GB2198815A - Optically programmable projectile and weapon system - Google Patents

Description

i 2198815 Optically Programmable Projectile and weapon system The

invention relates to projectiles of the type containing a programmable firing fuse and a source of electric energy having a sufficiently short activation time for it to deliver to the fuse the power required for -operation thereof after a very short time following firing of the projectile from a weapon.

Document FRA-2 554 069 describes such a projectile whose electric energy source includes a photo- electric converter placed so as to be subjected to an intense light flow following firing of the propulsive charge of the projectile.

When this light flow is due to the combustion of the propulsive charge itself, the source becomes oper- ational after an extremely short time following firing, typically at the end of 125 milliseconds. This delay is less, by several orders of magnitude, than the time interval which occurs between the activation of a traditional pile (thermal pile for example) and the moment when it is able to supply circuits.

Furthermore a device is known (FR-A-2 474 155) for optically programming a projectile and transferring thereto energy projectile. But, immediately before firing of this in automatic weapons, a projectile is already engaged in the barrel at the beginning of firing. It cannot then be programmed for this operation takes place at a location situated upstream of the introduction. And the fact that the projectile is already activated and programmed when it is inserted into the firing chamber is unfavorable, from the point of view of safety of use.

The invention provides an improved projectile of the above-defined type; it is an object of the invention to provide a projectile which is programmable upon firing, even in a weapon having a high firing rate, and is is safe because it is inert until the propulsive charge is fired.

To this end, there is provided a projectile of the above-defined type, characterized in that it has a photosensitive sensor disposed at the rear to receive a coded light signal from the weapon from which it is fired and contains a circuit for decoding signals delivered by the sensor and for programming the fuse responsive to said signals.

There is also provided a weapon system including a weapon for firing projectiles of the above type from a tube, a laser generator mounted as a boresight on the tube so that its beam intersects the trajectory of the projectile in a zone between 5 and 50 m, generally 5 to 30m, beyond the mouth of the tube and programming means which, in response to firing of the propulsive charge of a projectile, controls emission by the laser of a coded programming message in the form of a sequence of light pulses.

It would have been impossible to implement the invention using a projectile having a conventional electric source, such as a triggerable pile, for such a conventional source delivers the required energy after a delay of at least 100 milliseconds. The projectile could only be programmed after this delay and the distance travelled would be such that the light power required would become prohibitive and the risk of jamming excessive.

On the other hand, according to the invention, a laser can be used having a low power and a reduced angular emission field, of about 50 mrad, which corresponds to a diameter of the beam of about 1 m at a distance of 20 m; the programming data represents a sufficiently small amount of information for a time of 20 milli- seconds to be sufficient for transmitting them, which time corresponds to a path of 16 m for a projectile 3 having an initial speed of 800 m/second. Safety is complete since the projectile is inert (its electric source not being operative) until firing and since its fuse is inactive until programming takes place after the projectile left the weapon.

In a particular embodiment, the launching tube of the weapon has means for measuring the speed of the projectile at the outlet. Then high speed electronics -make it possible to take this speed into account for generating the data transmitted to the projectile, for example for adjusting the time delay before self destruction of the_warhead.

The invention will be better understood from the following description of a particular embodiment, given by way of example. The description refers to the accompanying drawings, in which:

- Figure 1 shows schematically one possible arrangement of a programming laser on a barrel tube in a weapon system, according to the invention; Figure 2 is a perspective view showing a possible relative arrangement of the light sensitive sensor carried by the base of the projectile and a photoelectric generator in a projectile according to a particular embodiment of the invention; - Figure 3 is a very schematic sectional fiew showing the distribution of the components of the programming device contained in the projectile of Figure 2; - Figure 4 is a general block diagram showing a construction of the decoding and firing for a projectile according to the invention; possible circuits and - Figure 5 shows a modification of the pro-jectile of Figure 2.

