655Number of days logged in space by Peggy Whitson - the most by an American astronaut, over a career spanning 15 years starting in 2002. Whitson, 58, retired from NASA on 15 Jun 2018. Last Modified: 07-Jul-2018 2:30 PM 191 Posted by Shoan Dhareshwar in People Tags Astronauts NASA 28W2018 Source Time Magazine