Satellite-borne OCXO anti-radiation and micron-level debris integrated protection structure

Abstract

The application discloses a satellite-borne OCXO anti-radiation and micron-level debris integrated protection structure, which comprises a composite armor composed of an outer high-density polyethylene layer, a middle aluminum alloy layer, an inner high-density polyethylene layer and a circuit substrate which are stacked in sequence from outside to inside. The outer PE absorbs debris cloud energy and cooperates with radiation shielding, the middle aluminum alloy breaks micron-level debris, and the inner PE dissipates debris kinetic energy and shields secondary radiation; the circuit substrate adopts an aluminum-based PCB or a SiC substrate to improve heat conduction and anti-neutron activation capability. The application also forms a trinity protection through anti-radiation device selection and circuit redundancy error correction reinforcement. The application simultaneously realizes anti-radiation and debris protection through a set of structure, and the surface density is as low as 13.55 kg / m 2 , the SEL threshold is greater than or equal to 75 MeV·cm 2 / mg, the TID is greater than or equal to 100 krad (Si), and the target test wall is not penetrated, and the application is suitable for local fine protection of low-orbit small satellite high-precision time and frequency equipment.

Description

Technical Field

[0001] This application relates to the field of spacecraft local protection technology, and in particular to an on-orbit protection structure for high-precision time and frequency equipment suitable for low-orbit small satellite platforms, specifically to an integrated protection structure for spaceborne OCXO radiation resistance and micron-level debris. Background Technology

[0002] As a core component of the spacecraft's time and frequency system, the performance and reliability of the spaceborne cryogenic crystal oscillator (OCXO) directly determine the execution quality of missions such as navigation, communication, and reconnaissance. With the large-scale deployment of low Earth orbit small satellite constellations, the complex space environment threats faced by spacecraft operating in low Earth orbit (LEO, 300~450km) for extended periods are becoming increasingly prominent.

[0003] The low Earth orbit (LEO) space environment presents two main threats: 1. The space radiation environment includes galactic cosmic rays (GCR), solar cosmic rays (SEP), particles from the Earth's radiation belts (Van Allen belts), and alpha / beta particles in device packaging materials. These high-energy particles can induce single-event latch-up (SEL), single-event upset (SEU), and total dose effect (TID), causing instantaneous or permanent damage to the CMOS circuitry inside the OCXO. In severe cases, this can lead to frequency jumps, loss of latch-up, or even system burnout. 2. Regarding micron-sized space debris, fragments smaller than 1 mm account for more than 99.9% of all space debris, impacting spacecraft surfaces at ultra-high speeds of 7–10 km / s. Although the mass of a single fragment is extremely small, long-term cumulative impacts can cause progressive damage to the OCXO shell, thermal control layer, PCB, etc., and may even cause short circuits or physical destruction.

[0004] Traditional spacecraft protection technology separates radiation resistance and debris protection into different structural modules, designing them as independent systems. This approach has the following problems:

[0005] 1. Radiation-resistant structures often use high atomic number (high Z) materials (such as tungsten and tantalum). Although high Z materials have good radiation shielding performance, they are prone to forming high-speed secondary fragments under ultra-high-speed impact of debris, which will increase the risk of damage to the rear wall.

[0006] 2. Debris protection often uses Whipple screens or fiber fabrics, which are large in size and heavy in weight, and are designed and applied independently from radiation-resistant structures. Small satellites are highly sensitive to mass, volume, and power consumption (SWaP). Independently stacking two sets of protection systems will seriously squeeze payload resources, which is not conducive to the application of small satellite platforms.

[0007] For example, Chinese invention patent CN114655472A discloses a composite protection method for the total radiation dose in mid-orbit space. Based on the energy loss characteristics of protons in materials, this method proposes using aluminum (Al) and polyethylene (PE) to construct a composite shielding material. Through theoretical calculations and experimental optimization, the mass ratio of Al to PE is determined to be 1:3 (i.e., Al accounts for 25%, and PE accounts for 75%). This method achieves good protection with relatively low mass and volume costs through a suitable material ratio combination. This technical solution utilizes the efficient proton moderation ability of PE as a hydrogen-rich material and the electron blocking ability of Al, achieving good results in radiation shielding.

