Large aperture visible wavelength aluminum alloy space mirror assembly and preparation method thereof

Abstract

The present application belongs to the technical field of space optical remote sensing, and particularly relates to a large-aperture visible light band aluminum alloy space mirror assembly and a preparation method thereof. The mirror assembly comprises a mirror unit and a flexible support unit. The mirror unit comprises an aluminum alloy mirror body, an optical mirror surface and a lightweight structure. The aluminum alloy mirror body and the flexible support unit are made of the same aluminum alloy material. The lightweight structure forms three support zones arranged uniformly in the circumferential direction on the back of the aluminum alloy mirror body. Each support zone is provided with a support cavity. The flexible support unit is placed in the support cavity and forms a three-point support structure as a whole. The support cavity is provided with a mounting table. The flexible support unit is connected to the mounting table through locking members. The optical mirror surface is subjected to secondary precise shaping processing with the assembled mirror assembly as a whole after the mirror unit and the flexible support unit are assembled. The present application can achieve high surface shape precision and long-term on-orbit stability.

Description

Technical Field

[0001] This invention belongs to the field of space optical remote sensing technology, and particularly relates to a large-aperture visible light band aluminum alloy space reflector assembly and its preparation method. Background Technology

[0002] With the continuous development of space-based Earth observation and astronomical exploration missions, space cameras are evolving towards larger apertures, longer focal lengths, and higher resolutions. This places stringent demands on the surface accuracy, structural rigidity, thermal dimensional stability, and lightweighting of mirror components. As one of the most important components in a reflective optical system, the surface accuracy and stability of the mirror directly affect the imaging quality of the optical system. To reduce the difficulty of supporting, processing, assembling, and testing the mirror, and to ensure surface accuracy, lightweight design is necessary to reduce structural weight. Currently, silicon carbide and glass-ceramic are the mainstream materials for large-aperture space mirrors. Silicon carbide has high specific stiffness and low thermal deformation, but its processing cycle is long and its manufacturing cost is high. Glass-ceramic has an extremely low coefficient of thermal expansion, but it is brittle and cannot be directly screwed together; metal bushings must be embedded to achieve mechanical interfaces, making the assembly process complex.

[0003] Compared to traditional optical materials such as silicon carbide, fused silica, optical glass, and single-crystal silicon, aluminum and its alloys have many advantages when used as optical components: aluminum alloy mirrors have outstanding advantages such as moderate specific stiffness, ultra-precision machinability, easy lightweighting, controllable cost, and good thermal compatibility with the same material. They have been widely used in small and medium-aperture space optical payloads. Aluminum alloys can achieve optical surface shaping through single-point diamond turning, and support secondary finishing of optical surfaces after component assembly, which can effectively release stress deformation introduced by assembly. They have good application prospects in visible light-infrared multi-spectral space payloads.

[0004] Currently, the design and manufacturing technology of domestic space aluminum alloy reflectors mainly follows two technical routes: First, the structural design and optomechanical integration technology route. This route has accumulated significant technical expertise in aluminum alloy mirror structural design, lightweight configuration, optomechanical integration, and space environment adaptability design. It has been validated in the external support structure design and on-orbit engineering applications of large-aperture aluminum mirrors. Its technical advantages are mainly reflected in the lightweight back topology, multi-point unloading support, and all-aluminum optomechanical heatless integrated design. The related solutions have high mechanical stability and structural reliability. However, this technical approach has the following shortcomings: First, most structural solutions are adapted to infrared band applications, and there are few complete structural solutions for large-aperture, high-resolution visible light imaging conditions of 600mm and above. There is insufficient design control for nanometer-level surface accuracy and extremely low assembly stress. Second, the assembly structure of large-aperture mirrors all use pre-embedded / bonded metal inlay bushings for support and connection. The interface of heterogeneous materials is prone to thermal mismatch stress, interface slippage and accumulation of assembly residual stress in the wide temperature alternation environment, which limits long-term on-orbit stability. Third, the design and manufacturing process generally adopts the process sequence of "first fine-tuning the mirror surface, then assembling the support", without adapting to the secondary fine-machining process after component integration at the structural level. Assembly stress cannot be eliminated, making it difficult to meet the high-precision surface stability requirements of large-aperture visible light mirrors.

