SpaceX’s historic launch of Falcon 9, scheduled for Wednesday, May 27, at 9:33pm BST, was set to to make history, not simply for being the first time in almost a decade that American astronauts left American soil for orbit.
Nasa crewmen Robert Behnken and Douglas Hurley have both been in space before, but they will be the first people ever put there by a private company.
“When starting SpaceX in 2002, I really did not think this day would occur,” said Mr. Musk - SpaceX's CEO and founder - during an appearance on Nasa Television. "I expected a 90 per cent chance we would fail to even get to a low-Earth orbit with a small rocket.”
Yet over the past 18 years, SpaceX has come to dominate the commercial satellite market. It now hopes to enter the business of space travel too.
So 12 hours after the scheduled takeoff, why are Mr Behnken and Mr Hurley still very much on the planet?
Why was the SpaceX launch postponed?
The rocket launch was aborted 17 minutes before takeoff due to poor weather conditions.
Spectators, including President Donald Trump and Vice President Mike Pence, faced disappointment when persistent clouds refused to part.
The US Air Force's 45th Weather Squadron, which monitors the weather for air and space operations, had estimated only a 40 per cent chance of suitable weather conditions. Nasa officials had unsuccessfully tried to discourage hopeful crowds from gathering along Florida’s Space Coast.
Meanwhile, an estimated 1.7 million people from around the world were tuned in to live streams of the spectacle at The Kennedy Space Centre.
Animation of Nasa SpaceX mission
When has it been moved to?
The event - which is the final big test before SpaceX can qualify for commercial crew-certification from Nasa - has been pushed back to the weekend, with Saturday and Sunday identified as the next potential windows of opportunity.
The first launch attempt will be on Saturday 30 at 9:20pm BST.
Can I watch it in the UK?
There are two ways of catching the Falcon’s flight from the British Isles: organically and digitally.
On the advice of astronaut Tim Peake, Brits looking south-west at time of takeoff should see evidence of the launch.
But they can also watch in closer detail on YouTube. Find out more about how to watch the SpaceX launch online.