August 20, 1977. NASA launched the phenomenal Voyager 2 space probe to the outer solar system on this date in 1977. They launched it some weeks before its twin craft, Voyager 1, which moved faster and eventually passed it to become the most distant human-made object from Earth, perhaps the first to leave the solar system. Voyager 2 has been operating for 35 years, 11 months, and 31 days as of August 20, 2013. Although its transmissions are faint, coming as they do from very far away, the craft still transmits data and receives messages via NASA’s Deep Space Network. Scientists believe it will be able to continue communications until around the year 2025.
NASA originally conceived of the Voyager mission in the 1960s as a planetary Grand Tour to study the outer planets. The fact that all four outer planets would be, temporarily, within one quadrant of the solar system around the decade of the 1980s inspired the idea. Inevitable funding difficulties intervened, and for a time it appeared the Grand Tour would never be realized. But Voyager 2’s launch took advantage not only of the particular configuration of planets – but also a new technique, called a gravity assist. This technique let the craft visit all four outer planets (Jupiter, Saturn, Uranus, Neptune), while requiring a minimal amount of propellant and a shorter transit duration between planets.
The plan hinged on whether Voyager 1 would be able to perform a successful flyby of Saturn’s large and intriguing moon Titan. It did, and Voyager 2 got the go-ahead to travel on toward Uranus and Neptune, ultimately realizing the vision of the planetary Grand Tour.
Voyager 2 remains the only craft from Earth to have visited Uranus and Neptune.
Bottom line: The phenomenal Voyager 2 spacecraft launched on August 20, 1977. It ultimately visited all four outer planets – Jupiter, Saturn, Uranus and Neptune – and remains the only craft from Earth to have done so.