Crew Dragon is the first commercially operated spacecraft created to carry astronauts, and the uncrewed demonstration mission to the International Space Station is a test to make sure everything works before humans are rocketed into space in the capsule.
The Crew Dragon launched lifted off from Cape Canaveral at 7.49 am GMT, (2.49am EST). That will be the first launch of American astronauts aboard a US rocket since the shuttle program ended in 2011.
This is the phase of the mission that SpaceX founder Elon Musk says worries him the most - the fiery, high-speed descent through the atmosphere.
Bridenstine said he's confident that astronauts will soar on a Dragon or Starliner - or both - by year's end.
The dummy riding in the capsule - which SpaceX's Hans Koenigsmann prefers to call a "smartie" - has been nicknamed Ripley in honour of the character played by Sigourney Weaver in the "Alien" movies.
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A SpaceX Falcon 9 rocket with the company's Crew Dragon spacecraft onboard is seen as it is rolled out of the horizontal integration facility at Launch Complex 39A as preparations continue for the Demo-1 mission at the Kennedy Space Center in Florida, February 28, 2019. "It's different", said Mark Geyer, director of the Johnson Space Center, where USA astronauts are based.
"It's been a long eight years", the Kennedy Space Center's director Bob Cabana, a former astronaut himself, said as SpaceX employees milled around the rocket.
If the test goes to plan, it will be approved to carry people. NASA now pays $82 million per seat. But he stressed it was more important to move deliberately so "we get it right".
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. The spacecraft will rely on its computers to autonomously fly the spacecraft gently alongside the station and then attach itself to one of the docking ports.
"We're going to learn a ton from this mission, " said NASA's commercial crew program manager, Kathy Lueders. The more immediate goal is to avoid harming the space station and its three occupants: an American, Canadian and Russian.
Early on Friday, Musk, who is also chief executive officer of electric carmaker Tesla Inc, tweeted a photo of the inside of Crew Dragon capsule with Ripley strapped inside.