The two astronauts hooked up electrical and fluid connections between the Destiny laboratory - the space station's main room - and the Harmony node.

They also moved a 136-kilogramme, 6-metre long fluid tray from its temporary location at the centre of the station's main truss to the Harmony module.

Built in Italy for the United States, Harmony is a high-tech hallway and Tinkertoy-like hub. It is a 23- by 14-foot passageway that connects the U.S. segment of the station to the European and Japanese modules, to be installed later this year and early next year, respectively.

Harmony is the first new U.S. pressurized component to be added to the station since the Quest Airlock was attached to one of Unity's six berthing ports in 2001.

The Harmony module was delivered last month by the space shuttle Discovery, but was left in a temporary parking space. The space station occupants have been busy since then moving Harmony to its permanent spot and rearranging various portals outside the station to accommodate the new arrangements.

Harmony will offer docking ports to the European Space Agency's Columbus laboratory and Japan's Kibo experiment module, to become a part of the International Space Station next year.

Columbus will be stowed aboard the Atlantis shuttle when it launches December 6, part of a dizzying schedule of shuttle flights being made in a rush to double capacity on the space station by 2010, when NASA's ageing shuttle fleet is set to retire.

The Columbus External Payload Facility (Columbus-EPF) consists of two identical L-shaped consoles attached to the starboard cone of Columbus in the zenith (top) and nadir (bottom), positions, each supporting two platforms for external payloads or payload facilities. In total, four external payloads (payload facilities) can be operated at the same time.

NASA said another spacewalk by Whitson and Tani during which they will complete the exterior hookup of Harmony is scheduled for Saturday.