GB2298052A - Process for the harmonisation of a day/night firing system for a missile guided by a laser beam - Google Patents

Abstract

Harmonization process for a day/night missile firing system in which the day channel includes a day telescope (1) (3), a laser beam guidance transmitter (7) (9), and a collimator/deviation measurer (10) (12) and (13) and the night channel includes a heat camera (17) (18). The harmonization of the guidance transmitter is carried out permanently by returning part of its emitted flux into a deviation-measuring receiver (14) by means of separators (16) (15) and (13). The harmonization of the heat camera is similarly obtained permanently by means of the invariant trihedron subassembly (19) (20) which returns the infra-red flux in the focal plane (18) of the camera. The infra-red image of the reticle of the collimator is thus superimposed on the image of the reticle of the terrain. The eyepiece of the day telescope is used for the observation. The IR reticle is projected in the heat camera at a wavelength shorter than the main operating band. <IMAGE>

Description

PROCESS FOR T;!E HARMONIZATION OF A DAYINIGHT FIRING SYSTEM FOR A MISSILE GUIDED EY LASER BEAM The invention relates to a process for the harmonization of a day/night missile firing system having a day channel including a day telescope with a real reticle, a laser beam guidance transmitter and a collimator/ deviation measurer, the night channel including in addition a heat camera operating in a specified spectral band.

This system is intended for the guidance of a missile by alignment.

The laser transmitter placed on the firing station illuminates a guidance tunnel of square cross-section centered on the line of sight.

The object of the process of the invention is to provide a permanent control of the harmonization before and during the firing of a missile between the axes of the guidance laser beam of the day telescope and of the heat camera. In addition, it enables a non-rigid fixing between the day firing post and the heat camera as well as the interchangeability of the heat camera assembly without changing the harmonization.

This object is achieved by the process of the invention which is characterized in that the said day telescope and the said collimator/deviation measurer forming a compact and rigid mechanical subassembly produced such that their respective optical axes are strictly parallel and maintain this parallelism in the long term under the required environmental conditions, the harmonization of the said guidance transmitter is carried out permanently by returning part of its emitted flux to a deviation-measuring receiver by means of successive reflections on two separators forming a compact subassembly before the objective of the collimator and a third separator after the said objective, a means of servo-control returning the deviation read by the deviation neasurer to zero at all times, the harmonization of the said heat camera being in the same way obtained permanently by forming in its focal plane by means of an invariant trihedron subassembly the infra-red image of the reticle of the collimator displayed after electronic processing on a display screen observed through the eyepiece of the day telescope, the said harmonizations being independent of the drifts of the guidance transmitter, the drifts of the heat camera, the drifts of the display cathode ray tube and of the position of the heat camera.

The following description in addition to the appended drawing, both given by way of example, will give a good understanding of how the invention can be embodied.

The single figure shows the basic diagram of the day/night missile firing system for the implementation of the harmonization process according to the invention.

The day firing post forms a rigid assembly comprising a day telescope, a laser beam guidance transmitter and a collimator/deviation measurer.

The day telescope is a visual telescope including an objective 1, a real reticle 2 and an eyepiece 3. The image erecting system is not shown. A separator 4 enables the observation of the screen 5 of a cathode ray tube, symmetrical with the reticle 2. The eye of the observer is at 6.

The laser beam guidance transmitter includes an objective 7, represented here by 2 component lenses referenced 7, a beam coding system 8 and a laser 9.

The collimator/deviation measurer comprises for the collimator function : an objective 10, a real reticle 11 and an illuminating source 12.

for the deviation-measuring function : the objective 10, a separator 13, a deviation-measuring receiver 14 and two separators 15 and 16 rigidly connected to each other in order to form an assembly that cannot be distorted. One of these plates can be a right-angled dihedron such that the assembly 15-16 is an invariant trihedron.

The aiming telescope and the collimator form a compact and rigid mechanical subassembly produced in such a way that the optical axes defined by the optical center of the objective 1 and the cross of the reticle 2, the optical center of the objective 10 and the cross of the reticle 11 are strictly parallel and retain this parallelism in the long term in the required environmental conditions. This stability is easy to obtain as the assembly is compact and the optical components are of small dimensions.

The heat camera includes an infra-red objective 1? whose focal plane is at 18. The d.etectors and the analysis system are not shown in the figure. The objective 17 is preceded by an invariant optical component formed by a dichroic plate 19 rigidly connected to a right-angled dihedron 20. A plate with two parallel surfaces 21 serves as a closing porthole and as an optical filter.

The principle of harmonization depends on the longterm stability of the following subassemblies : aiming telescope/collimator/deviation measurer, invariant 15+16 and invariant 19+20.

The laser beam guidance is carried out, for example, at a wavelength of X = 10.6.

A small part of the emitted flux is returned to the deviation measurer 14 by reflection on the parallel plate 16. A control system acting, for example, on the coding system 8 (or on a deviation optical component not shown) returns the deviation read by the deviation measurer 14 to zero at all times.

