This is one of the issues with manned Mars flights that I have often seen mentioned but find somewhat frivolous. Let's examine the situation of a crew in the Mars Direct scheme. We have a crew of four in a habitat with an area of approximately 1,000 square feet, and each crewmember has a private room. They are essentially confined to this space for the six months of the outbound flight if recreational EVAs are not done. Once on Mars, the crew has available about double the space they previously had (because their supplies are unloaded upon landing) in the Hab, the ERV cabin, with about half the space, and the pressurized rover. They will also be making a huge number of surface explorations and be working a large fraction of the day. The return trip will have them confined to the ERV cabin which has about 500 square feet of room.

Now, let's compare this to the average state of a World War II GI, who could have been away for three or more years. The soldiers faced constant threat from enemy attack, bad food, low pay, cold, heat, mud, rain, lice, disease, and armies of men and machines doing everything in their power to kill them. The crew of a Mars mission will have good food, warm beds, and a reasonably comfortable overall existence. In addition, they have the tremendous psychological boost of knowing that they are worldwide heroes; once home, their fortunes are made. The crew of a Mars mission would be a select, close-knit group of scientists of engineers; I do not see why they would be likely or even have a small possibility of going insane. Cosmonauts have spent up to 18 months on Mir, a much more confined space without the opportunity for surface exploration of another planet, and kept their sanity. I see the human mind being one of the strongest parts of a Mars mission, and not something that would stop it.

__________________
"Too low they build, who build beneath the stars". - Edward Young, 1745