GB2469737A

GB2469737A - Homing seeker head for a missile including at least two distinct detection channels

Info

Publication number: GB2469737A
Application number: GB1006603A
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: FR2944593A1; GB2469737B; FR2944593B1; DE102010015645A1; GB201006603D0

Abstract

A homing seeker head (10) for a missile, includes two channels (SAL, IR) for detecting light beams in two radiation bands distinct from each other. Each detection channel includes for each band an entry window (1051, 1052) transparent for said radiation band, a sensor (107, 108) for detecting the beams in said band, and a dioptric module (2031, 2032) located between said window (1051, 1052) and said sensor (107, 108).

Description

GENERAL TECHNICAL FIELD

The present invention relates to a homing seeker head for a missile, including at least two channels for detecting light beams in two radiation bands distinct *.a* from each other. * .

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

STATE OF THE ART

*S..S. * *

Fig. 1 schematically illustrates a standard example of the use of 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 pm and 1.54pm (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 (8pm-l2pm).

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 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) * 0 If the target 3 is visible from the launcher, the * SAL mode is also possible for detecting and determining * the angular deviation of the target with the purposes of guiding the missile 1 onto the target 3 without any preliminary inertial navigation phase. S.... * S

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 guiding 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 a generally hemispherical and transparent entry dome 101, 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 both with lenses and mirrors. Thus conventionally, the module 103 notably includes a * primary mirror 104 sending back a light flux F towards :.: e 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.

*S.*..

* 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 achromatizatiori 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 dome 101 is common to both channels, and its transmission is not optimum for each of the channels because of the restricted selection of wide band transparent materials (for operating both in band 1 (for the SAL channel) and in band 2 or even 3 * (for the IR channel)), and of the associated processing operations which are complex. * S..

As the selection for the material of the dome is restricted, limitations on the speed of the missile may therefore be induced, because of the small hardness of the material (the dome 101 should be able to resist to rainfall erosion) Further, the primary mirror 104 which has central occultation, has a greater real diameter than the useful pupil of the system. This large diameter leads to an increase in the size of the dome 101, and therefore of its manufacturing complexity and its cost.

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

Finally, the use of the beam splitter 106 forces lateral offset on the one hand, perpendicularly to the line of site V, of one of the two channels (the SAL in Fig. 2), and the extension of the platform 102 on the other hand along the direction of the line of site V for the other channel (the SAL channel in Fig. 2), which increases the bulkiness of the platform 102, while it is desirable that the head have minimum bulkiness for caliber and aerodynamic constraints of the missile.

PRESENTATION OF THE INVENTION

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

* * For this purpose, a homing seeker head is proposed * ** for a missile, including at least two channels for detecting light beams in two radiation bands distinct S..

* from each other, characterized in that each detection *:::: channel includes, for each band *S.*.S * -a transparent entry window for said radiation band, -a sensor for detecting the beams in said band, and -a dioptric module located between said window and said sensor, each window, each sensor and each module being respectively distinct from the window, the sensor and the module of the other channels.

The invention is advantageously completed by the following features, taken alone or in any one of their technical possible combinations: -the head includes a distinct IR channel and SAL channel, the window transparent to the SAL band, the SAL sensor and SAL module being respectively distinct from the window transparent to the IR band, from the sensor IR and from the module IR; -the IR module and the IR sensor are mounted on a platform orientable in elevation and in relative bearing relatively to the entry window transparent to the IR band; *** -the SAL module and the SAL sensor are fixed relatively to the entry window transparent to the SAL band; -at least one window has the shape of a hemispherical 4*** * * * .iL)itL, * S * * -at least one window has the shape of a flat plate.

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

The invention has many advantages.

Each channel, IR or SAL channel for example, has its own entry window, which gives the possibility of selecting for each entry window the suitable material and processing, without the constraint of a wide transmission band of the dome known from the mode of Fig. 2. The result of this is good transmission for each of the channels.

As the two channels are independent, the selection of the material for each entry window becomes wider (in particular for the band 3), which allows its hardness to be optimized. There is therefore the possibility of obtaining higher missile speeds.

The dimension of the IR window is minimum by the possilbity of using a dioptric optical module on the IR channel (and not catadioptric as in the prior art), without occultation, which leads to a minimum useful IR pupil size. The size of the IR window, and therefore its production cost, notably in the case of a hemispherical dome, are thus reduced.

IS

555 The absence of a catadioptric module also gives the possibility of having a larger optical field for each of the channels (of the order of 10°, as opposed to

fields of the order of 5° in the prior art). I..

S

There is no longer any dichroic plate, and therefore no longer any lateral offset of an optical channel, nor extension of another optical channel as in the prior art, and therefore the bulkiness of the head is further reduced.

Further, in the embodiment including windows as flat plates, each window may be tilted, from one edge, relatively to the air flow, first of all there is no stopping point as on a dome, which intrinsically promotes resistance to rainfall erosion as compared with a dome for an identical material. The flat windows are further less costly than their dome-shaped equivalent. Finally, the platform in this case does not need any accurate positioning of its orientation axes relatively to the window.

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; * *S d * I * -Fig. 2, already also discussed, schematically * illustrates an example of a known homing seeker head located at the front of a missile;

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5.55.5

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-Fig. 3 schematically illustrates a first possible embodiment of a homing seeker head according to the invention, and -Fig. 4 schematically illustrates a second 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

Figs. 3 and 4 each show 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 in two radiation bands distinct from each other, i.e. for example an SAL channel, in band 1, and an IR channel in band 2 or band 3. The invention may also be applied to other detection bands, and the head may for example include a visible channel.

