Page "Voyager program" Paragraph 9

Of the two space probes of the Voyager Program, Voyager 2 was launched first.

Its trajectory was designed to take advantage of an unusual alignment of the planets ( that occurs once every 177 years ) that allowed one space probe to fly by Jupiter, Saturn, Uranus, and Neptune, if everything went well.

Of course, in case of a serious malfunction, such as in all of the space probe's radio transmitters or receivers, then that would have been the end of the long mission ( to four planets ), since there was not a second space probe to fill the gap.

That was the gamble that NASA and the JPL were forced to take.