Lightweight design method for spatial large-aperture reflector based on Bipod support

Abstract

The invention discloses a lightweight design method for a spatial large-aperture reflector based on a Bipod support, and solves the problems that in an existing lightweight design method, lightweight design is independently carried out on a reflector body, and when the Bipod support is installed on the reflector body, the surface shape of the reflector body is affected due to the coupling effect of the Bipod support and the reflector body, and the standard before coupling cannot be met. According to the method, a solid model of the large-aperture reflector is established, then the position of a Bipod supporting boss on the solid model is determined, the lightweight structural form is determined according to the mirror body lightweight rate and the optical surface deformation root-mean-square RMS value of different lightweight structural forms, and then lightweight design is conducted on the solid model of the large-aperture reflector. The influence of the coupling effect between the Bipod support and the large-aperture reflector on the static rigidity and the surface shape of the large-aperture reflector is considered, so that the optical surface deformation index can meet the requirement after the Bipod support is assembled.

Description

Technical Field

[0001] The invention relates to an optical-mechanical structure design method for a large-aperture space reflector, and in particular to a lightweight design method for a large-aperture space reflector based on a Bipod support. Background Art

[0002] The optical performance of large-aperture space mirrors is affected by their own gravity and the change of the temperature of the environment in which they are located. The position accuracy and surface accuracy of the mirror are directly related to the imaging quality of the space telescope. First, as the aperture of the telescope increases, the mass of the mirror increases in a cubic geometric relationship. The rapid increase in self-weight causes the optical surface quality of the mirror to degrade under the influence of gravity. Under the combined action of its own large gravity and the support reaction force, the optical surface produces rigid body displacement and optical surface deformation. Rigid body displacement can be compensated by adjustment, but 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 optical performance of the system; secondly, when the ambient temperature of the space mirror changes, the thermal performance mismatch between the mirror and its supporting structure material will cause thermal stress, causing elastic deformation of the optical surface. When there is a temperature gradient in the axial direction of the mirror, the deformation is proportional to the square of the mirror aperture; thirdly, from a dynamic point of view, reducing the mass of large-aperture space mirrors 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 remote sensing satellites is high, it costs $20,000 to launch a 1kg payload, and reducing the mass of the camera composed of a large-aperture space reflector can effectively control the launch cost. Therefore, the reflector must be designed to be lightweight.

[0003] Whether the final configuration of the reflector is reasonable needs to be integrated into the overall structure of the camera for evaluation. The overall structure of the camera is complex, and other structural parts will affect the surface shape of the reflector. The support structure directly connected to the reflector can partially isolate the influence of other structural parts. Bipod is a type of support structure widely used in large-aperture mirrors, which can be used for side support or back support of reflectors. The Bipod structure has different rigidity and flexibility in different force directions of the mirror body. It has good rigidity in the direction of gravity, which can ensure reasonable rigid body displacement and good surface shape of the reflector under gravity load. It has a certain flexibility in the direction where thermal gradients and assembly stress exist to release assembly stress and thermal stress, and ensure the surface shape and optical spacing of the primary and secondary mirrors under temperature changes. There will be a coupling effect between the position of the Bipod support, the size of the flexible junction, and the lightweight form of the mirror body. Due to the limitations of the installation position and method of the reflector in the space camera, most of the existing lightweight design methods are to lightweight the mirror body alone. Although a high lightweight rate can be achieved while meeting the surface shape requirements, after the Bipod support is added, the coupling effect between the Bipod support and the mirror body affects the surface shape of the mirror body, causing the optical surface deformation of the mirror body to fail to meet the index requirements. Summary of the invention

[0004] The purpose of the present invention is to solve the technical problem that in the existing lightweight design method, the mirror body is designed 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, resulting in the optical surface deformation of the mirror body failing to meet the index requirements, and to provide a lightweight design method for a spatial large-aperture reflector based on a Bipod support.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A lightweight design method for a space large-aperture reflector based on Bipod support is special in that it includes the following steps:

[0007] S1. Determine the thickness of the large-aperture reflector according to the diameter of the large-aperture reflector and the diameter-to-thickness ratio formula, and select the structure of the back of the reflector;

