WO2024057102A1

WO2024057102A1 - Electro-optical tactical missile system

Info

Publication number: WO2024057102A1
Application number: PCT/IB2023/055742
Authority: WO
Inventors: Shimon ZEIERMAN; Tzachi LEVIN; Barak TUR
Original assignee: Rafael Advanced Defense Systems Ltd.
Priority date: 2022-09-13
Filing date: 2023-06-04
Publication date: 2024-03-21

Abstract

A missile system includes a sight having a targeting image sensor for obtaining a reference image and receiving an input defining a desired point of impact, and a missile. The missile has a seeker image sensor having an iFOV that is at least three times wider in each dimension than an iFOV of the targeting image sensor. A processing system of the missile receives the reference image, receives sampled images from the seeker image sensor during flight, and performs image registration between the reference image and the sampled image. The image registration includes down-sampling of the reference image so as to match a resolution of the sampled images. The image registration is used to determine the desired point of impact within the sampled images, and the missile is steered towards the desired point of impact.

Description

Electro-Optical Tactical Missile System

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to missile systems and, in particular, it concerns an electro-optical tactical missile system.

Electro-optical missiles are typically equipped with a seeker capable of imaging a target, detecting the target within the image, and deriving from the images and additional inputs the required control outputs for guiding the missile's flight towards the target. In typical missiles that operate using the fire-and-forget guidance, i.e., without the involvement of an operator after the missile has been launched, the target is designated by the operator on the image from the seeker image sensor before launch. A seeker image sensor with a night vision capability and sufficiently-high resolution to enable target selection and designation, as well as ensuring continuous locking-on to the target during flight, requires relatively expensive hardware components. Specifically, it will typically require a high- resolution thermal imager with narrow field-of-view optics either mounted on a gimbal or in a fixed (also known as a “stiff-necked”) arrangement. As long as these capabilities are implemented as part of the missile, they contribute significantly to the cost-per-unit of the missile, as well as the size, thereby limiting the suitable usescenarios. Since a missile is a one-shot product, reduction in cost of the components of the missile is critical to cost-effectiveness. SUMMARY OF THE INVENTION

The present invention is an electro-optical tactical missile system.

According to the teachings of an embodiment of the present invention there is provided, a missile system comprising: (a) a sight having a targeting image sensor with a first iFOV, the sight being configured to employ the targeting image sensor to obtain a reference image including a target, and to receive an input from an operator designating the target within the reference image, thereby defining a desired point of impact; (b) a missile for launching towards the target, the missile having a seeker image sensor having a second iFOV that is at least three times wider in each of two dimensions than the iFOV of the targeting image sensor, the missile further having a processing system including at least one processor and data storage, the processing system being in data communication with the seeker image sensor, and in data communication prior to launch with the sight, the processing system being configured to: (i) receive the reference image sampled by the targeting image sensor and the desired point of impact within the reference image; (ii) receive sampled images from the seeker image sensor during flight of the missile; (iii) perform image registration between the reference image and the sampled image, the image registration including down-sampling of the reference image so as to substantially match a resolution of the sampled images; (iv) employ the image registration to determine the desired point of impact within the sampled images; and (v) continuously steer the missile towards the desired point of impact. According to a further feature of an embodiment of the present invention, the data communication between the processing system and the sight is through a wired connection prior to launch of the missile.

According to a further feature of an embodiment of the present invention, the data communication between the processing system and the sight is through a wireless communications link prior to launch of the missile.

According to a further feature of an embodiment of the present invention, the targeting image sensor has an angular pixel resolution at least one order of magnitude higher than the seeker image sensor.

According to a further feature of an embodiment of the present invention, the seeker image sensor is rigidly mounted to a body of the missile.

According to a further feature of an embodiment of the present invention, the seeker image sensor is mounted with a gimbal to a body of the missile.

According to a further feature of an embodiment of the present invention, the second iFOV is at least three times wider in each dimension than the first iFOV.

