Lightweight design method for space large-aperture mirror based on bipod support

Abstract

The application discloses a lightweight design method of a space large-aperture mirror based on Bipod support, and solves the problem that in the existing lightweight design method, the mirror body is designed to be lightweight alone, and when the Bipod support is installed on the mirror body, the surface shape of the mirror body is affected due to the coupling effect between the Bipod support and the mirror body, and the standard before coupling cannot be reached; in the application, an entity model of the large-aperture mirror is constructed, the position of a Bipod support boss on the entity model is determined, the lightweight structure form is determined according to the lightweight rate of the mirror body with different lightweight structure forms and the root mean square (RMS) value of optical surface deformation, and then the entity model of the large-aperture mirror is designed to be lightweight; the application considers the influence of the coupling effect between the Bipod support and the large-aperture mirror on the static stiffness and surface shape of the large-aperture mirror, and makes the optical surface deformation index of the Bipod support after assembly meet the requirements.

Description

TECHNICAL FIELD

[0001] The application relates to a large-aperture space mirror optical machine structure design method, in particular to a light-weight design method for a large-aperture space mirror based on a Bipod support. BACKGROUND

[0002] The optical performance of a large-aperture space mirror is affected by its own gravity and the temperature change of the environment, and the position accuracy and surface accuracy of the mirror are directly related to the imaging quality of the space telescope. Firstly, with the increase of the aperture of the telescope, the mass of the mirror body increases in a cubic geometric relationship. The rapid increase of the self-weight causes the optical surface quality of the mirror body to degrade under the influence of gravity, and under the combined action of the self-weight and the supporting reaction force, the optical surface produces rigid body displacement and optical surface deformation. The rigid body displacement can be compensated by the adjustment mode, while the elastic deformation of the optical surface is difficult to compensate, which will cause the system wavefront difference and lead to the decline of the system optical performance; secondly, when the environment temperature of the space mirror changes, the thermal performance mismatch between the mirror and the support structure material will cause thermal stress and elastic deformation of the optical surface, and when there is a temperature gradient in the axial direction of the mirror, the deformation amount is proportional to the square of the aperture of the mirror; thirdly, from the perspective of dynamics, reducing the mass of the large-aperture space mirror is conducive to improving the first-order natural frequency of the space camera and improving its ability to resist external disturbances. Finally, since the cost of launching a remote sensing satellite is expensive, the cost of launching 1 kg of load is 20,000 US dollars, and reducing the mass of the camera composed of a large-aperture space mirror can effectively control the launch cost. Therefore, the mirror must be designed to be light in weight.

[0003] Whether the final configuration of the mirror is reasonable needs to be evaluated by integrating it into the overall structure of the camera, and the overall structure of the camera is complex, and other structural parts will have an impact on the surface shape of the mirror, while the support structure directly connected to the mirror can partially isolate the impact from other structural parts. Bipod is a kind of support structure widely used in large-aperture mirrors, which can be applied to the side support or back support of the mirror. The Bipod structure has different rigidity and flexibility in different stress directions of the mirror body. In the gravity direction, it has good rigidity to ensure the reasonable rigid body displacement of the mirror surface and good surface shape under the gravity load. In the direction where there is a thermal gradient and assembly stress, it has a certain flexibility to release the assembly stress and thermal stress, and ensure the surface shape and optical spacing between the primary mirror and the secondary mirror under temperature change. There is a coupling effect between the position of the Bipod support, the size of the flexible joint and the light-weight form of the mirror body. Due to the limited installation position and installation method of the mirror in the space camera, most of the existing light-weight design methods are to design the mirror body separately, which can achieve a high light-weight rate while meeting the surface shape requirements. However, after adding the Bipod support, the surface shape of the mirror body is affected due to the coupling effect between the Bipod support and the mirror body, so that the optical surface deformation of the mirror body cannot meet the index requirements. SUMMARY

