Essentially a mobile ring habitat bolted onto a gigantic fusion rocket. Generation ships are intended to sustain a population of thousands for the lengthy periods of time it takes to travel from one star system to another at slower-than-light speeds.

As they crawl through the void for centuries, sometimes millennia, entire generations of passengers and crew are born, live, and die without ever setting foot on a planet. Rumors persist of lost generation ships whose passengers have even forgotten they live aboard a ship, they believe the endless corridors and artificially lit parks are the whole world.