on the Moon, at age 47 years and 79 days. Charlie Duke was the youngest, at age 36 years and 201 days.

Jim Lovell and Fred Haise were scheduled to walk on the Moon during the Apollo 13 mission, but the lunar landing was aborted following a major malfunction en route to the Moon. Haise was again scheduled to walk on the Moon as commander of Apollo 19, but Apollo 18 and Apollo 19 were canceled on September 2, 1970.

Joe Engle had trained on the backup crew for Apollo 14 to explore the Moon with Cernan, but Engle was replaced by Schmitt on the primary crew for Apollo 17. Schmitt had previously been crewed with Apollo 12command module pilot Dick Gordon in anticipation of Apollo 18, but Schmitt replacedEngle on Apollo 17 after the cancellation of Apollo 18 and Apollo 19, leaving Gordon as the last Apollo astronaut to train extensively for lunar exploration without ever landing on the Moon.

Besides the twelve people who have walked on the Moon, twelve more have flown to within 0.001 lunar distance of its surface. During each of the six missions with successful lunar landings, one astronaut remained in lunar orbit while the other two landed. In addition, the three-person crews of Apollo 8 and Apollo 10 also entered lunar orbit, and the crew of Apollo 13 looped around the Moon on a free-return trajectory.

All nine manned missions to the Moon took place as part of the Apollo program over a period of just under four years, from 21 December