"Space Opera" is also the name of a SF role-playing game released in 1981 by Fantasy Games Unlimited, as a companion to their Space Marines tabletop strategy game.
As with other FGU games (e.g. Bushido and Chivalry and Sorcery) the system is almost ridiculously detailed. For instance, there are two full pages describing the rules for throwing an object to another player. The rule books are also extremely badly edited and type-set. Some important rules are hidden in sections apparently dealing with a completely different topic, others seem to be missing alltogether. There is a lot of information about carreer paths for the PCs and about the skills they learn, but very little about how these skills work in the game. All in all Space Opera is totally unplayable without heavy modifications.
Still, the rule books and the companion volumes (Several Star Sector Atlas-books, Seldon's Compendium of Star Craft I and II, Ground and Air Equipment, and others) are good sources of ideas for a game inpired by Doc Smith's Lensman books, Star Wars or Starship Troopers.
The Space Opera system has been out of print since the mid-80's and FGU no longer produces any new material, so there is not much chance that you will find this game in a store. Apart from some nostalgia felt by the people who actually tried to play the game, it is probably better off dead.
Update:
I just found out that FGU still exists and has actually reprinted "Space Opera" in a new single book edition. There is no indication on their home page that the material has been re-edited in any way except for this merging of the two rule books. If anyone owns both the old and the new editions and knows about any changes, please tell me, so I can update this writeup.