[0004] The purpose of the present application is to solve the technical problem that the optical surface deformation of the mirror does not meet the index requirements due to the influence of the coupling effect of the Bipod support and the mirror when the Bipod support is installed on the mirror in the existing lightweight design method of the mirror, and to provide a lightweight design method of a space large-aperture mirror based on Bipod support.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] A lightweight design method of a space large-aperture mirror based on Bipod support, characterized in that it comprises the following steps:

[0007] S1, determining the thickness of the large-aperture mirror according to the aperture of the large-aperture mirror and the thickness ratio formula, and selecting the mirror back structure form;

[0008] S2, constructing a quadric surface equation according to the optical design parameters of the large-aperture mirror, and establishing an entity model of the large-aperture mirror in combination with the aperture, thickness and mirror back structure form of the large-aperture mirror;

[0009] S3, determining the positions of three Bipod support bosses on the back of the entity model of the large-aperture mirror;

[0010] S4, selecting different lightweight structure forms to remove the entity on the back of the entity model of the large-aperture mirror on the basis of reserving the positions of the three Bipod support bosses, and reserving the effective thickness of the panel of the entity model of the large-aperture mirror;

[0011] S5, calculating the mirror lightweight rate and the root mean square RMS value of the optical surface deformation of the different lightweight structure forms, confirming the final lightweight structure form, and lightweight designing the large-aperture mirror according to the quadric surface equation, the aperture, thickness, mirror back structure form of the large-aperture mirror, the positions of the three Bipod support bosses and the final lightweight form. In the lightweight design of the space large-aperture mirror, the coupling effect between the Bipod support boss and the large-aperture mirror is considered to affect the static stiffness and surface shape of the large-aperture mirror, which avoids the problem that the optical surface deformation index does not meet the requirements when the support is added after the mirror is designed alone.

[0012] Further, the thickness ratio formula in S1 is:

[0013]

[0014] Wherein, δ is the maximum deformation of the mirror surface; r is the material density; r is the radius of the large aperture mirror, D is the diameter of the large aperture mirror, t is the thickness of the large aperture mirror; E is the elastic modulus of the large aperture material, and g is the acceleration of gravity.

[0015] Further, the mirror back structure in S1 is one of a flat back shape, a meniscus shape, a single-arch shape, a double-arch shape, a tapered shape, and a concave shape.

[0016] Further, the mirror back structure in S1 is a flat back shape.

[0017] Further, S3 is specifically:

[0018] S31, the solid model of the large aperture mirror is a rotationally symmetric body, and the three Bipod support bosses are uniformly distributed on a support circumference at the back of the solid model of the large aperture mirror;

[0019] S32, the diameter of the support circumference at the back of the solid model of the large aperture mirror where the three Bipod support bosses are located is determined by using a finite element analysis method.

[0020] S33, the positions of the three Bipod support bosses along the optical axis direction are determined by using a finite element analysis method.

[0021] Further, S32 is specifically:

[0022] In the finite element analysis, under the condition of a given initial diameter of the back support circumference, the three Bipod support bosses are fixedly constrained, a 1G gravity action is loaded on the solid model of the large aperture mirror, and the mirror surface shape change amount of the solid model of the large aperture mirror is calculated; the 1G gravity direction is collinear with the center of one of the three Bipod support bosses.

[0023] The diameter of the back support circumference is changed, and the mirror surface shape change amount corresponding to the back support circumference with different diameters is calculated by using the same method.

[0024] The diameter of the back support circumference corresponding to the minimum mirror surface shape change amount is selected as the diameter of the back support circumference where the three Bipod support bosses are located.

