Electro-optic infrared windows for hypersonic applications.

Abstract

A guidance system for a missile performs a method for guiding a missile. The guidance system includes a target detector and a window between the target and the target detector. The window includes a first glass sheet, a second glass sheet, and a channel between the second glass sheet and the first glass sheet. Radiation from the target passes through the window including the first glass sheet, the second glass sheet, and the channel that is detected at the target detector. Gas is transported through the channel between the first glass sheet and the second glass sheet to control a temperature of the window.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Patent Application No. 17 / 466,693, filed September 3, 2021, which is incorporated by reference in its entirety. [Background technology]

[0002] The present disclosure relates to guidance systems for missiles, and more particularly to systems and methods for reducing the effects of aerodynamic heating at high speeds on the operation of the guidance system electro-optical seeker.

[0003] A missile or other aerial projectile may employ a guidance system to locate a target. The guidance system includes a detector that detects light or radiation from the target and corrects the missile's trajectory based on this detection. The guidance system generally includes a window that protects the detector from the external environment and allows radiation to pass through to the detector. At high speeds through the atmosphere, the window experiences aerodynamic heating, whereby the window heats due to frictional, high-speed collisions with atmospheric molecules. The heated window expands and distorts, thereby affecting the path of the incoming radiation and, ultimately, the guidance system's ability to accurately locate the target. Generally, the distortion effect becomes more pronounced as the window thickness increases. Furthermore, the heated window may emit light at the detection wavelength, thereby causing undesirable background noise. The heated window may also conduct and radiate heat within the missile and guidance system, which may adversely affect the performance and function of the missile and guidance system. Therefore, it is desirable to reduce the effects of aerodynamic heating on the windows of guidance systems for missiles traveling at high speeds in order to reduce optical distortion and improve guidance accuracy. Summary of the Invention

[0004] According to one embodiment of the present disclosure, a method of guiding a missile is disclosed, wherein radiation from a target is detected by a target detector of a guidance system of the missile, and the radiation passes through a window between the target and the target detector, the window including a first glass pane, a second glass pane, and a channel between the second glass pane and the first glass pane, and a gas is transported through the channel between the first and second glass panes to control the temperature of the window.

[0005] In accordance with another embodiment of the present disclosure, a guidance system for a missile is disclosed, the guidance system including a target detector, a window including a first glass plate and a second glass plate separated from the first glass plate by a channel through which radiation from the target passes to be received by the target detector, and gas flowing through the channel between the first and second glass plates.

[0006] According to yet another embodiment of the present disclosure, a missile is disclosed that includes a target detector, a window including a first glass plate and a second glass plate separated from the first glass plate by a channel through which radiation from the target passes to be received by the target detector, and a gas flowing through the channel between the first and second glass plates.

[0007] Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the present disclosure are described in detail herein and are considered a part of the claimed disclosure. For a better understanding of the present disclosure, together with its advantages and features, reference is made to the description and drawings.

[0008] The subject matter which is regarded as the present disclosure is particularly pointed out and distinctly claimed in the claims at the conclusion of this specification. The foregoing and other features and advantages of the present disclosure will become apparent from the following detailed description taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0009] [Figure 1]1 is an illustration of a schematic diagram of a missile in an illustrative embodiment; [Figure 2] 2 illustrates the front end of the missile of FIG. 1 in an exemplary embodiment. [Figure 3] FIG. 1 illustrates a portion of a guidance system for a missile in an exemplary embodiment. [Figure 4] The relationship between emissivity and temperature for various materials is shown. DETAILED DESCRIPTION OF THE INVENTION

[0010] FIG. 1 shows a schematic diagram of a guided missile 100 in an exemplary embodiment. The guided missile 100 includes a flight control system 102, a guidance system 104, and a warhead 106. The guidance system 104 locates a target during flight of the guided missile 100 and generates instructions for guiding the guided missile 100 toward the target. The flight control system 102 may include a propulsion mechanism (e.g., a gas propulsion system) and a steering mechanism that changes the direction of the guided missile 100 based on the instructions generated by the guidance system 104. In various embodiments, the guided missile 100 travels through the atmosphere and collides with atmospheric molecules during its flight. This atmospheric collision causes aerodynamic heating, which heats various sections of the missile, including elements of the guidance system 104.

