Nasa is considering a medical evacuation from the International Space Station after an astronaut developed an unspecified “medical concern”.

The US space agency said that the situation involved a single crew member who was “stable” but that one of the possible next steps was to bring back to Earth all four of Crew 11, whose six-month stay on board the ISS is not due to end until February 20.

“Safely conducting our missions is our highest priority and we are actively evaluating all options, including the possibility of an earlier end to Crew 11’s mission,” the agency stated.

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Nasa has never evacuated crew from space due to a medical situation but has contingency plans in place for doing so, including leaving spacecraft docked at the ISS as “lifeboats” to get them back to Earth. “These are the situations Nasa and our partners train for and prepare to execute safely,” Nasa added in its statement.

Crew 11 arrived at the ISS in a SpaceX Crew Dragon capsule in August 2025 and were due to return to Earth on February 21. The crew comprises the American astronauts Mike Fincke, 58, and Zena Cardman, 38, along with Kimiya Yui, 55, from Japan, and Oleg Platonov, 39, from Russia.

Astronaut Mike Fincke in a spacesuit holding a helmet, with an American flag in the background.

Mike Fincke, an American

NASA/BILL STAFORD

Oleg Platonov in a blue flight suit with arms crossed, standing against a dark blue background.

Oleg Platonov from Russia

NASA/ROBERT MARKOWITZ

Nasa has not revealed which of the four is sick, to protect their medical privacy.

On Wednesday night, shortly before its initial announcement that a “medical concern” had arisen sometime during the afternoon, Nasa cut public access to its live radio feeds by which crew communicate with Mission Control in Houston, Texas.

A SpaceX Falcon 9 rocket launches from Launch Complex 39A, with a white plume of smoke and fire behind it, while a white bird flies in the cloudy sky to the right.

Crew 11 leaves in a SpaceX capsule on August 1 in Cape Canaveral

JOEL KOWSKY/NASA/GETTY IMAGES

Cardman and Fincke had been due to conduct a 6.5-hour spacewalk — known as an extra-vehicular activity (EVA) — on Thursday, to fit new hardware on the station’s exterior in readiness for the installation of new solar arrays later this year.

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Also on board the complex are one other American, Chris Williams, 42, who is a medical physicist, and two other cosmonauts, Sergey Kud-Sverchkov, 42, and Sergei Mikayev, 39, who arrived together in a Russian Soyuz capsule in November. Four new astronauts, Crew 12, are due to head to the ISS no earlier than February 15.

Astronaut Zena Cardman in a blue flight suit smiling in front of a white jet with its canopy open.

Zena Cardman of America

ROBERT MARKOWITZ/NASA

Astronaut Kimiya Yui aboard the International Space Station, smiling, with views of Earth from the cupola windows.

Yui Kimiya of Japan

SPACEX

Yui and Williams were supposed to have provided support for the EVA from inside the complex, including helping Fincke and Cardman into their spacesuits, “in my opinion the greatest responsibility on one of the most challenging and rewarding days for astronauts”, Cardman had stated in her most recent social media post yesterday, prior to Nasa’s announcement.

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She added: “Kimiya is a technical master, but I love him even more for his selfless nature, bottomless patience and perfect blend of humour and humility. When I’m having a rough day, Kimiya somehow shows up at exactly the right moment with a piece of chocolate, saying ‘thank you for your hard work’ — and everything becomes magically better.

“This week marked Yui-san’s 300th cumulative day in space, and I feel so lucky to have shared some of that time with him.”