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Post-war

After the war, he attained a first-class degree in mathematics and physics from King's College London. After this, he worked as assistant editor at Physics Abstracts. Clarke served as president of the British Interplanetary Society from 1946 to 1947 and again from 1951 to 1953.

Although he was not the originator of the concept of geostationary satellites, one of his most important contributions in this field was his idea that they would be ideal telecommunications relays. He advanced this idea in a paper privately circulated among the core technical members of the British Interplanetary Society in 1945. The concept was published in Wireless World in October of that year. Clarke also wrote a number of nonfiction books describing the technical details and societal implications of rocketry and space flight. The most notable of these may be Interplanetary Flight: An Introduction to Astronautics (1950), The Exploration of Space (1951), and The Promise of Space (1968). In recognition of these contributions, the geostationary orbit 36,000 kilometres (22,000 mi) above the equator is officially recognised by the International Astronomical Union as the Clarke Orbit.

His 1951 book, The Exploration of Space, was used by the rocket pioneer Wernher von Braun to convince President John F. Kennedy that it was possible to go to the Moon.

Following the 1968 release of 2001, Clarke became much in demand as a commentator on science and technology, especially at the time of the Apollo space program. On 20 July 1969, Clarke appeared as a commentator for the CBS News broadcast of the Apollo 11 Moon landing.