GB1597981A

GB1597981A - Method and apparatus for launching and guiding a misile

Info

Publication number: GB1597981A
Application number: GB2112277A
Authority: GB
Original assignee: Eltro GmbH and Co
Current assignee: Eltro GmbH and Co
Priority date: 1976-05-21
Filing date: 1977-05-19
Publication date: 1981-09-16
Also published as: FR2352271B1; FR2352271A1

Description

(54) METHOD AND APPARATUS FOR LAUNCHING AND GUIDING A MISSILE (71) ELTRQ.G.m.b.H. GESELL SCHAFT FUR STRAHLUNG STECHNIK, a German limited liability company, of 6900 Heidelberg 1, Kurpfalzring 106, Federal Republic of Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a method of launching and guiding a missile to a target in conditions of bad visibility or darkness, and in particular to a method whereby a missile guidance system including a day sighting unit for use in normal visibility is adapted for use at night.

In a known method of guiding a missile to a target the missile is launched from a combined launching, guidance and sighting unit and guided by means of a command link including an infrared goniometer in the sighting unit. The goniometer produces signals representative of the angular deviation of the missile from the sighting axis of the sighting unit, which signals are fed to electronic processing circuits which generate course correction signals for transmission to the missile. The missile is thereby caused to follow the axis of the sighting unit, so that aiming of the said axis at the target by pivoting the unit in elevation and azimuth results in the missile being guided onto the target.

This method of guidance is used in the second generation Milan and Hot anti-tank systems. With these pulse-controlled antitank systems, night firing is not possible.

Guidance systems are also known from the first generation Cobra and SS 11 anti-tank missile systems, in which, after the firing the missile, the gunner watches target and missile in the image field of a sight and by means of a control column directs control pulses to the missile via an electronic guidance system and guide wire, and so corrects its course. This requires considerable skill and lengthy training of the gunner in order to home the missile onto the target, since the gunner has to carry out two completely different activities: watch the flight of the missile and, by moving the control column, bring the target and missile images into a coincident relationship. The Cobra and SS 11 systems are likewise unsuitable for night use.

From the article "Eulenauge fir panzerjagd" (Owl's Eyes for Anti-tank Warfare) which appeared in the magazine "Soldat und Technik", July 1974, pp. 385 and 386, a similar method is known wherein, at night, a complete night sighting unit is fitted onto a raiI on the day sighting unit mounted on the weapon. This is a heavy anti-tank weapon which is either more or less a fixed part of a ground installation or is carried by for example a helicopter or tank.

It cannot be considered a portable infantry weapon. Apart from mentioning a pivoting lever operation for changing from day to night time use, there is no reference as to how the other components of the weapon have to be changed.

An object of the invention is to provide a method of rendering usable at night a portable guided missile weapon for infantry use, largely employing an existing day sighting unit or components thereof.

According to this invention, there is provided a method of launching and guiding a missile to a target in conditions of bad visibility or darkness by means of a missile launching and guidance system, which system includes a day sighting unit, an infrared goniometer and a night display device, the goniometer forming part of a missile guidance link; wherein the night display device, operable to produce a heat image of a target and of a launched missile, is connected to the day sighting unit, the said device being prealigned with the day sighting unit only to the extent that they are each oriented to produce respective images of substantially the same part of the target scene; and wherein an operator fires the missile and, observing images of the target and the missile in the night display device, pivots that part of the system containing the goniometer to guide the missile in accordance with the position of the goniometer thereby to bring the said target and missile images into coincidence, the missile image being employed in the night display device as a reference sight mark.

Accurate alignment of the respective viewing axes of the night display device and the day sighting unit is not necessary since the reference sighting mark is a variable position mark derived from outside the night display device. Whether the method of the invention is employed with a night display device which is rigidly mounted on the day sighting unit or one which is located separately, only coarse alignment is required, to ensure that the missile lies within the field of view of the night display device after launching. In the case of the night display device and the day sighting unit being rigidly connected together, this lack of a requirement for accurate alignment means that the interconnecting structure can be of relatively lightweight construction -- an important factor when the weapon is intended for infantry use.

According to another aspect of the invention, a missile launching and guidance system for use in conditions of bad visibility or darkness comprises: a missile launcher; a day, - sighting unit having an infrared oniometer which forms part of a guidance link to control the trajectory of a fired missile in accordance with the orientation of the goniometer axis; and a night display device operable to produce an image of a target and of a launched missile in conditions of bad visibility or darkness, the device being attached to the day sighting unit but mechanically aligned with respect to the goniometer axis only to the extent that the fired missile is positioned within the field of view of the device, so that, in use of the system, the image of the missile produced by the device is used as a reference sight mark, in that the missile is guided towards the target by pivoting the goniometer in such a direction as to bring the missile image into coincidence with the target image. The mounting of the night display device can be so arranged that a coarse adjustment can provide substantially trouble-free night-time use of the weapon even if the night display device has been removed and then re-fitted. Guiding the missile in this manner, in that the gunner swings the complete locating system, including night display unit mounted on it, in azimuth and elevation to bring into coincident relationship the heat images of target and missile provided by the night sighting unit, and so himself brings the missile to home on the target, provides for the Milan weapon the advantage that even at night, the gunner follows the same procedure as during the day when he is tracking a moving target while the missile is in flight.

In accordance with the method of the invention, it is not necessary for the night display unit to be equipped with a technically complicated and expensive electronic sight reticle, because of virtue of the characteristic differences between target image and missile image in the night display device the gunner is able to differentiate between target and missile.

