Inside the craft, astronauts Bob Behnken and Doug Hurley will lift off en route to the International Space Station. That will be the first time astronauts will have landed this way since 1975, before the days of the Space Shuttle program. Once safely returned to dry land, SpaceX will be able to reuse that booster on any number of upcoming commercial launches, possibly including missions for NASA.
Demo-2 marks the first launch of NASA astronauts on a commercial spacecraft and the first launch of American astronauts into orbit on a USA -built vehicle from America since 2011. Look carefully, and you'll see one on the wrist of Behnken during the pre-launch checks with the signature velcro strap.
Wednesday's scheduled rocket launch from Florida was scrubbed because conditions were considered too risky. If that doesn't work the next time is Sunday, May 31 at 12:00 p.m. The joint NASA-SpaceX collaboration means the USA no longer has to rely on Russian Soyuz launches to move astronauts to and from the International Space Station.
With its Crew Dragon spacecraft, SpaceX still hopes it will be the first private company to fly humans into orbit.
NASA-SpaceX Demo-2 successful separation of the second Falcon 9 stage.
It will take Falcon 9 nine minutes to reach orbit and then Crew Dragon will have a 19-hour journey to the International Space Station once it separates from the rocket.
Mr Vagner tweeted earlier to say he was waiting for the duo at the space station.
The astronauts will perform a variety of tasks aboard the Crew Dragon as part of the demo mission in addition to the manual-control demonstration.