[0008] However, the inventors believe that the above-mentioned patent solution still has the following shortcomings:

[0009] In existing radiation protection solutions, if high-Z materials (such as tungsten and tantalum) are used as the shielding layer, when micron-sized debris impacts at ultra-high speeds, the high-Z materials themselves will break apart, forming high-speed, high-energy secondary debris clouds, which can cause even more severe damage to downstream equipment. Although the aforementioned patented solution uses Al / PE composite shielding, it does not have a structural design specifically for debris protection, and the risk of secondary debris still exists.

[0010] In addition, existing protection solutions are mostly geared towards the overall satellite structure and lack localized, refined protection for high-precision time and frequency equipment such as OCXOs, making it difficult to meet their special requirements for thermal stability, vibration suppression, and radiation immunity.

[0011] In addition, the significant differences in the coefficients of thermal expansion between different materials can easily lead to thermal stress concentration under on-orbit temperature cycling, resulting in structural failure or frequency drift. Existing solutions do not provide effective thermal stress decoupling measures, nor do they design dedicated heat conduction paths and substrate materials for OCXO.

[0012] Therefore, existing radiation-resistant and debris-protective structures still have many shortcomings, and it is necessary to propose a new technical solution to address the problems existing in the current technology. Summary of the Invention

[0013] This application provides an integrated protection structure for spaceborne OCXOs that combines radiation resistance with micron-level debris protection, in order to solve the problem that existing radiation protection solutions cannot meet the fine protection requirements of spaceborne OCXOs.

[0014] To achieve the above objectives, this application provides the following technical solution:

[0015] This application provides an integrated radiation protection structure for a spaceborne OCXO that integrates radiation resistance and micron-level debris protection. The structure comprises, from the outside in, an outer high-density polyethylene layer, a middle aluminum alloy layer, an inner high-density polyethylene layer, and a circuit board for supporting the OCXO circuitry. The outer high-density polyethylene layer absorbs debris cloud energy and synergistically shields against space radiation. The middle aluminum alloy layer breaks up micron-level debris. The inner high-density polyethylene layer dissipates debris kinetic energy and shields against secondary radiation. The circuit board is an aluminum-based PCB or SiC substrate that enhances thermal conductivity and resistance to neutron activation.

[0016] Furthermore, in the above technical solution, the outer high-density polyethylene layer has a thickness of 5 mm, the middle aluminum alloy layer has a thickness of 1.5 mm, the inner high-density polyethylene layer has a thickness of 5 mm, and the total areal density of the protective structure is 13.55 kg / m³. 2 .

[0017] Furthermore, the aluminum alloy layer accounts for 25% to 35% of the mass, and the high-density polyethylene layer accounts for 65% to 75% of the mass.

[0018] Furthermore, a flexible thermally conductive interface material or gradient transition layer for relieving thermal stress is provided between the middle aluminum alloy layer and the outer high-density polyethylene layer; a flexible thermally conductive interface material or gradient transition layer for relieving thermal stress is provided between the middle aluminum alloy layer and the inner high-density polyethylene layer.

[0019] Furthermore, the OCXO circuit includes radiation-hardened electronics with a single-event latch-up threshold ≥37 MeV·cm⁻¹. 2 / mg, total ionization dose ≥30 krad(Si).

[0020] Furthermore, the radiation-resistant electronic devices include: a radiation-resistant RISC-V MCU, an FPGA, a SEL immune power supply, and an ECC memory.

[0021] Furthermore, the OCXO circuit has a redundancy and error correction reinforcement circuit structure, which includes: the analog end employs multiple redundant sensors, RC filter circuit, Σ-Δ ADC, and a median filter and Kalman filter combined algorithm circuit; the digital end employs a dual-core lockstep circuit, ECC circuit, triple-modulus redundancy circuit, watchdog circuit, and Scrubbing refresh circuit.

[0022] Furthermore, the outer high-density polyethylene layer, the middle aluminum alloy layer, and the inner high-density polyethylene layer, which are stacked in sequence, form a closed protective cavity for wrapping the circuit board.

