Orphans of the Sky

Orphans of the Sky is a science fiction novella by Robert A. Heinlein, consisting of two parts: Universe and Common Sense.

A gigantic, tube-shape starship is cruising pilotless toward a distant solar system, inhabited by a crew that has forgotten their origins over time and lapsed into superstition. Most crew members lead a simple bucolic life of farming, never venturing to the upper decks where the muties dwell. One day, Hugh Hoyland starts exploring and finds the astonishing secret of the ship's purpose.