Hard sci-fi, about the pitfalls of generation ships, and what can go wrong with the premises behind interstellar colonization. A fable with the moral "engineering isn't everything". Most of the book is narrated by the ship's computer. One of the main characters tells the computer to tell the story, and when the computer asks for guidance, she says "I'm not a writer". I wonder what this says about how Kim Stanley Robinson feels about writing. Also, with so much hard sci-fi, the characters are kind of secondary to the technology, and ideas, and so the approach of having the computer tell us the story seems especially apt. As with Red Mars, a plot device was used to extend characters' lives to the end of the story, which I don't think was that necessary. I think the book would have worked even if the computer was the only survivor at the end.