Published: Aug 16, 2010 12:14 PM EDT
Updated: Aug 16, 2010 9:14 AM EDT

CAPE CANAVERAL, Fla. (AP) - Space station astronauts are back outside again. They have one more spacewalking chore before they can declare success in their urgent repair work.

Douglas Wheelock and Tracy Caldwell Dyson ventured out Monday morning. It's their third spacewalk in just over a week. This time, they'll try to install a new ammonia coolant pump in an effort to restore full cooling to the International Space Station.

The orbiting lab has been operating on half its normal cooling capability ever since a crucial pump failed on July 31. It took two spacewalks, but Wheelock and Caldwell Dyson finally removed the broken pump last week.

The bathtub-size pumps are needed to drive ammonia through cooling loops and keep equipment from overheating.