Self-adaptive design method of long-focal-length main three-lens integrated lightweight space camera

Abstract

The invention provides a self-adaptive design method of a long-focus main three-lens integrated lightweight space camera, and relates to the technical field of optical system design. According to the method, a self-adaptive structure parameter search space is designed, and self-adaptive acquisition of the structure parameter search space for different design requirements and light path structure requirements is realized; a main three-lens distance discrimination model and a long-focus space camera size objective function are designed, and the installation and adjustment difficulty degree and the lightweight degree of the long-focus space camera are automatically judged; a main three-mirror distance discrimination model and a long-focus space camera size objective function are combined with an off-axis degree function, an image quality evaluation function and a light path cross function, and a structure parameter objective function is designed; a long-focus space camera parameter combination which is most suitable for easy installation and adjustment, light weight and high imaging quality is obtained by searching a minimum value of a structure parameter objective function, and a free-form surface design method is used to obtain a free-form surface space camera.

Description

Technical Field

[0001] The present invention relates to the technical field of optical system design, and in particular to an adaptive design method for a long-focal-length main three-mirror integrated lightweight space camera. Background Art

[0002] Space cameras are the core equipment of space remote sensing imaging technology and are widely used to obtain images and data of the earth's surface from satellites or spacecraft. In order to effectively monitor small-scale changes on the earth's surface, space cameras need to be able to clearly capture the details of the surface from a long distance. Therefore, long-focal-length space cameras are commonly used imaging devices in space remote sensing. Since space cameras are generally off-axis multi-reflective free-form surface systems, the asymmetry of their surface shape and system structure increases the difficulty of assembling and adjusting space cameras. To this end, it is necessary to use the main three-mirror integration method, that is, to integrate the main mirror and the three mirrors on the same substrate to achieve the purpose of reducing the difficulty of assembly and adjustment. At the same time, due to the limitations of the working conditions of space cameras, it is necessary to design lightweight space cameras to reduce launch costs and energy consumption and increase the payload and operating efficiency of spacecraft. However, the reduction in the size of space cameras usually leads to a decrease in imaging quality. None of the current long-focal-length space camera design methods have balanced the relationship between assembly and adjustment difficulty, lightweight and imaging quality during the design process, that is, there is no long-focal-length space camera design model that simultaneously guarantees easy assembly and adjustment, lightweight and imaging quality. At present, the design of the structural parameters of space cameras often needs to rely on the experience of the designer, resulting in a low degree of automation. Although some researchers have proposed the use of search algorithms, that is, searching for the structural parameters that best meet the requirements of the objective function within a certain range. However, this method is mainly applicable to non-telephoto space cameras, and the search space of structural parameters needs to be set based on empirical knowledge. If the search method is used directly to obtain the structural parameters of a long-focal-length space camera, the search space needs to be expanded exponentially, which will seriously increase the time cost of the search, and may even fail to search for a usable solution. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide an adaptive design method for a long-focal-length main three-mirror integrated lightweight space camera in view of the above-mentioned deficiencies in the prior art. The method adaptively designs a long-focal-length space camera with a free-form surface in view of the requirements of easy installation and adjustment, lightweight and high imaging quality.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: an adaptive design method for a long focal length main three-mirror integrated lightweight space camera, comprising the following steps:

[0005] Step 1: Construct the adaptive mirror spacing search space;

[0006] The expression of the adaptive mirror spacing search space is:

[0007] |d max |=τ1ED (1)

[0008] d min |=τ2ED (2)

[0009] Where ED is the entrance pupil diameter, τ1 and τ2 are the function weights of the upper and lower limits of the adaptive mirror spacing search space respectively; d max and d min are the upper and lower bounds of the adaptive mirror spacing search space, respectively;

[0010] The expressions of τ1 and τ2 are:

[0011]

[0012] Wherein, f is the focal length of the long focal length space camera, F represents the F number of the long focal length space camera, xfov and yfov are the maximum field of view angles of the long focal length space camera in the x and y directions respectively; and are the focal length and F number of the long focal length space camera in τ1 and the weight of the maximum field of view angle of the long focal length space camera in the x and y directions respectively; and are the focal length and F number of the long focal length space camera in τ2 and the weight of the maximum field of view angle of the long focal length space camera in the x and y directions respectively; and and Set according to actual needs;

