>>10839450So use in vitro fertilization and colony wide sex parties, incentivize people to breed at replacement levels. Raise kids in creches where you can indoctrinate them to the ship's mission.
Really though, if you can figure out how to maintain a habitable environment perpetually in deep space, then you just colonize the asteroid belt, kuiper belt, ort cloud, and the outer moons.
After that your generation ships would only have to get to the nearest star, and do the same thing there. You don't need to waste time scouting for a habitable planet.
Average distance between stars in the milky way is about 5 light years. Reinforce a big iron rich asteroid, slap some fusion rockets on it. If you can accelerate at 1g you wouldn't even need to simulate gravity in transit except when you turn around to start braking at the half way point.
It's still a long fucking trip, but a person could get from here to alpha centauri in a lifetime.
