Nasa rescheduled space shuttle Discovery's liftoff for early on Sunday morning after thick clouds forced a postponement of the first launch attempt last night.
Managers decided to skip today's attempt because meteorologists forecast a 90 per cent chance of another delay due to high winds stirred by a cold front pushing through central Florida.
Discovery's crew was strapped inside the orbiter for liftoff, but the clouds failed to part before the launch window expired and the attempt was cancelled.
Tomorrow's launch attempt was set for 8.48pm (1.48am Irish time on Sunday).
The launch will be Nasa's first in darkness since before the 2003 Columbiadisaster. Managers recently lifted the ban on night launches, imposed to ensure cameras had good lighting to spot any debris falling off the shuttle's fuel tank.
Debris damaged Columbia, triggering the breakup of the ship and the deaths of its seven astronauts as it re-entered Earth's atmosphere.
On the shuttle flight in September, astronauts delivered new solar arrays to provide power for additional modules scheduled to be installed next year.
The tricky task of wiring the arrays into the station's power grid falls to Discovery'screw. At least 14 more missions are needed to finish the $100 billion outpost.