Seriously, anyone going to Mars should be vetted with not just an MMPI but also a Hare Psychopathy Checklist and a functional MRI to rule out psychopathy.
Put in terms of 80/20, about 20% of the population could be considered "psychologically or socially marginal," with 20% of that first 20 =4% to be frankly malignant. This includes psychopaths and extreme narcissists (which happens to be about the rate in all human populations.)
Psychopaths have no conscience or empathic ability. It's hard-wired into their brains actually, and can be identified by MRI where the amygdala (emotion, etc) mis-communicates with the frontal lobe (consciousness). They can be very high-functioning individuals, appear totally normal or even super-normal, but would be thoroughly destructive in a closed social system. Most others just have squabbles, petty power plays, mini-breakdowns, etc the risk of which can be reduced by more routine psychological vetting, but will not willingly destroy the whole experiment for the purposes of a power thrill or some other amusement.
This type of vetting will need to take precedent over rank, scientific or political position. It's no joke - you can imagine a political figure like Stalin (easy example) being sent to Mars in his day, and what the effect would have been. Don't assume that people in these positions will have been naturally selected in this regard. A selection system will have to start from basic psychological principles, and proceed with rigor and independence if it's to be successful.
