GB2281258A - Disposal of explosive ordnance - Google Patents

Abstract

Explosive ordnance is disposed of by detonating a hollow charge device (12) adjacent the ordnance at a stand off distance (22) (Fig. 3B not shown) such that the diameter of the gas jet (18) impacting the ordnance is greater than its minimum (21). This ensures that a shock wave of sufficient velocity over sufficient diameter to detonate the explosive ordnance is generated. The device is carried to a mine by a submersible 5 guided by sonar 13 and camera 8. <IMAGE>

Description

DISPOSAL OF EXPLOSIVE ORDNANCE This invention relates to the disposal of explosive ordnance and, in particular, to the disposal of submerged mines.

Currently disposal of submerged mines involves deploying a remote controlled underwater vehicle or a diver to place an explosive charge adjacent the mine and then remotely detonating the explosive charge when the vehicle or diver is at a safe distance. The disadvantage of this method is the comparatively high risk involved to the vehicle or diver and the slowness of operation particularly where a large number of mines need to be disposed of. An alternative method is to use an expendable remotely controlled submersible, incorporating the explosive charge, to guide the submersible towards the mine and detonate the charge when it is in contact with it.

A problem, however, with both these methods is that due to the highly insensitive nature of some explosive fills used in explosive devices current blast explosive charges will fail to detonate them. As a result an alternative detonation inducing method is required.

It has been proposed to use 'shaped charge' (also known as 'hollow charge' or 'directed energy') devices in place of conventional explosives in the disposal of mines and directing their explosive energy to penetrate the warhead section of the mine in order to induce detonation. Conventionally such devices are designed for piercing armour plating and in order to do this are designed to produce the narrowest possible jet stream, typically several mm wide, at the highest possible velocity, typically several km/s, containing a large quantity of vapourised metal. It has been discovered that in practice the use of such devices often results in a hole being pierced through the explosive device without actually detonating it. The hole is so small that the remaining mine despite the damage remains fully operational and so still presents a danger.

It is an object of the present invention to overcome the problems associated with previous methods and provide a compact, reliable means of disposing of ordnance explosive devices whatever their composition.

This invention provides a method of disposal of explosive ordnance comprising detonating a shaped charge device at a pre-determined distance from the explosive ordnance in which the shaped charge device and pre-determined distance are selected such that the jet stream of particles striking the explosive has a greater diameter than the minimum diameter attainable such that a shock wave is induced in the explosive ordnance which propogates at or greater than the detonation velocity and whose extent exceeds the critical diameter of the explosive so as to detonate the ordnance.

Advantageously the shaped charge device is circular in cross-section and the pre-determined distance is approximately one half of a diameter of the shaped charge device.

A method of performing the invention will now be described by way of example only with reference to the accompanying diagrammatic figures in which: Figure 1 is a schematic representation of a method of disposal of a submerged mine in accordance with the invention, Figure 2 shows the remote controlled submersible used in Figure 1 in more detail, Figure 3A is a schematic representation of the 'shaped charge' or 'directed energy' warhead, used by the submersible of Figure 2, and, Figure 3B is an explanatory diagram, identical parts having the same reference numerals throughout.

Referring to Figure 1, there is shown a submerged mine 1 resting on the sea bed 2. A vessel 4 deploys a remote controlled submersible 5 which is propelled by steerable motors 6, powered from internal batteries (not shown). The remote controlled submersible is shown in more detail in Figure 2. The submersible 5 travels towards the mine 1. The bearing and velocity of the submersible 5 is controlled by control signals which are transmitted from the vessel 4 via an optical fibre 3 connected to the ship 4 and dispensed from a dispenser 7 mounted on the submersible 5. Velocity and directional control of the submersible is achieved by altering the power supply to the motors 6.

A video camera 8 and a short range sonar transducer 13 are mounted behind a transparent streamlined nose fairing 9 at the front of the sumbersible 5 and transmit optical and sonar images showing the view ahead of the submersible 5 to the vessel 4 via the optical fibre 3. The submersible 5 is also fitted with a sonar transponder (not shown). The locations of the submersible 5 and mine 1 are continuously tracked by a combination of acoustic positioning system (APS) data and a mine location sonar 10 (not shown) mounted on the vessel 4, the transmitted sound waves from the sonars 10 and 13 and the transponder are indicated by lines 11, 14 and 15 respectively An operative on the vessel uses the sonar data and the images from the camera 8 to guide the submersible 5 towards the mine 1.

The submersible 5 carries a 'shaped charge', or 'directed energy', warhead 12 behind the camera 8 and sonar 13 and pointed forwards along the boresight of the camera 8.

