He was selected to be a member of NASA's second astronaut class in September 1962 after graduating from the Air Force Experimental Test Pilot School and serving as an experimental test pilot at Edwards Air Force Base, California.In June 1965 he flew to space for the first time as commander of the Gemini IV mission alongside fellow Air Force pilot Ed White, who became the first American to venture outside his spacecraft for a spacewalk during the historic 4-day spaceflight, NASA said.That was followed by his second spaceflight as the commander of Apollo 9 mission — which launched from NASA's Kennedy Space Center on March 3, 1969 — alongside command module pilot David Scott and lunar module pilot Russell Schweickart.Following the launch, Apollo 9 entered Earth's orbit and the crew performed an engineering test of the first crewed lunar module, nicknamed "Spider," and simulated the maneuvers that would be performed during actual lunar missions, NASA said.He flew 145 combat missions during the Korean War in F-80 and F-86 aircraft, logging more than 5,000 flying hours during the course of his piloting career, NASA said."