How many apollo 11 astronauts walked on the moon?

Apollo 11 flew with three astronauts, but the mission architecture allowed only two of them to land. The lunar module Eagle carried Neil Armstrong and Buzz Aldrin down to the Sea of Tranquility, while Michael Collins stayed in orbit aboard the command and service module Columbia. That split was not a matter of seniority or luck: the lunar module was a two-person spacecraft, with standing positions for a commander and a lunar module pilot and no capacity for a third.

Armstrong stepped out first and Aldrin followed roughly twenty minutes later. Together they spent about two and a half hours on the surface, planting the flag, deploying a solar wind collector, a seismometer and a laser retroreflector, taking photographs and collecting some twenty-one kilograms of rock and soil for return to Earth.

The command module pilot's job was the mission's insurance policy. Columbia carried the only engine capable of leaving lunar orbit and the only heat shield able to survive re-entry. Collins circled the Moon roughly every two hours, losing radio contact with Earth on every far-side pass, and carried a book of contingency procedures covering the rendezvous cases in which he would have had to go down to meet a stranded Eagle, and the case in which he would have come home alone.

The pattern held for every Apollo landing mission: two astronauts down, one in orbit. Across the six successful landings, twelve men walked on the Moon and six more orbited without touching it.