CAPE CANAVERAL — Spacewalking astronauts relied on brute force Wednesday to remove a broken coolant pump that has hampered operations at the International Space Station.
Their first attempt at emergency repairs to the cooling system was thwarted last weekend by a large ammonia leak.
This time, to everyone's relief, there was no burst of toxic ammonia from a stubborn connector, just a few frozen flakes that drifted harmlessly away.
"That's great news," astronaut Douglas Wheelock reported.
"That's awesome news," Mission Control agreed.
The urgent repair job — now expected to require two more spacewalks — is considered one of the most challenging in the 12-year history of the space station. The cooling system is crucial for keeping electronics from overheating, and half of the system was knocked out when the ammonia pump failed 11/2 weeks ago.
Research is on hold and unnecessary equipment is off until the pump can be replaced. Engineers suspect an electrical short in the pump led to the shutdown.
It was five hours into Wednesday's spacewalk before the astronauts succeeded in removing the broken 780-pound pump, about the size of a bathtub. A spare pump is scheduled to be installed during a third spacewalk Monday.
NASA originally anticipated two spacewalks to complete the job, but added a third after Saturday's trouble. Yet another — the fourth — was added Wednesday.
"This team is good, but there's just so many hours in a spacewalk and there's a lot of work left to be done to get ourselves all buttoned up in the same condition we were before we started" these spacewalks, said space station program manager Mike Suffredini.
Three Americans and three Russians are on board. Their safety has not been jeopardized by the cooling system trouble, and their comfort has not been compromised as they work and live 220 miles above Earth.
The space station is meant to continue working until 2020. NASA will have to rely on Russia and other countries for crew and cargo transport once the shuttle fleet is retired next year.
Only two shuttle visits remain, in November and February 2011. A third shuttle mission is under consideration for next summer.