[0025] Further, S33 is specifically:

[0026] In the finite element analysis, the three Bipod support bosses are fixedly constrained in the case that the back support circumferential diameter where the three Bipod support bosses are located is determined, the entity model of the large aperture mirror is loaded with 1G gravity, and the direction of the 1G gravity is collinear with the center of one of the three Bipod support bosses; the mirror surface shape change amount of the entity model of the large aperture mirror is calculated when the three Bipod support bosses move to different positions along the optical axis of the entity model of the large aperture mirror under the back support circumferential diameter determined in S32; and the position of the three Bipod support bosses along the optical axis direction when the mirror surface shape change amount is the smallest is selected.

[0027] Further, the different lightweight structure forms in S4 include a triangle, a quadrilateral, a hexagon, a circle and a sector.

[0028] Further, the different lightweight structure forms in S4 include a triangle and a hexagon.

[0029] Further, S5 is specifically:

[0030] The mirror lightweight rate and the root mean square (RMS) value of optical surface deformation of different lightweight structure forms are calculated respectively, the lightweight structure form with the highest mirror lightweight rate in the lightweight structure form with the root mean square (RMS) value of optical surface deformation not higher than 5nm is selected as the final lightweight structure form, and the large aperture mirror is lightweight designed according to a quadric surface equation, the aperture of the large aperture mirror, the thickness, the mirror back structure form, the positions of the three Bipod support bosses and the final lightweight form.

[0031] The beneficial effects of the present application are as follows:

[0032] 1. The space large aperture mirror lightweight design method based on Bipod support can realize high lightweight design of the space large aperture mirror, has high static stiffness and dynamic stiffness while meeting high lightweight, can realize the use requirement of the large aperture mirror in space application, and reduces launch cost.

[0033] 2. In the space large aperture mirror lightweight design method based on Bipod support, the coupling effect between the Bipod support boss and the large aperture mirror on the static stiffness and surface shape of the large aperture mirror is considered, and the problem that the optical surface deformation index cannot meet the requirement after the support is added although the mirror body is designed separately to obtain high lightweight is avoided. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is an entity model of a large aperture mirror with a diameter-thickness ratio of 12:1 in the space large aperture mirror lightweight design method based on Bipod support.

[0035] Figure 2 is Figure 1 a cross-sectional view of A-A in FIG. 1;

[0036] Figure 3 is a structural schematic diagram of a mirror with three Bipod supports in an embodiment of a lightweight design method for a space large-aperture mirror based on Bipod support of the present application;

[0037] In the figure, 1. first Bipod support, 2. second Bipod support, 3. third Bipod support;

[0038] Figure 4 is an optimization process schematic diagram for finding the installation position of the three Bipod support bosses in an embodiment of a lightweight design method for a space large-aperture mirror based on Bipod support of the present application;

[0039] Figure 5 is a position schematic diagram of the back support circumference where the three Bipod support bosses are located in an embodiment of a lightweight design method for a space large-aperture mirror based on Bipod support of the present application;

[0040] Figure 6 is a position schematic diagram of the three Bipod support bosses along the optical axis direction in an embodiment of a lightweight design method for a space large-aperture mirror based on Bipod support of the present application; wherein a represents the position of the three Bipod support bosses along the optical axis direction;

[0041] Figure 7 is a schematic diagram of the back honeycomb hole of the mirror in two different lightweight forms in an embodiment of a lightweight design method for a space large-aperture mirror based on Bipod support of the present application;

[0042] Wherein (a) is a back structure schematic diagram when the lightweight hole is a hexagon; (b) is a back structure schematic diagram when the lightweight hole is a triangle;

[0043] Figure 8 is an optical surface surface shape diagram under 1G gravity in an embodiment of a lightweight design method for a space large-aperture mirror based on Bipod support of the present application, which adopts three Bipod boss supports and is in different lightweight forms;

[0044] Wherein (a) is an optical surface deformation schematic diagram corresponding to a triangular lightweight hole; (b) is an optical surface deformation schematic diagram corresponding to a hexagonal lightweight hole. DETAILED DESCRIPTION

[0045] The technical solutions of the present application will be described clearly and completely in connection with the drawings and embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, but not all. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0046] Embodiments

