Our heroine, Freya, grows up in transit. Her world is two huge wheels, spun to imitate gravity, fixed around a long central axle aimed at the star Tau Ceti. Inside are 12 separate ecosystems, from tundra to tropical, each with their own human population, maximised for diversity of flora and fauna. The ship has been flying for 160 years and is now approaching its target system, undertaking the ticklish business of slowing from 0.1-of-light-speed to a more manageable velocity. Tau Ceti has many planets, around one of which is a moon with good levels of oxygen and no indigenous life: a perfect blank slate for new colonists.