Story Continues BelowWeather had been forecast 80% "go" leading into the final hours of the countdown, but a cloud deck formed to the north and west of the space center moving south. As the clouds moved in, the forecast dropped to 30% about 3 hours before launch. The cloud deck presented concerns for both launch (range safety) as well as visibility at the Shuttle Landing Facility in case Endeavour was forced to abort early in its ascent and return to Kennedy Space Center in a risky but theoretically possible maneuver called a Return To Launch Site Abort.

The launch commit criteria call for a ceiling no lower than 4,000 feet and a thickness no greater than 500 feet but for the remainder of the countdown, the clouds drifted in and out of these limits. Finally, nin minutes before launch, with the cloud ceiling at 3,800 feet and 600 feet thick, today's attempt was scrubbed when the launch team was unable to get comfortable with flying so close to the limits.

Launch Director Mike Leinbach summed up the dynamics of the weather when he said the conditions were "certainly outside the experience base that I've been experiencing since I've had this job, so I would personally be no-go for launch tonight."

"We tried really, really hard to work the weather," Leinbach radioed his decision to the astronauts onboard Endeavour. "It was just too dynamic. We got to feeling good there at one point and then it filled back in and we just were not comfortable launching a space shuttle tonight.

"We're going to go into a 24-hour scrub. Thank you all for the efforts you all put in tonight. We'll see you back again tomorrow night and we hope the weather's a little bit better."

"And Mike, from Endeavour, we understand and we'll give it another try tomorrow night," Zamka replied.

The preferred launch time for a Monday liftoff is 4:14:07 a.m. EST. This will be preceded by loading of Endeavour's external tank with 529,000 gallons of liquid oxygen and hydrogen at 6:45 p.m.

The 24-hour scrub means that NASA's Solar Dynamics Observatory will face a one day slip in its launch, which had been scheduled for Tuesday and now will target a Wednesday morning blastoff on a United Launch Alliance Atlas 5 rocket.

(The Spacearium / SpaceflightNews.net)