They are set to try the launch again on Saturday afternoon, with another backup time on Sunday. NASA's Doug Hurley and Bob Behnken are headed to the International Space Station and will become the first astronauts to launch from the US since 2011, NPR reports. Called Demo-2, the mission is scheduled for launch at 6:33 am AEST from the Kennedy Space Centre in Florida. It will come over from the west, heading east, and could be visible for just a few minutes.
Crews had begun to fuel the Falcon 9 rocket carrying the capsule before the decision was taken to cancel due to cloudy skies and rain.
This launch of SpaceX's first crewed mission will put an end to NASA's nine-year hiatus in human spaceflight.
On Wednesday, SpaceX will for the first time launch astronauts into orbit.
NASA astronauts Douglas Hurley, left, and Robert Behnken, during a launch rehearsal.
Yes, today is the day when Behnken and Hurley ride the Dragon for what NASA is calling its Demo-2 mission, a test mission to help prove the systems meet NASA's requirements for certification to carry astronauts to the International Space Station (ISS) and back. That means it will begin offering regular transportation services for astronaut crew to and from the International Space Station, joining Russia's Soyuz as a means to travel to the orbital science platform.
Meanwhile, SpaceX has already begun plans to also offer berths on Crew Dragon to private citizens and potentially commercial scientists and other passengers.