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Aviation History
1951
1951 - 2008.PDF
FLIGHT, 5 October 1951 449 THE EARTH SATELLITE VEHICLE Summaries of Lectures Before The International Astronautics Congress AS briefly recorded in Flight of September 14th, thesecond International Congress on Astronautics took* place in London last month. The following are summaries of the lectures delivered on that occasion, and we give them as an indication of the large volume of responsible scientific opinion now being devoted to the subject. MR. L. R. SHEPHERD, Ph.D. (technical director, British Inter- planetary Society), spoke, in the introductory paper, on "The Artificial Satellite." He said that a stage had now been reached in the development of rocket propulsion where, with moderate advances in technique, it became possible to produce a manned satellite vehicle and later to proceed to interplanetary flight. It was, in fact, evident that some work was already in progress to develop the satellite vehicle for military purposes, but exclusive military exploitation of space-flight would be deplorable; it was desirable that a project, for purely scientific purposes, should come into being under a civilian authority. The importance of the satellite vehicle or orbital space-station lay mainly in its application to interplanetary flight. It was now generally agreed that the requirements of a vehicle, making a non- refuelling return flight to the Moon or other planets, were too severe to be met by existing methods of propulsion. However, if one could accumulate sufficient fuel and materials in a close orbit about the earth, it would be possible to proceed from there to the surface of the Moon and back. The attainment of a circular orbit at a height of 500 km above the earth's surface would not prove too difficult. A three-step rocket with an exhaust velocity of 3 km/sec, an effective mass-ratio of < 50 and a ratio of initial mass to pay- load of c 300 should be capable of achieving this orbit. This performance was not outside the range of present techni- ques. However, we should need to do better, before proceeding on to the next stage of interplanetary flight, otherwise we should be forced to carry out a "lift" involving hundreds of flights by satellite vehicles before we had accumulated sufficient materials in the orbit. Improvements would be required, both in the perfor- mance of the satellite vehicle and in the subsequent interplanetary vessel in order to bring the project down to a reasonable economic level. Improvements in the satellite vehicle might be achieved with chemical propellants or might lie in the application of nuclear energy. In the case of the inter-orbital vehicle, however, one might go to a new principle, making use of very high exhaust velocities (~ 100 km/sec) at very low accelerations (~io-3g). This could be done in an "ion-rocket," employing a propulsive jet consisting of a beam of electrically accelerated ions. Such a vehicle would not be capable of landing on the surfaces of planets but would be capable of executing large velocity-changes with low mass-ratios, operating exclusively between satellite stations— for example, between an earth-satellite and the tiny Martian moons Deimos and Phobos. Space-flight might, therefore, be carried out in two types of vehicle, viz., satellite vehicles having low exhaust-velocity and high thrust and operating from surface to orbit, and interplanetary space-ships having very high exhaust-velocity but very low acceleration and operating between orbits. Permanent orbiting space-stations might be included in this scheme to act as the junctions between the two types of vehicle, but they would not be essential to the scheme. Space-stations and ion-rockets might draw propellants and other massive materials from bases on small satellites or the asteroids to avoid having to lift these through large gravitational potentials. DR. WERNHER VON BRAUN (Honorary Fellow of the Society), discussed "The Importance of the Satellite Vehicle as a Step Towards Interplanetary Flight." Once the technique of establish- ing satellite rockets in stable orbits around the earth was perfected, he said, these could be used to refuel other rockets. Interplanetary flight would then become possible, even using present chemical propellants. By this means, it would be unnecessary to await the development of nuclear-powered rockets, which were unlikely to appear, in a form competitive with chemical types, for about 25 years. In any case, the danger from their radio-active exhausts would make it desirable to operate them also from initial satellite orbits, rather than from the Earth's surface. A successful satellite rocket would need to have at least three steps. Recovery of the lower steps by parachute, for re-use, was believed to be practicable; the final step could be landed back on earth by fitting it with wings, if its orbital velocity was initially reduced by rocket braking. Conditions of landing speed and aerodynamic