This story was updated at 12:22 p.m. EDT.
After more than a decade of construction, the
International Space Station is spreading its last pair of solar wings
Friday as astronauts and Mission Control watch with bated breath.
The new U.S.-built solar arrays are
the final piece of the $100 billion space station's power grid. Astronauts
attached them to the starboard side of the orbiting laboratory in
a Thursday spacewalk, but the real test comes later today, when they push
the button inside that will remotely unfurl the power-generating solar wings.
The last time astronauts attempted
to unfold similar arrays, one of the wings snagged on a guide wire and ripped,
sending engineers on Earth scrambling for a fix. Spacewalking astronauts
ultimately stitched
the tear back together and the wing has been working ever since.
NASA, and the shuttle Discovery
astronauts who delivered the new $298 million solar arrays, are hoping for less
drama today.
"We have made solar array deploys
exciting in the past," said Dan Hartmann, head of NASA's space station mission
management team, late Thursday, adding that his team will be on edge. "Pins and
needles? Yes, a little bit ... it's kind of the nature of the game."
The 115-foot (35-meter) long solar
arrays are vital since they will complete the station's power grid, boosting
the current system by 25 percent, Hartmann said. Their installation Thursday
completed the station's 335-foot (102-meter) backbone, which supports the
outpost's railcar, robotic arm base and three other sets of expansive solar
arrays. In all, the station is designed use all four sets of solar wings to
produce enough electricity to power 42 houses on Earth, NASA has said.
Astronauts and scientists are
counting on that power supply so they can ramp up science operations and double
the station's crew size up to six people later this year. This last set of
solar wings should generate about 36 kilowatts total, 15 kilowatts of which is
reserved for science. It would double the current science power supply, mission
managers said.
And when the new solar arrays are
deployed, the station will finally look like the nearly
complete orbital outpost depicted in artist illustrations throughout its
10-year construction history.
"We're looking forward to it,"
Hartmann said. "There will be all kinds of emotions and, hopefully, jubilation
at the end."
Flight controllers on Earth extended
each of the new solar arrays just slightly in the predawn hours early Friday.
Astronauts aboard the docked Discovery and station began the deployment
process in full at 11:06 a.m. EDT (1506 GMT).
Solar wing challenges
The space
station's new solar wings are mostly folded up, much like an accordion or
an oversized map, inside a set of storage boxes on the starboard edge of the
outpost's backbone-like main truss. They've been locked away in those boxes for
years - one for longer than any of the station's seven other wings - and
astronauts fully expect their folds to stick together.
NASA has seen the phenomenon - which
it calls "stiction" - before, in 2000. That glitch, too, required a spacewalk
fix. Now, NASA deploys solar arrays in stages, giving each wing time to warm up
so they are less conducive to sticking.
"We are a little concerned because
these arrays have been in the box longer than others," said Discovery astronaut
John Phillips before flight. Phillips will be the one with his finger on the
button, in charge of unfurling the solar arrays or hitting the emergency stop
if things go awry.
But he is not the lone solar wing
sentinel, space station flight director Kwatsi Alibaruho told reporters late
Thursday.
All 10 shuttle and
station astronauts will be watching, either through windows, cameras or on
computer screens. A host of engineers will be backing them up on Earth, staring
at the same views on consoles in Mission Control at NASA's Johnson Space Center
in Houston.
The goal, Alibaruho said, is to be
ready to spot any rip, tear or glitch from the past, or something new and
unexpected, as early as possible.
There is a time limit too: about
five hours.
In order to orient the new solar
arrays so they warm up - to reduce stiction - the station has to fly in a less
optimal orientation. The position can lead to communications drop outs and
expose some parts of the station to extreme cold, while risking overheating in
others. Mission Control wants to maintain constant communications while the
arrays are being extended.
"Right now, the biggest threat that
I see, barring some problem with the mechanism, are gaps in communications,"
Alibaruho said. "We may simply not get through the deployment of both solar
arrays before we're required by our mission rules to maneuver back to
equilibrium."
If Discovery astronauts are unable
to completely extend the arrays today, there is some extra time on Sunday,
which is when they were initially due to be unfurled. Mission managers moved
the deployment to today to fill in time originally reserved for an extra
shuttle heat shield inspection that was no longer needed.
While the solar arrays are extended
outside the station, astronauts plan to make repairs to the outpost's urine
recycling system inside the orbital lab. The spaceflyers will install a new
centrifuge to distill urine back into drinking water. The system is part of a
larger water recycler that converts urine, astronaut sweat and condensation back
into pure water for drinking, food preparation and bathing.
The fix is in
Even of Discovery's crew hits a snag
in today's solar wing deployment, mission managers have a stockpile of repair
methods and tools cobbled together from previous missions.
"All those tricks are in our hip
pocket, all those tools are in our bag," Discovery's lead spacewalk officer
Glenda Laws-Brown said Thursday night. "We have trained the crews on all those
prior techniques."
Discovery launched toward the
station late Sunday on a 13-day mission to swap out a member of the outpost's
crew and deliver the new solar arrays truss. Two of the mission's three
spacewalks remain. Four were originally planned, but NASA trimmed the flight
due to launch delays in order to complete the construction work and depart the
station before the launch of a previously scheduled Russian Soyuz spacecraft
next week.
Laws-Brown said she was confident
the solar arrays would be unfurled successfully. Watching their installation
during Thursday's spacewalk felt like being at the start of a rollercoaster,
she added.
"It's exciting and you're thinking
'Oh my, gosh it's too late to get off now, I better hold on for a great ride,'"
Laws-Brown said. "I told my team to pay attention and don't miss a minute. This
is the good stuff."
SPACE.com is providing continuous
coverage of STS-119 with reporter Clara Moskowitz and senior editor Tariq Malik
in New York. Click here
for mission updates and SPACE.com's live NASA TV video feed.
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