Also in accordance with the invention, the target image may be regarded as a movable sight line or reticle so that the gunner, by swinging the system guides the missile into the movable reticle" thereby automatically controlling the missile onto a coincident course with the target.

The method of the invention furthermore constitutes a saving as compared with the technically complicated process of axially harmonising goniometer and night display unit, and reduces weight and cost.

An advantageous arrangement of the individual component units provides for a day sighting unit containing a goniometer to be connected rigidly with the weapon and, for night time use, also rigidly with a night display device via a pre-aligned support means - e.g. a dove-tail mounting. In this way, the pre-aligned night display device can be adapted to the day unit with an accuracy of one to two mrad, such a type of supporting means rendering any readJustment superfluous. This accuracy of I to 2 mrad is not necessary if, as already mentioned, the image field of the night display unit is sufficiently large that, when the missile has been picked up by the goniometer, it also appears in the image field of the night display device.

The image provided by the night display unit may be perceived through a suitable eyepiece and/or an offset electro-optical eyepiece which may thereby be part of an offset night-observation and sighting device.

For operator convenience this eyepiece may be placed close to the eyepiece of the day sighting unit. Further, firing from a concealed location is possible.

According to a third aspect of the invention a missile launching and guidance system comprises: (i) at least one missile launcher, the or each launcher having a day sighting unit, an infrared goniometer, and an eyepiece for use in conditions of bad visibility of darkness; and (ii) a separate night display unit electrically connected to the or each launcher to transmit a heat image signal to the or each eyepiece; wherein the or each launcher includes means for prealigning the goniometer in accordance with directional information relating to the target generated by the night display unit so that a missile fired from the launcher is imaged in the eyepiece together with the target; and wherein the or each launcher, in use, is pivotable by an operator to guide the respective fired missile in accordance with the orientation of the goniometer, thereby at night or in bad visibility to bring the said missile and target images on the eyepiece into coincidence, the missile image being employed by the operator as a reference sight mark. The heat image information is preferably available in the form of an electrical video signal which can be transmitted over considerable lengths of cable from a heat image camera to the eyepiece or to a monitor. This independency of location between the component parts of the night display device has the advantage that a plurality of individual display units can be associated with one heat image camera. It is also possible to use one "master" heat image reconnaissance unit to monitor a wide angular range in which there may be several targets, and this monitoring range can be displayed on a monitor or electro-optical eyepiece watched by a group leader, the group leader having a cable link and an eyepiece by which he can transmit parts of the image, including selected targets, to the several gunners of the group, simultaneously allocating a target to each gunner by means of information sent with the image information. In this case the heat image camera may be a high-resolution instrument set up at a limited distance from the weapons themselves, each weapon comprising a launching device and day sighting unit, the latter having an electrooptical eyepiece attached to it for night use.

Since the heat image camera and the weapon are in this case not rigidly connected to each other, measures must be taken to ensure that the weapon is so oriented that the missile, after being directed onto the axis of the goniometer, is displayed in the image field of the gunner's night eyepiece together with the target selected by the group leader, so that in the manner described the gunner can guide the projectile onto a collision course with the target by moving the weapon in azimuth and elevation.

Therefore, the rough angular position of the target, for example with respect to North, may be transmitted in code to the weapons connected to the reconnaissance unit, the weapons being secondarily controlled directly or through an interposed indicating means, and being engaged on the click-stop principle into recesses associated with defined angular positions. The coded angle information of the selected target may be transmitted via the cable to the weapon and, by manual or automatic rotation of the weapon, it may be pivoted to the azimuthal target angle by means of a coding disc on the axis of azimuthal rotation, the transmitted signals being compared with those obtained from the coding disc, and the position of angular coincidence being indicated by an illuminated signal in the night eyepiece of the weapon. With both automatic servo controlled orientation and with manual orientation by the gunner, the direction North can be used as a reference direction. Directional information (regarding the bearing of the target) transmitted to a weapon may be indicated digitally, graphically or symbolically in the night monitor or eyepiece of the weapon, symbolic indication being effected by an angular disc indicating the particular deviation from the direction North.

Although images of both the target and the missile are provided in the night display device during the entire process of combat, the gunner can differentiate between the two images by virtue of their characteristic differences in the heat image area.

In accordance with the invention the aiming process may be simplified by providing a target mark for the gunner. To this end the different spectral radiation from target and missile in the heat wavelength range may be used to determine the position of the missile in relation to a reference direction and thereby to use the missile position in the field of view of the night display unit for positioning an electronic sight mark in the heat image of the.scene, the illustration of the missile being established as the centre of the sight mark. This is achieved by generating missile deviation signals which are then used to displace the heat image scene so that the punctiform or disc-shaped representation of the guided missile always appears in the centre of the electronically produced sight mark which is stationary on the screen of the night display device. Since the missile carries a tracer which radiates mainly on a 2 ,um wavelength (in the goniometer spectral range) and since the radiation from the target is mainly in the 10 ym range, it is therefore possible to distinguish between target and missile if suitable spectral filters and optronic sensors are used to isolate target and missile tracer composition radiation and the relevant angular coordinates are formed in separate channels in relation to a system of reference coordinates. It is also possible, in accordance with the invention, to use the fact that, a short time after it has been fired, the missile is homed on the goniometer axis by the guidance system, and that the angular coordinates of the missile (that is to say of the goniometer axis) can be used as a reference axis, the angular deviations of the target in respect of this reference line being used for control purposes. The electronic sight mark superimposed on the heat image of the night display device is controlled by the position of the spot image of the tracer so that the centre of the sight mark represents the position of the missile in the image field. It is up to the gunner, by moving the entire firing system in azimuth and elevation, to control the target image and line it up with the centre of the sight mark.

