Three years ago, when the New Horizons spacecraft sped toward Pluto on July 4th and began sending humans their first clear images of the tiny world at the end of the Solar System, it all seemed preordained.

Of course NASA would fund and build a spacecraft to complete its initial survey of the Solar System and visit the only “planet” found by an American. (For the purposes of this article, we will set aside the debate over Pluto’s planethood.) But as ever in spaceflight, the end result almost invariably looks far simpler and smoother to the casual observer than the messy reality experienced by those actually doing it.

For example, anyone tuning in to watch a spacewalk on NASA TV will see splendid views of Earth in the background as two astronauts float around holding funny tools, slowly unscrewing this, or installing that. It all looks so easy. Yet those six or seven hours in space represent the culmination of years of training, and the EVA activity itself is as physically punishing for the astronauts in their bulky spacesuits as running a marathon.