The lens 7 of the guidance transmitter is preferabLy a zoom tens with a very large focal length ratio in which the groups of lenses move during firing. The constant checking of the guidance axis and the control of the direction of this axis enables the mechanical tolerances of the zoom lens to be widened.

The axis of the heat camera is the axis defined by the collimator 10+11 which projects the image of the reticle 11 in the focal plane 18 of the heat camera by the invariant trihedron 19+20. The image supplied by the heat camera after electronic processing is displayed on the screen S of a cathode ray tube. The reticle which appears on this screen is therefore the image of the reticle 11. It perfectly defines the line of sight of the camera independently of all mechanical, electrical and magnetic drifts of the camera assembly even if the reticle which appears on the screen 5 is not exactly symmetrical with the reticle 2 in the separator 4. This symmetry can be obtained by adjusting the scannings of the cathode ray tube when it is required that the visible and infra-red images are superimposable.

The heat camera is generally sensitive in the band 8 to 12 p. The reticle 11 can be projected in this soectral band but this has the following disadvantages.

It is advantageous that the effective diameter of the beam transmitted by the collimator should be distinctly smaller than the diameter of the pupil of the heat camera so that the aiming telescope collimator assembly is compact and the trihedron 19+20 is small and easy to produce. In this case, the image of the reticle 11 projected in the focal plane 18 with a small pupil diameter is much more accurate than the image of the terrain formed with a pupil of large diameter because of the diffraction whose angular limit is in fact : a = 1.22 A , D being the diameter of the lens and X being the wavelength.The means used in order that the projected reticle should have good definition is to use a shorter wavelength 2 such that 1 = 2, B1 and D1 referring to the imagery of Dl D2 the scene, X2 and D2 referring to the imagery of the reticle. The spectral band of heat cameras is generally limited to the 8 to 12 p band in order to correspond to the atmospheric transmission window. An interference filter cuts off wavelengths below 8 u while the detector cuts off at 12 p. In the absence of this filter the camera is sensitive between 2 and 12 > , the cut-off at 2 U being that of the germanium used in the lens. The col- limator can therefore project the reticle in a narrow band situated near X = 2 > on condition that the 8-12 U filter is placed before the injection of the reticle.

This filter will advantageously be deposited on the porthole 21 which protects the fixed trihedron assembly 19+20 on the front of the objective 17.

The projection of the reticle at A = 2 , however, encounters a difficulty which is the chromatic aberration of the objective 17 of the heat camera. This objective is normally corrected in the 8-12 p band and the longitudinal chromatic aberration is very large for germaniumbased dioptric lenses. This defocusing at 2 V is corrected in the collimator.The reticle 11 is axially offset so that its image is formed exactly in the same plane 18 as the image of the scene at 8-12 U. The hardware of the projection path of the reticle is, for example, the following source 12 : low power halogen lamp, reticle 11 : metallized and photoengraved glass plate, separator 13 : glass plate with dichroic treatment reflecting at A 10.6 , objective 10 : germanium lens, separator 15 : glass plate (same as plate 13), dihedron 20 : glass Amici prism, separator 13 : germanium plate with reflection at A = 2 U, transmission at A = 8 to 12 U, porthole 21 : germanium plate with parallel faces with transmission from 8 to 12 u, cut-off from 2 to 8 .

The beam from the reticle must be sent into the objective 17 through the center of the pupil of this objective in order to avoid any parallax error in the case in which the focusing of the objective is not perfectly achieved.

In order not to produce the MTF drop in the infrared image, the plate 19 must be perfectly parallel and must not produce any phase shift between the center and the edge of the pupil of the objective 17 When the objective 17 is bifocal, the plate 19 is dimensioned such that it totally covers the large field pupil of the objective.

As the longitudinal chromatic aberration is generally different for the two focal lengths of the objective, it is advantageous to use two reticles 11 and gila, axially offset along the optical axis of the collimator, illuminated by two different sources 12 and 12a (11a and 12a are not shown in the figure).

As the numerical aperture with which the reticle is projected at the short focal length of the objective is larger than at long focal length, the illumination of the reticle is greater in short focal length. An attenuator is therefore placed on the reticle of the short focal length in order to maintain the same reticle brightness for both fields.

The reticles 11 and ila (the latter not being shown in the figure) can have different designs so that the firer knows whether he is in the small field or large field condition.

The switching of the sources 12 and 12a (the latter not being shown on the figure) is automatically controlled by the field change operation. The two sources are identical so that there is only one reticle brightness adjustment control.

Claims (7)

1. Process for the harmonization of a day/night missile firing system having a day channel including a day telescope with a real reticle, a laser beam guidance transmitter and a collimator/deviation measurer, the night channel including in addition a heat camera operating in a specified spectral band, characterized in that the said day telescope and the said collimator/deviation measurer forming a compact and rigid mechanical subassembly produced such that their respective optical axes are strictly parallel and maintain this parallelism in the long term under the required environmental conditions, the harmonization of the said guidance transmitter is carried out permanently by returning part of its emitted flux to a deviation measuring receiver by means of successive reflections on two separators forming a compact subassembly before the objective of the collimator and a third separator after the said objective, a means of servo-control returning the deviation read by the deviation measurer to zero at all times, the harmonization of the said heat camera being in the same way obtained permanently by forming in its focal plane by means of an invariant trihedron subassembly the infra-red image of the reticle of the collimator displayed after electronic processing on a display screen observed through the eyepiece of the day telescope, the said harmonizations being independent of the drifts of the guidance transmitter, the drifts of the heat camera, the drifts of the display cathode ray tube and of the position of the heat camera.