When the missile is fired, it must be expected that there will be a pronounced halation of the heat image scene by the missile tracer during the initial flight time of the missile, unless additional measures are adopted. This halation can be avoided if the aforementioned spectral filter for separating tracer composition and target radiation is so constructed that the detector of the night display heat image unit only receives radiation having a wavelength greater than 3.5 ym and if the radiation of wavelength less than 3.5 ,um is sent to the sensor for determining the missile position (sight mark follow-up).

If, advantageously, a common optical system is used for both channels, then the sensors for the 2 ,am range and the 10 ym range may be installed in a common vessel and spectral isolation achieved in that the relevant spectral filters are disposed in the Dewar vessel immediately in front of the sensor arrangements. This enables the same scanning arrangement to be used to produce the heat image in the 10 m range and to determine the position of the tracer in the 2 ,um range.

In order to make it easy for the gunner to track, it may be expedient for the sight mark to be shown in the centre of the heat image present in the night display device eyepiece.

This can be achieved by controlling x andy deviation voltages applied to the cathode ray tube in response to the signals from the tracer sensor. In this way the entire heat image of the scene is displaced, while the electronic sight mark remains stationary and always occupies the same position in the eyepiece. In this case, it is also possible for the sight mark to be applied permanently to the tube, or to be stationed in the image plane of the optical viewing system.

On the basis of what is described above, whereby the sensor arrangement for heat image generation (10 ,um) and the sensor arrangement for missile position determination are accomodated in a single Dewar vessel, then it is possible, via the sensor for missile position determination, to determine the deviation of the missile in relation to a fixed sight line of the heat image unit and for these deviation signals, after being classified as x- and y-deviation signals, to be fed into the electronic guidance circuits of the rocket firing system and, via a guide wire, to be used for automatic secondary control of the missile.

Since the night combat range is reduced to about half the day time range, the accuracy of deviation measurement is adequate to home the missile on its target. The night display device may have a fixed sight mark and/or a permanently adjusted sight mark projector and, as he does in daytime, the gunner keeps the target aligned on the centre of the sight mark so that tracking of the sight mark becomes unnecessary. This last-described system has the advantage that the night location system operates independently of the day location system and has only a cable linking it to the electronic guidance, through which deviation signals for secondary control of the missile are passed.

Embodiments of the invention will now be described by way of example, with reference to the drawings, in which: Figure 1 is a block diagram of three units: a weapon, a day sighting unit and a night display device; Figure 2 is a detail section showing a dove-tail mounting as an example of a rigid connection between the day and night units; Figures 2a and 2b are diagrams showing the change from day-time to night-time operation; Figure 3 shows a remote night observation and sighting device connected to two launches; Figure 3a is an enlarged view of an anglegraduated disc for indicating on the individual night display units of Fig. 2 information provided by the observation and sighting device; Figure 4 is a view in two parts showing the use of an apparatus in accordance with the invention; Figure 5 comprises three graphs showing the wavelength interdependency of a) missile tracer radiation and target radiation; b) detectivity D*re, of PbS and CdHgTe infra-red sensors; and c) bandwidth of a filter in a heat image unit, for filtering out tracer radiation; Figure 6 is a diagrammatic view of the heat image on the night display device showing an electronic sight reticle, the image of a scene, a missile, and a target; Figure 7a is a diagram showing the night sighting unit with a common optical system for receiving a heat image and for the missile tracer sensor, as well as a common receiving vessel for the heat image and the tracer sensor; Figure 7b is a diagram showing the night display device with a focal input objective for both channels, and separation of heat image and tracer radiation by a spectral filter, with two separate focusing objectives and sensor assemblies for heat image and tracer radiation; Figure 8 comprises five diagrams showing embodiments of sensors: a) g serial arrangement of PbS elements b) a quadrant sensor c) V-positioned rod sensors d) double-V-rod sensors e) a cross/rod sensor for rotating wedge scanning; Figure 9 comprises two diagrams showing embodiments of a combined heat image/tracer sensor: a) a double row arrangement of PbS and CdHgTe sensor elements; b) a combination of a CdHgTe row arrangement with PbS rod cells for determining tracer position in the short and long ranges of a missile; Figure 10 is a diagram of an automatic sight reticle control system using the tracer position sensor; Figure 11 is a diagram of a night display device with provision for internal deviation co-ordinate formation and co-ordinate conversion to generate guidance signals to guide the missile; Figure 12 is a diagrammatic view of the heat image scene produced in the apparatus of Fig. 10 or Fig. 11 when the weapon is aimed at a target.

Referring to the drawings, a portable missile launcher incorporating the invention is indicated as a whole by 1' (Figure 1) which also shows that a day sighting unit 1 incorporates an infrared goniometer 2 and an eye-piece 3, the latter having a reticle 4 (Fig. 2a). The launcher 1' includes a firing tube 5 to which the unit 1 is connected rigidly and also to a night display device 6 which operates on the heat image principle and which has an eyepiece 3'. The doubleheaded arrow 7 indicates azimuthal adjustment and the double-headed arrow 8 elevational adjustment. The day sighting unit 1 and the night display device 6 are oriented so that an image 9' of the fired missile 9 to be guided appears in the image field of monitor 11, 11' together with a target image 10 (Figs. 2a and 2b). In this case, a gunner, by tracking with the apparatus 1', can bring target image and fired missile image together in coincident relation, the guidance method used providing that once the missile has been automatically homed onto the day sighting axis, the latter becomes an adjustable aiming axis shown on the night display device as a missile image point, and has to be made coincident with the target image by a tracking operation so that the missile 9 is then automatically homed onto the target.

