The mission is NASA’s first full-fledged bid to send a crew into orbit aboard a privately owned spacecraft.

The company’s newly designed Crew Dragon capsule, dubbed Resilience, is set for liftoff atop a SpaceX Falcon 9 rocket at 7.27 pm local time on Monday from Kennedy Space Center in Cape Canaveral, Florida.

The 27-hour ride to the space station, an orbiting laboratory 400 km above Earth, was originally scheduled to begin on Saturday.

However the launch was postponed due to forecasts of gusty winds – remnants of Tropical Storm Eta – that would have made a return landing for the Falcon 9’s reusable booster stage difficult, NASA said.

Mission preparations were under way Sunday afternoon as officials pegged launch probability at 50 per cent, maintaining plans to launch but monitoring wind and cloud formation near the rocket pad that could postpone the mission to Wednesday.

The astronauts donned custom white flight suits and arrived at the launch pad on schedule at 4.30 pm in three white Tesla SUVs, flanked by NASA and SpaceX personnel.

NASA is calling the flight its first “operational” mission for a rocket and crew-vehicle system that was 10 years in the making.

It represents a new era of commercially developed spacecraft – owned and operated by a private entity rather than NASA – for sending Americans into orbit.

“This is the culmination of years of work and effort from a lot of people and a lot of time,” Benji Reed, SpaceX senior director of human spaceflight programs, told reporters on Friday.

“We have built what I would call one of the safest launch vehicles and spacecraft ever.”

A trial flight of the SpaceX Crew Dragon in August, carrying just two astronauts to and from the space station, marked NASA’s first human space mission to be launched from US soil in nine years, following the end of the space shuttle program in 2011.

In the intervening years, US astronauts have had to hitch rides into orbit aboard Russia’s Soyuz spacecraft.

The Resilience crew includes commander Mike Hopkins and fellow NASA astronauts, mission pilot Victor Glover and physicist Shannon Walker.

They will be joined by Japanese astronaut Soichi Noguchi, making his third trip to space after previously flying on the US shuttle in 2005 and Soyuz in 2009.

Musk, the billionaire SpaceX chief executive who is also CEO of electric carmaker and battery manufacturer Tesla, will likely not be watching the liftoff from the Kennedy Space Center launch control room as usual, NASA officials said.

Musk said on Saturday he “most likely” has a moderate case of COVID-19.

-AAP