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Earth Signals on the Moon
June 1962 Radio-Electronics

June 1962 Radio-Electronics

June 1962 Radio-Electronics Cover - RF Cafe[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Electronics, published 1930-1988. All copyrights hereby acknowledged.

Earth Signals on the Moon, June 1962 Radio-Electronics - RF CafeHugo Gernsback wrote in his June 1962 issue of Radio-Electronics magazine editorial "Earth Signals on the Moon" editorial that, "Within the next few years - certainly before 1970 - men will have landed on the moon, opening up a vast new world." That was a year after John F. Kennedy made his famous "man on the moon" speech. As he was wont to do, Mr. Gernsback accurately predicted the series of events that would lead up to the first manned moon landing. He mentions the need for automation to achieve a controlled, soft landing on the lunar surface because of the time lag for radio communications between the Earth and the moon - a little more than a second each way - which is not fast enough for a remotely controlled landing of an unmanned craft. He also addresses the necessity for accommodating the Doppler frequency shift due to relative motion, and line-of-sight communication being shorter on the moon for lack of a signal-refracting atmosphere to lengthen the effective distance to the horizon. Fortunately, NASA and its contractors had plenty of smart people working the problem, so we did, indeed, "land[ing] a man on the Moon and return[ing] him safely to the Earth," before 1970.

Earth Signals on the Moon

By Hugo Gernsback

... Coming Communications Problems Between Earth and Moon ...

Within the next few years - certainly before 1970 - men will have landed on the moon, opening up a vast new world.

However, before humans actually visit the moon, they will have been preceded by electronically equipped robots, specifically designed to pre-explore the moon's inhospitable environment. Many moon-landing vehicles and machines already have been designed, and prototypes built. These robot explorers will make "soft" landings on the lunar surface, after having been propelled by rocket over the 238,000 miles separating the moon from earth. Guided entirely by electronics and telemetric control, not everyone of the early lunar flights can be expected to turn out smoothly. There probably will be mislandings - not all moonshots will be successful, any more than all our first earth satellites succeeded. But we may be certain that before 1970 we will have succeeded in setting down a number of lunar robots that will make later manned landings reasonably safe.

One of the difficult problems in precise moon landings - possibly solved theoretically by now - is the time lag of telemetering the robots from earth. It takes 1.2 seconds for light or radio waves to span the 238,000 miles between earth and moon in one direction. Even if you could follow a rocket's flight to the moon via telescope, it would be impossible actually to see the last important 50 or so feet of the descent. Because light from the moon takes 1.2 seconds to reach the earth observer, he of course could not see the approach to landing till 1.2 seconds later. It would therefore be a most difficult operation to land a rocket robot telemetrically from earth.

There are, however, better and more precise means to soft-land lunar robots. Let us mention only one. The principles we used during World War II in the electronically operated proximity fuze - or similar ones - can conceivably operate the robot's retro-rockets, independent of earth telemetry. These means will be certain and automatic for all landing purposes. Once the robot equipment has arrived safely and intact on the moon, earth scientists can take over certain operations via telemetry. Because in all likelihood, the robot must be able to move over small distances for orientation and exploring purposes, it will be equipped with a TV camera so that earth observers can see the machine's immediate environment. Other vital information sent via radio for the benefit of physicists, geologists and astronomers would be transmitted automatically by the robot's exploratory instruments.

While we have made innumerable radio contacts with the moon since 1946,* bouncing signals off its surface successfully, there will be some future problems which cannot be solved with certainty until we actually get to the moon.

Because lunar robot receivers must of necessity be exceedingly sensitive, interference from earth transmitters to the special moon-beamed signals intended to operate the moon robots will become critical.

Consider that the moon always turns its same side to the earth. It is known today that all frequencies (even broadcast waves) penetrate our atmosphere to a certain degree. But frequencies, from the vhf range down to centimeter waves, probably reach the moon in various intensities from earth transmitters "visible" to the moon. As the earth turns, many earth transmitters will contact the moon once in 24 hours.

Note also the inevitable Doppler effect of the rapidly spinning earth - 1,000 miles an hour at the Equator - when it transmits vital signals to a moon robot. This complicates reception.

Earth signals will come in strongest on the moon robot's instruments when the earth station is exactly opposite to it. They will become progressively weaker as the earth transmitter nears a 90° angle vis-a-vis the receiver on the moon. This is because the radio waves now must pierce the vast horizontal mass of the earth's atmosphere, against the former 150 miles or so when the moon is overhead. To circumvent this, we require a number of transmitters located at different points on the earth, all connected in a radio network, if we intend to maintain 24-hour uninterrupted communication with moon robots.

Another completely unsolved problem is future radio communication on the moon. Because of its small diameter, the moon's horizon is much nearer than that on earth. The moon having no Heaviside layer, radio communication can reach only as far as the horizon, some 2 miles, if the transmitter and receiver are 10 feet above the ground.† We know nothing of the ground composition of the moon - whether it is conductive or riot. Hence we cannot know until we get to it if we can communicate through ground-wave conduction as we do on earth. If we can, the problem of radioing to any distance and to the far side of the moon will become simple and inexpensive. If not, we must set up a cumbersome and expensive radio relay system.

-H.G

* The author first predicted echo radio signals from the moon in his former magazine, Radio News, in the article "Can We Radio the Planets?" in the February, 1927 issue. In January, 1946, the US Signal Corps first established two-way radio contact with the moon in 2.4 seconds, as predicted by the author 19 years before. (His forecast time had been 2.5 seconds. an error of 1/10 second.)

† See also "Radio On the Moon," Radio-Electronics July, 1959, and "Lunar Radio and TV Traffic," December, 1961.

 

 

Posted May 27, 2024

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