People will never go to Space prison. If you're going to send someone into Space for an extended period of time — more than a few months — you are certainly disabling them, and almost certainly killing them. Microgravity is the first and most creative way to kill people. Even if the microgravity doesn't kill these unlucky lags, the radiation probably will. It costs ten thousand dollars to send a single pound of material into Space. That means even getting convicts up there is a roughly two million dollar investment per person.