FR2588373A1 - Infrared proximity fuse for ballistic or self-propelled projectile - Google Patents

Abstract

The subject of the invention is a device for firing a fuse 2 serving for priming a ballistic 1, self-propelled or combination projectile, the device being actuated by infrared radiation emitted by a source and re-radiated by the target. The device is characterised in that the source of infrared radiation is constituted by the body of the projectile naturally emitting an infrared flux. The invention applies without limitation to ballistic, self-propelled or combination projectiles.

Description

 The technical sector of the present invention is that of devices for firing a so-called proximity rocket used for priming a ballistic or self-propelled projectile.

 Rockets which use electromagnetic radiation specially generated on board have been proposed. In these rockets, part of the radiation emitted by the source located in the rocket is re-emitted by the surface of the target and a fraction of this energy returns to the rocket and is processed on board to determine the moment of firing of the military charge.

 We thus know of radio-electric rockets with "Doppler" effect, radio-electric pulse rockets and rockets using infrared radiation.

 Such rockets require an important source of energy to generate a sufficiently strong emission signal to be discerned after reflection on the objective. This energy source is bulky and involves a significant reduction in the military charge of the projectile.

 Because of the significant mechanical stresses to which it is subjected during flight, such a source of energy is delicate to manufacture and therefore very expensive. Another disadvantage of this type of rockets lies in the fact that they have a spatial sensitivity diagram too wide for their tactical use. In addition, they are easily identifiable due to the power of the on-board energy source.

 The present invention overcomes the aforementioned drawbacks by proposing a rocket which does not require an electrical source to generate the sounding signal. In the rocket according to the invention, only the reception of the signal and the firing require a source of energy. However, this source is of low power and due to this semi-passive characteristic, a rocket of this type is only difficult to locate.

The present invention therefore relates to a device for firing a rocket used for starting a self-propelled or mixed ballistic projectile, - the device being actuated by infrared radiation emitted by a source and rebroadcast by the target and comprising - at least one infrared radiation sensor which can be positioned axially
ment or laterally at any angle, - electronic means for processing the signal delivered by the sensor, - means for triggering the firing of said rocket, - and a source of electrical energy, this device being characterized in that
that the source of infrared radiation is formed by the body of the project
tile naturally emitting an infrared flux.

 In fact, a ballistic projectile is an oblong mass charged with a composition adapted to obtain a damaging power: perforating, explosive, incendiary or any other chosen type.

 This mass is driven by a high initial speed and a significant acceleration communicated in the barrel.

 Thus, the walls of the projectile are subjected to a first significant heating which results from the significant mechanical stresses that the shell undergoes during its passage through the barrel tube. In addition, during its flight, the shell reaches a supersonic speed. Its temperature therefore rises significantly due to the kinetic heating due to its penetration into the air.

The two aforementioned overheating therefore contribute to a significant rise in the temperature of the shell and in particular of its outer wall.

 Thus it is generally accepted that a shell whose speed is equal to twice that of sound, sees its temperature increase by about 700C compared to its initial temperature.

 Thus this shell emits a clean radiation discernible compared to the natural emission spectrum of its environment.

 More precisely, it is easy to calculate, in application of "Wien's laws", that a shell of 105 mm, for example, radiates along its longitudinal axis towards the front more than 2.18 Watts per steradian and this in a wavelength band centered on 8.42 voids.

 When approaching a material surface, the infrared energy radiated by the shell is transmitted back to the surface as a function of its reflection coefficient.

 In the wavelength band considered from 5 to 14 microns, the bodies generally have a reflection coefficient of between 0.3 and 0.6.

 A nonlimiting exemplary embodiment is described below with reference to the appended figures.

 Figure I shows a block diagram of a proximity rocket according to the invention.

 FIG. 2 shows a type of embodiment of the electronic chain for processing the signal delivered by the infrared sensor.

 FIG. 3 is a schematic diagram showing the emission of the natural infrared flux from the shell, its reflection by a target 10 and the reception of the flux reflected by the sensor 9.

 Figures 4 and 5 show embodiments of the warhead to compensate for insufficient heating of the latter to produce a discernible infrared flux.

 Such a shell includes a rocket 2 and a military charge 8.

