NASA's space shuttle Endeavour is ready for its planned launch into orbit this weekend, though stormy weather could delay liftoff, mission managers said Wednesday.

Endeavour and a crew of seven astronauts are slated to launch toward the International Space Station on Saturday evening at 7:39 p.m. EDT (2339 GMT). But the potential for thunderstorms and thick clouds near Endeavour's launch site at the Kennedy Space Center in Florida give the shuttle only a 40 percent chance of good flight weather, said shuttle weather officer Kathy Winters.

"That's definitely a concern for launch," Winters said during a televised mission briefing today.

A series of afternoon thunderstorms have peppered NASA's spaceport in Cape Canaveral, Fla., in recent days in a trend that is expected to weaken only slightly through the weekend, she added. If weather prevents a Saturday launch for Endeavour, the forecast will improve for Sunday, Winters said.

Aside from potentially foul weather, Endeavour is ready to fly after nearly a month of delays. A hydrogen gas leak associated with a vent line on the shuttle's 15-story external tank thwarted two consecutive launch attempts in mid-June. Since then, engineers have replaced a misaligned plate on the tank as well as vent line seal to plug the leak. The fix passed a fueling test last week.

"Endeavour's in great shape," NASA test director Charlie Blackwell-Thompson said, adding that there are no issues with the shuttle at all. "We're ready to fly this mission."

Commanded by veteran shuttle flyer Mark Polansky, Endeavour's six-man, one-woman crew is set to fly a marathon 16-day mission to the space station. The astronauts will deliver a new member of the orbiting laboratory's six-man crew and install the last piece of Japan's massive Kibo laboratory at the outpost. Five spacewalks are planned for the mission.

"This is a very busy mission," Blackwell-Thompson said. "We're all eager to get Endeavour and her crew to the International Space Station."

Polansky and his crew arrived at the Kennedy Space Center on Tuesday. NASA plans to begin the countdown toward Saturday's launch tonight at 10:00 p.m. EDT (0200 July 9 GMT).

Endeavour has a slim four-day day window to launch toward the space station due to other incoming traffic at the outpost. According to NASA's current plan, Endeavour must launch by July 14 or else stand down until July 27 to allow a previously scheduled unmanned Russian cargo ship to dock at the station. The unmanned cargo ship can loiter in orbit for a few days if required, NASA has said.

Blackwell-Thompson said NASA hopes to launch Endeavour by July 13 to avoid interfering with the cargo ship's normal flight plan.

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