Classic sci-fi. A surprisingly short read - more like a novella really. Written in the 1940s, at times it does feel a little dated, particularly with some of the dialogue. Other reviewers have also touched on the quite awful misogyny which I doubt any author would get away with today. I was actually quite enjoying it up to the point where women actually appear in the story only to be nameless, silent slaves whose only purpose is for the men to breed with or slap around. And no, I am not exaggerating. 
 The premise is really intriguing - a multigenerational ship adrift in space, where the current inhabitants have no living memory of Earth and their entire universe is contained within the spaceship. Like I said, it is very short and sometimes the plot is a little simplistic and the world building a little on the light side but still an intriguing idea. 
 Beth Revis does similar with Across the Universe which is probably a more accessible read but does suffer from some of the modern day YA-isms that were refreshingly absent from Orphans of the Sky.