent Tuesday completing preparations for their second spacewalk Wednesday out of the Quest airlock to replace the failed ammonia coolant Pump Module on the S1 truss of the complex while the International Space Station Mission Management Team gave its final approval to proceed with the spacewalk," the U.S. space agency reported on their website yesterday.

In preparation for this morning's activities, ground control team members activated a regulator valve to lower pressure in the inactive cooling loop assembly. Once they begin their extra vehicular activity (EVA), Wheelock and Caldwell Dyson will close quick disconnect valves, release any remaining ammonia from the damaged pump, then disconnect the unit. A spare pump will be installed during a third spacewalk, currently scheduled to occur no sooner than Sunday.

Wheelock and Caldwell Dyson began final preparations for the EVA starting at 2am EDT this morning.

On Saturday, the two ISS astronauts completed the sixth longest spacewalk in history, spending 8 hours and 3 minutes attempting to remove ammonia lines from the failed pump. The activities scheduled for Wednesday's spacewalk were originally schedule to be completed during the previous EVA, but repairs on the 780-pound took longer than expected, forcing NASA to add a third spacewalk to the slate in order to finish work on the coolant module.

According to Joe Palca of NPR, the damaged coolant unit marks "one of the biggest problems yet to afflict the orbiting outpost."

"Cooling is essential because like all electronic equipment, the space station equipment generates a lot of excess heat," the reporter explains in an August 10 article. "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."

Problems with the second pump could force the entire six-person crew to seek emergency shelter in the self-cooled Russian module, which Palca says would be "a tight squeeze."

"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," ISS manager Michael Suffredini told NPR last week. "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."

"This is an anomaly we knew someday would happen," Suffredini added. "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"¦ The challenge is to get through this problem before the next problem hits the other cooling system."


Image Caption: The Soyuz TMA-19 spacecraft (foreground), docked to the Rassvet Mini-Research Module 1, and ISS Progress 37 resupply vehicle, docked to the Pirs Docking Compartment, are featured in this image photographed by an Expedition 24 crew member on the International Space Station. Credit: NASA


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