How "Earth Radio" Would Launch ICBMs
May 1961 Popular Science

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.

At least two relatively new methods of wireless communications was employed in the "Earth Radio" system for intercontinental ballistic missile (ICBM) launch control in this 1961 issue of Popular Science magazine. Surface wave transmission would provide the signal medium from ICBM command and control centers to the underground silos where the missiles were stored, ready to launch at a moment's notice if Russia decided to initiate a nuclear attack on the homeland. Author Pursglove pays tribute to amateur radio's contribution to pioneering the science of surface waves. The other pioneering technology being used was spread spectrum encoding/decoding. Both methods provide innate security advantages. Surface waves are a relatively short range transmission means, so anyone wanting to transmit or receive bogus signals needs to be nearby. Spread spectrum, whether frequency hopping (FHSS) or direct sequence (DSSS) requires a key for decoding or encoding signals, so spoofing is nearly impossible. Another form of communications for through-the-earth signaling, called Lithocom (lithosphere communications), was also explored. It was eventually found useful in mining operations.

How "Earth Radio" Would Launch ICBMs

A novel method of subterranean signaling has evolved from a makeshift expedient of World War I. Now it's a practical and invulnerable launch-control system for our newest missiles. A deep-down version of earth radio, for civilian uses, gets a successful tryout at 1,000-foot depth.

By S. David Pursglove

If the command to fire must ever be flashed to Minuteman missiles at our newest bases, it will be transmitted by signals pulsing through the earth. The solid-fueled ICBMs' launch-control system will employ a method of communication unheard of, until now, by the general public-underground radio.

This will be its first practical installation. Its principle, long known to scientists, was crudely applied in World War I and has been experimented with by radio amateurs. But it is only within the last three years that new researches have perfected the radical technique.

As applied for military use, "earth radio" works this way: Signals from an underground transmitter are emitted by a grid like antenna buried a few feet beneath the ground. They travel upward to the surface, and proceed along it - both in the uppermost few feet of earth and in the air just above. Then, descending again, the signals are picked up by a second buried antenna like the first.

Scene of an installation will be a missile base of the latest "hardened" type, designed to withstand a surprise hydrogen attack and still launch its missiles. Out of sight below ground, the ready-to-go Minuteman ICBMs are poised in crewless, bombproof concrete silos, scattered widely about the countryside. The firing command would come by way of manned launch-control centers, "LCCs" for short, likewise underground. If any LCC had been knocked out by a bull's-eye hit, another one would be able to take over and launch its missiles.

Linking LCCs and missile silos, therefore, calls for an elaborate remote-control communication network, equally proof against full-scale attack or sabotage. Our first 150-silo Minuteman base near Great Falls, Mont., which was planned before the unconventional radio technique was perfected, will use an intricate system of underground signal cables. Earth radio will take the place of most of the cable network at other Minuteman bases soon to come.

It's Cheaper

Big advantage of the novel radio system is that it eliminates cable costing $20,000 to $25,000 a mile. That means a saving of about $300,000 per missile, the Air Force estimates.

"We are convinced that the system is practical," says Lt. Gen. B. A. Schriever, commander of the Air Research and Development Command. "It will be a virtually jamproof communication network, and highly invulnerable to sabotage."

While details are largely secret, this much more is revealed about the system: It will provide "a continuous report on the status of each missile" and of its silo. And it will use "spread-spectrum" transmission, meaning that its radio waves will have a wide range of frequencies. This guards against deliberate interference; a prohibitive amount of power would be required to jam the whole range.

The story behind earth radio goes back to World War I, when the German advance on Paris cut off a French army unit from its main force. The unit's signalmen, the tale goes, thrust two bayonets into the ground a few feet apart. They attached a buzzer, to serve as an oscillator, and had a crude wireless-telegraph transmitter. Meanwhile the main body of French troops - following instructions from a runner who had gotten through - set up a similar receiver, using headphones instead of a buzzer. The "earth wireless" worked - and the code messages led to the rescue of the trapped men.