[0013] In formula (4), The expression is:

[0014]

[0015] Where N is the number of reflectors in the long focal length space camera;

[0016] In order to obtain an upper limit of the adaptive mirror spacing that is more suitable for long focal length space cameras, it is necessary to use It changes dynamically with the focal length f, and the expression is:

[0017]

[0018] Said and The expression is:

[0019]

[0020] Among them, τ c is a parameter that changes with the focal length f, as shown in the following formula:

[0021]

[0022] Step 2: Construct an adaptive curvature radius search space;

[0023] The optical relationship between the adaptive mirror spacing and the focal length of the long focal length space camera is constructed using the ABCD matrix method. The expression is:

[0024]

[0025] in, is the focal length of the Nth reflector in the long focal length space camera; is the focal length of the N-1th reflector in the long focal length space camera; is the focal length of the primary mirror in the long focal length space camera; d N-1 is the distance between the N-1th reflector and the Nth reflector in the long focal length space camera; A, B, C, and D are all functions of the optical power and adaptive mirror spacing of the long focal length space camera;

[0026] Construct the objective function g of the adaptive curvature radius c , the expression is:

[0027]

[0028] Among them, i N is the refractive index of the Nth reflector in the long focal length space camera, n is the reflector serial number, 1≤n≤N; r n is the adaptive curvature radius of the nth reflector in the long focal length space camera;

[0029] The upper limit d of the adaptive mirror spacing search space max and the lower limit d of the adaptive mirror spacing search space min Substitute d into formula (11) respectively N In the above equation, we can get the corresponding adaptive curvature radius combination {r DMAX} and {r DMIN}, thus obtaining the adaptive curvature radius search space of each mirror, expressed as:

[0030]

[0031] in, and are the upper and lower limits of the adaptive curvature radius search space respectively;

[0032] Step 3: Construct an adaptive tilt angle search space;

[0033] The clockwise tilt angle is defined as a positive number, and the counterclockwise tilt angle is defined as a negative number; the adaptive tilt angle search space of the primary mirror is constructed in the form of absolute value:

[0034] |α1|∈[0.5arcsin(ED / 2 / |d max |),0.5arcsin(ED / |d min |)] (14)

[0035] Where α1 represents the tilt angle of the primary mirror;

[0036] The adaptive tilt angle search space of the secondary mirror is constructed; when α2>2α1, the rotation vector of the secondary mirror is -1; when α2<2α1, the rotation vector of the secondary mirror is 1; the angle between the incident light and the outgoing light is defined as an acute angle, and the search space of the adaptive tilt angle of the secondary mirror is obtained, and the expression is:

[0037]

[0038] Where α2 is the tilt angle of the secondary mirror, V s is the rotation vector of the secondary mirror;

[0039] Construct the adaptive tilt angle search space of the three mirrors; calculate that when the light incident on the three mirrors coincides with the light emitted from the three mirrors, the tilt angle of the three mirrors is 2(α2-α1), and the search space of the adaptive tilt angle of the three mirrors is obtained, and the expression is:

[0040]

[0041] Among them, V T is the rotation vector of the three mirrors, α3 is the tilt angle of the three mirrors;

[0042] Step 4: Construct a distance discrimination model for the main three mirrors of a long focal length space camera to evaluate the integration degree of the main three mirrors;

[0043] The main three-mirror distance of a long-focal-length space camera is the shortest distance between the main mirror and the three mirrors; the main mirror and the three mirrors are integrated on a substrate for manufacturing so that the distance between the main mirror and the three mirrors is less than a set threshold; the main three-mirror distance discrimination function g is defined ft , the expression is:

[0044]

[0045] Among them, d ft is the shortest distance between the primary mirror and the third mirror; Q is the set threshold, which is a constant;

[0046] For a long focal length space camera with a z-type structure, the primary and secondary mirror spacing and the secondary three mirror spacing are set equal to increase the search speed of the search algorithm, so that the long focal length space camera quickly converges to the goal of integrating the primary and three mirrors. When the optical path structure of the long focal length space camera is designed to be z-type, it is necessary to add an additional mirror spacing constraint condition on the basis of formula (17), that is, |d1|=|d2|, where d1 and d2 are the primary and secondary mirror spacing and the secondary three mirror spacing respectively.