[0005] Second, the ultra-precision manufacturing and process control technology route. This route has significant advantages in ultra-precision manufacturing of aluminum alloy mirrors, ultra-smooth surface processing, polishing modification, and residual stress control. It has formed a complete visible light-level ultra-precision processing system, including diamond turning, magnetorheological polishing, ion beam shaping, and composite chemical polishing. The related technologies can effectively solve the industry problems of high surface roughness and numerous grain boundary defects in aluminum alloy mirrors. However, this route still has the following shortcomings: First, the technology accumulation is mainly based on process methods. There is a serious lack of product structure solutions for large-aperture space mirrors, such as body structures, lightweight configurations, stress-free assembly interfaces, and overall support layouts. There is a lack of complete structural solutions for large-aperture space mirrors that can be directly applied in engineering. Second, existing structural solutions still use traditional inlaid bushing connection methods, which have not overcome the problem of heterogeneous interface stress. Third, the related high-precision processing technologies are mostly independent manufacturing methods and have not formed a structure-process integrated collaborative design with the overall assembly structure and support layout of the mirror. This makes it impossible to suppress assembly stress and thermal deformation from the source, resulting in insufficient engineering adaptability for large-aperture visible light space mirrors.

[0006] The existing publicly available literature and engineering solutions related to the two technical routes do not involve the direct connection structure without inlays, the overall secondary precision machining of the adapter components, or the all-aluminum high-stability reflector assembly solution for large-aperture visible light. As a result, the current large-aperture visible light aluminum alloy space reflectors generally suffer from technical bottlenecks such as high assembly stress, poor thermal stability, weak surface accuracy retention, and mismatch between structure and process. These bottlenecks restrict the lightweight, low-cost, and high-stability development of large-aperture, long-focal-length, high-resolution space visible light cameras.

[0007] Specifically, existing publicly available literature and engineering solutions for large-aperture aluminum alloy mirror assemblies generally suffer from the following technical limitations: First, they commonly employ inlaid bushing transition connection structures. Since the inlaid parts and the aluminum alloy mirror body are heterogeneous interfaces, thermal mismatch stress and assembly residual stress are easily generated under alternating temperature conditions in orbit, limiting long-term in-orbit stability. Second, the assembly-processing sequence is not sufficiently rational. Most existing structures first refine the mirror surface and then assemble the support, with assembly stress directly acting on the already processed optical mirror surface. There is a lack of a complete configuration design that involves "secondary processing of the optical surface after assembly." Third, flexible support configurations are lacking. The existing thin-plate and ear-plate flexible structures are not reasonable enough. Under large-diameter conditions, it is difficult to balance the support stiffness and stress unloading, which can easily lead to mirror body tilting and surface distortion. Fourth, the thermal matching design of the support and mirror body is insufficient. The flexible support of different materials generates additional thermal stress in a wide temperature range environment. The all-aluminum homogeneous support scheme lacks a specific configuration design that couples the cylindrical flexible support with the three-point support at the back. Fifth, the engineering implementation of large-diameter visible light band is difficult. Existing patents are mostly for small and medium-diameter aluminum reflectors, and there is a lack of complete structural solutions that match the use of inserts-free, screw-direct connection, and component integration followed by processing.

[0008] In summary, to avoid further engineering applications of aluminum alloy mirrors in large-aperture high-resolution space cameras being restricted, it is urgent to design an aluminum alloy mirror assembly solution that is oriented towards large-aperture visible light applications and can solve the problems of assembly stress and thermal deformation from both structural and process perspectives. Summary of the Invention

[0009] In view of this, the present invention aims to provide a large-aperture visible light band aluminum alloy space reflector assembly and its manufacturing method, so as to solve the problems of large assembly stress, poor thermal stability and weak surface accuracy retention caused by the inlaid bushing connection and the "precision repair of mirror surface before assembly and support" process of existing large-aperture visible light aluminum alloy reflector assemblies.

