In space no one can hear you scream.
Why it is hard sci-fi
The Nostromo is a working ship, not a hero ship. It is a deep-space tug hauling refined ore on a long return. The crew complain about hazard pay and read manuals. Cryosleep, ship AI, vacuum hazards, and a chain of command are treated as ordinary. The xenomorph itself is exotic but the human side is industrial in a way most space horror skips.
Science inside it
Hibernation for long-haul transit, atmospheric processing, parasitic biology. The creature has a multi-stage life cycle that mirrors real parasitoid wasps in compressed form. Acid blood is the only flagrant departure and the film gets one freebie.