This
story was updated at 8:34 a.m. EDT.
Two
astronauts will venture outside the International Space Station today to help
attach a massive girder that will bring the $100 billion orbital lab up to full
power.
Discovery
shuttle astronauts Steve Swanson and Richard Arnold II are set to
float outside the station at about 1:13 p.m. EDT (1713 GMT) in their NASA
spacesuits to install
the nearly 16-ton girder and its folded-up solar wings.
"We're
ready for a busy day to get that truss attached today," Discovery astronaut
Joseph Acaba radioed down to Mission Control this morning.
Swanson and
Arnold plan to spend 6 1/2 hours working outside the orbital lab to attach the
$298 million Starboard-6 (S6) girder and power plant, the last major
American-built piece of the International Space Station. It will be the third
spacewalk for Swanson and the first for Arnold, who like Acaba is a former
schoolteacher and making
his first spaceflight.
"I am
definitely looking forward to going out the door for the first time," Arnold
said before flight.
Today's
spacewalk is the first of three planned during Discovery's mission. The flight
was initially slated to include four spacewalks and run 14 days, but NASA
shortened the mission after a series of launch delays in order to complete the
construction work before the arrival of a previously scheduled Russian Soyuz spacecraft.
That Soyuz is due to launch a new crew and American space tourist toward the
station next week.
Space
station backbone
The 10
astronauts aboard the linked shuttle and space station set
the stage for today's work on Wednesday. With intricate precision, they
wielded robotic arms on both spacecraft to pluck the 45-foot (nearly 14-meter)
long girder from Discovery's payload bay - with only inches of clearance at
times - and park it overnight for today's installation.
The
spaceflyers will need more of that precision today. Astronauts inside the space
station will extend the outpost's Canadarm2 robotic arm about as far its
57-foot (17-meter) limb can reach to attach the S6 truss segment. They'll have
to rely on verbal signals from Swanson and Arnold to guide the new girder into
position on the starboard-most side of the orbital outpost.
"It's quite
a big choreography going on there," Arnold said before flight. "Basically, it's
like backing your car in the garage."
But this
"car" is weighs 31,000 pounds (14,061 kg) and carries two pop-up masts to
support twin solar arrays that are folded away in thin boxes like a bunch of
oversized maps.
The
station's new S6 girder is the final piece of the space station's 11-segment
main truss, which at more than 300 feet (91 meters) across will be longer
than an American football field when complete. Each of the two solar arrays at
its tip is 115 feet (35 meters) long. They are the fourth set of U.S. solar
arrays for the space station's power grid, which generate enough electricity to
power 42 average size homes once it is all plugged in, NASA has said.
The space
station needs that much power to fully support scientific research inside
laboratories and modules from the U.S., Russia, Europe and Japan, as well as
maintain life support for larger six-person crews. The outpost's current crew
numbers three astronauts, but that is slated to double by late May.
"The most
important thing is getting the solar arrays deployed," Swanson said before
flight.
Space
station flight director Kwatsi Alibaruho told reporters late Wednesday that
Swanson and Arnold must secure the new girder in place with four bolts, then
connect a series of four data and power cables for today's spacewalk to
succeed. The astronauts also plan to prepare a radiator on the girder to be
deployed, set up the solar wing masts and release a set of restraints and catches
on the boxes containing the folded up arrays.
Healthy
space shuttle
NASA
currently plans to unfurl the new solar wings on Friday, two days earlier than
scheduled, since mission managers decided late yesterday that Discovery's heat
shield is healthy after its March 15 launch into orbit.
Shuttle
managers cleared the heat shield of launch debris concerns after
a detailed inspection and photo survey of its heat-resistant panels and
tiles. A final inspection will be performed after Discovery leaves the station
to check for damage from space debris or micrometeorites.
NASA has
kept a close eye on the heat shield integrity of its three-shuttle fleet since
the tragic 2003 loss of the shuttle Columbia and seven astronauts during
re-entry. Damage to that shuttle's heat shield during launch left it vulnerable
to the scorching temperatures of re-entry, which destroyed the spacecraft.
Aside from
a minor ding to a tile located well aft on its tile-covered underbelly,
Discovery's heat shield is pristine, mission managers said. Mission Control
radioed the good news up to the shuttle astronauts late Wednesday and suggested
they'd likely get the chance to unfurl the station's new wings early.
"Thank you
very much," Discovery skipper Lee Archambault called back. "That's absolutely great news."
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. Live spacewalk coverage
begins at about 12:13 p.m. EDT (1613 GMT).
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