I decided to go out and look for information from someone who knew what they were talking about.
So I went to the library and found
The Science of Science Fiction Writing by James Gunn. This guy wrote his master's thesis in 1951; he wrote a four-volume anthology on the subject; the book was written in 2000. I'd say his 50-plus years of study, at the time, on the subject matter would be a wee bit more authoritative when trying to find a definition of the genre than my vicarious experiences on the matter and your considerable 30 year publication history.
In his chapter defining what science fiction is, he comes to the conclusion that the difference between science fiction and fantasy is that fantasy invents its own world and/or rules - Vampires, werewolves, ghosts,
Lord of the Rings - whereas science fiction is a continuity of the real world into the unknown, which responds to the laws of the real world.
Don't ask how Alice can go through a mirror into the world beyond. Feel free to ask how the guys stay on the floor in
2001: A Space Odyssey.
On this front
Alien is undoubtedly science fiction. You can ask it 'real' questions and it can still stand up; a cursory glance at the fan-made
Anchorpoint Essays shows just how technical you can get with the Alien creature itself; Ron Cobb's design notes explain, for the most part, how every aspect of the ship and human technology actually works.
True, the film doesn't dwell on technicalities. Ash's technobabble on his observations on the Alien is about as technical as it gets, but the film still allows you to ask questions about it within the context of reality without having to resort to fantasy.
But;
QuoteNo Ripley in suspended animation
What about the crew of the Nostromo in suspended animation?
Quoteno corporation looking for a war toy
You seem to have confused
Aliens with either
Alien or
Alien 3. The Company wasn't looking for the Alien in
Aliens - Burke was. He made it very clear he was doing the whole thing for personal gain, and not for the Company itself.
In that regard,
Aliens more closely follows the mad individual seeking the monster. Would you say that in
Alien, without science fiction there could be no Company?
That's an honest question - The Company's role was much larger in
Alien, even if it was only ever
mentioned, through its external influence of the plot. With no Company,
Alien never happens. With no Company, Burke is still out to make himself rich.
Quoteno atomic-powered plant terraforming a planet's atmosphere
No exploration of a hostile alien planet in
Alien - No suit? You freeze, you can't breathe, goodbye.
The atmosphere processor was a means to an end; you could just have the characters in a location that already had a breathable atmosphere.
Quoteno marines who have gone on bug hunts.
With the term 'bug hunt' never being define; you could still have the marines be battle hardened and cocky.
QuoteA1 is a ship -- a truck.
And yet, at the same time, so much more.