Good one. I think it's generally considered a Western in a sci-fi setting. They did try to stick to self-consistent rules and a realistic "feel" with the technology, physics, special effects and so on (no sound in space, etc) which would put it on the harder side of the spectrum perhaps. But since the sci-fi elements barely interact with the story, and so there's no deeply-considered exploration of how those sci-fi elements are consequential to the story / characters / society of that world, it could also be considered soft.
> I think it's generally considered a Western in a sci-fi setting.
This is how I think of it as well. I actually don't really consider it science fiction, it just uses the scenery. Although I equally wouldn't say anyone who calls it "science fiction" is wrong.
That brings up another thing: I think a story can be science fiction without involving anything futuristic or space-related at all.
