Sci-fi fans (who generally hate that mass-media term) have all sorts of subdivisions for their favourite genre. They probably wouldn't accept the idea of "Hard Sci-Fi": it's "Hard SF", faithfully extrapolated from known science (and many of them would insist that that the "S" stands for "speculative", not "science"). So no faster-than-light travel, no aliens with acid blood, no light sabres and so on. It seems to me that few Sci-Fi games settings are truly "hard". Most of them - like WH40K or pretty much all of our TV- and film-derived gaming - is what gets contemptuously termed "skiffy", or more generously "Space Opera". ERB's Barsoom, being old enough to be venerable, gets the more respectable term "Planetary Romance".