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May 1961 Popular Science
 [Table of Contents]
Wax nostalgic about and learn from the history of early
electronics. See articles from
Popular
Science, published 1872-2021. All copyrights hereby acknowledged.
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Heliographs (from Greek "sun,"
"to write") are used as signaling systems by reflecting flashes of sunlight reflected
by a mirror. That was fine for a sunny day. At night and when otherwise dark enough,
lamps and even bonfires were used to message between distant locations when the
time and/or effort needed to physically transmit a message via ground-based carrier
was untenable. Militaries used light signaling on the battlefield. As electronics
technology advanced to where it could support modulation and demodulation of light
signals, designers began devising systems which could reliably send messages. By
its nature optical communications is a line of sight phenomenon. On Earth, distance
over open, flat ground is limited to 3-4 miles due to surface curvature for a transmitter
and receiver about 5 feet off the ground. From a tower or mountaintop to a point
below or on another mountain, the range can be extended to 50 miles or more. In
space, between two satellites, thousands of miles are attainable. That is the topic
of this 1961 Popular Science magazine article. The inherent security of
using a narrowly focused light beam is a major advantage of lightwave communications.
Spacemen May Talk on Beams of Light
By adapting the old heliograph, a new signaling system would
serve future space explorers beyond the earth.
Flashing messages through space.
Socom System would link spaceships and bases
as in diagram. Transmitter, in large view, blinks out a message. Shown by itself
for clarity, it
would actually be mounted on a spaceship or space station.
By Wesley S. Griswold
Will lights twinkle across space to carry messages between the outposts of tomorrow's
interplanetary explorers?
That is the prospect raised by the recent successful trial in California's Mojave
Desert of a long-range system of signaling with sunbeams and mirrors. Under development
for the Air Force, it is called Socom, for solar orbital communications.
Socom amounts to an ultra-sophisticated, Space Age adaptation of the heliograph.
This old-time signaling device consisted of a pair of adjustable mirrors, to reflect
a beam of sunlight toward any point, and a key-operated shutter that interrupted
the beam to form dots and dashes of the Morse code. Applied first by the British
army in India and later by our own in the southwest U. S., it was reliable only
in the few relatively cloudless regions of the earth.
In contrast, Socom is to operate in space, where the sun always shines. It can
be designed to carry spoken messages as well as telegraphic ones. It incorporates
such electronic refinements as automatic sun-tracking and beam-aiming.
Maximum range of a single space heliograph would be 10,000,000 miles or more,
according to its designer, Electro-Optical Systems, Inc., of Pasadena.
How Transmitter Works: Diagram shows path of
ray of sunlight as it is caught by reflector, passes through shutterlike modulator,
and is projected in a message-carrying beam by second reflector.
In trial, transmitter on 30-foot tower, above,
flashed messages eight miles across desert to receiver, left. Light filters simulated
distance up to 10,000,000 miles. Reflectors of test rig had one-foot diameter; for
maximum range, full-scale ones would be larger.
Socom's transmitter has three principal parts. A dish-shaped reflector collects
the sun's rays and, with the help of a small auxiliary mirror, concentrates them
in a narrow beam. An electrical light valve called a modulator, replacing the old-style
shutter, impresses a message on the beam. Then a second reflector projects the beam
toward a distant receiver. Small, angled mirrors form optical "universal joints"
so that the two larger reflectors can be aimed in any direction.
The design of the modulator varies, according to the kind of messages to be transmitted.
If they are in dots and dashes, the modulator chops the beam into short and long
flashes, much as a mechanical shutter does. If the messages are spoken, the modulator
varies the brightness of the beam instead.
One promising new type of modulator contains a pair of light-polarizing disks
and, between them, a small block of plate glass. Normally this array is transparent.
But when electrically applied pressure strains the glass, the combination becomes
partially-to-completely opaque, in variable degree. This provides the control to
dim or extinguish the beam for signaling.
 Socom's receiver has a single dishlike reflector.
It concentrates the incoming beam on a photomultiplier tube, which converts the
flickering light into electrical impulses - and the message is made visible as a
written one, or is heard from a speaker.
The range of Socom can be extended by a relay station, a combination transmitter-receiver.
It catches a fresh beam of sunlight, applies incoming signals to its modulator,
and blinks out a duplicate of the original message.
A Socom network could flash messages back and forth among spaceships, orbiting
space stations, a moon base.
A Socom link between space and earth, even though operable only during cloudless
nights on earth, might be useful to transmit voluminous scientific data on a non-priority
basis.
Engineers expect that a Socom transmitter would be installed on a space vehicle
with a nuclear-power source. A relay station, with solar batteries for power, might
ride an unmanned satellite. The reflectors that project and receive the message-carrying
beam could be aimed by magnetic tape, carrying pre-launch instructions on where
to point them. A space version of a Socom transmitter, experts declare, could weigh
as little as 30 to 40 pounds.
Why use Socom instead of radio? Because, its developers say, it's simpler, more
reliable, lighter, longer-range than radio of equal message-traffic capacity, provides
clearer signals, and can't easily be jammed.
Posted May 2, 2024
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