Flashes of flame from space shuttle Discovery lit up the darkened sky as the space shuttle blazed off the launch pad for the first nighttime liftoff in four years. The shuttle's seven astronauts are on a mission to rewire the international space station, one leg of a three-year race to finish construction on the orbiting outpost before shuttles are retired in 2010. The illumination from the shuttle turned night into day for the spectators at the Kennedy Space Center on Saturday. A cloudy sky with blustery winds earlier in the day gave way to clear skies and a gentle breeze at launch time. Low clouds forced the space agency to scrub an 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 Discovery crew. Commander Mark Polansky responded, "We look forward to lighting up the night sky." During their 12-day mission, Discovery's crew will rewire the space station, deliver an $11 million (â‚¬8.3 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. U.S. astronaut Sunita Williams will replace him, staying for six months.