exploring the heliosheath on their way to interstellar space.
Voyager’s primary mission was to study the giant outer planets. It began in 1965 when the Jet Propulsion Laboratory was looking for times when the outer planets were aligned so that swinging by one could be used as a gravitational slingshot to speed a spacecraft onto the next. Although there are frequent opportunities for gravity assists involving two or three planets, once every 175 years Jupiter, Saturn, Uranus, and Neptune are aligned so that a spacecraft can swing by all four, picking up speed at each flyby. This Grand Tour trajectory reduced the flight time to Neptune from 30 years to only 12.
Fortunately, an opportunity for launching on a Grand Tour trajectory came in the late 1970s. However,