If you hang a satellite over the equator, 22,300 miles up, it will appear to remain stationary. Everybody knows that, or should, since global communications is based on the fact. A generation ago, everyone in the science fiction world also knew that this cornerstone of modern society was “invented” or discovered by Arthur C. Clarke.
I’m not sure that Clarke is still generally remembered for this. The origins of everyday things tend to be forgotten.
Clarke’s observation first appeared February 1945, in a letter written to the periodical Wireless World.
When Wireless World began in 1913, wireless had a completely different meaning than it has today. It referred to wireless telegraphy, invented by Marconi, which used radio waves, interrupted by a telegraph key, to send messages. That allowed ships at sea to send and receive messages.
Wireless World remained on the cutting edge of electronic technology. so it was the right place for Clarke to write his February 1945 letter, which included these words:
An “artificial satellite” at the correct distance from the earth would make one revolution every 24 hours; i.e, it would remain stationary above the same spot . . . Three repeater stations, 120 degrees apart in the correct orbit, could give . . . coverage to the entire planet.
In October of that same year, Clarke was back in print in Wireless World with his article Extra-Terrestrial Relays, in which he fleshed out his idea.
Fig 3. Three satellite stations would ensure complete coverage of the globe.
Illustration from the 1945 Wireless World article.
Clarke discussed the difficulties of early radio and television transmission. Radio, particularly the lower frequency AM radios in use then, were erratic. Sometimes they only carried a short distance from the transmitter; at other times, they would bounce off the ionosphere and travel for a thousand miles. Television signals, being higher frequency, did not bounce off the ionosphere and so were limited to line of sight.
Relaying through orbital repeaters was the answer to both range and reliability. An orbit of 42,000 kilometers above the center of the Earth would provide a geosynchronous station.
The figure given at the top of this post –23,300 miles — appeared in every early popularization of space travel. It is not only a switch to miles, but also that distance is above the surface of the Earth, not the center.
To power his satellite, Clarke suggests mirrors concentrating the sun’s rays to heat water in boilers for turbines to run generators. He also suggests that “photoelectric developments may make it possible to utilize the solar energy more directly”. That is exactly what happened; only thirteen years later, Vanguard became the first satellite to use solar cells.
Clarke then went on to specify what kind of rockets would be needed to place these geosynchronous satellites into orbit and predicted, correctly, that such rockets would soon be available.
He also said:
The advent of atomic power has at one bound brought space travel half a century nearer. It seems unlikely that we will have to wait as much as twenty years (i.e. 1965) before atomic-powered rockets could reach even the remoter planets with a fantastically small fuel/mass ration — only a few per cent. The equations developed in the appendix still hold, but v(elocity) will be increased by a factor of about — a thousand.
Oh, if he had only been right about that, too. Then our world might come closer to resembling the world envisioned by Harold Goodwin in his Rip Foster novel.