Keenan was inspired by an event in 1936 involving birds flying blissfully into the sky, it drove him to pursue a career in the air and by extension space.
Keenan was commissioned into the USAF in 1951 and flew over 1000 hours over MiG Alley during the Korean War. He retired as a Colonel in 1974 after 23 years of service.
Keenan's first space flight was as Second Pilot aboard Gemini 10 in 1965.
NASA: Apollo (Lunar Fly-by)
Keenan's second spaceflight was as Command Module Pilot aboard Apollo 10 in 1969.
NASA: Apollo (Lunar Landing)
Keenan's third spaceflight was as Commander of Apollo 16 in 1972.
Keenan's fourth spaceflight was as Pilot on Skylab 5 in 1974.
NASA: Space Shuttle
Keenan flew twice aboard the space shuttles: Columbia and Challenger in 1981 and 1983, respectively. Making Keenan the first human to have flown into space six times at that point.
NASA: Criticism & Retirement
On January 28, 1986, the Space Shuttle Challenger was destroyed only about a minute into lift off, Keenan criticized NASA about the mistake and cited the AS-204 flash fire in 1967 as a major incident that also should've never taken place. Keenan parted ways with NASA later that year.
In 2001, Keenan was given the honorary rank of Brigadier General at a gala held in Florida, celebrating his accomplishments as well as his 72nd birthday. Between 1986 and 2001, Keenan wrote a lot of books both non-fiction and fiction about space exploration and space travel. Much of it retaining scientific accuracy. In 1992, a film was produced from one of his fictional novels...
In 2009, he was offered a spaceflight aboard Virgin Galactic, though humbled he declined.
In the early 2010s, the U.S. government constructed a new military base in a desolate dry lake bed near the then small town of Mojave, it is currently named John Keenan Air and Space Port and is located in Mojave, California.