Nasa has announced that the four-member Crew‑11 mission will return early from the International Space Station (ISS) due to a medical issue affecting one of the crew.

The unprecedented decision to return Crew‑11 from the ISS to Earth was announced during a news conference held by the agency.

The Crew‑11 mission – which includes two Nasa astronauts, a Japanese astronaut and a Russian cosmonaut – is operated by Nasa under contract with SpaceX.

The four crew members lifted off aboard a SpaceX Crew Dragon Endeavour on 1 August 2025 for what was originally planned as a six-month stint on the ISS, with a scheduled return in February 2026.

The mission will now be cut short due to a medical concern with a crew member, marking the first evacuation specifically due to a health concern in the ISS’s 25-year history.

During the news conference, Jared Isaacman, Nasa’s administrator, told reporters that the previous day a “single crew member onboard the station experienced a medical situation and is now stable”.

However, following discussions with medical officials and leadership within Nasa, the decision has been taken to return the crew because “the capability to diagnose and treat this properly does not live on the ISS”.

During the news conference, Amit Shah Raju, Nasa’s associate administrator, said: “Our crews are extensively trained to manage unexpected medical situations and other off nominal events, including onboard training, which we conduct regularly for these situations. Yesterday was a textbook example of that training in action. Once the situation on the station stabilised, careful deliberations led us to the decision to return Crew-11.”

He added that they would not name the astronaut – citing the crew member’s privacy – or what the medical issue was, but wanted to reassure the press that the “astronaut is absolutely stable [and] this is not an emergent evacuation.”

Nasa’s chief health and medical officer James Polk also wanted to reiterate that “this was not an injury that occurred in the pursuit of operations. It’s mostly having a medical issue in the difficult areas of microgravity, and with the suite of hardware that we have at our avail to complete a diagnosis.”

In a statement that followed on Nasa’s website, the agency said it anticipates a decision on a target Crew-11 return date to be made in the coming days. It said it will also work with SpaceX, and its international partners, to review the options available to advance launch opportunities for the Crew-12 mission, which was originally scheduled to launch on 15 February 2026.

The health impact of space on astronauts can be considerable, with changes in bone density, muscle mass and cardiovascular function due to microgravity. Prolonged exposure to space radiation can also have adverse risks, including increasing the likelihood of cancer and other conditions. One 2022 study even found major changes in the brains of astronauts who had endured long durations in space.