Astronauts Extracting Failed Pump From Station Truss

Four hours into a spacewalk outside the International Space Station, U.S. astronauts Doug Wheelock and Tracy Caldwell-Dyson are extracting a failed coolant pump module from the central truss of the outpost.

Riding at the end of the station's 57-foot robot arm, Wheelock handed off a payload attachment device to Caldwell-Dyson. Fellow flight engineer Shannon Walker is operating the crane-like arm from a control station inside the outpost. The spacewalkers aim to attach the device to the 780-pound module so it can be removed from its slot on the S1 truss segment and then moved to temporary storage on the station's mobile rail cart.

Wheelock will pull the module about halfway out of its slot in the truss so Caldwell-Dyson can attach the payload handling mechanism.

The spacewalk is scheduled to last about six hours. The astronauts are running about a half-hour ahead of schedule. A spare pump module will be installed on the truss during a spacewalk Sunday.