Nasa has postponed its first launch of astronauts from US soil in nine years due to bad weather, just minutes before lift-off.
Robert Behnken and Douglas Hurley were due to travel to the International Space Station (ISS) on a rocket and capsule system built by billionaire entrepreneur Elon Musk's firm SpaceX.
But with rain and thunderstorms looming, the launch date has now been moved to Saturday at 20:22 pm UK time.
An estimated 1.7 million people from around the world tuned in to the launch from The Kennedy Space Centre in Florida.
However, as the weather conditions became worse, the US space agency "scrubbed" the mission for safety reasons less than 17 minutes before the Falcon 9 rocket was due to take off, along with the Crew Dragon spacecraft.
Everything you need to know about the Nasa SpaceX launch
Mission will be the first time astronauts have been launched from US soil in nearly a decade – and could start a new era of American spaceflightWeather looking up
The odds of acceptable launch weather improved Tuesday to 60%. But that didn't factor in conditions along the Dragon's route to orbit.
SpaceX needs relatively calm waves and wind up the U.S. and Canadian seaboard and across the North Atlantic to Ireland, in case astronauts Hurley and Behnken need to make an emergency splashdown.
If SpaceX does not launch during Wednesday's split-second window, the next try would be Saturday.
President Donald Trump and Vice President Mike Pence are expected at Kennedy for the planned 4:33 p.m. liftoff, but "our highest priority" will remain the astronauts' safety, according to Bridenstine.
Bridenstine said he texted the two astronauts Monday and told them, "'If you want me to stop this thing for any reason, say so. I will stop it in a heartbeat if you want me to.' They both came back and they said, 'We're go for launch.' "
Hans Koenigsmann, a SpaceX vice president, said Monday evening that he and other company workers have imagined themselves in the astronauts' shoes on launch day — "or their helmets."
"That changes the equation pretty dramatically," he said.
SpaceX raises $350 million of funding a day before launch
Elon Musk's SpaceX said on Tuesday that it raised $346.2 million in a new round of funding, a day before it launches two American astronauts to the International Space Station.
The private rocket company's launch of its first crewed mission on Wednesday from NASA's Kennedy Space Center in Florida will put an end to the U.S. space agency's nine-year hiatus in human spaceflight.
The launch, which will be attended by President Donald Trump, is crucial for Musk, SpaceX and NASA.
A successful flight will mark a milestone in the quest to produce reusable spacecraft that can make space travel more affordable. Musk is the founder and chief executive officer of SpaceX and CEO of Tesla Inc.
Including the latest round, the company has raised more than $567 million and is valued at about $36 billion, according to a CNBC report.
Behnken will be the joint operations commander for the mission, responsible for activities such as rendezvous, docking and undocking, as well as Demo-2 activities while the spacecraft is docked to the space station. He was selected as a NASA astronaut in 2000 and has completed two space shuttle flights. Behnken flew STS-123 in March 2008 and STS-130 in February 2010, and he performed three spacewalks during each mission. Born in St. Anne, Missouri, he has bachelor’s degrees in physics and mechanical engineering from Washington University and earned a master’s and doctorate in mechanical engineering from California Institute of Technology. Before joining NASA, Behnken was a flight test engineer with the U.S. Air Force.
Hurley will be the spacecraft commander for Demo-2, responsible for activities such as launch, landing and recovery. He was selected as an astronaut in 2000 and has completed two spaceflights. Hurley served as pilot and lead robotics operator for both STS‐127 in July 2009 and STS‐135, the final space shuttle mission, in July 2011. The New York native was born in Endicott but considers Apalachin his hometown. He holds a Bachelor of Science degree in Civil Engineering from Tulane University in Louisiana and graduated from the U.S. Naval Test Pilot School in Maryland. Before joining NASA, he was a fighter pilot and test pilot in the U.S. Marine Corps.
Here from the Press Association is a rundown of Elon Musk's ambitions to get into space:
Elon Musk is on the cusp of a historic moment in his space ambitions, as SpaceX prepares to take two astronauts to the International Space Station (ISS) on Wednesday.
It is a crucial point for the entrepreneur, marking the first time a private company has attempted to send astronauts into space.
But his eye is very much set further than the ISS, and is locked on Mars...
Why is Elon Musk so interested in reaching Mars?
Musk said he started doing background research on space exploration in early 2002, after wondering why the US had made so little progress in putting humans in space since the Apollo missions - the last of which took place in 1972.
He spent some time inquiring about the cost of rockets and even went to Russia to find a cheaper alternative.
His first idea was called Mars Oasis, in which he conceptualised sending a small robotic lander to the Red Planet with seeds to start growing plants in martian radiated conditions.
SpaceX was founded in 2002, when Musk's wider space ambitions became serious, though Mars has remained one of his ultimate goals.
So is Elon Musk's plan for humans to one day visit Mars?
Musk's desire is not only for people to be able to visit Mars one day, but eventually to live there.
The 48-year-old wants to establish a self-sustaining city on the Red Planet, complete with iron foundries and even pizzerias.
And Musk fully intends to live there himself, previously saying he believes there is a "70% chance" he will make the trip.
How does he plan to get there?
Current efforts at SpaceX are focused on its Starship spacecraft, which Musk wants to use to not only reach the Moon and Mars, but also planets far beyond.
SpaceX says Starship will be the world's most powerful launch vehicle ever developed, able to carry more than 100 metric tonnes to Earth orbit.
Starship, coupled with a Super Heavy rocket, is intended to be a reusable transportation system capable of on orbit refuelling and utilising natural H2O and CO2 resources on Mars to refuel.
When does Musk want to reach Mars?
In 2017, Musk said he hoped to send unmanned spacecraft to Mars by 2022, followed by the first crewed flight in 2024.
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