The invention will be described when used in a weapon system including a weapon formed by a gun whose 4 tube 10 is each having projectile jectile 12 sensor 14 nulsed shown in Figure 1 and rounds of ammunition a propulsive charge (not shown) and a 12 (Figures 2 and 3). The base of the pro- carries an axially located light sensitive for receiving light pulses delivered by a laser 16 carried by tube 10. Sensor 14 is surrounded by photovoltaic cells 18 for converting energy from the combustion of the propulsive charge and delivering electric energy required for operating the fuse of the projectile. To increase the lifespan of the photovoltaic cells 18 on ignition, they may typically be protected by a resin layer, a vitrified layer or any other covering which reduces heating. Sensor 14 must be of a type which is not damaged by combustion of the propulsive charge. For that, the sensor may be a photodiode or a phototransistor covered by a light filter whose pass band is centered on the emission wavelength of the laser 16, sufficiently thick for protecting the sensor from the intense heat flow on firing of the propulsive charge. The filter fulfils two functions. It protects the sensor on ignition and it increases the signal-to-noise ratio during transmission of messages from the laser 16.

The projectile 12 further contains a programmable electronic fuse 20 having a capacitor (not shown) for storing electrical energy delivered by cells 18 and a safety device 22 which may for example be a conventional pyrotechnic chain alignment device.

Finally, the projectile contains a warhead (not shown) and a firing igniter 24 which may be combined with an impact sensor so that detonation is caused with a time delay or upon impact.

An arrangement similar to that which has just been described may be used on a shell of any caliber and on a rocket.

The decoding and firing circuits may be as shown 1 in Figure 1 when the parameter to be programmed is the flight time before it becomes operative or before selfdestruction.

These circuits include parts which are Common with those of the device described in detail in document FR-A-2 474 155 to which reference may be made and will therefore only briefly be described.

As mentioned above, the projectile is inert until ignition of its propulsive charge and programming only takes place after it has left tube 10. For this reason, the embodiment illustrated on Figure 4 has no conventional accelerometer (piezoelectric ceramic for example) for defining an initial instant from which time measurement takes place. This function is fulfilled by decoding the programming signals. However, a conventional safety chain may be used.

The photoelectric sensor 14 feeds a conventional shaping amplifier circuit 36 which drives an up-down counting assembly.' The construction of the assembly will depend on the firing range and caliber.

one solution (not shown) consists in programming the projectile by using one word of n bits (n being an integer greater than 1), the transmission taking place bit per bit. Then, a data word will be used conveying a heading and error and/or correction bits in addition to useful data.

on the other hand, the embodiment shown in Figure 4 can be used for high firing rates, usual with medium caliber weapons (35 mm for example). It is then necessary to reduce-the number of laser pulses required for each firing so as to lower the frequency of the pulses to be supplied to a value compatible with the peak light power required (typically several watts).

As shown, programming is carried-out by modul- ating the time interval between two laser pulses emitted successively while the projectile is within a given 6 distance range from start which is also determined.

The assembly shown in Figure 4 includes an AND gate 38 only passing the pulses from sensor 14 during a predetermined time interval after firing. For that, the AND gate 38 receives:

- the output signal the amplifier 36; - the inverted output square wave of a mono stable flip-flop 40 of duration t,(5 ms for example); and from sensor 14, shaped by - the output square wave of a monostable 42, whose "set" duration t 2 is greater than t, (15 ms for example).

The two monostables 40 and 42 are triggered for example by a reset signal RAZ generated responsive to the rise of the voltage charging the storage capacitor.

The output of the AND gate 38 is connected to the clock input of two clocked D-type flip-flops 44 and 46 for respectively detecting the first and the second programming pulses defining the time interval before detonation.

The /Q output of flip-flop 44 is connected to the D input whereas the Q input is connected to an AND gate 48. The second input of gate 48 receives the outut square wave of monostable 42. When the output of gate 48 is at the high level, it enables an AND gate 50 which receives the pulses from a high speed clock 52. With a medium caliber projectile, the initial acceleration of the projectile is very high (about 80,000 g) which is hardly compatible with the mechanical resistance of the crystal generally used in clocks. It will be seen that a very high accuracy of clock 52 is not necessary, as long as its frequency remains stable for a time of a few seconds, that is to say during the time of flight; such stability is easily achieved.

