GB2469736A

GB2469736A - Catadioptric homing seeker head with two detection channels for a missile

Info

Publication number: GB2469736A
Application number: GB1006602A
Authority: GB
Inventors: Vincent Fraysse; Vincent Paccard
Original assignee: Sagem Defense Securite SA
Current assignee: Safran Electronics and Defense SAS
Priority date: 2009-04-20
Filing date: 2010-04-20
Publication date: 2010-10-27
Anticipated expiration: 2030-04-20
Also published as: DE102010015644A1; FR2944594A1; GB201006602D0; FR2944594B1; GB2469736B

Abstract

The invention relates to a homing seeker head for a missile, including two channels (semi active laser, SAL, and infra red, IR) for detecting light beams. The seeker head includes an entry window 101 which may be made of ZnS, a first sensor 107 for detecting the beams for a first, IR channel; a second sensor 108 for detecting the beams for a second, SAL channel and a catadioptric optical module having an optical axis V and including a primary mirror 104 and a secondary mirror 1052. The first sensor 107 is located downstream from the secondary mirror 1052. The second sensor, 108 is located coaxially with the first sensor 107 relative to the optical axis V, between the window 101 and the secondary mirror 1052. The second, SAL sensor may receive beams directly from the window (fig.4). In a further embodiment the secondary mirror 1051 (fig.3) reflects a portion of the beams towards the first, IR sensor and passes a portion of the flux from the primary mirror towards the second sensor. The invention avoids the use of laterally offset detectors and dichroic plates of prior art (fig.1).

Description

GENERAL TECHNICAL FIELD

The present invention relates to a homing seeker head for a missile.

S

The invention also relates to a missile including such a head. * **

STATE OF THE ART *

S

:. Fig. 1 schematically illustrates a standard example :** of the use of a ground combat missile 1 including a bi-modal homing seeker head 10. The head 10 for example includes a semi-active laser (SAL) channel and an infrared channel, known per se to one skilled in the art. The SAL channel may conventionally operate over wavelengths comprised between 1.06 pin and l.54prn (reference is then made to near infrared or band 1), and the infrared channel (IR) may as for it operate on band 2 (3pm-5pm) or band 3 (8im-12pm).

As illustrated in Fig. 1, the missile 1 is launched at instant to from a launcher 2. The missile 1 sets off under inertial navigation towards a target 3 on the trajectory T. The target 3 is not visible to the missile 1 upon launching the missile 1.

When at instant t1, the missile 1 arrives close to the target 3 (this distance corresponds to the average range of the SAL channel), an external illuminator 4 designates the target 3 by illumination.

The SAL channel of the head 10 then detects the thereby illuminated target 3 and determines the angular deviation of the target 3. The angular deviation is finally used for directing the missile 1 on the target 3 (this is then referred to as an SAL mode) If the target 3 is visible from the launcher, the SAL mode is also possible for detecting and determining a** * * the angular deviation of the target with the purposes * *. 15 of guiding the missile 1 onto the target 3 without any preliminary inertial navigation phase. *** *

An infrared mode is also possible, where only the IR channel is used, for the launcher up to the impact on the target 3, for the detection and angular deviation measurement of the target with the purpose of final guidance of the missile 1 onto the target 3.

An example of a known homing seeker head 10 located at the front of a missile 1 is schematically illustrated in Fig. 2.

It mainly includes an entry dome 101, generally hemispherical and transparent in the near IR band (band 1), for the SAL channel and the band 3 (or band 2) for the IR channel.

The head 10 also includes a platform 102 which may be oriented according to two axes Y (in elevation) and Z (in relative bearing). The orientation of the platform 102 has the effect of stabilizing the line of sight V and of orienting it typically over an angular displacement of several tens of degrees about each axis.

The head 10 also includes a catadioptric optical module 103. A catadioptric module is an optical system operating with both lenses and mirrors. Thus conventionally, the module 103 notably includes a primary mirror 104 sending back a light flux F towards a secondary mirror 105 (inducing central occultation of the primary mirror 104), in order to let the flux F through the pierced centre of the primary mirror 104.

