Spacewalk ends amid mission to attach Japanese lab

(Updates with end of spacewalk, details)

By Ed Stoddard and Irene Klotz

HOUSTON, June 3 (Reuters) - A pair of astronauts on Tuesday completed the first of three scheduled spacewalks on a mission by U.S. shuttle Discovery to install a huge Japanese research lab at the International Space Station.

Conducted by veteran spacewalker Michael Fossum and his rookie partner, Ronald Garan, the outing went smoothly for the most part and lasted six hours and 48 minutes.

The primary goal of Discovery's mission, which began Saturday with liftoff from the Kennedy Space Center in Florida, was to deliver Japan's $1 billion Kibo laboratory, the cornerstone of that country's 20-year effort to join in as a permanent player in human space exploration and research.

Describing Tuesday's activities as they were set to unfold 210 miles (338 km) above Earth on the 43rd anniversary of the first U.S. spacewalk, space station flight director Emily Nelson called it "a really big day for Japan."

The spacewalkers prepared the lab for installation, retrieved a sensory inspection boom and scraped some debris off a metal ring on one of the orbital outpost's solar power wing panels.

As the spacewalk wrapped up, astronauts working from inside the station used the station's robot arm to attach the Kibo lab onto the Harmony module, which serves as a connecting node for several station components.

At 37 feet (11 metres) long and just over 14 feet (4.4 metres) wide, Kibo, which means "Hope," is so big that Discovery didn't have room in its cargo bay for its inspection boom, a piece of equipment that doubles the length of the shuttle's 50-foot (15-metre) robot arm so that cameras and sensors can inspect the ship's wings and nosecap for damage.

The boom was part of NASA's safety upgrades following the fatal 2003 Columbia accident, which was triggered by damage from a debris impact.

The last shuttle crew to visit the space station left its boom behind, temporarily stashed alongside a segment of the station's external framework, for the Discovery astronauts to use and return to Earth.

Fossum and Garan removed protective covers from the boom's laser and camera, disconnected cables and transferred it to the shuttle's robotic arm.

Work was also done on a damaged metal ring needed to pivot a pair of the station's solar wing panels to track the sun for power.

Engineers last year discovered the rotary joint was using more power than expected and sent a pair of astronauts outside to investigate. They found widespread contamination of the main metal ring, which should be completely smooth.

Fossum used a tool similar to a dentist's pick to scrape the debris away and then wipe the area with a light lubricant.

"We got the loose stuff cleaned up," he said by radio as he scraped away. If the method is deemed successful it may be used on future shuttle missions.

The U.S. space agency has seven space station construction missions remaining and two resupply flights. Upon completion in 2010, the shuttle fleet, which has been flying since 1981, will be retired. (Editing by Tom Brown)