SpaceX, the rocket company of high-tech entrepreneur Elon Musk, was due on Sunday to launch four astronauts on a flight to the International Space Station, NASA's first full-fledged mission sending a crew into orbit aboard a privately-owned spacecraft.

The company's newly designed Crew Dragon capsule, which the crew has dubbed Resilience, was set for liftoff atop a SpaceX Falcon 9 rocket at 7:27pm Eastern time from NASA's Kennedy Space Center in Cape Canaveral, Florida.

The 27-hour ride to the space station, an orbiting laboratory some 250 miles (400 km) above Earth, was originally scheduled to begin on Saturday.

But the launch was postponed for a day 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 officials said.

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 two 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 the electric carmaker and battery manufacturer Tesla Inc, will likely not be watching the liftoff from the Kennedy Space Center launch control room, as usual, NASA officials said. Musk said on Saturday that he "most likely" has a moderate case of Covid-19.

SpaceX and NASA have conducted contact-tracing and determined that Musk had not come into contact with anyone who interacted with the astronauts.

"Our astronauts have been in quarantine for weeks, and they should not have had contact with anybody," NASA chief Jim Bridenstine said on Friday. "They should be in good shape."

NASA contracted SpaceX and Boeing in 2014 to develop competing space capsules aimed at replacing its shuttle program and weaning the United States from dependence on Russian rockets to send astronauts to space.