JUSTICE SYSTEM
Police department
There is a huge police station down on the 4th floor, with police officers of every species and from every planet in the galaxy, and a few other places as well. This means that they are not all pathetic little aliens that your character can slaughter at will - some of them are very powerful in their own right, and these will be called in when necessary. This means that even your superpowered character stands the risk of being arrested.
Spread out over the ship, there are smaller police stations, and there are visible patrols at all times of the day. Occasionally newcomers are hired to help, but they do not rely entirely on their help.
Prison
It's large enough to hold every criminal on the S.S. Thor, and the cells are of every shape and size. They're built to withstand meteor impact and worse, which means that yes, even overpowered characters will have a hard time breaking free. Occasionally there's a glitch in the walls though, usually when the Infinite Improbability Drive is on. When that happens, prisoners just waltz out the doors, and the crime rate increases until they can be hunted down again.
The more clever ones find other means of escape as well. They might bribe someone to fake the paperwork, although getting anything past the Vogons is difficult. Maybe they'll sneak out with the laundry. Maybe they'll give sexual favours to one of the guards and then run off with his, her or its keys. They can be very inventive!
Punishment
To make things simple, we're dividing the types of crime into three categories. Keep in mind, this is the amount of punishment they'll end up with for OOC reasons, and not necessarily what they were sentenced to IC-ly.
Serious offenders
For murderers and the like, we expect them to stay locked up for at least a week or two, and leaning strongly towards the latter for repeat offenders. If you'd like for them to stay there longer, that's fine, too. Considering the amount of crime on the Thor, they should have a lot of company!
Medium offenders
Robbery, theft, etc. Keep them locked up for a few days to a week, leaning towards the latter for repeat offenders.
Minor offenders
Public indecency, property damage (taken lightly since the ship heals itself), pissing off the vogons, etc. They'll probably just be thrown in a cell for the night, maybe a few days at most, before the guards get bored of them and let them out.
Visiting hours are from 3-6pm, and attempting to sneak in outside of that will get you thrown in a cell for the night if you're caught. Hey, if you wanted in that badly, you might as well stay a while. Phonecalls are a privilege, but prisoners keep their Guides if they have them, allowing them to communicate with the outside. There's also modern facilities, including entertainment, that they'll have access to during the day. Of course, all prisoners are also made to work.
Keep in mind: No matter how hated they are, no character will ever be arrested for crimes committed in their canon. They come to the S.S. Thor with a clean slate, and have an equal chance to everyone else at proving their worth. After all, good luck finding any evidence when your planet's blown up.
Edit 12/3/10: The Permanent criminal record post is up!