There was nothing unrealistic about human interstellar space travel when a willfully ignorant professor declared it to be unrealistic at a university seminar in 1966, and is far less unrealistic with what we know and can do in 2013. Multi-generation interstellar travel is possible with current technology. Ion propulsion is quite capable as a method of sub-light propulsion. For the inhabitants of the interstellar habitat, the trip would be little different in their lives than staying home in the Solar System.
I’m sorry, but I don’t think multi-generation travel is possible, simply because I don’t think enough people would sign up.
I wouldn’t condemn my children and theirs to such a life without choice otherwise, and I would sign up in a minute for myself.
These plans are all based on the notion that multiple generations would be happy to exist in a very constrained environment so some future generation would reach some predetermined goal. I don’t buy it, people just don’t work that way. I will sacrifice for myself and my children and grandchildren. My descendants to the 5th generation are on their own.
Maybe I’m wrong, but I don’t think so.