Luna-1 is a moonbase populated by the various Earth Mega-Cities.
Each Mega-City takes it in turns to appoint a Judge Marshal, to govern the colony and lay down the law. Each of these stretches last for six months, before a Judge from another Mega-City is appointed.
Judge Dredd completed a tour of duty on Luna-1 for six months in late 2099 to early 2100 (2000AD progs 42 to 58).
Luna-1 also featured in the nine-part 2000AD story Breathing Space (progs 1451-1459).