[0023] Furthermore, the SiC substrate is fabricated using direct copper plating or active metal brazing processes to create metallized circuitry, and its surface is treated with chemical nickel plating / immersion gold plating.

[0024] Compared with the prior art, this application has at least the following beneficial effects:

[0025] 1. This application constructs a locally enclosed protective structure integrating radiation resistance, debris protection, and thermal management by sequentially stacking an outer high-density polyethylene layer, a middle aluminum alloy layer, an inner high-density polyethylene layer, and an aluminum-based PCB or SiC circuit substrate from the outside in. Specifically, the outer high-density polyethylene layer, with its hydrogen-rich characteristics and high damping deformation capacity, can effectively slow down space neutrons and suppress secondary radiation while absorbing the energy of the debris cloud, providing initial radiation immunity and vibration buffering for the OCXO; the middle aluminum alloy layer, on the one hand, utilizes its high atomic number to generate ionization energy loss from high-energy protons, and on the other hand, rigidly breaks up micron-sized debris, dispersing it into a low-kinetic-energy debris cloud, avoiding further damage to the back wall from secondary debris of high-density materials, thereby strengthening the synergy between shock resistance and radiation shielding; the inner high-density polyethylene layer further dissipates the kinetic energy of residual debris and absorbs penetrating secondary particles, forming the ultimate protection for the OCXO circuit. Secondly, this application uses an aluminum-based PCB or SiC substrate as the circuit board. Utilizing its high thermal conductivity (approximately 350 W / mK for SiC) and low coefficient of thermal expansion, the heat generated during OCXO operation is rapidly and uniformly conducted to the entire substrate, eliminating localized hot spots and significantly improving temperature stability. Meanwhile, the high stiffness and low neutron activation characteristics of the SiC substrate effectively suppress mechanical vibration transmission and long-lived isotope interference induced by space radiation, meeting the stringent requirements of OCXO for vibration suppression and radiation immunity. Therefore, this application systematically solves the technical challenges of existing solutions being unable to provide precise localized protection for OCXOs and simultaneously meeting the special requirements of thermal stability, vibration suppression, and radiation immunity, from material selection and layering sequence to functional synergy.

[0026] 2. In the integrated protective structure provided in this application, the outer high-density polyethylene layer has a thickness of 5mm, the middle aluminum alloy layer has a thickness of 1.5mm, and the inner high-density polyethylene layer has a thickness of 5mm, with a total areal density of 13.55kg / m³. 2 This optimized combination of thickness and areal density ensures the OCXO's resistance to radiation and debris impacts, meeting the lightweight requirements of small satellite platforms, under the constraint that low-orbit small satellites are highly sensitive to mass.

[0027] 3. This application optimizes the mass ratio of the aluminum alloy layer and the high-density polyethylene layer based on the principles of radiation shielding physics: Aluminum has high ionization loss efficiency for high-energy electrons and protons, but it produces bremsstrahlung and has extremely weak shielding ability against neutrons; while PE, as a hydrogen-rich material, has strong neutron moderation absorption ability, a higher energy loss rate for charged particles than aluminum, does not produce significant secondary radiation, and can effectively absorb the secondary bremsstrahlung generated by the aluminum alloy layer. This application optimizes the overall shielding effect of the unit mass shield against all spectrums of space particles (protons, neutrons, electrons, and heavy ions) by controlling the mass ratio of PE to about 70%, while maintaining the energy dissipation efficiency of the composite structure against ultra-high-speed debris impacts. This ratio solves the problem that existing high-Z materials or single-material shields are difficult to simultaneously provide protection against multiple types of radiation and have large mass, achieving an effective integration of lightweight and high-efficiency protection.