[0008] S2. Constructing a quadratic surface equation according to the optical design parameters of the large-aperture reflector, and establishing a solid model of the large-aperture reflector in combination with the aperture, thickness and back structure of the large-aperture reflector;

[0009] S3, determine the positions of three Bipod support bosses on the back of the solid model of the large-aperture reflector;

[0010] S4. On the basis of retaining the positions of the three Bipod support bosses, different lightweight structural forms are selected to physically remove the back of the solid model of the large-aperture reflector, and the effective thickness of the solid model panel of the large-aperture reflector is retained;

[0011] S5. Calculate the mirror body lightweight rate and optical surface deformation root mean square RMS value of different lightweight structural forms, confirm the final lightweight structural form, and design the large-aperture reflector lightweight according to the quadratic surface equation, the diameter and thickness of the large-aperture reflector, the reflector back structure, the location of the three Bipod support bosses, and the final lightweight form. In the lightweight design of the space large-aperture reflector, the present invention considers the effect of the coupling between the Bipod support boss and the large-aperture reflector on the static stiffness and surface shape of the large-aperture reflector, avoiding the problem that the optical surface deformation index does not meet the requirements after the support is added, although the mirror body is designed alone to obtain a high lightweight rate.

[0012] Furthermore, the diameter-to-thickness ratio formula in S1 is:

[0013]

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

[0015] Furthermore, the back structure of the reflector in S1 is one of a flat back shape, a meniscus shape, a single arch shape, a double arch shape, a cone shape and a concave shape.

[0016] Furthermore, the back structure of the reflector in S1 is a flat back shape.

[0017] Furthermore, S3 is specifically:

[0018] S31. The solid model of the large-aperture reflector is a rotationally symmetrical body, and three Bipod support bosses are evenly distributed on a support circumference on the back of the solid model of the large-aperture reflector;

[0019] S32, using a finite element analysis method to determine the diameter of the back support circle of the solid model of the large-aperture reflector where the three Bipod support bosses are located;

[0020] S33. Use finite element analysis method to determine the positions of the three Bipod support bosses along the optical axis.

[0021] Further, S32 is specifically:

[0022] In the finite element analysis, under the condition of the given initial back support circle diameter, three Bipod support bosses are fixedly constrained, and the solid model of the large-aperture reflector is loaded with 1G gravity, and the surface shape change of the solid model of the large-aperture reflector 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 circle is changed, and the mirror surface shape change corresponding to the back support circle with different diameters is calculated by the same method;

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

[0025] Furthermore, S33 is specifically:

[0026] In the finite element analysis, when the back support circle diameter where the three Bipod support bosses are located is determined, the three Bipod support bosses are fixedly constrained, and the solid model of the large-aperture reflector 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 change in the mirror surface shape of the solid model of the large-aperture reflector when the three Bipod support bosses are moved to different positions along the optical axis of the solid model of the large-aperture reflector under the back support circle diameter determined in S32 is calculated; the positions of the three Bipod support bosses along the optical axis direction when the change in the mirror surface shape is minimized are selected.

[0027] Furthermore, the different lightweight structural forms described in S4 include triangle, quadrilateral, hexagon, circle and fan.

[0028] Furthermore, the different lightweight structural forms described in S4 include triangle and hexagon.

[0029] Furthermore, S5 is specifically:

[0030] The mirror body lightweighting rate and the RMS value of the optical surface deformation of different lightweight structural forms are calculated respectively, and the lightweight structural form with the highest mirror body lightweighting rate among the lightweight structural forms with the RMS value of the optical surface deformation not higher than 5nm is selected as the final lightweight structural form. The large-aperture reflector is lightweight designed according to the quadratic surface equation, the diameter and thickness of the large-aperture reflector, the structure of the back of the reflector, the positions of the three Bipod support bosses and the final lightweight form.

[0031] Beneficial effects of the present invention:

[0032] 1. The present invention discloses a lightweight design method for a large-aperture space reflector based on Bipod support, which can realize a high lightweight design of a large-aperture space reflector, and has both high static stiffness and dynamic stiffness while meeting the requirements of high lightweight, so as to realize the use requirements of large-aperture reflectors proposed in space applications and reduce launch costs.

