"Any story where a space-pirate wielding a space-axe could chop through a ray-shielded space-airlock, kidnap a beautiful space-princess and escape in a space-superdreadnought over a mile long, destroying at least one or perhaps two planets during the resulting space-battle, without this seeming in any particular out of place with the scale, scope, drive or moral code portrayed in the rest of the story, then the story is a Space Opera."