[0047] Step 5: Construct the size objective function g of the long focal length space camera s Used to calculate the size of long focal length space cameras;

[0048] Based on Snell's law and the inverse tracing method, the center and edge rays of the field of view (0,0), (0,yfov / 2), (0,-yfov / 2) and (xfov / 2,0) are traced to obtain the coordinates of the intersection of each ray with the reflector and the image plane, as well as the set of x, y and z coordinates of all intersections {X}, {Y} and {Z}, and the size objective function g of the space camera s The expression is:

[0049] g s =|max{Y}-min{Y}|×|max{Z}-min{Z}|×2max{|X|} (18)

[0050] Step 6: Construct the structural parameter objective function G of the long focal length space camera;

[0051] The structural parameter objective function G of the telephoto space camera is composed of the main three-mirror distance discrimination model, the size objective function, the image quality evaluation function, the off-axis degree function and the optical path intersection function, and the expression is:

[0052]

[0053] Among them, δ1, δ2, δ3, δ4 and δ5 are the weights of the objective functions of the structural parameters of the long focal length space camera, α n is the tilt angle of the nth reflector in the long focal length space camera, g q , g oa and g p They are image quality evaluation function, off-axis degree function and optical path intersection function respectively;

[0054] The image quality evaluation function g q , off-axis function g oa and the optical path intersection function g p The expressions are:

[0055]

[0056] Among them, K is the total number of sampling rays, i is the serial number of the sampling ray, (x c ,y c ,z c ) is the coordinate of the ideal image point, (x i ,y i ,z i ) is the coordinate of the imaging point of the i-th sampling light; OA n is the off-axis degree discrimination number, OAM n is the margin discrimination number, σ1 and σ2 are the off-axis degree discrimination numbers OA n OAM n The weight of The pth optical path intersection vector of the space camera with medium and long focal length is required for design; is the pth light path intersection vector of the current long focal length space camera;

[0057] Step 7: Use a search algorithm to search for the minimum value of the structural parameter objective function of the long focal length space camera to obtain the most suitable structural parameters for the long focal length space camera; then combine the obtained structural parameters that are most suitable for the long focal length space camera with the free-form surface design method to optimize the reflector into a free-form surface to obtain a free-form surface long focal length space camera.

[0058] The beneficial effects of adopting the above technical solution are: compared with the prior art, the adaptive design method of a long-focal-length main three-mirror integrated lightweight space camera provided by the present invention has the following beneficial effects:

[0059] 1. Through the adaptive structural parameter search space setting model, the mirror spacing, curvature radius and tilt angle search space applicable to different design and optical path structure requirements are designed; compared with the existing long focal length space camera design method, it further reduces the dependence on design experience, has higher flexibility, and improves the search coverage and efficiency;

[0060] 2. By setting the distance discrimination module of the main three mirrors of the long focal length space camera and the size objective function of the long focal length space camera, the integration degree of the main three mirrors of the space camera is automatically improved and the size of the long focal length space camera is reduced; compared with the existing design method of the long focal length space camera, the generated long focal length space camera has lower installation difficulty and higher lightness;

[0061] 3. By setting the structural parameter objective function of the long-focal-length space camera, a unified evaluation standard is designed to automatically evaluate the difficulty of installation and adjustment, lightweight degree and imaging quality of the long-focal-length space camera. Compared with the existing long-focal-length space camera design method, it more effectively balances the imaging requirements with the installation and adjustment and lightweight requirements, and it is easier to screen out long-focal-length space cameras that are easy to install, lightweight and have high imaging quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 A flow chart of an adaptive design method for a long focal length main three-mirror integrated lightweight space camera provided by an embodiment of the present invention;

