NASA astronauts prepare to leave the space station due to a medical issue

Four astronauts are set to leave the International Space Station on Wednesday evening, weeks earlier than planned, in a first-of-its-kind departure due to a medical issue.

NASA astronauts Zena Cardman and Mike Fincke, Japanese astronaut Kimiya Yui and Russian cosmonaut Oleg Platonov will return to Earth in the same SpaceX Dragon capsule that they flew to the space station. The group, known as Crew-11, is scheduled to undock at around 5:05 p.m. ET.

It will be the first time in the space station’s 25-year history that a mission is cut short because of a medical problem that arose in orbit. NASA officials have not provided details about the affected crew member or the nature of the medical issue, citing medical privacy concerns. The agency has, however, said the situation is stable and not considered an emergency evacuation.

“First and foremost, we are all OK,” Fincke wrote on LinkedIn over the weekend. “Everyone on board is stable, safe, and well cared for. This was a deliberate decision to allow the right medical evaluations to happen on the ground, where the full range of diagnostic capability exists. It’s the right call, even if it’s a bit bittersweet.”

If undocking occurs as planned, the Crew-11 astronauts are expected to splash down in the Pacific Ocean, off the coast of California, at approximately 3:41 a.m. ET on Thursday. The roughly 11-hour journey will include a deorbit burn to slow the spacecraft before it plunges through Earth’s atmosphere and lands with parachutes in the water.

Cardman, Fincke, Yui and Platonov arrived at the International Space Station in August and were slated to stay until late February. But NASA revealed last week that a crew member had experienced a medical incident while at the orbiting outpost, prompting the agency to call off a spacewalk in which Cardman and Fincke were to perform upgrades to the exterior of the station. Days later, agency officials announced their decision to bring the crew home about a month early as a precautionary measure.

“After discussions with 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 interest of our astronauts to return Crew-11 ahead of their planned departure,” NASA Administrator Jared Isaacman said Thursday.

The astronauts are scheduled to land back on Earth before the next space station crew arrives in orbit, though NASA flight engineer Chris Williams and two Russian cosmonauts will remain onboard. NASA officials said they are evaluating options to move up the next launch, a mission known as Crew-12, which is scheduled to lift off no earlier than Feb. 15. But Williams will likely be the only NASA astronaut overseeing U.S. science experiments and operations on the station for several weeks.

In a predeparture “change of command” ceremony Monday, Fincke passed his leadership of the space station to cosmonaut Sergey Kud-Sverchkov.

“Sergey, it’s a honor and a pleasure to be a commander, and I cannot imagine being happier than to hand over command to you,” Fincke said.

He called his crew’s unexpectedly early departure “interesting times,” but spoke fondly about his stay in orbit.

“We’re from all over the planet, and we’re working together,” Fincke said. “It’s a great symbol of what human beings can do.”

This article was originally published on NBCNews.com