heating had been discussed and were acceptable. As an illustration of the use of orbital refuelling technique in interplanetary flight, a hypothetical expedition to land about50 men on Mars was considered, using hydrazine as fuel and nitric acid as oxidant. Forty-six three-step satellite rockets would haulspaceship components and propellants out to the starting orbit, making 950 flights in the process. Each would have a take-offweight of 6,400 tons. After assembly of ten space-ships in the orbit, 70 men would flyto another terminal orbit around Mars. These ten ships would each weigh 3,720 tons initially, would require no streamlining,and use motors of low thrust. About 50 men with supplies would land on Mars, in three small 200-ton rockets. They would abandonone on the surface, and return to the waiting parent space-ships in the remaining two. These, in turn, together with three of thespace-ships, would be abandoned in the Martian orbit, and the 70 men would return to Earth in seven of the space-ships, beingmet in the satellite orbit by sufficient of the first satellite rockets to land them back on the surface. The whole expedition wouldlast two years 239 days, plus about eight months for the prepara- tory supply operation, and would admittedly be expensive, thoughthe expenditure would be small compared with armament budgets. ING. G. VON PIRQUET (Austria) said that the first step towardsthe establishment of a space-station would be the "long-distance rocket" having a maximum range of about one half the Earth'scircumference. Much of this distance would have to be used for braking, as would also be the case with transport rockets to andfrom a space-station. The maximum speed of these long-range rockets would be 6-7 km/sec and considerable problems wouldarise from aerodynamic heating. Later, orbital rockets would be built for practising manoeuvring, refuelling in space, etc. The finalstep would be orbital transport rockets and the construction of the space-station. In the first instance, the hulls of a number of thetransport rockets could be used as a skeleton. The space-station would have a number of uses—as an astro-nomical observatory, for astrophysical spectro-analysis, for radio and television transmission and weather observation. Astro-nautically speaking it would be of inestimable value for refuelling space-ships. The Problem of Descent MR. T. R. F. NONWEILER, B.SC, B.I.S., described the applica-tion of some of his theoretical work (mostly as yet unpublished) to the problem of the descent of an aircraft from a circular orbit.When the aircraft reached the denser regions of the atmosphere, it was assumed that the remainder of the descent was a shallowdive during which the aircraft, supported by the lift of its wings, gradually slowed down. The theoretical work was intended toprovide an estimate of the temperature reached by the aircraft. PROFESSOR LYMAN SPITZER, Jr., of Princeton University Obser-vatory, dealt with interplanetary travel between satellite orbits. While it appeared possible, he said, to project a multi-step rocketinto a close orbit about the Earth, with the help of existing techni- ques, the next step of proceeding from this orbit to the surface ofthe Moon or another planet and back would require prohibitive quantities of conventional propellants. The application of nuclearenergy to heat up a propcllant in a conventional type of rocket did not appear to offer a substantial improvement on the chemicalrocket because of limitations on temperature and power rating, which prevented the achievement of very high exhaust-velocitiesand the high thrusts needed to lift against gravitational fields. In the case of an interplanetary ship operating between a circularorbit around one planet and a similar orbit around another, without making a landing, however, it was possible to employ a new prin-ciple which might effect great economies in the amounts of pro- pellants and materials which must be carried up into the orbits.This principle depended on the fact that such a ship could be propelled by very low thrusts whence it was possible to use highexhaust-velocities without involving excessive power production. The high velocity would result from accelerating a beam ofions in an electric field, power being provided by a nuclear reactor. DIPL. ING. H. KUHME (Stuttgart) spoke of the start, return andlanding of an "optimum satellite step rocket." The aerodynamics of such a rocket were considered and it was pointed out that atvarious times during its operation flight in four different regimes was necessary, namely, subsonic, transonic, supersonic (Machnumber up to 20), and in the condition encountered at great heights, where the mean free path and air molecules was largecompared with the linear dimensions of the rocket. In practice the flight Mach number would simultaneously be high (20 or above).Different laws of flow applied for all four regimes, which compli- cated the aerodynamic design.
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