[0063] Figure 2 Schematic diagram of the adaptive search space for the tilt angle of the secondary mirror provided in an embodiment of the present invention, wherein (a) is a case where the incident light on the secondary mirror coincides with the outgoing light, (b) is a case where the rotation vector of the secondary mirror is -1, and (c) is a case where the rotation vector of the secondary mirror is 1;

[0064] Figure 3 A schematic structural diagram of a long focal length space camera provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0065] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0066] An adaptive design method for a long focal length main three-mirror integrated lightweight space camera of this embodiment is as follows: Figure 1 As shown, the following steps are included:

[0067] Step 1: Construct the adaptive mirror spacing search space;

[0068] The expression of the adaptive mirror spacing search space is:

[0069] |d max |=τ1ED (1)

[0070] |d min |=τ2ED (2)

[0071] Where ED is the entrance pupil diameter, τ1 and τ2 are the function weights of the upper and lower limits of the adaptive mirror spacing search space respectively; d max and d min are the upper and lower bounds of the adaptive mirror spacing search space, respectively;

[0072] The expressions of τ1 and τ2 are:

[0073]

[0074]

[0075] Wherein, f is the focal length of the long focal length space camera, F represents the F number of the long focal length space camera, xfov and yfov are the maximum field of view angles of the long focal length space camera in the x and y directions respectively; and are the focal length and F number of the long focal length space camera in τ1 and the weight of the maximum field of view angle of the long focal length space camera in the x and y directions respectively; and are the focal length and F number of the long focal length space camera in τ2 and the weight of the maximum field of view angle of the long focal length space camera in the x and y directions respectively; and and Set according to actual needs;

[0076] In this embodiment,

[0077] In formula (4), The expression is:

[0078]

[0079] Where N is the number of reflectors in the long focal length space camera;

[0080] In order to obtain an upper limit of the adaptive mirror spacing that is more suitable for long focal length space cameras, it is necessary to use It changes dynamically with the focal length f, and the expression is:

[0081]

[0082] Said and The expression is:

[0083]

[0084] Among them, τ c is a parameter that changes with the focal length f, as shown in the following formula:

[0085]

[0086] Step 2: Construct an adaptive curvature radius search space;

[0087] The optical relationship between the adaptive mirror spacing and the focal length of the long focal length space camera is constructed using the ABCD matrix method. The expression is:

[0088]

[0089] in, is the focal length of the Nth reflector in the long focal length space camera; is the focal length of the N-1th reflector in the long focal length space camera; is the focal length of the primary mirror in the long focal length space camera; d N-1is the distance between the N-1th reflector and the Nth reflector in the long focal length space camera; A, B, C, and D are all functions of the optical power and adaptive mirror spacing of the long focal length space camera;

[0090] Construct the objective function g of the adaptive curvature radius c , the expression is:

[0091]

[0092] Among them, i N is the refractive index of the Nth reflector in the long focal length space camera, n is the reflector serial number, 1≤n≤N; r n is the adaptive curvature radius of the nth reflector in the long focal length space camera;

[0093] The upper limit d of the adaptive mirror spacing search space max and the lower limit d of the adaptive mirror spacing search space min Substitute d into formula (11) respectively N In the above equation, we can get the corresponding adaptive curvature radius combination {r DMAX} and {r DMIN}, thus obtaining the adaptive curvature radius search space of each mirror, expressed as:

[0094]

[0095] in, and are the upper and lower limits of the adaptive curvature radius search space respectively;

[0096] In equation (12), the upper limit d of the adaptive mirror spacing search space is max Substituting d into equation (11) N The adaptive curvature radius combination {r DMAX The N adaptive curvature radii contained in} are not necessarily the upper limit of the adaptive curvature radius search space, so it is necessary to use the maximum value operation to obtain the upper limit of the adaptive curvature radius search space, and the same is true for formula (13);

[0097] Step 3: Construct an adaptive tilt angle search space;

