A hard-science author with a poet's gift for evocation.
There is nothing "retro" or science-fantasy about the writings of Clarke: he writes of what was believed to be possible at the time; nevertheless his style, at its best, can work such magic as to bathe the "realistic" in quite as much enchantment as the purest fantasy. (Perhaps this is to be seen most of all in his epic of the far future, The City and the Stars.)
The fact remains, that his OSS output is OSS only by virtue of the date at which it was written. Hence, as far as this site is concerned, the later the story, the more likely it is that it's "not our pidgin".
For example the great A Meeting with Medusa (1971) is hard to classify as OSS. On the other hand the equally realistic-for-its-time Before Eden, published a decade earlier, is easy to include under the OSS umbrella.
Both tales tell of the discovery of alien life - the 1961 story, life on Venus; the 1971 novella, life on Jupiter. But whereas Before Eden was soon made "out of date" by the discoveries of Mariner 2, and so can be granted its passport to OSS-land, the accuracy of A Meeting with Medusa remained un-refuted by the Pioneer and Voyager probes, so that if we're challenged to say what's OSS about it, we have to answer - nothing, seemingly.
Harlei: But if it describes life on Jupiter...
Stid: Yes but, you see, there might actually be life on Jupiter. Here in our up-to-date New Solar System. And if there is, it could well be as Clarke describes it. Nothing to do with our quaint old OSS...
Zendexor: We could argue all night about A Meeting with Medusa. I'm the webmaster and I'm listing it.
Stid: You might as well, at that. I'm going to do a little volte face here and declare that perhaps Clarke is not always as much of a hard-science man as most people think. Or at any rate, that on occasion, in playful or in optimistic mood, he allows his hard science to be softened with wishful thinking.
Zendexor: Point taken. Clarke's place in the OSS is a complicated issue. His career straddles the onset of the Space Age. And his style straddles the matter-of-fact and the poetic. Personally, I believe he himself was confused and rather shallow philosophically - his intellect never did catch up with his far more profound imagination. But that's veering towards another issue... Here let's just agree that if you want to study the borderline, the fuzzy transition between OSS and NSS, you could do worse than investigate Clarke's work.
To illustrate the fluctuations of that OSS/NSS boundary, you could even narrow your focus to one particular year.
We've been arguing about A Meeting with Medusa. Well, in the same year (1971) appeared Transit of Earth, his late Mars story, in which (despite the results from Mariners 4, 6 and 7, and despite the story's grimly realistic tone) he goes so far as to hint at the presence of heavy, advanced animal life on Mars.
There are no oceans here on Mars, nor have there been for at least five billion years. But there is life of some kind, down there in the badlands of Chaos II, which we never had time to explore.
Those moving patches on the orbital photographs. The evidence that whole areas of Mars have been swept clear of craters, by forces other than erosion. The long-chain, optically active carbon molecules picked up by the atmospheric samplers.
And, of course, the mystery of Viking 6. Even now, no one has been able to make any sense of those last instrument readings, before something large and heavy crushed the probe in the still, cold depths of the Martian night...
On the Sun and Mercury: Out of the Sun.
On Venus: Before Eden.
On the Earth:
for the oceans, The Deep Range and The Shining Ones;
for the far future, The City and the Stars
On the Moon: Earthlight and A Fall of Moondust.
On Jupiter: A Meeting with Medusa (a great story, but hardly OSS, but it would be a shame not to mention it).
On Amalthea: Jupiter Five.
Arthur C Clarke, The Sands of Mars (1951); Prelude to Space (written 1947, published 1951); Earthlight (1955); The City and the Stars (1956); The Deep Range (1957); A Fall of Moondust (1961); "Jupiter Five" (written in 1951; published in If, March 1953); "Out of the Sun" (If, February 1958); "The Awakening" published in Reach for Tomorrow (1956); "Before Eden" (Amazing Stories, June 1961); "Loophole" (Astounding, April 1946); "A Meeting with Medusa" (Playboy, December 1971); "The Shining Ones" (Playboy, August 1964); "Transit of Earth" (published 1971; written 1970); the last three stories all reprinted in The Wind from the Sun (1972); "Trouble with Time" (Ellery Queen's Mystery Magazine, July 1960, as "Crime on Mars".
For Clarke and technology, see the OSS Diary for 28th March 2017.
For Clarke at the OSS/NSS boundary, see the Diary, Niven and Clarke on the Cusp.
For Trouble with Time see Wide-Eyed Forward Gaze at 2012.
See Clarke Contradicting Himself for his Kalinga award acceptance speech, 1962.