One of the astronauts aboard the International Space Station (ISS) suffered what NASA Administrator Jared Isaacman described as a serious medical condition on Jan. 7, triggering the first medical evacuation in the orbiting laboratory’s 25-year history.

That astronaut, and his or her condition, remains anonymous due to medical privacy. However, it appears to be one of a four-person crew who flew aboard the SpaceX Crew Dragon Endeavor in August 2025.

Speaking at a press conference on Jan. 8, Isaacman confirmed that work would begin to bring NASA Astronauts Zena Cardman (mission commander) and Mike Fincke (mission pilot), as well as Russian Cosmonaut Oleg Platonov of Roscosmos and Kimiya Yui of the Japan Aerospace Exploration Agency (JAXA), back home earlier than expected.

Cardman and Fincke were preparing to conduct a 6.5-hour spacewalk on Jan. 8 as part of their larger Expedition 74 mission aboard the floating laboratory when one of the seven astronauts aboard the ISS suffered a medical incident.

Isaacman was joined by Dr. James Polk, chief health and medical officer for NASA, who clarified that the medical incident had nothing to do with spacewalk preparations or any other ongoing operation.

“This actually had nothing to do with the operational environment and preparing for a spacewalk at all,” he said. “This was totally unrelated to any operations on board.”

The ISS houses a vast suite of medical equipment which has been used to treat astronauts for various issues over the years, but Polk explained that while the equipment in orbit was enough to stabilize the astronaut, it was insufficient to treat the matter fully.

“We don’t have the complete amount of hardware that I would have in the emergency department, for example, to complete a workup of a patient,” he explained. “And in this particular incident, the medical incident was sufficient enough that we were concerned about the astronaut, that we would like to complete that workup, and the best way to complete that workup is on the ground, where we have the full suite of medical testing hardware.”

Isaacman said that with the combination of the medical equipment, the training the astronauts receive beforehand, and NASA’s pack of flight surgeons on the ground, the astronaut’s stabilization and the decision to bring the crew home early would have remained the same.

That being said, officials are not declaring the early departure as an emergency evacuation. They argued the decision was made out of an abundance of caution for the astronaut, who Polk emphasized was completely stabilized, and that standard reentry procedures are already prepared for various medical contingencies that can occur as the crew is brought aboard the recovery ship.

Crew-11 was scheduled to stay aboard the station for at least six months. They have less than a month left in their original mission time, and they have been able to complete nearly all of their objectives.

“We retain the capability to bring astronauts home in a matter of hours if necessary,” Isaacman said. “So this is recognizing, first of all, we’re always going to do the right thing for our astronauts, but it’s recognizing it’s the end of the Crew-11 mission right now. They’ve achieved almost all of their mission objectives. Crew-12 is going to launch in a matter of weeks anyway. This is an opportune time, when the vehicle is ready, when weather supports, to bring our crew home.” 

JAXA and Roscosmos officials have also been briefed on Isaacman’s decision.

The purpose of the delayed spacewalk was to install a modification kit and routing cables ahead of the rollout of a new solar array. It is unclear when work on the laboratory’s power source will continue, but Assistant Administrator Amit Kshatriya said that power supplies remained sufficient and the work was not an urgent matter. Cardman and Fincke were also set to take photos of outside hardware and collect microorganism samples.

Officials remained tight-lipped throughout the press conference on any details regarding the astronaut in question, even declining to mention whether or not he or she was in favor of returning home early.

NASA is expected to provide more details of Crew-11’s deorbit procedures. Once they leave, NASA Astronaut Chris Williams will remain the only American on the space station. He is joined by Roscosmos cosmonauts Sergey Kud-Sverchkov and Sergei Mikaev, with whom he flew to space aboard the Russian Soyuz. Isaacman cited this situation as the reason why the Americans and Russians continue their ride-sharing partnership to the ISS.

Up next is NASA’s Crew-12 mission, which will feature NASA astronauts Jessica Meir and Jack Hathaway as the mission’s commander and pilot, respectively, European Space Agency (ESA) astronaut Sophie Adenot, and Roscosmos cosmonaut Andrey Fedyaev.

They were due to fly a SpaceX Crew Dragon capsule from the Kennedy Space Center in Florida no earlier than Feb. 15. However, Isaacman said NASA was looking at possibly launching them sooner to compensate for the lack of on-orbit personnel. He said that any advance in Crew-12’s launch would have no effect on Artemis II’s first launch window for its moon mission beginning Feb. 6.