[0028] 4. This application incorporates flexible thermally conductive interface materials or gradient transition layers between the middle aluminum alloy layer and the outer and inner high-density polyethylene layers. Due to the thermal expansion coefficient of aluminum alloy (approximately 23 × 10⁻⁶), -6 / K) and high-density polyethylene (approximately 150×10) -6 The significant difference in thermal expansion coefficients (C / K) between the two materials can lead to substantial thermal stress during on-orbit temperature cycling (-40°C to +85°C), causing interlayer delamination or structural warping, which in turn affects the frequency stability of the OCXO. Therefore, this application addresses this issue by introducing a flexible thermally conductive interface material (such as a thermally conductive silicone pad) or a gradient transition layer (creating a continuously varying transition zone between the two materials using existing processes to achieve a "gradual" change in the coefficient of thermal expansion at the microscopic level) between the layers. This absorbs and compensates for the shear strain caused by the difference in thermal expansion while maintaining unobstructed heat conduction paths. Furthermore, introducing a flexible thermally conductive interface material or a gradient transition layer between the layers solves the thermomechanical mismatch problem between dissimilar materials, ensuring the long-term integrity of the protective structure under extreme temperature cycling and the temperature control uniformity of the OCXO.

[0029] 5. Radiation environment assessment based on the typical mission lifetime (e.g., 3-5 years) of low-orbit small satellites: SEL threshold ≥ 37 MeV·cm 2The device is designed to withstand radiation exposure from galactic cosmic rays and Earth's radiation belts without latch-up failure, and a TID ≥ 30 krad (Si) ensures that the cumulative radiation dose will not cause electrical parameter drift to exceed limits. This application improves radiation resistance from the source through device selection, such as prioritizing radiation-hardened RISC-V MCUs, FPGAs, SEL-immune power supplies, and ECC memories, and strictly implementing radiation testing and derating design. At the circuit level, analog filtering, sensor redundancy, digital phase-locked loop triple redundancy, median / Kalman filter combination algorithms, and layout hardening are used to suppress SET / SEU propagation and accumulation. Therefore, the integrated protection structure provided by this application ensures radiation protection effectiveness while taking into account thermo-mechanical stability and the security of the domestic supply chain, providing a reliable and feasible engineering implementation path for spaceborne high-precision time and frequency systems.

[0030] 6. This application selects existing mature devices that have undergone irradiation testing, eliminating the need for additional local shielding or redundant design costs, and directly meets the stringent requirements for single-event effects and total dose effects. By selecting appropriate devices, the radiation resistance is improved from the source, complementing the structural shielding, enabling the OCXO to operate reliably under residual radiation. This solves the problem that relying solely on structural shielding cannot completely block high-energy particles, forming a dual protection of "external shielding and internal tolerance." It also solves the problem in existing technologies where insufficient radiation resistance of devices necessitates increasing the thickness of the structural shielding, leading to mass expansion. This achieves a synergy between lightweight protective structures and high circuit reliability.

[0031] 7. The OCXO circuit of this application features a redundancy and error correction hardening circuit structure: the analog end employs multiple redundant sensors, RC filtering, Σ-Δ ADC, and a combination of median filtering and Kalman filtering algorithms; the digital end employs dual-core lockstep, ECC, triple modulo redundancy, watchdog timer, and Scrubbing refresh circuitry. This circuit structure provides fault tolerance for residual radiation effects (such as single-event upsets and transient pulses) that cannot be completely eliminated by structural shielding and device selection: the redundancy and filtering algorithms on the analog end can eliminate abnormal sampling values ​​caused by SET; the dual-core lockstep and TMR on the digital end can immediately detect and correct logic errors caused by SEU; and ECC and Scrubbing prevent the accumulation of memory errors. Therefore, this application solves the technical requirement of zero tolerance for frequency jumps in high-precision time and frequency equipment through a redundancy and error correction hardening circuit structure, ensuring the continuity and stability of the OCXO output frequency at the circuit level, forming a complete radiation-resistant system integrating "structure-device-circuit". Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. It should be understood that the specific shapes and structures shown in the drawings should not generally be regarded as limiting conditions for implementing this application. For example, based on the technical concepts disclosed in this application and the exemplary drawings, those skilled in the art are able to easily make conventional adjustments or further optimizations to the addition / reduction / classification, specific shapes, positional relationships, connection methods, and size ratios of certain units (components).

[0033] Figure 1 This is a schematic diagram of the layer structure of the integrated protective structure provided in this application in one embodiment.