[0047] The light-weight design method of a large-aperture mirror based on Bipod support in the embodiment comprises the following steps:

[0048] S1, determining the thickness of the large-aperture mirror according to the aperture of the large-aperture mirror and the diameter-thickness ratio formula, and selecting the mirror back structure form; the diameter-thickness ratio formula is:

[0049]

[0050] In the formula, δ is the maximum deformation of the mirror surface; r is the material density; r is the radius of the large-aperture mirror, D is the diameter of the large-aperture mirror, t is the thickness of the large-aperture mirror; E is the elastic modulus of the large-aperture material, and g is the acceleration of gravity.

[0051] The mirror back structure selected in the embodiment is flat back.

[0052] In the embodiment, the mirror aperture is 660 mm, and the diameter-thickness ratio will affect the stiffness, light weight ratio, and centroid position of the mirror. According to the above formula, the diameter-thickness ratio of the mirror is determined to be 12, the mirror body thickness is greater than 66 mm, considering that the SiC mirror has higher specific stiffness, and a higher light weight ratio needs to be achieved, the diameter-thickness ratio is taken as 12, and the mirror body center thickness is 55 mm.

[0053] S2, constructing a quadratic surface equation according to the optical design parameters of the large-aperture mirror, and establishing a solid model of the large-aperture mirror in combination with the aperture, thickness, and mirror back structure form of the large-aperture mirror, such as Figure 1 and As shown in Figure 2 the solid model obtained when the mirror thickness ratio is 12:1;

[0054] S3, in the design, the mirror structure supported by three Bipod support bosses is considered as shown in Figure 3 , wherein 1 represents the first Bipod support, 2 represents the second Bipod support, and 3 represents the third Bipod support, but the positions of the three Bipod support bosses on the back of the solid model of the large-aperture mirror need to be determined, and the light weight form of the back of the solid model of the large-aperture mirror needs to be determined; specifically:

[0055] S31, the entity model of the large-aperture mirror is a rotationally symmetric body, three Bipod support bosses are uniformly distributed on a support circumference at the back of the entity model of the large-aperture mirror, and the central angle between two adjacent Bipod support bosses is 120°;

[0056] S32, the finite element analysis method is used to determine the diameter of the support circumference at the back of the entity model of the large-aperture mirror where the three Bipod support bosses are located; specifically:

[0057] In the finite element analysis, the diameter of the initial back support circumference is given, the three Bipod support bosses are fixedly constrained to be uniformly distributed on the back support circumference, the entity model of the large-aperture mirror is loaded with 1G gravity, and the mirror surface shape change amount of the entity model of the large-aperture mirror is calculated;

[0058] The diameter of the back support circumference is changed, and the corresponding mirror surface shape change amount of the back support circumference with different diameters is calculated by the same method;

[0059] The diameter of the back support circumference corresponding to the minimum mirror surface shape change amount is selected as the diameter of the back support circumference where the three Bipod support bosses are located.

[0060] According to Figure 4 It can be seen that when the diameter of the back support circumference where the Bipod support boss is located is in the range of 360mm-500mm, that is, the horizontal coordinate code is between 19-23, the RMS value of the optical surface deformation is relatively small, which is the selectable range of the back support circumference. Figure 4 The horizontal coordinate in the table is the code of the size of the back support circumference, and the vertical coordinate is the RMS value of the optical surface. The horizontal coordinate has no unit, and the vertical coordinate has a unit of mm.

[0061] S33, the finite element analysis method is used to determine the position of the three Bipod support bosses along the optical axis;

[0062] Specifically:

[0063] In the finite element analysis, in the case where the diameter of the back support circumference where the three Bipod support bosses are located is determined, the three Bipod support bosses are fixedly constrained, the entity model of the large-aperture mirror is loaded with 1G gravity, and the 1G gravity direction is collinear with the center of one of the three Bipod support bosses; the mirror surface shape change amount of the entity model of the large-aperture mirror is calculated when the three Bipod support bosses move to different positions along the optical axis of the entity model of the large-aperture mirror under the diameter of the back support circumference determined in S32; the position of the three Bipod support bosses along the optical axis is selected when the mirror surface shape change amount is minimum.

