WO2004107065A2

WO2004107065A2 - Predetermined miss-distance homing missile

Info

Publication number: WO2004107065A2
Application number: PCT/IL2004/000437
Authority: WO
Inventors: Itshak Marom; Gyorgy Hexner
Original assignee: Rafael - Armament Development Authority Ltd.
Priority date: 2003-06-03
Filing date: 2004-05-23
Publication date: 2004-12-09
Also published as: WO2004107065A3; IL156289A0

Abstract

A method to guide a homing missile (10) having a seeker head (14) to an aim point (42) which is a miss-vector (34) away from a target. The method includes the steps of tracking the target, using the seeker head, and guiding the homing missile to the point.

Description

PREDETERMINED MISS-DISTANCE HOMING MISSILE

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to a guidance system for a homing missile and, in particular, it concerns a system and method to guide a homing missile to a given position, which is offset from a target which is being tracked by the missile's seeker head.

By way of introduction, a typical method for guiding a homing missile to a target is by using the principle of proportional navigation. The seeker head of the homing missile, generally in conjunction with a processor inside the missile's body, measure the rate of change of the angle between an imaginary line, which joins the seeker head and a target, and an inertial reference coordinate axis. The homing missile then accelerates perpendicular to this imaginary line at a rate which is proportional to the measured angular rate. A missile using the principle of proportional navigation is capable of high performance, that is, the missile is able to hit the tracked target with a high degree of accuracy. However, for some applications it is advantageous not to hit the target which is being tracked by the seeker head, but to miss the target by a predetermined distance in a predetermined direction, known as a miss-distance in a predetermined direction or a miss-vector. For example, it is desirable for an anti-personnel missile to explode at a distance above the tracked target. However, the seeker head only has the ability to track a target and not a point which is a miss-vector away from the target. This is because the seeker head tracks an object generally by sensing the electromagnetic radiation which emanates from or reflects off the target.

There is therefore a need for a system and method to guide a homing missile to a point that is a miss-vector away from a target which is being tracked by the seeker head of a homing missile. SUMMARY OF THE INVENTION

The present invention is a system to guide a homing missile to a given position which is offset from a target which is being tracked by the missile's seeker head and a method of operation thereof. According to the teachings of the present invention there is provided, a method to guide a homing missile having a seeker head to an aim point which is a miss-vector away from a target, comprising the steps of tracking the target, using the seeker head and guiding the homing missile to the point.

According to a further feature of the present invention, the step of guiding is performed using proportional navigation.

According to a further feature of the present invention, there is also provided the step of estimating a distance from the seeker head to the target from a time history of an angle subtended by the target at the seeker head.

According to a further feature of the present invention, there is also provided the step of estimating a distance from the seeker head to the target using kinematic ranging.

According to a further feature of the present invention, there is also provided the step of measuring a distance from the seeker head to the target.

According to the teachings of the present invention there is also provided, a system for guiding a homing missile to an aim point which is a miss-vector away from a target, comprising: (a) a target sensor which is configured to sense the target; (b) a steering device; and (c) a processor configured to send a plurality of commands to the steering device to guide the homing missile to the aim point.

According to a further feature of the present invention, the processor is configured to prepare the commands using proportional navigation. According to a further feature of the present invention, there is also provided a range finder for measuring the distance.

According to a further feature of the present invention, at least one of the processor and the target sensor is configured to estimate the distance from a time history of an angle subtended by the target at the target sensor. According to a further feature of the present invention, the processor is configured to estimate the distance using kinematic ranging.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

Fig. 1 is a schematic cross-sectional view of a homing missile that is constructed and operable in accordance with a preferred embodiment of the invention;

Fig. 2 is a schematic cross-sectional view of the homing missile of Fig. 1 tracking a point which is a miss-vector away from a target being tracked by a seeker head of the homing missile;

Fig. 3 is a schematic cross-sectional view of the homing missile of Fig. 1 estimating a distance to the target; and

Fig. 4 is schematic view showing an alternative method for the homing missile of Fig. 1 to estimate the distance to the target.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a system to guide a homing missile to a given position which is offset from a target which is being tracked by the missile's seeker head and a method of operation thereof.

