This is not the same as taking an analogue of a European medieval culture and inserting it into a fantasy world (unless, of course, you have a lot of magic and have made no effort to demonstrate how magic changes the cultures of a medieval society). There are at least reasonable assumptions one can make about early technological developments in human cultures. But it does not work in a science fiction universe as a cultural standard.
This is one of the few things that will make me toss a book across the room: when your world makes no sense. Mashing together ancient cultures with advanced future worlds simply does not work. No matter how hard you cram an eagle into a pig, you will not come out with a flying pig.
Sadly, a lot of people try to do this, and their books suffer as a result, because the moment I stop and say, "This doesn't make any sense," is the moment when I've been pulled out of the story. It won't be easy to go back after that.