Beyond Earth. Beyond Mars. Beyond belief.
Why it is hard sci-fi
The reference standard for hard sci-fi on television. Ships accelerate at fractions or multiples of one g and the crew strap into crash couches under burn. There is no faster-than-light travel. Inertia, vacuum decompression, radiation exposure, and the Coriolis effect on a spinning station are the recurring engineering problems. The political and economic structure across Earth, Mars, and the Belt is consistent across the series.
Science inside it
Constant-acceleration thrust gravity using a fictional but internally consistent Epstein drive, the Coriolis effect inside spinning stations like Tycho, vacuum exposure with realistic timing, and the protomolecule as the only flagrant fiction in the show. The Belters develop a creole and a body type appropriate to long-duration low-gravity living, which is a piece of real biology applied at series scale.