The US space shuttle Endeavour and its crew of six astronauts reached orbit this morning after a successful launch from the Kennedy Space Center in Cape Canaveral, Florida.
The Endeavour's mission is to install the last two main pieces of the International Space Station.
The shuttle blasted off at 4.14am (9.14am GMT).
Low clouds forced NASA to postpone Endeavour's first launch attempt on Sunday morning. Scattered clouds also threatened visibility today but cleared in time to meet flight safety rules.
The shuttle carries the International Space Station's last connecting hub and a dome-shaped cupola with seven windows to provide the crew with panoramic views outside the station.
The modules were built in Italy for NASA and will complete US assembly of the orbital outpost, a $100bn project of 16 nations that has been under construction since 1998.
Four more shuttle missions remain to deliver cargo platforms, spare parts and experiments before the fleet is retired later this year.
With Endeavour's delivery of the Tranquillity module and its cupola, the International Space Station will be 90% complete, NASA said.
The mission comes as NASA begins to re-evaluate its future after US President Barack Obama effectively abandoned the US space agency's plan to send astronauts back to the moon by 2020.
The Constellation programme was intended to develop a successor spacecraft to the shuttle, which could be used to carry astronauts to the moon where they would use a lunar base to launch manned missions to Mars.
Constrained by soaring budget deficits, President Obama submitted a budget to Congress that encourages the agency to instead focus on developing commercial transport alternatives to ferry astronauts to the ISS after the shuttle program ends.
