"For the next several years, while
others in NASA perfected the spacecraft systems and rendezvous
techniques thru the Mercury and Gemini programs, the Marshall
team expanded its facilities and concentrated on the development
of the Saturn launch vehicles for the three-man Apollo Program.
The Marshall effort established the basic design for clustered
engines and clustered propellant tanks as well as the instrument
unit, which controlled the functions required to keep the
vehicle operating properly and on course."