[0010] To achieve the above objectives, the technical solution created by this invention is implemented as follows: Large-aperture visible light band aluminum alloy space mirror assembly, including mirror unit and flexible support unit; The reflector unit includes an aluminum alloy mirror body, an optical reflector surface disposed on the front of the aluminum alloy mirror body, and a lightweight structure disposed on the back of the aluminum alloy mirror body; the aluminum alloy mirror body is a one-piece structure formed by machining and milling, and the aluminum alloy mirror body and the flexible support unit use the same aluminum alloy material. The lightweight structure forms three support areas evenly arranged circumferentially on the back of the aluminum alloy mirror body. Each support area has a support cavity, and the flexible support unit is placed in the support cavity to form a three-point support structure. The support cavity is equipped with a mounting platform integrally formed with the aluminum alloy mirror body, and the flexible support unit is connected to the mounting platform by a locking device. After the optical mirror is assembled with the mirror unit and the flexible support unit, it undergoes a second precision shaping process based on the assembled mirror assembly as a whole.

[0011] Furthermore, the flexible support unit includes a support body that is cylindrical in shape, with its axial ends connected to the mounting platform and an external support structure, respectively; the support body is a hollow structure and includes a cylindrical wall, on which flexible grooves are formed.

[0012] Furthermore, the flexible groove includes a circumferential annular groove and / or an axial straight groove; the cylinder wall of the supporting body is a thin-walled structure, and the temperature cycle stress and assembly micro-stress are released through the elastic deformation of the cylinder wall and the flexible groove.

[0013] Furthermore, the support body is provided with a top connecting flange and a bottom connecting flange at both axial ends. The top connecting flange is connected to the mounting platform, and the bottom connecting flange is connected to the external support structure. The top connecting flange and the mounting platform are respectively provided with mutually cooperating locking holes. The top connecting flange is locked to the mounting platform through the cooperation of locking parts and locking holes.

[0014] Furthermore, the lightweight structure is composed of a ribbed groove group milled into the back of the aluminum alloy mirror body; the ribbed groove group includes multiple parallel main ribs I and multiple parallel main ribs II, with the main ribs I and main ribs II arranged intersectingly; the spacing between adjacent main ribs I is equal, and the spacing between adjacent main ribs II is equal; the acute angle between main ribs I and main ribs II is 60°; the ribbed groove group also includes auxiliary ribs disposed around each support cavity; the auxiliary ribs around each support cavity are evenly distributed, and the auxiliary ribs extend from the edge of the support cavity away from the support cavity.

[0015] Furthermore, the effective light-transmitting aperture of the optical reflector is Ф650mm, and the reflection aperture of the optical reflector is Ф660mm; both the aluminum alloy mirror body and the flexible support unit are made of RSA-6061 or RSA-443 aluminum alloy materials.

[0016] Furthermore, the optical reflective mirror surface is provided with a low-phosphorus Ni-P precision coating, and the roughness Ra of the optical reflective mirror surface is ≤2nm.

[0017] Furthermore, the aluminum alloy mirror body is also provided with a counterweight hole on its center plane in the circumferential direction. The counterweight hole is used to clamp the counterweight block when the optical mirror surface is aligned with the machine tool during the single-point machining stage.

[0018] A method for fabricating a large-aperture visible light band aluminum alloy space mirror assembly, comprising the following steps: S1. Select an aluminum alloy mirror blank and perform overall rough milling to obtain an aluminum alloy mirror body. The front of the aluminum alloy mirror body forms the base surface of the optical reflective mirror, and the back of the aluminum alloy mirror body forms a lightweight structure including three support cavities. Locking holes are machined on the mounting platform of the support cavities. Three flexible support units are machined simultaneously. S2. Perform the first stress-relieving aging on the rough-machined aluminum alloy mirror body to release the residual stress from the rough machining. S3. Perform semi-finish milling on the aluminum alloy mirror body to trim the contour of the aluminum alloy mirror body, the base surface of the optical reflective mirror, and the locking holes; perform a second stress-relieving aging on the semi-finish milled aluminum alloy mirror body. S4. Fine-machine the optical reflective mirror surface, and after preparing a low-phosphorus Ni-P coating on the optical reflective mirror surface, complete the initial polishing. S5. Secure the three flexible support units to the three mounting platforms respectively using locking devices to complete the assembly of the three-point support structure; complete the assembly of the aluminum alloy space reflector assembly; S6. Perform low-temperature aging treatment on the assembled aluminum alloy space reflector assembly to release assembly locking stress. S7. Using the assembled aluminum alloy space reflector assembly as the processing benchmark, perform secondary precision shaping on the optical reflector surface to compensate for the surface shape error introduced by assembly, and obtain an optical reflector surface that meets the imaging requirements of the visible light band.

