Four astronauts are hours away from strapping into a spacecraft and departing the International Space Station about a month early after one of them experienced a health issue. The impending departure would mark the first time in the station's 25-year history that a crew on the orbital outpost has cut a mission short in order to be medically evacuated.

NASA is launching an emergency return for an astronaut with a "serious medical condition" on the International Space Station.

The four returning astronauts are Zena Cardman and Michael Fincke of NASA; Kimiya Yui of JAXA, the Japanese space agency; and Oleg Platonov of Roscosmos, the Russian space agency.