In the 1960s, mission designers recognized that
a unique opportunity was going to present itself more than a decade
later. Starting in the late 1970s, the giant gaseous outer planets
-- Jupiter, Saturn, Uranus and Neptune -- would line up in such
a way that single spacecraft might hop from one to the next, using
the gravity of each one to help propel it. Taking advantage
of this alignment -- which occurs only once every 175 years -- NASA
approves the Voyager Project, designed to send twin spacecraft to
the outer solar system.
Voyager 2 is the first of the twin spacecraft
to launch on what will become a space exploration odyssey that still
continues in 2002.