The Q output of the second flip-flop 46 is 1 W 1 7 connected to one of the inputs of an OR gate 54 whose other input receives theinverted output square wave from monostable 42. The output of gate 54, when high, enables an AND gate 56 whose other input receives the output pulses from clock 52, through a divider 58.

In the assembly shown in Figure 4 the time after which self-destruction occurs is determined by the zero crossing of an up-down counter 60 which receives the output pulses from gate 50 on its up counting input, the output pulses from gate 56 on its downcounting input. The pulses from gate 56 are at a much lower frequency so that the time interval before destruction may be a high multiple of the time interval between the two programming laser pulses. The output of the up-down counter 60 controls the firing chain 62.

For safety in the case of faulty operation, the assembly further includes an RS flip-flop 64 and the firing circuit receives the output from counter 60 through an AND gate 66 which is only enabled when the output of flip-flop 64 is high. The set input S of the flip-flop receives the inverted square wave from the output of monostable 40. The reset input R receives a signal from the counter 60 when the contents thereof is equal to a given value, for example half the maximum count of the counter (which is greater than the number corresponding to the maximum time before destruction).

By way of example, for a projectile of medium caliber whose initial speed is 1000 m/s, the following numerical values may be used. The times t, and t2 may be respectively 5 ms and 15 ms. The divide-by-258 divider 58 leads to a maximum actual flight time before explo sion of 2.56 s. The capacity of counter 60 may be 212 1 corresponding to a counting time of 16 ms, substantially greater than the maximum time interval anticipated between the laser pulses. The laser may be controlled so that the laser pulse indicating the beginning of the 0 8 time interval is emitted 6 ms after ignition, corresponding to the appearance of the signal RAZ. The time t 1 of 5 ms is sufficient for avoiding operation disturbances due to parasite flashes and particularly the barrel mouth flash. A programming range of 3 ms would lead to emitting the second pulse 9 ms at maximum after the firing time.

The device operates as follows: on firing, the reset signal causes an upgoing edge to appear at the output of monostables 40 and 42, places the Q outputs of flip-flops 44 and 46 at logic level 0 and resets counter 60 to 0. As long as the square wave of duration t 1 (level 1) lasts, the Q output of flip-flop 64 is at the logic level 0.

At the end of time tl, the S input of flip-flop 64 and the reset input of counter 60 ate reset to zero. The AND gate 38 is enabled and may pass the pulses coming from the shaping amplifier 36. Since the rise time of the laser is extremely short (a few nanoseconds) the arrival time of the pulses may be defined with a high degree of accuracy.

The transmission of the first laser pulse to flip-flop 44 and 46, through the AND gate 38, causes:

- the Q output of flip-flop 42 to pass to level 1, since theD input is connected to the /Q output; - consequently, the Q output of flip-flop 46 to become low (zero level), for the D input of flip-flop 46 is connected to the Q output of flip-flop 44.

The output of gate 48, since it is at the high level, allows counter 60 to be incremented at the rate of clock 52, of 256 kHz for example.

When the second laser pulse is received, it reverses the state of the output of flip-flops 44 and 46. The output of gate 54 becomes high and enables gate 56 through which arrive the pulses for decrementing the counter, at a frequency of 1 kHz in the above example.

k 9 Since the counting, importance flight time.

same clock is used for upcounting and downa lack of accuracy of this clock is of no as long as it remains stable during the When the contents of counter 60 becomes 0, a tripping signal is delivered to the firing circuit 62 through the AND gate 56.

If the time interval t 2 has elapsed without a second laser pulse being received, the downgoing edge of the square wave of monostable 42 interrupts increment ation of the counter and causes decrementation thereof - by disabling gate 48 and enabling gate 54.

Since the maximum content of counter 66 is higher than the number of pulses corresponding to the time t 2, there cannot be overflow of the counter.

The role of the flipflop 64 is two fold. In the case of a programming error, resulting in a time interval between the two pulses less than the minimum flight distance scheduled before firing, the output pulse of counter 60 is emitted when the gate 66 is still dis abled: flip-flop 64 then ensures safety.

If no pulse for incrementing counter 60 is received, flip-flop 64 prevents immediate detonation, which takes place when the condition of the flip-flop is reversed because decrementation leads to a transition on an intermediate output which is connected to the input R (for example the sixth bit, i.e. output 26 in the above case).

