Spacewalk Sets Stage for ISS Solar Array Deployment
STS-115 astronauts Daniel Burbank (right) and Steven MacLean - of the Canadian Space Agency - prepare the International Space Station's Port 3/Port 4 truss to deploy new solar arrays during a Sept. 13, 2006 spacewalk.
CREDIT: NASA TV.
This story was updated at 4:51 p.m. EDT.
HOUSTON - Two spacewalking astronauts freed a new piece of the International Space Station (ISS) to rotate independently from the rest of the 233-ton orbital laboratory, paving the way for the deployment of two solar arrays this week.
Despite a broken socket, sticky bolts and another runaway bit of metal, STS-115 mission specialists Daniel Burbank and Steven MacLean successfully removed a series of locks and restraints from a pivot point between the space station's newly delivered Port 3 (P3) and Port 4 (P4) truss segments.
"This is more of an endurance kind of thing," Burbank said as he and MacLean grunted and struggled to remove one particularly stubborn bolt with a bit of extra elbow grease during their seven-hour and 11-minute spacewalk. "That would be a showstopper for rotation and deploy."
"You guys didn't spend enough time at the gym," Tanner told the spacewalkers from inside their Atlantis shuttle, calling their work an amazing effort. "You wouldn't imagine the drama inside here and, I'm sure, on the ground right now."
The orbital construction job freed a 10-foot (three-meter) wide, motorized gear mechanism known as the Solar Alpha Rotary Joint (SARJ) - to rotate the outboard P4 truss a full 360 degrees so its solar arrays can track the Sun once deployed and activated.
The 2,500-pound (1,133-kilogram) SARJ assembly must rotate the P4 truss at least 180 degrees from its current position before the two expansive solar arrays can unfurl Thursday to avoid interfering with a set of older U.S.-built solar wings spread about 90 feet (27 meters) above the P4 truss.
"We can't rotate right now without running into the other array," John McCullough, NASA's lead ISS flight director during Atlantis' mission, said Tuesday.
Mission controllers plan to put the SARJ through a 12-hour checkout that included the 180 degree turn, then the entire test revolution. Atlantis astronauts confirmed that the device was in fact rotating the P4 truss by 1:03 p.m. EDT (1703 GMT).
MacLean did lose another small bolt, similar to one that escaped their fellow STS-115 spacewalker Joseph Tanner on Tuesday, when the retaining washer latching it to a thermal cover apparently failed.
"I did not see it go," MacLean told mission controllers, though flight controllers were not concerned that the lost bolt posed a threat to the SARJ assembly, ISS or shuttle. "When I removed the cover, the four bolts were on it."
A small pin also popped free from Burbank's trash bag near the end of the spacewalk, but the spacewalker reached out and grabbed it before it could escape.
NASA's STS-115 mission is the agency's first dedicated ISS construction effort since late 2002, and kicks off an expected 15-flight marathon of orbital assembly. The shuttle's six-astronaut crew attached the station's new 35,000-pound (15,875-kilogram) trusses and solar arrays during a Tuesday spacewalk.
While Burbank and MacLean are both veteran shuttle astronauts, they each made their spacewalk debut today at 5:05 a.m. EDT (0905 GMT).
"Boy that is pretty," Burbank said of the Earth after stepping into space. "It's not something you see every day."
They had a tedious, but crucial, job ahead of them: the removal of 14 launch locks and six restraints that held fast the SARJ assembly during Atlantis' Sept.
It was repetitive work. Each launch lock required the astronauts to unscrew up to six bolts and remove a thermal cover, remove four more bolts to unlock the mechanism, and then replace the cover and secure its own screws.
The launch restraints too required more bolt work, which was so grueling at one point that both men strained together to pry a single stubborn bolt from its lock point.
"Woohoo!" Burbank rejoiced as the bolt came free.
One of MacLean's tools even broke while trying to loosen one of the bolts.
"They're going to take it out of my wages, you know," MacLean said.
"We appreciate you answering that age-old question for MCC, how many astronauts does it take to unscrew a bolt," said NASA astronaut Pam Melroy, serving as ISS spacecraft communicator, from mission control here at Johnson Space Center. "Apparently it takes three, two outside and one inside."
MacLean, a Canadian Space Agency astronaut, is only the second Canadian ever to walk in space after his fellow countryman Chris Hadfield helped deliver the space station's Canadarm2 robotic arm in April 2001.
"It was an absolutely wonderful experience," MacLean said.
Flight controllers woke the spacewalkers and this four STS-115 crewmates Tuesday with Bachman-Turner Overdrive's "Takin' Care of Business" picked just for MacLean.
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