John Watts Young (born September 24, 1930) is a former NASA astronaut who walked on the Moon on April 21, 1972 during the Apollo 16 mission.
Young enjoyed one of the longest and busiest careers of any astronaut in the American space program. He was the first person to fly into space six times, twice journeyed to the Moon, and as of 2007, is the only person to have piloted four different classes of spacecraft: Gemini spacecraft, Apollo Command/Service Module, Apollo Lunar Module, and Space Shuttle

Early life and Navy career

NASA career
Joining NASA in 1962, Young was the first of Astronaut Group 2 to fly in space. (He replaced Thomas Stafford as pilot of Gemini 3 when Alan Shepard, the original commander, was grounded.) Making the first manned flight of the Gemini spacecraft with Virgil Grissom, Young scored another space "first" by smuggling a corned beef sandwich onto the spacecraft - a feat for which he was reprimanded.
Young then trained as backup pilot for Gemini 6, but after the sandwich episode, for a time it seemed that NASA did not know what to do with Young. Other Group 2 astronauts with flight experience were quickly moved to Apollo, while other astronauts such as Scott Carpenter and Gordon Cooper had been sidelined for lesser infractions. The deaths of Charles Bassett and Elliott See the prime crew of Gemini 9 created a hole in the astronaut corps so that Young was confirmed as Commander of Gemini 10. The mission performed the first dual docking to two Agena Target Vehicles, and his pilot, Michael Collins, performed two spacewalks.

Project Gemini
Young was assigned to the backup crew on Apollo 7 and later made the second manned flight to the Moon on Apollo 10 with Thomas Stafford and Eugene Cernan. While Stafford and Cernan flew the lunar module in lunar orbit for the first time, Young flew the command module solo - the first person to do so in lunar orbit. Young was backup commander of Apollo 13, the troubled mission in which the moon landing was aborted because of an explosion on the service module. Young had a central role in rescuing the Apollo 13 crew by leading the team that devised the makeshift carbon dioxide filters that kept the astronauts' air supply breathable.
By rotation, Young became commander of Apollo 16. Young became an enthusiastic student of geology while preparing for the moon mission. Apollo 16's lunar landing was almost aborted at the last moment when a malfunction was detected on the command module. On the surface, Young trod the Descartes Highlands with Charles Duke (making Young the ninth man to walk upon the surface of the moon), while Ken Mattingly flew the command module in lunar orbit. Young set a speed record with the lunar rover but was troubled by the effects of potassium in the orange juice they drank during the moonwalks. He carried with him the badge and flag of the Sigma Chi Fraternity; these are on display at Sigma Chi's headquarters in Evanston, Illinois.
His final assignment in Apollo was as the backup commander on Apollo 17. This almost resulted in his second moon landing when Gene Cernan injured his knee playing softball a few months before the flight. The injury, had it been any more severe, would have resulted in Cernan being medically dropped from the flight and John Young commanding the last two moon landings of Apollo (as a note, fellow Group 2 astronaut Pete Conrad would have done the same if he would have commanded the cancelled Apollo 20 mission, but as he already flew as commander of Apollo 12, he would have been transferred to either Skylab or the Space Shuttle and Apollo 14 CMP Stuart Roosa would have flown on Apollo 20 as commander).

Project Apollo
After the Apollo program ended, Young stayed on as an astronaut and flew two missions of the Space Shuttle, including commanding the Shuttle's maiden flight, STS-1, and the flight STS-9 which used Spacelab for the first time. Young had been in line to make a record seventh flight to deploy the Hubble Space Telescope, but the Challenger Disaster thwarted NASA's schedule.
Young was openly critical of the administration following the disaster, and in April 1987 was taken out of the Astronaut Office and made special assistant of engineering, operations and safety to the center director Aaron Cohen. It was denied that his criticism of NASA triggered the move.

Space Shuttle
Young worked for NASA for 42 years and announced his retirement on December 7, 2004. He retired on December 31, 2004 at the age of 74.
While Young may have been overshadowed by other pioneering astronauts, his career experience is massive. As a member of the second astronaut intake, he contributed to all of the pioneering NASA projects. As the only commander of a Gemini, Apollo and Shuttle mission, John Young holds a unique place in the history of manned space exploration.
John still attends the Monday Morning Meeting in the Astronaut Office at Johnson Space Center.