NASA Clears Shuttle Endeavour for Saturday Launch

NASA has officiallycleared the space shuttle Endeavour for its third launch attempt on Saturday,with the chance of thunderstorms posing the only threat to the mission after nearlya month of delays.

Endeavouris poised to blast off from NASA?s Kennedy Space Center in Florida at 7:39 p.m.EDT (2339 GMT) to begin an ambitious16-day flight to the International Space Station. But the potential forthunderstorms, rain and clouds near the Cape Canaveral spaceport give theshuttle just a 40 percent chance of good flight weather.

?I don?tworry about things I can?t control, and I can?t control the weather,? said NASA?sMike Moses, who leads Endeavour?s Mission Management Team, during a Fridaybriefing.

Moses addedthat some people joke that, because his last name is Moses, he should have somesay in the weather. ?But I really can?t,? he said with a smile.

Launch weatherconditions will improve slightly on Sunday and Monday, but NASA hopes to flytomorrow evening to avoid a spacetraffic conflict with an unmanned Russian cargo ship also due at thestation this month.

Commandedby veteran spaceflyer Mark Polansky, Endeavour?s six-man,one-woman crew plans to deliver an external experiment-carrying porch forthe space station?s massive Japanese lab Kibo. It is the third, and last, pieceof the $1billion Japanese facility. Five spacewalks are planned to install the spaceporch and perform station maintenance.

The sevenEndeavour astronauts will boost the station?s current six-man crew up to 13people - its highestpopulation ever - when the shuttle arrives.

OneEndeavour crewmember, NASA astronaut Tim Kopra, will replace Japanese spaceflyerKoichi Wakata as part of the station?s Expedition 20 crew. Wakata has livedaboard the station since March and will return to Earth aboard the shuttle.

Endeavour?smission has been delayed since mid-June due to a vexing hydrogen gas leak thatstalled two launch attempts. Engineers tracked the problem to a misalignedplate on the shuttle?s 15-story external tank. They replaced the plate and ahydrogen vent line seal, and successfully tested the fix last week.

Moses saidhe is confident the glitch will not appear during Saturday?s launch attempt. Endeavour?sflight will mark NASA?s third shuttle mission of up to five planned for thisyear.

Missionmanagers have said Endeavour has until July 14 to try and launch toward thestation before NASA would stand down to allow the Russian cargo ship?s launchand docking at the orbiting lab. If the shuttle does not launch by then, theagency would consider holding the flight until July 27 to wait out the space cargorun.

While thereis some potential room to extend Endeavour?s launch window, Moses said that itis easier for NASA to shift its space shuttle launch date than for Russia tomove a Soyuz rocket launch.

?It?s amatter of launch processing,? Moses said. ?It?s much easier to let [the cargoship] launch and get it out of the way.?

• New Video - The Kibo Lab: Japan's Hope in Space - Part 1, Part 2
• Image Gallery - Shuttle Endeavour Blasts Off at Night
• Video - Meet the STS-127 Shuttle Astronauts

SPACE.comis providing continuous coverage of STS-127 with reporter Clara Moskowitz atCape Canaveral and senior editor Tariq Malik in New York. Click here for missionupdates and SPACE.com's live NASA TV video feed. Live launch coveragebegins Sat. at 2:30 p.m. EDT (1830 GMT).