Jet Propulsion Laboratory (U.S.). Voyager Project.

Project Voyager, originally called "Mariner Jupiter/Saturn '77" (MJS '77) was approved by NASA and the U.S. Congress in June 1972. It was a dual spacecraft long-range mission that conducted a "Grand Tour" of the Outer Planets, visiting Jupiter, Saturn, Uranus, Neptune, as well as various planetary satellites, and continued beyond to the outer reaches of the Solar System.

The name of the project was changed from "Mariner Jupiter/Saturn" to "Voyager" in early March 1977. A March 16, 1977 memo, distributed to personnel, officially notified them that the project was to be known only as Voyager. Three spacecraft were fabricated. VGR77-1 was the Proof-Test Model, and was not launched. VGR77-2 was designated as Flight 1 (Voyager 2) and VGR77-3 was designated as Flight 2 (Voyager 1). The proof-test model, VGR77-1 is on display in the von Kármán Auditorium at JPL.

The Proof-Test Model was identified as having possible later use in two instances. The first use would be in case of a failure of one of the Voyager spacecraft. In that case, the remaining spacecraft would not be deflected to Uranus because of what was deemed the more important Titan encounter and occultation.

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 Jet Propulsion Laboratory'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.

Voyager 2 was launched on August 20, 1977, and Voyager 1 was launched on September 5, 1977 to take advantage of a favorable alignment of the Jupiter, Saturn, Neptune and Uranus. Both launches took place from the Cape Canaveral Air Force Station in Florida.

Using gravity assist flybys and well-planned trajectories, the spacecraft encountered all four planets without the need for an impractical amount of propellant. The flyby of each planet both accelerated the spacecraft and bowed its flight path. Without these gravity assists, the flight time to Neptune would have been 30 years.

From the description of Mariner Jupiter / Saturn 1977 Pre-Assembly Requirements Collection, 1969-1977. (Jet Propulsion Laboratory Library and Archives). WorldCat record id: 733100835