Mission of Gravity - Hal Clement

The usual caveats apply here for SF first published in 1954. Cameras with film in them, laying out prints to form maps of the surface of a world etc. The digital, computer, internet age sat firmly in a future not imagined by SF writers then. Nevertheless a wonderfully visualised alien world, characters one cared about, albeit the main ones being hydrogen-breathing caterpillars, with pincers, living on a world whose gravity varied from 3g to 700g, and a stonking good tale too. Very enjoyable.