Method for in-orbit tuning of a space telescope

Abstract

This invention relates to the field of optical system technology, and more particularly to an on-orbit optimization method for a space telescope, comprising: obtaining the sensitivity matrix of each field of view of the imaging system corresponding to the secondary mirror offset using optical design software; obtaining the point spread function of each field of view based on the sensitivity matrix of each field of view; acquiring captured images of each field of view; for each field of view, performing deconvolution processing on the corresponding captured image based on the point spread function to obtain a latent image with optimized image quality; for each field of view, based on the image quality optimized latent image and the captured image, using image entropy... H To obtain the deconvolution normalized boost for image quality evaluation metrics, a global evaluation function is constructed based on the deconvolution normalized boost for each field of view. An optimization algorithm is then used to obtain the optimal offset when the global evaluation function reaches its minimum value. The pose of the secondary mirror is corrected based on the optimal offset. This invention is at least beneficial for achieving accurate compensation of aberrations across the entire field of view.

Description

Technical Field

[0001] This invention belongs to the field of optical system technology, and in particular relates to an on-orbit optimization method for space telescopes. Background Technology

[0002] To achieve higher resolution and detect faint targets, space telescopes often employ large-aperture reflective structures. In a space telescope system, the primary mirror and the rear optical system are mounted in a single integrated structure. The primary mirror and the rear optical system are relatively close together. The secondary mirror and its adjustment mechanism are fixed to the telescope tube via connecting rods. The secondary mirror has a large span compared to other optical components. After the reflective system is launched into orbit, it is subjected to disturbances from factors such as force and heat, causing deformation of the connecting structure. Furthermore, because the primary mirror, the three mirrors, the folding mirror, and the detector are mounted on the same structure and are relatively close together, the relative rigidity offset between the primary mirror, the three mirrors, the folding mirror, and the detector is small. However, the long span and large deformation of the telescope tube result in a large offset of the secondary mirror relative to other components. This leads to different optical aberrations across the entire field of view of the system, affecting image quality and reducing image resolution.

[0003] By employing an adjustment mechanism to perform on-orbit adjustment of the secondary mirror's pose, this disturbance factor can be compensated. The current common technical approach involves sequentially performing aberration detection, calculating the secondary mirror's adjustment amount, and then adjusting the secondary mirror. This approach typically includes the following methods: First, manual interpretation, which involves manually judging the blurred shapes of typical targets (such as points, lines, and circles) in the system-captured image to roughly determine the aberration type and the secondary mirror's adjustment amount. Multiple rounds of adjustment and testing are then conducted to gradually reduce system aberrations. This method is limited by human experience, requires a large number of iterations, has poor timeliness, and low adjustment accuracy. When facing blur inconsistencies across the entire field of view, the adjustment difficulty increases exponentially. Second, blur kernel estimation based on blind deconvolution of the blurred image. For optical systems, this method can be recognized... Because the blur kernel (optical point spread function) changes relatively little in a small field of view, the point spread function can be estimated and the secondary mirror adjusted using methods such as blind deconvolution. However, the blind deconvolution method relies on prior knowledge, and there is no one-to-one mapping between optical aberrations and the point spread function. This method has significant drawbacks and is also difficult to handle situations where the point spread function is inconsistent across the entire field of view. The third method is precise aberration measurement. By using detection methods such as phase difference or Shack-Hartmann, the aberrations of the system can be accurately measured. Combined with the secondary mirror sensitivity matrix (the correspondence between the secondary mirror displacement and the Zernike aberration coefficient change), the adjustment amount can be precisely detected. This method requires additional equipment or the acquisition of multiple images, making it more complex, and its reliability in complex spatial environments needs to be improved. Summary of the Invention

[0004] In view of this, the present invention aims to provide an on-orbit optimization method for space telescopes, which is at least beneficial for achieving accurate compensation of aberrations across the entire field of view.