[0064] The final position of the three Bipod support bosses is as shown in Figure 5 andFigure 6 As shown in Figure 6 In the formula, a represents the position of the three Bipod support bosses along the optical axis direction.

[0065] S4, on the basis of reserving the positions of the three Bipod support bosses, different lightweight structure forms are selected for the physical removal of the back of the physical model of the large-aperture mirror, and the effective thickness of the physical model panel of the large-aperture mirror is reserved to be 5mm. After the physical removal, a rib plate is formed between the adjacent two honeycomb holes, and the thickness of the rib plate is 3mm.

[0066] The different lightweight structure forms include triangle, quadrilateral, hexagon, circle and sector.

[0067] The lightweight structure forms of triangle and hexagon are as shown in Figure 7 (a) and (b) of the formula.

[0068] S5, the mirror lightweight rate and the root mean square RMS value of the optical surface deformation of different lightweight structure forms are calculated respectively, the lightweight structure form with the highest mirror lightweight rate is selected as the final lightweight structure form from the lightweight structure forms with the root mean square RMS value of the optical surface deformation not higher than 5nm, and the large-aperture mirror is lightweight designed according to the quadratic surface equation, the aperture, the thickness of the large-aperture mirror, the mirror back structure form, the positions of the three Bipod support bosses and the final lightweight form.

[0069] Compared with the physical mirror, the specific stiffness of the honeycomb lightweight structure is larger, and the lightweight mirror removes the physical material with less contribution to the stiffness of the mirror back, so that the specific stiffness of the mirror increases in the overall stiffness. The lightweight hole form of the mirror includes triangle, quadrilateral, hexagon, circle and sector, the structure of the lightweight hole form of triangle is as shown in Figure 7 (b) of the formula, the structure of the lightweight hole form of hexagon is as shown in Figure 7 (a) of the formula, wherein the triangle hole has better rigidity and stability, and the hexagon has a higher lightweight rate.

[0070] The root mean square RMS value of the optical surface deformation of the lightweight structure forms of triangle and hexagon is as shown in Figure 8 (a) and (b) of the formula, Figure 8 The surface deformation distributions of (a) and (b) are close, the RMS root mean square value under the triangle lightweight scheme is 4.6nm, and the RMS root mean square value under the hexagon lightweight scheme is 4.8nm.

[0071] In this embodiment, the lightweight rate of the triangle scheme is 85.2%, the lightweight rate of the hexagon scheme is 86%, and the hexagon scheme is finally selected.

