a device for automatically tracking

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    1960 IRE TRANSACTIONS ON SPACE ELECTRONICS AND TELEMEETRY 67A Device for Automatically Tracking the Roll Positionof a Missile*

    RICHARD WV. LOWRIEt

    Summary Many short range missiles are guided in angle or images will remain stationary on the focal plane. If therange by optical means. S in ce t he se m is si le s a re usually caused images are aligned on a radial of the focal plane as shownto roll in flight for stability reasons, some type of roll position images A and on a r of th e a plan as shreference device is necessary. The only type of roll reference in lmages A and C of Fig. 4 or 5, then a scan disc withdevice in us e is a gyro, although various horizon scanners, Doppler, two slits 1800 apart, as shown in Fig. 4, will cross bothand optical methods have been considered. images (A and C) simultaneously. However, when theThis paper describes an optical method of roll reference which missile rolls out of phase with the optics, as shown in Fig.utilizes the relative positions of two flares of different color attached 5(b) the scan disc slits do no t cross the images simul-to the rear of the missile. Since the roll position is known at thelaunch point, commands to the missile are commutated at th e taneously. This time difference is a measure of the rolllaunch point rather than in th e missile as is necessary when a position tracking error. It is necessary that various colorgyro or other missile-borne roll reference device is used. Thus, filters and inverting prisms be used as described below.the roll tracker removes from the missile two subsystems (gyro The unit is aimed at the missile during flight with aand commutator) while adding two components (two colored flares . tolerance in angle of 50 or more. Manual or automaticangle tracking may be used. The missile must have two mIHE problem of roll orientation measurement of flares which ar e mounted on opposite tail fins, and are ofmissiles is almost always solved by installing a roll two colors, such as red and blue. Of course other colorsreference gyro in the missile, together with a com- and other methods of generating the light may be used.mand commutator to allow th e directional commands to The essential parts of the roll tracker ar e shown in Fig.actuate th e proper control surfaces as th e missile rolls. 1 and ar e as follows:For missiles which ar e controlled from the launch pointby an observer or other optical device, the following 1) A lens assembly together with color filters. Thismethod permits th e gyro and commutator to be removed assembly is automatically rotated at the missile rollfrom th e missile and preeommutated commands tc be rate by a servomotor. A commutator is attached togenerated at the launch point. The only items required the rotating assembly to allow directional commandsin th e missile fo r roll reference purposes ar e two colored to be coded into the proper transmitter channels.flares. Thus th e cost and complexity of expendable hard- 2) A scanning disc and two photo detectors.

    ware in the missile is kept to a minimum. The tracker 3) Circuits to analyze the photo detector outputs andunit is installed at the launch point and can easily be control the servomotor.contained in a cylinder 6 inches X 18 inches long. Trackingto ranges of several kilometers with accuracies of a few Rotatingdegrees in roll angle are attainable. Directionat Assemblv PhotocellsThe method is based on th e resolution of two flares Commands Scanner Circuitryor lights on the missile by means of a rotating, scanningtype optical system at or near th e launch point. A scanning type detector is used to improve accuracy and make theaiming of th e unit quite uncritical. Continuous, un- Flares I -M~~~~~~~~~~~~~~~~~~ tambiguous, and automatic roll position is obtained. TransmitterTemporary loss of visibility such as small clouds need notbe serious since the unit ha s enough inertia to maintainroll reference for short periods. The unit will acquire androll track a missile automatically and without roll am- The function of the lenses is simply to form images ofbiguity at any time it is visible. the missile flares at th e plane of th e scanning disc. FourThe essence of the operation of the device is the genera- identical lens are used to generate four images 900 aparttion of four equal images of the missile at a focal plane. on the disc and equidistant from the center of the disc,These images ar e equally spaced about the centerline of wvhen the roll tracker is pointing directly at the lightthe optical axis (see Fig. 3). As the missile rolls, each source (see Fig. 3).0One lens could also be usedwxith mirrorsimnage rolls in the same manner. to form four images. In this case, the lens need not beIf the optics also roll at the same rate as the images, the attached to the rotating assembly. A zoom lens would bemore practical if only one lens were used. Four lenses wvere* Manuscript received by the PGSET, Februarvr 3 1960. used in the present system for simplicity of the optics.t The Martin Co., Orlando, Fla v?Two of the images (900 apart, not 1800) must be in-

