Help is only 140 million miles away
Why it is hard sci-fi
A botanist astronaut is left for dead on Mars and survives by running the habitat as a working life-support system. Caloric budget, water reclamation, soil chemistry, communications via Pathfinders salvaged hardware, and a return rendezvous that requires a mass-stripped MAV and an Earth-Mars trajectory rebuilt with Hermes still in flight. The film is dense with engineering and almost every solution is an actual engineering solution.
Science inside it
Radioactive thermal generators as heat sources, stoichiometric water synthesis from hydrazine, soil microbiology with human waste as the nitrogen source, atmospheric processing for oxygen, low-bandwidth communication via a 1996 Sojourner relay, and a free-return slingshot trajectory that pays for itself in delta-v. The films one cheat is a Martian dust storm with implausible kinetic force, and Andy Weir has owned that one in print.