[0019] Furthermore, in S7, the secondary precision shaping process sequentially includes single-point diamond turning, CNC small grinding head polishing, magnetorheological polishing, and ion beam shaping.

[0020] 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.

[0021] Compared with the prior art, the present invention can achieve the following beneficial effects: 1. Eliminates thermal mismatch at the interface of heterogeneous materials and residual stress in assembly, improving long-term on-orbit stability: This application adopts an integral aluminum alloy structure without inserts. The flexible support unit and the aluminum alloy mirror body are made of the same aluminum alloy material, with completely consistent coefficients of thermal expansion, eliminating thermal mismatch between heterogeneous materials; the absence of insert bushings eliminates residual stress caused by bonding and pressing, avoiding the risks of mechanical vibration, interface slippage and loosening after thermal cycling, which is beneficial to the long-term on-orbit stability of large-aperture reflectors.

[0022] 2. Relief of assembly stress, ensuring nanometer-level surface accuracy in the large-aperture visible light band: This application adopts a "first assembly, then secondary precision machining" process sequence. After the reflector assembly completes the three-point support integration and screw tightening, the optical reflector surface is subjected to secondary precision shaping machining based on the entire reflector assembly as the machining datum. This offsets the surface distortion introduced by the pre-tightening stress of the three-point support screws and the assembly pre-stress, ultimately achieving a visible light band mirror surface RMS ≤ λ / 50 (λ = 632.8 nm). High and low temperature cycle stress relief aging ( The shape change after 50℃~+120℃ is ≤λ / 80 (λ=632.8nm).

[0023] 3. Balancing lightweight ratio, structural stiffness, and stress unloading capability: This application is designed for large-aperture visible light imaging applications with a Ф650mm aperture. It adopts a three-point symmetrical support structure on the back combined with a cylindrical flexible support configuration. The flexible release groove on the flexible support prevents the stress from the screw tightening from spreading to the optical reflector surface. The lightweight structure on the back adopts a composite structure of main ribs and auxiliary ribs. After the reflector is lightweighted, the model mass is 19.3kg, with a lightweight ratio of 85.3%. The overall stiffness of the reflector assembly meets the requirements of aerospace mechanical environment, and the first-order natural frequency of the reflector assembly is ≥135Hz.

[0024] 4. The structure and assembly process are simplified, and the manufacturing cost and assembly difficulty are reduced: This application adopts a matching design of all-aluminum homogeneous materials, which eliminates the need for complex thermal compensation structures, reduces the number of parts, and simplifies the assembly process; the aluminum alloy can achieve optical surface forming through single-point diamond turning, and supports secondary finishing of the optical surface after the component is assembled, which can effectively release the stress deformation introduced by assembly, which is conducive to the further engineering application of aluminum alloy mirrors in large-aperture high-resolution space cameras. Attached Figure Description

[0025] 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 This is a schematic diagram of the overall structure of the aluminum alloy space reflector assembly in an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of the reflector unit in an embodiment of the present invention; Figure 3 This is a schematic diagram of the flexible support unit in an embodiment of the present invention.

[0026] Reference numerals: 1. Aluminum alloy mirror body; 2. Optical reflecting mirror surface; 3. Support cavity; 4. Mounting platform; 5. Support body; 6. Circumferential annular groove; 7. Axial straight groove; 8. Top connecting flange; 9. Bottom connecting flange; 10. Locking hole; 11. Main rib one; 12. Main rib two; 13. Auxiliary rib; 14. Flexible support unit; 15. Counterweight hole. Detailed Implementation

[0027] To make the purpose, technical solution, and advantages of this invention clearer, the following description is provided in conjunction with the appendix. Figures 1-3 The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and do not constitute a limitation thereof.