According to a further feature of an embodiment of the present invention, an angular field of view of the seeker image sensor is at least twice the angular field of view of the targeting image sensor.

There is also provided according to the teachings of an embodiment of the present invention, a method of operating a missile system comprising the steps of: (a) employing a sight associated with a missile launching system, the sight having a targeting image sensor with a first iFOV, to obtain a reference image including a target and designating the target within the reference image, thereby defining a desired point of impact; (b) launching a missile towards the target, the missile having a seeker image sensor having a second iFOV that is at least three times wider in each of two dimensions than the iFOV of the targeting image sensor; (c) during flight of the missile, sampling images from the seeker image sensor; (d) employing a processing system to perform image registration between the reference image and the sampled image, the image registration including down- sampling of the reference image so as to substantially match a resolution of the sampled images; (e) employing the image registration to determine the desired point of impact within the sampled images; and (f) continuously steering the missile towards the desired point of impact.

According to a further feature of an embodiment of the present invention, the sight is located at the launch location of the missile.

According to a further feature of an embodiment of the present invention, an angular field of view of the seeker image sensor is at least twice the angular field of view of the targeting image sensor. 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 representation of an electro- optic al missile according to an embodiment of the present invention;

FIG. 2 is a schematic representation of an electro-optical missile system including the missile of FIG. 1, constructed and operative according to an embodiment of the present invention;

FIG. 3 is a flow diagram illustrating operation of the missile of FIG. 1 according to an aspect of the present invention;

FIG. 4A is an exemplary image from a targeting sensor at a launch position in which a target has been designated;

FIGS. 4B (i)-(iv) are a sequence of image from a seeker image sensor of the missile of FIG. 1 from the launch location and from a sequence of subsequent positions during flight of the missile;

FIGS. 5A-5D are image pairs showing (ii) a tile generated from a targeting sensor reference image by down sampling, and (i) a corresponding image from FIG. 4B illustrating the result of image registration marked with a dashed line;

FIG. 6 is a more extensive sequence of images sampled by the seeker image sensor at successively decreasing ranges to the target, together with the targeting image sensor reference image (bottom right); and FIG. 7 is a flow diagram illustrating an overall workflow of a missile system constructed and operative according to an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is an electro-optical tactical missile system and corresponding method.

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

Referring now to the drawings, FIGS. 1-7 illustrate the structure and operation of a missile system, generally designated 10, constructed and operative according to an aspect of the present invention. In general terms, the missile system 10 includes a missile launcher system 12 and a sight 14 having a targeting image sensor 16 with a first pixel count and a first field-of-view (FOV) that defines a first iFOV. The sight may be integrated with the missile launcher or may be interchangeably connected to the launcher (e.g., for use with different launch canisters). In the case of an interchangeable sight configuration, an adjustment process may be required to align the sight with the missile image sensor, as will be clear to a person ordinarily skilled in the art.

The targeting image sensor may support several FOVs for the sake of searching, allocating and investigating suspected targets. In such a case, the FOV and iFOV referred to above are the narrowest FOV and iFOV used for marking the target, and thereby defining a point of impact. The sight 14 is configured to employ the targeting image sensor 16 to obtain a reference image including a target, and to receive an input designating the target within the reference image, thereby defining a desired point of impact.

The missile system also includes a missile 18, typically housed in a launch tube 40, for launching from the missile launcher system 12 towards the target. All components of the launcher system (excluding the missile and possibly the launch tube) are preferably reusable components, for use with successive missiles. Each missile 18 has a seeker image sensor 20 having a pixel count and FOV that defines its iFOV that is at least three times wider than the targeting image sensor 16 iFOV in each of the two dimensions. Preferably, the launch tube 40 and sight 14 are in close proximity, for the purpose of sharing substantially the same line-of-sight with the designated target.

Each missile also has a processing system 22 including at least one processor 24 and data storage 26, the processing system being in data communication, typically a wired connection, with the seeker image sensor 20, and in data communication, prior to launch, with the sight 14.

