A pair of US astronauts stuck for more than nine months on the International Space Station will be returned to Earth on Tuesday evening, NASA said.

Butch Wilmore and Suni Williams are to be transported home with another American astronaut and a Russian cosmonaut aboard a SpaceX Crew Dragon craft, which arrived at the ISS early Sunday. 

The stranded duo have been on the ISS 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.

NASA said in a statement on Sunday evening that it had moved forward the astronauts' anticipated ocean splashdown off the Florida coast to approximately 5:57 PM Tuesday (2157 GMT). It was initially slated for no sooner than Wednesday.

"The updated return target continues to allow the space station crew members time to complete handover duties while providing operational flexibility ahead of less favorable weather conditions expected for later in the week," the space agency said.

NASA astronaut Nick Hague and Roscosmos cosmonaut Aleksandr Gorbunov will also return on the Dragon capsule, with the journey to be broadcast live from Monday evening when hatch closure preparations begin.

For Wilmore and Williams, it will mark the end of an ordeal that has seen them stuck for nine months after what was meant to have been a days-long roundtrip.

Their prolonged stay was 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.

Still, the unexpected nature of their prolonged stay away from their families — they had to receive additional clothing and personal care items because they hadn't packed enough — has garnered interest and sympathy.