In the 1970s NASA embarked on a mission it had never attempted before. Due to a fortunate alignment of planets, they were going to attempt to send robotic probes on a flyby mission to Jupiter, Saturn, Uranus, and Neptune, before being sent to deep space, out of the solar system.

Some of the mission planners figured if they were going to send a probe all that way, maybe they might as well add something extra to the payload.

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