[0005] To achieve the above objectives, the technical solution created by this invention is implemented as follows: This invention provides an on-orbit optimization method for a space telescope, comprising: obtaining the sensitivity matrix of each field of view of the imaging system corresponding to the secondary mirror offset using optical design software; obtaining the point spread function of each field of view based on the sensitivity matrix; acquiring captured images of each field of view; for each field of view, performing deconvolution processing on the corresponding captured image based on the point spread function to obtain a latent image with optimized image quality; and for each field of view, using the image entropy... H To obtain the deconvolution normalization improvement for image quality evaluation metrics Improvement based on deconvolution normalization for each field of view A global evaluation function is constructed, and an optimization algorithm is used to obtain the optimal offset when the global evaluation function reaches its minimum value; the pose of the secondary mirror is corrected based on the optimal offset.

[0006] Furthermore, deconvolution normalization improves the efficiency. The expression is as follows: ,in, Represents the entropy of the captured image. Entropy representing the latent image, Represents the captured image. This represents the latent image after image quality optimization.

[0007] Furthermore, , L Represents the total number of gray levels. Representing the c The probability of a gray level appearing in the corresponding image.

[0008] Furthermore, the global evaluation function The expression is as follows: Where n represents the total number of fields of view. This represents the secondary mirror offset. i Represents the field of view number.

[0009] Furthermore, obtaining the sensitivity matrix of each field of view of the imaging system corresponding to the secondary mirror offset using optical design software includes: establishing a space telescope system model using optical design software; obtaining the initial Zernike polynomial coefficients of each field of view when the secondary mirror is in an ideal position; for each field of view, applying a unit offset to a single degree of freedom of the secondary mirror to obtain the misaligned Zernike polynomial coefficients; subtracting the misaligned Zernike polynomial coefficients from the corresponding initial Zernike polynomial coefficients to obtain the aberration change; dividing the aberration change by the unit offset of the corresponding degree of freedom to obtain the column vector of the corresponding degree of freedom in the sensitivity matrix; obtaining the column vectors of all degrees of freedom; and combining the column vectors of all degrees of freedom to obtain the sensitivity matrix of the corresponding field of view.

[0010] Furthermore, obtaining the point spread function for each field of view based on the sensitivity matrix of each field of view includes: setting the unit offset of the secondary mirror as... For each field of view, Zernike polynomial coefficients are obtained based on the sensitivity matrix and unit offset; wavefront aberrations are obtained based on the Zernike polynomial coefficients; photoluminescence function is obtained based on the wavefront aberrations; and point spread function is obtained based on the photoluminescence function.

[0011] Furthermore, obtaining the Zernike polynomial coefficients based on the sensitivity matrix and unit offset includes: ;in, Represents the sensitivity matrix. Indicates the wavefront aberration of the system. Denotes the coefficients of the Zernike polynomial. i Indicates the field of view number.

[0012] Furthermore, wavefront aberrations obtained based on Zernike polynomial coefficients include: , Represents wavefront aberration. q This represents the total number of terms in the Zernike polynomial. The first Zernike polynomial item, Describe the Zernike polynomial of the th The coefficients of the term; obtaining the photon function based on wavefront aberration includes: ,in, Represents the shape of the pupil. It is an imaginary number. Representing wavelength; the point spread function obtained based on the photon function includes: ,in, Represents the inverse Fourier transform. This represents the point spread function.

[0013] Furthermore, the captured image is deconvolved based on the point spread function to obtain a latent image with optimized image quality, including: ;in, iRepresents the field of view number. To indicate complex conjugate, Indicates the inverse Fourier transform. Represents the point spread function. Represents the captured image. This represents the latent image after image quality optimization.

[0014] Compared with existing technologies, the present invention achieves the following beneficial effects: The on-orbit optimization method for space telescopes provided by the present invention uses the captured images of each field of view as input to obtain the common secondary mirror adjustment amount (i.e., the optimal offset) that achieves the best deconvolution effect of the image. This enables accurate compensation of aberrations across the entire field of view and directly obtains the optimal secondary mirror adjustment amount, effectively improving adjustment efficiency and accuracy. The present invention comprehensively considers the aberration situation of multiple fields of view, effectively solving the problem of differences between fields of view. By using the secondary mirror sensitivity matrix as prior knowledge and combining it with the inversion of the point spread function of multi-field images, the accuracy and efficiency of adjustment amount calculation are improved. The entire adjustment process is simple and efficient. No additional equipment or multiple image acquisitions are required, which helps to save costs and has high reliability. Attached Figure Description

