Cape Canaveral, Fla. Spacewalking astronauts replaced a failed electrical unit at the International Space Station on Wednesday, restoring full power to the orbiting lab.

The space station had been operating since spring with only seven of its eight solar-power channels. Wednesday's work by Reid Wiseman and Butch Wilmore NASA's second spacewalk in two weeks brought the energy capability back up to 100 percent.

The spacewalkers encountered balky bolts but still managed to complete the job in the allotted time, with less than two minutes to spare.

"Yoo-hoo!" they cheered as NASA declared victory.

The voltage regulator shorted out in May but could not be replaced until now because of a yearlong hiatus in nonemergency spacewalks by NASA. The stoppage was caused by spacesuit problems, most notably a flooded helmet that nearly cost an astronaut's life in 2013.

Wiseman took part in the Oct. 7 spacewalk that jump-started NASA's outside maintenance, accompanied by a German. This time, Wiseman was joined by Wilmore, who made his first spacewalk.

To avoid an electrical shock, the two spacewalkers waited until darkness before attempting to remove the old voltage regulator, so there would be no discharge. They took in the view 260 miles below as they waited for the space station to fly into the night side of Earth.

"I see Cairo!" Wiseman said. "Can't quite make out the pyramids, though."

Sunset came over Kazakhstan and China, and Wiseman began to undo the bolt holding down the bad regulator. His pistol grip tool failed to loosen the bolt. "I can feel it binding up," he said. A ratchet wrench along with some muscle did the trick.

Wiseman removed the 330-pound boxy regulator from its slot and, with Wilmore's help, popped in the new one. But once again, they ran into bolt trouble, this time in securing the new device.

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Astronauts restore full power to International Space Station (+video)