John Glenn was trained to pilot a spacecraft.
An astronaut or cosmonaut is a person trained by a human spaceflight program to command , pilot , or serve as a crew member of a spacecraft . John Herschel Glenn Jr. ( July 18 , 1921 -- December 8 , 2016 ) was a United States Marine Corps aviator , engineer , astronaut , and United States Senator from Ohio . Mercury-Atlas 6 ( MA-6 ) was the third human spaceflight for the U.S. and part of Project Mercury .