Astronaut Douglas Wheelock, anchored on the end of the space station's robot arm, has retrieved an adjustable grapple bar from external storage platform No. 2. Tracy Caldwell Dyson, meanwhile, has removed three of four bolts holding a faulty coolant pump in place on the starboard one, or S1, truss segment.

After the final bolt is removed and the grapple bar is attached to the pump module, the astronauts will move the pump to a nearby attachment fitting at the base of the space station's robot arm transporter.

Riding the arm to ESP-2 to retrieve the AGB, Wheelock took a moment to marvel at the view, thanking arm operator Shannon Walker for a smooth ride.

"I really can't in good conscience call this 'spacewalking.' This is awesome," Wheelock radioed. "Thanks, Shannon."

After the faulty pump is removed and stowed, the astronauts plan to loosen bolts holding a spare pump in place on ESP-2 before calling it a day.

Assuming that schedule holds up, Wheelock and Caldwell Dyson will attach the new pump during a spacewalk Sunday and reconnect ammonia lines and electrical cables.

Four hours into today's spacewalk, the astronauts were running about a half hour ahead of schedule.

Flight controllers looked into the possibility of going ahead and moving the new pump into place today, but there does not appear to be enough time to accommodate the additional work.

The astronauts are still protecting a block of time at the end of the spacewalk for possible decontamination procedures. There were no major leaks from a final ammonia line that was disconnected earlier but a small amount of ammonia ice could be seen escaping for a few moments. That was not considered a problem, however.