The possibility of an overshoot is obviated by mechanical or hydraulic damping elements (not shown) in the day sighting unit.

The night display device 6 is not connected to the day sighting unit 1, which is adjusted for day-time use, until the change is to be made from day to night or bad visibility operation. Figure 2a shows the image depicted in the reticle 4 of the day sighting unit when the gunner is sighting the target 10, the infrared goniometer 2 (Fig. 1) being exactly aligned with the reticle of the day-time channel, the gunner having only to keep the target in the centre of the reticle, as shown.

The night display device is mounted by a rigid support, e.g. the dove-tail mounting 12 shown in Figure 2, on the day sighting unit and is thereby coarsely adjusted to the aiming and goniometer axes of the day sighting unit. By virtue of this coarse preadjustment, there is no accurately defined spatial relationship between the reticle of the day sighting unit, Figure 2a, and the heat image of the night display device. Figure b, and therefore the reticle centre does not in general coincide with the target heat image. In the method of the invention, there is generated in the image field of an electro-optical eyepiece 3' a heat image of the target 10, the resolution of which is adequate for identification. The fired missile 9 appears as an intense image spot 9' (Fig. 2b) in the image field and thus can be readily distinguished from the target image 10. After the missile 9 has been picked up by the tracker 2 of the day unit and brought into the axis thereof, the image spot 9' represents a variable sighting mark on the night unit. All the gunner now has to do is to move the image spot 9' and the target image 10 coincidence, as indicated by the arrow 13. The low axial stability as between the day and night units, occasioned by the necessarily lightweight construction of the portable launcher 1', is compensated by this method. Thus despite the relative inaccuracy of aiming, it is possible without undue difficulty to bring the missile onto a coincident course with the target and to achieve at night that probability of scoring hits already associated with day-time use.

Figure 4 shows that an offset electrooptical eyepiece 14 of the night display device 6 opens up a number of possibilities of application in portable guided weapon systems. In addition to the separate location of the night unit 6 and its eyepiece 14 mounted on the day sighting unit 1, which makes possible night firing from a concealed, protected position, it is possible as shown in Figure 3 for a plurality of day sighting units 1, each with an integrated electro-optical eyepiece 14, to be linked by cables 16 to form one assembly of units with a common night observation and sighting device 15. The image field of the device 15 will be made large to permit of reconnaissance and guidance of the two weapons 1' used in this embodiment. For example, if, as shown, three tanks appear simultaneously on the monitor screen 17 of the device 15 and if the assembly has two launchers 1', then the group leader operating the assembly can, if the device 15 is suitably constructed, allocate to for example the relevant launcher 1' the two tanks marked in broken circles 18, at the same time transmitting to the respective display eyepieces 14 the information in the scene within the circles 18. With the allocation of targets to the gunners, it is possible at the same time to transmit a rough preliminary instruction as to azimuth direction in respect of the direction North, via the cables 16, insofar as there is provision for automatic coarse aiming of the launchers, or there is a coarse display of the position of the target on the monitors 19 of the launchers 1' which makes it possible for the relevant gunner roughly to line up his launcher 1' on the target allocated by the group leader. Referring to Figure 3a, an angle-coding disc 22 is adjusted to the direction North and, by adjusting a launcher 1' on a tripod 21, a correlation is established between binary coded angular position given by the device 15 and the angular position signal of the launcher. The distance between the individual launchers and the device 15 is in practice limited to 5 to 10 m, by virtue of the weight of the cable and in order to allow verbal communication between the members of the group.

Referring now to Figures 5 to 11, Figure 5 compares the black body radiation spectra from a rocket tracer composition and a target (Fig. Sa), the detectivity D* spectra of selected detector materials PbS, (for detecting tracer composition radiation) and CdHgTe (for detecting target radiation) (Fig. Sb), and the tranmission spectrum of a spectral filter (Fig. Sc). Figure Sa shows that the tracer composition radiation 111, as black body radiation, with a black body temperature of 15000 K, has its maximum radiation at 1.5 to 2.7 ym wavelength and, in the region of the so-called 3rd infra-red window, from 7.5 to 14 clam, has fallen to below 10% of the maximum value, while the inherent heat radiation 112 of a moderately heated target vehicle, at 300 K, has its maximum radiation in this window and has dropped almost to zero at 2 ym wavelength.

Upon comparison of Figure 5a with the relative detectivity spectra 113 and 114 of the PbS sensor the heat image sensor respectively in Figure 5b, it is evident that filtering out of the radiation from the target is not necessary for the PbS sensor. In the case of the heat image (CdHgTe) sensor, it is advisable to use a high-pass filter 115 (Fig.

5c) to remove intense radiation from the tracer composition, that is to remove radiation of wavelength less than for example, 3.5 vm, so as to avoid halation of the heat image. A high pass filter with a cutoff wavelength in the range 3 to 6 ,um as shown in Fig. Sc is suitable for this purpose.

