SpaceX, the private rocket company of billionaire entrepreneur Elon Musk, was forced by foul weather to scrub a planned launch on Wednesday of two Americans into orbit from Florida, a mission that would mark the first spaceflight of Nasa astronauts from US

soil in nine years.

The countdown was halted less than 17 minutes before the SpaceX Falcon 9 rocket was due to lift off from the Kennedy Space Center, propelling Doug Hurley and Bob Behnken on a 19-hour ride aboard the company's newly designed Crew Dragon capsule bound for the International Space Station.

The next launch window is set for Saturday afternoon.

Earlier the hatch had been closed on the capsule and the access ramp to the spacecraft had been retracted.

The pair could be seen on a video feed wearing futuristic white uniforms adorned with the US flag and the logos of Nasa and SpaceX as they performed checks on their touch screens.

The launch was scheduled for 4.33pm (2033 GMT) from the Kennedy Space Center's Launch Pad 39A.

Neil Armstrong and his Apollo 11 crewmates lifted off from the same spot on their historic journey to the Moon.

The mission has proceeded despite shutdowns caused by the coronavirus pandemic, with the crew in quarantine for the past two weeks.

President Donald Trump and First Lady Melania Trump were at the space centre to watch the launch.

A tropical storm had earlier formed off the coast of South Carolina, presenting a possible risk if astronauts were forced to carry out an emergency landing in the Atlantic shortly after takeoff, but it weakened after making landfall.

Founded in 2002, Space Exploration Technologies Corp has torn up the rules to produce a lower-cost alternative to human spaceflight that has gradually won over skeptics.

By 2012, it had become the first private company to dock a cargo capsule at the ISS, resupplying the station regularly ever since.

Two years later, Nasa ordered the next step: to transport its astronauts there by adapting the Dragon capsule.

"SpaceX would not be here without Nasa," Musk said last year, after a successful dress rehearsal without humans for the trip to the ISS.

The space agency paid more than $3bn for SpaceX to design, build, test and operate its reusable capsule for six future space round trips.

The project has experienced delays, explosions, and parachute problems - but even so, SpaceX has beaten aerospace giant Boeing to the punch.

Boeing's Nasa entry, the Starliner, is still not ready.

The move by Nasa to invest in privately developed spacecraft - a more budget-friendly proposition than spending tens of billions of dollars developing such systems itself, as it had done for decades - was begun under the presidency of George W Bush for cargo, and then under Barack Obama for human flight.

At the time, there was immense hostility in Congress and Nasa to the start-up's claims of what it could achieve.

A decade on, it is Trump.

The Republican is trying to reaffirm American domination of space, militarily but also by ordering a return to the Moon in 2024.

If Nasa can entrust "low Earth orbit" space travel to the private sector, it would free up dollars for its more distant missions.

"We envision a future where low Earth orbit is entirely commercialized, where Nasa is one customer of many customers," Bridenstine said.

Crew Dragon is a capsule like Apollo, but updated for the 21st century.

Touch screens have replaced switches.

The interior has more subtle lighting.

It looks entirely different from the huge winged space shuttles that carried astronauts into space from US soil from 1981 to 2011.