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Aviation History
1953
1953 - 1107.PDF
FLIGHT, 28 August 1953 259 ARE WE NEARER TO SPACE-FLIGHT? Delegates to Fourth International Astronautical Congress Discuss the Problems By ERIC BURGESS, F.R.A.S. ROCKET experts, engineers and scientists meeting at Zurich for the Fourth International Astronautical Con-"gress have shown that there are many fundamental difficulties which must limit man's aspirations towards space flight. At this congress, sponsored by the International Astro nautical Federation, thirty papers were read during the technical sessions. They covered diverse subjects, ranging from problems in celestial mechanics to the possible uses of atomic energy for space-ship propulsion. It is possible to comment here on only the more important papers. Generally it was shown that theoretical problems in celestial mechanics were soluble at the present time and that the process was greatly eased by modern electronic computing machines. Nevertheless, although the courses of space-ships could be accurately plotted in space, neither engineering design nor chemical technology were sufficiently far advanced to make the success of any interplanetary venture a reasonably certain eventuality. In a paper by Milton W. Rosen (associated with the Viking rocket experiments) and Richard B. Snodgrass, both of the U.S. Naval Research Laboratory, it was pointed out that experience with high-altitude sounding rockets had proved disappointing so far as space-flight was concerned. Due to errors in adjust ment and unpredictable variations in performance of these rockets, full theoretical capabilities are rarely achieved. Yet interplanetary flight by the use of chemical propellants calls for control within narrow limits of the final velocity of the rocket. Some of the limitations of chemical propellants were discussed by W. N. Neat (England), from whose paper it could be seen that without atomic energy the take-off masses of interplanetary rockets must be exceedingly great and that little reserves of propellant could be included to allow for errors. As modern rockets may have a variation in performance which would call for additional propellant reserves exceeding the pay- load in an interplanetary mission, it was concluded by the N.R.L. scientists that there is not sufficient margin for error. The future development must be made in two ways; a reduction in the probable error and an increase in the margin. Back to Earth A paper by Prof. General G. A. Crocco (Italy) considered the best places and orbits for contacting space-ships in order to transfer additional material to them, i.e. for refuelling. Of most interest in his paper were conclusions concerning the descent of empty freighters. Two problems presented themselves, the optimum trajectory for a safe landing and that of the rise in temperature due to the high velocity of penetration of the atmosphere. By tracing the lines of optimum slope of descent and of constant temperature, Prof. Crocco arrived at the con clusion that at speeds above Mach 15 it would be necessary to have some means of artificial refrigeration for the descending tankers, whereas, if the velocity could be kept lower than the critical figure, descent would be safe with reliance only on natural cooling. H. Langemeyer of Austria spoke on the problems of generating electric power in space. He was of the opinion that the power requirements in space-vehicle projects have always been under-estimated. These requirements could be quite con siderable. Discounting machines of all kinds as being trouble some from the maintenance standpoint, especially if used in unmanned satellite vehicles, Langemeyer was in favour of using thermocouples heated either by nuclear energy or solar power. It would appear that solar power must be preferable in any small instrumented rocket where ionization from a nuclear power source would upset the instruments and weight requirements could not allow adequate shielding. Despite Langemeyer's claim to have developed an element developing twenty times the voltage of normally known thermocouples, it would appear that thermo-electric methods of power generation can be used only on fairly large satellites where, in any case, it may be more economical to use turbines. H. Preston Thomas has shown* that solar thermopile power stations can reasonably be expected to deliver power at overall specific masses of the order of 10 kg/kW compared wiui 2 kg/kW for turbines. *"Joumal of the British Interplanetary Society," Vol. 11, No. 4, p.188. Dr. S. F. Singer (England) presented a paper concerning the minimum orbiting instrument-carrying rocket. This type of machine would be used to enter a circular orbit at the limits of the Earth's atmosphere. It could continue with the high- altitude research programme and would have the great advantage that the instruments would be beyond the atmosphere for at least several hours instead of the few minutes which are at present permissible with high-altitude rocket techniques. Many problems in solar physics and associated with primary cosmic radiation need for their complete investigation a greater time of stay outside the atmospheric absorbing layers. To assume a specific impulse of 300 seconds gives an idea of the orders of magnitude involved: a three-step rocket for an orbital vehicle of this nature would have to weigh about 100 tons at take-off. A desirable feature of any satellite or other high-altitude rocket vehicle is that of gathering and transmitting information. One interesting use—for military purposes, for example— would be observations of the earth's surface. Kurt R. Stehling, of Princeton University, suggested two possible methods. Assuming a restricted payload, he then proceded to find whether these methods would give the required results. The con clusions were disappointing. One system of observation which was discussed was an optical objective-lens image-converter ^vstem, while the other was a microwave radar scanner. For his analysis he assumed an orbit at 500 miles altitude which would give a circular velocity of some five miles per second. The target to be detected was taken as being about 600 yards in diameter. The two systems were compared and it was shown that the optical-video method would have the advantage in weight and resolving power but that its daylight dependence and atmospheric cloud attenuation limitations would be quite severe. They were bad enough to indicate questionable feasibility from the operational standpoint. On the other hand, the low resolving power of the radar unit from the 500-mile altitude, together with attenuation losses, limited that system's usefulness. Stehling concluded that, despite weight requirements of food, air and water, the substitution of a human observer for instruments might give a decided reduction in take-off weight. The difficulty is, of course, that arrangements must be made to bring the human observer back again! And return journeys always increase tremendously the take-off masses for interplanetary missions, driving them into fantastic figures. Atomic Power Several papers were concerned with atomic rockets, their working fluids and their cooling problems. One conclusion, by H. J. Kaeppeler (Germany) was that film-cooling could be developed to cool effectively the reaction chambers of atomic rockets which were using a working fluid heated by fissile material. Dr. Sanger (France) explained the advantages of a photon rocket and appeared optimistic concerning its ultimate development for use in space-ships when fusion reactions can be controlled. The organization of the space-flight programme was also discussed in some detail. Cdr. R. C. Truax of the U.S. Navy suggested that it was important that popular support should be obtained and that other ways and means of raising finances for the interplanetary venture should be sought for in the coming years. Dr. W. von Braun outlined his proposals for reducing the cost of a space-flight programme. He was of the opinion that a definite programme must be followed and that space-flight would not be a natural evolution from other work, such as that con cerned with military rockets or rocket-propelled aircraft. By concentrating on a few types of rocket motors which could be employed in clusters in several different projects, both in aero nautics and high-altitude sounding, it would be possible to reduce considerably the cost of the programme. These motors in large clusters could then be employed for the various steps of a space vehicle. In conclusion, the Fourth International Congress seems to have avoided the fanciful schemes for interplanetary projects which have tended to mar the technical sessions during previous years. The concensus of opinion appears to be that the way to space-flight is longer and steeper than many people would like to admit.
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