A serious health issue involving one of the astronauts aboard the International Space Station (ISS) has forced Nasa to bring the affected astronaut and three fellow crew members back to Earth several months ahead of schedule, marking the first emergency return in the ISS’s 25-year history, according to senior agency officials.

Speaking at a hastily arranged press conference in Washington on Thursday (Jan 8), Nasa Administrator Jared Isaacman explained that the decision was made because the necessary medical diagnosis and treatment could not be properly carried out in space. He declined to identify the astronaut or reveal the nature of the condition.

Nasa officials also withheld which of the four Crew-11 astronauts was affected, citing medical privacy. James Polk, Nasa’s Chief Health and Medical Officer, emphasized that the condition was not related to any operational activity, meaning it did not occur while the astronaut was working. The agency had already cancelled a planned spacewalk scheduled for Thursday after flagging a medical concern on Wednesday, later announcing that it was considering ending the astronaut’s mission early.

The crew consists of Zena Cardman and Mike Fincke from the United States, Kimiya Yui of Japan, and Russian cosmonaut Oleg Platonov. They launched from Florida in August and were originally expected to return in May. Fincke, the station’s commander, and Cardman, the flight engineer, had been preparing for a 6.5-hour spacewalk to install equipment outside the station.

Medical matters aboard the ISS are typically treated with strict confidentiality, and astronauts rarely discuss such issues publicly. Spacewalks themselves are demanding and hazardous operations that require extensive preparation, bulky protective suits, and precisely coordinated procedures while astronauts remain tethered to the station. Nasa has previously cancelled spacewalks for health reasons, including one in 2024 due to spacesuit discomfort and another in 2021 when astronaut Mark Vande Hei withdrew because of a pinched nerve.