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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