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Twenty years ago this month the first of two Voyager spacecraft was launched on a Grand Tour of four of the Outer Planets, the Gas Giants. Voyager 1 and 2 are still traveling, now leaving the Solar System, their planetary encounters completed.

NASA and JPL initially referred to this long term project as the Mariner-Jupiter-Saturn 1977 Project, MJS'77 for short. The two Voyagers were advanced versions of the Mariner-class spacecraft that JPL had flown successfully to Venus, Mars, and Mercury. Shown here is a composite of the 1976 abstract image used by NASA's Space Science Division to portray the new project and a 1975 JPL artist's rendering of Voyager after it had encountered Jupiter and, with a gravity assist, now approached Saturn.