The US space agency shuttle, Discovery, has taken off from its launch pad in Cape Canaveral in Florida.
The launch marks the first manned mission by NASA since the Columbia disaster in 2003.
Seven crew members are on board the Discovery, which is on a 12-day supply mission to the International Space Station.
The mission sees new safety measures which were put in place after the Columbia tragedy being tested for the first time.
On 1 February 2003, the Columbia shuttle burst into flames upon re-entering the earth's atmosphere, killing all seven astronauts on board.
NASA officials had earlier said today's launch would go ahead despite them not being able to identify a fault in one of the craft's hydrogen fuel sensors.
Earlier this month the problem forced NASA to postpone Discovery's first launch attempt.
Officials said NASA was willing to waive the safety rule requiring all four sensors to be working because it was felt there were sufficient safeguards. Two of the four are back-ups.
