Mission specialists Joe Tanner and Heidemarie Stefanyshyn-Piper ventured outside the ISS at 4:17 a.m. Houston time (0917 GMT) to connect power cables to a truss segment containing solar arrays.

The walk -- the first of three -- is scheduled to last six-and-a-half hours, NASA said.

The solar arrays, which will provide a quarter of the ISS's power once installed, were transferred from the shuttle's cargo bay to the ISS earlier Tuesday in a handoff by the two space vehicles' robotic arms.

Two other spacewalks are planned to complete installation of the solar panels this week.

Six astronauts -- one woman and five men -- arrived at the station Monday aboard the Atlantis. After docking with the station, the astronauts warmly shook hands with the three ISS occupants and then quickly went to work in the first construction mission since November 2002.

The Columbia disaster three months later forced the National Aeronautics and Space Administration to focus on improving shuttle flight safety.

Following two Discovery shuttle missions aimed at making space flight safer, NASA said it was ready to resume space station construction.

The 11-day Atlantis mission which launched Saturday has been billed as the most complex station assembly work to date.

US space officials at the Johnson Space Center in Houston, Texas, were pleased with how the mission has gone so far -- particularly the picture-perfect docking.

"It was very spectacular stuff today," said Paul Dye, NASA's lead flight director for the mission. "The rendezvous this morning was probably just about as perfect as any rendezvous I have ever been part of."

On its way to the ISS, Atlantis' heat shield went through a thorough examination in what has become a routine safety check since the Columbia accident that killed seven astronauts.

Before docking, Commander Brent Jett steered the orbiter into a backflip 200 meters (yards) below the ISS to allow the station crew to photograph Atlantis' underbelly.

On Sunday, the Atlantis astronauts used the orbiter boom sensor system, attached to the end of the robotic arm, to closely inspect the wing leading edges and the nose cap for potential damage from debris during the launch.

A NASA spokeswoman said late Monday that the space agency decided that a "focused" inspection was unnecessary.

The decision indicates that officials found Atlantis free of damage from debris that could have hit its heat shield during liftoff from the Kennedy Space Center in Cape Canaveral, Florida.

The extra inspection would have forced NASA to add another day to an already busy mission.

Columbia was doomed by foam insulation that peeled off its external fuel tank during liftoff and pierced its heat shield, causing it to disintegrate as it returned to Earth in February 2003.

The Discovery missions in 2005 and in July focused on boosting safety to set the stage for regular shuttle flights to the space station.

NASA plans 15 more shuttle trips to complete the orbiting laboratory by 2010, when the three-shuttle fleet is to be retired.

Completing the ISS is central to US ambitions to fly humans back to the Moon and eventually to Mars.

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