It's a new chapter in manned space flight, the first time an all-private crew goes into space on a private non-government spacecraft.
The commander, a former NASA astronaut, spoke before the flight.
"It's been a real privilege to work and train alongside these three remarkable gentlemen," said Axiom Mission 1 Commander Michael Lopez-Alegria. "And I can say with zero hesitation that we are ready to fly."
The group is composed of an American, a Canadian and an Israeli, all with deep pockets. The ride isn't cheap.
They're reportedly paying close to $55 million dollars per ticket for more than a week in space, and a trip to the international Space Station.
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"The company Axiom is a space tourist company, and they basically got some private citizens together who paid their way to go up," said Benjamin Dickow, executive director of the Columbia Space Center in Downey.
Each visitor will have a set of experiments to run while they're up there -- one reason they prefer to not be called "tourists."
As a gift for their hosts on the space station, they'll be bringing up some food prepared by celebrity chef Jose Andres.
Dickow says just the interest in a trip like this gets people talking about science.
"And that I think is the big takeaway from this," he explained. "There's something about space that really gets people involved in science, and that's good for all of us."