The space shuttle Endeavour has begun an 11 to 14 day assembly mission to the International Space Station.
The shuttle blasted off as planned at 2336 BST (1836 EDT) on Wednesday from the Kennedy Space Center in Florida.
The mission is the second of four that Nasa plans this year to finish the $100bn (£49.1bn) space station before the shuttle fleet retires in 2010.
On board was Barbara Morgan, once the reserve behind Christa McAuliffe, who died in the Challenger shuttle in 1986.
Endeavour has not flown since before the Columbia disaster in 2003, in which seven astronauts were killed when their spacecraft disintegrated on re-entry into the atmosphere.
The shuttle, which enjoyed a hitch-free launch from Cape Canaveral, has undergone an extensive overhaul since its last flight five years ago, and Nasa managers say the spacecraft is virtually new.
Once Endeavour was safely past the 73-second mark of the flight - the moment when Challenger exploded - mission control exclaimed that Morgan was "racing toward space on the wings of a legacy".
The re-fitted orbiter has a new piece of equipment that can tap into the power grid of the ISS and could allow the shuttle to extend its 11-day mission to 14 days.
The mission is carrying aloft a "truss" section about the size of a small car and weighing 1.58 tonnes, to extend the space station to a length of 108m (354ft).
Former teacher Barbara Morgan is in space for the first time
The astronauts will also replace a defective gyroscope, one of four keeping the ISS on an even keel, and will install a 3.3-tonne exterior stowage platform.
Endeavour is also carrying in its cargo bay a pressurised container with 2.7 tonnes of supplies, foodstuffs and equipment.
Three spacewalks, lasting about six hours and 30 minutes each, will allow the two-astronaut teams to accomplish the assembly and repair tasks.
However, if Nasa chooses to extend the mission by three days, astronauts could fit in a fourth spacewalk, to prepare for installation of a boom that will allow crews to inspect for damage to the heat shields of future shuttles while docked with the space station.
Waiting to fly
Flying on the shuttle is schoolteacher-turned-astronaut Barbara Morgan.
Ms Morgan, 55, originally trained at Nasa as a back-up for Christa McAuliffe, who was selected for Nasa's Teacher in Space programme, announced by US President Reagan in the 1980s.
The Endeavour enjoyed a smooth ascent into orbit
McAuliffe and six other astronauts were killed in 1986 aboard the shuttle Challenger, when a leaky booster rocket triggered an explosion 73 seconds into launch.
After the incident, Nasa asked Ms Morgan to stay on as its Teacher in Space representative and pledged a shuttle flight to fulfil McAuliffe's educational agenda.
But then the agency also banned civilians from flying in its spacecraft, so Ms Morgan had to become a fully trained astronaut, joining Nasa's corps in 1998.
She will operate a robot arm in space and, if time permits, speak with school children at locations around the US via a link-up.
The launch of Endeavour comes less than two weeks after outside medical experts issued a provocative report on astronaut behaviour and health.
According to the report, astronauts were drunk just before scheduled flights. Launch preparations were also overshadowed by news that a non-critical computer headed for the ISS was sabotaged.