I think that either the first or second option as the major backstory would work well. The outside imposition of order from an orbiting space station makes perfect sense, insofar as directing the prisoners in where to put their mining efforts to best use. But the idea that this particular settlement has been shorthanded for however long due to insufficient workers from losses lends itself well to the settlement as a whole being glad to see new arrivals. More workers to help meet and exceed the quota for mining, and shiny new playthings for the more dominant and superior prisoners to enjoy.