The two astronauts carried out the work two weeks before the next set of components are to arrive at the orbiting laboratory.

Space station flight director Derek Hassmann described today's excursion as a "hugely successful spacewalk."

"We were able to connect the node 2/Harmony module to the other string of the permanent ammonia cooling system," he said. "And because the crew got out the door early today as they always do, we were able to move early our node 2 final activations. Both node 2 thermal cooling systems are up and running inside the Harmony module, both MDMs, or computers, are powered up and both strings of power systems are up and running. That was an activity that wasn't scheduled until tomorrow. So once again, the crew has enabled us to get ahead."

Earlier this week Whitson and Tani already moved another 300-pound, 18.5 foot fluid tray, the Loop B fluid tray, from a temporary location on the station’s main truss to the Destiny lab. The Loop B fluid tray was placed on the opposite side of where the Loop A fluid tray was placed on Tuesday.

Also during the spacewalk the two astronauts installed a portable foot restraint on Node 2 for upcoming spacewalks when the European Columbus laboratory will be installed during the STS-122 mission.

Harmony, which was delivered by the space shuttle Discovery, will serve as a docking port for the European-made Columbus module, which is set to arrive with the next shuttle, Atlantis. Atlantis is due to be launched December 6 from the Kennedy Space Centre on Florida's Atlantic Coast at Cape Canaveral.

Flight controllers on the ground were checking all of Harmony's systems Saturday to make sure the module would be ready to accommodate the new lab.

At 23 feet long and 15 feet in diameter, Columbus is designed to host specialized experiments examining how humans react to microgravity and the effect of space on various fluids and objects such as crystals.

Columbus will join NASA's Destiny lab which was taken into orbit in 2001. Next year, a series of space shuttle missions will carry the components of a Japanese laboratory into orbit. Together, the three research units are expected to provide a cutting-edge platform for space science.