Space exploration was always an expensive business, and throughout NASA's history, the agency has had to justify to Congress its need for every dollar it intended to spend. This problem has helped NASA to be more careful and more creative with the money they did receive, and scientists had to justify the equipment they wanted to include on each space probe. They had to justify the size and the power demand, too. If they wanted too much, the entire mission might be scrubbed, and all their work would have been for naught. This made planning and designs leaner and more efficient, as scientists and engineers were more careful with their recommendations.
In fact, the Pioneer program was the most diversified sequence of any of NASA's programs, and though they're now remembered for being among the first probes in history to reach the Outer Solar System, the elaborate planning changed goals several times over several years before resulting in historic successes. NASA had wanted to do a Grand Tour of the Solar System toward the end of the 1970s to take advantage of the scheduled alignment of planets, which meant the Pioneer missions were meant to be test runs prior to the main events (Voyager 1 and Voyager 2), and a great many things discovered by Pioneer 10 and Pioneer 11 were essential to the successful planning of the Voyager probes.
Voyager 1 and 2 have done far more than accomplish their original missions. In fact, they are now exploring interstellar space, far beyond the outer planets in the cold wasteland between the stars. Each spacecraft carries a copy of a golden record which contains an introduction to Earth, should some alien civilization happen to encounter either Voyager 1 or Voyager 2. In the first*Star Trek*movie, writers imagined just that, creating a story of a Voyager spacecraft being captured and adapted for its own uses.
