The cast of sci-fi television hit “Galaxy Quest” (Tim Allen, Sigourney Weaver, Alan Rickman) makes their living signing autographs at conventions and telling stories about their glory days on the small screen. But when actual aliens intercept reruns of the show and mistake the actors for actual space heroes, the burned-out performers must play along and re-enact their old heroics — this time for real — to save a doomed civilization from a terrifying galactic warlord. Can the out-of-work television has-beens muster the courage to so much as fly an actual spaceship? And what will happen if anyone realizes the mistake — especially the enemy?