The Hams Tried It, Too

In later years, amateur radio experimenters have tinkered with the scheme. Instead of connecting his sending-receiving outfit to antenna and ground, a ham would make one connection to a grounded water pipe - and the other to a metal rod sunk in the earth some distance away. Then he could exchange signals with another amateur, living nearby, who had done the same.

The trouble was, such experiments showed, that earth radio had a much shorter range than conventional radio - and took more power to span equal distance. So it remained just a scientific curiosity, until the coming of the missile age finally brought a use for it.

Development of Minuteman's shallow or surface-hugging system of earth radio began in mid-1958. Under an ARDC contract, experimenters of Space Electronics Corp., Glendale, Calif., conducted sub-surface trials under water and in a mine. Eventually they reported obtaining a strong signal more than 1,000 miles from a transmitter of 250-kilowatt power output.

Special antennas for the system were tested by the Boeing Airplane Company in earth-radio trials of its own, and transmitting and receiving equipment was developed by Sylvania Electric Products. The National Bureau of Standards also lent a helping hand.

Early last December, the Air Research and Development Command - considering the adoption of the earth-radio launch-control system for Minuteman - began a full-scale trial to confirm its practicality and reliability. In February of this year, the ARDC announced that it intended to use the system.

Radio Through Rocks

Meanwhile another kind of earth radio, called Lithocom, has been independently developed by an Eastern firm. In contrast with the Air Force's "shallow" system, this is a "deep" one - its waves travel through subterranean rock without ever approaching the surface. Civilian applications, principally, are foreseen for it.  tried out by Deco engineers to transmit signals through earth.

Lithocom was born in mid-1959, when recent geophysical studies suggested that deep-down radio was feasible. Although radio waves peter out comparatively quickly in deep rock, engineers of the Developmental Engineering Corp., Washington, D. C., theorized that their range could be greatly extended by taking advantage of favorable rock formations.

In the earth's upper crust, for example, a dry layer of sedimentary rock bounded by moist conducting ones should form a natural "waveguide" or conduit for subterranean radio waves. And so should a readily available "laboratory model" - a natural underground bed of salt, with an overburden of more-conductive rock.

Ready for actual trials by February, 1960, Deco engineers invaded two mines near Carlsbad, N. M., that had offered to cooperate. They set up their transmitter in an abandoned portion of the Potash Company of America workings, where the ore had become too thin to mine - an ideal place to work undisturbed. Their receiver went into a tunnel of the U. S. Borax and Chemical Company mine.

At the start of their day the electronic engineers could truthfully say, "Well, back to the salt mine." They reported at seven a.m. with the first mining shift, rode three miles underground by narrow-gauge railway - and still had a half-mile walk, through a passage only 4 1/2 feet high, to their transmitting test site. The reddish salt of the mine walls made cuts, scratches, and closely shaven faces sting. Taking so long to reach their location and return, the engineers had to stay during two mining shifts; usually they got back to the surface with the swing shift at 11 p.m.

Coming: Voice Transmission

On July 28, 1960, after numerous attempts, the first signal was successfully transmitted. It traveled a record 4 1/2 miles, at 1,000-foot depth. The feat was performed with a radio-teletype circuit, and a low-power transmitter operating at less than 200 watts' output. With more power, Deco engineers say, voice transmission and 100-mile range would be feasible.

For the Lithocom system of earth radio, the Deco engineers see many possible applications.

Installed in a large mine, a communication system of this kind could aid everyday operations - and, in an emergency, speed mine-rescue work.

The shielding effect of overlying earth makes the Lithocom system virtually noiseless. Therefore it has interesting possibilities for supplementing more-conventional channels of communication wherever static from electrical storms or man-made electrical noise interferes with their use.

Finally, the engineers note, the alternating wet and dry layers of the earth's crust offer multiple paths for Lithocom channels. Even on the same frequency, messages could be transmitted through different rock belts without interference between them. Will the answer to the problem of overcrowded air waves be to detour radio traffic through the earth?

So new is earth radio in its first practical forms that it is still too early to foresee how far this development may go.

Posted May 1, 2024