NASA is preparing to conduct its first-ever medical evacuation from the International Space Station (ISS), activating a contingency plan to return a crew to Earth months ahead of schedule.

The plan, developed decades ago for medical emergencies in space, has never before been implemented during an ISS mission, agency officials said Thursday.

Under the program, the returning astronauts will seal themselves inside the capsule, undock from the ISS, perform a controlled departure and reenter Earth's atmosphere for a parachute-assisted splashdown in the Pacific Ocean off the California coast.

A recovery ship with medical personnel will retrieve the capsule, conduct immediate health evaluations at sea, and transport the astronauts by helicopter and jet to NASA's Johnson Space Center in Houston for further care.

The evacuation was triggered after a Crew-11 astronaut experienced a medical issue that could not be fully treated in microgravity, prompting NASA flight surgeons to recommend an early return.

The American space agency has declined to identify the individual or disclose the nature of the condition, citing medical privacy. 

However, NASA Administrator Jared Isaacman noted on Thursday that the agency considers this a 'serious medical condition' that forced officials to conclude that the first-ever evacuation was necessary. 

He added that NASA expects to provide an updated return timeline within 48 hours as mission managers finalize landing conditions.

NASA Chief Medical Officer Dr James Polk said on Thursday that the astronaut is not in immediate danger and is being cared for by fellow crew members until the return is completed.

'This is not related to a spacewalk or station operations,' Polk said. 'It's primarily a medical issue made more complex by the challenges of microgravity.'

Crew-11 consists of NASA astronauts Zena Cardman and Mike Fincke, Japanese astronaut Kimiya Yui and Russian cosmonaut Oleg Platonov. 

A Japan-based news outlet reported that Yui has no health issues, narrowing the concern to the remaining crew members.

Before departure, the crew will conduct vehicle health checks, secure cargo, seal hatches and depressurize the docking vestibule while mission control verifies the spacecraft's readiness.

Once undocked, the return capsule, dubbed Crew Dragon, will execute a series of separation burns to move safely away from the station before performing a deorbit burn several hours later. 

The capsule will then reenter Earth's atmosphere, deploying drogue parachutes followed by its main parachutes before splashing down at sea. 

The station was recently joined by Japanese astronaut Koichi Wakata and NASA astronaut Chris Williams, who arrived aboard a Russian Soyuz spacecraft in November 2025. 

Isaacman said Williams will remain on the station with the Soyuz crew to maintain the United States' continuous presence in orbit.

The evacuation follows NASA's Spaceflight Human-System Standard, which mandates contingency return procedures whenever onboard medical resources are insufficient. 

Although statistical models have long predicted that such an event could occur roughly once every three years, the plan has never before been used.

While NASA has not yet determined the return data for Crew-11, its Crew Transportation System Design Reference Missions states: 'Emergencies could result from ISS system failures, an uninhabitable crew environment, or a medical event requiring the return of the crewmembers. 

'The crew will return to Earth within 24 hours of a declaration of an intention to return early.'

Crew-11 arrived at the ISS on August 1, 2025, meaning their return date had been scheduled for late February.

The four astronauts were supposed to leave after Crew-12 arrived on a SpaceX Dragon capsule no earlier than February 15.

Isaacman said that any decision to potentially move up the launch of Crew-12 would not impact the upcoming Artemis II mission planned for February 2026.

He called the two launches 'totally separate campaigns,' meaning there should be no issue in launching Artemis on time. Artemis II will be the first manned spaceflight to orbit the moon since 1972.

Meanwhile, the ISS is required to have astronauts aboard at all times, as they are essential to carry out maintenance, repairs, operate complex experiments, manage life support, and perform spacewalks, tasks that automation cannot fully handle, ensuring constant human oversight for safety and scientific output.

Until now, there had never been a crew evacuated ahead of their scheduled departure time from the ISS; however, two spacewalks were recently cancelled because of various health issues among the astronauts.

A mission was cancelled in 2021 when Mark Vande Hei experienced a pinched nerve and was unable to travel outside the ISS.

Another spacewalk in 2024 was called off at the last minute because an astronaut experienced 'spacesuit discomfort'.