Two U.S. astronauts left the International Space Station on Saturday for a spacewalk to prepare the last piece of Japan's Kibo laboratory for installation on the orbital complex, Reuters reported.
Lead spacewalker David Wolf and rookie astronaut Timothy Kopra slipped out of the station's airlock at 12:30 p.m. EDT (1630 GMT) to begin the first of five spacewalks planned during shuttle Endeavour's stay at the station. The shuttle arrived Friday for an 11-day mission.
"Welcome to EVA," Endeavor astronaut Chris Cassidy, who was directing the spacewalk -- or extravehicular activity in NASA parlance -- told the astronauts as they began what was expected to be a 6.1/2-hour outing.
The main goal of Saturday's spacewalk is to prepare a Japanese-built platform to be attached to the front of the station's $2.4 billion Kibo laboratory. The platform is designed to hold experiments that need to be exposed to the open environment of space.
Wolf and Kopra plan to remove thermal covers and reconfigure cables so that robotic cranes aboard the station and shuttle can be used to lift the four-tonne platform out of Endeavour's cargo bay and mount it onto Kibo. Experiments will be loaded aboard later during the mission.
The spacewalkers also have some station maintenance chores on their to-do list, including working on an equipment cart and preparing a docking port for Japan's new cargo ship, which is scheduled to make its debut flight later this year.
NASA also completed its initial analysis of Endeavour's heat shield on Saturday, and determined that no additional inspections would be needed by the shuttle crew.
The agency however is trying to figure out why Endeavour lost so much insulating foam from its external fuel tank during the climb to orbit on Wednesday.
NASA has been concerned about flyaway foam since losing shuttle Columbia in 2003. The shuttle was hit by a piece of falling foam during launch. The impact broke a panel on one of its wings, allowing hot gases to blast inside the structure as the shuttle flew through the atmosphere for landing 16 days later. All seven astronauts aboard died in the accident.
Any debris impacts on Endeavour were minor, but NASA has said it will not clear any more shuttles for launch until it is sure future tanks will not shed foam like Endeavour's. NASA said on Friday it expects the work will delay launch of its next flight from Aug. 18 to later in the month.
The U.S. space agency has seven missions remaining after Endeavour's to complete construction of the $100-billion space station, a project of 16 nations, and then retire the shuttle fleet.