Editing List of Apollo astronauts (section)

== Prime crew members ==
NASA's Director of Flight Crew Operations during the [[Project Gemini|Gemini]] and Apollo programs was [[Deke Slayton|Donald K. "Deke" Slayton]], one of the original [[Mercury Seven]] astronauts, who was medically grounded in September 1962 due to a minor cardiac [[arrhythmia]] – paroxysmal atrial fibrillation. Slayton was responsible for making all Gemini and Apollo crew assignments. In March 1972, Slayton was restored to flight status, and flew on the 1975 [[Apollo–Soyuz Test Project]] mission.

The prime crew members selected for actual missions are here grouped by their NASA astronaut selection groups, and within each group in the order selected for flight. Two versions of the [[Apollo Command/Service Module]] (CSM) spacecraft were developed: Block I, intended for preliminary low Earth orbit testing; and Block II, redesigned for the lunar landing. The Block I crew position titles were Command Pilot, Senior Pilot (second seat), and Pilot (third seat).  The corresponding Block II titles were: Commander, Command Module Pilot, and Lunar Module Pilot. The second seat pilot was given secondary responsibility for [[celestial navigation]] to keep the CSM's guidance computer accurately calibrated with the spacecraft's true position, and the third seat pilot served as a flight engineer, monitoring the health of the spacecraft systems.