GB2345952A

GB2345952A - Missile guidance

Info

Publication number: GB2345952A
Application number: GB8906778A
Authority: GB
Inventors: Enoch James; Raymond John Paul Stafford
Original assignee: British Aerospace PLC; Matra Bae Dynamics UK Ltd
Current assignee: BAE Systems PLC; Matra Bae Dynamics UK Ltd
Priority date: 1988-03-28
Filing date: 1989-03-23
Publication date: 2000-07-26
Anticipated expiration: 2009-03-23
Also published as: GB8807355D0; GB2345952B; GB8906778D0

Abstract

A system to enable a CO. . laser beam rider missile guidance system to be accurately collimated to one or more target tracking sensors such as to minimise the miss distance during the terminal phase of missile flight. This is done by gathering the projectile in a field of view of a first tracking system e.g. thermal imager 2, using said first tracking system to guide said projectile into a second narrower field of view of a second tracking system e.g. laser beam projector 5, determining the projectile boresight within said second FOV using target position error information from said first tracking system and correction for the relative positions of the two systems, and then guiding said projectile to the target with said second tracking system.

Description

MISSTLE GUIDANCE This invention relates to an optical beam rider (OBR) missile guidance system in which a laser beam is scanned over a field-of-view (FOV) and, by reference to the radiation which it receives, a missile guides itself within the field-of-view. For example, the optical beam projector may be aimed so its boresight is directe onto a target and the missile may be operable to guide itself onto and along that boresight until it reaches the target.

Owing to errors in the guidance system on board the missile and collimation errors of the projector field-of-view, the system as described above may not achieve a good enough guidance accuracy.

Thus, an object of the invention is to provide a means whereby the guidance system on board an OBR missile can more accurately determine its position within the scan field of an optical beam projector, such as to minimise the miss distance during the terminal phase of missile flights.

According to a first aspect of the invention there is provided a method of guiding a projectile to a target comprising the steps of: gathering the projectile in a field of view of a first tracking system ; using said first tracking system to guide said projectile into a second narrower field of view of a second tracking system; determining the projectile boresight within said second FOV using target position error information from said first tracking system and correction for the relative positions of the two systems ; and guiding said projectile to the target with said second tracking system.

According to a second aspect of the invention, there is provided a missile guidance system comprising: an optical radiation beam projector for scanning an optical radiation beam over a field-of-view of the projector; missile sensing means for tracking the missile and sensing its position within a field-of-view of the sensing means which field-of-view has a pre-determined position relationship to the field-of-view of the beam projector; wireless communication means connected to said sensing means for transmitting to the missile information about the position of the missile as determined by the sensing means; and on board a missile, a guidance system which includes means for receiving said information and for comparing the missile position as determined by the sensing means with the missile position as determined on board the missile by reference to the optical radiation beam.

For a better understanding of the invention, reference will be made, by way of example, to the accompanying drawings, in which: Figure 1 is a diagram for explaining the relationship between the fields of view of a laser beam scanner and a thermal imager used in one system according to the invention, and Figure 2 is a diagram for explaining how the guidance apparats on board a missile uses information transmitted to it to collimate the scan pattern of the laser beam.

Referring to Figure 1 of the drawings, the missile (not shown) is gathered within a wide field of view (FOV) (not shown) and brought into the thermal imager FOV 1. Upon entering this FOV 1 the missile signature will be acquired by the thermal imager error measurement channel of a thermal imager 2 and thermal imager errors will be formed. These errors may be used to continue to guide the missile via a microwave command link 3 into a relatively narrow laser beam rider (LBR) scan pattern 4 generated by a beam projector 5. Upon entering scan pattern 4 the missile will be receiving two sets of error data, thermal imager errors from the command link and LBR code from the scan pattern. The thermal imager errors are used for a short period from LBR entry to transform the LBR scan pattern code into missile error signals which define the missile boresight, (i, j). The missile will further use a range time look-up table to provide a parallax correction due to the separation of the thermal imager 2 and the beam projector 5. This transformation of the LBR errors occurs during only about the first lkm of the missile flight.

