On August 20 and September 5, 1977, NASA launched two spacecraft, Voyager 1 and 2, on a grand tour of the solar system and into the mysteries of interstellar space. It was an incredibly audacious mission, and it's still going. My friend Timothy Ferris produced the Voyager golden record that's attached to each of the spacecraft and went on to write a dozen enlightening books about science and culture. (Tim also wrote the liner notes for the Voyager Golden Record vinyl box set I co-produced that's now available here.) In the new issue of National Geographic, Tim tells the remarkable story of the Voyager mission and why "it almost didn't happen." From National Geographic:
The prospect of a "grand tour" of the outer planets emerged in 1965 from the musings of an aeronautics graduate student named Gary Flandro, then working part-time at NASA's Jet Propulsion Laboratory in Southern California, the world's preeminent center for interplanetary exploration. At age six, Flandro had been given Wonders of the Heavens, a book that showed the planets lined up like stepping-stones. "I thought about how neat it would be to go all the way through the solar system and pass each one of those outer planets," he recalled.
Assigned at JPL to envision possible missions beyond Mars, Flandro plotted the future positions of Jupiter, Saturn, Uranus, and Neptune with paper and pencil. He found that they would align in such a way that a spacecraft could tap the planets' orbital momentum to slingshot from one to the next, gaining enough velocity to visit all four planets within 10 or 12 years rather than the decades such a venture would require otherwise. The mission launch window would open for a matter of months in the late 1970s, then close for another 175 years.
It was an ambitious idea at a time when the apex of interplanetary exploration was Mariner 4 shooting 21 grainy photos as it flew past Mars. No probe had ever functioned for anything close to a decade in space. None had the intelligence to manage complex planetary encounters at vast distances without constant human hand-holding. Playing crack-the-whip past multiple planets might work in theory but had never been attempted in practice. "I was told, 'This is impossible; stop wasting my time,'" Flandro recalled.
"Why NASA's Interstellar Mission Almost Didn't Happen" (National Geographic)