The U.S. space agency says American astronaut Scott Kelly, who recently completed a year-long mission on the International Space Station, will retire from NASA next month.
NASA says Kelly will continue to participate in the ongoing research related to his one-year mission, providing periodic medical samples and supporting other testing.
Kelly joined the astronaut corps in 1996 and flew in space four times.
He completed a 340-day mission aboard the International Space Station earlier this month, the longest continuous stay in space for an American astronaut.
After returning to Earth, the 52-year-old said he was feeling unwell, suffering from sore muscles and joints.