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Aviation History
1957
1957 - 1793.PDF
6 December 1957 883 being no air drag to confer what is called "weathercock stability";but the only factors which matter to the trajectory are the thrust- line of the engine, the weight and the overall acceleration. Somewhere along its journey the missile will require no furtherthrust, and the feed to the engine must then be cut off with very great accuracy (a delay of as little as one second may cause thetarget to be overshot by three "miles or more). The job of the biggest part of the missile, the tankage and motor used for pro-pulsion, is now completed. Accordingly it may well be discarded, and the remaining propellants—along with the airframe and motor—allowed to burn up as a result of the intense aerodynamic heating exparienced by the body when it descends into the atmosphere—say, at a height from 100 down to 50 miles. No way of preventing this intense heating or slowing the missile down has yet beenfound; forward-facing rockets have been exhaustively investigated, as have large air brakes or parachutes, along with cooling systemswhereby tons of water are forced through the nose; but each new suggestion has proved either unworkable or practicable only at theexpense of ruining the performance of the weapon. We are, therefore, left with a warhead moving at some 15,000m.p.h. along a gently climbing trajectory, right outside the last vestiges of any real atmosphere. On it goes, slowing down verygently and climbing less and less steeply, until finally it reaches the zenith of its trajectory—technically called the apogee—800miles from the nearest point of the Earth's surface beneath it. It seems almost infinitely lonely, a tiny package made by humanhands and bearing wiring diagrams and instructions intelligible to its operators; were it to contain a sentient being he would feelutterly remote from the Earth, despite his knowledge that he would reach it in a mere fifteen minutes' time. Should our imagined ICBM have been fired in anger the targetarea may well be expecting to receive it, and super-powerful radars will detect the intruder when it still has over one thousand milesto go. But the warhead has quite a hard enough task ahead without interference from defensive devices. Already, it is beginning tocurve down again towards the earth, maintaining its enormous speed in a manner which for ponderous persistence is quitefrightening. In fact it actually moves faster and faster, and there is nothing at hand to stop it—just infinite miles of outer space.Soon the space becomes less empty; increasing amounts of dust and gas are encountered and the resulting drag slowly swings there-entry body round until it is falling nose-first, like a bomb. And in a few seconds the skin becomes warm, and then hot, and thenglows a dull red. The red becomes brighter, and the whole structure would very soon vaporize—were it not for two factors,each the result of literally millions of hours of work by an army of scientists: the nose is blunt and very smooth, and the wholeassembly is very carefully constructed from unusual materials. It may seem strange to have a blunt nose on the fastest thingmade by man, but the American National Advisory Committee for Aeronautics, and Air. H. Julian Allen in particular, discovered thatwhen a device such as a ballistic-missile nose-cone re-enters the atmosphere it can withstand the arduous mechanical and thermalconditions better if its nose is given a fair radius. This shape rejects more than 90 per cent of the heat back into the surroundingair. Nevertheless, the nose-cone and what is called the re-entry GAS TUV&OPUMP THRUST STXUCTUKE T.C. ACTUATOR OX/D/ZSM THRUST CHAMB£/l EXHAUST over Left, checking possible human error on the Convair Atlas ICBM fuel- transfer test console. Right, steel platforms in an Atlas test facility at Convair's San Diego plant. Seen are Mortimer Rosenbaum, chief engineer, and J. R. Dempsey, manager of Convair-Astronautics. body (housing the warhead) still get very hot, and their construc-tion makes greater demands than does that of any piloted aircraft. Moreover, lie plummeting object leaves behind it a trail of ionizedgas, readily detectable by radar and yet completely enveloping the nose-cone itself, further complicating the proceedings. When the nose-cone is down to 50,000ft it has less than threeseconds to go. Final arrival on target is something of an anti- climax, unless the warhead happens to be armed; and in any case,one big bang is much like another. W. T. G. A thrust unit for a Chrysler Redstone of the U.S. Army, suspended from a 25-ton crane, is lowered into place to be joined to the forepart of the missile. e, a rocket engine assembly employing separately-driven propellant pumps—o drawing by the Aerojet-General Corporation. Right, an M >s en route from San Diego to Patrick A.F.B.—a picture which, on c/o ,e study, gives more cause for reflection than any other in this issue.
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