Robert Heinlein’s Orphans of the Sky is one of those annoyingly seminal works that Heinlein oh-so-casually tossed off on a regular basis: it’s more or less impossible to write stories about generation ships without at least referencing this work. If you’re unfamiliar with it, you’re in luck: X Minus One did a radio play based on ‘Universe’ (the story that takes up the first half of the book). It’s not exact, but it’ll give you the gist. Also, you should be listening to more radio shows anyway. We all should, really.