The setup: Near future (maximum 50 years in future) where "only" thing changed is, that company SpaceX together with NASA and ESA found out, how to get cargo and people to space very cheap
USA decides to build a space prison. Because - it would be nearly impossible to escape from it.
Now the question. We hand wave away economical aspects (basically, we have money):
What drawbacks would we face, if we would like to build a prison in space? What challenges need to be considered? What would be impact on society? And how long can I keep prisoners there?