[0098] The clockwise tilt angle is defined as a positive number, and the counterclockwise tilt angle is defined as a negative number; the main purpose of the primary mirror tilt is to eliminate the obstruction of the secondary mirror to the incident light, and the positive or negative tilt angle has no effect on the optical path structure. Therefore, the adaptive tilt angle search space of the primary mirror can be expressed in the form of absolute value as follows:

[0099] |α1|∈[0.5arcsin(ED / 2 / |d max|),0.5arcsin(ED / |d min |)] (14)

[0100] Where α1 represents the tilt angle of the primary mirror;

[0101] The tilt angle of the secondary mirror will affect the optical path structure. According to the definition of the optical path structure, when the extension line of the incident secondary mirror light rotates counterclockwise and can coincide with the outgoing light at an angle less than 180 degrees, the rotation vector of the secondary mirror is -1, otherwise it is 1. To this end, the adaptive tilt angle search space of the secondary mirror can be constructed according to the requirements of the optical path structure, such as Figure 2 As shown. It can be concluded that when α2>2α1, the rotation vector of the secondary mirror is -1; when α2<2α1, the rotation vector of the secondary mirror is 1; at the same time, in order to ensure the compactness of the structure, the angle between the incident light and the outgoing light is defined as an acute angle, so the search space of the adaptive tilt angle of the secondary mirror is obtained, and the expression is:

[0102]

[0103] Where α2 is the tilt angle of the secondary mirror, V s is the rotation vector of the secondary mirror;

[0104] Construct the adaptive tilt angle search space of the three mirrors; calculate that when the light incident on the three mirrors coincides with the light emitted from the three mirrors, the tilt angle of the three mirrors is 2(α2-α1), and the search space of the adaptive tilt angle of the three mirrors is obtained, and the expression is:

[0105]

[0106] Among them, V T is the rotation vector of the three mirrors, α3 is the tilt angle of the three mirrors;

[0107] Step 4: Construct a distance discrimination model for the main three mirrors of a long focal length space camera to evaluate the integration degree of the main three mirrors;

[0108] The main three-mirror distance of the long focal length space camera is the shortest distance between the main mirror and the three mirrors; in order to achieve the purpose of easy installation and adjustment, the main mirror and the three mirrors need to be integrated on a substrate for manufacturing, so that the distance between the main mirror and the three mirrors is less than a set threshold; define the main three-mirror distance discrimination function g ft , the expression is:

[0109]

[0110] Among them, d ft is the shortest distance between the primary mirror and the third mirror; Q is the set threshold, which is a constant and Q < 150;

[0111] In this embodiment, Q=100;

[0112] For a long focal length space camera with a z-type structure, the primary and secondary mirror spacing and the secondary three mirror spacing are set equal to increase the search speed of the search algorithm, so that the long focal length space camera quickly converges to the goal of integrating the primary and three mirrors. When the optical path structure of the long focal length space camera is designed to be z-type, it is necessary to add an additional mirror spacing constraint condition on the basis of formula (17), that is, |d1|=|d2|, where d1 and d2 are the primary and secondary mirror spacing and the secondary three mirror spacing respectively.

[0113] Step 5: Construct the size objective function g of the long focal length space camera s Used to calculate the size of long focal length space cameras;

[0114] Based on Snell's law and the inverse tracing method, the center and edge rays of the field of view (0,0), (0,yfov / 2), (0,-yfov / 2) and (xfov / 2,0) are traced to obtain the coordinates of the intersection of each ray with the reflector and the image plane, as well as the set of x, y and z coordinates of all intersections {X}, {Y} and {Z}, and the size objective function g of the space camera s The expression is:

[0115] g s =|max{Y}-min{Y}|×|max{Z}-min{Z}|×2max{|X|} (18)

[0116] Step 6: Construct the structural parameter objective function G of the long focal length space camera;

[0117] The structural parameter objective function G of the telephoto space camera is composed of the main three-mirror distance discrimination model, the size objective function, the image quality evaluation function, the off-axis degree function and the optical path intersection function, and the expression is:

[0118]