In operation the operator guides the submersible 5 into a position where the warhead section of the mine 1 is centred in the field of view of the camera 8 at a predetermined distance from the submersible 5.

A schematic representation of the warhead 12 is shown in Figure 2. Referring to Figure 2a there is shown a cylindrical container 24 which has one end closed. The container 24 contains an explosive 25 in which there is a hemi-spherical or conical indent 26 coaxial with the cylinder 12 extending into the explosive 25 from the open end of the container 24. This indent 26 is lined by a liner 16 of suitable metal, such as aluminium or copper. The warhead is protected by a cover 17.

Figure 2b shows a schematic representation of the behaviour of the warhead 12 upon detonation. A jet 18 of high energy, high velocity gas containing a high proportion of metal atoms from the liner 16 is ejected from the container 12 coaxial with the indent 26. The distance remote from the mine 1 at which the warhead is detonated is referred to as the 'stand off' distance. Conventionally, in armour piercing applications, the highest possible energy density per unit area is desired, requiring as small a jet diameter as possible. The stand off distance 19 to provide this has been found to be an optimum at several times the container's diameter 20 so that the jet 18 strikes the target at the point 21 where its diameter is a minimum. The exact ratio between stand off distance and diameter varies with the precise design of the warhead.

For the disposal of mines or other explosive ordnance this has been found to be ineffective in detonating some of the explosives used which can be in these devices such as some types of PBX.

It has been realised that the reason why a conventionally employed shaped charge may fail to detonate a modern inert explosive is that although the energy density within the gas jet is very high it only strikes a narrow tube of the target explosive within the mine 1. The condition for initiating a sustained detonation in an explosive is the generation of a shock wave of a certain velocity at or greater than the speed of sound in the explosive and over a certain diameter (referred to as the critical diameter). The detonation velocity and critical diameter vary with type of explosive.

Although the velocity of a shaped charged jet is high enough to produce a shockwave of sufficient velocity to detonate even insensitive explosives the jet can be too narrow to fulfil the critical diameter requirement of insensitive modem explosives.

It has been realised that the volume of explosive affected by the shaped charge can be increased to achieve the critical diameter by using a specially designed shaped charge generating a much broader jet than a conventional armour piercing shaped charge, but this would involve the expense of designing and manufacturing such a specialist device. It is more convenient to use a conventional armour piercing shaped charge and to detonate it at a stand off distance at which the jet is not fully focussed and so has a larger diameter and affects a larger volume of the target explosive.It has been found that when the stand off distance is reduced so that the diameter of the explosive target affected by the jet is equal to or exceeds the critical diameter the energy density coupled into the target explosive from the jet is still high enough to generate a shockwave velocity in excess of the detonation velocity.

Accordingly the stand off distance 19 is tailored to give a jet 18 capable of inducing within the explosive in the mine a shock wave at or greater than the detonation velocity with an extent equal to or greater than the critical diameter of the explosive within the mine, and where a conventional armour piercing warhead is employed the stand off distance 22 is reduced to about 1/2 the diameter 20 for maximum effectiveness. This"nearfield application is quite the opposite of previously proposed uses of 'directed energy' or 'hollow charge' weapons.

This results in the jet 18 striking the ordnance at point 23 where it has a much greater cross-sectional area than at the point 21 at the conventional stand off distance.

Where a specifically designed shaped charge device is used the device would be designed to generate a gas jet 18 with a wide enough minimum diameter that the device would be effective at this minimum diameter. However this minimum diameter will be greater than the minimum diameter attainable for the device if it had been designed for maximum armour penetration.

It will be realised that since armour penetration is not important in ordnance disposal the metal line 15 of the shaped charge may be omitted if convenient.

It should be understood that the present invention is not limited to the disposal of mines and that it is equally applicable to the general disposal of explosive ordnance. For example in the disposal of land based explosive devices the submersible could be replaced by a suitable remotely controlled vehicle.

Claims (4)

1. A method of disposal of explosive ordnance comprising detonating a shaped charge device at a pre-determined distance from the explosive ordnance in which the shaped charge device and pre-determined distance are selected such that the jet stream of particles striking the explosive has a greater diameter than the minimum diameter attainable such that a shock wave is induced in the explosive ordnance which propogates at or greater than the detonation velocity and whose extent exceeds the critical diameter of the explosive so as to detonate the ordnance.

2. A method according to claim 1 in which the shaped device generates a jet stream having a minimum diameter at a specific distance and the pre determined distance is less than this specific distance.

3. A method according to claim 2 in which the shaped device has a circular cross section and the pre-determined distance is approximately one half of a diameter of the shaped charge device.

4. A method of disposal of explosive ordnance substantially as shown in or as described with reference to the accompanying drawings.