HOUSTON --
Two astronauts will step outside the International Space Station (ISS) Saturday
on what will likely be a shortened spacewalk as NASA casts a wary eye toward
Hurricane Dean.
Clad in
their bulky NASA spacesuits, Endeavour shuttle astronaut Dave Williams and ISS
flight engineer Clayton Anderson are scheduled to begin their orbital work at
about 10:01 a.m. EDT (1401 GMT). But they may cut short their planned
6.5-hour spacewalk, which is aimed at priming the ISS for future
construction, in order to prepare Endeavour for an early departure from the
orbital laboratory, NASA has said.
The
excursion will mark the fourth extravehicular activity (EVA) of NASA's
STS-118 mission to the space station.
"Due
to Hurricane Dean, and its potential impact to the Gulf Coast, we're working
towards a plan that would land us a day early," NASA astronaut Shane
Kimbrough told Endeavour's crew Friday from Mission Control here at the Johnson
Space Center. "The way we're going to get there is to give up some [cargo]
transfer activities tomorrow and possibly shorten EVA-4."
Endeavour's
STS-118 crew is scheduled to return to Earth Wednesday, but the looming threat
of Hurricane Dean to NASA's shuttle and ISS Mission Control centers at JSC
prompted the agency to work towards a possible
Tuesday landing. The space agency is hoping to preserve the option of
landing Endeavour early in case the hurricane forces the evacuation of Mission
Control, which would then require NASA to transfer shuttle operations to a
backup site at the Kennedy Space Center in Cape Canaveral, Florida.
As of late
Friday, Dean had winds of near 145 miles per hour (230 kph) and reached
category four hurricane status, according to the National Hurricane Center. The
storm was expected to strengthen over the next 24 hours reach the Gulf of
Mexico by Wednesday.
Space
station flight controllers told astronauts aboard the ISS and Endeavour late
Friday that they would likely leave out extra and low priority tasks from the
docket of today's spacewalk. Once high priority tasks - such as installing a
shuttle inspection boom stand to the ISS and securing an antenna mount - were
complete, Anderson and Williams would be ordered back inside the space station,
even if they were ahead of schedule, ISS spacecraft communicator Lucia
McCullough told the joint crews.
"Alright,
well I think we can handle that," said STS-118 mission specialist Tracy
Caldwell, who will choreograph today's spacewalk from inside Endeavour.
NASA's
worries over Hurricane Dean came one day after the agency cleared
its concerns over a small gouge in Endeavour's belly-mounted heat shield.
The deep, 3 1/2-inch (nine-centimeter) long gash was caused by a 0.021-pound
(about one-third of an ounce) piece of foam insulation during the shuttle's
Aug. 8 launch, but later found not to pose a threat to the safe return of
Endeavour and its crew, NASA said.
One last
time
Saturday's
spacewalk will mark the fourth and final excursion of NASA's STS-118 mission to
continue assembly of the ISS. Mission managers added the extra spacewalk to the
mission after the success of a new power
transfer system that allows Endeavour to siphon electricity from the space
station's solar arrays rather than relying on its own power supplies.
"Clay
and I are really excited to go outside, we've got all our tools together,"
Williams told reporters Friday, adding that the entire STS-118 spacewalking
team has been a joy to work with. "It's just been an amazing team and
experience."
During the
spacewalk, Anderson and Williams are expected to secure restraint bolts on an
ISS antenna mount to prepare them for additional work planned for NASA's next
shuttle flight in October.
The
spacewalkers are also slated to install attachment points for a sensor-laden
space shuttle inspection boom used by NASA astronauts to scan their orbiter's
heat shield for signs of damage. The 50-foot (15-meter) inspection boom is too
heavy to ride aboard an upcoming shuttle flight next year that will haul a
massive Japanese laboratory to the ISS. The new attachment points will allow
astronauts to store an inspection boom at the space station for that coming
flight to ensure its crew will be able to scan the orbiter, mission managers
have said.
A wireless
sensor system antenna installation is also on the spacewalkers' task list, but
plans to wrangle a few stubborn aluminum micrometeorite debris shields back
into place may be put on hold to end the spacewalk early in response to
Hurricane Dean.
The
spacewalk will mark the third for both Anderson and Williams. But for Williams,
a veteran Canadian Space Agency astronaut, the excursion will set a new
national record for the most spacewalking time spent by a Canadian spaceflyer.
He is going into today's excursion with 12 hours and 45 minutes across two
spacewalks under his belt.
"For
me it's just a real thrill being part of this whole mission and getting a
chance to go outside and do three spacewalks," Williams said.
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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