During a scheduled 61/2-hour spacewalk, astronauts Michael Fossum and Ronald Garan Jr. prepped the $1billion lab for installation by removing power and heating cables and restraints that connect it to the shuttle.
“Wow, this is incredible,” Garan, a spacewalking rookie, said just after he stepped outside.
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Astronauts working from inside will use the space station's robot arm later in the day to lift the lab from the shuttle and anchor it to the station.
Later in the spacewalk, the astronauts were going to try out some cleaning methods on a jammed solar rotating joint that has hampered energy production at the space station since last fall. The joint enables the space station's solar arrays, which provide electrical power, to rotate and track the sun.
“It's going to lead to a really busy day for all of those guys,” said Emily Nelson, a space station flight director.
The start of the spacewalk was delayed nearly an hour as a faulty communications cap, which allows spacewalkers to talk with other crew members and controllers on the ground, was replaced in Fossum's spacesuit.
The lab is named Kibo, Japanese for hope. At 37 feet long, it is bigger than the U.S. and European labs already attached to the space station. The Japanese lab also has a pair of robot arms, the larger of which flew up on this shuttle mission.
The shuttle astronauts, who arrived at the space station on Monday, will use the boom next week to check Discovery for any damage that could endanger them during re-entry.