Page 59 - Communications Satellites Global Change Agents

2. EVOLUTION OF SATELLITE TECHNOLOGY 35

Arthur Clarke has a truly magical gift for writing solid works of science and
engineering while also spinning yarns of science fiction, including 2001: A Space
Odyssey. In 1945 he was an unknown; consequently, his brief but seminal article
was largely ignored. Yet the entire vision was there. In succinct but clear terms, he
spelled out a remarkably practical vision of what the future of space applications
might bring. He described how we might someday establish a global communica-
tions system with just three satellites by calculating the speed necessary to launch
a "space station" into geostationary orbit and establish radio stations beyond the
ionosphere. The satellite application he used as a way of illustration was the relay
of TV signals, although TV was then in its infancy. Today, TV relay still remains
the most dramatic application of communications satellites.
Clarke described a special orbit, which was the only one whereby a satellite
precisely encircles the earth once a day without losing altitude or escaping the
world's gravitational field and thus flying off into space. This magical orbit where
the "g" force is exactly 0.22 meters/second 2 allows a satellite to remain stationary
with respect to a constant point on the earth's equator. Thus, a satellite, once posi-
tioned in orbit some 22,230 miles or 35,870 kilometers above the equator (with
only modest orbital adjustments from microjets to correct for small north-south
or east-west excursions) will stay in place for long periods of time. A
geosynchronous satellite, located in what is now called a GEO orbit, thus be-
comes much like a very, very tall radio relay tower in the sky. The satellite re-
ceives the faint up-link signal, filters out noise and interference, translates it to the
down-link frequency (to prevent interference), amplifies it, and then retransmits it
back to earth (see Fig. 2.1).
With such a high tower, a radio transmission can reach across the oceans and,
in fact, "see" 40% of the way around the earth at the equator. Clarke's land-
breaking (or rather space-breaking) article explained how three such satellite ra-
dio stations equally spaced above the equator could connect the world together
and serve the entire planet except at the polar caps.
Due to the earth's curvature, a microwave tower over 500 miles (or over 800
kilometers) high would be required to "see" across the Atlantic Ocean and a much
taller one still to "see" across the Pacific Ocean. Of course such towers were not
economically or technically feasible. Yet, Arthur Clarke discussed how it was
possible to build one that was over 22,230 miles (or 35,870 kilometers) high.
Such a relay tower in space could do what a physical tower built up from the
earth's surface could not do in a practical manner.
Brilliance and vision is not always immediately recognized. Galileo, Colum-
bus, Kopernicus, Goddard, and many others found their "new ideas" ridiculed or
ignored at first. Such was the case with Clarke, whose article was only recog-
nized for its greatness in retrospect. This was, in part, due to Clarke's own be-
liefs that these radio towers in space would need human crews to constantly re-
place burnt-out radio tubes, and that space travel and reliable rocket systems
were simply too far in the future to be seriously considered in the short term.