One of the most infamous weapons in science-fiction movie history is the Death Star, a moon-size planet destroyer from the "Star Wars" universe. In the upcoming movie "Rogue One: A Star Wars Story," a band of renegades tries to steal the plans for the Death Star from the evil Empire, in order to ultimately destroy the spherical death machine. Does the Death Star lie completely in the realm of fiction, or could such a thing ever be constructed in real life? In 2012, more than 25,000 people signed a petition asking the U.S. government to construct its own Death Star. The White House (as it is bound to do when petitions receive a certain number of signatures) considered the application and penned a discouraging but tongue-in-cheek response — among the concerns cited in the rejection letter were the cost of such a project, and the fact that a single, small spacecraft was apparently enough to destroy it (a significant flaw for such a massive project). But it turns out that the biggest