CAPE CANAVERAL, Fla. - NASA is trying yet again to launch
the space shuttle Endeavour Monday, despite a good chance of rain showers that
threaten to delay the mission for a potential fifth time.
Rain poses a special risk to today's
liftoff plans because of an exposed thruster on the shuttle's nose. The
plastic cover that usually guards the thruster - one of 44 small rocket
thrusters on the shuttle used for minor course changes - came loose yesterday
during Endeavour's failed
fourth launch attempt.
While the loose cover posed no risk for launch yesterday
(the seal is designed to drop off during liftoff anyway), if any moisture gets
into the thruster it could freeze into ice and render the thruster useless.
That means that if any rain falls on the pad, NASA will
likely be forced to call off today's launch, set for 6:51 p.m. EDT (2251 GMT).
"The idea is if you get rain then you start to risk
moisture in the thruster, and you don't want it to freeze," said NASA
spokesman Allard Beutel. NASA would most likely not launch with a disabled
thruster, even though it is not critical for liftoff.
While Sunday's launch attempt was cancelled because of
thunderstorms near the launch pad and landing site here at Kennedy Space
Center, no precipitation actually fell on Endeavour's Launch Pad 39A.
"If we had had rain at the pad it would have bumped us
out for sure," Beutel said of today's liftoff plans.
Rain is a serious threat for Endeavour's flight attempt
today, with a 60 percent chance of thunderstorms predicted. Despite the gloomy
forecast, NASA decided to begin fueling the shuttle's massive external tank in preparation
for launch early this morning, just in case the weather cooperates.
"They thought it was worth at least taking the
chance," Beutel said.
If today's launch is cancelled, NASA can try again tomorrow
if ground crews have enough time to reattach the thruster cover. This procedure
takes three to four hours, because the giant Rotating Service Structure
scaffolding on the launch pad must be moved back into place to give crews
access to Endeavour's nose.
If the process can't be completed in time, NASA may be able
to push the launch window out a few days, though the shuttle is currently
scheduled to stand down to let an unmanned Russian cargo ship launch to the
space station later this month.
"We can talk to the Russians and maybe we can get some
extra time," Beutel said.
Endeavour's oft-delayed
mission is a construction visit to the International Space Station to
install spare supplies and a new exposed research platform for the Japanese
Kibo laboratory. Today is the beleaguered shuttle's fifth attempt to lift
off on its STS-127 mission, which has been held at the ground by bad weather
and a pesky gas leak, which has since been repaired.
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 will begin at 1:30 p.m. EDT (1730 GMT).
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