[0028] This invention provides a large-aperture visible light band aluminum alloy space reflector assembly, including a reflector unit and a flexible support unit 14. The reflector unit includes an aluminum alloy mirror body 1, an optical reflector surface 2 disposed on the front of the aluminum alloy mirror body 1, and a lightweight structure disposed on the back of the aluminum alloy mirror body 1. The aluminum alloy mirror body 1 is an integrally machined and milled structure without welding or additive manufacturing. The optical reflector surface 2 is disposed on the front of the aluminum alloy mirror body 1, which is adapted to the high-precision imaging and detection requirements of the visible spectrum band and meets the indicators of low roughness, low stray light, and high surface stability of visible light.

[0029] The effective light-passing aperture of the optical reflector 2 is Ф650mm, and the reflection aperture of the optical reflector is Ф660mm. In this embodiment, the reflection aperture refers to the outer diameter of the optical reflector, and the effective light-passing aperture refers to the diameter of the beam that actually participates in imaging. At the same time, the optical reflector 2 is provided with an 80–120μm low phosphorus Ni-P precision coating and is ultra-fine polished. The roughness Ra of the optical reflector 2 is ≤2nm, which can adapt to the requirements of low stray light and high resolution imaging of visible light and meet the requirements of low scattering and high signal-to-noise ratio imaging of visible light.

[0030] The aluminum alloy mirror body 1 and the flexible support unit 14 are made of the same aluminum alloy material. In this embodiment, both the aluminum alloy mirror body 1 and the flexible support unit 14 are made of RSA-6061 or RSA-443 aluminum alloy material, which has low residual stress and small long-term creep, ensuring the on-orbit stability of the large-diameter mirror. The structure in this embodiment adopts an integral aluminum alloy structure design without inserts, abandoning the traditional Invar and titanium alloy dissimilar metal inserts and bonding structures, and fully utilizing the structural strength of the aluminum alloy body material to achieve assembly and load-bearing.

[0031] The lightweight structure forms three support areas evenly arranged circumferentially on the back of the aluminum alloy mirror body 1. The three support areas have the same radius, and each support area has a support cavity 3. The flexible support unit 14 is placed in the support cavity 3 and forms a three-point support structure. In this embodiment, the inner diameter of the support cavity 3 is 70mm, the cavity thickness is 8mm, and the cavity depth is 77.5mm. After the lightweighting of the aluminum alloy mirror body 1, the model mass is 19.3kg, the lightweighting rate is 85.3%, and the overall rigidity meets the requirements of aerospace mechanical environment.

[0032] like Figure 1 , Figure 2 As shown, the lightweight structure is composed of a rib groove group milled into the back of the aluminum alloy mirror body 1. The rib groove group includes multiple parallel main ribs 11 and multiple parallel main ribs 2 12. The main ribs 11 and main ribs 2 12 are arranged in a cross pattern. The spacing between adjacent main ribs 11 is equal, and the spacing between adjacent main ribs 2 12 is equal. The acute angle between the main ribs 11 and main ribs 2 12 is 60°. The rib groove group also includes auxiliary ribs 13 disposed around each support cavity 3. The auxiliary ribs 13 are evenly distributed around each support cavity 3. The auxiliary ribs 13 extend radially from the edge of the support cavity 3 to the main ribs 11 or main ribs 2 12 or the peripheral surface of the aluminum alloy mirror body 1 in a direction away from the support cavity 3.

[0033] In this embodiment, the thickness of the finished optical reflective mirror 2 is 5mm, the thickness of the first main rib 11 and the second main rib 12 is 4mm, the thickness of the auxiliary rib 13 is 3mm, and the cavity depth of the support cavity 3 is 77.5mm. By optimizing the above parameters, while achieving a high weight reduction rate, the overall rigidity of the Ф660mm large-aperture mirror body can be guaranteed, and the visible light imaging surface drift caused by spatial micro-vibration and temperature change can be suppressed.