Once the LBR boresight co-ordinates (i, j) have been defined the missile continues to fly under normal LBR guidance control.

In the event that there are severe pyrotechnic decoy counter measures (ie. flares) present in the environment then the thermal imager will only provide missile errors from non-decoy areas. This may mean that in some cases the LBR errors may be transformed on the edge of its scan pattern.

Hence any known non-linearity of the thermal imager or LBR scan system is stored in the missile to allow for necessary linearity corrections.

In certain instances where sensor linearity is a problem the target tracking sensor may choose to form a new boresight position outside any possible decoy areas and collimate on the new position.

A simple example of the system is shown by reference to Figure 2. The target tracking sensor will track the missile, within its FOV 6, until the missile settles on the boresight with a low rate. At this time the missile is sent a collimation signal (o, o). At the same time the missile will receive an LBR signal (icol, jcol). This co-ordinate is stored by the missile and used to collimate the two systems by subsequently adding to all further received LBR guidance signals any collimation errors.

Claims

CLAIMS 1. A method of guiding a projectile to a target comprising the steps of: gathering the projectile in a field of view of a first tracking system; using said first tracking system to guide said projectile into a second narrower field of view of a second tracking system; determining the projectile boresight within said second FOV using target position error information from said first tracking system and correction for the relative positions of the two systems; and guiding said projectile to the target with said second tracking system.

2. A method according to claim 1 wherein, in use, said first tracking system is a thermal imager.

3. A method according to claim 1 and claim 2 wherein, in use, said second tracking system is an optical beam rider guidance system.

4. A method according to claims 1,2 or 3 wherein, in use, said second tracking system is a laser beam rider guidance system.

5. A method according to any one of the preceding claims wherein, in use, said projectile stores information of any non-linearity of said tracking systems in order to be guided within any part of the FOV of the respective systems. fi. A missile guidance system comprising: an optical radiation beam projector for scanning an optical radiation beam over a field-of-view of the projector; missile sensing means for tracking the missile and sensing its position within a field-of-view of the sensing means which field-of-view has a pre-determined position relationship to the field-of-view of the beam projector; wireless communication means connected to said sensing means for transmitting to the missile information about the position of the missile as determined by the sensing means; and on board a missile, a guidance system which includes means for receiving said information and for comparing the missile position as determined by the sensing means with the missile position as determined on board the missile by reference to the optical radiation beam.

7. A missile guidance system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

8. A method of guiding a projectile to a target substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

Amendments to the claims have been filed as follows 1. A method of guiding a projectile to a target comprising the steps of: gathering the projectile in a field of view of a first tracking system; using said first tracking system to guide said projectile into a second narrower field of view of a second tracking system; determining the projectile's position within said second FOV using projectile position error information from said first tracking system and correction for the relative positions of the two systems ; and guiding said projectile to the target with said second tracking system.

2. A method according to claim 1 wherein, in use, said first tracking system is a thermal imager.

3. A method according to claim 1 and claim 2 wherein, in use, said second tracking system is an optical beam rider guidance system.

4. A method according to claims 1, 2 or 3 wherein, in use, said second tracking system is a laser beam rider guidance system.

5. A method according to any one of the preceding claims wherein, in use, said projectile stores information of any non-linearity of said tracking systems in order to be guided within any part of the FOV of the respective systems. fi. A missile guidance system comprising: an optical radiation beam projector for scanning an optical radiation beam over a field-of-view of the projector; missile sensing means for tracking the missile and sensing its position within a field-of-view of the sensing means which field-of-view has a pre-determined position relationship to the field-of-view of the. beam projector; wireless communication means connected to said sensing means for transmitting to the missile information about the position of the missile as determined by the sensing means; and on board a missile, a guidance system which includes means for receiving said information and for comparing the missile position as determined by the sensing means with the missile position as determined on board the missile by reference to the optical radiation beam.

7. A missile guidance system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

8. A method of guiding a projectile to a target substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.