[0072] The above merely illustrates the specific embodiments of the present application, and the effects of the specific embodiments and the related comparative examples are compared, but the protection scope of the present application is not limited thereto, any change or replacement within the technical scope disclosed by the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for lightweight design of a space large-aperture mirror based on Bipod support, characterized in that, The method comprises the following steps: S1, determining the thickness of the large-aperture mirror according to the aperture of the large-aperture mirror and a thickness-to-aperture ratio formula, and selecting a mirror back structure form; S2, constructing a quadric surface equation according to optical design parameters of the large-aperture mirror, and establishing an entity model of the large-aperture mirror in combination with the aperture, the thickness and the mirror back structure form of the large-aperture mirror; S3, determining positions of three Bipod support bosses on the back of the entity model of the large-aperture mirror; S3 is: S31, the entity model of the large-aperture mirror is a rotationally symmetrical body, and the three Bipod support bosses are uniformly distributed on a support circumference on the back of the entity model of the large-aperture mirror; S32, the diameter of the support circumference on the back of the entity model of the large-aperture mirror where the three Bipod support bosses are located is determined by using a finite element analysis method; S33, the positions of the three Bipod support bosses along the optical axis are determined by using the finite element analysis method; S33 is: In the finite element analysis, under the condition that the diameter of the back support circumference where the three Bipod support bosses are located is determined, the three Bipod support bosses are fixedly constrained, and the entity model of the large-aperture mirror is loaded with a 1G gravity action, and the direction of the 1G gravity is collinear with the center of one of the three Bipod support bosses; The mirror surface shape change amount of the entity model of the large-aperture mirror is calculated when the three Bipod support bosses move to different positions along the optical axis of the entity model of the large-aperture mirror under the back support circumference diameter determined in S32; The positions of the three Bipod support bosses along the optical axis are selected when the mirror surface shape change amount is the smallest; S4, different lightweight structure forms are selected to remove the back of the entity model of the large-aperture mirror on the basis of retaining the positions of the three Bipod support bosses, and a honeycomb structure is formed on the back, and the effective thickness of the panel of the entity model of the large-aperture mirror is retained; S5, the mirror body lightweight rate and the optical surface deformation amount root mean square (RMS) value of different lightweight structure forms are calculated, the final lightweight structure form is confirmed, and the large-aperture mirror is lightweight designed according to the quadric surface equation, the aperture, the thickness, the mirror back structure form, the positions of the three Bipod support bosses and the final lightweight form of the large-aperture mirror.

2. The lightweight design method of a large-aperture space mirror based on Bipod support according to claim 1, characterized in that, The thickness-to-aperture ratio formula in S1 is: ； wherein is the maximum deformation of the mirror surface of the large aperture mirror; is the material density of the large aperture mirror; is the radius of the large aperture mirror, is the diameter of the large aperture mirror, is the thickness of the large aperture mirror; is the elastic modulus of the large aperture material, is the acceleration due to gravity.

3. The lightweight design method of a space large-aperture mirror based on Bipod support according to claim 1, characterized in that, The mirror back structure form in S1 is one of a flat back shape, a crescent shape, a single-arch shape, a double-arch shape, a conical shape and a concave shape.

4. The lightweight design method of a space large-aperture mirror based on Bipod support according to claim 1, characterized in that, The mirror back structure form in S1 is a flat back shape.

5. The lightweight design method of a space large-aperture mirror based on Bipod support according to claim 1, characterized in that, S32 is: In the finite element analysis, under the condition that the initial back support circumference diameter is given, the three Bipod support bosses are fixedly constrained, the entity model of the large-aperture mirror is loaded with a 1G gravity action, and the mirror surface shape change amount of the entity model of the large-aperture mirror is calculated; the direction of the 1G gravity is collinear with the center of one of the three Bipod support bosses; The diameter of the back support circumference is changed, and the mirror surface shape change amount corresponding to the back support circumferences with different diameters is calculated by using the same method; The back support circumferential diameter corresponding to the minimum mirror surface shape variation is selected as the diameter of the back support circumferences of the three Bipod support bosses.

6. The method of claim 1, wherein the method is a method of lightweight design of a space large-aperture mirror based on a Bipod support. The different lightweight structure forms in S4 include triangle, quadrilateral, hexagon, circle and sector.

7. The method of claim 1, wherein the method is a method of lightweight design of a space large-aperture mirror based on a Bipod support. The different lightweight structure forms in S4 include triangle and hexagon.

8. The method of claim 1, wherein the method is a method of lightweight design of a space large-aperture mirror based on a Bipod support. S5 is: The mirror lightweight rate and the optical surface deformation root mean square (RMS) value of different lightweight structure forms are calculated respectively, the lightweight structure form with the highest mirror lightweight rate and the optical surface deformation root mean square (RMS) value not higher than 5nm is selected as the final lightweight structure form, and the large aperture mirror is lightweight designed according to the quadric equation, the aperture, the thickness, the mirror back structure form, the positions of the three Bipod support bosses and the final lightweight form.

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