In September 1962, Young was selected to join
NASA Astronaut Group 2. The Gemini 3 backup commander was
Wally Schirra, with Stafford as the backup pilot. The primary mission of Gemini 3 was to test the ability of the spacecraft to perform
orbital maneuvers throughout the flight. Biological experiments were assigned to test the effects of
radiation on
human blood and
microgravity on
cell division, and an experiment to test
reentry communications was created. Both crews initially trained in simulators at the
McDonnell Aircraft Corporation facilities in
St. Louis, Missouri, and moved their training when the simulators were set up at the
Manned Spacecraft Center and
Kennedy Space Center (KSC) in October 1964. Both primary and backup crews participated in Gemini 3's capsule system tests before it left the McDonnell facility. Young advocated for a longer mission than the planned three orbits, but his suggestion was rejected. Twenty minutes into flight, Young recognized multiple anomalous system readings and determined that there might be issues with the instrument power supply. He switched from the primary power supply to the backup, which solved the issue. Young successfully completed the radiation experiment on human blood, but Grissom accidentally broke a handle and was unable to complete his assigned experiment on cell division. Gemini 3 successfully conducted its orbital maneuver tests that allowed it to circularize its orbit, change its
orbital plane, and lower its
perigee to . On the third orbit, Young fired the
retrorockets to begin re-entry. The
lift the capsule experienced during reentry was less than predicted, and Gemini 3 landed short of its target area. After the parachutes deployed, the crew shifted the capsule to its landing orientation, which caused both of them to be thrown forward into the windshield and damaged the faceplates on their helmets. The crew remained inside the capsule for 30 minutes as they waited for a helicopter to retrieve them, and they and the capsule were successfully recovered aboard . On May 18, 1969, Apollo 10 launched at 11:49 a.m. After the
trans-lunar injection (TLI) burn, Young successfully docked the command module with the lunar module. On March 3, 1971, Young was assigned as the commander of
Apollo 16, along with Duke and Mattingly. The mission's science objective was to study material from the
lunar highlands, as they were believed to contain volcanic material older than the
lunar mare that had been the sites of the previous Apollo landings. To prepare for their EVAs, Young and Duke participated in field exercises in geological research. They conducted field work at the
Mono craters in California to learn how to identify
lava domes and
tuff and the
Sudbury Basin to study
breccia. Apollo 16 successfully launched at 12:54 p.m. on April 16, 1972. After the spacecraft reached
Earth orbit, several problems developed with the
S-IVB attitude control system, but Apollo 16 was still able to perform its trans-lunar injection burn. Mattingly docked the command module with the lunar module, and the crew decided to perform an early checkout of the lunar module over concerns that it had been damaged but found no issues. Apollo 16 flew behind the Moon 74 hours into the mission and entered into a elliptical orbit. The next day, Duke and Young entered the lunar module and undocked, but Mattingly soon reported an issue with the thrust vector controls on the
service propulsion system, which would have prevented the command module from maneuvering in case the lunar module was unable to complete its rendezvous. After a delay, Mission Control approved the landing, and Young and Duke began their descent 5 hours and 42 minutes later than scheduled. As the lunar module descended, its projected landing location was north and west of its target location. Young took corrective action to adjust their landing location, and the lunar module landed north and west of its target location. The two astronauts set up the
lunar rover, and deployed the
Apollo Lunar Surface Experiments Package (ALSEP). Young tripped over the cables to the
heat flow sensors, which irreparably broke the sensors' communication link with Earth. and began a traverse to
Flag crater, which was west of the landing site. They set up a geology station at the crater, and collected
Big Muley, a breccia that was the largest lunar rock collected during the Apollo program. Young and Duke traveled back towards the lunar module, stopping at
Spook and Buster craters along the way. Before ending the EVA, they tested the maneuverability of the lunar rover. They finished the EVA after seven hours on the lunar surface. After they traveled to collect samples at the nearby Wreck crater, the rover's navigation system failed, forcing the two astronauts to manually navigate back to the lunar module. On April 24, the lunar module successfully ascended into lunar orbit and docked with the command module. After the mission, Young was assigned as the
Apollo 17 backup commander, along with Duke as the backup lunar module pilot and Stuart A. Roosa as the backup command module pilot. The backup crew was originally the
Apollo 15 crew, but were removed after NASA management learned of their
plan to sell the unauthorized postal covers they took to the lunar surface. Their backup crew,
Joe H. Engle and
Richard H. Truly, was the primary crew for
STS-2. The first stage of the launch flew higher than anticipated, and the
solid rocket boosters separated approximately higher than the original plan. The rest of the launch went as expected, and STS-1 successfully entered Earth orbit. The crew inspected their thermal tiles and determined that some had been lost during launch. Amid concerns that the underside of
Columbia might have also lost some thermal shielding, a
KH-11 KENNEN satellite was used to image the orbiter and it was determined that the orbiter could safely reenter the atmosphere. It carried the first
Spacelab module into orbit, and the crew had to conduct a shift-based schedule to maximize on-orbit research in astronomy, atmospheric and space physics, and
life sciences. Young tested a new portable onboard computer, and attempted to photograph Soviet airfields as
Columbia orbited overhead. Young had been scheduled to fly as the commander of
STS-61-J to deploy the
Hubble Space Telescope, but the mission was canceled as a result of the
Challenger disaster. In May 1987, Young was replaced as the chief of the Astronaut Office by
Daniel C. Brandenstein and was reassigned as Special Assistant to Johnson Space Center Director
Aaron Cohen for Engineering, Operations and Safety. Young believed that his reassignment was the result of his public criticism of NASA management. In November 2011, Young and Crippen met with the crew of
STS-135, the last Space Shuttle mission. In 2012, Young and
James R. Hansen co-authored his autobiography,
Forever Young. == Personal life ==