According to certain particularly preferred implementations of the present invention, processing system 22 is configured to perform an electro-optic homing sequence 100 as illustrated in FIG. 3, including the following steps:

• Receiving the reference image sampled by the targeting image sensor and designation of the target within the reference image (step 102). Receiving sampled images from the seeker image sensor during flight of the missile (step 104).

• Performing image registration between the reference image and the sampled image, including down-sampling of the reference image so as to substantially match a resolution of the sampled images (step 106).

• Employing the image registration to determine the desired point of impact within the sampled images (step 108).

• Steering the missile continuously towards the desired point of impact (step 110).

The significance of the design of the missile system 10 and its advantages will be better understood by reference to FIGS. 4A-6. Specifically, FIG. 4 A illustrates an exemplary reference image sampled by targeting image sensor 16 of sight 14. The targeting image sensor is preferably implemented with a relatively high-resolution image sensor with high quality optics which provide a narrow field- of-view (FOV) image, typically in the range of 3-5 degrees, and is typically a thermal imaging sensor, thereby providing day and night operation capability. The term iFOV is used herein in its normal sense, and is defined as the angle subtended by a single detector element. In the non-limiting example illustrated in the exemplary images, a targeting image sensor with an angular FOV of 3.7 X 2.8 degrees and a pixel resolution of 384*288 was used. Therefore, according to this example, iFOV of this image sensor is about 0.17 milliradians for both the horizontal and the vertical axes. A high-quality thermal camera of this resolution and the accompanying narrow FOV optics are relatively expensive components of the system. Since, however, this sensor is part of the reusable sight, this is a onetime investment used to launch successive missiles.

In contrast, the seeker image sensor 20 that is included with each missile is here preferably implemented as a relatively low-resolution thermal imaging sensor, in certain preferred cases having a pixel count that is at least an order of magnitude less than the pixel count of the targeting image sensor 16 and/or an iFOV that is at least 3 times wider in each dimension than that of the targeting image sensor. The seeker image sensor 20 is exemplified here as an 80*80-pixel sensor, and implemented using a relatively low-cost uncooled bolometric sensor. In certain nonlimiting but preferred implementations, to further reduce complexity and costs of the missile, the sensor 20 is rigidly mounted to body 28 of missile 18, i.e., as a “stiffnecked” implementation without gimbals. In some cases, in order to ensure that a target remains within the seeker image sensor FOV during flight, it is advantageous to use a wider FOV than the targeting image sensor. Thus, the seeker image sensor angular FOV is typically at least twice that of the targeting image sensor angular FOV. In the examples given herein, the seeker image sensor FOV is 12.1 degrees. This corresponds to an iFOV in both the X and Y dimensions of 2.64 milliradians, which is more than 15 times the iFOV of the targeting sensor in the above example.

In an alternative non-limiting but preferred embodiment of the presented invention, a wider Field of Regard (FOR) is achieved by mounting the sensor on a low-cost inaccurate gimbal that increases the sensor's actual coverage area. It is clear that the use of a low-resolution image sensor in a stiff-necked configuration provides a highly-advantageous low-cost implementation of an electro-optical tactical missile. However, it poses a clear challenge for implementation, as will be appreciated by referring to FIG. 4B(i), which shows an image sampled from the missile seeker image sensor from the same range as FIG. 4A was sampled from the targeting image sensor. The spatial resolution of the seeker image sensor is much lower than that of the targeting image sensor, typically with an angular pixel resolution at least one order of magnitude (10 times) lower for the seeker image sensor than for the targeting image sensor. By way of one numerical example, in the case used for generating the exemplary images herein, the targeting image sensor has a 384x288 pixel resolution and a horizontal FOV of 3.7 degrees, while the seeker image sensor has an 80x80 pixel count and a horizontal FOV of 12.1 degrees. The resulting ratio of the pixel angular resolution (referred to as “iFOV”) between the targeting image sensor and the seeker image sensor is given by:

