NASA officials said Thursday they have decided to bring home four of the seven crew members on the International Space Station after one of them experienced a “medical situation” earlier this week.

The space agency has said little about the incident, and officials have not identified which crew member suffered the medical issue. James “JD” Polk, NASA’s chief health and medical officer, told reporters Thursday the crew member is “absolutely stable” but that the agency is “erring on the side of caution” with the decision to bring to return the astronaut to Earth.

The ailing astronaut is part of the Crew-11 mission, which launched to the station August 1 and was slated to come back to Earth around February 20. Instead, the Crew-11 astronauts will depart the International Space Station (ISS) in the coming days and head for reentry and a parachute-assisted splashdown in the Pacific Ocean off the coast of California.

“After discussions with our chief health and medical officer, Dr. JD Polk, and leadership across the agency, I’ve come to the decision that it’s in the best interests of our astronauts to return Crew-11 ahead of their planned departure,” NASA Administrator Jared Isaacman said Thursday.

The Crew-11 mission is led by commander Zena Cardman, 38, who is wrapping up her first mission to space. Second in command is pilot Mike Fincke, a 58-year-old astronaut on his fourth spaceflight. Japanese astronaut Kimiya Yui, 55, and Russian cosmonaut Oleg Platonov, 39, round out the crew.

Isaacman said NASA will release more information about the schedule for Crew-11’s undocking and reentry within the next 48 hours. The crew will home home aboard the same SpaceX Crew Dragon spacecraft they launched in more than five months ago. The entire crew must return to Earth together because they rely on the same Dragon spacecraft as a lifeboat.

“For over 60 years, NASA has set the standard for safety and security in crewed spaceflight,” Isaacman said. “In these endeavors, including the 25 years of continuous human presence onboard the International Space Station, the health and well-being of our astronauts is always and will be our highest priority.”

Lingering risk

Polk, a physician who has served as NASA’s chief medical officer since 2016, said the agency is not ready to release details about the medical issue, citing privacy concerns. “I’m not going to speak about any particular astronaut or any particular specific diagnosis,” Polk said. “I’d ask that we still respect the privacy of the astronaut.”