Andreas "Andy" Mogensen had shared on X a Fox News clip featuring Musk and his boss, US President Donald Trump, where Musk claimed NASA's Butch Wilmore and Suni Williams were left stranded on the orbital outpost for "political reasons" by Biden, and that the new administration was now coming to the rescue.

"What a lie. And from someone who complains about lack of honesty from the mainstream media," wrote the 48-year-old European Space Agency astronaut, who has flown to the ISS twice, including aboard a SpaceX Crew Dragon capsule during a 2023 mission.

Musk responded by calling Mogensen "fully retarded," adding that "SpaceX could have brought them back several months ago" and that he had made such an offer to the Biden administration, without elaborating on what that offer entailed.

Wilmore and Williams flew to the ISS in June aboard a Boeing Starliner for what was meant to be an eight-day test mission to certify the new spaceship.

But thruster problems led NASA to decide that Starliner should return without its crew, and the agency tasked SpaceX with bringing the veteran astronauts home.

NASA then announced the pair would return on the SpaceX Crew-9 mission's spaceship, which launched in September with a crew of two instead of four in order to accommodate them.

The voyage home was initially scheduled for February but later shifted to March due to delays by SpaceX in preparing the spacecraft for Crew-10, whose crew will replace Crew-9's.

If there was an alternate rescue plan that could have been executed sooner, Musk has not revealed it.

"Elon, I have long admired you and what you have accomplished, especially at SpaceX and Tesla," Mogensen replied to Musk's missive.

"You know as well as I do, that Butch and Suni are returning with Crew-9, as has been the plan since last September. Even now, you are not sending up a rescue ship to bring them home. They are returning on the Dragon capsule that has been on ISS since last September."