Building a spaceship that can travel to other star systems on human timescales — over the course of mere decades — will be a challenging and expensive proposition, with costs likely running into the hundreds of billions of dollars.

But the economic and technological hurdles won't be so steep if our species has begun tapping the vast riches locked up in asteroids and other bodies beyond Earth orbit, advocates say.

Interstellar flight is so daunting because of the vast distances separating stars.