The principles and operation of a homing missile according to the present invention may be better understood with reference to the drawings and the accompanying description.

Reference is now made to Fig. 1, which is a schematic cross-sectional view of a homing missile 10 that is constructed and operable in accordance with a preferred embodiment of the invention. Homing missile 10 includes a fuselage 12, a seeker head 14, a processor 16, a steering device 18 generally having four deflectable fins and a means of propulsion 20. Means of propulsion 20 is generally a solid-state rocket motor. Before the launch of homing missile 10, homing missile 10 is stored in a launch tube 36. The launch of homing missile 10 as well as subsequent communication, if any, between the operator of homing missile 10 and homing missile 10 is generally controlled by a command launch unit 38. Reference is now made to Fig. 2, which is a schematic cross-sectional view of homing missile 10 tracking a target 24 using seeker head 14 of homing missile 10. Target 24 is a miss-vector 34 away from a point 42, point 42 being the intended hit point. Seeker head 14 includes a sensor 22 which is configured to sense target 24. Processor 16 is configured to send a plurality of commands to steering device 18 in order to guide homing missile 10 to point 42. Typically, processor 16 is configured to prepare these commands using a proportional navigation method. The embodiments described hereinbelow employ proportional navigation to guide homing missile 10 to point 42, however it will be apparent to those skilled in the art that other navigation methods may be adapted to guide homing missile 10 to point 42. In accordance with a preferred embodiment of the present invention, seeker head 14 is gimbaled, whereby an actuator 26 is configured to ensure that sensor 22 always points in the direction of target 24. In accordance with this preferred embodiment, seeker head 14 also includes an angular velocity measurement device 28, typically based on one or more gyroscopes, which measures the angular velocity of sensor 22. Therefore, measurements received from measurement device 28 are used to calculate the rate of change of an angle between an imaginary line 40 between sensor 22 and target 24 and a coordinate axis of an inertial frame of reference. Optionally, homing missile 10 also includes one or more angular rate sensors 30, which are configured to measure the angular rate of change of fuselage 12 with respect to the coordinate axis of the inertial frame of reference, either in addition to or instead of measurement device 28.

In accordance with an alternate embodiment of the present invention, seeker head 14 is fixed. In accordance with this alternate embodiment, homing missile 10 must include angular rate sensors 30, which are configured to measure the angular rate of change of fuselage 12 with respect to the coordinate axis of the inertial frame of reference. Processor 16 performs several functions. First, processor 16 stores miss- vector 34. Command launch unit 38 (Fig. 1) is configured to transfer miss-vector 34 to processor 16 prior to launch of homing missile 10. Command launch unit 38 (Fig. 1) may also be configured to transfer an update of miss- vector 34 to processor 16 during the flight of homing missile 10, if necessary. Second, processor 16 receives measurements from sensor 22. Third, processor 16 generates signals for actuator 26 to cause sensor 22 to point in the direction of target 24. Fourth, processor 16 receives signals from all the sensors in the missile, including angular rate sensors 30 and/or measurement device 28 as well as any inertial measurement devices. Fifth, processor 16 is configured to calculate an acceleration rate based on the rate of change of the angle between an imaginary line 44 joining sensor 22 and point 42 and the coordinate axis of the inertial frame of reference. Sixth, processor 16 generates commands so that the steering device 18 causes homing missile 10 to accelerate in a direction 46 which is perpendicular to imaginary line 44 using the acceleration rate calculated by processor 16. Therefore, even though sensor 22 is only able to track target 24, homing missile 10 is guided to point 42 by implementing the principle of proportional navigation based on imaginary line 44 in a similar way to a conventional homing missile being guided to target 24 by implementing the principle of proportional navigation based on imaginary line 40. The rate of change of the angle between imaginary line 44 and the coordinate axis of the inertial frame of reference is calculated by processor 16 by summing the rate of change of the angle between imaginary line 40 and the coordinate axis of the inertial frame of reference and an angle 48 which is subtended by imaginary line 40 and imaginary line 44. Processor 16 calculates angle 48 from miss-vector 34 and a distance 50 from sensor 22 to target 24 using trigonometry. Distance 50 is either estimated or measured. According to a preferred embodiment of the present invention homing missile 10 includes a range finder 52 which is configured to measure distance 50. If homing missile 10 does not include range finder 52, there are a number of well-known methods for estimating distance 50. These methods generally operate on the basis of two principles. The first principle is discussed with reference to Fig. 3 and the second principle is discussed with reference to Fig. 4.

