How did NASA decide which astronaut got to step on the Moon first?

 It was part luck, part merit, says Teasel Muir-Harmony, curator of the Apollo collection at the National Air and Space Museum. During the Apollo missions, different groups of astronauts rotated through the schedule, and backup crews became primary crews three missions later. Neil Armstrong was originally scheduled for a later mission, but delays in developing the lunar module shifted him to Apollo 11. Based on Armstrong’s performance in the earlier Gemini missions, NASA made him the commander of Apollo 11, positioning him to step on the Moon first and take that giant leap for mankind.