[0034] The support cavity 3 is provided with a mounting platform 4 integrally formed with the aluminum alloy mirror body 1. The flexible support unit 14 is directly connected to the mounting platform 4 through locking components to achieve direct assembly. Specifically, the flexible support unit 14 includes a support body 5 that is cylindrical in shape. The two axial ends of the support body 5 are respectively connected to the mounting platform 4 and the external support structure. In this embodiment, the external support structure refers to the overall structure on which the aluminum alloy space mirror assembly is installed, such as the main load-bearing structure of the space camera or the mirror support back plate.

[0035] The support body 5 is provided with a top connecting flange 8 and a bottom connecting flange 9 at its two axial ends. The top connecting flange 8 is connected to the mounting platform 4, and the bottom connecting flange 9 is connected to the external support structure. Specifically, the bottom connecting flange 9 of the flexible support unit 14 is connected to the external support structure through a locking device, thereby fixing the aluminum alloy space reflector assembly to the whole structure.

[0036] The top connecting flange 8 and the mounting platform 4 are respectively provided with mutually cooperating locking holes 10. The top connecting flange 8 is locked to the mounting platform 4 through the cooperation of the locking element and the locking hole 10. In this embodiment, the locking element is a locking screw and the locking hole 10 is a threaded hole. The pre-tightening load of the three-point flexible support is borne by the thickness and bearing strength of the aluminum alloy substrate itself. All dissimilar metal inserts and adhesive layers are eliminated. No Invar or titanium alloy inlay bushings are pre-embedded or bonded. This can completely eliminate defects such as thermal mismatch, adhesive layer aging and insert falling off.

[0037] The support body 5 is a hollow structure and includes a cylindrical wall. Flexible grooves are provided on the cylindrical wall to achieve flexible unloading, such as... Figure 3 As shown, the flexible groove includes a circumferential annular groove 6 and / or an axial straight groove 7. In this embodiment, multiple sets of circumferential annular grooves 6 and axial straight grooves 7 are provided simultaneously. The bottom connecting flange 9 and the top connecting flange 8 are connected to the corresponding components by locking screws to achieve direct connection assembly without inserts. The circumferential annular groove 6 and the axial straight groove 7 can prevent the locking stress from spreading to the Ф650mm optical reflector surface 2. In this embodiment, the inner diameter of the support body 5 is 57mm, the outer diameter is 66mm, and the wall thickness is 4.5mm. The cylindrical wall of the support body 5 is a thin-walled structure. The temperature cycle stress and assembly micro-stress are released through the elastic deformation of the cylindrical wall and the flexible groove.

[0038] The aluminum alloy mirror body 1 is also provided with a counterweight hole 15 on its centroidal surface. The counterweight hole 15 is a threaded hole structure. The counterweight hole 15 is used to clamp the counterweight block when the aluminum alloy mirror is aligned and aligned with the machine tool during the single-point machining stage of the optical mirror surface 2. After the mirror unit and the flexible support unit 14 are assembled, the optical mirror surface 2 is subjected to secondary precision shaping machining based on the assembled mirror assembly as a reference. This offsets the pre-tightening stress of the three-point support locking screw and the surface distortion introduced by the assembly pre-stress, ensuring high-precision imaging quality of visible light in space over a long period of time.

[0039] As can be seen from the above, in this embodiment, both the reflector unit and the flexible support unit 14 are made of the same aluminum alloy with completely consistent coefficients of thermal expansion. There is no thermal mismatch between heterogeneous materials, and there is no inlaid bushing, which eliminates the residual stress caused by bonding and pressing. After the components are assembled, the optical reflector surface 2 is processed uniformly. The assembly stress is removed in the secondary processing stage, which can effectively ensure the nanometer-level mirror precision required in the visible light band. The three-point support structure on the back is combined with a flexible groove, which is a release groove structure. It can unload the stress caused by mechanical impact during the launch stage and temperature changes in orbit, and suppress mirror distortion. Compared with the traditional aluminum alloy reflector solution with inlaid bushing, this embodiment can avoid the risk of thermal stress and interface slippage at the bushing-mirror interface, does not require a complex multi-thermal compensation structure, has fewer parts, simplifies the assembly process, and is more suitable for long-term on-orbit service in space.

