The US Air Force’s 45th Weather Squadron, which monitors the weather for air and space operations, had forecast between a 40 per cent and 60 per cent chance of favourable conditions at the launch site in Florida.
NASA, which has strict rules about the conditions for crewed missions, said of one of which was being violated just minutes before the launch.
Speaking from the Crew Dragon capsule, Mr Hurley, who is the commander of the spacecraft, said: “We could see some raindrops on the windows and just figured that whatever it was, was too close to the launch pad at the time we needed it not to be.
“Understand that everybody’s probably a little bit bummed out. That’s just part of the deal.
He added: “We’ll do it again, I think, on Saturday.”
British astronaut Tim Peake said on Twitter: “What a shame – @SpaceX launch is scrubbed, but the rules are there in the interest of safety.
“A great rehearsal and reset for the next launch attempt in 3 days, Sat 30th at 15:22 (ET).”
How can I watch the launch on TV?
NASA was streaming the launch live on YouTube through its NASA TV channel and is likely to do the same again this Saturday.
Why is this mission so important?
The mission, known as Demo-2, will allow the US to once again send humans into space rather than relying on paying Russia for a lift on their spacecraft as they have done for the past nine years.
According to NASA, this is a demonstration mission to show SpaceX’s ability to ferry astronauts to the space station and back safely.
It is the final major step required by SpaceX’s astronaut carrier, the Crew Dragon, to get certified by NASA’s Commercial Crew Programme for more long-term crewed missions to space.
Alexander is the Online Editor at BBC Science Focus and is the one that keeps sciencefocus.com looking shipshape and Bristol fashion. He has been toying around with news, technology and science on internet for well over a decade, and sports a very fetching beard.