Interstellar ark

An interstellar Ark would be used to travel from galaxy to galaxy. It would have to be large, and would require the orion propulsion system of nuclear impulses. The largest Orion Space craft theorized was 400m x 400m and wieghed approximately 8,000,000 Tons. It could be large enough to be a city holding upwards of 100,000 people.

Assuming that we could launch this craft into space it would be large enough to be self sufficient. The issue posed by such an ark is that humans might drastically change in the many generations that it would take to reach even our nearest neighboring galaxy Alpha Sentori.