What about Mutants and Death Ray Guns? It's got the campaign aspect, plus random character generation as an option.
It's notionally a post-apocalyptic game, but it can cover pretty much any sort of sci-fi. To ditch the post-apocalyptic aspect, all you need do is drop the rules for weapon/armour malfunction (which are meant to suggest ill-maintained gear).
It's essentially the sci-fi version of Song of Blades and Heroes, with the necessary detail added (i.e. weapons and armour types are much more distinguished from each other).