GB2183057A

GB2183057A - Target acquisition systems

Info

Publication number: GB2183057A
Application number: GB08308833A
Authority: GB
Inventors: Ronald George Guttridge
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1983-03-30
Filing date: 1983-03-30
Publication date: 1987-05-28
Also published as: GB2183057B; GB8308833D0

Abstract

The field-of-view of a conically scanned target acquisition system, such as might be used in a homing missile, is extended by increasing the angular separation 57 of the axis 59 of the scanning parabolic mirror 31 from the centre line 58 of the missile. The extension of the field-of- view prevents the acquisition system field of view from being filled by the target as the missile closes on the target, and thus target-background contrast is maintained allowing the missile to be steered to the centre of the target. The increase in angular separation may be actuated in response to the time of flight 55 of the missile. As shown, a flywheel 38 rotates on a bearing 39. The scanning angle 57 is increased by lever 50, slider 41 and flywheel 38 moving in the direction of arrow B. <IMAGE>

Description

SPECIFICATION Edge tracking eliminator The present invention relates to missile guidance systems wherein the target tracking system on the missile has a field of view which is filled by the target as the missile nears the target.

Some target tracking systems on missiles which utilise sky radiation reflected from the target include a rotating centre feed parabolic mirror to direct radiation into the target detection system of the missile. The rotation of the parabolic mirror is usually arranged to sample a cone of space in front of the missile with the axis of the parabola set at a small angle from the axis of the missile.

The target detection system of the missile is sensitive to the sky radiation reflected from the target in contrast to the target's surroundings. The tracking system in the missile is arranged to steer the missile so that the target lies in the centre of the conical field of view of the rotating parabolic mirror, that is the target lies on the axis of the missile. If the target moves from the centre of the field of view, an appropriate signal is generated by the tracking system which results in a steering command to the missile to return the target to the centre of the field of view. The tracking system operates satisfactorily only when the target can be distinguished from its surroundings, that is while the target does not fill the field of view of the target tracker.When the missile closes on the target there is a distance between the target and the missile below which the target fills the field of view of the tracker. Thus no error signals will be generated and the missile will wander from the desired impact point on the centre of the target to a direction in which the tracker views an edge of the target against the target surroundings and the missile will be steered to hit the edge of the target.

According to the present invention a homing missile having a conically scanned field of view target acquisition system includes means for increasing the conical scanning angle to maintain the field of view greater than the target.

An embodiment of the invention will now be described with reference to the following drawings in which: Figures 1A and 1B show schematically a conically scanned tracker with a target in the field of view and filling the field of view.

Figure 2 shows schematically a conically scanned tracker with the field of view extended to the edge of target as the missile closes on the target.

Figure 3 shows schematically a scanning tipping mechanism.

In Fig. 1A a missile 1 approaching a target 2 has acquired the target and positioned itself so that the centre line of the missile 3 points at the centre 4 of the target. The extent of the field of view of the conical scanner (not shown) in the missile is given by the lines 5 and 6. The field of view encompasses the target and part of the surrounding area 7.

In Fig. 1B the missile 1 is now so close to the target 2 that the field of view of the conical scanner (not shown) shown by lines 5 and 6 is smaller than the angle 8 subtended by the target at the missile.

In Fig. 2 a missile 21 has closed on a target 22. The field of view of the conical scanner (not shown) shown by lines 25 and 26 has been displaced from a position adjacent to the centre line 23 of the missile so that the circular scanning pattern 24 at the target overlaps the edge 28 of the target and part of the surrounding area 27.

Fig. 3 shows schematically a conically scanned parabolic mirror 31 driven via a universal joint 32 and shaft 33 by an electric motor 34. The rear 35 of the mirror is attached by spherical joints 36 and a drive link 37 to a flywheel 38. The flywheel rotates on a bearing 39 between the inner periphery of the flywheel 40 and a slider 41. The slider 41 carries a bearing on the inner surface 42 which allows the shaft 33 to rotate relative to the slider and the slider 41 to translate axially relative to the shaft 33. A thrust pad 43 is provided between the slider flange 44 and the adjacent region 45 of the flywheel. A stirrup shaped lever arm 46 provided with pegs 47 to cooperate with holes 48 (shown dashed in the figure) in the slider rotates about the pivot 49.The lever arm 50 furthest from the stirrup shaped arm has a socket 51 into which is fitted a ball 52 attached to the push-rod 53 of an electrically operated screwjack 54.

In operation, a time of flight clock 55 is actuated when the missile is launched. After a predetermined time the clock activates the screwjack 54, causing the push-rod 53 and the attached joint and arm to move in the direction of arrow A. The further end of the lever, the slider and flywheel are urged to move in the direction of arrow B, and the rotating mirror, linked to the flywheel, moves about the joint 32 to increase the scanning angle 57 separating the centre line of the missile 58 and the axis of the parabolic mirror 59.

In use, to reduce the out of balance forces on the missile caused by tipping the rotating mirror, it has been found advantageous to construct the mirror from a lightweight plastic material, with a metallized reflecting surface.

