Sick astronaut returns to Earth in NASA's first medical evacuation.

A sick astronaut and three crewmates left the International Space Station early and splashed down near San Diego; officials say the astronaut is stable and was taken to a hospital for further checks.

A sick astronaut returned to Earth with three crewmates after NASA moved the crew's return forward following an in-orbit medical issue. SpaceX guided the capsule to a nighttime splashdown in the Pacific near San Diego less than 11 hours after the crew left the International Space Station. NASA said the medical issue began on Jan. 7 and prompted cancellation of a planned spacewalk. Officials described this as the agency's first-ever medical evacuation that cut a NASA flight short. Key facts: - The returning crew included Zena Cardman and Mike Fincke from NASA, Kimiya Yui from Japan, and Oleg Platonov from Russia; officials would not identify the astronaut who developed the health problem, citing medical privacy. - The capsule splashed down near San Diego and the astronauts were taken to a San Diego-area hospital overnight; NASA Administrator Jared Isaacman said the affected astronaut is "fine" and undergoing medical checks. - NASA said the entry and splashdown required no special changes and the recovery ship had its usual medical team on board. - NASA and SpaceX said they will try to move up the launch of a replacement four-person crew currently targeted for mid-February, and the station will be unable to perform spacewalks until the reinforcements arrive. Summary: The early return ended the mission sooner than planned and temporarily reduced the station's ability to conduct spacewalks. The astronaut in question will receive in-depth medical evaluations before flying back to Houston with the rest of the crew, and NASA is working to schedule a replacement crew launch in mid-February. It is too soon to know whether this situation will affect the timing of the agency's upcoming moon mission.