The rocket itself consists of an infrared detector 3, an optical assembly
9, an amplifier stage 4, a differentiator stage 5, a comparator stage 6 and a firing stage 7.

 The functional organization of such a rocket according to the invention is essentially ensured by the infrared detector 3 which delivers a signal to a chain for preparing the firing decision.

 The infrared detector 3 is sensitive in the required spectrum, or in a fraction of this spectrum. In the digital example cited above, the useful spectrum will be chosen in the band between 5 or 9 microns in wavelength.

 The sensitivity field of this infrared detector is equal to 2x as shown in FIG. 1 appended and defined on the basis of a catoptric, diopter or mixed optical assembly 9 associated with the delay detector to optimally adapt the function proximity to the needs of the tactical system embedded in the projectile.

 The signal delivered by the detector 3 is amplified by an amplifier circuit 4 then is transmitted to a differentiating stage 5 which performs its first derivative in order to eliminate the signals of parasitic origin, such as, among others, that the signal attributable to the tilting from the axis of the projectile on the horizon.

 The signal thus delivered by stage 5 and proportional to the first derivative of the signal received by the sensor is then applied to a comparator stage 6 where it is compared with a pre-established reference level.

 This comparator stage may also consist of a trigger in which the comparison is made between the signal and the trigger's own switching threshold.

 As soon as the trigger switches, it sends a control signal to the firing stage 7, either directly or via a power amplifier stage.

 The present invention is applicable without limitation to purely ballistic projectiles but also to self-propelled projectiles or to mixed, semi-ballistic then self-propelled projectiles on their trajectory.

 In some of these cases, the natural heating of the warhead may prove to be insufficient to generate discernible infrared radiation.

Tests have shown that it is possible to compensate for this by providing an artificial auxiliary heating device for the warhead from an exothermic composition 11 suitably chosen, distributed over the surface.
facing or adjacent to the surface of the warhead, as shown in Figures 4 and 5.

 This composition can be constituted, for example, by a mixture of aluminum powder and iron oxide.

 Another embodiment of this heating consists in adding to the warhead a thermal insulator, such as for example an epoxy resin, as a sublayer or as a surface layer so as to reduce the heat exchange between the external surface and the body. of the rocket, the heating thus remaining localized.

 According to an advantageous embodiment, or juxtaposing insulating layers and exothermic layers, arranged either in surface layers, or in underlying layers.

 The device according to the invention can also be used without limitation in combination with other devices of known type and ensuring other complementary functions such as storage, mouth, trajectory security, self-destruction functions or self-neutralization.

Claims (8)

 l - Device for firing a rocket used for firing a projectile, said device being actuated by infrared radiation emitted by a source and re-emitted by the target, and comprising - at least one infrared radiation sensor - means for processing the signal delivered by the sensor, - means for triggering the firing of the rocket, - a source of electrical energy, characterized in that the source of infrared radiation consists of the body of the projectile naturally emitting an infrared flux. 2 - Device according to claim l characterized in that the electronic means for processing the signal delivered by the sensor comprise - means for amplifying said signal, - a differentiating stage whose output signal is proportional to the first derivative of the transmitted signal by the sensor, - means for comparing the output signal of the differentiating stage with respect to a reference level, - means for firing the rocket triggered as soon as the output signal from the differentiating stage is higher said reference level. 3 - Device according to any one of claims l or 2, charac terized in that the radiation sensitivity field is defined by a catoptric, dioptric or mixed optical assembly associated with the detector. 4 - Device according to claim 2, characterized in that the comparison means are constituted by a trigger stage where the comparison is made with respect to the trigger's own switching threshold. 5 - Device according to any one of claims l to 5 characterized in that it comprises a composition of exothermic nature on the surface or underlying the surface of the rocket. 6 - Device according to claim 6, characterized in that the exothermic composition consists of a mixture of iron oxide and aluminum powder. 7 - Device according to any one of claims l to 5 characterized in that it comprises a thermally insulating composition on the surface or underlying the surface of the rocket. 8 - Device according to any one of claims l to 7, characterized in that it comprises insulating layers and juxtaposed exothermic layers, and arranged either in surface layer or in underlying layers.