A Nasa astronaut suffering an unknown medical problem has returned to Earth after the space agency launched a medical evacuation of the International Space Station.
The ailing astronaut – whose identity and health concern remains unknown – returned along with three other members of the mission, ending it more than a month early.
It is the first ever time that Nasa has been forced to bring a stay on the International Space Station to an early end for medical reasons.
Nasa administrator Jared Isaacman said that the affected crew member is “fine” and that the agency would share further updates on their status when it was appropriate to do so.
"It's so good to be home," said Nasa astronaut Zena Cardman, the capsule commander.
It was an unexpected finish to a mission that began in August and left the orbiting lab with only one American and two Russians on board.
Nasa and SpaceX said they would try to move up the launch of a fresh crew of four; lift-off is currently targeted for mid-February.
Nasa's Zena Cardman and Mike Fincke were joined on the return by Japan's Kimiya Yui and Russia's Oleg Platonov.
Officials have refused to identify the astronaut who had the health problem or to explain what happened, citing medical privacy.
While the astronaut was stable in orbit, Nasa wanted them back on Earth as soon as possible to receive proper care and diagnostic testing.
The entry and splashdown required no special changes or accommodations, officials said, and the recovery ship had its usual allotment of medical experts on board.
It was not immediately known when the astronauts would fly from California to their home base in Houston. Platonov's return to Moscow was also unclear.
Nasa stressed repeatedly over the past week that this was not an emergency. The astronaut fell sick or was injured on January 7, prompting Nasa to call off the next day's spacewalk by Cardman and Fincke, and ultimately resulting in the early return.
It was the first time Nasa cut short a spaceflight for medical reasons. The Russians had done so decades ago.
The space station has functioned with three astronauts before, sometimes even with just two.
Nasa said it will be unable to perform a spacewalk, even for an emergency, until the arrival of the next crew, which has two Americans, one French and one Russian astronaut.
Additional reporting by agencies
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