CAPE CANAVERAL, Fla. �” Seven astronauts blew kisses as they climbed into a fully fueled Discovery for liftoff today for a backbreakingly difficult space station construction mission, despite a gloomy forecast calling for rain right around launch time.

The space shuttle was set to blast off at 11:38 a.m.

Just before dawn, scattered showers drenched the area. Meteorologists expected more rain clouds to move into the area later in the morning and quite possibly force a delay.

Hoping to beat the poor weather odds, NASA pumped more than 500,000 gallons of super-cold liquid hydrogen and oxygen into Discovery’s external tank, modified since the last mission to prevent dangerous ice buildup and reduce the potential for launch debris.

The wings, however, were not altered in any way, even though a safety engineering group pressed for a delay because of concern over three panels with possible flaws.

The sun peeked from behind thick clouds as the astronauts lined up in front of NASA’s so-called astrovan, waving to a cheering crowd and posing for pictures before heading to the launch pad. As they boarded Discovery one by one, a few of them held up small signs for their families watching on TV.

“Have a good flight,” a controller radioed.

Commander Pamela Melroy, only the second woman to lead a shuttle mission, expressed her confidence late last week about flying Discovery, as have many of the senior managers who decided to skip wing repairs. A possible cracking problem with the protective coating on three of the wing panels was deemed an acceptably low risk.

A hole in the wing brought down Columbia in 2003.

Discovery and its crew of seven will embark on a two-week mission that is considered the most challenging and complex in the nine years of orbital assembly of the international space station.

The shuttle will carry up an Italian-built live-in compartment, about the size of a small bus, that the astronauts will attach to the space station. It’s named Harmony, the choice of schoolchildren who took part in a national competition. About 130 of those youngsters traveled to Cape Canaveral to witness the launch.

Also on hand for the launch was “Star Wars” director and writer George Lucas. Packed aboard Discovery is the lightsaber used by the character Luke Skywalker in 1983’s “Return of the Jedi,” to mark the 30th anniversary of the first “Star Wars” film.

Europe and Japan’s laboratories will link up with Harmony once they are launched by shuttles over the next few months.

Discovery’s astronauts also will move a massive girder and set of solar wings from one part of the space station to another. That work will involve extending radiators as well as the folded solar wings �” 240 feet from tip to tip when outstretched.

In all, five spacewalks are planned, four to complete this construction job and one to test a method for fixing damaged shuttle thermal tiles using a caulking gun and high-tech goo. The demonstration with sample tiles was added after Endeavour suffered a gouge to its belly during the last launch in August from a piece of flyaway fuel-tank foam.

Once Discovery leaves, the three space station residents �” one of whom will be dropped off by the shuttle �” will face even more construction work to prepare for the European lab’s arrival as early as December.

Discovery’s crew includes an Italian astronaut making his first spaceflight, Paolo Nespoli.

�”�”�”