"Hard" SF based on real physics made huge demands on 1950's writers with no desktop computers. Perfectionists like Hal Clement did all their calculations of gravity, orbits and centrifugal forces using just a slide rule and book of log tables. Clement also worked hard to conceal this laborious effort: in Mission of Gravity (1953) there are no equations, but simply the convincing reality of the extraordinary planet Mesklin.
Mesklin is unusually massive and spins particularly fast: its "day" lasts not 24 hours but 18 minutes. The huge mass means an unthinkable gravity of 700 times Earth's, but only at the poles. Where the spin has most counter-effect, at the equator, the overall pull is a mere three times the earth's gravity. Humans can walk there, on crutches, to bargain with the centipede-like, hydrogen-breathing Mesklinites for the recovery of an expensive research probe that's been lost near the unreachable south pole.
It's Barlennan of Mesklin, captain of the native ship Bree, who steals the show. He's bright, brave, and experienced in sailing his world's liquid-methane seas. The immense journey to recover Earth's stranded treasure confronts Barlennan's crew with unexpected but ingeniously logical obstacles and menaces. Constantly in touch with humans by radio link, Barlennan is both grateful for the scientific insights these visitors provide and suspicious about what--as a mere "primitive"--he's carefully not being told. As journey's end approaches, Barlennan makes some quiet plans of his own... Mission of Gravity is an acknowledged classic of old-fashioned SF world-building. --David Langford [via]