[0040] This embodiment also provides a method for fabricating a large-aperture visible light band aluminum alloy space mirror assembly, which includes the following steps: S1. Select an aluminum alloy mirror blank and perform overall rough milling to obtain an aluminum alloy mirror body 1. The front of the aluminum alloy mirror body 1 forms the base surface of the optical reflective mirror 2, and the back of the aluminum alloy mirror body 1 forms a lightweight structure including three support cavities 3. Locking holes 10 are machined on the mounting platform 4 of the support cavity 3. Three flexible support units 14 are machined simultaneously.

[0041] S2. Perform the first stress-relieving aging on the rough-machined aluminum alloy mirror body 1 to release the residual stress from the rough machining.

[0042] S3. Perform semi-finish milling on the aluminum alloy mirror body 1 to trim the contour of the aluminum alloy mirror body 1, the base surface of the optical reflecting mirror 2, and the locking hole 10; perform a second stress-relieving aging on the semi-finish milled aluminum alloy mirror body 1.

[0043] S4. Finely process the optical reflective mirror 2, and after preparing a low-phosphorus Ni-P coating on the optical reflective mirror 2, complete the initial polishing.

[0044] S5. Secure the three flexible support units 14 to the three mounting platforms 4 respectively using locking devices to complete the assembly of the three-point support structure; complete the assembly of the aluminum alloy space reflector assembly.

[0045] S6. Perform low-temperature aging treatment on the assembled aluminum alloy space reflector assembly to release assembly locking stress.

[0046] S7. Using the assembled aluminum alloy space reflector assembly as the processing benchmark, the optical reflector surface 2 undergoes secondary precision shaping to compensate for the surface shape error introduced by the assembly, thereby obtaining an optical reflector surface 2 that meets the imaging requirements of the visible light band. The secondary precision shaping process includes single-point diamond turning, CNC small grinding head polishing, magnetorheological polishing, and ion beam shaping in sequence. Specifically, single-point diamond turning is performed in sequence, followed by CNC small grinding head polishing, magnetorheological polishing, and ion beam shaping to obtain an optical reflector surface 2 that meets the imaging requirements of the visible light band. The secondary precision shaping is an in-situ optical shaping under the constraint of the three-point flexible support of the whole machine, which can specifically offset the micro-deformation caused by the assembly of the three-point symmetrical flexible support structure, and significantly improve the surface shape accuracy of large-aperture visible light imaging.

[0047] After the second precision shaping process, a visible light high reflectivity film layer needs to be deposited on the optical reflective mirror surface 2. The two stress relief aging processes adopt a gradient temperature and time regime to release the residual stress of roughing and semi-finishing in stages, which can avoid long-term stress relaxation and deformation of large-aperture mirror bodies.

[0048] 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.

[0049] 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 large-aperture visible light band aluminum alloy space mirror assembly, characterized in that, Includes a reflector unit and a flexible support unit; The reflector unit includes an aluminum alloy mirror body, an optical reflector surface disposed on the front of the aluminum alloy mirror body, and a lightweight structure disposed on the back of the aluminum alloy mirror body; the aluminum alloy mirror body is a one-piece structure formed by machining and milling, and the aluminum alloy mirror body and the flexible support unit use the same aluminum alloy material. The lightweight structure forms three support areas evenly arranged circumferentially on the back of the aluminum alloy mirror body. Each support area has a support cavity, and the flexible support unit is placed in the support cavity to form a three-point support structure. The support cavity is equipped with a mounting platform integrally formed with the aluminum alloy mirror body, and the flexible support unit is connected to the mounting platform by a locking device. After the optical mirror is assembled with the mirror unit and the flexible support unit, it undergoes a second precision shaping process based on the assembled mirror assembly as a whole.

2. The large-aperture visible light band aluminum alloy space mirror assembly according to claim 1, characterized in that, The flexible support unit includes a support body that is cylindrical in shape. The two ends of the support body are connected to the mounting platform and the external support structure, respectively. The support body is a hollow structure and includes a cylindrical wall with flexible grooves.

