This story was updated at 10:11 p.m. EST.
Two astronauts ventured outside the International Space Station Saturday on their mission's longest spacewalk to clean a clogged gear needed to restore full power to the orbiting laboratory.
Endeavour shuttle astronauts Heide Stefanyshyn-Piper and Steve Bowen spent nearly seven hours cleaning and greasing up a 10-foot (3-meter) wide gear that rotates the station's starboard solar wings so they always face the sun.
It was the third, and most grueling, spacewalk dedicated to the task and left at least one of the spacewalkers breathing hard by the end.
"I think I'm finally getting the hang of this," Stefanyshyn-Piper said during the spacewalk.
While she and Bowen toiled outside, engineers on Earth wrestled with glitches afflicting the space station's new water recycler, which is designed to convert astronaut sweat and urine back into drinking water.
Delivered by NASA's space shuttle Endeavour, the water recycler is the centerpiece of a $250 million environmental control system that is crucial to the station's ability to double its crew size next year.
A sensor is apparently interfering with a motor that drives the system's urine processor centrifuge, leading to shut downs after about two hours of operations. Astronauts will remove some shock absorbers tomorrow in an attempt to fix it, station flight director Ginger Kerrick said late Saturday.
The water recycler has distilled some water from urine, though not the quantity hoped for by flight controllers. But the amount, about one-third of that sought after, is enough to collect much-needed samples for the return trip to Earth, Kerrick said.
Flight controllers told Endeavour's crew today that, with those samples in hand, they currently don't plan to extend the planned 15-day shuttle flight by a day.
Gear-greasing in space
Saturday's six-hour and 57-minute spacewalk marked the third of four planned for Endeavour's seven-astronaut crew.
The astronauts swapped out five of the six bearings they hoped to replace while cleaning and greasing up the massive rotary joint. The mechanism hasn't worked properly for more than a year, when it was found to be clogged with metal shavings from grinding components.
Stefanyshyn-Piper and Bowen used mitten-like cloths to wipe metal shavings from the gear and grease-spewing guns to lubricate its mottled metal ring.
They had to share grease guns and prepared a makeshift backup cobbled together from one of the caulk guns in Endeavour's heat shield repair kit to make up for equipment lost when a $100,000 tool bag escaped from Stefanyshyn-Piper's grasp in a Tuesday excursion.
The last bearing, one of 12 total spaced around the paddlewheel-like gear, will be replaced during their mission's fourth spacewalk on Monday. The other six were replaced during earlier excursions.
"We really appreciate how hard you guys are all working," Mission Control called up to the spacewalkers. "I know it's painful to call it quits like that, but we think it's the right thing to do."
Final spacewalk ahead
Monday's spacewalk will send astronauts out to a similar rotary joint on the space station's port side. That joint is working fine, but NASA wants it greased up for good measure. A series of maintenance chores on the station's Japanese Kibo laboratory are also on tap.
Saturday's orbital work marked the 117th spacewalk dedicated to the construction and maintenance of the 10-year-old International Space Station.
"Ah, what a beautiful sunset," Stefanyshyn-Piper said as the spacewalk neared its end.
It was the second career spacewalk for Bowen, who now has 13 hours and 49 minutes of orbital work and will venture outside the station once more on Monday with crewmate Shane Kimbrough, who choreographed today's work from inside Endeavour. Bowen and Kimbrough are making their first spaceflight and spacewalks on the mission.
Space station commander Michael Fincke commended the spacewalkers and Stefanyshyn-Piper in particular as she completed her third and last spacewalk for Endeavour's mission.
"You helped build us. You helped fix us. You've always been here for us," Fincke told her. "Thank you very much."
The spacewalk was the fifth for Stefanyshyn-Piper, who ended with 33 hours and 42 minutes and is leading Endeavour's spacewalking team. She is second most experienced female spacewalker, behind fellow NASA astronaut Peggy Whitson, and ranks 25th on the list of the most experienced spacewalkers in the world.
"This was my last one, so I'm now turning it over to you and Shane," Stefanshyn-Piper said to her crewmates. "It's time for the new guys."