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    68 IRE TRANSACTIONS ON SPACE ELECTRONICS AND TELEMETRY JuneMirror Lens Half Silveredverted, while two ar e normal. Also, any two of the adjacent Mlirrorimages must be filtered through one color filter while th e Tht\o IRed FiterFour Four Invertinother two images are filtered through the other color. Lenses Filters PrismsEach image becomes a re d or blue spot. Thus, at th e focal \

    plane (the plane of the scanning disc) four images of the Lightmissile flares are formed. Due to th e color filters, however, -- 1

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    1960 Fowler: A Six-Channel High-Frequency Telemetry ystem 695(a), 5(b), and 5(c) show, for three conditions of mnissile By noting which color, red or blue, comes first, theposition and lens assembly position, th e relative outputs ambiguity is resolved. Also, the difference in time betweenfrom the re d and blue photocells. Note that pulses A and the outputs from B and D is proportional to th e image size,C ar e simultaneous when th e tracker roll position corre- which in turn is proportional to the range of the missile.sponds to the missile roll position. The time difference Range information can be extracted directly from thebetween pulses A and C is used in conventional circuitry time between B and D outputs, knowing th e flare separa-to control the lens assembly rotation motor. One possible tion on the missile. However, to measure range accurately,circuit is shown in Fig. 6. Only two relays are used, which the roll tracker must be properly tracking the missile.have a fast close and slow dropout characteristic as a result Range error will be somewhat dependent on roll trackingof th e large charging capacitors C. When either photocell error.receives a pulse, its relay closes for about 50 msec alnd locks Since the A and C images are scanned simultaneously,out th e other relay. This action is repeated at th e repetition object motion or jitter of th e image has no effect onl rollr at e of the scan disc, so long as one photocell is energized accuracy. Since a slit is used as the photosensitive area,before th e other. The relays are used directly to control th e radial position of th e image on th e disc is not critical,th e direction of rotation of th e lens assembly motor. Other which means that accurate pointing of the unit at therefinements can be added to make th e relay actuiation time missile is not required.proportional to th e time difference between pulses into th e To avoid flare masking by th e rocket motor, it isphotocells. A similar circuit may be used to check for 1800 necessary to select an optical or infrared frequency outsideambiguity. th e major rocket energy band. If commands during burninlgTo avoid 1800 ambiguity, images B and D ar e necessary. ar e not necessary, this requirement vanishes.

    Six-ChannelHigh-FrequencyTelemetry System*T. C. R. S. FOWLERt

    Summary-A frequency-multiplex FM AM system is described be usable together with an RAE 24-channel sender,1 thewhich provides six continuous channels vi a which waveforms with t tfrequency components in the approximate band 10 cps to 10 kc 46m band sang aomm misiles aertiasthemay be simultaneously telemetered; extension of the frequency 456-mc band, sharing a common missile aerial system.coverage to include th e band 0-10 cps is achieved by the us e of A six-channel frequency-multiplex FM AM system wascommutated reference levels. A radio frequency in the 465-mcs selected for development. Work proceeded, with encourag-band and subcarrier frequencies between 25 0 and 50 0 kc are ing results, and by the autumn of 1952 gr-ound-to-groundused. A short historical introduction is followed by description transmission tests had been made, and the system wa sof the system and of units of the flight and ground equipment,and details of operational results. Future uses of the system are ready for flight trials.discussed and methods of increasing the useful range are suggested. The first two flight tests were carried out at Aberporth,Wales, in December, 1952, with successful results, and theI. INTRODUCTION practical use of the system there started in 1953; the useof the system at Woomera, Australia, began in 19505.r OWARDS the end of 1950 investigations were Although it incorporates various improvements and addi-started at Filton, England into the design of a tions, thepresent Bristol HF telemetrysystem isbasicallysystem to telemeter simultaneously, from a missile in similar to the system as first tested in 1952.flight, a number of vibration waveforms in the frequency Asatcpedthsyem asbnuedfraweband 50-6000 cps, with an over-all amplitude accuracy of10 per cent and a range suficient to cover th e boostvaitofelmryppssindiintohergnlone of vibration measurement. Examples are rotation ratephase-say at least two miles. The flight sender was to 1 Telemetry as an ai d to guided weapons research, British*Reprinted from J. Brit. IRE, vol. 19, pp . 493-507; August, 1959. XCommunications and Etectronlics vol. 3, pp. 130-133; March, 1956.t Bristol Aircraft Ltd., Guided Weapons Engrg. Dept., Filton Also, W. M. Rae, The Airborne Sender for 24-Channel Telemetry.Bristol, Eng. To be published.)AlultIXDoM1a1UfIX Ra