It can be seen that programming takes place by sending laser pulses over a travel path of about 9 m and consequently which can be carried out without an excessive light power, thus making it possible to use a semiconductor laser. The fuse remains blind until about 5 ms after firing and from about 15 ms, that is after travelling over about 15 m.

The part of the programming device which is 1 carried by the weapon may be similar to that described in document FR-A-2 474 155 already mentioned, except that there is no transmission and summation of a variable number of pulses but modulation of the time interval between two successive pulses.

The programming device may be completed so as to take into account the initial speed of the projectile, measured for example with two sensors placed at two successive positions in the end part of the launching tube 10.

The device may be coupled to a laser range f inder.

Then, from the distance of the target delivered by the range finder and from the initial speed of the projectile, the flight time before detonation may be determined from a table stored in a memory.

It is possible to control not only the flight time before detonation but also other parameters such as the firing delay after percussion in the case of an impact fuse.

In the embodiment which has just been described, the electric energy source is a capacitor charged by photovoltaic cells 18 which take energy from the combustion of the propulsive charge. In the modification shown in Figure 5, the photovoltaic cells 18a are spaced apart angularly over the side wall of the projectile in shallow pockets and they are placed in electrical series relation. This arrangement makes the cells practically insensitive to directional light such as that from the sun: in the case of such illumination, the non-lighted cells have a very high electrical resistance which limits the current flowing therethrough to a low value. In the case of use on a canon or mortar, all cells are subjected to the barrel mouth flash emitted from a toroidal zone when the projectile leaves the tube.

11 This arrangement has advantages: the photovoltaic cells are protected from the high temperature of the combustion gases of the charge during firing itself. The electric source is only energized when the pro jectile has actually left the tube and can only be so in the case in illumination occuring at the outlet of the tube. The source cannot therefore be energized as a the projectile being left exposed to a 1 source such as the sun.

result of directiona r 11 12 CTAIMS A projectile containing a programmable firing fuse and a source of electric energy having a sufficiently short activation time for it to deliver to the fuse the power required for operation thereof after a very short time following firing of the projectile from a weapon, wherein said projectile carries a photosensitive sensor disposed to receive a coded light signal from the weapon from which it is fired and contains a circuit for decoding signals delivered by the sensor and for programming the fuse responsive to said signals.

2. Projectile according to claim 1, further having photovoltaic cells located on a rear portion thereof for delivering electrical energy to a storage capacitor constituting said source.

3. Projectile according to claim 2, wherein said cells are located around said sensor on a rear surface of the projectile.

4 Projectile according to having lateral longitudinal claim 1, further a plurality of photovoltaic cells located on a surface thereof, angularly distributed around a axis of the projectile and connected in series relation together and with said source which consists of a storage capacitor.

5. Projectile according to any one of claims 1-4, wherein said decoding circuit comprises a up-down counter, a clock and means for detecting light pulses received by said sensor, for incrementing said counter at the rate of said clock during the time interval comprised between two successive ones of said light pulses, then downcounting by the counter at a frequency which is lower than the clock frequency from the time of the second light pulse.

6. A weapon system comprising a projectile according to any one of claims 1-5 and a weapon having a k 13 projectile launching tube, said tube carrying a laser generator mounted as a bore sight on the tube so that its beam intersects the trajectory of the projectile in a zone between 5 and 50m, typically 5 to 30m, beyond the mouth of the tube and said weapon having programming means which, in response to firing of the propulsive charge of the projectile, controls emission by the laser of a coded programming message in the form of a sequence of light pulses.

7. A weapon system according to claim.6, wherein the tube of the weapon has means for measuring the speed of the projectile at the outlet thereof and said programming means take said speed into account for generating the data transmitted to the projectile.

8. Projectile,-- and weapons systems substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.

e Published 1988 PI The Patent Office, State House, 6671 High Holborn, London W01R 4TP. Further cuples may be obtaaned from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Priy-.ted kv Multiplex techniques ltd. St Mary Cray, Kent. Con. 1157,