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 7:30 p.m. EDT.
HOUSTON - A massive new motorized gear aboard the International Space Station (ISS) is postitioned to aid the deployment of two sunlight-hungry solar arrays despite a stubborn bolt that challenged two Atlantis astronauts and lost, mission managers said Wednesday.
"It's true that just one of those bolts may have prevented the [gear] from rotating, but we got it done and you can see the fruit of our labor," said John Haensly, lead spacewalk officer for Atlantis' STS-115 mission, in a briefing here at NASA's Johnson Space Center.
STS-115 astronauts Daniel Burbank and Steven MacLean - of the Canadian Space Agency - worked for more than seven hours outside the ISS and Atlantis to successfully ready a gear assembly dubbed the Solar Alpha Rotary Joint (SARJ) to slowly turn a new truss into position.
The first motion of two new solar arrays aboard the ISS is now set to begin at about 7:00 p.m. EDT (2300 GMT) tonight while astronauts aboard Atlantis and the ISS - where the shuttle remains docked - sleep. The arrays will then be deployed in several stages throughout early Thursday to warm up the solar panels and prevent from sticking together, ISS managers said.
Located between the Port 3 (P3) and Port 4 (P4) truss segments - which Atlantis' STS-115 crew delivered to the ISS in a Tuesday spacewalk - the SARJ unit is a 2,500-pound (1,133-kilogram) set of motors, gears and wheels built to rotate P4 and other station hardware 360 degrees so their U.S.-built solar arrays to track the Sun and generate power.
"It's almost like giving birth today, the fighting that we went through and the labor pains," lead ISS flight director John McCullough said after the successful spacewalk. "This is a turn we could get used to, everything is going really well."
Burbank and MacLean had to succeed in removing some 243 bolts that held the SARJ wheel in place for its flight to the ISS. If they failed, and SARJ would not budge, the two solar arrays packed away at the end of P4 could not be unfurled on Thursday because they would cross paths with two other U.S.-built solar arrays already aboard the ISS.
But the two spacewalkers put their backs into to it and in the end, the SARJ unit made its 180-degree turn into solar array deploy position.
"We numerous battles with the hardware, but that's the reason we have people in space...working out there," McCullough said. "Today it took a couple of strong folks to get the job done."
When fully activated, the SARJ is designed to make one full rotation every 90 minutes - which is the time it takes the ISS to circle the Earth, but can be slowed or sped up to one revolution an hour if needed, McCullough said.
Solar arrays set to unfurl
Attention now turns to the P4 truss' four power-producing solar blankets - two per array - which have been folded up like an accordion in their respective boxes, while their pop-up masts are tucked in large cylindrical drums. The arrays represent one-fourth of the space station's final electrical grid, but will double the outpost's power capability once fully brought online in December.
The two solar arrays carry a wing span of about 240 feet (73 meters) and four their individual panels fold up into a box 15 feet (4.5 meters) long by 20 inches (50 centimeters) high. The solar array mast is split into more than 30 bays of interlocking battens that pop into place as the array itself deploys.
ISS flight controllers on Earth will reel out the first mast bay - which stands between three and four feet (just over one meter) - of both new arrays to save time for the STS-115 astronauts tomorrow.
"We're going to take a day off from spacewalks tomorrow," Haensly said.
The forward solar array will roll out to one mast bay at 7:00 p.m. EDT (2300 GMT) tonight while the aft solar array reels out to the same distance at about 10:05 p.m. EDT (0200 Sept. 14 GMT).
"The one bay deploy is basically to start the relaxation of the blankets, and basically to get ahead," McCullough said. "We want to have the Sun in a certain cone to warm the back of the blankets."
Atlantis' STS-115 crew will awake at 11:15 p.m. EDT (0315 Sept. 14 GMT) tonight and oversee the final solar array deployment beginning at 2:40 a.m. EDT (0640 GMT) Thursday morning.
Once fully deployed, the new solar arrays will power its own systems until it is brought into the space station's power grid in earnest later this year, NASA officials said.
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