NASA will make a fifth try at launching space shuttle Endeavour this evening, after storms twice delayed attempts over the weekend. The shuttle's mission to the International Space Station (ISS) was originally slated to begin in June but was twice postponed that month due to leaks in a venting system that carries hydrogen gas away from the launch pad.

Tonight's attempt at liftoff is scheduled for 6:51 P.M. (Eastern Daylight Time), but NASA is projecting only a 40 percent chance of favorable weather for that time. Both and NOAA are predicting scattered rainfall and thunderstorms in the evening around Kennedy Space Center (KSC) in Florida.

Saturday's attempt was scrubbed by dramatic lightning storms at the launch site the day before. In a statement Saturday, NASA said it needed time to check for possible damage from the strikes, 11 of which were detected within 0.35 mile (0.56 kilometer) of the orbiter.

Despite Endeavour's clean bill of health, last night's launch was thwarted by storms too close to KSC for comfort. "Though the weather wasn't a constraint for liftoff," reports, "Kennedy's Shuttle Landing Facility must be clear within a 20 nautical mile radius in case an emergency forces the shuttle to make an abort landing." The Associated Press reports that the shuttle "launch team came within minutes of sending Endeavour and seven astronauts to the International Space Station" before the storms rolled in from the west.

Photo of Endeavour under storm clouds Friday: NASA/Bill Ingalls