Launched 1977
Decommissioned 1990

In 1965 Gary Flandro, an engineer at the Jet Propulsion Laboratory of the National Aeronautics and Space Administration (NASA), discovered a curious planetary alignment through his calculations: the outer planets of the solar system in the late 1970s would be in a rare configuration. The outer planets are Jupiter, Saturn, Uranus, and Neptune—the fifth, sixth, seventh, and eighth planets from the Sun—known collectively as the Jovian planets. The configuration, which happens once every 175 years, would make possible an Earth-launched spacecraft that could fly by the four largest planets. Acting on Flandro’s discovery, NASA scientists planned a mission called “Grand Tour.”

Spacecraft built

At first scientists proposed construction of four spacecraft, but federal budgetary problems, caused by the cost of building the space shuttle, made only two vehicles possible. Construction of the spacecraft, which were named Voyagers 1 and...