[0033] 2. In the lightweight design method of a spatial large-aperture reflector based on Bipod support of the present invention, the influence of the coupling effect between the Bipod support boss and the large-aperture reflector on the static stiffness and surface shape of the large-aperture reflector is taken into consideration, thereby avoiding the problem that although a high lightweight rate can be obtained by designing a mirror body alone, the optical surface deformation index cannot meet the requirements after the support is added. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a solid model of a large-aperture reflector with a diameter-to-thickness ratio of 12:1 in an embodiment of a lightweight design method for a space large-aperture reflector based on Bipod support of the present invention;

[0035] Figure 2 yes Figure 1 Sectional view of AA in the middle;

[0036] Figure 3 It is a schematic structural diagram of a reflector supported by three Bipods in an embodiment of a method for lightweight design of a space large-aperture reflector based on Bipod support of the present invention;

[0037] In the picture, 1. First Bipod support, 2. Second Bipod support, 3. Third Bipod support;

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

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

[0040] Figure 6 1 is a schematic diagram of the positions of three Bipod support bosses along the optical axis in an embodiment of a lightweight design method for a space large-aperture reflector based on Bipod support of the present invention; wherein a represents the positions of the three Bipod support bosses along the optical axis;

[0041] Figure 7 Schematic diagram of two different lightweight forms of honeycomb holes on the back of a reflector in an embodiment of a lightweight design method for a large-aperture space reflector based on Bipod support of the present invention;

[0042] Among them, (a) is a schematic diagram of the back structure when the lightweight hole is a hexagon; (b) is a schematic diagram of the back structure when the lightweight hole is a triangle;

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

[0044] Among them, (a) is a schematic diagram of the optical surface deformation corresponding to the triangular lightweight hole; (b) is a schematic diagram of the optical surface deformation corresponding to the hexagonal lightweight hole. DETAILED DESCRIPTION

[0045] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] Example

[0047] In this embodiment, a lightweight design method for a space large-aperture reflector based on Bipod support includes the following steps:

[0048] S1. Determine the thickness of the large-aperture reflector according to the diameter of the large-aperture reflector and the diameter-to-thickness ratio formula, and select the structure of the back of the reflector; the diameter-to-thickness ratio formula is:

[0049]

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

[0051] The back structure of the reflector selected in this embodiment is a flat back shape.

[0052] In this embodiment, the diameter of the reflector is 660mm, and the diameter-to-thickness ratio will affect the stiffness, lightweight ratio, center of mass position, etc. of the reflector. According to the above formula, the diameter-to-thickness ratio of the reflector is 12, and the mirror body thickness is greater than 66mm. Considering the high specific stiffness of the SiC reflector and the need to achieve a higher lightweight ratio, the diameter-to-thickness ratio is 12, and the center thickness of the mirror body is 55mm.

[0053] S2. Construct a quadratic surface equation based on the optical design parameters of the large-aperture reflector, and establish a solid model of the large-aperture reflector in combination with the aperture, thickness and back structure of the large-aperture reflector, such as Figure 1 and Figure 2 Shown is the solid model obtained when the mirror thickness ratio is 12:1;

[0054] S3. When designing, consider the reflector structure supported by three Bipod support bosses. Figure 3 As shown, 1 represents the first Bipod support, 2 represents the second Bipod support, and 3 represents the third Bipod support. However, it is still necessary to determine the positions of the three Bipod support bosses on the back of the solid model of the large-aperture reflector and the lightweight form of the back of the solid model of the large-aperture reflector; specifically:

[0055] S31. The solid model of the large-aperture reflector is a rotationally symmetrical body. Three Bipod support bosses are evenly distributed on a support circle on the back of the solid model of the large-aperture reflector. The central angle between two adjacent Bipod support bosses is 120°.

[0056] S32. Determine the diameter of the back support circle of the solid model of the large-aperture reflector where the three Bipod support bosses are located by using a finite element analysis method; specifically:

[0057] In the finite element analysis, the diameter of the initial back support circle is given, and three Bipod support bosses are fixedly constrained to be evenly distributed on the back support circle. The solid model of the large-aperture reflector is loaded with 1G gravity, and the surface shape change of the solid model of the large-aperture reflector is calculated.

