Mission Control Center. Popularly known as “Houston” (as in “Houston, we have a problem”)
Massachussets Institute of Technology. In these memos, MIT is shorthand for the MIT Instrumentation Laboratory, created and led by avionics pioneer Charles Stark Draper. It is now known as the Charles Stark Draper Laboratory and became independent of MIT in 1973.
Mission Planning and Analysis Division (part of MSC).
Manned Spacecraft Center. Now known as Johnson Space Center.
Manned Space Flight Network (pronounced "misfin").