CAPE CANAVERAL, Fla. - NASA is trying yet again to launchthe space shuttle Endeavour Monday, despite a good chance of rain showers thatthreaten to delay the mission for a potential fifth time.
Rain poses a special risk to today'sliftoff plans because of an exposed thruster on the shuttle's nose. Theplastic cover that usually guards the thruster - one of 44 small rocketthrusters on the shuttle used for minor course changes - came loose yesterdayduring Endeavour's failedfourth 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 getsinto the thruster it could freeze into ice and render the thruster useless.
That means that if any rain falls on the pad, NASA willlikely 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 riskmoisture in the thruster, and you don't want it to freeze," said NASAspokesman Allard Beutel. NASA would most likely not launch with a disabledthruster, even though it is not critical for liftoff.
While Sunday's launch attempt was cancelled because ofthunderstorms near the launch pad and landing site here at Kennedy SpaceCenter, no precipitation actually fell on Endeavour's Launch Pad 39A.
"If we had had rain at the pad it would have bumped usout for sure," Beutel said of today's liftoff plans.
Rain is a serious threat for Endeavour's flight attempttoday, with a 60 percent chance of thunderstorms predicted. Despite the gloomyforecast, NASA decided to begin fueling the shuttle's massive external tank in preparationfor launch early this morning, just in case the weather cooperates.
"They thought it was worth at least taking thechance," Beutel said.
If today's launch is cancelled, NASA can try again tomorrowif ground crews have enough time to reattach the thruster cover. This proceduretakes three to four hours, because the giant Rotating Service Structurescaffolding on the launch pad must be moved back into place to give crewsaccess to Endeavour's nose.
If the process can't be completed in time, NASA may be ableto push the launch window out a few days, though the shuttle is currentlyscheduled to stand down to let an unmanned Russian cargo ship launch to thespace station later this month.
"We can talk to the Russians and maybe we can get someextra time," Beutel said.
Endeavour's oft-delayedmission is a construction visit to the International Space Station toinstall spare supplies and a new exposed research platform for the JapaneseKibo laboratory. Today is the beleaguered shuttle's fifth attempt to liftoff on its STS-127 mission, which has been held at the ground by bad weatherand a pesky gas leak, which has since been repaired.
- New Video - The Kibo Lab: Japan's Hope in Space - Part 1, Part 2
- Final Countdown: A Guide to NASA's Last Space Shuttle Missions
- SPACE.com Special Report - THE MOON: Then, Now, Next
SPACE.com is providing continuous coverage of STS-127 withreporter Clara Moskowitz at Cape Canaveral and senior editor Tariq Malik in NewYork. Click here formission updates and SPACE.com's live NASA TV video feed. Live launchcoverage will begin at 1:30 p.m. EDT (1730 GMT).
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Clara Moskowitz is a science and space writer who joined the Space.com team in 2008 and served as Assistant Managing Editor from 2011 to 2013. Clara has a bachelor's degree in astronomy and physics from Wesleyan University, and a graduate certificate in science writing from the University of California, Santa Cruz. She covers everything from astronomy to human spaceflight and once aced a NASTAR suborbital spaceflight training program for space missions. Clara is currently Associate Editor of Scientific American. To see her latest project is, follow Clara on Twitter.