Figure 6 diagrammatically shows the heat image scene appearing to the gunner after he has fired the missile and after automatic orientation of an electronic reticle 116 onto the infrared goniometer axis at the eyepiece 3 (Fig. 1), with the missile 117 in the middle of the electronic reticle 116, and a target 118.

The arrow 119 indicates that by pivoting the weapon, the gunner has to line up the reticle 116 on the target 118 to home the missile 117 onto it. In a manner not shown, the scene depicted is so shifted that the reticle 116 and the missile 117 remain oriented in the centre of the field of vision and, in the scene shown, the rest of the scene will be displaced upwardly and to the right until the target is in the centre of the reticle.

Figure 7a diagr characteristic 115 shown in Figure 5c, long wave radiation 126 between 7.5 and 14 ssm passing through the filter without attenuation and being displayed on heat image sensor 127 by an image forming objective 122', while short wave radiation 128 (less than 3.5 ,am) from the tracer composition is reflected through 90" and displayed on a tracer sensor 129 via an image-forming objective 122". Further signal processing is not shown in Figures 7a and 7b.

Figure 8 shows various embodiments of tracer sensor for determining the position of the missile in relation to a reference axis of the night sighting unit. Fig. 8a shows a simple type of sensor in the form of a row of n sensors 130 which, by means of the oscillatory mirror 123 (Fig. 7), are periodically pivoted in azimuth over the field of vision with the image of the tracer, the elevation image field angle being predetermined by the angular extension of the row of sensors in the field of vision of the objective 122". The position of the.

tracer is revealed in the x-direction from the time tL at which the row of sensors is pivoted while the position in the y-direction is determined by the number of the sensor which receives the signal from the tracer. In Figure 8b a quadrant receiver 131 is disposed outside the focal plane of the infrared objective 122" and therefore the tracer spot is depicted as a disc 132, the radiation from which is arranged in proportion over the four quadrants I to IV of the quadrant receiver 131, and concentrically when the tracer is on the sight line and eccentrically when there is a deviation from the sight line. By comparing the sums and differences of the output signals of oppositely disposed quadrants, it is possible to determine the deviation with sufficient accuracy.

In a method known from infrared tracking techniques and shown in Figure 8c, two rod-shaped sensors 133 are located at an angle 5 in respect of each other, which angle is between 30 and 609, their disposition being symmetrical in relation to the centre point 134 of the field of vision and in relation to the axis of symmetry 135.

The scanning movement of the oscillatory mirror 123 (Fig. 7) moves a spot 136 representing the tracer in the directions illustrated by the arrow 137 over the field of view of the infrared objective, and as it passes over the rod cells 133, two brief, steep pulses are generated. It will be appreciated that if the speed of passage of the image spot is shown, by measuring the time differential At between the two pulses, the angular position of the tracer in respect of the centre point 134 of the sensor can be determined with sufficient accuracy in the x- and y-directions. In Figure 8c, the tracer sensor has two field of vision angles, a rough area with rod sensors 133' for the initial phase of missile guidance and a fine area with rod sensors 133 for the final phase when the missile is at a greater distance, and having a smaller field of vision angle. The same effect can be achieved with a single pair of rod sensors and with an afocal optical system 121 with a focal length change-over. The sensor of Figure 8c has the disadvantage that if the axis of oscillation of the mirror 123 becomes tilted, errors occur in determining the x- andy-co- ordinates. This tilting error can be compensated if, according to Figure 8d, the axis of symmetry 135 is marked by a further rod sensor 138. The tilt is zero when At=At2; at Att t2, it is possible from the time difference At1-At2=At12 to deduce the angle of tilt between oscillating axis and axis of symmetry 135 and 138 respectively and by. transforming the co-ordinates, to ascertain arithmetically the exact angle values in respect of the x, yco-ordinate system. In the method shown in Figure 8e, four rod sensors are associated at right-angles to form a cross 139. The field of view is scanned via a rotating optically transparent rotating wedge which is disposed either in the parallel ray path in front of the objective 122 (Fig. 7a) or in the convergent ray path of the objective 122" in front of the sensor 129 (Fig. 7b) and rotates with the optical axis as its axis of rotation. It is known that in the image plane a spot 136 on a concentric circle 140 rotates at the speed of rotation of the rotating wedge when the depicted spot target is on the optical axis of the system and that the image spot 136 moves on an eccentric circle 141 when there is deviation from the optical axis. By measuring the time difference between the electrical pulses generated at the rod cells by the rotating spot, again the x- and y- angular deviations can be determined. With this method, it is necessary for spectral division to occur, in a manner not shown, in front of the oscillatory mirror 123 and for this to scan only the rays for the heat image channel.

Figures 9a and 9b show the arrangement of combined heat image/tracer sensor 120 (Fig. 7a) with a wide band optical system 121, 122 for both spectral ranges and one common Dewar vessel 120. Figure 9a shows two rows 142 and 143 of m and n individual elements respectively, combined on one carrier plate 144, the row 142 being selected for the tracer composition spectral range of 2 ,um wavelength and the row 143 for heat image range from 7.5 to 12.5 Nm. To avoid halation from the tracer, there is on the sensor surface an interference filter 145 which reflects the short wave radiation in the manner described with reference to Fig.

5. In Figure 9b, rod cells 133 for the tracer sensor and serial sensors 143 for depicting a heat image are combined on a carrier plate 144. The interference filter 145 described avoids excessive radiation striking the heat image sensor. However, the latter can be used for the tracer sensor as a symmetry sensor 138 as described above and as shown in Figure 8d.