[0119] Among them, δ1, δ2, δ3, δ4 and δ5 are the weights of the objective functions of the structural parameters of the long focal length space camera, α n is the tilt angle of the nth reflector in the long focal length space camera, g q , g oa and g p They are image quality evaluation function, off-axis degree function and optical path intersection function respectively;

[0120] The image quality evaluation function g q , off-axis function g oa and the optical path intersection function g p The expressions are:

[0121]

[0122] Among them, K is the total number of sampling rays, i is the serial number of the sampling ray, (x c ,y c ,z c ) is the coordinate of the ideal image point, (x i ,y i ,z i ) is the coordinate of the imaging point of the i-th sampling light; OA n OA is the off-axis degree judgment number. When the nth reflector does not block any light, n =0, otherwise OA n The value of is the shortest distance from the reflector to the blocked light; when n = N + 1, it represents the image plane; OAM n is the margin judgment number. When the shortest distance between the nth reflector and any light in the system is greater than 10 mm, OAM n =0, otherwise OAM n The value is the absolute value of the difference between the shortest distance from the reflector to the blocked light and 10mm; σ1 and σ2 are the off-axis degree discrimination numbers OA n OAM n The weight of The pth optical path intersection vector of the space camera with medium and long focal length is required for design; is the pth light path intersection vector of the current long focal length space camera;

[0123] In this embodiment, δ1=1×10 -8 , δ2=δ3=50, δ4=δ5=1, σ1=5, σ2=1, Q=100;

[0124] In terms of volume, the design requirements are the same, but the volume of the long focal length space camera is 4.36m obtained by empirical method. 3 ,Comparatively speaking, the space camera obtained by this method is lighter and smaller, achieving the purpose of lightweight;

[0125] Step 7: Use a search algorithm to search for the minimum value of the structural parameter objective function of the long focal length space camera to obtain the most suitable structural parameters for the long focal length space camera; then combine the obtained structural parameters that are most suitable for the long focal length space camera with the free-form surface design method to optimize the reflector into a free-form surface to obtain a free-form surface long focal length space camera.

[0126] Before using the search algorithm in this embodiment, it is necessary to determine the design requirement parameters to be input into the algorithm, including the focal length, F number, maximum field angle and optical path structure requirements of the system. Then, the curvature radius, tilt angle and reflector spacing of the reflector are set as variables. Next, the maximum number of searches is entered, and random structural parameters are generated within the search space as the initial values ​​of the search. After searching for suitable structural parameters, a free-form surface design method (such as SMS method, CI method, improved WW method, etc.) is used to optimize the reflector into a free-form surface, thereby obtaining a free-form surface long focal length space camera.

[0127] In this embodiment, the focal length f is 5000 mm, the F number is 12, the maximum field of view is 10°×1°, and the optical path structure is required to be [-1, 1, 0, 0, 0] (i.e., a z-type structure); the simulated annealing method is used as the search algorithm, the initial temperature is 1500 degrees, and when the search times reach more than 90 times, the stable minimum value of the comprehensive objective function is 17.28. The layout diagram of the long focal length space camera is as follows: Figure 3 As shown;

[0128] In this embodiment, the surface design method used is the improved WW method; the results show that the integration of the three main mirrors of the generated space camera is good, and the light rays of each field of view converge at the ideal image plane; and the volume of the space camera is 1.28m 3 , indicating that the structure is compact; it can be concluded that the adaptive design method for a long-focal-length main three-mirror integrated lightweight space camera proposed in the present invention can adaptively generate a long-focal-length space camera that meets the requirements of easy installation and adjustment and lightweight and has good imaging quality, wherein the adaptive design method for searching the distance between mirrors, radius of curvature and tilt angle can generate the structural parameter search space of the long-focal-length space camera in a targeted manner based on the design requirements, the main three-mirror distance discrimination model can ensure that the generated long-focal-length space camera has the advantage of easy installation and adjustment, the size objective function can ensure that the long-focal-length space camera meets the requirements of lightweight, and the structural parameter objective function can simultaneously ensure that the long-focal-length space camera has the characteristics of easy installation and adjustment, lightweight and high imaging quality.