[0015] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A schematic diagram of the structure of the space telescope system described in the embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the coordinate establishment method and field of view distribution of the secondary mirror as described in the embodiments of the present invention. Figure 2 (a) in the diagram is a schematic diagram of how the coordinates of the secondary mirror are established. Figure 2 (b) in the diagram is a schematic diagram of the field of view distribution of the secondary mirror. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0018] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0019] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0020] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] This invention provides an on-orbit optimization method for a space telescope, comprising: obtaining the sensitivity matrix of each field of view of the imaging system corresponding to the secondary mirror offset using optical design software; obtaining the point spread function of each field of view based on the sensitivity matrix; acquiring captured images of each field of view; for each field of view, performing deconvolution processing on the corresponding captured image based on the point spread function to obtain a latent image with optimized image quality; and for each field of view, using the image entropy... H To obtain the deconvolution normalization improvement for image quality evaluation metrics Improvement based on deconvolution normalization for each field of view A global evaluation function is constructed, and an optimization algorithm is used to obtain the optimal offset when the global evaluation function reaches its minimum value. The pose of the secondary mirror is corrected based on the optimal offset, which can effectively compensate for the secondary mirror misalignment, reduce system aberrations, and improve imaging quality.

[0022] Furthermore, deconvolution normalization improves the efficiency. The expression is as follows: ,in, Represents the entropy of the captured image. Entropy representing the latent image, Represents the captured image. This represents the latent image after image quality optimization. The more accurate the point spread function estimation of the corresponding field of view, the better the normalization enhancement effect of the image. The higher, The larger the value, the greater the value.

[0023] Furthermore, , L This represents the total number of gray levels. Common images typically have 8, 12, or 16 gray levels. Representing the c The probability of a gray level appearing in the corresponding image. It is understandable that when calculating the entropy of a latent image, Representing the c The probability of a gray level appearing in the latent image. L The total number of gray levels representing the latent image is used when calculating the entropy of the captured image. Representing the c The probability of a gray level appearing in the captured image. L This represents the total number of gray levels in the captured image.

[0024] Furthermore, the global evaluation function The expression is as follows: Where n represents the total number of fields of view. This represents the secondary mirror offset. i Represents the field of view number. V i This represents the deconvolution normalization boost corresponding to the field of view numbered i, when R The closer it is to the actual secondary mirror offset, The smaller the value, the better the optimization algorithm can be obtained. R Based on the best R The secondary mirror's position and pose are precisely adjusted through the secondary mirror adjustment mechanism, ensuring that the secondary mirror has virtually no offset, thereby achieving high-quality imaging.

[0025] Furthermore, obtaining the sensitivity matrix of each field of view of the imaging system corresponding to the secondary mirror offset using optical design software includes: establishing a space telescope system model using optical design software; obtaining the initial Zernike polynomial coefficients of each field of view when the secondary mirror is in an ideal position; for each field of view, applying a unit offset to a single degree of freedom of the secondary mirror to obtain the misaligned Zernike polynomial coefficients; subtracting the misaligned Zernike polynomial coefficients from the corresponding initial Zernike polynomial coefficients to obtain the aberration change; dividing the aberration change by the unit offset of the corresponding degree of freedom to obtain the column vector of the corresponding degree of freedom in the sensitivity matrix; obtaining the column vectors of all degrees of freedom; and combining the column vectors of all degrees of freedom to obtain the sensitivity matrix of the corresponding field of view.

[0026] Furthermore, obtaining the point spread function for each field of view based on the sensitivity matrix of each field of view includes: setting the unit offset of the secondary mirror as... For each field of view, Zernike polynomial coefficients are obtained based on the sensitivity matrix and unit offset; wavefront aberrations are obtained based on the Zernike polynomial coefficients; photoluminescence function is obtained based on the wavefront aberrations; and point spread function is obtained based on the photoluminescence function.

