After more than nine months on the International Space Station, two astronauts are a step closer to returning home following the launch of a crew swap mission on Friday.

A Falcon 9 rocket with a Crew Dragon fixed to its top blasted off from the Kennedy Space Center in Florida, carrying a four-member team bound for the orbital outpost.

"We celebrate the countless individuals all over the world that have made this journey possible," said astronaut Nichole Ayers, the designated pilot of the Crew-10 mission, just before launch.

But the real focus is what their arrival enables - the long-overdue departure from the ISS of NASA duo Butch Wilmore and Suni Williams.

The two former US Navy pilots have been stuck aboard the orbital lab since June after the Boeing Starliner spacecraft they were testing on its maiden crewed voyage suffered propulsion issues and was deemed unfit to fly them back to Earth.

Instead, Starliner returned empty, without experiencing further major issues and what was meant to have been a days-long round-trip for Wilmore and Williams has now stretched past nine months.

That is significantly longer than the standard ISS rotation for astronauts of roughly six months.

But it is much shorter than the US space record of 371 days set by NASA astronaut Frank Rubio aboard the ISS in 2023, or the world record held by Russian cosmonaut Valeri Polyakov, who spent 437 continuous days aboard the Mir space station.

What began as a technical failure has also spiraled into a political flashpoint, as President Donald Trump and his close advisor, Elon Musk, who leads SpaceX, have repeatedly suggested that former president Joe Biden "abandoned" the pair intentionally and rejected a plan to bring them back sooner.

Trump, meanwhile, has drawn attention for his bizarre remarks about the situation, referring to Williams, a decorated former naval captain, as "the woman with the wild hair" and speculating about the personal dynamic between the two.

"They've been left up there. I hope they like each other, maybe they love each other, I don't know," he said during a recent White House press conference. (AFP)