[0011] FIG. 2 illustrates a forward end 200 of the guided missile 100 in an exemplary embodiment. The guidance system 104 can be included at or near the forward end 200. The guidance system 104 includes a target detector 202 and a processor 204 housed within a housing 206 of the guided missile 100. A window 208 in the housing 206 allows radiation 210 from an external environment 214 to enter the housing 206 so that the radiation 210 can be measured at the target detector 202. The radiation 210 can be received from a target 212 and thus used to guide the guided missile 100 toward the target 212. The target detector 202 detects the radiation 210 and sends a signal to the processor 204, which determines the direction of the target 212 from the signal. The processor 204 then communicates guidance commands to the flight control system 102. The flight control system 102 may adjust or maintain the course of the guided missile 100 based on the guidance signals.

[0012] The housing 206 and window 208 isolate the target detector 202 from the external environment 214. In various embodiments, the target detector 202 is an infrared detector and the window 208 is transparent or transmissive at one or more infrared wavelengths.

[0013] 3 shows a section 300 of guidance system 104, including, in an exemplary embodiment, housing 206 and window 208. Window 208 includes a first glass pane 302 and a second glass pane 304. First glass pane 302 is an outer glass pane that contacts external environment 214. Second glass pane 304 is an inner glass pane that contacts an interior 308 of guided missile 100. First glass pane 302 and second glass pane 304 are parallel or substantially parallel to each other and are separated by a gap or channel 306.

[0014] The first glass pane 302 has an outer window thickness t1, and the second glass pane has an inner window thickness t2. In various embodiments, the inner window thickness t2 can be greater than the outer window thickness t1, although this is not a limitation on the windows. In one embodiment, the outer window thickness t1 is about 0.2 inches (about 0.51 cm) and the inner window thickness t2 is about 0.4 inches (about 1.01 cm). The width t of the channel 306 p (i.e., the distance between the first glass plate 302 and the second glass plate 304) is about 1 / 4 inch (about 0.64 cm).

[0015] The first (outer) glass pane 302 is heated by aerodynamic heating, while the second (inner) glass pane 304 forms a channel 306 with the first glass pane 302. The second glass pane 304 also provides indirect structural support to the first glass pane 302 via pressurized gas within the channel 306. The first glass pane 302 acts as a heat shield, isolating the second glass pane 304 from the onset of aerodynamic heating. When the guided missile 100 is traveling at hypersonic speeds (e.g., greater than about Mach 5), the first glass pane 302 can heat up to temperatures greater than 1000°C, typically greater than 1200°C, if no cooling is applied. The second glass pane 304 also provides a thermal barrier between the external environment 214 and the interior 308 and / or target detector 202.

[0016] A housing passageway 310 within the wall of the housing 206 provides a conduit for gas 312 through the channel 306. The housing passageway 310 has a first section 310a connecting a pressurized tank 314 to the channel 306 and a second section 310b connecting the channel 306 to a port or outlet 316. The pressurized tank 314 stores the gas 312 in a pressurized or liquefied state. A regulator 318 transfers and regulates the gas 312 from the pressurized tank 314 through the first section 310a, the channel 306, and the second section 310b. The gas 312 enters the channel 306 from the first section 310a at the side of the channel 306, moves or flows parallel to the surfaces of the first and second glass sheets 302, 304, and exits the channel 306 at the side of the channel 306 into the second section 310b. Within the channel 306, the gas 312 absorbs heat from the first glass sheet 302, thereby reducing the temperature of the first glass sheet 302 from its "uncooled" temperature. The gas 312 then flows through the second section 310b and transfers the heat out of the channel 306.

[0017] In various embodiments, the gas 312 is a pressurized gas, which can be nitrogen or dry air. The gas 312 moderates the temperatures of both the first glass sheet 302 and the second glass sheet 304 to maintain a low temperature (e.g., in the range of about 50°C to about 80°C). The first glass sheet 302 is intentionally designed to be as thin as practical to minimize or reduce optical distortion due to high thermal gradients across its body, while the layer of gas 312 within the channel 306 provides indirect structural support. The regulator 318 maintains the pressure of the gas 312 to maintain the first glass sheet 302 within its structural limits based on external environmental conditions. Maintaining a low temperature for the second glass sheet 304 prevents the second glass sheet 304 from suffering from heating effects such as expansion and distortion. The second glass sheet 304 provides structural support for the entire window assembly due to its greater thickness than the first glass sheet 302. As a result, radiation 210 passes through second glass plate 304 with a minimal amount of thermally induced optical distortion, allowing for an accurate reading of the position of target 212 .

