Radio Signals to Venus
June 1958 Radio-Electronics[Table of Contents]These articles are scanned and OCRed from old editions of the Radio & Television News magazine. Here is a list of the Radio-Electronics articles I have already posted. All copyrights (if any) are hereby acknowledged.
That Hugo Gernsback was a profound and prolific visionary is obvious by anybody's estimation. Throughout the early and middle 20th century, the man both predicted and participated in as many technical creations as any of his contemporaries. Being a publisher of both science fiction and science fact books and magazines, Gernsback wrote of fantastic inventions ranging from weapons to medical equipment to space travel (and the vehicles that would shuttle mankind about his quests). Just as Arthur C. Clarke's talents extended beyond sci-fi adventures to include devising a scheme for geosynchronous orbit satellite communications, Hugo Gernsback designed and sold many electronics experimenters' kits, instruments, components, and even proposed a method for determining the rotational period of cloud-covered Venus. Because of Venus' perpetual atmospheric shroud of sulfuric acid which is impenetrable by visible light, radar is needed to map the planet's surface and determine when a full rotation has occurred. Gernsback describes his method here, which he first proposed in February 1927.
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... Radio to the Planets Is Now Assured ...
The idea of bouncing radio signals from heavenly bodies is not new. It originated with the writer in an article entitled "Can We Radio the Planets?" in the February, 1927, issue of Radio News. It was then proposed to send a radio signal from the earth to the moon and back via short waves. The calculated elapsed time of the signal transit was 2.5 seconds to cover the two-way distance - twice 238,854 miles, or 477,708 miles, to and from the moon. Nineteen years later, on Jan. 10, 1946, Lt. Col. John H. DeWitt and associated scientists of the US Signal Corps first established actual radio contact with the moon. The elapsed time was 2.4 seconds. Our original predicted time was 2.5 seconds, an error of 0.1 second. In the article mentioned, we also spoke of signaling Mars and Venus, but refrained from giving elapsed signal time, because of the extreme complexity of the problem. In 1927, we had little practical knowledge of the penetration of short waves beyond the earth's atmosphere and into space, as well as eventual reflection of the returning high-frequency waves on the Heaviside layer.
It is gratifying to note that in the fall of 1959 man will at last attempt to signal the planets - Venus and Mars, not as a stunt but for serious astronomic and scientific purposes. British radio astronomers, using the world's largest radio telescope at the Jodrell Bank radio observatory, intend to radio-contact Venus first. The scientists state that they will have a power output 3,000 times greater than the average military or air field radar installation! Many new and important facts will be learned from such a series of experiments in bouncing signals off Venus. One will be the rotation of Venus on its axis, not known now. Our closest sister planet is constantly shrouded in dense clouds. Hence man has so far not seen the surface of Venus. Its rotation period is thought to be 20 to 30 days - a guess at best. Radio astronomy via reflected signals may give us a clue to Venus' exact time of rotation.
Let us now consider how the scientists will "shoot" Venus at its inferior conjunction in the fall of 1959, when Venus will approach within 30,000,000 miles of the earth. (The closest approach was 26 million miles on Jan. 28, 1958.) At the speed of 186,000 miles a second, the radio signal will take 5.36 minutes to cover the distance out and back between the two planets (2.68 minutes to go to Venus, 2.68 minutes to return).
The inherent difficulty with the present-day state of the art of radio is our inability to concentrate a beam of radio-frequency signals - the diffusion is too great. The same is true of light. With the tremendous distances with which we have to work, the beam spreads. It is as if we aimed a high-pressure stream of water at a distant large football. Most of the water will not hit the object. A large part of that which hits will splash and reflect at different angles and only a comparatively minute amount will come back in the direction of the nozzle.
It is for this reason that the British scientists must use a large power output if they hope to get back an intelligible radio echo signal from Venus.
The Jodrell Observatory radio telescope, the largest known in the world today, has a great advantage in making these experiments. On account of its large size, it can concentrate the transmitter power output into a narrower beam and, again due to its large size, it concentrates the weak echo of the returned signal more effectively.
If in the future it should become possible to concentrate and narrow the radio beam further, much less power would be required to contact the various planets. Obviously, the greater the distance between earth and the outlying planets, the more difficult the problem of bouncing back signals.
It can be seen from the above that as earth and Venus pull apart, the distance between them increases rapidly, until at maximum separation - at superior conjunction - the distance is 161 million miles. Here it would take the round-trip signal 28.8 minutes to bridge the space. But now the sun would become an obstacle, partly blocking the path of the signal.
Would the signal be absorbed by the sun? Yes. Another interesting and perhaps far-reaching test would be the effect of the sun's gravitational attraction on the returning radio echo. This is known as the Einstein shift. If, before or after superior conjunction of Venus, we send a signal to Venus in such a manner that the return signal comes close to the sun, the signal should be bent toward the sun. The Einstein shift has been confirmed with light rays, but not with radio waves up to now. This, however, at the present time can only remain a theoretical consideration. The experiment could not possibly be conducted with present radio frequencies unless we had a radio-astronomical bowl transmitting and receiving antenna at least 60 miles in diameter!
In the future when we can produce super high frequencies of the electron optical variety, which approach the frequency of light, it will be possible to record the Einstein shift electronically.
There will not be very much practical difference when we try to signal Mars, because the distances between our two planets are not too great at nearest approach - about 35 million miles for Mars, 26 million for Venus. We can therefore look forward to an early radio contact with Mars, too.
What about the further outlying planets? Possible, but increasingly difficult the further out we go. To bounce a radio signal off Jupiter will take 1 hour and 10 minutes for the two-way transit; 2 hour 22 seconds for Saturn; 12 hours, 50 minutes for Pluto. To hit squarely such a distant planet, say Neptune, 2,677 million miles away at its closest is in itself a difficult feat; for the signal to return earth without missing it altogether would be an achievement of a high order - at least at the present state of the art. -H.G.
Posted June 8, 2014