Clarke was the first Science Fiction writer generally considered a credible guy by scientists. You didn't find salt-sucking monsters or such in Clarke's novels. Indeed I know of only one Clarke story to use a faster-then-light starship.
Clarke wasn't the only one proposing communications satellites in the mid-1940's: George O. Smith published a number of short stories, some during WW2 and probably security violations, about a manned satellite in a solar orbit chosen to act as a continuous communications relay to Venus, even when Venus was behind the Sun. However nobody's had a need for a full-time link to Venus yet so this doesn't get mentioned much...
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"If they can't picture me with a knife, forcing them to strip in an alley, I don't want any part of it. It's humiliating." - windsock