ISS set for Friday chill-out

First spacewalk to replace failed ammonia pump

The first spacewalk to replace the International Space Station's failed ammonia pump module will take place on Friday, NASA has announced.

The ISS is in a "stable configuration" following Saturday's breakdown of the "Pump Module for loop A that feeds ammonia to maintain the proper cooling for systems and avionics".

Attempts to revive the pump were unsuccessful, although with half of the station's cooling system still operative, the situation is not critical.

Expedition 24 members Tracy Caldwell Dyson and Doug Wheelock are tasked with swapping out the failed unit, which sits on the orbiting outpost's S1 truss.

There's a spare pump bolted to an external stowage platform attached to the Quest airlock, which the two astronauts will use to exit and re-enter the ISS.

NASA explains: "In the first spacewalk, they will unbolt and remove the failed pump module, and install the spare. A second spacewalk to hook up a variety of electrical and fluid connections for the new pump module is targeted for Monday."

At Johnson Space Center’s Neutral Buoyancy Laboratory, astronauts Cady Coleman and Suni Williams lent their support to Caldwell Dyson and Wheelock by "practicing underwater the tasks needed to restore the cooling loop over the course of two spacewalks".

Friday's EVA marks the fourth spacewalk for Wheelock, while Caldwell Dyson will be on her first external jaunt. NASA has more on the preparations here. ®