This is asking the wrong question. We don’t know how to create a robust artificial biosphere, we don’t know how to shield such a large ship from radiation effic

This is asking the wrong question. We don’t know how to create a robust artificial biosphere, we don’t know how to shield such a large ship from radiation efficiently, we don’t know how to maintain or create the human microbiome, because we’re nowhere near understanding it. We’re so far from being able to survive off of Earth that we don’t even know all of the challenges that exist. Even if we had the propulsion, which we don’t, we’d still be screwed.