What are the human challenges of a long-duration mission to Mars. Can the psychological and physiological challenges of this trip be met?
I think they can. As many mentioned, artificial gravity (quite do-able with current tech, centrifuge idea) would offset most of that. Not to
mention, they exercise with resistance (i.e. something holding them down on a treadmill, etc. with force to mimic gravity) to avoid the bone loss,
etc. Still, for long-term trips, the fluid issue is of concern, and that's why you'd want artificial g's.
As for the radiation, the big kicker here is time...how long are they exposed, etc. Sure, if you were to try and COMPLETELY shield them you'd need
the 6 feet, etc. However, this has never been the case. For the moonshots, they simply passed thru, took their lumps, until they reached a limit
(see Val's comments). No different here for the Mars trip.
As for psychological, this would depend on communication back and forth, etc. With e-mail, video phones, internet, news, etc., I doubt they'd have
much to cope with there really....especially if some effort was made to make the ship comfortable and homey.... The biggest challenge would be
palatable food for that long, hehe.....
Which brings us to the real challenges, water, waste disposal, food, fuel, etc. NASA has already come up with some great solutions, so I'd bet
they're up for the task. Sadly though, I'd bet that our first attempt on it will NOT go smoothly.....