Figs. 3 and 4 notably show that each detection channel includes for each band, an entry window transparent for said radiation band, a sensor for detecting the beams in said band, and a dioptric module located between said window and said sensor. A dioptric * module, as opposed to a catadioptric module, is a :.: * module which only uses transmission lenses and does not include any reflective mirror. For each channel, each window, each sensor and each module are respectively : distinct from the window, the sensor and the module of the other channel.

In other words, in Figs. 3 and 4, the head 10 includes an IR channel and an SAL channel, i.e. for the IR channel, an entry window 1051 transparent to the IR band (band 2 or band 3), a sensor 107 for detecting the beams in the IR band and forming from a light flux Fl, an IR image by known processing means not shown, and a dioptic module 2031 located between the window 1051 and the IR sensor 107 for forming the image on the sensor 107.

The module 2031 for example includes two convergent lenses 110 and 111 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.

Moreover, the head 10 includes for the SAL channel, an entry window 1052 transparent to the SAL band, a sensor 108 for detecting from a flux F2, the beams in the SAL band, and a dioptric module 2032 located between the window 1052 and the SAL sensor 108, for forming the image on the sensor 108.

The module 2032 for example includes a convergent lens 112 for obtaining a large field as explained in the following, 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 * S. * 108. *** S

S *S.

I

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 type.

The window 1052, the sensor 108 and the module 2032 are respectively distinct from the window 1051, from the sensor 107 and from the module 2031.

Each window 1051 or 1052 may be transparent only for its band, which allows an increase in the selection of the material for each window. Provision may thus be made for the following materials: -for the IR channel band II (window 1051) sapphire, MgF2, ZnS, ZnSe, germanium -for the IR channel band III (window 1051) ZnS, ZnSe, germanium -for the SAL channel (window 1052) : glass of the BK7 type for example.

For the IR channel, the module 2031 (possibly including the lenses 110 and 111) and the sensor 107 are mounted on 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 1051. *..*

The orientation of the platform 102 has the effect of stabilizing the line of site Vi of the IR channel and * of orienting it, typically over an angular displacement :.:. of several tens of degrees along each axis Y or Z. I. * In Fig. 3, each window 1051 and 1052 has the shape of a hemispherical dome. * *

In this case, the centre 0, intersection of the axes Y and Z and centre of rotation of the platform 102 around said axes, should be located at the geometrical centre of the hemispheric IR dome with good accuracy (of the order of a few tens of microns), in order to preserve the quality of the images formed on the sensor 107 during the angular displacement of the platform 102, since the dome 1051 has low but non-zero optical power.

On the other hand, the SAL channel is fixed, i.e. the SAL module 2032 and the SAL sensor 108 are fixed and stationary relatively to the window 1052. Although the SAL channel is not stabilized, taking into account the very short duration of laser pulses of the external illuminator 4 (10-20 ns), and the speeds of rotation of the missile 1 on its trajectory, the introduced blurring remains negligible.

By the module 2032 including the convergent lens

112, the SAL channel has a very large field of

observation (typically of a few tens of degrees), so as to be of the same order as the angular displacements of the IR channel described above and made possible by the platform 102. *S.* * *

The line of site V2 of the SAL channel may be tilted by a few degrees relatively to a longitudinal axis X of the missile, in order to give preference to the downward field of observation when the missile 1 is on its trajectory T and to obtain better detection of *: the ground target 3. *

S..... * S

The window of the SAL channel may have the shape of a hemispherical dome (case of Fig. 3) or the shape of a flat plate (case of Fig. 4) In the case of a hemispherical dome for the SAL channel, there is no strong constraint on the positioning of the module 2032 relatively to the dome 1052 (as this is the case for the IR channel of Fig. 3), said channel not being able to be oriented.

As shown in Fig. 4, the window of the IR channel may have the shape of a flat plate. In this case, the platform 102 does not need accurate positioning of its centre of rotation relatively to the window 1051, the latter not having any optical power.

The head may include any combination of windows, i.e. a window as a dome for one of the two channels, and a window as a flat plate for the other channel.

However, in the case of Fig. 4, each window may be tilted from an edge 1053 relatively to the air flow, first of all there is no stopping point as on a dome, which intrinsically promotes resistance to rainfall erosion as compared with a dome for an identical material. Flat windows are further less costly than their dome-shaped equivalent. * * * ** * * S S** S * *

S S... * S. S. S

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S..*. S

S S

Claims

CLAII"IS 1. A homing seeker head (10) for a missile1 including at least one IR channel and one SAL channel distinct from each other, and including -an entry window (1051) transparent to an IR band, an IR sensor (107) for detecting the beams in the IR band, and a dioptric IR module (2031) located between said window (1051) and said IR sensor (107); and -an entry window (1052) transparent to an SAL band, an SAL sensor (108) for detecting the beams in the SAL band, and a dioptric SAL module (2032) located **.* between the window (1051) and the SAL sensor (108), S..... * S* .* the window (1052) transparent to the SAL band, the SAL sensor (108) and the SAL module (2032) being S..* respectively distinct from the window (1051) transparent to the IR band, from the IR sensor (107) * and from the IR module (2031) S..... * .
2. The head (10) according to claim 1, wherein the IR module (2031) and the IR sensor (107) are mounted on a platform (102) which may be oriented in elevation and in relative bearing relatively to the entry window (1051) transparent to the IR band.
3. The head according to any of claims 1 or 2, wherein the SAL module (2032) and the SAL sensor (108) are fixed relatively to the entry window (1052) transparent to the SAL band.
4. The head according to any of claims 1 to 3, wherein at least one window (1051, 1052) has the shape of a hemispherical dome.
5. The head according to any of claims 1 to 4, wherein at least one window (1051, 1052) has the shape of a flat plate.
6. A missile, including a head according to any of claims 1 to 5. * * * .. * . * S.. *S *SS. * S* S. SS0*S SIS