The shuttle Discovery roared into space Saturday night on a 12-day mission to continue construction of the International Space Station and reconfigure the station's electrical system.
It was the third launch in the last five months and the first nighttime launch in more than four years as the American space agency continues its recovery from the 2003 Columbia disaster.
"We look forward to lighting up the night sky and rewiring the ISS," shuttle Commander Mark Polansky said just before the shuttle's engines ignited at 8:47 p.m. EST at Kennedy Space Center in Florida.
The three main engines and two solid rocket boosters, providing 7 million pounds of thrust, propelled the shuttle from a standing start to its orbiting speed of 17,400 mph as it made its eight-minute climb to space.
Early reports from ground safety officers indicated that the launch appeared clean.
Launch Director Mike Leinbach said the successful launch was the best sign yet that NASA had fully recovered from the Columbia disaster.
"We're getting back in the groove. We're getting back in business," Leinbach said.
NASA Administrator Michael D. Griffin said the launch marked another milestone in finishing the space station and going beyond.
"The space station is on the footpath toward becoming a space-faring nation," Griffin said, referring to plans to return to the moon and then head on to Mars.
Navigating space is one of the most technologically difficult tasks mankind has faced, he said.
"We do it as well as we can. Sometimes we stumble. Today, we didn't stumble," Griffin said.
Several days of analysis of radar images from the ground and an on-orbit inspection by the shuttle crew will be required to make sure there were no problems, such as the one that doomed Columbia. A piece of foam insulation flaked off the external fuel tank during Columbia's launch and hit the left wing, tearing a hole in it.
NASA ground managers and the crew were unaware of the problem until the shuttle attempted to land, and atmospheric forces widened the damage and finally destroyed the shuttle.
The seven-person crew of Discovery has three major tasks.
It will deliver a replacement crew member to the space station, Sunita Williams, to replace European astronaut Thomas Reiter, who has been at the station since July.
Discovery will also deliver a 2-ton truss as NASA continues assembling the backbone of the station. The final task is the most challenging: to take the station off the temporary power grid it has been using for the last six years and bring online the giant set of solar arrays that were delivered by the last shuttle mission.
Power will be routed through four Main Bus Switching Units on the central truss attached in April 2002. These units have never been activated and were last checked in December 2002.
Three spacewalks will be required to complete the work. To minimize the danger of something going wrong and leaving the station without power, the spacewalkers will shut down only half of the station at a time.
The new truss section will be attached on the fourth day of the flight. The power and thermal reconfiguration will take place on Day 6 of the 12-day mission. The second half will take place during the third spacewalk on the eighth day of the mission.
NASA had required daylight launches for the first three missions after Columbia so the space agency could obtain good daytime photos of the fuel tank. NASA now believes it understands the foam problem well enough to launch at night, relying on radar to spot any debris flaking off the fuel tank.
Nighttime launches are necessary for NASA to stick to its announced schedule of completing construction of the station and retiring the shuttle fleet by 2010.
Another reason to get the flight in before the end of the year is that shuttle computers are not designed to make the changeover from the 365th day of the year to the first day of a new year.
NASA managers think they have a solution but are reluctant to try it if they don't have to.