CAPE CANAVERAL (Florida) • A SpaceX rocket with an unmanned crew capsule blasted off yesterday for the International Space Station, in a key milestone for billionaire Elon Musk's space company and Nasa's long-delayed goal to resume human spaceflight from US soil later this year.

SpaceX's 4.9m Crew Dragon capsule, atop a Falcon 9 rocket, lifted off from Florida's Kennedy Space Centre at 2.49am, carrying a test dummy nicknamed Ripley.

The capsule successfully separated from the rocket about 11 minutes later, sparking cheers in the control room, and began its journey to the space station.

"I almost thought we would fail. I thought maybe we'd have a 10 per cent chance of reaching orbit starting out," Mr Musk said of his feelings when he founded the space company in 2002.

"I'm a little emotionally exhausted because that was super stressful, but it worked."

The station's three-member crew was expected to greet the capsule, carrying 181kg of supplies and test equipment, early this morning, Nasa said. During its five-day stay, US astronaut Anne McClain and Canadian astronaut David Saint-Jacques will run tests and inspect Crew Dragon's cabin.

Nasa has awarded SpaceX and Boeing US$6.8 billion (S$9.2 billion) to build competing rocket and capsule systems to launch astronauts into orbit from American soil for the first time since the US Space Shuttle was retired from service in 2011.

Either SpaceX or Boeing will have bragging rights as the first private company to launch humans into space on its own rocket, although plans call for the rockets built to carry astronauts into space.

The launch systems are aimed at ending US reliance on Russian rockets for rides to the US$100 billion orbital research laboratory, which flies about 402km above Earth.

REUTERS