[0034] Explanation of reference numerals in the attached figures:

[0035] 1. Outer high-density polyethylene layer; 2. Middle aluminum alloy layer; 3. Inner high-density polyethylene layer; 4. Internal circuit board; 5. High-speed fragments. Detailed Implementation

[0036] The present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] In the description of this application: unless otherwise stated, the terms "comprising", "including", "having", etc. in this application also mean "not limited to" (certain units, components, materials, steps, etc.).

[0038] Example 1

[0039] This application provides an integrated protection structure for spaceborne OCXO against radiation and micron-level debris. Through the design concept of unified materials, shared structure, and synergistic function, it solves the problems of separate protection systems, mass redundancy, and thermo-mechanical mismatch in the prior art. It achieves comprehensive protection against the dual threats of space radiation and hypervelocity debris under a limited mass budget, ensuring the high reliability and frequency stability of spaceborne OCXO during long-term on-orbit operation in low Earth orbit.

[0040] The integrated protection structure for radiation resistance and micron-level debris protection of a spaceborne OCXO (hereinafter referred to as the integrated protection structure) proposed in this application can be regarded as an integrated protective armor of aluminum alloy-PE composite laminate. Its structural design goal is to attenuate the incident energy of external high-energy particles, reduce the LET value when they reach the internal sensitive chip, and make it lower than the device threshold (especially 37 MeV·cm). 2 / mg). This integrated protective structure mainly adopts a stacked composite shielding structure of "high Z material (aluminum alloy) + low Z hydrogen-rich material (PE)". It utilizes the ionization energy loss capability of aluminum alloy to high-energy charged particles and the absorption capability of PE to neutrons and secondary particles to achieve synergistic shielding.

[0041] The integrated protective structure provided in this application is a layered structure; see [link / reference]. Figure 1 From the outside to the inside, they are as follows:

[0042] ① Outer high-density polyethylene (PE) layer 1, used to absorb energy from debris clouds and to shield space radiation, with its thickness optimized according to radiation shielding requirements;

[0043] ② The middle aluminum alloy layer 2 bears the functions of fragment breakage and structural load-bearing;

[0044] ③ Inner high-density polyethylene (PE) layer 3, used to further dissipate fragment kinetic energy and shield secondary radiation, the thickness of which is optimized according to radiation shielding requirements;

[0045] ④ Internal circuit board 4 (aluminum-based PCB or SiC substrate) carries the OCXO circuit, replacing the traditional FR4 or alumina substrate, and improving thermal conductivity and resistance to neutron activation.

[0046] The integrated protective structure provided in this application completely encloses the core circuit area of ​​the OCXO, forming a partially sealed protective cavity. The aluminum alloy layer and the PE layer are thermally and mechanically decoupled through a flexible thermally conductive interface material or a gradient transition layer.

[0047] The integrated protective structure provided in this application must be designed in conjunction with the core functions of the OCXO:

[0048] (1) Heat conduction path design: The main structural components are aluminum alloy-PE material-SiC substrate. Thermal simulation is required to ensure that the heat from the temperature-controlled heater can be uniformly conducted to the crystal resonator, while the shielding does not cause excessive thermal resistance or temperature gradient. In addition, although the protective layer has good thermal conductivity, a thicker layer will increase the heat capacity. The thickness needs to be optimized to achieve a balance between shielding and thermal response time.

[0049] (2) Stress Matching and Reliability: Given the significant differences in thermal expansion coefficients among aluminum alloy, PE, SiC, and chip materials, a thermo-mechanical coupled finite element analysis must be performed to simulate stress distribution and deformation under typical on-orbit temperature cycles (-40°C to +85°C). The focus is on assessing the stress concentration risks at the composite protective material interface and between the SiC substrate and the outer casing mounting surface. The design employs a gradient material transition layer (such as aluminum alloy-PE composite material) or flexible thermally conductive interface materials to alleviate thermal stress, and verifies structural integrity through vibration and thermal vacuum tests. For flexible thermally conductive interface materials, flexible thermally conductive pads and low-stress adhesives can be used for interface connection to avoid protective layer peeling, weld cracking, or chip damage due to thermal stress. The gradient transition layer can be prepared on the aluminum alloy surface using vacuum hot pressing or plasma spraying processes, creating a transition layer with continuously varying Al / PE composition, allowing the thermal expansion coefficient to gradually change from the aluminum alloy value to the PE value, eliminating stress concentration at abrupt interfaces.

