Four crewmembers departed the International Space Station on Wednesday after a medical issue prompted their mission to be cut a month short, marking a first for the orbiting laboratory.

NASA video showed American astronauts Mike Fincke and Zena Cardman, Russian cosmonaut Oleg Platonov and Japanese astronaut Kimiya Yui undocking from the station at 10:20 p.m. GMT after spending about five months in space.

The U.S. space agency has declined to identify which crewmember experienced the health issue or provide details, but emphasized the return was not an emergency.

The affected astronaut “was and continues to be in stable condition,” NASA spokesperson Rob Navias said Wednesday.

The SpaceX Dragon capsule carrying the four crewmembers was scheduled to splash down off the California coast early Thursday, around 8:40 a.m. GMT.

“First and foremost, we are all OK. Everyone on board is stable, safe, and well cared for,” Fincke, the pilot of SpaceX Crew-11, said in a recent social media post.

“This was a deliberate decision to allow the right medical evaluations to happen on the ground, where the full range of diagnostic capability exists,” he said. “It’s the right call, even if it’s a bit bittersweet.”

Why the mission was shortened

The Crew-11 team arrived at the station in early August and was expected to remain until mid-February, when the next crew rotation was scheduled. NASA Chief Health and Medical Officer James Polk said a “lingering risk” and uncertainty over the diagnosis led officials to opt for an early return.

American astronaut Chris Williams and Russian cosmonauts Sergey Kud-Sverchkov and Sergei Mikaev, who arrived aboard a Russian Soyuz spacecraft in November, will remain on the space station.

NASA and Russia’s Roscosmos space agency jointly operate the ISS, and the two countries continue to exchange seats on missions despite broader political tensions.

Ready for the unexpected

Continuously inhabited since 2000, the International Space Station is a symbol of multinational cooperation involving the United States, Russia, Europe, and Japan.

Orbiting about 400 kilometers, or 248 miles, above Earth, the station serves as a research platform for experiments supporting future deep-space missions, including planned human journeys back to the Moon and eventually to Mars.

The four returning astronauts were trained to respond to unexpected medical situations, said Amit Kshatriya, a senior NASA official, who praised the crew’s handling of the circumstances.

The ISS is scheduled to be retired after 2030, when its orbit will be gradually lowered until it breaks apart in Earth’s atmosphere over a remote stretch of the Pacific Ocean known as Point Nemo.