Reference is now made to Fig. 3, which is a schematic cross-sectional view of homing missile 10 estimating distance 50 to target 24. According to a first alternate embodiment of the present invention, processor 16 in conjunction with sensor 22 is configured to estimate distance 50 from a time history of an angle A subtended by target 24 at sensor 22. This is achieved by configuring processor 16 to estimate distance 50 by multiplying a velocity of homing missile 10 by a ratio of angle A to a rate of change of angle A. Assuming that A is sufficiently small, then tan(A) may be approximated by A and an apparent size 56 of target 24 as seen by sensor 22 is constant.

Therefore, the following equations are valid:

Equation (1),

R = T x v Equation (2),

where R is distance 50, T is the time for homing missile 10 to reach target 24, d(A)/dt is the rate of change of A, d(R)/dt is the rate of change of R and v is the velocity of homing missile 10.

Therefore, the following equation is valid:

R = Equation (3).

Therefore it is seen from equation (3) that distance 50 is equal to velocity v of homing missile 10 multiplied by the ratio of angle _4 to the rate of change of angle A.

Reference is now made to Fig. 4, which is schematic view showing an alternative method for homing missile 10 of Fig. 1 to estimate distance 50 to target 24. For purposes of illustrating this alternate method, homing missile 10 is shown twice in this Figure, once at a first position at time 1 and again at a second position at a later time, time 2. According to a second alternate embodiment of the present invention, processor 16 (Fig. 2) in conjunction with sensor 22 is configured to estimate distance 50 using kinematic ranging. By way of introduction, the estimation of the range to a target from a moving platform from the time history of the line of sight angle with respect to an inertial reference is known as kinematic ranging. The simplest principle for kinematic ranging is described below. Processor 16 is configured to estimate distance 50 by applying trigonometry to: (i) an angle B subtended by imaginary line 40 and an inertial reference, at time 1; (ii) an angle C subtended by imaginary line 40 and the inertial reference, at a time 2; and (iii) a distance 62 traveled by homing missile 10 between time 1 and time 2. A recursive algorithm is generally required, usually implemented by means of a Kalman filter in order to decrease the sensitivity of the algorithm to measurement errors. When seeker head 14 is fixed, angle B and angle C are typically measured by processor 16 in conjunction with sensor 22 and angular rate sensors 30 (Fig. 2). When seeker head 14 is gimbaled angle B and C are measured using measurements of measurement device 28.

It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof that are not in the prior art which would occur to persons skilled in the art upon reading the foregoing description.

Claims

WHAT IS CLAIMED IS:

1. A method to guide a homing missile having a seeker head to an aim point which is a miss-vector away from a target, comprising the steps of:

(a) tracking the target, using the seeker head; and

(b) guiding the homing missile to the point.

2. The method according to claim 1, wherein said step of guiding is performed using proportional navigation.

3. The method according to claim 2, further comprising the step of:

(c) estimating a distance from the seeker head to the target from a time history of an angle subtended by the target at the seeker head.

4. The method according to claim 2, further comprising the step of:

(c) estimating a distance from the seeker head to the target using kinematic ranging.

5. The method according to claim 2, further comprising the step of: (c) measuring a distance from the seeker head to the target.

6. A system for guiding a homing missile to an aim point which is a miss-vector away from a target, comprising:

(a) a target sensor which is configured to sense the target;

(b) a steering device; and

(c) a processor configured to send a plurality of commands to said steering device to guide the homing missile to the aim point.

7. The system according to claim 6, wherein said processor is configured to prepare said commands using proportional navigation.

8. The system according to claim 7, further comprising: (d) a range finder for measuring said distance.

9. The system according to claim 7, wherein at least one of said processor and said target sensor is configured to estimate said distance from a time history of an angle subtended by the target at said target sensor.

10. The system according to claim 7, wherein said processor is configured to estimate said distance using kinematic ranging.