From Wikipedia
Clarke's most important scientific contribution may be his idea that geostationary satellites would be ideal telecommunications relays. He described this concept in a paper titled Extra-Terrestrial Relays — Can Rocket Stations Give Worldwide Radio Coverage?, published in Wireless World in October 1945.[68] The geostationary orbit is now sometimes known as the Clarke Orbit or the Clarke Belt in his honour.
However, it is not clear that this article was actually the inspiration for the modern telecommunications satellite. John R. Pierce, of Bell Labs, arrived at the idea independently in 1954 and he was actually involved in the Echo satellite and Telstar projects. Moreover, Pierce stated that the idea was "in the air" at the time and certain to be developed regardless of Clarke's publication. In an interview given shortly before his death, Clarke was asked whether he thought communications satellites would become important; he replied
"I'm often asked why I didn't try to patent the idea of communications satellites. My answer is always, ‘A patent is really a license to be sued.' "[69]
Though different from Clarke's idea of telecom relay, the idea of communicating with satellites in geostationary orbit itself had been described earlier. For example, the concept of geostationary satellites was described in Hermann Oberth's 1923 book Die Rakete zu den Planetenräumen[70] (The Rocket into Interplanetary Space) and then the idea of radio communication with those satellites in Herman Potočnik's (written under the pseudonym Hermann Noordung) 1928 book Das Problem der Befahrung des Weltraums — der Raketen-Motor (The Problem of Space Travel — The Rocket Motor) sections: Providing for Long Distance Communications and Safety[71] and (possibly referring to the idea of relaying messages via satellite, but not that 3 would be optimal) Observing and Researching the Earth's Surface[72] published in Berlin. Clarke acknowledged the earlier concept in his book Profiles of the Future.[73]
