Why does NASA use the position title "Pilot"' for crew members who are not in charge of piloting the spacecraft? For example famously Buzz Aldrin's position was Lunar Module Pilot but his spacecraft was piloted by Neil Armstrong as the Commander of the Lunar Module. This terminology frequently causes confusion in the public since people commonly and (somewhat understandably) assume the dictionary definition of a pilot as "a person who operates the flying controls of an aircraft".
During his tenures as Chief of the Astronaut Office and Director of Flight Crew Operations, Deke Slayton had the greatest influence over the titles of astronauts.
NASA's predecessor agency -- the National Advisory Committee for Aeronautics (NACA) -- was more involved in aircraft than spacecraft. Their research resulted in the Bell X-1 supersonic aircraft and the North American X-15 rocket plane. Both aircraft were flown by test pilots, as they required great skill and experience to properly control.
One of the groups at NACA with the most experience in spaceflight was the Pilotless Aircraft Division:
NACA was not an inevitable choice. A small applied-research agency oriented mainly to work on aircraft, it had no experience in developing hardware or managing big programs.... But it was already at least on the fringes of space with the X-15 research craft, and its Pilotless Aircraft Division and the Lewis Flight Laboratory were doing significant research on space (the latter campaigned actively for space activities).
So when NACA got absorbed into NASA, many of the Mercury capsule engineers (including Maxime Faget) ironically came from the Pilotless Aircraft Division:
The Pilotless Aircraft Research Division (PARD) at the Langley Research Center was renamed NASA's Space Task Group, and in 1962 relocated as the Manned Spacecraft Center in Houston. These engineers were charged with the responsibility of Project Mercury.
Their attitude was that a "piloted" spacecraft merely had a human occupant, and there was no need for such an occupant to control the vital systems of the spacecraft. This did not go over well with the Mercury astronauts, and Slayton was one of the most vocal:
Astronaut Deke Slayton spoke to the issue before the Society of Experimental Pilots, when he observed that "Objections to the pilot range from the engineer, who semiseriously notes that all problems of Mercury would be tremendously simplified if we didn't have to worry about the bloody astronaut, to the military man who wonders whether a college-trained chimpanzee or the village idiot might not do as well in space as an experienced test pilot...." Slayton argued that the human role was vital: the astronaut should be "not only a pilot, but a highly trained experimental test pilot is desirable ... as in any scientific endeavor the individual who can collect maximum valid data in minimum time under adverse circumstances is highly desirable."
Eventually NASA relented to the wishes of the astronauts. They were given some control over the capsule, and gained the title pilot.
Slayton was grounded because of a heart condition, and became Chief of the Astronaut Office, assigning astronauts to missions. It also gave him the power to assign astronaut titles.
Gemini was the first multi-crew NASA spacecraft. Although the more senior of the crew flew the spacecraft, there was always the possibility that he could become compromised; thus, the other crewmember also needed training and experience flying. So they both needed to be "pilots". But how do you distinguish between the two positions?
Having served in the U.S. Air Force, Slayton used the Air Force terminology to distinguish between the two astronauts:
- The astronaut more experienced in space would be called the command pilot.
- The other astronaut was simply called pilot.
The earliest plans for Apollo assumed that all three astronauts would take one spacecraft to the moon. This was called the "Block I" design. The first crew roles resembled traditional aircraft duties:
- Control of the spacecraft in manual or automatic mode in all phases of the mission
- Selection, implementation, and monitoring of the navigation and guidance modes
- Monitoring and control of key areas of all systems during time-critical periods
- Station in the left or center couch
- Second in command of the spacecraft
- Support of the pilot as alternative pilot or navigator
- Monitoring of certain key parameters of the spacecraft and propulsion systems during critical mission phases
- Station in the left or center couch
- Responsibility for all systems and their operation
- Primary monitor of propulsion systems during critical mission phases
- Responsibility for systems placed on board primarily for evaluation for later Apollo spacecraft
- Station in the right-hand couch
The Apollo Spacecraft: A Chronology, 1961 November 27
However, NASA eventually chose to have a separate lunar lander. This led to a new "Block II" design with a lunar module, and the above titles were scrapped, as they no longer made sense. For the next few years, Apollo documents refer to "astronauts" or "crew". They also use the terms "pilot", "CSM pilot", "LEM pilot", and (later) "CM pilot" and "LM pilot" to refer to whichever crewmember is controlling a spacecraft at that moment. But they didn't yet use those as astronaut titles.
Some Block I command modules had already been built. They were satisfactory for most of the unmanned Apollo flights and for the first manned flight, as none of those missions needed a lunar module. For the (doomed) first manned flight, Slayton decided to go back to Air Force terminology:
Apollo-Saturn 204 was to be the first manned Apollo mission [...] Crewmen for the flight would be Virgil I. Grissom, command pilot; Edward H. White II, senior pilot; and Roger B. Chaffee, pilot.
The Apollo Spacecraft: A Chronology, 1966 Oct 19
However, the next month he announced that all following flights would use newer titles:
MSC's Director of Flight Crew Operations Donald K. Slayton said that the Block I flight crew nomenclature was suitable for the AS-204 mission, but that a more descriptive designation was desirable for Block II flights. Block I crewmen had been called command pilot, senior pilot, and pilot. Slayton proposed that for the Block II missions the following designations and positions be used:
- commander, left seat at launch with center seat optional for the remainder of the CSM mission, and left seat in the LM;
- CSM pilot, center seat at launch with left seat optional for remainder of mission; and
- LM pilot in the right seat of both the CSM and LM.
ibid, 1966 Nov 29
This was formalized the next year:
Designations and abbreviations for flight crewmen on all manned Apollo missions were selected:
- Commander -- CDR
- Command module pilot -- CMP
- Lunar module pilot -- LMP
This terminology was to be used throughout the Apollo spacecraft program and compliance was required to minimize confusion.
The Apollo Spacecraft: A Chronology, 1967 June 14
The CDR did most of the flying. However, the CMP did the rendezvous/dockings, and both CMP and LMP were trained to fly their spacecrafts in a contingency situation.
Four scientists trained as astronauts, and one (Harrison Schmitt) actually went to the moon. However, they all received flight training, and retained the title "lunar module pilot" as noted above to minimize confusion.
The Space Shuttle had two pilot seats. It retained similar titles to those of Apollo: commander and pilot.
The other roles on the shuttle did not involve flying and did not have "pilot" in their name: mission specialist and payload specialist.