By Paul Rincon
BBC News science reporter, at the Kennedy Space Center
Nasa has launched its first manned space mission in two-and-a-half years.
Space shuttle Discovery blasted off on its 12-day flight at 1039 local time (1539 BST) from the Kennedy Space Center in Florida.
It roared up into a bright blue sky to the cheers of spectating astronaut families and US space agency staff.
Discovery's crew will test safety measures brought in after the Columbia accident in 2003 and resupply the International Space Station.
US space agency officials said they were happy with the launch, despite the sighting of what appeared to be some debris falling around the vehicle during the flight to orbit.
They said they would wait for detailed photo analysis to be done before coming to any conclusions about the structural integrity of Discovery.
According to plan
"On behalf of the many millions of people who believe so deeply in what we do, good luck, God speed and have a little fun up there," Nasa launch director Mike Leinbach told Commander Eileen Collins and her crew just before lift-off.
It was Nasa's second go at a lift-off in the current launch window.
SHUTTLE RETURN TO FLIGHT
Mission known as STS-114
Discovery's 31st flight
17th orbiter flight to ISS
Payload: Raffaello Multi-Purpose Logistics Module
Lift-off: 1039 EDT, 26 July
Location: Kennedy Space Center, Launch Pad 39B
Discovery crew: Collins, Kelly, Noguchi, Robinson, Thomas, Lawrence and Camarda
An earlier attempt on 13 July had to be scrubbed because of the failure of a fuel sensor; but the problem did not recur on Tuesday and the countdown proceeded without interruption.
Collins and her crew were strapped in and the hatch closed as launch controllers went through the pre-flight checks.
On cue, the orbiter raced skyward leaving a huge exhaust plume in its wake.
The separation of solid boosters and external tank all occurred without incident; and after eight-and-a-half minutes, Discovery shut down its engines to enter the planned preliminary orbit.
A series of thruster firings will gradually raise its altitude over the next couple of days.
"We know that the folks back on the planet Earth are just feeling great right now and our thanks to everybody for all the super work that's been done over the past two-and-ahalf-years to get us flying again," Collins told mission control in Houston not long after launch.
"Take note of what you've seen today," said Nasa chief Dr Mike Griffin.
"Of the power and majesty of launch, of course; but also the competence and professionalism, the sheer gall, the pluckiness, the grittiness of this team that pulled this programme out of the depths of despair two-and-half-years ago and made it fly."
PERFECT FLORIDA DAY
Everything seemed to go right for Nasa and the cheering spectators
Nasa says it has learnt the safety lessons of the Columbia disaster, which cost the lives of seven astronauts, and has made this the most scrutinised shuttle flight ever.
Columbia broke up as it attempted to re-enter Earth's atmosphere.
Super-heated gases entered a hole punched in the wing during take-off by a suitcase-sized chunk of foam from the external tank, tearing the vehicle apart.
Nasa had positioned more than 100 cameras both on the ground and in the air to capture as much detail as possible on Discovery's ascent into orbit.
The launch was watched by First Lady Laura Bush and Florida Governor Jeb Bush
Shuttle managers expect to have all the imagery in and checked over by day six of the flight. If there is an issue over the debris sighted at launch, engineers should have ample information to judge the seriousness of the situation.
US President George W Bush watched the launch on television.
"I thank the men and women of Nasa who have dedicated themselves to putting our space programme back on track," he said in a statement.
"Our space programme is a source of great national pride, and this flight is an essential step toward our goal of continuing to lead the world in space science, human spaceflight, and space exploration."
Discovery will take parts and supplies to the ISS and test new safety features such as a repair-kit for heatshield tiles and a 15m-long robotic arm that will inspect the shuttle for damage in orbit.
Discovery is due to touch down at Kennedy Space Center on 7 August at 0546 EDT (0946 GMT; 1046 BST).