To boldly go where no man has gone before
Why it is hard sci-fi
The original 1966 series. Soft on the engineering, rigorous about the show s ethical premise. The Prime Directive, the multiethnic command staff, the captain s log, and the away-team procedure are all real institutional inventions. The shows physics is post-war optimistic and uses warp drive, transporters, and phasers without a working theory. The shows hardness is in its institutional design, not in its mechanics.
Science inside it
Warp drive, matter-energy transporters, universal translators, phaser-grade directed-energy weapons, and a working future Federation as a multi-species political entity. The shows interest in alien civilisations is anthropological rather than physical, and the Prime Directive is the shows working ethical claim.