[0129] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. An adaptive design method for a long focal length main three-mirror integrated lightweight space camera, characterized in that: The following steps are involved: Step 1: Construct the adaptive mirror spacing search space; Step 2: Construct an adaptive curvature radius search space; Step 3: Construct an adaptive tilt angle search space; Step 4: Construct a distance discrimination model for the main three mirrors of a long focal length space camera to evaluate the integration degree of the main three mirrors; Step 5: Construct a size objective function of the long focal length space camera to calculate the size of the long focal length space camera; Step 6: Construct the structural parameter objective function G of the long focal length space camera; Step 7: Use a search algorithm to search for the minimum value of the structural parameter objective function of the long focal length space camera to obtain the most suitable structural parameters for the long focal length space camera; then combine the obtained structural parameters that are most suitable for the long focal length space camera with the free-form surface design method to optimize the reflector into a free-form surface to obtain a free-form surface long focal length space camera.

2. The adaptive design method of a long focal length main three-mirror integrated lightweight space camera according to claim 1, characterized in that: The specific method of step 1 is: The expression of the adaptive mirror spacing search space is: |d max |=τ1ED (1) <h2 style=";text-align:left;direction:ltr">|d<h2 style=";text-align:left;direction:ltr"> min <h2 style=";text-align:left;direction:ltr"> |=τ2ED (2) Where ED is the entrance pupil diameter, τ1 and τ2 are the function weights of the upper and lower limits of the adaptive mirror spacing search space respectively; d max and d min are the upper and lower bounds of the adaptive mirror spacing search space, respectively; The expressions of τ1 and τ2 are: Wherein, f is the focal length of the long focal length space camera, F represents the F number of the long focal length space camera, xfov and yfov are the maximum field of view angles of the long focal length space camera in the x and y directions respectively; and are the focal length and F number of the long focal length space camera in τ1 and the weight of the maximum field of view angle of the long focal length space camera in the x and y directions respectively; and are the focal length and F number of the long focal length space camera in τ2 and the weight of the maximum field of view angle of the long focal length space camera in the x and y directions respectively; and and Set according to actual needs; In formula (4), The expression is: Where N is the number of reflectors in the long focal length space camera; In order to obtain an upper limit of the adaptive mirror spacing that is more suitable for long focal length space cameras, it is necessary to use It changes dynamically with the focal length f, and the expression is: Said and The expression is: Among them, τ c is a parameter that changes with the focal length f, as shown in the following formula:

3. The adaptive design method of a long focal length main three-mirror integrated lightweight space camera according to claim 2, characterized in that: The specific method of step 2 is: The optical relationship between the adaptive mirror spacing and the focal length of the long focal length space camera is constructed using the ABCD matrix method. The expression is: in, is the focal length of the Nth reflector in the long focal length space camera; is the focal length of the N-1th reflector in the long focal length space camera; is the focal length of the primary mirror in the long focal length space camera; d N-1 is the distance between the N-1th reflector and the Nth reflector in the long focal length space camera; A, B, C, and D are all functions of the optical power and adaptive mirror spacing of the long focal length space camera; Construct the objective function g of the adaptive curvature radius c , the expression is: Among them, i N is the refractive index of the Nth reflector in the long focal length space camera, n is the reflector serial number, 1≤n≤N; r n is the adaptive curvature radius of the nth reflector in the long focal length space camera; The upper limit d of the adaptive mirror spacing search space max and the lower limit d of the adaptive mirror spacing search space min Substitute d into formula (11) respectively N In the above equation, we can get the corresponding adaptive curvature radius combination {r DMAX } and {r DMIN }, thus obtaining the adaptive curvature radius search space of each mirror, expressed as: in, and are the upper and lower limits of the adaptive curvature radius search space respectively.