12.1 / 3.7

- /- — = 15.7

80 # 384

In other words, when both the missile and the sight view a target from the same distance, a horizontal distance covered by ~16 pixels width in the targeting image sensor of the sight is rendered by only 1 -pixel width in the seeker image sensor. In two dimensions, each pixel of the seeker image corresponds to the same

FOV covered by about 250 pixels in the targeting image sensor. As a result, in most cases, the seeker images do not contain enough information to allow a target to be detected or tracked, and in some usage scenarios, the entire target may be a subpixel size in images from the seeker image sensor, rendering target tracking clearly impossible based on those images.

An aspect of the present invention, corresponding to processing system 22 as defined above, overcomes this hurdle, allowing accurate guidance of the missile to the target based on the low-resolution imagery from seeker image sensor 20. The image processing performed by processing system 22 will be better understood with reference to FIGS. 4A-5D. As mentioned, FIGS. 4A and 4B(i) correspond, respectively, to the images from the targeting image sensor 16 and the seeker image sensor 20 before launch, in this example, at a range of 815 meters from a target. FIGS. 4B(ii), (iii) and (iv) are subsequently-sampled images from the seeker image sensor 20 taken during the flight of the missile towards the target, and specifically, at ranges of about 640 meters, about 330 meters, and about 130 meters from the target, respectively.

Although the target is not discernable in the images taken by the seeker image sensor before launch and through the first stage of flight while the missile is far from the target and advancing towards it, as can be demonstrated in FIGS. 4B(i) and (ii), the guidance methodology of the missiles of the present invention manages to achieve reliable guidance of the missile towards the target by performing image registration processing between images from the seeker image sensor and a downsampled version of a tile of a chosen size, taken out of the stored reference image from the targeting image sensor. In this example, at launch, at a range of 815 meters from a target, the down-sampling ratio is initially set to the ratio of iFOV between the targeting image sensor and the seeker image sensor, in this example calculated to be 15.7.

Specifically, FIG. 5 A(ii) shows a down-sampled tile of the reference image 4A. The center of the tile coincides with the pixel chosen to define the target location, designated on the reference image. The size of the tile can be chosen according to a balance between processing efficiency, and having sufficient image information to achieve reliable correlation and image registration. In the example illustrated here, after the required down-sampling is calculated in order to achieve a similar spatial resolution between the down-sampled reference image and the current seeker image, a target tile corresponding to 17*17 pixels of the seeker image sensor, FIG. 5A(ii), is generated, and this is correlated against the 80*80 seeker image, FIG. 5A(i). The processing system 22 looks for a best match for the tile of FIG. 5A(ii) in the sampled image from the seeker image sensor and identifies the target location (red cross) in the seeker image, FIG. 5A(i). The size of the target tile is typically at least 10*10 pixels, and typically no larger than 30*30 pixels, with a square of about 15-20 pixels in each dimension typically optimum.

Once a tile corresponding to the reference image has been registered with the current seeker image, the location of the designated target within the reference image can readily be used to determine the target position within the current seeker image, thereby allowing steering towards the target, despite the fact that the target does not explicitly appear in the seeker image. Each image registration result is preferably used as a starting point for the next matches between the reference image and next seeker images obtained.

As the missile advances towards the target, the fixed angular FOV of the seeker image sensor sees a smaller area of the scene at a higher spatial resolution. In the extreme case of lack of any information related to the velocity of the missile or distance to target, the processing system 22 uses correlation techniques in order to optimize the down-sampling ratio, number of pixels per tile and the location of the designated target pixel within the current seeker image. In this example, the results of the optimization at 3 distances of the seeker from the target are illustrated in FIGS. 5B-5D. The optimized number of pixels per tile has been calculated to be 19x19, 31x31 and 47x47 pixels, respectively, in FIGS. 5B, 5C and 5D. The green asterisk on FIGS. 5B(i)-5D(i) designates the location of the target in the previous seeker image and the red cross in the same figures designates the location of the target found using the algorithm.