Figure 10 diagrammatically shows apparatus for the production of missile tracer co-ordinates in relation to a reference direction, generation of a sight mark on the illuminated screen of the electro-optical eyepiece, and displacement of the heat image in relation to the sight mark. The radiation 146 striking the infrared objective 121 from the left and emanating from the target, the target environment and the missile tracer are diverted by an oscillatory mirror 123 and, in a spectral divider 125, divided into a long wave portion 126 to depict the heat image and a short wave portion 128 to establish the missile deviation co-oridnates. The long wave portion 126 is depicted via the image forming objective 122' on the row 127 of n individual sensors. The electrical signals occurring parallel to the outputs of n sensors are raised in n preamplifiers 146 to a signal level which can be processed and converted in the electronic multiplexer 147 into a series signal which, via a video amplifier 148, is used to modulate the brilliance of the electron beam of a cathode ray tube (CRT) 149. The multiplexer 147 passes a signal to the y deviation amplifier 150 for the CRT to achieve ay deflection of the electron beam of the CRT synchronous with the electronic interrogation of the preamplifier outputs by the multiplexer 147 in order to display the heat image. To generate the x-deflection voltage, the angular position of the oscillatory mirror 123 at any given time is converted in known manner in the angular position transmitter 151 into an electrical signal which is fed via an x-deflection amplifier 152 to the xdeflection electrode of the CRT. In the electronic sight mark generator 153, an electronic sight mark is produced, the sight mark signals generated periodically at the image sequence requency are superimposed on the video signal and are likewise used to control the brightness of the electron beam of the CRT. In this respect, the groups of signal pulses of the sight mark are, in a manner not illustrated, so synchronised with the angular position of the oscillatory mirror 123 that the electronic sight mark is given a fixed position on the screen 154 of the CRT. In operation, the point of intersection of the sight reticle is brought to the middle of the screen 154. In the static case, when the missile is not fired and no radiation from a tracer is being received, it will coincide with the optical axis 146 of the afocal optical system; however, if need be, any other relationship may be selected between the optical axis 146 and the intersection point of the sight mark or reticle. In the static state, when the tracer sensor 129 is not receiving any signals, then in order to initiate the combat process, the target will be retained in the centre of the sight mark. Shortly after firing the missile and when its tracer has been picked up in the image field of the night display unit 6, (Fig. 1), the sensor 129 will receive radiation emitted by the tracer composition via the spectral divider 125 and the image forming objective 122 and will establish the deviation of the missile from the optical axis 146. In the co-ordinate converter 155, this angular deviation will be converted into a x- and y-angle deviation in respect of a cartesian system of reference co-ordinates. The x-deviation signal is brought, in the x-deviation amplifier 156 to an angle-proportional value and is passed via the x-deviation amplifier 152 to the xdeviation electrode of the CRT, the direction and amplitude of the superimposed correction signal being such that the measured x-deviation of the image point representing the tracer composition in respect of the sight mark is compensated in the x-direction. The procedure is the same with the y-deviation signal which is brought by the deviation amplifier 157 to an angleproportional value and fed via the ydeviation amplifier 150 to the y-deviation electrode of the CRT and a displacement of the heat image scene in the y-direction is used to compensate for the y-deviation.

During the entire flight, the missile should be depicted in the centre of the sight mark and in the event of a deviation of the target's position from the position of the missile, the target will be depicted outside it and must be homed on to the centre of the sight mark by orientation of the guidance system.

Thus, the apparatus of Figure 10 produces an image scene which represents an improvement over the image scene of Fig. 2b. In Fig. 2b the missile image, which acts as a sighting mark, appears off-centre due to the misalignment of the night display device central axis and the goniometer axis.

However, with the apparatus of Fig. 10, the missile image, or rather the electronically generated sight mark which is coincident with the missile image, appears at the centre of the heat image scene thereby compensating for the mechanical misalignment.

Figure 11 diagrammatically shows a night display unit 6 (Fig. 1) having a sensor arrangement according to Figure 7a in which a common Dewar vessel 157 is used for both heat image and tracer sensors, the latter sensor being used as an infrared goniometer for an autonomous night location device operating independently of the day location system. With this arrangement, which can also be used in the system shown in Figure 7b, the signal from the tracer sensor is, in the co-ordinates converter 155, converted into x- and y-deviation signals of the missile from the homing line 146 of the night display unit 15 and converted in the xdeviation amplifier 156 and the y-deviation amplifier 157 into electrical signals proportional to the angle of deviation, these electrical signals then being fed by an interface electronic system 158 and a plugin connection 159 into the electronic guidance unit 160 which also has a plug-in connection 161 for the day location system 1 (Fig. 1). In the guidance system, the deviation signals are converted to control pulses for guiding the missile 9 onto a collision course with the target.

Figure 12 shows the heat image of the night scene with the cross 116 on the sight reticle and the target 118 in the centre of the sight mark. The firing system with a night location device is operated in the same way as when the day location system is being used.

WHAT WE CLAIM IS: 1. A method of launching and guiding a missile to a target in conditions of bad visibility or darkness by means of a missile launching and guidance system, which system includes a day sighting unit, an infrared goniometer and a night display device, the goniometer forming part of a missile guidance link; wherein the night display device, operable to produce a heat image of a target, and of a launched missile, is connected to the day sighting unit, the said device being prealigned with the day sighting unit only to the extent that they are each oriented to produce respective images of substantially the same part of the target scene; and wherein an operator fires the missile and, observing images of the target and the missile in the night display device, pivots that part of the system containing the goniometer to guide the missile in accordance with the position of the goniometer thereby to bring the said target and missile images into coincidence, the missile image being employed in the night display device as a reference sight mark.