I

The use of the primary mirror 104 is imposed, in particular in the case of bimodal SAL (band 1) and IR (band 3), since the extent of the wavelength of use (1 pm-12 pm) would make achromatization difficult with a solution of the dioptric type (i.e. without any mirror).

The module 103 further includes a dichroic plate 106 downstream from the secondary mirror 105, behind the primary mirror 104 as shown in Fig. 2. The flux F is transmitted by the dichroic plate 106 on the one hand in order to form a flux Fl and reach an IR sensor 107 (possibly after focusing by a lens 109) . The dome 101, the module 103 and the sensor 107 thereby form the IR channel.

The flux F is reflected by the dichroic plate 106 on the other hand in order to form a flux F2 in order to reach a SAL sensor 108. The dome 101, the module 103 and the sensor 108 form the SAL channel.

The known head 10 has drawbacks.

First of all, the use of the plate 106 downstream from the mirror 104 first forces extension of the platform 102 along the direction of the line of sight V for one of the channels (the IR channel in Fig. 2).

Such an extension may prove to be redhibitory for integration in a homing seeker head: indeed the angular displacements of the platform (desirably as large as possible: +1-30° class) become rapidly incompatible with the caliber allocated to the head in the missile.

Further, the bulkiness of the head of Fig. 2 is I. * amplified because of a lateral offset of the other * channel (the SAL channel in Fig. 2), related to the plate 106, which introduces dissymmetry relatively to the line of site V. oreover, a ballast must be provided on the platform 102 in order to compensate for the lateral dissyrometries of the head, which leads to increasing its inertia.

The platform should therefore include a motorization device, for orienting the platform 102 which is a constraint, since it has to be powerful in order to allow orientation of the platform having strong inertia.

Further, the introduction of a dedicated splitter

plate in the optical path is a penalty for overall transmission of both channels.

Finally, it is difficult to obtain large optical fields with a catadioptric module at the entry of the head.

PRESENTATION OF THE INVENTION

According to the invention, it is proposed to * overcome at least one of these drawbacks. *.* * S *

.: ** For this purpose, a homing seeker head according to claim 1 is proposed according to the invention. r S * 0.

* 15 The invention is advantageously completed by the features of claims 2 to 6.

The invention also relates to a missile including such a head. The invention has many advantages.

The head no longer includes any dichroic plate downstream from the primary mirror. In this way, lateral offset of an optical channel and extension of

the other optical channel as in the prior art, are

avoided and therefore the bulkiness of the head is reduced.

The catadioptric module has axial symmetry, allowing maximum misalignment in given missile caliber and window diameter. The useful pupil may thus represent up to 75% of the diameter of the entry window.

The module has natural balancing and the platform has minimum inertia, allowing less demanding motorization, notably less bulky and less heavy.

According to a first example, the module includes a secondary mirror as a splitter lens having dual functionality, i.e. it has optical power and allows splitting of the flux, thereby optimizing the optical transmission result.

*..... * S

: According to an embodiment of the invention, the * 15 module does not include any splitter plate. S.. S...

: Also according to this embodiment, it is easier to obtain a large field for the channel which does not pass through the catadioptric module, i.e. the SAL channel.

Also according to this embodiment, it is easier to replace the SAL sensor with a visible light sensor for

example.

favorable to large angular displacements.

PRESENTATION OF THE FIGURES

Other features, objects and advantages of the invention will become apparent from the following

description which is purely illustrative and

non-limiting and which should be read with reference to the appended drawings wherein: -Fig. 1, already discussed, schematically illustrates a standard example of use of a ground combat missile including a bimodal homing seeker head; -Fig. 2, already also discussed, schematically illustrates an example of a known homing seeker head located at the front of a missile; * S -Fig. 3, schematically illustrates a possible * embodiment of a homing seeker head according to the invention, and 5.. * S * S. S

-Fig. 4 schematically illustrates a possible embodiment of a homing seeker head according to the invention.

