In movies, asteroids careening towards Earth confront determined humans with nuclear weapons to save the world! But a real NASA mission to change the course of an asteroid (one not hurtling towards Earth), the Double Asteroid Redirection Test (DART), is about to launch. NPR science correspondent Nell Greenfieldboyce joins the show to talk about what it takes to pull off this mission and how it could potentially protect the Earth in the future from killer space rocks. Email the show at shortwave@npr.org.