GB2370342A - Terminally-corrected sub-munition - Google Patents

Abstract

A terminally-corrected sub-munition (TCSM) has coincident centres of pressure and gravity and is provided with a gyroscope 31, 36, 32 which maintains the TSCM in a stable attitude during descent. Explosive charges 13 are mounted around the body of the TCSM so as to react, when fired, through the coincident centres of pressure and gravity to manoeuvre the TCSM laterally during descent. This arrangement obviates the need for weathercocking fins used in hitherto known TCSM's and responsible for rotational instability during manoeuvring.

Description

TpMiNLLY-COPPECTED SUB-MUNITIONS

This invention relates to terminally-corrected sub-munitions (TCSM) and relates particularly to the way in which such devices are manoeuvred during descent.

As is known in the art, terminally-corrected sub-munitions are manoeuvred towards a target by firing charges to apply an impulse in a desired direction of steering. A TCSM often carries a sensor (typically an IR sensor) used for target detection during descent and hitherto, in an attempt to achieve stability in flight, conducive to satisfactory operation of the sensor, the TCSM has been provided with fixed fins which cause it to"weathercock"into a vertical attitude.

A problem associated with an arrangement of this kind is that the centre of gravity and the centre of pressure of the TCSM are spaced from one another axially along its body so that the firing of charges inevitably results in a rotation of the TCSM away from the vertical, thereby disturbing operation of the sensor. This can prove to be unsatisfactory since it is frequently found that the TCSM returns to the vertical only after a time interval which constitutes a prohibitively large fraction of the total available homing time.

It is an object of the invention to provide an improved form of TCSM in which the above-mentioned problems, associated with the manoeuvring of the device are substantially overcome.

According to the invention there is provided a terminally-corrected sub-munition wherein the centre of gravity and the centre of pressure are coincident and a gyroscope is capable of maintaining the sub-munition in a vertical attitude C3 during descent.

In a preferred arrangement the gyroscope may be mounted within the body of the TCSM, and the axis of the gyroscope may be substantially coincident with that of the body.

A sensor, responsive to electromagnetic radiation, especially IR radiation, may be mounted to the body which may be caused to rotate to permit scanning of the sensor. Such rotation may be achieved by one or more fins arranged in helical formation along the outer surface of the body.

In order that the invention may be more readily understood and carried into effect a specific embodiment thereof is now described, by way of example only, by reference to the accompanying drawings of which, Figure 1 shows a schematic, side elevation sectional view of a terminally-corrected sub-munition of the present invention, and Figures 2 and 3 show respectively an external side view of

a portion of the body of the TCSM, and a cross-sectional end view of the body.

In the example described hereinafter, the fins used in hitherto known arrangements for weathercocking are absent and stability during descent of the TCSM is maintained

gyroscopically. In these circumstances, it is found to be relatively simple to arrange that the centres of gravity and pressure are substantially coincident and so manoeuvring, free from rotational instability, can be achieved by firing explosive charges positioned to react through the coincident centres of gravity and pressure.

Referring now to Figure 1, the TCSM has an aerodynamically shaped body which comprises a generally cylindrical casing represented schematically at 10. An IR sensor and associated electronic circuits, designated at 20, are mounted at one end of the casing and IR radiation emanating from the field of view of the sensor is admitted thereto through a window 21. In this example, in addition to the IR sensor and circuits 20 there may also be included a proximity fuzing system, of known kind and a trigger signal is fed to a detonator, associated with a shaped

charge (shown at 32) along signal lines L and via a pair of slip C > rings R.

The gyroscope used to maintain stability during descent is designated generally at 30 in Figure 1 and comprises a turbine blade or alternatively a squib wheel 31 which is mounted to a shaft 33 supported by two sets of bearings 34, 35, for rotation about the longitudinal axis AA of the TCSM. So as to minimise the overall weight of the TCSM the gyroscope, in this example, also includes the shaped charge 32, and an optional flywheel 36 may also be provided to increase the overall weight to an extent commensurate with a preferred rotation speed. The flywheel 36 may be relatively thin in practice especially when formed of

relatively dense materials such as lead or depleted uranium.

It will be appreciated, therefore, that in an arrangement of this kind the only parts of the TCSM which are not incorporated in the gyroscope are the outer casing 10 and the IR sensor and associated circuits 20.

