Project Telstar is actually an extension into space of microwave
communications methods that have been thoroughly proved on the ground.
For Project Echo and other early experiments in satellite
communications, Bell Laboratories built a large antenna of the type
known as a _horn-reflector_ in Holmdel, New Jersey. For Project Telstar,
a similar but much larger antenna was designed. It was located in a
relatively isolated spot at Andover, in the western part of Maine, where
it would be close to Europe. The site is nicely protected by a
surrounding ring of low hills—high enough to keep out interfering radio
signals, but low enough not to block the satellite when it is near the
horizon.
The giant Andover horn is a steel and aluminum structure 177 feet long
and 94 feet high that weighs 380 tons. At one end is a giant opening of
3600 square feet; from there the horn tapers down to a cab in which the
very sensitive receiver and powerful transmitting equipment is located.
The entire antenna—horn, cab, and supporting framework—moves smoothly on
tracks that allow it to rotate in a 360-degree circle around its
vertical axis (changing _azimuth_). It also can swing about its
horizontal axis from the horizon up to the zenith (changing
_elevation_). Despite its size, the antenna can revolve steadily and
precisely in a complete circle in just four minutes.
Signals are beamed to the satellite on a frequency of 6390 megacycles,
using modified Bell System microwave equipment and a special
traveling-wave tube with an output of 2 kilowatts. Signals come back on
a 4170-megacycle frequency at a much lower power level—as small as a
_trillionth_ of a watt. They are amplified by a ruby crystal maser that
operates at the temperature of liquid helium—just a few degrees above
absolute zero. The whole antenna structure and its associated equipment
are enclosed in a huge “radome”—a bubble made from Dacron and synthetic
rubber only a sixteenth of an inch thick but measuring 210 feet in
diameter and 160 feet high. It is one of the largest air-supported
structures ever erected.
The Andover ground station includes a lot more equipment—most of it
having to do with tracking the satellite, computing its orbits, sending
and receiving command and telemetry signals, and interconnecting the
satellite with regular telephone and television land links. Most of this
is located in a control building about a quarter mile from the giant
radome.
[Illustration: _The French radome looms over the Brittany
countryside_]
A ground station very similar to the Andover installation has been built
by the French National Center of Telecommunications Studies at
Pleumeur-Bodou in Brittany. The British General Post Office has
established a station at Goonhilly Downs in Cornwall, England, which
uses a large, deep parabolic dish rather than a horn-reflector antenna.
Both British and French stations participated in the first Telstar
experiments. Satellite communications ground stations also have been set
up in Fucino, Italy, and near Rio de Janeiro, Brazil, and others are
under construction in West Germany and Japan.