Instead of remaining at the International Space Station (ISS) for the full duration of their mission, the four crew members are coming home a month early due to a medical issue with one of the astronauts.

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.

The four-person crew from NASA's SpaceX Crew-11 mission to the International Space Station safely splashed down into the Pacific Ocean off the coast of San Diego County early Thursday morning.

The NASA International Space Station (ISS) crew that included a sick astronaut splashed down in the Pacific Ocean off the coast of San Diego, California, early on Thursday morning. "Welcome home, Crew-11!" NASA said in an update, adding that the SpaceX Dragon spacecraft hit the on water on schedule at 12:41 a.m. PT.

Depending on the timing, NASA could launch a fresh crew to the space station while four other astronauts are flying around the moon.

The SpaceX Dragon spacecraft is set to splash down off Southern California following a rare medical evacuation from orbit.

With Crew-11 set to depart shortly, command of the ISS will fall to Russian cosmonaut Sergey Kud-Sverchkov. He'll remain on the station with fellow Soyuz travellers, NASA astronaut Chris Williams and Roscosmos cosmonaut Sergei Mikaev. They will be the only crew aboard the station until SpaceX Crew-12 launches in February.