[0050] The protective mechanism of the integrated protective structure provided in this application is as follows:

[0051] When high-speed fragments impact a panel perpendicularly, two scenarios can occur: If the fragment penetrates the panel, it breaks into smaller fragments that combine with the panel fragments to form a fragment cloud. This cloud then impacts the polymer network structure, causing it to deform and deflecting its trajectory, thus reducing its destructive power. Alternatively, if the fragment does not penetrate the panel, localized deformation of the panel can cause the polymer network structure behind it to deform in tandem, similarly altering the fragment's incident direction.

[0052] Regardless of whether it penetrates, the polymer network structure deflects the fragments off-center through geometric deformation, lengthening the energy dissipation path and thus reducing their penetration capability against the backing plate. For non-perpendicularly incident fragments, their destructive power is already low, and the protective structure can effectively intercept them.

[0053] Because PE (polyethylene) possesses both excellent ultra-high-speed impact energy absorption properties and space radiation shielding capabilities, the debris protection material in this application utilizes an aluminum alloy + PE composite structure to achieve a unified material structure for radiation resistance and debris protection. The aluminum alloy has a density of 2.7 g / cm³. 3 It has high specific strength, mature processing technology, and the difference in thermal expansion coefficient between it and PE can be mitigated through a flexible interface. PE has a density of 0.95 g / cm³. 3Hydrogen-rich materials have a radiation shielding efficiency 1.9 times that of aluminum (per unit mass) and excellent energy absorption characteristics. Therefore, the integrated protective structure provided in this application reduces the LET value of external particles to below the device SEL threshold based on the synergistic effect of the combination of light and heavy materials. It provides ionization energy loss for high-energy electrons and protons through the aluminum alloy layer (high Z material), but at the same time, the aluminum alloy layer generates bremsstrahlung radiation (secondary X-rays) and has extremely weak shielding ability against neutrons. On this basis, this application absorbs neutrons and secondary particles through the PE layer (hydrogen-rich properties), reducing the risk of neutron activation in the device. The PE layer does not generate significant secondary radiation and can suppress bremsstrahlung radiation.

[0054] Based on radiation shielding simulations, the inventors obtained the optimal mass allocation table for the protective structure corresponding to different particle types, as shown in Table 1 below:

[0055] Table 1. Optimal mass allocation of protective structures for different particle types.

[0056]

[0057] Therefore, the optimal allocation in this application is approximately 30% aluminum and 70% PE by mass.

[0058] Protective surface density for low-orbit small satellites ≤15kg / m 2 Requirement: Use the thickness calculation formula:

[0059]

[0060] The areal density of the 5mm thick outer high-density PE layer is: 5mm × 950 = 4.75kg / m³ 2 ;

[0061] The areal density of the 1.5mm thick intermediate aluminum alloy layer is: 1.5mm × 2700 = 4.05kg / m³ 2 ;

[0062] The areal density of the 5mm thick inner high-density PE layer is: 5mm × 950 = 4.75kg / m³ 2 ;

[0063] The total surface density of the protective structure is 4.75 kg / m³. 2 +4.05kg / m 2 +4.75kg / m 2 =13.55kg / m 2 Of which, aluminum alloy accounts for approximately 29.89%, and the inner and outer PE layers account for approximately 70.11% of the total mass.

[0064] The integrated protective structure provided in this application can simultaneously achieve three functions: radiation resistance, space debris protection, and thermal management.

[0065] (1) Principle of radiation resistance: The aluminum alloy layer provides energy loss for the ionization of high-energy protons, and the PE layer absorbs neutrons and secondary particles through hydrogen-rich materials, thus synergistically reducing the LET value of internal devices and ensuring that the SEL threshold meets ≥37 MeV·cm 2 / mg design requirements. The SEL threshold can be increased to 75 MeV·cm through electrical component selection. 2 / mg and above.

