Voyager 2 launched in 1977 funded to visit only two planets

NASA launched Voyager 2 on August 20, 1977, aboard a Titan IIIE-Centaur from Cape Canaveral, Florida, 16 days before its twin, and it remains the only spacecraft to visit Uranus and Neptune. Yet when it left Earth it was funded to fly past only Jupiter and Saturn.

A Grand Tour on a budget

The famous “Grand Tour” had already been cancelled. NASA’s original plan would have sent four complex spacecraft to the five outer planets, but it was scrapped in January 1972 over projected costs of about $1 billion. Two simpler probes, built on Mariner designs, replaced it. In 1974, planners suggested that if the first Voyager succeeded, the second could be redirected to Uranus and Neptune. Of more than 10,000 trajectories studied, the one picked for Voyager 2 kept that door open.

The opening came from a lineup of the giant planets that lets one craft swing from world to world by gravity assist, cutting the flight time to Neptune from about 30 years to 12. NASA’s fact sheet says the arrangement recurs about every 175 years; the Smithsonian says 176. Both are rounded figures for the same rare alignment.

Permission came one planet at a time. After the 1981 Saturn flyby showed Voyager 2 could probably reach Uranus with every instrument working, NASA funded that leg, and later the Neptune one. It passed Uranus on January 24, 1986, discovering 10 new moons, then skimmed about 2,980 miles above Neptune’s cloud tops on August 25, 1989, the closest of its four flybys.

In 2018 it became the second spacecraft to enter interstellar space. Slower than Voyager 1, it is on course to reach one light-day from Earth in November 2035.