Nasa SpaceX launch - as it happened: Historic liftoff cancelled moments before takeoff over weather

Welcome to The Independent's coverage of the SpaceX and Nasa launch this evening. Liftoff is at 9.30pm UK time, or 4.30pm eastern time.

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Weather 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.

'I will stop in a heartbeat if you want me to'

Yesterday, Nasa Administrator Jim Bridenstine said from Kennedy Space Center that both the space agency and SpaceX have been diligent about making sure everyone in the launch loop knows they're free to halt the countdown if there's a concern.

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 to become first ever private company to put people in space – beating almost every country

If SpaceX is successful today, it will be the first private company ever to put humans into space. Such a feat has only been achieved by three countries: the US, Russia and China.

The company has been sending cargo to the International Space Station since 2012. But it has said that sending humans is an entirely different proposition.

"It's a huge step, obviously, going from cargo ... to launching two people that are dads as we call them and have families, kids, wives.," said Hans Koenigsmann, a SpaceX vice president.

Oxford astronomer Chris Lintott says you should be able to see the spacecraft from the UK as it flies off to the International Space Station.

Here's what you need to be looking out for:

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.

Countdown procedure

SpaceX's website has a great rundown of what will happen in the 45 minutes before launch, as the astronauts wait to be propelled up into the sky. (This will all begin about 8.45pm UK time, if the launch goes ahead today.)

And here's what the various parts of the spacecraft will do after that:

Here's what Nasa has to say about Robert Behnken and Douglas Hurley, the two experiences astronauts at the centre of today's launch:

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.

This doesn't look good for anyone planning a rocket launch from Florida today...

If today's launch gets scrubbed, it'll be put back to Saturday.