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Aviation History
1961
1961 - 0938.PDF
38 FLIGHT, 13 July 1961 From the paper "Engineering Aspects of Satellites and their Launching Rockets" by Mr G. K. C. Pardoe of de Havil'tand Aircraft, this diagram indicates the reliability of various rocket launch vehicles, expressed as the percentage of suc- cess in placing payloads in orbit Missiles and Spaceflight... 1957 1938 1959 (vi) If radar guidance is used, the very low acceleration permitsvery long smoothing times both during climb and cut-off so that radar guidance becomes very accurate and early correction of orbitis possible. If a high perigee is required for the orbit for either the thrust-coast-thrust system or the continuous-thrust system, it is clear that during the injection phase the whole of the perigee altitude must be gained.Since for the sake of efficiency the climb angle must be small this inevitably means that: (a) the end stage or stages must possess orbital or very-near-orbital velocity at the beginning of the climb, and (b) the point of final injection must be a long way round theEarth from the point of launch. For low orbits (300 n. miles) it can be shown that, down to 3,000miles range, there is little change in rocket performance required; but for 5,000 n. miles circular orbits a sharp rise in rocket perfor-mance is required if the coasting phase is reduced below one-half of a revolution round the Earth.This has two major effects; any guidance or tracking stations must cover a much larger flight path if no uncovered periods are tobe left, and final cut-off has to be observed from an area remote from launch; and secondly, if a continuous-thrust system is used,extremely low values of motor thrust are necessary. The use of a very low thrust in the continuous thrust system has a very attrac-tive feature in that it permits an even larger radar smoothing time than for injection into low orbits; thus even though the radar rangeis very much greater for the high-perigee orbits than for the low ones, the required angular accuracy of the radar used is virtuallythe same in order to achieve roughly constant velocity accuracy for the two classes of orbits. Though the major portion of the speed needed for injecting asatellite into orbit must be given outside the atmosphere, in order to avoid too high aerodynamic heating effects, there are some potentialadvantages in using an aeroplane-like device for the first stage. The most obvious of these is the possibility of easier recovery andre-use of the first stage by making the first stage an aeroplane which can land in the normal way. Employment of present-day aircraft is possible in this role,though the performance gains are not striking. An aircraft, say, with a high subsonic speed of M = 0.8, will only reduce the appa-rent velocity requirement of the rocket stages by 1,500 - 2,500 ft/sec. This reduction is larger than the actual velocity of the aeroplanestage by virtue of the altitude of the aeroplane at rocket launch (taken to be 40,000ft) with the consequential increase in specificimpulse and the avoidance of much of the aerodynamic drag losses in the rocket stage. The reduction in weight of the rocket stages required to be carriedby the aeroplane as compared with an all-rocket vehicle depends a lot on the number of stages assumed and to some extent on orbitdesired. If the aeroplane is counted as one stage, for the subsonic aircraft quoted above the total rocket weight may be about thesame or even increased, but a 30-50 per cent rocket-weight decrease may be obtained by keeping the same number of rocket stages asbefore. An increase in the aircraft speed to M = 5 will materially improve matters, the weight reduction for an equal number ofrocket stages being of the order of 65-75 per cent. The economies involved in the use of aircraft first stages need a lot more study. In Engineering Aspects of Satellites and their Launching Rockets,Mr G. K. C. Pardoe of de Havilland Aircraft emphasized that most of these aspects were interdependent in a complex manner andsome were far more advanced in technique than others. At present, he said, certain aspects seemed out of proportion, one examplebeing the cost of producing a very modest amount of electrical power for a satellite. In a three-stage vehicle which might costabout one million pounds including the satellite, the solar cells accounted for "almost one-eighth of this sum."There would thus seem to be a very good case, Mr Pardoe continued, for the development of more-efficient and cheaper elec-trical power sources for use in space. Low-weight high-reliability electronics, particularly that concerned with radio communication,would play a vital part in the evolution of space equipment for satellites and space probes and to some degree in the developmentof launching vehicles. Control-system engineering would also be of importance in bothvehicle and satellite design, particularly in the case of communica- tion satellites. Here long life and high reliability coupled with lowweight and power requirements were essential in a system destined to play a paramount part in world communication. This wouldundoubtedly be the first direct use of space by the world at large and would also be the first example of how this new space tech-nology would yield large financial returns to support and justify the enormous investment which would be necessary to establishsuch new engineering techniques. Details of experiments to be carried in the first Scout-launchedjoint US/UK satellite were given in four papers at the Convention: The Use of Probing Electrodes in the Study of the Ionosphere by DrR. L. F. Boyd of University College, London; Measurements of Solar Radiation by Dr K. A. Pounds of Leicester University; X-raySpectrometer for Scout Satellite by J. Ackroyd, R. T. Evans and P. Walker of Bristol Aircraft; and Cosmic Rav Measurements in theUK Scout I Satellite by Prof H. Elliott, Dr. J. J. Quenby, D. W. Mayne and A. C. Durney. Other papers included Radio Tracking of Artificial Earth Satel-lites by Dr B. G. Pressey of the Radio Research Station; Navigation Satellites with particular reference to Radio Observation by W. A.Johnson of the RAE, Farnborough; The Australian 210ft Radio Telescope by Dr E. G. Bowen and J. P. Wilde of CSIRO, Sydney;Radar Measurements on the Planet Venus by L. R. Mailing and Dr S. W. Golomb of JPL; Radiation and other Environmental Effectson Satellites by D R. Innes of Marconi; Advantages of Attitude Stabilization and Station-keeping in Communications Satellite Orbitsby Dr W. F. Hilton and B. Steward of Hawker Siddeley Aviation: and Proposal for an Active Communication Satellite System basedon Inclined Elliptic Orbits by B. Buss and J. R. Millburn of Hawker Siddeley Aviation. GERMANY AGREES TO ANGLO-FRENCH PLAN (continued from page 36) tons can be put into a near-300 n.m. orbit, but half a ton can beplaced in a 7,000-mile circle. "As expected, the optimum third stage weight with liquidhydrogen/oxygen motor increases (due to the fact that this stage is now more efficient and should therefore be used to provide a largerfraction of the total velocity increment). The optimum third-stage weight (including payload) will be in the region of 7,OOO-8,OOOlb. "Due to the increased third-stage weight it has been found thatthe third-stage thrusts should also be increased somewhat, compared with the case of the low-energy third stage."It is clear that the capabilities of the Blue Streak satellite- launching vehicle will cover an enormously wide variety of possibleradio-satellite requirements; but, if it is found necessary to use it, still further development potential exists by converting the secondstage to liquid hydrogen, first by itself and later with two stages above Blue Streak."
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