I'm going on a bit of a rant so please bear with this thought exercise. ------- >you could possibly be sent back to earth? I'd guess that'd be a bigger cost

I'm going on a bit of a rant so please bear with this thought exercise. ------- >you could possibly be sent back to earth? I'd guess that'd be a bigger cost than that of keeping Billy (the prisoner to-be) in the habitat, with damages and loss of working man-hours included. I presume the colonists agree on what'd happen if anyone became a problem in the colony before they set off, but just for thought's sake, if we go into the costs-first way of doing things then it wouldn't be out of the question that the other colonists would just kill Billy, or put him into some other not-alive state: - Putting Billy into some sort of prison would be a loss of food, man-hours (he's no longer working and someone must keep tabs on him, feed him, and stuff) and space, all precious commodities in Mars. - Exile would mean certain death without giving Billy a surface-suit (big cost, not replaceable), and even with one it'd also mean an even worse fate in the barren landscapes of Mars. Knowing there's nothing out there for him just means he'd stay around banging at the windows or being an active threat to the survival of the colony. - I mentioned shipping Billy back in the earlier paragraph. - Using Billy for compost would be extremely unethical and life-scarring for the other colonists but also the only (I think) cost-positive way to put an end to an irreversibly disruptive colonist. Key-word is 'irreversibly'. - Rehabilitation is a problem we haven't solved here on Earth yet, hence it's not mentioned as an option, but if you think it can be done please say so in the comments. Maybe holding Billy captive and replacing him in the next supply-ship cycle could work, and its not the worst option in terms of cost. I guess that's why they screen and test you so hard before taking you in as a candidate. The morals of this are... don't optimize for costs, and talk things out with those you have a problem with.