3. The large-aperture visible light band aluminum alloy space mirror assembly according to claim 2, characterized in that, The flexible groove includes a circumferential annular groove and / or an axial straight groove; the cylinder wall of the supporting body is a thin-walled structure, and the temperature cycle stress and assembly micro-stress are released through the elastic deformation of the cylinder wall and the flexible groove.

4. The large-aperture visible light band aluminum alloy space mirror assembly according to claim 3, characterized in that, The support body is provided with a top connecting flange and a bottom connecting flange at both axial ends. The top connecting flange is connected to the mounting platform, and the bottom connecting flange is connected to the external support structure. The top connecting flange and the mounting platform are respectively provided with mutually cooperating locking holes. The top connecting flange is locked to the mounting platform by locking parts and locking holes.

5. The large-aperture visible light band aluminum alloy space mirror assembly according to claim 1, characterized in that, The lightweight structure is composed of a rib groove group milled into the back of the aluminum alloy mirror body; the rib groove group includes multiple parallel main ribs I and multiple parallel main ribs II, with the main ribs I and main ribs II arranged intersecting; the spacing between adjacent main ribs I is equal, and the spacing between adjacent main ribs II is equal; the acute angle between main ribs I and main ribs II is 60°; the rib groove group also includes auxiliary ribs arranged on the periphery of each support cavity; The auxiliary ribs around each support cavity are evenly distributed, and the auxiliary ribs extend from the edge of the support cavity away from the support cavity.

6. The large-aperture visible light band aluminum alloy space mirror assembly according to claim 1, characterized in that, The effective light-transmitting aperture of the optical reflective mirror is Ф650mm, and the reflection aperture of the optical reflective mirror is Ф660mm; both the aluminum alloy mirror body and the flexible support unit are made of RSA-6061 or RSA-443 aluminum alloy materials.

7. The large-aperture visible light band aluminum alloy space mirror assembly according to claim 1, characterized in that, The optical reflective mirror is provided with a low-phosphorus Ni-P precision coating, and the roughness Ra of the optical reflective mirror is ≤2nm.

8. The large-aperture visible light band aluminum alloy space mirror assembly according to claim 1, characterized in that, The aluminum alloy mirror body is also provided with a counterweight hole on its center plane in the circumferential direction. The counterweight hole is used to install the counterweight block when the optical mirror is aligned with the machine tool during the single-point machining stage.

9. A method for fabricating a large-aperture visible-light band aluminum alloy space mirror assembly, used to fabricate the large-aperture visible-light band aluminum alloy space mirror assembly as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Select an aluminum alloy mirror blank and perform overall rough milling to obtain an aluminum alloy mirror body. The front of the aluminum alloy mirror body forms the base surface of the optical reflective mirror, and the back of the aluminum alloy mirror body forms a lightweight structure including three support cavities. Locking holes are machined on the mounting platform of the support cavities. Three flexible support units are machined simultaneously. S2. Perform the first stress-relieving aging on the rough-machined aluminum alloy mirror body to release the residual stress from the rough machining. S3. Perform semi-finish milling on the aluminum alloy mirror body to trim the contour of the aluminum alloy mirror body, the base surface of the optical reflective mirror, and the locking holes; perform a second stress-relieving aging on the semi-finish milled aluminum alloy mirror body. S4. Fine-machine the optical reflective mirror surface, and after preparing a low-phosphorus Ni-P coating on the optical reflective mirror surface, complete the initial polishing. S5. Lock the three flexible support units onto the three mounting platforms respectively using locking devices to complete the assembly of the three-point support structure. Complete the assembly of the aluminum alloy space mirror assembly; S6. Perform low-temperature aging treatment on the assembled aluminum alloy space reflector assembly to release assembly locking stress. S7. Using the assembled aluminum alloy space reflector assembly as the processing benchmark, perform secondary precision shaping on the optical reflector surface to compensate for the surface shape error introduced by assembly, and obtain an optical reflector surface that meets the imaging requirements of the visible light band.

10. The method for fabricating a large-aperture visible light band aluminum alloy space mirror assembly according to claim 9, characterized in that, In S7, the secondary precision shaping process includes single-point diamond turning, CNC small grinding head polishing, magnetorheological polishing, and ion beam shaping.

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