HOUSTON – Two astronauts stepped outside to begin rewiring the international space station Thursday after NASA powered down large sections of the orbiting lab for their own safety.
U.S. astronaut Robert Curbeam and Christer Fuglesang of the European Space Agency began their spacewalk about a half-hour earlier than scheduled. It was their second spacewalk since space shuttle Discovery arrived at the space lab for a seven-day visit.
The spacewalk was scheduled to last six hours.
"I think I see I sunlight," Curbeam said.
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The spacewalkers' task was to switch the space station from its old, temporary power source to its brand-new one — a pair of solar arrays that were delivered in September. The job involved unhooking three dozen electrical hoses and reconnecting them.
Before the start of the spacewalk, NASA flight controllers on the ground powered down sections of the station that used those hoses so that electricity was not flowing through them when the astronauts touched them.
For a short time, NASA lost some of the redundancy it likes to have in its systems.
Half of the lights in the station's U.S. laboratory went dark. Cameras at the station stopped working and some ventilation ducts were turned off. Communication between the U.S. and Russian sides of the space station was cut off.
Even a smoke detector was turned off. Mission Control, as a precaution, asked astronaut Nicholas Patrick if he smelled smoke. He said no.
The spacewalk required careful choreography. Fuglesang planned to work in an area called "the rat's nest" because it is a tight corner jammed with power hoses.
Once the power lines were reconnected, NASA had to race to get the space station's ammonia cooling system operating again before the equipment overheated.
A third spacewalk set for Saturday will repeat the rewiring job, but on the flip side of the station's U.S. segment.
NASA also considered a fourth spacewalk in which astronauts could manually fold up an old solar array that failed to retract fully by remote control on Wednesday.
The accordion-like 115-foot array, which had provided temporary power to the space station, retracted about halfway — still enough to allow the new pair of solar arrays to rotate.
The half-retracted array presents no danger, NASA said. In a worst-case scenario, it could be jettisoned.
"It's a little disappointing with the solar array, but folks ... understand you're going to have a little hiccup," said Joel Montalbano, a space station flight director. "NASA probably does its best with their back against the wall."