Less noticed perhaps than it should be has been the urgent, impressive replacement of the arrant quarter-ton ammonia pump that caused failure to half the station's cooling system, requiring the third of four spacewalks from ISS, Monday, August 16. It's the 150th EVA since the first ISS section was carried to low-Earth orbit in 1998. Above, Expedition 24 Flight Engineers Dr. Tracy Caldwell Dyson (left) and Col. Doug Wheelock work to set up the spare ammonia pump module (stored on-board since 2006) after installation on the S1 Truss [NASA TV ].
