This story was updated at 2:49 p.m. EST (1949 GMT).
Two spacewalking astronauts brought the International Space Station (ISS) a step closer to full power Wednesday after replacing a broken motor at the base of one of their orbiting lab's wing-like solar arrays.
Taking great care to avoid electrical shocks, station commander Peggy Whitson and flight engineer Dan Tani successfully restored the vital electricity-producing wing to full operations during their seven-hour spacewalk.
"It's an important step for us to get that power generation back up to where it's optimized," Whitson said before the repair.
The space station's power grid has been afflicted by a pair of major glitches centered on its starboard side since last fall. In late October, Tani discovered metal debris contaminating a massive, 10-foot (3-meter) wide gear that rotates the outpost's starboard solar wings like a paddlewheel to maximize power production by continuously track the sun.
The second malfunction, which station astronauts fixed today, occurred in early December when a garbage can-sized motor that pivots its solar wing on a different axis than the larger gear suffered three different electrical failures. The new motor, known as a Bearing Motor Roll Ring Module, successfully performed 360-degree test spin during today's spacewalk.
"Yay, it works!" cheered Whitson as she and Tani watched the solar wing turn. "Excellent, outstanding - isn't that cool?"
Without the new motor, the station could support NASA's next shuttle mission — set to launch a European lab to the ISS on Feb. 7 — but not much more, space station managers said. But the motor's successful activation should allow the station to host shuttle flights delivering new European and Japanese lab modules through this summer.
"We had clean sweep today," said Expedition 16 flight director Kwatsi Alibaruho after the repair. "The [spacewalk] went flawlessly."
NASA hopes to launch up to five shuttle flights to the ISS this year to add European and Japanese laboratories and prepare the station for larger, six-person crews.
In addition to the motor repair, Whitson and Tani also performed another inspection — the fourth so far — of the station's starboard Solar Alpha Rotary Joint, the gear contaminated with metal debris. The spacewalkers evaluated damage from the debris and collected samples from areas previously unseen.
Alibaruho said the new debris samples will help shape future repair plans for the larger gear later this year. They will be shipped back to Earth along with the broken solar wing motor aboard one of the next NASA shuttles to fly, he said.
Wednesday's spacewalk began at 4:56 a.m. EST (0956 GMT) and marked the fifth excursion of the station's current Expedition 16 mission, as well as the sixth career excursion for both Whitson and Tani.
A communications glitch left the spacewalkers without direct contact to Mission Control in Houston briefly, but a backup system worked fine during the seven-hour, 10-minute excursion. Russian cosmonaut and flight engineer Yuri Malenchenko remained inside the ISS during the spacewalk and served as a go-between during the short glitch.
Whitson and Tani used extra caution during today's spacewalk because of the added risk of electrical shock near the starboard solar wing.
Each U.S. solar wing extends produces about 160 volts when awash in sunlight and feeds power through the so-called beta gimbal assembly that houses the motor replaced in today's orbital work. To avoid shocks and electrical arcs, Whitson and Tani worked only in safe, 33-minute periods of darkness as the station orbited the Earth.
"This is an incredibly tricky box that has to be changed out," said Keith Johnson, Expedition 16's lead spacewalk officer, of the 200-pound (90-kg) motor. "Never was it considered a task that a station-based team would do."
Because of the tight timing, most mission planners assumed a heavily trained shuttle-based spacewalking team would be required, he added.
Whitson, who squeezed inside the station's starboard truss girder to swap out the broken motor, said there was also the risk of accidentally disconnecting vital latches that anchor the 115-foot (35-meter) solar wing to the space station.
"That would lose us a whole lot of style points," Whitson said before the spacewalk, though the actual repair appeared go smoothly.
Wednesday's excursion marked the final planned spacewalk of the Expedition 16 mission and the 101st dedicated to space station assembly and maintenance. The spacewalk also marked the sixth career excursions for both Whitson and Tani, who repeatedly commented on view of Earth and space.
"It's beautiful," Tani said as the station passed over South Africa. "Reds, blacks - such colors."
Tani also beamed an orbital good morning call down to his wife Jane and two daughters, Keiko and Lilly, on what he expected to be the last spacewalk of his mission. He is scheduled to return to Earth next month with the STS-122 crew aboard NASA's Atlantis shuttle.
The spacewalk was Tani's first since the unexpected death of his 90-year-old mother Rose in a car accident before Christmas last month. ISS flight controllers said Tani has coped with the tragic loss admirably and that it has not affected his work.
Whitson, who holds the world record for most spacewalking time by a female astronaut, closed the excursion with a new total 39 hours and 46 minutes. Tani, meanwhile, concluded with 39 hours and 11 minutes of spacewalking time under his belt. Together, Whitson and Tani rank 15th and 16th among the world's most experienced spacewalkers.
"Five spacewalks in three months, that's been fantastic," said Tani, as he thanked flight controllers and engineers on Earth for their help planning today's spacewalk. "It's been a great run here."