On the whole of the figures, similar elements bear identical numerical references.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 4 shows a possible embodiment of a homing seeker head 10 for a missile 1.

The head 10 includes at least two channels for detecting light beams i.e. for example a first IR channel in band 2 or band 3 and a second for example SAL channel, in band 1. The invention may also be applied to other detection bands, as this will be seen later on, and the head may for example include a visible channel.

The head 10 mainly includes an entry window 101 transparent to light beams. Typically, the material of the window is ZnS.

The head 10 also includes a first sensor 107 for detecting the beams for the first band and a second *S.* sensor 108 for detecting the beams for the second band.

* ***** * * As stated, the first band is for example an IR band and the second band is for example an SAL band.

The SAL sensor 108 may be of the retina type (array of detectors), a PSD (Positioning Sensing Device), or four quadrants (or even n quadrants) . The IR sensor 107 may be of the array type, of the cooled band II type, or non-cooled or cooled band III.

In all the cases, the sensors 107 and 108 are equipped with their proximity electronics allowing the forming and processing of images formed on the sensors 107 and 108.

The head also includes a catadioptric module 203 having an optical axis V, materializing the line of site of the head 10.

The module 203 conventionally includes a primary mirror 104 and a secondary mirror 1051 (Fig. 3) or 1052 (Fig. 4).

The first sensor 107 is located downstream from the secondary mirror 1051 or 1052 on the optical path of a flux F from a scene to be observed. Preferentially, the first sensor 107 is located behind the primary mirror 104 relatively to the secondary mirror 1051 or 1052, as shown in Figs. 3 and 4.

The second sensor 108 is located, coaxially with the first sensor 107 relatively to the optical axis V1 between the window 101 and the secondary mirror 1051 or 1052. The use of the inner space of the missile 1 is therefore more efficient. * S.

With this assembly of both sensors 107 and 108, on either side of the secondary mirror 1051 or 1052, or even preferentially of the primary mirror 104, the catadioptic module 203 has axial symmetry relatively to the axis V (as opposed to the assembly of Fig. 2), and reduced length allowing maximum misalignment in given missile caliber and window diameter. The head actually no longer includes any dichroic plate downstream from the secondary mirror. Balancing of the module is also facilitated, because of the distribution of the sensors, preferentially on either side of the primary mirror 104.

The module 203 further includes a platform 102 which may be oriented according to the axis Y (in elevation) and according to the axis Z (in relative bearing) . The platform 102 may therefore be oriented relatively to the window 101 by means of motorization not shown. The orientation of the platform 102 has the effect of stabilizing the line of site V for both channels and for orienting it, typically over an angular displacement of several tens of degrees around each axis Y or Z. The first sensor 107 and the second sensor 108 are mounted on the platform 102 and are mobile and integral with each other during angular displacement of the platform.

Because of the axial symmetry of the module 203, the inertia of the platform 102 is more favourable, S...

S.'... thus the motorization is less demanding than in the

prior art, notably less bulky and less heavy. * S. * . *

In Figs. 3 and 4, the window 101 has the shape of a S. * hemispherical dome. In this case, the centre 0, intersection of the axes Y and Z and centre of rotation * S * of the platform 102 around said axes, should be located S....

* at the geometrical centre of the hemispherical dome with good accuracy (a few tens of microns), in order to preserve the quality of the images formed on the sensors 107 and 108 during the angular displacement of the platform 102, since the dome 101 has low, but non-zero optical power.

Fig. 3 describes a possible example.