In this example the axis of the gyroscope is coincident with the axis AA of the TCSM (although this need not necessarily be the case) which is thereby caused to assume a vertical attitude during descent. The TCSM is steered so as to home in on a target on the ground by firing selected ones of a plurality of explosive charges, illustrated by way of example only at 13, mounted circumferentially to the outside of the casing 10. As described hereinbefore, these charges are positioned so as to react, when fired, through the coincident centres of gravity and pressure of the TCSM to cause movement thereof (laterally in this case) appropriate for homing in on the target, while ensuring that rotational movement (away from the vertical, in this example) does not occur. In the illustrated example the charges 13 are positioned so as to act only in a direction normal to the axis AA of the TCSM (as indicated by the arrows E).

In practice, the sensor 20 which typically has a response pattern in the form of a thin pencil beam, inclined to the vertical (AA) is scanned in azimuth so as to sweep out a spiral track on the ground during descent. Such scanning could be achieved electronically, but in this example is alternatively and more-cheaply implemented by causing rotation of the TCSM itself. This can be conveniently achieved by way of a number

of fins extending in a helical formation along the outer cylindrical wall of the casing 10 and, if a multistart screw arrangement is used the desired rotation, induced by movement of the TCSM through the air, can be achieved using only relatively shallow fins. The fins are not shown in Figure 1, but are represented at 14 in the side elevation view of the casing 10 shown in Figure 2, and the end sectional view BB shown in Figure 3. In this example, a multistart arrangement having eight screw threads (1-8) is used. The explosive charges 13 (eight in all) used to steer the TCSM during descent are also shown.

In use, a TCSM is typically ejected from the nose section of a missile which is caused to break off from the body of the missile to deploy a parachute (or rotorchute or similar).

After a short time the nose section will have assumed an attitude at or close to vertical and the gyroscope can then be accelerated up to full speed prior to deployment. When, for example, the gyroscope includes a turbine blade (shown at 31 in Figure 1) such acceleration can be achieved by application thereto of a gas jet supplied either by a gas bottle housed"on board"the TCSM or by a common gas bottle housed"off board"in the nose section and used to service a number of TCSM's. If, alternatively, the gyroscope includes a squib wheel then an"on board"drive may be applied thereto. When full rotational speed of the gyroscope has been reached the TCSM is deployed in a vertical attitude by ejection laterally from the nose, the line of action of the lateral thrust being applied so as to act through the coincident centres of gravity and pressure of the TCSM to prevent rotational movement away from the vertical.

It will be appreciated, that although in the above-described example the axis of the gyroscope is assumed to lie along the axis of the TCSM, this need not necessarily be the case and the gyroscope axis could be aligned along a different axis appropriate for maintaining an attitude during descent other than vertical.

Claims (9)

1. A terminally-corrected sub-munition wherein the centre of gravity and the centre of pressure are coincident and a gyroscope is provided to maintain the sub-munition in a selected attitude during descent.

2. A terminally-corrected sub-munition according to Claim 1 wherein the gyroscope is mounted within the body of the sub-munition and the axis of the gyroscope is substantially coincident with the vertical axis of the body.

3. A terminally-corrected sub-munition according to Claim 1 or Claim 2 including a plurality of explosive charges mounted on an external surface of the body of the sub-munition so as to react, when fired, through the coincident centres of gravity and pressure thereby to manoeuvre the sub-munition laterally during descent.

4. A terminally-corrected sub-munition according to any one of Claims 1 to 3 wherein the body of the sub-munition is adapted to rotate about its vertical axis during descent, thereby to scan a sensor which is responsive to electromagnetic radiation and is mounted in the body, relative to a field of view on the ground.

5. A terminally-corrected sub-munition according to Claim 4 wherein the body is provided with a fin arranged to extend helically along the vertical axis of the body, thereby to cause the sub-munition to rotate during descent.

6. A terminally-corrected sub-munition according to Claim 5 including a plurality of fins mounted in a multistart formation on the body.

7. A terminally-corrected sub-munition according to any one of Claims 1 to 6 wherein the gyroscope comprises an explosive charge and means capable of being driven to rotate the gyroscope relative to the body of the sub-munition.

8. A terminally-corrected sub-munition according to Claim 7 wherein a member of relatively dense material is mounted on the explosive charge.

9. A terminally-corrected sub-munition substantially as hereinbefore described by reference to and as illustrated in the accompanying drawing.