Chasing New Horizons: Inside Humankind's First Mission to Pluto

by Alan Stern

Such a mission would allow all the planets, even distant Pluto, to be reached in less than a decade, rather than the multiple decades such a journey would otherwise take. But this trick cannot be attempted at any random time, even in any random year or century. The planets, each one on its own orbit around the Sun, need to be arranged in just the right way, like beads strung on an arc, stretching from Earth to Pluto. Like a secret passageway appearing only briefly every couple of centuries, the motions of the planets line up to create such a conduit only once every 175 years.

Farquhar (who, sadly, died in late 2015, shortly after witnessing the Pluto flyby just months before) was a genius of orbital mechanics and had a legendary knack for finding crafty solutions to get from planet to planet with less fuel than others thought possible, primarily by using clever gravitational assists. One of his innovations that greatly lowered the anticipated costs of the Pluto 350 mission was to plan a launch on a relatively small rocket, a Delta II. A liability of this plan was that it wouldn’t have enough velocity to fly straight to Jupiter for the gravity assist toward Pluto. Instead, in Farquhar’s scheme, Pluto 350 would first go inward toward the Sun, use gravity boosts from Venus and then also Earth to get out to Jupiter, and then on to Pluto. This enabled a smaller rocket to do the job of getting to Pluto, but it meant the Pluto 350 craft would be in space for fifteen years en route to Pluto and would have to take the heat near hot Venus before the long journey out to cold Pluto. It was not the ideal way to go, but it kept costs within the tight mission box the study team was aiming for, and the sheer ingenuity of it turned heads.