Astronauts Unfurl New Solar Wings at ISS

One of two new solar arrays, known as 4A, delivered to the International Space Station (ISS) this week by NASA's STS-115 crew rolls out to expose one mast bay on Sept. 14, 2006. CREDIT:

This story was updated at 4:21 p.m. EDT.

HOUSTON - The International Space Station (ISS) unfurled a new set of solar wings Thursday despite a software glitch that cast early doubt on the entire activity.

Two shimmering solar arrays reached their full wingspan of about 240 feet (73 meters) at 8:44 a.m. EDT (1244 GMT) as they extended from the space station's new Port 4 (P4) truss.

"We're very happy to get the array out today," said Atlantis shuttle commander Brent Jett after the solar arrays deployed. "The team obviously did a great job."

That job included a late night scramble by engineers on Earth to first diagnose, then fix, a software command issue with a gear assembly between the space station's Port 3 (P3) truss and the Port 4 (P4) segment which includes the new power-generating solar arrays. Jett and his STS-115 crewmates installed both portside segments to the ISS on Tuesday.  

The gear assembly, known as a Solar Alpha Rotary Joint, will rotate the entire P4 truss - and eventually future outboard segments - to keep its solar arrays aimed at the Sun while the ISS orbits the Earth. One of the SARJ motors did not appear to be properly engaged in the gear's teeth. The issue was resolved late Wednesday, delayed today's solar array deployment by several hours.

"We are quite a few hours behind the timeline for the [solar array wing] deploy, it definitely is not going to happen on time today," NASA astronaut Kevin Ford, serving as spacecraft communicator, told the ISS crew early Thursday.

John McCullough, ISS flight manager for Atlantis' mission, said the SARJ glitch delayed today's solar array deployment by about three hours, but gave the STS-115 crew a bit of extra time for chores planned for later today.

By mid-afternoon, the joint ISS-shuttle crews were just 15 minutes behind schedule, he said.

No sticky issues

NASA's plan to reel out the station's two new U.S.-built solar arrays in stages to prevent severe sticking - dubbed "stiction" by engineers - of the paper-thin layers of photovoltaic cells worked flawlessly.

Both new solar wings were reeled out first a few feet, then to the halfway mark to warm in the Sun for 30 minutes before extending to their full length. At the same time, tension lines were kept in a high-tension mode to separate any sticky panels.

"The high-tension mode did its job and released the panels successfully," Jett told mission control.

About 11 panels appeared to stick together on each array as they deployed, but they easily unfolded once the solar wings reached their full extension, Jett said.

Jett commanded NASA's STS-97 mission in 2000 to deliver the first U.S.-built solar arrays now in use atop the space station's Port 6 (P6) truss.

During that flight, astronauts - including current STS-115 spacewalker Joseph Tanner - deployed the first array in a low-tension mode without warming the arrays, leading to severe stiction that caused one tension line to pull free from its spool. A spacewalk was later required to repair the spool.

John McCullough, lead ISS flight director for Atlantis' mission, said flight controllers and engineers took the lessons learned from the STS-97 mission and would apply them to today's solar array deployment.

"We're looking forward to solar array deploy," McCullough said Wednesday.

New power plant

The P4 trusses port and starboard solar arrays - individually known as 4A and 2A, respectively - were built by Lockheed Martin and will generate about 23 kilowatts of usable power, enough for six average homes, using 64,000 solar cells.

"It's really a very stunning sight to see," McCullough said of the solar array deployment.

The P4 arrays represent one-fourth of the final power grid for the ISS, and will not be brought fully online until December, when spacewalkers are expected to rewire power and data cables between the new solar wings and the ISS.

Two additional solar array modules, destined for yet-to-fly starboard ISS trusses, await launch on Earth.

STS-115 mission specialist Heidiemarie Stefanyshyn-Piper said before launch that today's solar array deployment would be one of the highlights of her spaceflight.

"That's going to be another exciting moment to look at the cameras and say, 'Wow,' as these giant arrays fold out," Stefanyshyn-Piper said.

Stefanyshyn-Piper and Tanner are now preparing to head back outside for the third and final spacewalk of the STS-115 mission on Friday to complete the new solar arrays' installation.

That spacewalk is slated to begin at 5:15 a.m. EDT (0515 GMT) Friday morning.

NASA is broadcasting Atlantis' STS-115 mission to the ISS live via NASA TV. You are invited to follow the shuttle's progress using SPACE.com's NASA TV feed, which is available by clicking here.

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