2. Harmonization process according to Claim 1, characterized in that the obtaining of a projected reticle in the heat camera with good definition despite the compactness of the small diameter collimator consists in carrying out the projection at a shorter wavelength, within the spectral band of the camera and in having an interference filter producing the cut-off at the lower limit of the said spectral band ahead of the injection device, the cut-off at the higher limit being produced by the IR detector.

3. Harmonization process according to Claim 2, characterized in that the said interference filter is advantageously deposited on a porthole protecting the said trihedron subassembly fixed on the front of the objective of the camera.

4. Harmonization process according to Claims 2 and 3, characterized in that the defocusing due to longitudinal chromatic aberration of the objective of the heat camera at the said projection wavelength of the reticle is cor- rected on the collimator by an axial offset of the said reticle so that its image is formed in exactly the same plane as the image of the scene.

5. Harmonization process according to Claims 2 and 3, characterized in that the objective of the camera being bifocal and the longitudinal chromatic aberration generally being different for the two focal lengths Of the said objective, the correction for chromatic aberration is advantageously obtained by means of two reticles axially offset on the optical axis of the collimator, illuminated by two different sources and being of different designs.

6. Harmonization process according to Claim 5, characterized in that an attenuator is placed on the source illuminating the reticle corresponding to the short focal length in order to retain the same reticle brightness for both fields, the said sources being identical in order to have a common control for adjusting the brightness of the reticles.

7. A process for the harmonization of a day/night missile firing system sub.tant ia 1 ly dj dscribed hereinbetore u:tli lefCrpnct to and as shown In th, accoml)rlnylng drawing.

7. A process for the harmonisation of a day/night missile firing system substantially as described hereinbefore with reference to and as shown in the accompanying drawing.

8. Any other novel feature or combination disclosed hereinbefore or shown in the accompanying drawing.

Amendments to the claims have been tiled as follows

1. Process for the harmonization of a day/night missile firing system having a day channel including a day telescope with a real reticle, a laser beam guidance transmitter and a collimator/deviation measurer with an objective, another real reticle and an illuminating source for the collimator function and in addition, two separators in front of said collimator deviation measurer objective, a third separator at the back of said collimator deviation measurer objective and a deviation measuring receiver for the deviation measuring function, the night channel including in addition a heat camera operating in a specified spectral band and forming in its focal plane the infrared image of the scene, characterized in that the said day telescope and the said collimator/deviation measurer form a compact and rigid mechanical subassembly produced such that their respective optical axes are strictly parallel and maintain this parallelism in the long term under the required environmental conditions, the harmonization of the said guidance transmitter is carried out permanently by returning part of its emitted flux to said deviation measuring receiver by means of successive reflections on said two separators forming a compact subassembly and said third separator, a means of servo-control returning the deviation read by the deviation measurer to zero at all times, the harmonization of the said heat-camera being in the same way obtained permanently by forming in its focal plane by means of an invariant trihedron subassembly the infra-red image of said collimator-deviation measurer reticle acting as the aiming reticle of the camera and displayed after electronic processing on a display screen, the image of the scene viewed by the camera also being displayed with the reticle image on said display screen and observed through the eye piece of the day telescope, the said harmonizations being in dependent: of the drifts of the guidance transmitter, the drifts of the heat camera, the drifts of the display cathode ray tube and of the position of the heat camera - 2.Harmonization process according to claim 1, characterized in that the obtaining of a projected reticle in the heat camera with good definition despite the compactness of the small diameter collimator consists in carrying out the projection at a shorter wavelength, within the spectral band of the camera and in having an interference filter producing the cut-off at the lower limit of the said spectral band ahead of the injection device, the cut-off at the higher limit being produced by the IR detector.

3. Harmonization process according to claim 2, characterized in that the said interference filter is advantageously deposited on a porthole protecting the said trihedron subassembly fixed on the front of the objective of the camera.

4. Harmonization process according to claims 2 and 3, characterized in that the defocusing due to longitudinal chromatic aberration of the objective of the heat camera at the said projection wavelength of the reticle is corrected on the collimator by an axial offset of the said reticle so that its image is formed in exactly the same plane as the image of the scene.

5. Harmonization process according to claims 2 and 3, characterized in that the objective of the camera being bifocal and the longitudinal chromatic aberration generally being different for the two focal lengths of the said objective, the correction for chromatic aberration is advantageously obtained by means of two reticles axially offset on the optical axis of the collimator, illuminated by two different sources and being of different designs.

6. Harmonization process according to claim 5, characterized in that an attenuator is placed on the source illuminating the reticle corresponding to the short focal length in order to retain the same reticle brightness for both fields, the said sources being identical in order to have a common control for adjusting the brightness of the reticles.