Two spacewalking astronauts will
venture outside the International Space Station (ISS) today to attach a new
piece of the orbital laboratory's metallic backbone.
Clad in their bulky NASA spacesuits,
Endeavour shuttle astronauts Rick Mastracchio and Dave Williams are due to step
outside the ISS at about 12:31 p.m. EDT (1631 GMT) for their planned 6.5-hour
construction job in space.
"It's going to be a really
exciting spacewalk for us," Williams, a veteran Canadian Space Agency
astronaut, said in a preflight NASA interview. "We're both highly trained
spacewalkers, and we've both been to space, but neither one of us has actually
done a spacewalk before."
The two astronauts, working
alongside their crewmates inside Endeavour and the ISS, will help install the Starboard
5 (S5) truss to the station's starboard-most edge. The new addition will prime
the space station for the delivery of new solar arrays next year.
Mastracchio will lead today's
spacewalk with Williams while their STS-118 crewmate Tracy Caldwell
choreographs the excursion from inside Endeavour. Shuttle pilot Charlie Hobaugh
will wield the station's robotic arm during the extravehicular activity.
Their crewmates, meanwhile, will
prepare for a Sunday
inspection of a small gouge in the heat-resistant tiles lining Endeavour's
underbelly.
Space station's 'Stubby' piece
Built by Boeing, the S5 truss is a
spacer segment about the length of a small compact car. It is designed to serve
as a bridge between the station's current starboard solar array segment, delivered
last June, and a second solar wing still awaiting launch.
"The S5 truss, actually we call
it 'Stubby,' is a little structural piece," said schoolteacher-turned-astronaut
Barbara Morgan, an STS-118 mission specialist who waited 22 years for her
spaceflight since first joining NASA in 1985 as its backup Teacher in Space.
Weighing in at 4,010 pounds (1,818
kilograms), the $11 million S5 truss is about 11 feet (3.3 meters) long, 14
feet (4.5 meters) wide and stands 13 feet (4.2 meters) tall. Mastracchio and
Williams help guide the new truss into position, with only inches of clearance
at some points, then remove a series of launch locks and restraints before
securing it in place with drill-driven bolts.
The task is a mirror image of the installation
of Port 5 (P5) truss - or "Puny" - to the station's port side in
December 2006 during NASA's STS-116 mission.
"We watched it intently, of
course, to make sure that we understood any challenges they had," Hobaugh
said of the STS-116 crew's Port 5 truss installation.
In addition to the S5 installation,
Mastracchio and Williams will retract a radiator extending from the space
station's mast-like Port 6 truss, preparing the segment for its relocation to
the port-most side of the orbital laboratory later this year.
Today's spacewalk is the first of three
planned excursions for the STS-118 crew. The successful activation of a new
space station-to-shuttle power transfer system Friday gave shuttle mission
managers confidence that they will be able to extend Endeavour's flight by
three days and add a fourth spacewalk to the STS-118 crew's docket, lead
shuttle flight director Matt Abbott said.
Commanded by veteran spaceflyer
Scott Kelly, the shuttle astronauts are delivering about 5,000 (2,267
kilograms) of cargo and a new spare parts platform to the ISS in addition to
the S5 truss.
Mastracchio has said he expects
today's spacewalk and others planned for the STS-118 mission will be the high
point of his spaceflight.
"[T]here's going to be nothing
but space below me and Earth, and it's going to be a fantastic view,"
Mastracchio said in a NASA interview. "I'm really looking forward to
that."
NASA is broadcasting Endeavour's
STS-118 mission live on NASA TV. Click
here for mission updates and SPACE.com's NASA TV feed.
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