Officials said the health problem was unrelated to spacewalk preparations or other station operations, but offered no other details.

Two Americans and astronauts from Japan and Russia landed in a SpaceX capsule in the Pacific Ocean after a medical issue prompted NASA to move up their return to Earth.

Wednesday’s return cut the missions of NASA astronauts Zena Cardman and Mike Fincke, Japanese astronaut Kimiya Yui, and Russian cosmonaut Oleg Platonov short by over a month.