A YA book, from before 1995, where a society of kids is stuck on a deteriorating generation ship. The adults and maintenance machines have died or broken down, and they have very little fuel left. The kids are now teens and have formed a society with leaders. Unbeknownst to them the captain of the ship had been stuck in an area with low gravity for years because higher gravity would kill him. For some reason, I think it has "exile" in the title.