Discovery lit up the sky late Saturday, blazing off for the first nighttime space shuttle launch in four years -- the latest step in NASA's ambitious schedule to complete the International Space Station.

The shuttle's fiery ascent turned night into day for spectators at the Kennedy Space Center. A cloudy sky with blustery winds earlier in the day gave way to clear skies and a gentle breeze at launch time.

"I think we have five people who just haven't stopped smiling yet," commander Mark Polansky said after Discovery reached space.

The mission is one leg of a three-year race to finish construction on the orbiting outpost before shuttles are retired in 2010. After Discovery's mission, 13 more shuttle flights are needed to complete the space lab.

Low clouds forced the space agency to scrub a launch attempt Thursday night during a countdown that ran down to the wire. Managers decided not to try again Friday because the forecast looked even worse.

"Forty-eight hours makes a tremendous difference," launch director Mike Leinbach told the crew. Later at a news conference, he said, "Everything just clicked. Everything felt good today."

During their 12-day mission, Discovery's crew will rewire the space station, deliver an $11 million addition to the space lab and bring home one of the space station's three crew members, German astronaut Thomas Reiter of the European Space Agency. American astronaut Sunita "Suni" Williams will replace him, staying for six months.

The launch was the first at night since Endeavour's flight in November 2002 and only the 29th in darkness of NASA's 117 total shuttle launches.

There were no initial reports of any serious problems. But engineers still needed to review imagery and radar to look for damage to the shuttle from debris falling off the external tank, the problem that doomed Columbia.

"What you've seen tonight is the successful accomplishment of the most challenging, demanding, technically state of the art, difficult thing that this nation or any nation can do," NASA Administrator Michael Griffin said.

NASA had required daylight launches for three flights after the Columbia accident in 2003 so that clear images could be taken of the external fuel tank. Foam broke off Columbia's tank at liftoff and struck the spacecraft's wing, leading to the disaster that killed seven astronauts.

Waiting at the space station for his visitors to arrive on Monday, U.S. astronaut Michael Lopez-Alegria told Mission Control, "We're going to head out and turn our porch light on so they can find us."

Referring to Williams' first flight, Lopez-Alegria told the shuttle crew: "I hope Suni likes it. She's going to be there for a while."

Discovery's crew is the greenest in eight years when it comes to spaceflight experience. Five astronauts have never flown in a shuttle before. The last time a shuttle mission had five rookies was a Columbia crew that flew in April 1998.

The two veterans are commander Polansky and Robert Curbeam, who will spacewalk three times. The others are pilot William Oefelein, and mission specialists Joan Higginbotham, Nicholas Patrick, Williams and the European Space Agency's Christer Fuglesang, who was the first Swede in space.

It also is among the most culturally diverse of any shuttle crew.

Besides the Swede, there are two black astronauts, an astronaut of Indian descent, a British-born mission specialist, an Alaskan and a New Jersey boy.

Three of Discovery's astronauts will take three complicated spacewalks and play the role of electricians by rewiring the space station from a temporary to a permanent power source.

NASA officials were glad to get the shuttle off their ground since they wanted it back on Earth by the new year.

Shuttle computers are not designed to make the change from the 365th day of the old year to the first day of the new year while in flight. The space agency has figured out a solution for the New Year's Day problem, but managers are reluctant to try it.

It was the third shuttle launch of the year, and only the fourth since the Columbia disaster in 2003.