2. A method according to claim 1 wherein the missile image, as displayed in the night display device, comprises a variable position reticle, the position of the reticle relative to the scene imaged in the device being automatically controlled in response to the position of the missile as sensed by the device.

3. A method according to claim 1 or claim 2, wherein the scene imaged in the night display device is automatically displaced so that the missile image is substantially in the centre of the displayed field of vision.

4. A method according to any preceding claim, wherein the goniometer forms part of the day sighting unit.

5. A method according to claim 4, wherein the night display device includes a heat image sensor and a display eyepiece, and is attachable to the day sighting unit by means of a rigid mechanical connection, so that the operator pivots the assembly of the day sighting unit and the night display device when bringing the target and missile images into coincidence.

6. A method according to any of the claims 1 to 4, wherein an electrical signal representative of the approximate angular position of a target relative to a reference direction is transmitted from a remote night sighting unit forming part of the night display device via an electrical cable to an electro-optical eyepiece mounted on that part of the system containing the goniometer.

7. A missile launching and guidance system comprising: (i) at least one missile launcher, the or each launcher having a day sighting unit, an infrared goniometer and an eyepiece for use in conditions of bad visibility or darkness and (ii) a separate night display unit electrically connected to the or each launcher to transmit a heat image signal to the or each eyepiece; wherein the or each launcher includes means for prealigning the goniometer in accordance with directional information relating to the target generated by the night display unit so that a missile fired from the launcher is imaged in the eyepiece together with the target; and wherein the or each launcher, in use, is pivotable by an operator to guide the respective fired missile in accordance with the orientation of the goniometer, thereby at night or in bad visibility to bring the said missile and target images on the eyepiece, into coincidence, the missile image being employed by the operator as a reference sight mark.

8. A system according to claim 7, wherein the directional information relating to a target is transmitted from the night display unit to the respective launcher via the electrical connection in the form of a coded directional signal, the or each launcher

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. compensating for the mechanical misalignment. Figure 11 diagrammatically shows a night display unit 6 (Fig. 1) having a sensor arrangement according to Figure 7a in which a common Dewar vessel 157 is used for both heat image and tracer sensors, the latter sensor being used as an infrared goniometer for an autonomous night location device operating independently of the day location system. With this arrangement, which can also be used in the system shown in Figure 7b, the signal from the tracer sensor is, in the co-ordinates converter 155, converted into x- and y-deviation signals of the missile from the homing line 146 of the night display unit 15 and converted in the xdeviation amplifier 156 and the y-deviation amplifier 157 into electrical signals proportional to the angle of deviation, these electrical signals then being fed by an interface electronic system 158 and a plugin connection 159 into the electronic guidance unit 160 which also has a plug-in connection 161 for the day location system 1 (Fig. 1). In the guidance system, the deviation signals are converted to control pulses for guiding the missile 9 onto a collision course with the target. Figure 12 shows the heat image of the night scene with the cross 116 on the sight reticle and the target 118 in the centre of the sight mark. The firing system with a night location device is operated in the same way as when the day location system is being used. WHAT WE CLAIM IS:

1. A method of launching and guiding a missile to a target in conditions of bad visibility or darkness by means of a missile launching and guidance system, which system includes a day sighting unit, an infrared goniometer and a night display device, the goniometer forming part of a missile guidance link; wherein the night display device, operable to produce a heat image of a target, and of a launched missile, is connected to the day sighting unit, the said device being prealigned with the day sighting unit only to the extent that they are each oriented to produce respective images of substantially the same part of the target scene; and wherein an operator fires the missile and, observing images of the target and the missile in the night display device, pivots that part of the system containing the goniometer to guide the missile in accordance with the position of the goniometer thereby to bring the said target and missile images into coincidence, the missile image being employed in the night display device as a reference sight mark.

including means for receiving the direction signal to enable the prealignment of the launcher to be performed.

9. A system according to claim 8 wherein the or each launcher is pivotable in azimuth and includes a coding disc centred on the axis of rotation, which disc forms part of a device operable to produce an electrical azimuth signal representative of the azimuthal orientation of the launcher, the or each launcher further including a comparator for comparing the azimuth signal with the respective directional signal transmitted from the night display device.

10. A system according to claim 9, wherein the or each launcher includes a servo-controlled pivoting device coupled to the comparator to orient the launcher automatically in accordance with the directional information.

11. A system according to claim 8 or claim 9, wherein the or each launcher is rotatably mounted on a base and is biassed towards a plurality of discrete angular positions by a click-stop device.

12. A system according to any of claims 8 to 11, wherein the or each eyepiece includes an indicator connected to be activated when the orientation of the respective launcher corresponds to the directional information.

13. A system according to any of claims 8 to 12, wherein the or each eyepiece includes a display device for displaying the relevant directional information digitally, graphically, or symbolically in the margin of the eyepiece field of vision.

14. A system according to claim 12 wherein the indicator is operable to cause an illuminated symbol to be displayed over or adjacent an angle graduated scale to indicate the relevant deviation of the launcher from the direction North.

15: A method according to claim 1, wherein the different spectral characteristics of the radiation from the target and the missile in the heat radiation range are used to determine the position of the missile in relation to a reference direction.