1. A conically scanned field-of-view target acquisition system, for use in a homing missile, having means for increasing the conical scanning angle to maintain the field-of-view equal to or greater than that required to en

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Edge tracking eliminator The present invention relates to missile guidance systems wherein the target tracking system on the missile has a field of view which is filled by the target as the missile nears the target. Some target tracking systems on missiles which utilise sky radiation reflected from the target include a rotating centre feed parabolic mirror to direct radiation into the target detection system of the missile. The rotation of the parabolic mirror is usually arranged to sample a cone of space in front of the missile with the axis of the parabola set at a small angle from the axis of the missile. The target detection system of the missile is sensitive to the sky radiation reflected from the target in contrast to the target's surroundings. The tracking system in the missile is arranged to steer the missile so that the target lies in the centre of the conical field of view of the rotating parabolic mirror, that is the target lies on the axis of the missile. If the target moves from the centre of the field of view, an appropriate signal is generated by the tracking system which results in a steering command to the missile to return the target to the centre of the field of view. The tracking system operates satisfactorily only when the target can be distinguished from its surroundings, that is while the target does not fill the field of view of the target tracker.When the missile closes on the target there is a distance between the target and the missile below which the target fills the field of view of the tracker. Thus no error signals will be generated and the missile will wander from the desired impact point on the centre of the target to a direction in which the tracker views an edge of the target against the target surroundings and the missile will be steered to hit the edge of the target. According to the present invention a homing missile having a conically scanned field of view target acquisition system includes means for increasing the conical scanning angle to maintain the field of view greater than the target. An embodiment of the invention will now be described with reference to the following drawings in which: Figures 1A and 1B show schematically a conically scanned tracker with a target in the field of view and filling the field of view. Figure 2 shows schematically a conically scanned tracker with the field of view extended to the edge of target as the missile closes on the target. Figure 3 shows schematically a scanning tipping mechanism. In Fig. 1A a missile 1 approaching a target 2 has acquired the target and positioned itself so that the centre line of the missile 3 points at the centre 4 of the target. The extent of the field of view of the conical scanner (not shown) in the missile is given by the lines 5 and 6. The field of view encompasses the target and part of the surrounding area 7. In Fig. 1B the missile 1 is now so close to the target 2 that the field of view of the conical scanner (not shown) shown by lines 5 and 6 is smaller than the angle 8 subtended by the target at the missile. In Fig. 2 a missile 21 has closed on a target 22. The field of view of the conical scanner (not shown) shown by lines 25 and 26 has been displaced from a position adjacent to the centre line 23 of the missile so that the circular scanning pattern 24 at the target overlaps the edge 28 of the target and part of the surrounding area 27. Fig. 3 shows schematically a conically scanned parabolic mirror 31 driven via a universal joint 32 and shaft 33 by an electric motor 34. The rear 35 of the mirror is attached by spherical joints 36 and a drive link 37 to a flywheel 38. The flywheel rotates on a bearing 39 between the inner periphery of the flywheel 40 and a slider 41. The slider 41 carries a bearing on the inner surface 42 which allows the shaft 33 to rotate relative to the slider and the slider 41 to translate axially relative to the shaft 33. A thrust pad 43 is provided between the slider flange 44 and the adjacent region 45 of the flywheel. A stirrup shaped lever arm 46 provided with pegs 47 to cooperate with holes 48 (shown dashed in the figure) in the slider rotates about the pivot 49.The lever arm 50 furthest from the stirrup shaped arm has a socket 51 into which is fitted a ball 52 attached to the push-rod 53 of an electrically operated screwjack 54. In operation, a time of flight clock 55 is actuated when the missile is launched. After a predetermined time the clock activates the screwjack 54, causing the push-rod 53 and the attached joint and arm to move in the direction of arrow A. The further end of the lever, the slider and flywheel are urged to move in the direction of arrow B, and the rotating mirror, linked to the flywheel, moves about the joint 32 to increase the scanning angle 57 separating the centre line of the missile 58 and the axis of the parabolic mirror 59. In use, to reduce the out of balance forces on the missile caused by tipping the rotating mirror, it has been found advantageous to construct the mirror from a lightweight plastic material, with a metallized reflecting surface. CLAIMS

1. A conically scanned field-of-view target acquisition system, for use in a homing missile, having means for increasing the conical scanning angle to maintain the field-of-view equal to or greater than that required to en compass the field-of-view subtended by the target at the target acquisition system.

2. A conically scanned field-of-view target acquisition system as claimed in claim 1 having a rotating parabolic mirror.

3. A conically scanned field-of-view target acquisition system as claimed in claim 2, the parabolic mirror being of plastics material with a metallized reflecting surface.

4. A homing missile having a conically scanned field-of-view target acquisition system including means for increasing the conical scanning angle to maintain the field-of-view of the target acquisition system equal to or greater than that required to encompass the field-of-view subtended by the target at the missile, to steer the missile to the centre of the target.

5. A homing missile as claimed in claim 4 having means for increasing the conical scanning angle actuated with respect to the time of flight of the missile.

6. A target acquisition system for a homing missile substantially as herein described and as illustrated with reference to Fig. 3.

6. A homing missile substantially as herein described and as illustrated with reference to Figs. 1A and 2.

7. A conically scanned field-of-view target acquisition system substantially as herein described and illustrated with reference to Fig.

3.

CLAIMS (15 Aug 1986) Superseded claims 1 to 7 New or amended claims:

1. A target acquisition system for a homing missile includes a conically scanned mirror rotated about an axis, the scanning angle of the mirror being increased continuously as the missile approaches a target such that the field of view of the target acquisition system is always greater than the angle subtended by the target at the missile.

2. A target acquisition system for a homing missile as claimed in claim 1 wherein the conically scanned mirror is parabolic in shape.

3. A target acquisition system for a homing missile as claimed in claim 2, wherein the mirror is made of plastics material with a metallized reflecting surface.

4. A target acquisition system for a homing missile as claimed in claim 1 having means for increasing the scanning angle actuated with respect to the time of flight of the missile.

5. A target acquisition system for a homing missile as claimed in claim 1 in which the means for increasing the scanning angle includes a link between the mirror and a member rotatable about and slideable along the rotation axis of the mirror.