SpaceX Crew Dragon astronauts prepare for launch to International Space Station

After an overnight launch readiness review, NASA and SpaceX early Tuesday cleared a Falcon 9 rocket and Crew Dragon spacecraft for blastoff Thursday on a commercial flight to ferry a three-man, one-woman crew to the International Space Station.

Liftoff from historic pad 39A at the Kennedy Space Center will mark only the third piloted flight to orbit from U.S. soil since the space shuttle's retirement 10 years ago, and the first featuring a previously flown Crew Dragon capsule and a "used" first stage booster. A series of in-depth reviews, culminating in Tuesday's Launch Readiness Review, "have been extremely thorough, especially with a refurbished Falcon and Dragon. We're very convinced that it's safe to fly," said Norm Knight, deputy manager of flight operations at the Johnson Space Center in Houston.