4. The adaptive design method of a long focal length main three-mirror integrated lightweight space camera according to claim 3, characterized in that: The specific method of step 3 is: The clockwise tilt angle is defined as a positive number, and the counterclockwise tilt angle is defined as a negative number; the adaptive tilt angle search space of the primary mirror is constructed in the form of absolute value: |α1|∈[0.5arcsin(ED / 2 / |d max |),0.5arcsin(ED / |d min |)] (14) where α1 represents the tilt angle of the primary mirror; The adaptive tilt angle search space of the secondary mirror is constructed; when α2>2α1, the rotation vector of the secondary mirror is -1; when α2<2α1, the rotation vector of the secondary mirror is 1; the angle between the incident light and the outgoing light is defined as an acute angle, and the search space of the adaptive tilt angle of the secondary mirror is obtained, and the expression is: Where α2 is the tilt angle of the secondary mirror, V s is the rotation vector of the secondary mirror; Construct the adaptive tilt angle search space of the three mirrors; calculate that when the light incident on the three mirrors coincides with the light emitted from the three mirrors, the tilt angle of the three mirrors is 2(α2-α1), and the search space of the adaptive tilt angle of the three mirrors is obtained, and the expression is: Among them, V T is the rotation vector of the three mirrors, and α3 is the tilt angle of the three mirrors.

5. The adaptive design method of a long focal length main three-mirror integrated lightweight space camera according to claim 4, characterized in that: The specific method of step 4 is: The main three-mirror distance of a long-focal-length space camera is the shortest distance between the main mirror and the three mirrors; the main mirror and the three mirrors are integrated on a substrate for manufacturing so that the distance between the main mirror and the three mirrors is less than a set threshold; the main three-mirror distance discrimination function g is defined ft , the expression is: Among them, d ft is the shortest distance between the primary mirror and the third mirror; Q is the set threshold, which is a constant; For a long focal length space camera with a z-type structure, the primary and secondary mirror spacing and the secondary three mirror spacing are set equal to increase the search speed of the search algorithm, so that the long focal length space camera can quickly converge to the goal of integrating the primary and three mirrors. When the optical path structure of the long focal length space camera is designed to be z-type, it is necessary to add an additional mirror spacing constraint condition on the basis of formula (17), that is, |d1|=|d2|, where d1 and d2 are the primary and secondary mirror spacing and the secondary three mirror spacing, respectively.

6. The adaptive design method of a long focal length main three-mirror integrated lightweight space camera according to claim 5, characterized in that: The specific method of step 5 is: Based on Snell's law and the inverse tracing method, the center and edge rays of the field of view (0,0), (0,yfov / 2), (0,-yfov / 2) and (xfov / 2,0) are traced to obtain the coordinates of the intersection of each ray with the reflector and the image plane, as well as the set of x, y and z coordinates of all intersections {X}, {Y} and {Z}, and the size objective function g of the space camera s The expression is: g s =|max{Y}-min{Y}|×|max{Z}-min{Z}|×2max{|X|} (18)。 7. The adaptive design method of a long focal length main three-mirror integrated lightweight space camera according to claim 6, characterized in that: The structural parameter objective function G of the telephoto space camera is composed of the main three-mirror distance discrimination model, the size objective function, the image quality evaluation function, the off-axis degree function and the optical path intersection function, and the expression is: Among them, δ1, δ2, δ3, δ4 and δ5 are the weights of the objective functions of the structural parameters of the long focal length space camera, α n is the tilt angle of the nth reflector in the long focal length space camera, g q , g oa and g p They are image quality evaluation function, off-axis degree function and optical path intersection function respectively.

8. The adaptive design method of a long focal length main three-mirror integrated lightweight space camera according to claim 7, characterized in that: The image quality evaluation function g q , off-axis function g oa and the optical path crossover function g p The expressions are: Among them, K is the total number of sampling rays, i is the serial number of the sampling ray, (x c ,y c ,z c ) is the coordinate of the ideal image point, (x i ,y i ,z i ) is the coordinate of the imaging point of the i-th sampling light; OA n is the off-axis degree discrimination number, OAM n is the margin discrimination number, σ1 and σ2 are the off-axis degree discrimination numbers OA n OAM n The weight of The pth optical path intersection vector of the space camera with medium and long focal length is required for design; It is the pth light path intersection vector of the current long focal length space camera.

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