An astronaut requiring medical attention has left the International Space Station (ISS) in what marks NASA’s inaugural medical evacuation, departing alongside three fellow astronauts. This group, representing the United States, Russia, and Japan, is set to make a splashdown in the Pacific Ocean near San Diego early Thursday morning, courtesy of SpaceX. This unexpected conclusion comes as their mission is cut short by more than a month.

“Although our departure wasn’t planned, it was heartening to see how our team came together like a family, providing support and care for one another,” remarked NASA astronaut Zena Cardman prior to the return journey.

NASA officials have chosen not to disclose the identity of the astronaut in need of medical attention, nor have they revealed the nature of the health issue.

Outgoing space station commander Mike Fincke took to social media earlier this week to assure the public that the astronaut in question is “stable, safe, and well cared for.” He emphasized that the decision to expedite their return was made to ensure comprehensive medical evaluations could be conducted on Earth, where a full spectrum of diagnostic resources is available.

The ailing astronaut is “stable, safe and well cared for,” outgoing space station commander Mike Fincke said earlier this week via social media. “This was a deliberate decision to allow the right medical evaluations to happen on the ground, where the full range of diagnostic capability exists.”

Launched in August, Cardman, Fincke, Japan’s Kimiya Yui and Russia’s Oleg Platonov should have remained on the space station until late February. But on Jan. 7, NASA abruptly canceled the next day’s spacewalk by Cardman and Fincke and later announced the crew’s early return. Officials said the health problem was unrelated to spacewalk preparations or other station operations, but offered no other details, citing medical privacy. They stressed it was not an emergency situation.

NASA said it would stick to the same entry and splashdown procedures at flight’s end, with the usual assortment of medical experts aboard the recovery ship in the Pacific. It was another middle-of-the-night crew return for SpaceX, coming less than 11 hours after undocking from the space station. NASA said it was not yet known how quickly all four would be flown from California to Houston, home to Johnson Space Center and the base for astronauts.

One U.S. and two Russian astronauts remain aboard the orbiting lab, just 1 1/2 months into an eight-month mission that began with a Soyuz rocket liftoff from Kazakhstan. NASA and SpaceX are working to move up the launch of a fresh four-person crew from Florida, currently targeted for mid-February.

Computer modeling predicted a medical evacuation from the space station every three years, but NASA hasn’t had one in its 65 years of human spaceflight. The Russians have not been as fortunate. In 1985, Soviet cosmonaut Vladimir Vasyutin came down with a serious infection or related illness aboard his country’s Salyut 7 space station, prompting an early return. A few other Soviet cosmonauts encountered less serious health issues that shortened their flights.

It was the first spaceflight for Cardman, a 38, biologist and polar explorer who missed out on spacewalking, as well as Platonov, 39, a former fighter pilot with the Russian Air Force who had to wait a few extra years to get to space because of an undisclosed health issue. Cardman should have launched last year but was bumped to make room on the way down for NASA’s Butch Wilmore and Suni Williams, who were stuck nearly a year at the space station because of Boeing’s capsule problems.

Fincke, 58, a retired Air Force colonel, and Yui, 55, a retired fighter pilot with the Japan Air Self-Defense Force, were repeat space fliers. Finke has spent 1 1/2 years in orbit over four missions and conducted nine spacewalks on previous flights, making him one of NASA’s top performers. Last week, Yui celebrated his 300th day in space over two station stays, sharing stunning views of Earth, including Japan’s Mount Fuji and breathtaking auroras.

“I want to burn it firmly into my eyes, and even more so, into my heart,” Yui said on the social platform X. “Soon, I too will become one of those small lights on the ground.”

NASA officials had said it was riskier to leave the astronaut in space without proper medical attention for another month than to temporarily reduce the size of the space station crew by more than half. Until SpaceX delivers another crew, NASA said it will have to stand down from any routine or even emergency spacewalks, a two-person job requiring backup help from crew inside the orbiting complex.

The medical evacuation was the first major decision by NASA’s new administrator Jared Isaacman. The billionaire founder of a payment processing company and two-time space flier assumed the agency’s top job in December.

“The health and the well-being of our astronauts is always and will be our highest priority,” Isaacman said in announcing the decision last week.