[0018] A temperature sensor 320 can be incorporated into the interior 308 to measure the temperature of the interior 308 and / or the inner edge of the first glass sheet 302. In various embodiments, the temperature sensor 320 can measure the temperature of the second glass sheet 304. The temperature can be provided to a processor (such as processor 204). The processor 204 can use the temperature to control or adjust the operation of the regulator 318 and, in turn, the flow rate and pressure of the gas in the channels 306, thereby controlling the temperature of the second glass sheet 304. For example, if the temperature exceeds a selected threshold, the processor 204 can adjust the regulator 318 to increase the flow rate of the gas 312 through the channels 306 and the gas pressure in the channels 306. In various embodiments, the gas pressure in the channels 306 is in the range of about 0.5 atmospheres to about 3 atmospheres.

[0019] FIG. 4 shows the relationship 400 between emissivity and temperature for various materials. Curve 402 shows the relationship between emissivity and temperature for sapphire. Curve 404 shows the relationship for nanocomposite optical ceramic (NCOC). NCOC includes polycrystalline materials with grains having nanoscale dimensions. The grain dimensions are typically less than 1 / 10 of the wavelength of light, and preferably 1 / 20 of the wavelength. NCOC exhibits low emissivity at temperatures up to at least 1600° C. In various embodiments, the first glass sheet 302 is made of NCOC. The second glass sheet 304 can also be made of NCOC. In another embodiment, the second glass sheet 304 can be made of sapphire.

[0020] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. Furthermore, it should be understood that the terms "comprises" and / or "comprising," as used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0021] Corresponding structure, materials, acts, and equivalents of all means or step-plus-function elements within the scope of the following claims are intended to include any structure, material, or acts for performing the function in combination with other specifically claimed claim elements. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the invention. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, and to enable those skilled in the art to understand the invention in various embodiments, with various modifications as suited to the particular use intended.

[0022] While exemplary embodiments of the present disclosure have been described, it will be appreciated that those skilled in the art may make various improvements and enhancements, both now and in the future, that fall within the scope of the following claims, which should be interpreted to maintain appropriate protection for the invention as originally described.

Claims

1. 1. A method for guiding a missile, comprising: detecting radiation from a target at a target detector of the missile's guidance system; the radiation passes through a window between the target and the target detector; the window includes a first glass pane and a second glass pane separated by a channel to isolate the second glass pane from aerodynamic heating caused by collisions with atmospheric molecules; Steps and delivering a pressurized gas through the channel between the first and second glass panes to control the temperature of the window; the second glass sheet provides indirect structural support to the first glass sheet via the pressurized gas in the channel; Steps and measuring the temperature at the second glass sheet; controlling the temperature at the second glass sheet; A method comprising:

2. The first glass sheet is heated by aerodynamic heating. The method of claim 1.

3. controlling the temperature of the window further comprises controlling the temperature of the second glass sheet. The method of claim 2.

4. controlling the temperature of the second glass sheet includes adjusting a flow rate and a pressure of the pressurized gas in the channel; The method of claim 3.

5. The method further comprises: circulating the pressurized gas through the channel from a pressurized tank within the missile via a regulator; The method of claim 1 , comprising:

6. The method further comprises: circulating the pressurized gas from the pressurized tank through a housing passageway associated with a housing of the induction system and into the channel; The method of claim 5 , comprising:

7. the pressurized gas is at least one of (i) nitrogen and (ii) dry air; The method of claim 1.

8. 1. A guidance system for a missile, comprising: a target detector; 1. A window comprising a first pane of glass and a second pane of glass separated from the first pane of glass by a channel, the second pane of glass isolating the second pane of glass from aerodynamic heating caused by collisions with atmospheric molecules; a window through which radiation from a target passes and is received at the target detector; a pressurized gas flowing through the channel between the first and second glass panes to control the temperature of the window; the second glass sheet providing indirect structural support to the first glass sheet via the pressurized gas in the channel; and a temperature sensor for measuring the temperature of the second glass sheet; a processor for controlling the temperature at the second pane of glass; Including, the system.

9. The first glass sheet is heated by the aerodynamic heating. The system of claim 8.

10. the pressurized gas flowing through the channel controls the temperature of the second glass sheet. The system of claim 9.

11. a processor for controlling the temperature at the second glass sheet that adjusts the flow rate and pressure of the pressurized gas in the channel; The system of claim 10.

12. The system further comprises: a pressurized tank for storing the pressurized gas; a regulator for circulating the pressurized gas from the pressurized tank through the channel; The system of claim 8 , comprising:

13. The system further comprises: a housing including a housing passageway for flowing the pressurized gas from the pressurized tank to the channel; The system of claim 12 , comprising:

14. the first glass plate is made of a nanocomposite opto-ceramic material; and The second glass plate is made of sapphire. The system of claim 8.

15. the pressurized gas is at least one of (i) nitrogen, and (ii) dry air; The system of claim 8.

16. A system comprising the system described in any one of claims 8 to 14. missile.

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