In August 1977 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 or MJS'77. 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 1975 JPL artist's rendering of Voyager after encountering Jupiter and, after a gravity assist, approaching Saturn.
NASA/JPL Archives
<a rel="nofollow" class="external free" href="https://pub-lib.jpl.nasa.gov/docushare/dsweb/Services/Document-950">https://pub-lib.jpl.nasa.gov/docushare/dsweb/Services/Document-950</a>