[0027] Furthermore, obtaining the Zernike polynomial coefficients based on the sensitivity matrix and unit offset includes: ;in, This represents the sensitivity matrix corresponding to the field of view numbered i. Indicates the wavefront aberration of the system. Let i represent the Zernike polynomial coefficients corresponding to the field of view numbered i. i Indicates the field of view number.

[0028] Furthermore, wavefront aberrations obtained based on Zernike polynomial coefficients include: , This represents the wavefront aberration corresponding to the field of view numbered i. q This represents the total number of terms in the Zernike polynomial. The i-th Zernikal polynomial corresponding to the field of view numbered i item, This represents the Zernike polynomial numbered i corresponding to the field of view. The coefficient of the term.

[0029] Furthermore, obtaining the pupil function based on wavefront aberration includes: ,in, Represents the shape of the pupil. It is an imaginary number. Represents wavelength, The luminous function represents the field of view numbered i.

[0030] Furthermore, obtaining the point spread function based on the photon function includes: ,in, Represents the inverse Fourier transform. This represents the point spread function corresponding to the field of view numbered i.

[0031] Furthermore, the captured image is deconvolved based on the point spread function to obtain a latent image with optimized image quality, including: ;in, i Represents the field of view number. To indicate complex conjugate, Indicates the inverse Fourier transform. This represents the point spread function corresponding to the field of view numbered i. Represents the captured image. This represents the latent image after image quality optimization.

[0032] refer to Figure 1 The secondary mirror is the secondary mirror 121 in the space telescope system. The space telescope system may include the primary mirror 11, the secondary mirror 121, and the back-end system 13. The back-end system 13 includes three mirrors 131, a folding mirror 132, and a detector 133. Since the primary mirror 11 and the back-end system 13 are fixed on the same main structure, the relative rigid displacement of the primary mirror 11 and the back-end system 13 is small when subjected to mechanical impact. The secondary mirror 121 is fixed on the mirror tube 14 located on the side of the primary mirror 11 away from the back-end system 13 by the connecting rod 123 and the adjustment mechanism 122. Since the span between the secondary mirror 121 and the primary mirror 11 is long, the rigid body offset of the secondary mirror 121 is large. Therefore, the present invention mainly performs attitude correction on the secondary mirror 121.

[0033] Figure 2 The diagram illustrates the coordinate system establishment and field-of-view distribution of the secondary mirror. Typically, the rigid body offset of the secondary mirror includes six dimensions: translation along the X-axis, translation along the Y-axis, translation along the Z-axis, rotation along the X-axis, rotation along the Y-axis, and rotation along the Z-axis. This represents the unit translation along the X-axis. This represents the unit translation along the Y-axis. This represents the unit translation along the Z-axis. This represents the unit rotation along the X-axis. This represents the unit rotation along the Y-axis. This represents the unit rotation along the Z-axis.

[0034] In some embodiments, the total number of fields of view n=5, and the 5 fields of view can be Figure 2 The fields of view are (0,0), (0,1), (1,0), (0,-1), and (-1,0). It is understandable that more fields of view can be added on this basis to further improve the detection capability.

[0035] System imaging can be obtained from the following formula: ;in, The captured image corresponding to the field of view numbered i. For an ideal image, For convolution operations, since Due to reasons such as the unknown nature of the formula and the irreversibility of convolution operations, it is impossible to directly perform inverse operations to solve the problem. Existing research has shown that deconvolution methods can estimate the point spread function to some extent and improve the capture image quality. Quality, making it closer to the ideal image. The case where the point spread function is unknown is called the blind method. The point spread function is estimated based on prior knowledge, and then the image is deconvolved. Due to insufficient prior knowledge and the non-single mapping between wavefront aberrations and the point spread function, the non-blind method can only estimate the point spread function and cannot obtain wavefront information. However, since there is a certain correlation between the Zernike coefficients of the wavefronts of each field of view when the system aberration is mainly due to the secondary mirror offset, a set of secondary mirror offsets can be obtained by selecting multiple fields of view to capture images. The aberrations caused by this offset satisfy all fields of view. When the number of selected field points is large and widely distributed, the calculated offset is accurate enough. Therefore, the on-orbit tuning method for space telescopes provided by this invention can improve the calculation accuracy of the adjustment amount.

