Spacewalking astronauts at the international space station noticed a rip in a solar panel they were unfurling to provide much-needed power to the spacecraft.
After admiring the first golden panel they deployed, the two spacewalkers suddenly stopped when they saw the tear in the edge of the second one.
They sent photos of the torn and crumpled section so NASA engineers can determine the extent of the damage, then retracted the panel to ease the pressure on it.
The space agency needs to get the tower up and running to prevent some other balky equipment on the station from delaying the addition of a European research lab on the next shuttle mission.
The solar power tower to the international space station on Tuesday, completing an ambitious three-day moving process that ended with elation when the beam's giant solar panels began to unfurl.
Their joy turned to concern, however, when a rip was spotted in the second solar panel.
The solar panels on the 17½-ton girder that was installed at its new location Tuesday were folded up like an accordion for the move, and the first one slowly was unfurled as the seven-hour spacewalk wrapped up.
NASA needs to get the tower up and running to prevent malfunctioning station equipment from delaying the addition of a much-anticipated European research lab.
The crew kept spacewalker Scott Parazynski and Douglas Wheelock apprised of the first solar wing's unfurling as they floated back inside. Their reaction: "Wow, that's great," and "Awesome!"
"It's a good day's work right there," Parazynski said.
The astronauts abruptly stopped the unfurling of the second panel, however, as soon as they saw the rip right next to the edge.
A spacewalking astronaut found black dust resembling metal shavings inside the motorized joint on Sunday. NASA has limited the joint's motion to prevent the debris from causing permanent damage, but that also limits the system's ability to generate power for the station.
Parazynski spent part of Tuesday inspecting the matching rotary joint that turns the space station's left set of solar wings toward the sun. NASA will examine images he gathered of the perfectly running unit to compare it to the malfunctioning one.
There were no shavings inside the joint, and Parazynski said everything looked pristine.
"It's right out of the shop, no debris whatsoever," he said.
Parazynski and Wheelock guided astronauts inside the station as they used a robotic arm to hook up the beam to the orbiting outpost's backbone. The spacewalkers then began installing bolts to hold the beam in place and connecting wires to provide power.
The space agency added a day to Discovery's mission so spacewalking astronauts could conduct a detailed inspection of the troublesome joint. That work is scheduled for Thursday.
To make room for that inspection, managers canceled a shuttle thermal tile repair demonstration that was scheduled for that spacewalk. The test was added to the mission after a piece of fuel-tank foam gouged Endeavour's belly on the last shuttle flight in August.
Any repairs to the malfunctioning gear would be put off until after Discovery departs.
Discovery is now scheduled to undock from the space station on Monday and return to Earth on Nov. 7.
From NPR reports and The Associated Press