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

[0059] The diameter of the back support circle corresponding to the minimum change in mirror surface shape is selected as the diameter of the back support circle 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 circle where the Bipod support boss is located is in the range of 360mm-500mm, that is, when the horizontal coordinate code is between 19-23, the RMS value of the optical surface deformation is relatively small, which is the optional range of the back support circle. Figure 4 The horizontal axis is the code for the size of the back support circumference, and the vertical axis is the RMS value of the optical surface. The horizontal axis has no unit, and the vertical axis unit is mm.

[0061] S33, using a finite element analysis method to determine the positions of the three Bipod support bosses along the optical axis;

[0062] Specifically:

[0063] In the finite element analysis, when the back support circle diameter where the three Bipod support bosses are located is determined, the three Bipod support bosses are fixedly constrained, and the solid model of the large-aperture reflector 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 change in the mirror surface shape of the solid model of the large-aperture reflector when the three Bipod support bosses are moved to different positions along the optical axis of the solid model of the large-aperture reflector under the back support circle diameter determined in S32 is calculated; the positions of the three Bipod support bosses along the optical axis direction when the change in the mirror surface shape is minimized are selected.

[0064] Finally, the locations of the three Bipod support bosses are determined as follows: Figure 5 and Figure 6 As shown, Figure 6 In the figure a, the positions of the three Bipod support bosses are shown along the optical axis.

[0065] S4. On the basis of retaining the positions of the three Bipod support bosses, different lightweight structural forms are selected to physically remove the back of the solid model of the large-aperture reflector, and the effective thickness of the solid model panel of the large-aperture reflector is retained at 5 mm. After the physical removal, a rib plate is formed between two adjacent honeycomb holes, and the thickness of the rib plate is 3 mm.

[0066] Different lightweight structural forms include triangles, quadrilaterals, hexagons, circles and sectors.

[0067] Among them, the lightweight structural forms of triangle and hexagonal structures are as follows Figure 7 As shown in (a) and (b).

[0068] S5. Calculate the mirror body lightweighting rate and the RMS value of the optical surface deformation of different lightweight structural forms respectively, select the lightweight structural form with the highest mirror body lightweighting rate among the lightweight structural forms with the RMS value of the optical surface deformation not higher than 5nm as the final lightweight structural form, and perform lightweight design of the large-aperture reflector based on the quadratic surface equation, the diameter and thickness of the large-aperture reflector, the structure of the back of the reflector, the locations of the three Bipod support bosses and the final lightweight form.

[0069] Compared with solid reflectors, honeycomb lightweight structures have a higher specific stiffness. Lightweight reflectors remove solid materials that contribute less to the stiffness on the back of the reflector, thereby increasing the specific stiffness of the reflector in terms of overall stiffness. The lightweight hole forms of reflectors include triangles, quadrilaterals, hexagons, circles, and sectors. When the lightweight hole form is a triangle, the structure is as follows: Figure 7 As shown in (b), when the lightweight hole is in the form of a hexagon, the structure is as follows Figure 7 As shown in (a), the triangular hole has better rigidity and stability, while the hexagonal hole has a higher lightweight rate.

[0070] The RMS value of the optical surface deformation of the lightweight structural form of the triangular and hexagonal structure is as follows Figure 8 As shown in (a) and (b), Figure 8 The surface deformation distributions of (a) and (b) are relatively close, with the RMS value of the triangular lightweight solution being 4.6nm and the RMS value of the hexagonal lightweight solution being 4.8nm.

[0071] In this embodiment, the lightweight rate of the triangular solution is 85.2%, and that of the hexagonal solution is 86%. Finally, the hexagonal solution is selected.

