The Voyager Project was originally called Mariner Jupiter-Saturn '77 (MJS '77). Voyagers 1 and 2 were launched September 5, 1977 and August 20, 1977 to take advantage of a favorable alignment of the Jupiter, Saturn, Neptune and Uranus. Using gravity assist flybys and well-planned trajectories, the spacecraft encountered all four planets without the need for an impractical amount of propellant. The Voyager Project was the longest and most complex of any unmanned mission so far. The design philosophy adopted for MJS '77 was to design a spacecraft based on the existing Mariner and Viking designs, particularly JPL's experience with the 1975 Viking Orbiter.
Spacecraft design had to meet the environmental requirements from the time of initial assembly through ground test, transportation, launch, cruise and encounter operations, the latter two planned to take place over a twenty year period. The spacecraft was instrumented, to the extent practical, to obtain diagnostic telemetry in the event of failure, whether the failures were caused by system malfunction or by encountering unanticipated environments.
From the description of Mariner Jupiter / Saturn 1977 Functional Requirements Document 1974-1978. (Jet Propulsion Laboratory Library and Archives). WorldCat record id: 733100195