It is possible to continue this form of guidance for the entire flight, even when the seeker image spatial resolution matches or even exceeds the spatial resolution of the reference image. Alternatively, once the spatial resolution of images from the seeker image sensor is sufficiently high, for example, matching the spatial resolution of the reference image, the processing system 22 may switch to guidance based on tracking algorithms that track the previously designated target directly within the images sampled from the seeker image sensor, employing conventional tracking techniques.

The required processing techniques for achieving registration between two images of differing spatial resolution, including deriving the appropriate downscaling of the higher resolution image to achieve the registration, are well known in the art, and can be performed using standard libraries of graphics processing function such as OpenCV. Optionally, processing efficiency can be optimized by providing a relatively accurate estimation of the relative spatial resolution of the seeker image relative to the reference image based, for example, on the previous image registration results and/or based on elapsed time from launch together with pre-launch range information and the kinetic profile of the missile’ s flight trajectory. The processing may also take into account different grid positions for downsampling of the reference image, which may impact the appearance of the target in the down-sampled tile.

A fuller sequence of sampled images from the seeker image sensor 20 during flight of the missile, and the reference image from the targeting image sensor 16 are shown in FIG. 6, including a target designation symbol (in red) in each seeker image, as derived by the processing described above.

Referring now back to FIGS. 1 and 2, FIG. 1 shows schematically various additional components of an implementation of missile 18 while FIG. 2 shows schematically other components of an implementation of the launcher system 12. According to certain implementations, the onboard processing system 22 of missile 18 is associated with a communications subsystem 30« for communicating with a corresponding communications subsystem 306 of the launcher system 12. The communications subsystems 30« and 306 may be either a wired or wireless connection for maintaining communication between the missile and the launcher before launch. The missile system 10 of the present invention is designed for “fire- and-forget” operation.

In the case of fire-and-forget operation, it is sufficient for communications subsystems 30« and 306 to provide data transfer from the launcher system 12 to the processing system 22 of the missile 18 prior to launch, thereby providing the reference image and target location information within the reference image before launch. Such interfaces may be implemented as wired or wireless connections between the sight 14 and a launch canister 40, as is known in the art.

Guidance outputs generated by onboard processing system 22 typically actuate steering actuators 32 to guide missile 18 along a flight path to a target. The steering actuators 32 may be any type of known steering actuator including, but not limited to, electro-mechanical actuators linked to aerodynamic control surfaces, pyrotechnic steering actuators, and thrust-vectoring control, all as is known in the art. In some cases, missile 18 may include an inertial navigation system (INS) 34, which provides inputs to the processing system to facilitate maintaining stable flight, and may allow the missile to follow a predefined initial flight path from launch until designated target is visible. Missile 18 typically also includes a payload 36 (e.g., a warhead with a suitable fuze and initiator system, all chosen according to the intended target type), and one or more stages of a propulsion system 38.

Turning now to FIG. 2, according to the exemplary implementation illustrated here, missile 18 is deployed prior to launch in a canister (interchangeably referred to as a “launch tube”) 40 of launching system 12. Canister 40 may be of any conventional type, and may be configured for mounting on a vehicle (terrestrial or aerial), for shoulder launching, or may be free-standing. As described above, launching system 12 includes targeting image sensor 16. Optionally, a rangefinder 42 may provide a range to a selected target, thereby facilitating calculation of an approximate remaining range to the target during flight of the missile and/or allowing determination of an initial flight path to be followed inertially until the missile locks onto the target. To complete the user interface operations, integrated sight 14 preferably also includes a display 44 and an operator input device 46, implementing track and fire commands, all operating under the control of a suitable processing system 48, all as is known in the art.

