Haha, the comments on this page are funny. The human body relies on gravity and physical activity to work properly, that includes brain function. There is no such thing as a brain that can operate independent of the body so the body must be healthy. This is the biggest thing that prevents manned missions to mars. People seem to think the fact they are not in space on a momentous journey matters. It doesn't matter at all. The brain will shut down as time goes on. And with the muscular atrophy and bone loss from a zero gravity environment, it will happen even faster. Before the first manned moon mission (trying saying that five times fast), scientists surmised that the energy saved from not using the body would supercharge the brain. It seemed like all win, men to go the moon, they get smarter being in space, and they come home and everyone is better off. The reality is that a zero gravity environment turned them into lethargic lumps after only 8 days in zero g. They couldn't walk unassisted at all when they got back. If you were to sleep for that time, you would still be able to get up and walk on your own (not without a little discomfort, mind you). And their IQ's tested lower after touch down as well. Combine that with little to no way to mentally stimulate the astronauts in such a small environment and you have an impossible mission.
My boss has the idea the best. Build a mobile space station that will travel slower but give the opportunity for more activity and mentally stimulating activities. Even if you build it and it take 8-10 years for the journey, it would still be a much better proposition. They would still need to find a way to stimulate some sense of gravity though. I mean, massive rotating sections may not be possible, but certainly are a step in the right direction.