The European Space Agency’s ExoMars spacecraft is currently cruising down a celestial highway, eight days into its seven-month journey to the Red Planet. We know it’ll land on Mars on October 19, but where will it be in a month? Or the Fourth of July? Its location seemed calculable to me. Given the spacecraft’s acceleration time, cruising speed, and distance from Mars at launch, I figured I could crunch some numbers. This was — I know now — pure hubris. Rocket science is a cultural touchstone, a cliché even, for a reason.

I found this out while trying to find a spacecraft.

Space highways aren’t like terrestrial roads, Michael Khan, Ph.D., a celestial mechanics expert at the ESA’s Mission Analysis Office, explained when I asked for his advice on locating ExoMars. If there’s one thing to keep in mind, he says, it’s this: There are no straight lines in space. In a beautifully written e-mail, he explained why we’ll all have to learn to drive on a curve — and why the future of space travel is infinitely more complicated than we think.

Rather than attempting to summarize his explanation, I’m going to paste it below because it is beautiful.

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