On August 20th, on two separate years, two major probes in NASA’s unmanned planetary exploration mission were launched to the final frontier.
On August 20th, 1975, the Viking 1 probe launched aboard a Titan-Centaur rocket to begin a nearly-year-long journey to the Red Planet, Mars. Once there, a lander fell to the surface while a separate craft stayed in orbit. Together, they took pictures and data of the planet and its two moons. The Viking 1 lander stayed operational for over six Earth years.
Two years later, in 1977, the Voyager 2 spacecraft blasted off, also onboard a Titan rocket. This probe would make history—not only traveling to Jupiter and Saturn, but also becoming the first Earth spacecraft to travel to the outer planets of Uranus and Neptune. The mission of Voyager 2 to the planets took place over many years, and the probe is in fact, still operational after 35 years of service!
Ironically, one original proposal for what became the Viking Mars landers was called the Voyager program.