Thick clouds thwarted the attempted predawn launch of NASA's space shuttle Endeavour on Sunday, forcing the orbiter's six-astronaut crew to wait at least one more day before rocketing into orbit.

Despite early predictions of good weather, a thick layer of low-lying clouds crept in over NASA's Kennedy Space Center here, preventing Endeavour's planned 4:39 a.m. EST (0939 GMT) launch toward the International Space Station. The astronauts were already strapped inside their seats awaiting liftoff.

"We were just not comfortable with launching the space shuttle tonight so we're going to go into a 24-hour scrub," NASA launch director Mike Leinbach radioed Endeavour's crew. "Thank you all for the effort you all put in tonight."