Four astronauts departing the International Space Station were all smiles during a change of command ceremony on Monday, despite a medical issue prompting an early return to Earth set for later this week.

Outgoing space station commander Mike Fincke, a member of the returning Crew 11, turned the station over to cosmonaut Sergey Kud-Sverchkov, saying the combined crew had developed deep friendships during their stay in space together for over five months.

"So one part of us are getting ready to leave this beautiful space station, and another part is getting ready to take over full command and get (it) ready for another Dragon crew to come," Fincke said.

"This is the International Space Station. We've had continuous human habitation for 25 years. It's a wonder of engineering, a wonder of science and a wonder of diplomacy. We're from all over the planet, and we're working together. It's a great symbol of what human beings can do."

Fincke thanked each crewmate for their performance during the shortened mission, telling Crew 11 commander Zena Cardman, making her first flight, "you are a rock star, superstar, awesome star."

"It's been a pleasure serving with you, watching you see Earth for the first time, riding on the rocket, and now it's coming to an end where we get to go home," he said. "It's bittersweet."

All four Crew 11 fliers looked healthy and in good spirits on a space-to-ground television broadcast of the change of command ceremony with no indication of which astronaut may have experienced the undisclosed medical issue that triggered Crew 11's early departure.

Fincke then presented Kud-Sverchkov with a symbolic key to the space station.

"Despite all the changes and all the difficulties, we're going to do our job on board ISS, performing scientific tasks, maintenance tasks, whatever happens. It's a big honor to be a commander of space station," Kud-Sverchkov said. "Thank you, Mike. And I want to (issue) the first command: let's make a group hug!"

And with that, all seven station crew members floated together to hug each other as suggested by Fincke before he handed over the key to the space station.

Fincke, Cardman, Japanese astronaut Kimiya Yui and cosmonaut Oleg Platonov were told to cut their mission short last week after an unidentified crew member reported a medical issue.

NASA said the early return was not an emergency. But by bringing the crew down right away, agency officials said, flight surgeons will be better able to diagnose the issue with facilities and expertise not available aboard the station.

Cardman, Fincke, Yui and Platonov plan to undock from the station around 5 p.m. Eastern Time Wednesday, about a month earlier than originally planned.

If all goes well, their SpaceX Crew Dragon capsule will splash down in the Pacific Ocean off the southern California coast at 3:40 a.m. Thursday.

Kud-Sverchkov and his two Soyuz MS-28 crewmates — Sergey Mikaev and NASA astronaut Chris Williams — will have the station to themselves until mid February when Crew 12 commander Jessica Meir, Jack Hathaway, European Space Agency astronaut Sophie Adenot and cosmonaut Andrey Fedyaev arrive.

Crew 11 originally planned to depart around Feb. 20, a few days after the arrival of Crew 12. But with Crew 11's early departure, NASA and SpaceX are working to move up the Crew 12 launch to shorten the gap.

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