Aurora by Kim Stanley Robinson

might contain spoilers of the story

Far enough into the future the human kind manages to launch a huge multi-generation ship to the stars. Its final destination, an Earth-like planet in the closest solar system, 10 light years away… The story is following (at least in the first third) the lives of the main engineer, or probably troubleshooter is a better name, of the ship as they try to repair various things from inside the ship biomes. The biomes are an interesting concept, in the sense that the ship is sort of an ark which manages to hold various Earth ecosystems on a smaller scale.

After they reach the planned destination and send some people/teams on the planet to start work they encounter some difficulties, and at this turning point, various disagreements start popping up inside the ship and on the ground. As the main reason of the trip is slowly lost, we see human behavior confronted with perilous situations in which factions try to take over the ship, saying that their decision is best.

Spoilers: After some of the people die, the Ship decides to “take matter into its own hands”, as it’s selectively freeing and directing various crowds throughout the ship. At this point the Ship discloses that initially there were 2 ships but one most likely was destroyed by similar factions which emerged in the shio #2 as disagreements escalated regarding the end goal of their mission.