NASA has decided to bring the Crew-11 astronauts home a month earlier than originally planned due to a “medical concern” with one of them. This is the first time in its history that the space agency is cutting a mission short due to a medical issue, but it didn’t identify the crew member or divulge the exact situation and its severity. The agency is targeting a return date no earlier than January 14, with the exact schedule depending on the weather. If NASA’s original plan pushes through, the crew will splash down off the coast of California at approximately 3:40 AM on January 15.

The agency previously postponed an International Space Station (ISS) spacewalk scheduled for January 8, citing a medical concern with a crew member that appeared the day before. NASA’s chief health and medical officer, James “JD” Polk, said the affected astronaut is “absolutely stable” and that this isn’t a case of an emergency evacuation. The ISS has a “robust suite of medical hardware” onboard, he said, but not enough for a complete workup to determine a diagnosis. Without a proper diagnosis, NASA doesn’t know if the astronaut’s health could be negatively affected by the environment aboard the ISS. That is why the agency is erring on the side of caution.

Crew-11 left for the space station on August 1 and was supposed to come back to Earth on or around February 20. After they leave the station, only three people will remain: Two cosmonauts and one astronauts who’ll be in charge of all the experiments currently being conducted on the orbiting lab. The team’s replacement, Crew-12, was supposed to head to the ISS mid-February, but NASA is considering sending the astronauts to the station earlier than that.

Update, January 10, 2025, 5:15AM ET: This story has been updated to include Crew-11’s tentative return date.