EXPLORING THE SOLAR SYSTEM

Wanganui Chronicle, 22 November 1950, Page 6

EXPLORING THE SOLAR SYSTEM

Some Scientific Aspects Of InterPlanetary Travel

(By FRED HOYLI-J, Lecturer in Mathematics in the University of Cambridge)

Inter-planetary flight is already a half-serious scientific project. It has recently emerged from the science fiction era and is now being widely discussed in sober terms. Can rockets •“aoable of visiting the moon and other planets of the solar system really be made? Could men travel in such rockets? These questions are quite naturally of interest to everybody, for success in such an enterprise would be a major feat that could properly be ranked with the most outstanding achievements in the history of mankind.

The performance of a rocket is governed by one overwhelming factor, namely, the speed at which the gases stream out of the exhaust. The exhaust speed in a present-day rocket is somewhat in excess of one mile a second. When this is compared with the speed of about 10 miles a second that would be required to make space travel a reasonable practical possibility, it is clear that a great deal of progress has still to be made before visits to Mars become commonplace. ROCKET MOTOR TEMPERATURE

There are two ways of increasing exhaust speeds. The most obvious is to increase the operating temperature inside the rocket motor. This suffers, however, from the obvious limitation that the heating, caused by the burning of the fuel, must not be so great that the metal structure of the motor is melted. Increasing the operating temperature might perhaps raise exhaust speeds to two miles a second, but it is doubtful whether a significantly higher speed can be achieved by this means alone. The feasibility or otherwise of interplanetary travel therefore rests on the second method of increasing exhaust speeds. Tais involves a change in the chemical nature of the exhaust gases themselves. If the gas were ionized hydrogen, instead of a mixture of steam, carbon monoxide, and carbon dioxide, the exhaust speed would be increased more than sixfold. Such an increase, combined with the maximum possible operating temperature, would bring exhaust speeds up to the order necessary for space travel. This sounds very much simpler than it really is. Free pure hydrogen is not produced by the burning of any chemical fuel. Hydrogen would have to be carried in the rocket and it would have to be heated by the energy released in a suitable nuclear transmutation process. Such a project abounds in difficult problems. The nuclear equipment would have to be very light, not weighing more, say, than a ton. The release of nuclear energy would have to be far more flexible than anything yet known. The hydrogen would have to outweigh the rest of the rocket by as much as a factor of 10, and would have to be stored in liquid form. . These are just the more obvious difficulties. Although one is hopeful that eventually every difficulty will be overcome, it is clear that the problems of space travel cannot be compressed within a five-year plan. Indeed one has to be an optimist to believe that a trip to the moon and back will be safely accomplished within the next hundred years. But the odds are that it will be accomplished one day. Then there is a host of questions about the planets that might be cleared up. What are the clouds of Venus? Does Venus rotate as slowly as astronomers believe? Is there life on Mars? Do the planets have magnetic Helds? It must not be thought, however that all questions can be settled'by the direct look-and-see method Indeed, it is usually the deepest issues that cannot be setted in such a fashion. For instance, we cannot expect that space travel will clear up the mystery of the direction of the polar axis of Uranus. Outside astronomical circles, the romantic aspects of planetary exploration probably make a far greater appeal than the purely scientific interests. What will close photographs of the moon and the planets look like? A bold attempt to answer this question has been made in "The Conquest of Space," published by Messrs. Sidgwick and Jackson. This book contains an imaginative text by Willy Ley accompanying a beautiful set of paintings by Chesley Bonestell. Both authors have evidently been at pains to maintain the greatest possible accuracy in their respective fields, and m appreciation I cannot do better than

quote the opinion of R. S. Richardson of the Mount Wilson and Palomar Observatories:— OUTSTANDING PAINTING Mr. Bonestell’s paintings far surpass ■ in y portrayals of astronomical scenes that I have ever seen. They are real contributions to descriptive astronomy, quite aside from their intrinsic artistic merit. All who are interested in space travel should undoubtedly make a point of consulting this outstanding book. However optimistic a view one takes of the feasibility of inter-planetary exploration, it seems clear that there can be no extension of space travel to regions far outside the solar system. Rockets might indeed be fired entirely out of the solar system, but humans would not live long enough for a trip to even the nearest star. Space travel to many people means a manned rocket. So let it be said that, even under the best conditions, any trip outside the earth’s atmoj sphere must be reckoned an extremely hazardous undertaking. Quite apart from physiological issues it has to be remembered that inter-planetary space contains a large number of small solid particles. From time to time one of these particles would be certain to strike the rocket, the relative speed of impact being perhaps in excess of 40 miles a second. No antitank bullet has anything like the penetrating power of a particle moving at such a speed. From a strictly scientific point of view, too, a manned rocket would be a nuisance. Its manoeuvrability would be no greater than a radio-controlled unmanned rocket, its pay-load would be considerably greater, and the quantity of hydrogen carried would have to be greater by many tons. It would have no advantage except in the case of an actual landing: and, apart from the moon, it is unlikely that landings will be made, at any rate during the early phases of inter-planetary exploration, for a rocket of vastly increased size would be required to effect such a landing. Leaving now the problems of rocket design, we might also consider what the fruits of inter-planetary exploration may turn out to be. Scarcely any’ observation made outside the atmosphere of the earth could fail to be of scientific interest. It would be easy, for instance, to find out whether the material of the outer corona is sreaming away from the sun or inwards into the sun. A near approach to the moon would very likely settle the long-standing controversy about the origin of the Tunar craters: whether they are of volcanic origin as the majority of British astronomers seem to think, or whether they were produced by large-scale meteoric bombardment as the writer is disposed to believe. Nor could radio control extend much beyond the most distant planet, Pluto. Consequently there can be no means of ensuring the return into space. FEEBLE EXHAUST SPEEDS The impossibility of galactic exploration is due to comparatively feeble exhaust speeds. As we have seen, an exhaust speed of 10 miles a second is probably adequate for exploring the solar system, and this is just about the limit of any conceivable system of rocket construction. To explore the galaxy an exhaust speed close to the velocity of light , 186,000 miles a second, would be necessary. Such a speed is so vast as to justify the word hnposible—which is a pity, as it prevents us from verifying one of the mot intersting predictions of Einstein’s theory of relativity. According to relativity strange things wou.d happen if a rocket were accelerated to this sort of speed. It would be possible to visit distant stars, or even distant galaxies, within ihe normal span of human life—that is to say, within the normal span of life for individuals inside the rocket, but not for people on the earth. The Astronomer Royal’s Clocks would measure hundreds of thousands, or even millions, of years for the duration of such a trip. The clocks in the rocket, on the other hand, might measure only a few years, or even a portion of a year. In short, you might go for a few months’ rocket cruise to the far side of the galaxy and return to find the earth say 100.000 years older —escapism carried to a fine art. —Published in “The Times,’’ London.