Launched 16 days apart in 1977, the twin Voyager space probes are perhaps humankind's greatest achievement. The probes have traveled 12 billion miles in 40 years, leaving our solar system behind for the vastness of interstellar space, the first human-made objects to do so. Beginning with stock footage of the original design and construction process, the documentary relates how this monumental project was conceived and executed. The probes were the pinnacle of technology when launched but have less computing power than a modern-day hearing aid. Yet the two probes on their revolutionary odyssey have unlocked stunning secrets within our solar system, from the discovery of volcanic activity on Jupiter's moons to the "great dark spot" on Neptune.