Japan's elaborate research laboratory ready for installation on the International Space Station.Two U.S. astronauts floated out into open space on Thursday .
Four-time flier Richard Linnehan and his rookie partner Garrett Reisman left the station's airlock around 8:30 p.m. EDT (0030 GMT Friday) to begin the first of five spacewalks planned during shuttle Endeavour's 16-day mission.
The astronauts' first job is to remove protective thermal covers from a Japanese-built equipment storage chamber that flew into orbit in the shuttle's cargo bay.
The shuttle reached the station on Wednesday night.
The storage chamber, which contains computers and experiment racks, is the first part of Japan's space laboratory, known as Kibo, or "hope." The main part of the Kibo lab, which is about the size of a double-decker bus, is due to arrive at the space station in May.
An outdoor porch for exposing experiments to the vacuum of space will follow in 2009.
The spacewalkers also plan to disconnect a power cable to the module, clearing the way for Japanese astronaut Takao Doi, stationed inside Endeavour, to use the shuttle's robot arm to pluck the chamber from the cargo bay and twirl it into position on the station's Harmony connecting node.
Linnehan and Reisman will then turn their attention to a Canadian robot, named Dextre, that will add manual dexterity and 30 feet of reach to the station's crane.
NASA and the Canadian Space Agency were working on a software patch to bypass a problem that is preventing the $209 million robot from tapping into the station's electrical system.
"There's not a sense of great urgency," shuttle mission management team chairman LeRoy Cain told reporters. "We don't have our hair on fire."
Dextre can go at least five days before the cold of space becomes a problem, NASA's space station program manager Mike Suffredini told reporters at Houston's Johnson Space Center.
About half of the five spacewalks planned during Endeavour's 12-day stay at the station are dedicated to building Dextre, which has never been assembled on the ground.
With 11-foot-long arms and a mass of more than 1.5 tons, the robot would topple in Earth's gravity.
"It comes up in nine different pieces," Reisman said in a preflight interview. "We have to put him together."
NASA hopes to use the robot to help with detailed exterior station maintenance, cutting down the amount of time astronauts have to spend on risky spacewalks.
The space agency has two years to complete 10 remaining missions to the station before the aging shuttle fleet is retired. After that, the number of people who will have access to the station for part-time work will be greatly reduced.
A typical shuttle flight ferries seven visitors to the outpost. But NASA plans to rely on the Russian Soyuz capsule -- which carries three people -- to transport astronauts to the station after shuttle flights end in 2010.
The Endeavour crew won't have to spend any extra time surveying their ship for heat shield damage, managers decided on Thursday. After analyzing photographs taken by the space station crew as Endeavour approached for docking, engineers said the shuttle appeared in good shape for landing at the end of its planned 16-day mission.
NASA implemented a series of in-flight inspections after losing the shuttle Columbia and its crew in 2003 due to undetected heat shield damage.
