The shuttle rose from its seaside launch pad through a partly cloudy sky at 11:15 a.m. ET.
"It was worth the wait and we're ready to get to work," said Atlantis commander Brent Jett.
Jett and his team have trained for longer than any crew in the past, and the extra time will probably be an advantage. They face one of the most challenging construction tasks in space history.
As the shuttle streaked into space, more than 100 cameras zoomed in for any signs of foam breaking off its external fuel tank, the problem that doomed Columbia.
A chunk of the hard foam appeared to hit the shuttle's belly, but "it didn't look like there was any damage," Mission Control told the Atlantis crew. That foam loss, and another, came more than four minutes into the launch, when they pose less of a damage threat, said LeRoy Cain, chairman of the mission management team.
NASA also observed some ice falling off after the shuttle had reached orbit, again too late in the ascent to worry the space agency.
Launch director Mike Leinbach called the liftoff "really, really clean," and NASA Administrator Michael Griffin described it as "majestic."
"Not everything in the count leading up to this day was easy," Griffin said. "We had to dodge tropical storms, lightning strikes and things like that."
There was a slight problem when a freon coolant system did not work properly during ascent, but NASA did not view it as a major concern. The fuel cells that forced launch delays earlier in the week were working as expected, NASA spokesman Kyle Herring said.
"Great work!" astronaut Jeff Williams said minutes after the launch from the space station 220 miles above Earth.
Atlantis carried one of the heaviest payloads ever launched into space — a 17 1/2 ton truss section that will be added to the half-built space station. It includes two solar arrays that will produce electricity for the orbiting outpost. Atlantis' weight was so much that it only had a crew of six, instead of the usual seven astronauts.
The astronauts will make three spacewalks during the 11-day flight to install the $372 million addition.
"In terms of spacewalk tasks, clearly these are the most complicated spacewalk and assembly tasks that ever have been done before," said Wayne Hale, NASA shuttle program manager.
Construction of the space station has been on hold since Columbia disintegrated over Texas, killing seven astronauts on their return to Earth in February 2003. Since then, NASA has struggled to find ways to prevent the breakaway of hard foam chunks like those that had fatally damaged Columbia's wing during liftoff.
Atlantis has four years to finish the construction project and retire the shuttle, reports CBS News space consultant Bill Harwood.
The space agency plans 14 more flights besides the Atlantis mission to complete the station before the shuttle fleet is retired in 2010 and NASA turns its attention to flying to the moon and Mars.
Atlantis' mission was supposed to take place in 2003. After training for the flight for a record 4 1/2 years, the six astronauts had to wait a little longer, when the launch was scrubbed four times over the past two weeks: first because of a lightning bolt that hit the launch pad, then Tropical Storm Ernesto, then a problem with the shuttle's electrical system, and then a faulty fuel gauge.
On Friday, the astronauts were already strapped in and the hatch sealed when NASA scrubbed an hour before the launch time because a sensor in the hydrogen fuel tank gave an abnormal reading as the shuttle was being fueled. That delay cost NASA $616,000.
If the shuttle did not get off the ground this week, NASA would have had to wait until late September or even late October to try again.
Russia plan to send a Soyuz capsule to the space station on Sept. 18, and it would be too crowded to have both spacecraft there at the same time. The Soyuz will bring two new crew members to the space station and Anousheh Ansari, a Texas entrepreneur who is to become the first female space tourist.
Atlantis' six crew members are commander Brent Jett, pilot Chris Ferguson and mission specialists Joe Tanner, Dan Burbank, Heidemarie Stefanyshyn-Piper and Steve MacLean of the Canadian Space Agency.