Turning finally to FIG. 7, this illustrates the overall workflow 200 of the tactical missile system 10 of the present invention. After loading (not shown) the launching system 12 with a missile 18, typically in a canister 40, the integrated sight 14 is used by an operator (or alternatively by an automated system) to detect a target and to designate the target within an image from the targeting image sensor 16 (step 202). All or part of that image becomes the “reference image” for the purpose of the guidance algorithm. The reference image and the target location within that image are then transferred to the missile (step 204), and the missile is launched towards the target (step 206). Optionally, if the electro-optical guidance process has not locked onto the target before launch (e.g., due to being launched at an elevation angle relative to direct LOS), an initial stage of the missile flight may be controlled based on inertial navigation 208. Once the target enters the seeker FOV, it then acquires the designated target by the process detailed above with reference to FIG. 3 (step 210), and the missile is steered towards the target based on that tracking (step 212).

Immediately after firing, the launching system 12 is ready to be loaded with a next missile 18 and to repeat the firing process as needed.

It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the scope of the present invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A missile system comprising:

(a) a sight having a targeting image sensor with a first iFOV, said sight being configured to employ said targeting image sensor to obtain a reference image including a target, and to receive an input designating the target within the reference image, thereby defining a desired point of impact;

(b) a missile for launching towards the target, said missile having a seeker image sensor having a second iFOV that is at least three times wider in each of two dimensions than the iFOV of said targeting image sensor, said missile further having a processing system including at least one processor and data storage, said processing system being in data communication with said seeker image sensor, and in data communication prior to launch with said sight, said processing system being configured to:

(i) receive the reference image sampled by said targeting image sensor and the desired point of impact within the reference image;

(ii) receive sampled images from the seeker image sensor during flight of the missile; (iii) perform image registration between said reference image and said sampled image, said image registration including downsampling of the reference image so as to substantially match a resolution of the sampled images;

(iv) employ the image registration to determine the desired point of impact within the sampled images; and

(v) continuously steer the missile towards the desired point of impact.

2. The missile system of claim 1 , wherein said data communication between said processing system and said sight is through a wired connection prior to launch of the missile.

3. The missile system of claim 1 , wherein said data communication between said processing system and said sight is through a wireless communications link prior to launch of the missile.

4. The missile system of claim 1, wherein said targeting image sensor has an angular pixel resolution at least one order of magnitude higher than said seeker image sensor.

5. The missile system of claim 1, wherein the seeker image sensor is rigidly mounted to a body of said missile.

6. The missile system of claim 1, wherein the seeker image sensor is mounted with a gimbal to a body of said missile.

7. The missile system of claim 1, wherein the second iFOV is at least three times wider in each dimension than the first iFOV.

8. The missile system of claim 1, wherein an angular field of view of said seeker image sensor is at least twice the angular field of view of said targeting image sensor.

9. A method of operating a missile system comprising the steps of:

(a) employing a sight associated with a missile launching system, the sight having a targeting image sensor with a first iFOV, to obtain a reference image including a target and designating the target within the reference image, thereby defining a desired point of impact;

(b) launching a missile towards the target, the missile having a seeker image sensor having a second iFOV that is at least three times wider in each of two dimensions than the iFOV of said targeting image sensor; (c) during flight of the missile, sampling images from the seeker image sensor;

(d) employing a processing system to perform image registration between said reference image and said sampled image, said image registration including down-sampling of the reference image so as to substantially match a resolution of the sampled images;

(e) employing the image registration to determine the desired point of impact within the sampled images; and

(f) continuously steering the missile towards the desired point of impact.

10. The method of claim 9, wherein the second iFOV is at least three times wider in each dimension than the first iFOV.

11. The method of claim 9, wherein the seeker image sensor is rigidly mounted to a body of the missile.

12. The method of claim 9, wherein the seeker image sensor is mounted with a gimbal to a body of said missile.

13. The method of claim 9, wherein the sight is located at the launch location of the missile.

14. The method of claim 9, wherein an angular field of view of the seeker image sensor is at least twice the angular field of view of the targeting image sensor.