NASA astronauts Douglas Hurley, left, and Robert Behnken, during a launch rehearsal.
Weather at Florida's Kennedy Space Centre was expected to clear 10 minutes after launch but due to the movements of the Space Station the possible launch window was "instantaneous", meaning any delay at all would have meant cancellation.
This launch of SpaceX's first crewed mission will put an end to NASA's nine-year hiatus in human spaceflight.More news: Muharram Day of Ashura 2020, Know More
NASA astronauts Bob Behnken and Doug Hurley are trying to become the first men launched into space from US soil since the Space Shuttle program ended in 2011.
History could be made at 9.33pm United Kingdom time tonight, Wednesday, May 27, when SpaceX Falcon 9 is scheduled to launch from the Kennedy Space Centre in Florida, carrying two astronauts inside a new Crew Dragon Spacecraft to join the International Space Station.
For the last decade, NASA has bought seats aboard Russian Soyuz rockets to fly U.S. crews to the International Space Station. After Wednesday's launch, the coverage will continue on Thursday, May 28, for docking of Crew Dragon at the International Space Station.More news: Insect spray chemical can kill coronavirus, United Kingdom study shows
In 2010, NASA began looking for private contractors to deliver the crew to the ISS under the CCDev program.
The launch, which will be attended by President Donald Trump, is crucial for Musk, SpaceX and NASA.
In the event the launch is scrapped due to weather, backup dates and times have been scheduled for Saturday, May 30, at 2:22 p.m. CDT, and Sunday, May 31, at 3:00 p.m. CDT.More news: Shinzo Abe Resigns as Japan Prime Minister