By Jonathan Amos
The demonstration of a new US system to get astronauts into orbit is under way.
The SpaceX company has launched a capsule designed to carry people from the Kennedy Space Center in Florida.
The mission is uncrewed for this flight, but if it goes well, the American space agency is likely to approve the system for regular astronaut use from later this year.
SpaceX founder Elon Musk said this could be the first step towards opening space travel to commercial customers.
Not since the retirement of the shuttles in 2011 has the US been able to put humans in orbit.
It has been paying to use Russian Soyuz vehicles instead.
SpaceX’s Falcon 9 rocket and Dragon crew capsule lifted off from Kennedy’s historic Pad 39A at the precise planned time of 02:49 EST (07:49 GMT).
The 11-minute ascent put the Dragon on a path to rendezvous with the International Space Station (ISS) on Sunday.
Who is this character Ripley?
Because this is just a demonstration, there are no astronauts aboard – but there is a “test dummy”.
Dressed in a spacesuit and sitting next to a window, this anthropomorphic simulator is fitted with sensors around the head, neck, and spine.
It will gather data on the type of forces that humans will experience when they get to ride in the spacecraft.
SpaceX has nicknamed the dummy “Ripley” – after the Sigourney Weaver character in the Alien movies.
For the California company, this mission is a key milestone in its short history. Mr Musk, a technology entrepreneur and engineer, set up the organisation with the specific intention of taking people into space.
“It’s been 17 years to get to this point, from 2002 to now. To be frank, I’m a little emotionally exhausted because it was super stressful,” he told reporters immediately after the launch.
“Our focus has been on serving Nasa’s needs but once Dragon is in regular operation, I think we will seek commercial customers of which the Nasa administrator, and Nasa in general, has been very supportive.”
Mr Musk said those customers could include private citizens going to the ISS, just as they have done on Soyuz vehicles in the past.
Separately, the entrepreneur is developing a much bigger system – which he calls the Starship and Super Heavy rocket – to transport people to the Moon and Mars.
The Dragon crew capsule is a variant on the ISS cargo freighter flown by SpaceX.
Upgrades include life-support systems, obviously; and more powerful thrusters to push the vessel to safety if something goes wrong with a rocket during an ascent to orbit.
It also has four parachutes instead of the freighter’s three to control the return to Earth.
Dragon crew capsules will splashdown in the Atlantic not far from Kennedy.