In this example, the secondary mirror 1051 is adapted so as to reflect a portion Fl of the beams of the flux F, from the primary mirror 104 towards the first sensor 107, and to transmit a portion F2 of the beams of the flux F, from the primary mirror 104 towards the second sensor 108 located upstream from the secondary mirror 1051. The face of the sensor 108 for forming an image is oriented towards the secondary mirror 1051 and towards the primary mirror 104. Fl in this embodiment of Fig. 3 corresponds to the useful infrared band of the IR channel (band 2 or 3), and F2 corresponds to the useful band of the SAL channel (between 1pm and 2pm depending on the external illuminator 4 used) The mirror 1051 forms a splitter lens (or further a dichroic filter) having dual functionality, i.e. it has optical power for forming an image on the sensor 108, and also allows splitting of the flux, thereby optimizing the optical transmission result relatively

to the prior art. * *S * * S S.. S

In the case of Fig. 3, the first sensor 107 is an IR sensor (band 2 or 3) and the module 203 for example * includes a convergent lens 109 for forming the image on the sensor 107, but it is understood that the number and the conformation of the lenses may vary depending on the desired bulkiness, and on the nature of the sensor 107.

The second sensor 108 is an SAL sensor (band 1) and the module 203 for example includes a lens 112, which associated with the mirror 1051 forms an optical system for forming the image on the sensor 108, but it is understood that the number and the conformation of the lenses may vary depending on the desired bulkiness, and on the nature of the sensor 108.

Fig. 4 describes a possible embodiment according to the invention.

In this embodiment, the mirror 1052 is adapted for reflecting the totality Fl of the beams of the flux F, from the primary mirror 104 towards the first sensor 107, for forming an IR image. The face of the second sensor 108 for forming an SAL image is oriented towards the window 101 and is adapted for receiving the beams directly from the window 101.

In the case of Fig. 4, the module 203 for example includes a lens 109 for forming the image on the sensor 107 but it is understood that the number and the conformation of the lenses may vary depending on the desired bulkiness, and on the nature of the sensor 107. * ** * * *

The module 203 for example includes two lenses 110 *** * and 111 forming an objective 204 for forming the image in the sensor 108, but it is understood that the number and the conformation of the lenses may vary depending * 1 on the desired bulkiness, and on the nature of the sensor 108. The objective 204 may be dioptric (only using lenses) or even catadioptric (by using mirrors) In the case of a dioptric objective 204, it is therefore possible to obtain a relatively large field of observation for this channel, not passing through the catadioptric module 203 (of the 10° or more class).

According to this embodiment, the module does not include any splitter plate.

example.

The embodiment has a good spherical form factor * * **** ****** * * * ** * S * S.. *

S * . . S. S

*SS*SS

S

Claims

CLAIMS1. A homing seeker head (10) for a missile, including two channels (SAL, IR) for detecting light beams, including: -an entry window (101) transparent to light beams, -a first sensor (107) for detecting the beams for a first channel (IR), -a second sensor (108) for detecting the beams for a second channel (SAL), and *..I S * S...-a catadioptric module (203) having an optical axis (V) and including a primary mirror (104) and a secondary mirror (1051, 1052),Ithe first sensor (107) being located downstream from * the secondary mirror (1051, 1052), the second sensor * * 15 (108) being located, coaxially with the first sensor (107) relatively to the optical axis (V) of the catadioptric module (203), between the window (101) and the secondary mirror (1051, 1052), said head being characterized in that the secondary mirror (1052) is adapted for reflecting the totality of the beams from the primary mirror (104) towards the first sensor (107), the second sensor (108) being oriented towards the window (101) and being adapted for receiving the beams directly from the window.
2. The head (10) according to claim 1, wherein the first sensor (107) is also located behind the primary mirror (104) relatively to the secondary mirror (1051, 1052)
3. The head (10) according to any of claims 1 or 2, wherein the module (203) includes a platform (102) which may be oriented in elevation and in relative bearing relatively to the entry window (101), a platform (102) on which are mounted the first sensor (107) and the second sensor (108)
4. The head according to any of claims 1 to 3, including an objective (204) between the window (101) and the second sensor (108) for forming an image on the second sensor (108) * * ** * * *
5. The head according to claim 4, wherein the objective *..(204) is catadioptric. S... * * S ** .
6. The head according to claim 4, wherein the objective (204) is dioptric.
7. A missile, including an head according to any of claims 1 to 6.