NASA to evacuate 4 astronauts from ISS before scheduled return due to 'serious medical condition'

The ISS in orbit above the Earth.

NASA has said it will return a four-person crew aboard the International Space Station (ISS), cutting short their mission a month early because of a "serious medical condition" affecting one of the astronauts.

The agency did not disclose the name of the crew member or the medical condition, citing health privacy, but said the person was in a stable condition.

"This is not an emergency evacuation," said a Nasa official, adding: "We always err on the side of the astronaut's health."

The sick crew member was now stable but there was a “lingering risk”, said Nasa’s chief health and medical officer, Dr James Polk, adding that the issue has not been properly diagnosed, The Guardian reported.

This comes after Nasa abruptly cancelled a spacewalk on Wednesday due to take place on Thursday, when two astronauts were set to step outside the ISS, citing a "medical concern", BBC reported.

The decision to bring back the crew early was announced by Nasa Administrator Jared Isaacman and other agency officials at a news conference on Thursday.

What the medical issue might be is a matter of speculation, but it is clear that it was not properly treatable on the ISS. Isaacman said that even if a doctor had been aboard, the agency would still have wanted to bring the astronaut home.

The US space agency said in a press conference that the crew of four led by the US commander Zena Cardman would return to Earth in the coming days, earlier than planned.

Serious medical issues have been dealt with in the past on the station, which has been continuously inhabited since 2000. They include one astronaut suffering a blood clot in their jugular vein, suggesting that the current situation is particularly serious.

The only other time a space agency has ended a space station mission early because of health concerns was in 1985, when the cosmonaut Vladimir Vasyutin returned from the Soviet station with an infection and high fever.

The crew of four arrived on a SpaceX capsule in August for a stay of at least six months. Cardman is accompanied by the US astronaut Mike Fincke, Japan’s Kimiya Yui and Russia’s Oleg Platonov.

Only one person on the current Nasa mission is sick, but all four need to return because the agency aims to make sure the ISS never has more crew on board than there are available seats in docked space capsules. Those capsules need to serve as lifeboats or rescue vehicles.

The ISS will not be left empty. Three other people are living and working aboard. The US astronaut Chris Williams and Russia’s Sergei Mikayev and Sergei Kud-Sverchkov, arrived in November on board a Soyuz rocket for an eight-month stay.