Are we still talking about physically packing specimens of homo sapiens in some kind of gross physical vessel and somehow propelling it across interstellar space? Seriously?? This is the 21st Century, man! It's been obvious for a while now -- several decades at least -- that there are far, far more efficient ways to colonize the galaxy.
By the time interstellar travel becomes feasible, in terms of both technology and resources, surely our AI technology, our robotics technology, our molecular synthesis and manufacturing technology, and our understanding of biology and genetics should be easily advanced enough to ship a manufactory to the destination star system and then FAX across everything and everyone else that is needed there. The explorers and colonists are most likely to be AIs and robots -- although there's nothing to prevent transmitting and synthesizing human beings as well, if it makes any kind of sense to do so. (A human being off planet Earth is like a fish out of water, unless and until we win the cosmic lottery and stumble onto Earth 2.)
I just... I don't know what people are thinking when they trot out these star travel ideas that sound like something from the 1960s. Star travel is an idea about the future. Why do so many people look at this with their minds stuck in the past?