This story was updated at 10:52 p.m. EST.
Two NASA astronauts ventured outside the International Space Station on the orbiting lab?s 10th birthday Thursday in a spacewalk to continue tune-up work on the outpost?s massive starboard side gear.
Astronauts Heide Stefanyshyn-Piper and Shane Kimbrough floated outside the station on the tenth anniversary of the launch of its first module and were determined not to let any tools escape while they cleaned metal grit out of the solar array-turning gear.
?Hopefully I won?t lose anything on the way,? Stefanyshyn-Piper said as she moved tools around near the spacewalk?s end. ?Everything?s tethered, so it?s just a matter of what?s going to stay in the bag.?
A $100,000 bag of tools escaped from Stefanyshyn-Piper during a spacewalk two days ago when she and a crewmate began the complicated clean-and-grease job on the 10-foot (3-meter) wide gear. The lost bag carried some of the grease guns and other tools that were to be used during today?s spacewalk.
To make up for the lost equipment, Stefanyshyn-Piper used terry cloth-like wipes loaded with the special space lubricant as a makeshift grease mitt to limit the amount of time lost by having to share tools with Kimbrough. They started their work at 12:58 p.m. EST (1758 GMT), more than 40 minutes early.
The spacewalk was the fourth for veteran spaceflyer Stefanyshyn-Piper and the first for Kimbrough, who was ordered back to the airlock near the end by Mission Control due to increased levels of carbon dioxide in his spacesuit. He also had problems hearing Mission Control, neither issue was a major concern, mission managers said. The mission?s next spacewalk is set for Saturday.
?Nice job on your first EVA,? Stefanyshyn-Piper told Kimbrough using NASA?s technical term for spacewalk. ?It was a good day.?
Greasing space gears
Thursday?s six-hour and 52-minute spacewalk was the second of four excursions by the docked shuttle Endeavour?s crew to tune up the space station?s starboard side gear. The mechanism is designed to rotate the station?s starboard solar wings like a paddlewheel so they always face the sun and maximize power production.
But unlike a similar gear on the station?s port side, which is working fine, the starboard gear has been grinding on itself, littering its delicate turning surface with metal shavings that have eaten away at its bearings.
Endeavour spacewalkers have been steadily removing the damaged bearings, cleaning out the metal grit, applying a new layer of lubricant and installing brand new bearings. The work will take all four spacewalks, with the preventative lubrication of the port gear thrown in for good measure.
The complicated spacewalk is part of Endeavour?s planned 15-day mission to outfit the $100 billion International Space Station to accommodate larger, six-person crews sometime next year. Inside the station, astronauts have been installing new gear to expand it from a three-bedroom, one-bath outpost into a five-bedroom facility with two bathrooms, two kitchens, a gym and a recycling system that turns sweat and urine into drinking water.
In addition to the gear tune-up, Stefanyshyn-Piper moved a pair of equipment carts outside the station and added a touch of grease to the end of the outpost?s Canadian-built robotic arm.
The space station decade
Thursday?s excursion marked the 116th spacewalk dedicated to space station construction and maintenance. By sheer coincidence, it took place on the 10th anniversary of the launch of Zarya, a Russian-built module that was the first piece of the station ever launched into space.
Zarya, whose name translates to ?Sunrise? in Russian, rocketed into orbit on Nov. 20, 1998 at 1:40 a.m. EST (0640 GMT) atop a Proton booster launching from the Central Asian spaceport of Baikonur Cosmodrome in Kazakhstan.
"Today is a special day aboard the International Space Station," said the station's current commander Michael Fincke in a recorded video commemorating its 1998 birth. "And since then, the space station has gotten larger and larger."
Since then, eight more pressurized modules have been added to give the now 313-ton space station the internal living space comparable to the cabin of a jumbo jet. NASA and 15 different partner nations have been working to assemble the station, which includes Russian and U.S. core modules accentuated by American, Japanese and European space laboratories.
NASA space shuttles, Russian Soyuz and Progress vehicles and a European freighter have all visited the outpost, with Japan set to launch its own cargo ship to the station next fall.
Since Zarya?s launch, the space station has orbited the Earth more than 57,309 times, traveling some 1.3 billion miles (2 billion km) - or almost enough to reach out beyond the orbit of the planet Pluto, NASA has said. Some 167 different people from 15 countries have visited the outpost. Astronauts have spent 732 hours and 25 minutes working outside the space station to put it together.
It?s fitting that the shuttle Endeavour is currently docked at the space station, as it was the very same spacecraft that launched NASA?s Unity connection module to the outpost in its early days of construction.
Under the command of veteran spaceflyer Chris Ferguson, Endeavour?s crew is now laying the foundation for the space station to double its population in May 2009.
?This fine crew and its cargo will enable the space station to plus up to a crew of six people living full-time,? Ferguson said in the video. ?After 10 years, we wish the International Space Station a happy birthday and we hope to see many, many more."
NASA is providing live coverage of Endeavour's STS-126 mission on NASA TV. Click here for SPACE.com's mission coverage and NASA TV feed.
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