Proxima b, our nearest neighboring exoplanet, is almost 25 trillion miles away. Even one of our fastest spaceships—the 31,600-?mile-?per-?hour New Horizons—would take hundreds of thousands of years to get there. Assuming we can't figure out how to warp space-time (seems unlikely, but fingers crossed), we're still looking at a couple-hundred-year trip in the best-case scenario, which leads to the real problem: No human crew could survive the entire ride. Science-fiction writers have long floated so-?called generation ships as a solution. Designers would outfit these interplanetary cruise vessels to support a ­community of adults and their children, and their children's children, and their children's children's children…until humanity finally reaches a new celestial shore. Here's our best guess for what it would take to sow the seeds of an extrasolar species.

Career planning

Successive generations need to fill all the vital crew roles—such as medics and mechanics—which doesn't leave much room for freedom of choice. A version of modern career tests would assign occupations based on aptitude, passions, and available jobs.

Propulsion

We're gonna need a mighty push. So far, no one's had any better ideas than Freeman Dyson: Slap A-bombs on the back of a ship and physically shove ourselves forward with constant ­nuclear explosions. It's not safe or healthy, but it's all we've got.

Waste management

Sinelab