[0036] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0037] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for on-orbit optimization of a space telescope, characterized in that, include: The sensitivity matrix of each field of view of the imaging system corresponding to the secondary mirror offset is obtained by using optical design software. The point spread function of each field of view is obtained based on the sensitivity matrix of each field of view; Acquire captured images for each field of view. For each field of view, perform deconvolution processing on the corresponding captured image based on the point spread function to obtain a latent image with optimized image quality. For each field of view, based on the image quality optimized latent image and captured image, using image entropy... H To obtain the deconvolution normalization improvement for image quality evaluation metrics Improvement based on deconvolution normalization for each field of view Construct a global evaluation function and use an optimization algorithm to obtain the optimal offset when the global evaluation function reaches its minimum value; The pose of the secondary mirror is corrected based on the optimal offset.

2. The on-orbit optimization method for space telescopes according to claim 1, characterized in that, Deconvolution normalization improves performance The expression is as follows: ,in, Represents the entropy of the captured image. Entropy representing the latent image, Represents the captured image. This represents the latent image after image quality optimization.

3. The on-orbit optimization method for space telescopes according to claim 2, characterized in that, , L Represents the total number of gray levels. Representing the c The probability of a gray level appearing in the corresponding image.

4. The on-orbit optimization method for a space telescope according to claim 1, characterized in that, Global evaluation function The expression is as follows: Where n represents the total number of fields of view. This represents the secondary mirror offset. i Represents the field of view number.

5. The on-orbit optimization method for a space telescope according to claim 1, characterized in that, The sensitivity matrices of the imaging system for each field of view, corresponding to the secondary mirror offset, are obtained using optical design software, including: A model of the space telescope system was created using optical design software. Obtain the initial Zernike polynomial coefficients for each field of view when the secondary mirror is in the ideal position; For each field of view, a unit offset is applied to a single degree of freedom of the secondary mirror to obtain the misaligned Zernike polynomial coefficients. The difference between the misaligned Zernike polynomial coefficients and the corresponding initial Zernike polynomial coefficients is used to obtain the aberration change. The aberration change is divided by the unit offset of the corresponding degree of freedom to obtain the column vector of the corresponding degree of freedom in the sensitivity matrix. The column vectors of all degrees of freedom are obtained, and the column vectors of all degrees of freedom are combined to obtain the sensitivity matrix of the corresponding field of view.

6. The on-orbit optimization method for a space telescope according to claim 1 or 5, characterized in that, The point spread function for each field of view is obtained based on the sensitivity matrix of each field of view, including: Set the unit offset of the secondary mirror to ; For each field of view, Zernike polynomial coefficients are obtained based on the sensitivity matrix and unit offset. Wavefront aberrations are obtained based on the Zernike polynomial coefficients. Photon function is obtained based on wavefront aberrations. Point spread function is obtained based on photon function.

7. The on-orbit optimization method for a space telescope according to claim 6, characterized in that, Obtaining Zernike polynomial coefficients based on the sensitivity matrix and unit offset includes: ; in, Represents the sensitivity matrix. Indicates the wavefront aberration of the system. Denotes the coefficients of the Zernike polynomial. i Indicates the field of view number.

8. The on-orbit optimization method for a space telescope according to claim 7, characterized in that, Wavefront aberrations obtained based on Zernike polynomial coefficients include: , Represents wavefront aberration. q This represents the total number of terms in the Zernike polynomial. The first Zernike polynomial item, Describe the Zernike polynomial of the th The coefficient of the term; Obtaining the pupil function based on wavefront aberration includes: ,in, Represents the photophoretic function. Represents the shape of the pupil. It is an imaginary number. Represents wavelength; Point spread functions obtained based on photophoretic functions include: ,in, Represents the inverse Fourier transform. This represents the point spread function.

9. The on-orbit optimization method for a space telescope according to claim 2, characterized in that, Deconvolution processing of the captured images based on the point spread function is performed to obtain latent images with optimized image quality, including: ； in, i Represents the field of view number. To indicate complex conjugate, Indicates the inverse Fourier transform. Represents the point spread function. Represents the captured image. This represents the latent image after image quality optimization.

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