I think the way I would draw a line between hard science fiction and futuristic fantasy is that in hard science fiction, known science is extrapolated as far as possible to serve the needs of the story, and when that still doesn't allow for the needs of the story, additional science is invented, with rules that govern the invented science strongly enough to maintain self-consistency. In futuristic fantasy, there's no strong effort to make science behave according to strong rules, real or invented. However, I don't see it as a sharp line so much as a continuum.
The Martian is hard science fiction in the strictest sense; the only divergence from real science that I saw is that hydrazine is so toxic that even a trace of unburned fuel would have been very bad. (I'm not sure whether that's a tiny touch of creative license or just a slip-up.)
Star Wars is pretty much the other end of the scale. None of the science seems to operate according to any rules of than spectacle.
Star Trek is in between, conceptually, but not much in practice. There seems to be an attempt to aim for self-consistency in the science, but there was never much clear thought to define the rules of the invented science, so each writer chooses the rules for the episode or movie.
Traveller leans toward hard science, but doesn't go all the way there, though some editions have tried pretty hard. It breaks down here and there, often in cases where real science developed in directions that the original writers didn't anticipate (computers, for example), sometimes in cases where the original writers appeared not to understand real science (such as "mesons" that decay energetically after a specific time, rather than exponentially), and often in cases where invented science behaves badly (such as the possibility of relativistic planet busters based on reactionless maneuver drives). But in most cases, real science is respected, and major examples of invented science (jump drive, psionics, etc.) follow reasonably self-consistent rules.
