NASA has officially
cleared the space shuttle Endeavour for its third launch attempt on Saturday,
with the chance of thunderstorms posing the only threat to the mission after nearly
a month of delays.
Endeavour
is poised to blast off from NASA's Kennedy Space Center in Florida at 7:39 p.m.
EDT (2339 GMT) to begin an ambitious
16-day flight to the International Space Station. But the potential for
thunderstorms, rain and clouds near the Cape Canaveral spaceport give the
shuttle just a 40 percent chance of good flight weather.
"I don't
worry about things I can't control, and I can't control the weather," said NASA's
Mike Moses, who leads Endeavour's Mission Management Team, during a Friday
briefing.
Moses added
that some people joke that, because his last name is Moses, he should have some
say in the weather. "But I really can't," he said with a smile.
Launch weather
conditions will improve slightly on Sunday and Monday, but NASA hopes to fly
tomorrow evening to avoid a space
traffic conflict with an unmanned Russian cargo ship also due at the
station this month.
Commanded
by veteran spaceflyer Mark Polansky, Endeavour's six-man,
one-woman crew plans to deliver an external experiment-carrying porch for
the space station's massive Japanese lab Kibo. It is the third, and last, piece
of the $1
billion Japanese facility. Five spacewalks are planned to install the space
porch and perform station maintenance.
The seven
Endeavour astronauts will boost the station's current six-man crew up to 13
people - its highest
population ever - when the shuttle arrives.
One
Endeavour crewmember, NASA astronaut Tim Kopra, will replace Japanese spaceflyer
Koichi Wakata as part of the station's Expedition 20 crew. Wakata has lived
aboard the station since March and will return to Earth aboard the shuttle.
Endeavour's
mission has been delayed since mid-June due to a vexing hydrogen gas leak that
stalled two launch attempts. Engineers tracked the problem to a misaligned
plate on the shuttle's 15-story external tank. They replaced the plate and a
hydrogen vent line seal, and successfully tested the fix last week.
Moses said
he is confident the glitch will not appear during Saturday's launch attempt. Endeavour's
flight will mark NASA's third shuttle mission of up to five planned for this
year.
Mission
managers have said Endeavour has until July 14 to try and launch toward the
station before NASA would stand down to allow the Russian cargo ship's launch
and docking at the orbiting lab. If the shuttle does not launch by then, the
agency would consider holding the flight until July 27 to wait out the space cargo
run.
While there
is some potential room to extend Endeavour's launch window, Moses said that it
is easier for NASA to shift its space shuttle launch date than for Russia to
move a Soyuz rocket launch.
"It's a
matter of launch processing," Moses said. "It's much easier to let [the cargo
ship] launch and get it out of the way."
SPACE.com
is providing continuous coverage of STS-127 with reporter Clara Moskowitz at
Cape Canaveral and senior editor Tariq Malik in New York. Click here for mission
updates and SPACE.com's live NASA TV video feed. Live launch coverage
begins Sat. at 2:30 p.m. EDT (1830 GMT).
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