big, bureacuratic space empire in decline.
I have a trouble how to name law enforcers (the institution). Space Police does not fit empire theme at all, it gives the feel of a democratic society instead of an absolute dictatorship of an emperor...
The fact that "space" is a place where they operate does not have to be part of their name. We don't say "sea police," "air police," and certainly not "land police."
Just call them something enforcement-like. For instance...
Guardians of the Peace
Breakers Of Doors