WASHINGTON:Four astronauts were poised to launch on the SpaceX Crew Dragon "Resilience" to the International Space Station on Sunday, the first of what the US hopes will be many routine missions following a successful test flight in late spring.

Three Americans -- Michael Hopkins, Victor Glover and Shannon Walker -- and Japan's Soichi Noguchi will blast off at 7:27 pm Sunday (0027 GMT Monday) from the Kennedy Space Center in Florida.

In May, SpaceX completed a demonstration mission showing it could take astronauts to the ISS and bring them back safely, thus ending almost a decade of reliance on Russia for rides on its Soyuz rockets.

"The history being made this time is we're launching what we call an operational flight to the International Space Station," NASA administrator Jim Bridenstine told reporters Friday.

The launch will be attended by Vice President Mike Pence and second lady Karen Pence.

The crew will dock at their destination at around 11:00 pm Monday night (0400 GMT Tuesday), joining two Russians and one American onboard the station, and stay for six months.

The Crew Dragon earlier this week became the first spacecraft to be certified by NASA since the Space Shuttle nearly 40 years ago.

It is a capsule, similar in shape to the spacecraft which preceded Space Shuttle, and its launch vehicle is a reusable SpaceX Falcon 9 rocket.

At the end of its missions, the Crew Dragon deploys parachutes then splashes down in water, just as in the Apollo era.

NASA turned to SpaceX and Boeing after shuttering the checkered Space Shuttle program in 2011, which failed in its main objectives of making space travel affordable and safe.

The agency will have spent more than $8 billion on the Commercial Crew program by 2024, with the hope that the private sector can take care of NASA's needs in "low Earth orbit" so it is freed up to focus on return missions to the Moon and then on to Mars.

SpaceX, founded by Elon Musk in 2002, has leapfrogged its much older rival Boeing, whose program has floundered after a failed test of its uncrewed Starliner last year.

But SpaceX's success won't mean the US will stop hitching rides with Russia altogether, said Bridenstine.

"We want to have an exchange of seats where American astronauts can fly on Russian Soyuz rockets and Russian cosmonauts can fly on commercial crew vehicles," he said, explaining it was necessary in case either program was down for a period of time.

The reality, however, is that space ties between the US and Russia, one of the few bright spots in their bilateral relations, have frayed in recent years, and much remains uncertain.

Russia has said it won't be a partner in the Artemis program to return to the Moon in 2024, claiming the NASA-led mission is too US-centric.

Dmitry Rogozin, the head of Russia's space agency has also repeatedly mocked SpaceX's technology, and this summer announced Roscosmos would build rockets that surpass Musk's.

He told a state news agency he was unimpressed with the Crew Dragon's water landing, calling it "rather rough" and saying his agency was developing a methane rocket that will be reusable 100 times.

But the fact that a national space agency feels moved to compare itself to a company is arguably a validation of NASA's public-private strategy.

SpaceX's emergence has also deprived Roscosmos of a valuable income stream.

The cost of round-trips on Russian rockets had been rising and stood at around $85 million per astronaut, according to estimates last year.

- Presidential transition -

Presidential transitions are always a difficult time for NASA, and the ascension of Joe Biden in January is expected to be no different.

The agency has yet to receive from Congress the tens of billions of dollars needed to finalize the Artemis program.

Bridenstine has announced that he will step down, in order to let the new president set his own goals for space exploration.

So far, Biden has not commented on the 2024 timeline.

Democratic party documents say they support NASA's Moon and Mars aspirations, but also emphasize elevating the agency's Earth sciences division to better understand how climate change is affecting our planet.