16. A method according to claim 15, wherein a deviation signal corresponding to the said position is used to control the position of an electronically generated sight mark relative to the heat image of the scene produced in the night display device, the missile being established as the centre of the sight mark, and the deviation signal being further used constantly to displace the heat image scene so that a punctiform or discshaped representation of the missile appears in the centre of the electronically generated sight mark which appears stationary on the illuminated screen of a cathode ray tube in the night display device.

17. A method according to claim 15 or claim 16, wherein a spectral divider in the night display device is used to separate radiation emitted by the missile from that emitted by the target.

18. A method according to claim 17 wherein the spectral divider reflects radiation of less than 3.5 Nm wavelength arriving from an afocal infra-red objective and transmits heat radiation of between 7.5 ssm and 14 ,um wavelength without substantial attenuation, or vice versa.

19. A method according to claim 15, wherein the position of the missile in relation to a reference direction is determined in the night display device by using a tracer radiation sensor which is sensitive to radiation from a tracer mounted on the missile, the tracer radiation having different spectral characteristics from heat radiation from the target, and wherein a deviation signal representative of the deviation of the missile from a reference optical axis in the night display device is obtained in response to the sensor output, which signal is then used to control the trajectory of the missile so as to bring the missile onto the said reference axis.

20. A method according to claim 19, wherein the tracer radiation sensor comprises four sensor rods arranged in a cruciform relationship, radiation from the tracer being directed to the sensor via rotating wedge prism.

21. A missile launching and guidance system for use in conditions of bad visibility of darkness, comprising: a missile launcher; a day sighting unit having an infrared goniometer which forms part of a guidance link to control the trajectory of a fired missile in accordance with the orientation of the goniometer axis; and a night display device operable to produce an image of a target and of a launched missile in conditions of bad visibility or darkness, the device being attached to the day sighting unit but mechanically aligned with respect to the goniometer axis only to the extent that the fired missile is positioned within the field of view of the device, so that, in use of the system, the image of the missile produced by the device is used as a reference sight mark, in that the missile is guided towards the target by pivoting the goniometer in such a direction as to bring the missile image into coincidence with the target image.

22. A system according to claim 21, in the form of a portable rigid assembly comprising the launcher, the day sighting unit and the goniometer, the night display device being removably mounted on the day sighting unit.

23. A system according to claim 22, wherein the night display device is attached to the day sighting unit by a dovetail mounting.

24. A system according to any of claims 21 to 23, wherein the night display device includes an electronic circuit to vary continuously the position of a sight reticle forming part of the display produced by the device in relation to the image of the target scene, the reticle position being controlled in response to the position of the missile as sensed by the device so that the reticle coincides with the missile image.

25. A system according to claim 24, wherein the reticle is electronically generated.

26. A system according to claim 24 or claim 25, wherein the circuit is operable to vary continuously the position of the target scene in the display in such a manner that the missile image remains fixed at the centre of the display.

27. A system according to any of claims 21 to 26, wherein the day sighting unit has an eyepiece for use in daylight conditions, and the night display device has an eyepiece for use in conditions of bad visibility or darkness mounted adjacent the day sighting unit eyepiece.

28. A system according to any of claims 21 to 27, wherein the night display device has (i) a broadband input objective with a focal length which is substantially constant over the wavelength range of from 1.5 to 14 ,um, and (ii) two sensors arranged to receive radiation from the target scene via the objective, one of the sensors being a missile tracer radiation sensor and the other sensor being a target radiation sensor.

29. A system according to claim 28 wherein the tracer radiation sensor is sensitive to radiation in the wavelength range of from 1.5 to 2.7 4m and the target radiation sensor is sensitive to radiation in the wavelength range of from 7.5 to 14 clam.

30. A system according to claim 28 and claim 29, wherein the two sensors are contained in a common Dewar vessel.

31. A system according to any of claims 28 to 30, wherein the target radiation sensor is masked by a filter which reflects tracer radiation of a wavelength less than 3.5 ,um and transmits radiation of a wavelength in the range of from 7.5 to 14 clam.

32. A system according to claim 28 or claim 29, wherein the night display device includes two Dewar vessels, one containing the tracer radiation sensor and the other containing the target radiation sensor.

33. A system according to claim 32, including a spectral divider arranged to direct tracer radiation in the wavelength range of from 1.5 to 2.7 ,um to the tracer radiation sensor, and target radiation in the wavelength range of from 7.5 to 14 ,um to the target radiation sensor.

34. A system according to any of claims 28 to 33, wherein the tracer radiation sensor is a quadrant receiver.

35. A system according to any of claims 28 to 33, wherein the tracer radiation sensor is a rod sensor comprising one or more pairs of sensor rods, the rods of the or each pair being at an angle of 300 to 600 with respect to each other.

36. A system according to claim 35 wherein the tracer radiation sensor includes two pairs of sensor rods, one pair being used as a symmetry sensor for correcting tilting errors between an oscillating mirror axis and the sensor axis.

37. A system according to any of claims 28 to 33, wherein the night display device includes a rotatable wedge prism mounted between the objective and the tracer radiation sensor to cause the missile tracer image to oscillate about a central optical axis, and wherein the tracer radiation sensor is a rod sensor comprising a plurality of sensor rods arranged in a cruciform relationship centred on the said axis.

38. A method of launching and guiding a missile to a target, the method being substantially as herein described with reference to the drawings.

39. A missile launching and guidance system constructed and arranged substantially as herein described and shown in the drawings.