(CNN) -- A pair of astronauts from the space shuttle Discovery safely completed a six-hour spacewalk outside the International Space Station on Thursday, installing a set of solar panels that will help the station handle twice as many crew members.
The solar panels installed to the space station are seen Thursday with Earth in the backdrop.
Astronauts Richard Arnold and Steve Swanson bolted into place solar arrays that will be the last piece of the station's expanded power system. It's part of an expansion that will allow the size of the station's crew to be doubled from three to six.
"We're very proud of their work," said NASA spacewalk director Glenda Laws-Brown. "They were very efficient. I've watched several of these and this was a joy to watch."
The walk, which NASA timed at 6 hours and 7 minutes, was completed at 7:23 p.m. ET.
It was Swanson's third spacewalk and Arnold's first, and the 121st spacewalk done in support of assembling the space station.
Lead space station flight director Kwatsi Alibaruho said the walk, and operation of robotic arms by astronauts John Phillips and Koichi Wakata, were "executed flawlessly."
The crew also worked Thursday to make sure members of the space station stay physically fit -- repairing a treadmill and exercise bicycle that had broken down, Alibaruho said.
Discovery, with its seven-member crew, lifted off from the Kennedy Space Center in Cape Canaveral, Florida, on Sunday. The launch originally was scheduled for last Wednesday, but was delayed after engineers discovered a leak in a hydrogen gas vent line.
The 13-day mission also will drop off Wakata at the station. He will replace NASA's Sandy Magnus, becoming the first Japanese astronaut to stay at the station for an extended amount of time.
Discovery will leave the station by March 25 to make way for the Russian Soyuz capsule, which will deliver the station's next crew.