Cape Canavarel, Fla. ? Thunderstorms forced NASA to call off Sunday evening’s launch of shuttle Endeavour, the fourth delay for the space station construction mission.

The launch team came within minutes of sending Endeavour and seven astronauts to the international space station. But storms quickly moved in from the west and violated NASA’s safety rules, and managers halted the countdown. They will try again today, despite an outlook calling for more bad weather.

“We got the vehicle ready, and the weather unfortunately did not cooperate with us today,” launch director Pete Nickolenko told the seven astronauts aboard Endeavour.

“We understand and we’ll be ready,” replied commander Mark Polansky.

NASA has until Tuesday, possibly Wednesday, to launch Endeavour with the final piece of Japan’s space station lab. Otherwise, it will have to wait until the end of July because of a Russian supply ship that’s awaiting liftoff.

The three previous countdowns never made it this far.

Saturday’s launch attempt was foiled by a series of lightning strikes around the pad that required extra checks of the many critical shuttle systems. Back in June, hydrogen gas leaks held everything up.

No leaks popped up this time, thanks to all of the repairs, as NASA fueled Endeavour’s external tank for an early evening liftoff. The tight plumbing allowed Polansky and his crew to board the shuttle for the first time for a real launch try.