A pair of Endeavour shuttle astronauts will venture outside the International Space Station (ISS) today on the first of four scheduled spacewalks to clean up a clogged solar array gear.
Spacewalkers Heide Stefanyshyn-Piper and Steve Bowen are due to don their NASA-issue spacesuits and float outside the station at about 1:45 p.m. EST (1845 GMT) today to begin the complicated chore of de-griming and lubricating a starboard-side gear that helps the space station continuously turn its solar panels toward the sun.
?We?re going to going to be working on the starboard solar array system, trying to make it come back to life,? Bowen said in a televised interview Monday. ?We?ve got a little cleaning and greasing to do.?
Today?s planned spacewalk is just the first of a four-part plan to clean the ailing solar array gear, which has been jammed by metal grit from grinding into itself for more than a year.
Stefanyshyn-Piper, a veteran of two spacewalks, and first-time spaceflyer Bowen are taking the first shift. They also plan to retrieve a station nitrogen tank for return to Earth and perform other maintenance tasks, but all eyes will be on how their gear cleaning goes.
?Certainly, the first [spacewalk] of any mission you want to go well,? space station flight director Holly Ridings said Monday. ?We have a lot of confidence that tomorrow?s going to go well.?
Stefanyshyn-Piper is leading Endeavour?s spacewalking crew on the orbital clean-up job. For today?s planned 6 1/2-hour excursion, Donald Pettit and Sandra Magnus will operate the station's robotic arm in an orbital assist.
NASA's shuttle Endeavour launched Friday night and docked two days later on a planned 15-day mission to the space station. Besides the four spacewalks, the seven-astronaut shuttle crew is also delivering a cargo pod full of life support equipment to prepare the space station to double its crew size up to six astronauts next year.
"For the most part, during the early part of the mission, there?s very little free time," said Stefanyshyn-Piper said in a preflight interview.
Stefanyshyn-Piper and her spacewalking crew will don some new NASA spacesuit gloves during their excursions. The new space mitts are designed to be more durable and resistant to potentially fatal cuts or slices from sharp edges on the station?s exterior.
Space station tune-up
The astronauts will use grease and space wipes to clean the metal filings and grit from the starboard solar array gear, where a previous spacewalker discovered the damage in October 2007.
That critical Solar Alpha Rotary Joint (SARJ) is a massive, 10-foot (3-meter) wide gear that allows the station's starboard solar panel to turn like a paddlewheel. Future enlarged crews will draw additional power from the space station, and so the extravehicular activities (EVAs) are focused on getting the solar array gear unstuck.
"The lion?s share of those EVAs will be devoted to repairing this large alpha joint which was deemed to be in a state of disrepair because it was essentially disintegrating," explained Endeavour commander Chris Ferguson in a preflight interview.
"Parts of the protective coating were coming off and we had to lock one of those critical alpha joints," he added. "So it?s hoped through the efforts of our four EVAs that we could lubricate and change out some components to enable those alpha joints to completely function normally again."
Astronauts will remove 11 bearings in the joint and replace them with new ones over the course of the four spacewalks, while also cleaning off troublesome debris. They will also do preemptive cleaning on the portside solar array gear during the fourth spacewalk, after taking care of the ailing starboard gear.
"We?ll replace some of the bearing assemblies, and then we?ll bring them home so that that will give more information for the engineers here on the ground to look at and to try to come up with the, with the root cause," Stefanyshyn-Piper noted.
The spacewalkers have repurposed a space caulk gun initially developed as part of NASA?s shuttle heat shield repair plan to squeeze out gray Braycote vacuum grease to lubricate the joint. A scraper similar to a putty knife can dislodge debris that has become stuck on any surfaces. Wet wipes will help clear away metal filings and grit, and special bags are available to catch the clouds of filings.
Stefanyshyn-Piper expressed hope that the four spacewalks would both fix the current problem and help extend the life of the solar array gear.
"But that?s not a task that can be done in just a couple of hours so our work on the SARJ is spread out over three EVAs," she added. "On EVA 1 we just start it."
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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