Expedition 24 Flight Engineers Doug Wheelock and Tracy Caldwell Dyson switched their spacesuits to battery power at 8:27 a.m. EDT, signaling the start of the second of three spacewalks focused on removing the ammonia pump module that failed July 31 and putting its replacement in place. Today's spacewalk is expected to last about six hours.

This is the fifth spacewalk for Wheelock, who is wearing the suit bearing the red stripes, and the second for Caldwell Dyson, who is wearing the unmarked suit.

Wheelock successfully closed the quick disconnect valve for the final fluid connector for the failed ammonia pump module. There are no visible leaks. Then he successfully unattached the final fluid line from the failed ammonia pump module. This will lead to the disconnection of five electrical and data cables and four bolts from the old pump so it can be extracted from the truss through the use of a grapple bar and parked on a payload bracket on the station's Mobile Base System.

If all goes as planned, the spare pump will be installed during the third spacewalk targeted for no earlier than Sunday.

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