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Aviation History
1960
1960 - 1958.PDF
458 Round the Stands ... MISSILES and SPACECRAFT ALL three British anti-aircraft guided weapons are continuouslybeing improved, without losing the reliability which stems from years of development. Seaslug, for which the AWA/GEC/Sperryteam were recently able to claim six hits out of six firings, appeared this year in production form with wing tips cropped at the trailingedge to reduce local heating during the boost phase, and with a repacked guidance receiver incorporating a great deal of printedwiring in the sub-units and interconnecting cable forms. Blood- hound, by Bristol Aircraft (airframe), Ferranti (guidance andcontrol, launch control and test gear), AEI (Sting-Ray target- tracking and illuminating radar) and Bristol Siddeley (Thorramjets) is in its Mk 2 form guided by CW (continuous-wave) radar and has new airborne guidance based upon printed circuitryand transistorization, and with inter-wire connections made by wrapped joints. Thunderbird, by English Electric Aviation, hasalso been developed with CW radar, and numerous small modifica- tions improve its mobility and performance in adverse conditions. All three missiles were on display with selected portions of theirinterior revealed for all to see. It is perhaps advisable briefly to outline the essential differences between the pulse form of radaremployed in the guidance systems of Bloodhound Mk 1 and Thunderbird Mk 1 with the CW radars of the Mk 2 weapons(Seaslug is a beam-rider). The pulse systems rely upon the transmission from the groundof a coded signal towards the target. The guidance receiver then has to wait for the signal to bounce off the target and return tothe receiver dish aerial in the nose of the missile, whereupon the direction and timing of the reflected signal may be used in thedetermination of target range and bearing. It is, however, essential to endow the guidance system with the power of discriminatingbetween spurious and real returns, so that it may accept, and home on to, only the true target signal. This must be unerringlylocked on to, and all else must be rejected. Since the time parameters can be measured to within abouta microsecond, accuracy in range is excellent. But any modern bomber is capable of trying to play tricks with the oncomingmissile, either by the brute-force method of jamming the guidance signal or by sending back false returns. The most direct way offoxing the system is to dispense "window," in any of a number of forms all designed to give an echo resembling as closely aspossible that from the target itself. Even existing pulse systems can minimize this effect, but it nevertheless makes the task ofinterception much more difficult. In a CW system the ground target-illuminating radar sends outa continuous emission, so that the missile receiver dish is always in receipt of a reflected signal. In order to produce a continuoussignal on to which the missile can home it is essential to choose waveforms which can be processed and converted to steeringinformation which can be fed to the missile control system. If the target knew enough about the missile guidance system it coulddistort these waveforms by altering their phase or shape, and so throw the missile off-course. To do this the target would have tohave extraordinary intelligence. Any window or chaff discharged from the target normally driftswith the wind, although it may be fired from a small rocket or decoy vehicle. Such countermeasures can be very effective inexactly the right place and at the right time, but normally a CW- homing missile can at once detect that the flight speed of thechaff or other countermeasure is not that of the real target. This discrimination in velocity overcomes the greatest foe of pulsesystems. The teams responsible for both Bloodhound Mk 2 (Bristol andFerranti) and Thunderbird Mk 2 (English Electric Aviation) have been able to build on a vast background of experience with thepulse-guided Mk 1 weapons. In their approach tc the problem of producing the Mk 2 systems they have been able to keep the entirefield of ECM (electronic countermeasures) in the forefront of their minds. Both teams have taken into account all known methods ofdisrupting semi-active radar homing systems, and have done their best to ensure that the Mk 2 missiles will have an answer to all of FLIGHT, 16 September In the dissertation on this page upon how Britain's anti-aircraft weapons are being made ever more lethal and reliable the emphasis is placed upon Bloodhound and Thunderbird. The Seaslug, in contrast, is a beam- riding missile, and its new GEC guidance equipment incorporates a great deal of printed circuitry, as this photograph shows them. Details of trials so far completed are naturally classified,but current experience is that all design goals will be met. Considerations of security still protect almost all portions of theThunderbird 2 weapon system, but certain facts can be stated and more can be deduced. The facts which can be stated arethat the entire weapon system has been designed to be air-portable in current Transport Command aircraft, that the CW radarconfers far greater lethality against hedge-hopping targets and much greater resistance to countermeasures, that the flight per-formance of the missile has been substantially increased and that engineering details have been generally cleaned up. In external configuration Thunderbird 2 differs only slightlyfrom its predecessor (the differences may not be elaborated upon). The launcher has been modified to achieve optimum compatibilitywith the CW guidance, and, of course, completely new ground radars are incorporated. Many portions of the weapon system aremounted not on prime movers as in the Mk 1 system but on pallets, trailers or units like railway containers. The total weightof the system is almost certainly less than that of the Mk 1. English Electric Aviation were prevented from showing anyMk 2 hardware, but they were allowed to cut open a Thunderbird 1 more extensively than heretofore. This year the actuators for thefour control fins were revealed, and seen to be conventional hydraulic devices. The solid-charge a.p.u. was fully sectioned,the warhead was replaced by a telemetry bay and the homing head was devoid of aerials and waveguides, had a spurious dish and thedish-actuation systems hidden from view. One could study the guidance electronics in detail and note the cunning packaging intodiscrete subassemblies for rapid servicing by replacement—a technique continued in the Mk 2 missile. Development of the Bloodhound weapon system, including"directly associated" radars (which doubtless do not include the Metrovick strategic radar), has so far cost approximately £45m.It is noteworthy that Bloodhound has never been subject to criticism in the Civil Appropriation Accounts as have so manyother British weapons. Examination of the cut-open Mk 1 missile was most rewarding in the guidance bay, which, as our dravsjugpublished last October 23 revealed, is divided into three 120° segments respectively occupied by the power supplies (with ahydraulically driven generator), a radar receiver (which processes the target signal into a form suitable for the third sector), and theelectronic part of the control system (which transforms the signal into commands which work the homing dish and the missilewings). Reiterating what may be common knowledge, all semi- active homing missiles carry a radar aerial in the nose whichreceives a target signal (a coded radar transmission sent out from the ground and reflected from the target). This aerial is therebyautomatically locked-on to the target, so that the latter is held exactly on the radar axis of the dish. The control system of themissile then tries to bring the body of the weapon into line with this axis and steers towards a collision point ahead of the target. In the text on page 459 the importance of the ground- conditioning of guided weapons is emphasized. The principle oi operation of the Godfrey SCU-8 system can be clearly seen from this diagram (arrows at left show the flow to and from the missile): A, electric motor; B, gearbox; C, SRM compressor; D, venturi; E, heat exchanger; F, filter; G, brake turbine; H, compressor; J, water separator; K, sensing unit; L, control valve; M, ceramic filter; N, filter; P, orifice plate; Q, main return flow; R, by-pass flow; S, cooling air (a proportion oi which may be dumped overboard, as shown)
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