Brains Trust.Question No. 5. Is it theoretically possible to hold wireless communication with other planets? And is there anything in the nature of inexplicable radiations (i.e., apart from cosmic rays) reaching us from outer space?
(Answer on P. 231.)
The mere fact that we are able to observe the light which is reflected from other planets shows that there is nothing to prevent an electromagnetic wave traversing the space intervening between the earth and those planets or rather between the earth and the planetary atmospheres. For it must be noticed that this light which originally comes from the sun is not necessarily reflected by the surface of the planet itself, but may come from its outer atmosphere. Some planets have very dense atmospheres, others atmospheres of great rarity, while, in the case of Mercury, there is hardly any atmosphere at all. The spectra of some planets contain strongly marked absorption bands, indicating that the light has penetrated the planetary atmosphere, the gases of which have caused absorption of certain frequencies. The light waves in these cases have probably reached the surface of the planets themselves. In other cases the planetary spectra are very similar to that of the solar spectrum, which would indicate either that the planet had no atmosphere, or that the light had been reflected from the outer part of the atmosphere itself...
In the November 1942 edition the following letter from Arthur C Clarke was published.
ARTHUR C. CLARKE, Hon. Treasurer of the British Interplanetary Society, adds a note :THE fantastic figure of six million kW, quoted as necessary to produce a 5 microvolt/metre field on the nearest planet, presumably relates to spherical radiation, which no one for a moment considers. The use of beam technique would reduce power requirements to a minute fraction of this. Moreover, there seems very good evidence that radio waves from comparatively low-powered transmitters have travelled distances which are almost interplanetary. The existence of echoes of several seconds' duration (equivalent to the distance of the moon) is well established, and delays of up to ten minutes or so have been reported—corresponding to distances of several times those of Mars or Venus at perigee.
Secondly, the evidence that radiation reaches the earth from space is quite strong, and I am surprised that your contributor did not mention it. I refer to Jansky's reports on the subject (Proc. I.R.E., Oct., 1935). Jansky reports this " star-static " as lying between 9-21 Mc/s and being 10-30 db. above the level of thermal agitation. (See also Jansky, Proc. I.R.E.. Dec., 1937, and Friis and Feldman, Proc. I.R.E., July, 1937, for a further discussion of this matter.)
Finally, if radio is incapable of really long-range communication (which I doubt) the solution to the problem lies in the modulated light beam. Light can be focussed with extreme accuracy and the sensitivity of a photo-cell collecting light at the focus. of a giant reflector, and backed by an electron multiplier and the usual amplifying stages, is so enormous as to be almost meaningless. It is certainly capable of maintaining communication between all the planets in so small a space as the Solar System! As to the objection that most planets have opaque atmospheres, I would answer that all except Venus have airless satellites very close to them to which they could be linked by UHF.
That last sentence is worth repeating -
"As to the objection that most planets have opaque atmospheres, I would answer that all except Venus have airless satellites very close to them to which they could be linked by UHF."
So here we have it, in late 1942 Arthur C Clarke had already imagined a future role for active communication satellites using UHF radio signals, albeit using natural satellites.
In February 1945 Wireless World published another letter from Arthur C Clarke.
V2 for Ionosphere Research? ONE of the most important branches of radio physics is ionospheric research and until now all our knowledge of conditions in the ionosphere has been deduced from transmission and echo experiments. One of the more modest claims of the British Interplanetary Society was that rockets could be used for very high altitude investigations and it will not have escaped your readers' notice that the German long-range rocket projectile known as V2 passes through the E layer on its way from the Continent. If it were fired vertically without westward deviation it could reach the F1 and probably the F. layer.
The implications of this are obvious: we can now send instruments of all kinds into the ionosphere and by transmitting their readings back to ground stations obtain information which could not possibly be learned in any other way. Since the weight of instruments would only be a few pounds—as compared with V2's payload of 2,000 pounds—the rocket required would be quite a small one. Its probable take-off weight would be one or two tons, most of this being relatively cheap alcohol and liquid oxygen. A parachute device (besides being appreciated by the public!) would enable the rocket to be re-used.
This is an immediate post-war research project, but an even more interesting one lies a little farther ahead. A rocket which can reach a speed of 8 km/sec parallel to the earth's surface would continue to circle it for ever in a closed orbit; it would become an "artificial satellite." V2 can only reach a third of this speed under the most favourable conditions, but if its payload consisted of a small one-ton rocket, this upper component could reach the required velocity with a payload of about 100 pounds. It would thus be possible to have a hundredweight of instruments circling the earth perpetually outside the limits of the atmosphere and broadcasting information as long as the batteries lasted. Since the rocket would be in brilliant sunlight for half the time, the operating period might be indefinitely prolonged by the use of thermocouples and photo-electric elements...
Again the full text can be found in the attached PDF.
After the war, in January 1948 Wireless World published the following piece by M.G. Scroggie about a lecture given by Arthur C Clarke.
Electronics and Space Flight. New Uses for Radio ?
IT is not many years since flight outside the earth's atmosphere was entirely visionary; fit for fantastic fiction, but not a subject for practical engineering. Although space flight has not yet been developed to the point at which cruises round the moon or planets can be advertised, that is an extension in detail, rather than in principle, of what has already been accomplished_ So when Arthur C. Clarke spoke to the British Interplanetary Society* on the uses of electronics in this far-flung activity, he did not have to begin by apologizing for the subject matter. So far from being pure speculation, his lecture naturally included present-day practice in such initial ventures as the V2 and moon radar, and proceeded to quantitative examination of more ambitious projects for the future.
The word " electronics " in the title was used, for lack of a better one, to include not only valve and circuit devices but possible applications in the entire electromagnetic spectrum. It was pointed out that the longer radio waves on the one hand, and ultra-violet on the other, are stopped by the earth's atmosphere...
*8th November, 1947.
But I've jumped ahead too far, as it was in Wireless World February 1945 that the idea of the geostationary satellite was first spelled out. See http://lakdiva.org/clarke/1945ww/ for the now famous October 1945 paper "Extra-Terrestrial Relays".
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