The stage is now set for the ISS team to unfurl the huge solar array on Friday at 1458 GMT, allowing the orbiting laboratory to power up to its full capacity for the first time in its 10-year history.

Steve Swanson and Richard Arnold, exiting the ISS 212 miles (354 kilometers) over the Pacific near New Guinea, bolted a girder to the space station to hold panels forming the orbiting outpost's fourth and last solar antenna.

The payload is one of the last major tasks of the more than decade-long effort to construct the 100-billion-dollar outpost in space.

The 14-ton piece was carried into space by Discovery, which blasted off Sunday from Florida, and the orbiter's robotic arm was used to lift it out of the shuttle's bay.

The solar panels, which measure 35 meters (yards) by 11.58 meters (yards) when deployed, contain 32,800 cells that convert the light of the sun into electricity.

Once deployed, the panels will boost the outpost's full power generation from 90 to 120 kilowatts, providing the power the space station needs to carry out scientific experiments programmed by the European Columbus laboratory and the Japanese Kibo laboratory.

As Swanson and Arnold worked to plug in power and data connectors to the equipment, floating in the frigid void, astronauts John Phillips and Koichi Wakata -- the ISS's first Japanese team member on a long stay -- guided the station's robotic arm.

Wakata is replacing US astronaut Sandra Magnus, who has spent four months on the ISS. The Japanese is scheduled to return to Earth in June.

The space walk, which lasted six hours and seven minutes, was the first of three walks on the 13-day mission. To get to this stage in the outpost's construction, 121 space walks have taken place, totaling a working time of 762 hours, according to US space agency NASA.

A fourth space walk from the shuttle flight scheduled after the mission was shortened by a day, after Discovery's launch was pushed back from March 11 to 15.

The delay was due to the discovery of a hydrogen leak from the fueling system for the external fuel tank just hours before the March 11 launch.

In all, NASA has scheduled nine shuttle flights through 2010 to complete the construction of the space station, a project backed by 16 countries.

Upcoming shuttle flights also include the last mission to service the orbiting Hubble telescope in May.

Discovery will return to Earth on March 27, one day after a Russian Soyuz mission takes off for the ISS carrying a crew of three, including US billionaire businessman Charles Simonyi, who has shelled out 35 million dollars for his second trip as a space tourist.

It has been a near picture-perfect mission so far, barring the delayed lift-off and some pesky space rubble that had US and Russian experts braced to move the ISS in an "avoidance maneuver."

The alert over the space junk, believed to be from a Soviet satellite that broke up shortly after it lifted off in 1981, was called off when data showed the debris posed no danger to the space station.

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