[0072] The above description is only a specific embodiment of the present invention, and a comparison of the effects of the specific embodiments and the related comparative examples, but the protection scope of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A lightweight design method for a space large-aperture reflector based on Bipod support, characterized in that: The following steps are involved: S1. Determine the thickness of the large-aperture reflector according to the diameter of the large-aperture reflector and the diameter-to-thickness ratio formula, and select the structure of the back of the reflector; S2. Constructing a quadratic surface equation according to the optical design parameters of the large-aperture reflector, and establishing a solid model of the large-aperture reflector in combination with the aperture, thickness and back structure of the large-aperture reflector; S3, determine the positions of three Bipod support bosses on the back of the solid model of the large-aperture reflector; S4. On the basis of retaining the positions of the three Bipod support bosses, different lightweight structural forms are selected to physically remove the back of the solid model of the large-aperture reflector, and a honeycomb structure is formed on the back, and the effective thickness of the solid model panel of the large-aperture reflector is retained; S5. Calculate the mirror body lightweight ratio and the root mean square (RMS) value of the optical surface deformation of different lightweight structural forms, confirm the final lightweight structural form, and perform lightweight design of the large-aperture reflector based on the quadratic surface equation, the diameter and thickness of the large-aperture reflector, the reflector back structure, the locations of the three Bipod support bosses, and the final lightweight form.

2. According to claim 1, a lightweight design method for a space large-aperture reflector based on Bipod support, characterized in that: The diameter-to-thickness ratio formula described in S1 is: Wherein, δ is the maximum deformation of the large-aperture reflector; r is the material density of the large-aperture reflector; r is the radius of the large-aperture reflector, D is the diameter of the large-aperture reflector, t is the thickness of the large-aperture reflector; E is the elastic modulus of the large-aperture material, and g is the acceleration of gravity.

3. According to claim 1, a lightweight design method for a space large-aperture reflector based on Bipod support, characterized in that: The back structure of the reflector in S1 is one of a flat back shape, a meniscus shape, a single arch shape, a double arch shape, a cone shape and a concave shape.

4. According to claim 1, a lightweight design method for a space large-aperture reflector based on Bipod support, characterized in that: The back structure of the reflector in S1 is a flat back shape.

5. According to claim 4, a lightweight design method for a space large-aperture reflector based on Bipod support is characterized in that: S3 is specifically: S31. The solid model of the large-aperture reflector is a rotationally symmetrical body, and three Bipod support bosses are evenly distributed on a support circumference on the back of the solid model of the large-aperture reflector; S32, using a finite element analysis method to determine the diameter of the back support circle of the solid model of the large-aperture reflector where the three Bipod support bosses are located; S33. Use finite element analysis method to determine the positions of the three Bipod support bosses along the optical axis.

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

7. The lightweight design method for a space large-aperture reflector based on Bipod support according to claim 5 is characterized in that: S33 is specifically: In the finite element analysis, when the diameter of the back support circle where the three Bipod support bosses are located is determined, the three Bipod support bosses are fixedly constrained, and a 1G gravity is applied to the solid model of the large-aperture reflector, and the direction of the 1G gravity is collinear with the center of one of the three Bipod support bosses; Calculate the change in the mirror surface shape of the solid model of the large-aperture reflector when the three Bipod support bosses are moved to different positions along the optical axis of the solid model of the large-aperture reflector under the back support circumferential diameter determined in S32; select the positions of the three Bipod support bosses along the optical axis direction when the change in the mirror surface shape is the smallest.

8. The lightweight design method for a space large-aperture reflector based on Bipod support according to claim 1, characterized in that: The different lightweight structural forms described in S4 include triangle, quadrilateral, hexagon, circle and fan.

9. The lightweight design method for a space large-aperture reflector based on Bipod support according to claim 1, characterized in that: The different lightweight structural forms described in S4 include triangle and hexagon.

10. The lightweight design method for a space large-aperture reflector based on Bipod support according to claim 1, characterized in that: S5 is as follows: The mirror body lightweighting rate and the RMS value of the optical surface deformation of different lightweight structural forms are calculated respectively, and the lightweight structural form with the highest mirror body lightweighting rate among the lightweight structural forms with the RMS value of the optical surface deformation not higher than 5nm is selected as the final lightweight structural form. The large-aperture reflector is lightweight designed according to the quadratic surface equation, the diameter and thickness of the large-aperture reflector, the structure of the back of the reflector, the positions of the three Bipod support bosses and the final lightweight form.

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