[0066] (2) Principle of fragment protection function: When micron-sized fragments collide with the outer PE layer at ultra-high speed, the PE layer absorbs energy through high-damping deformation; the aluminum alloy layer causes the fragments to break and diffuse into a fragment cloud; the inner PE layer further dissipates kinetic energy, protecting the internal circuit board and OCXO circuit.

[0067] (3) Thermal management function implementation principle: This application uses SiC or aluminum substrate to provide an efficient heat conduction path, ensuring the uniformity and response speed of the OCXO temperature control loop. SiC ceramic substrate has high thermal conductivity (~350 W / mK), far exceeding that of alumina ceramic, which is beneficial to the thermal balance of the precision temperature control loop inside the OCXO and improves frequency temperature stability. Secondly, SiC ceramic substrate has high hardness and stiffness, which can provide excellent dimensional stability and reduce the influence of vibration and stress on crystal frequency. Thirdly, in the space neutron radiation environment, SiC produces fewer long-lived radioactive isotopes, which is in line with the concept of "low-activation material", which is beneficial to the handling after the spacecraft mission and to reduce background radiation. In addition, SiC has good radiation resistance and stronger resistance to displacement damage than silicon. In specific manufacturing applications, direct copper plating (DPC) or active metal soldering (AMB) processes can be used to fabricate highly reliable metallized circuits on SiC substrates, and chemical nickel / immersion gold (ENIG) treatment can be performed on the surface to provide excellent solderability, conductivity and shielding against α / β particles (high gold layer density can effectively block low-energy particles).

[0068] Compared with existing technologies, this application has the following application advantages based on existing space debris protection and electronic device radiation resistance technologies:

[0069] Compared to high-Z materials such as titanium alloys, the aluminum alloy + PE composite protective material system has lower secondary debris density and lower kinetic energy under ultra-high-speed collision conditions, resulting in a lower risk of damage to the rear wall; it has sufficient phase change energy absorption and high energy dissipation efficiency; it is environmentally friendly, with the generated secondary debris having a short orbital dwell time and being harmless upon reentry; and it meets the requirements of international space debris mitigation guidelines.

[0070] In terms of functional synergy, this application achieves both radiation resistance and debris protection with a single structure, avoiding the weight overlap of dual protection systems. Regarding performance assurance, the SEL threshold is ≥37 MeV·cm⁻¹.2 / mg, TID≥30 krad(Si), meeting the requirements for long-term missions of low-orbit small satellites.

[0071] In terms of engineering applicability, aluminum alloy-PE composite material is used, which has low material cost, lightweight protective surface, and compact structure. It is easy to integrate into existing spaceborne platforms, supports the application of domestically produced components, and minimizes secondary environmental pollution caused by space debris installation.

[0072] Example 2

[0073] Based on the integrated protection structure provided in Example 1, this example performs device selection and circuit reinforcement design on the OCXO circuit carried on its circuit board.

[0074] Spaceborne electronic equipment is exposed to a complex and harsh space radiation environment during operation. This environment mainly includes the continuous radiation damage to the internal components of electronic equipment caused by galactic cosmic rays (GCR), solar cosmic rays (SEP), particles from the Earth's radiation belts (Van Allen belts), and alpha / beta particles. This application focuses on the two main types of destructive effects currently known: total dose effect and single-event effect, for discussion and design purposes.

[0075] This embodiment constructs a systematic radiation protection technology system integrating "structural protection, device selection, and circuit hardening". At the structural protection level, an "aluminum alloy-PE" composite material shield is used to reduce the LET value and absorb neutron radiation, achieving functional synergistic protection against near-Earth orbit space debris and electronic devices from space radiation.

[0076] At the device selection level, the "single-particle 37" threshold is used as the benchmark, prioritizing radiation-hardened devices from domestically produced radiation-hardened device platforms, such as radiation-hardened RISC-V MCUs, FPGAs, SEL-immune power supplies, and ECC memories, while strictly adhering to radiation testing and derating design. This device selection ensures an SEL threshold ≥75 MeV·cm⁻¹. 2 / mg, TID≥100 krad(Si).

[0077] The circuit hardening layer involves implementing redundancy and error correction hardening circuit structures within the OCXO circuit. These redundancy and error correction hardening circuit structures include: on the analog side, multiple redundant sensors, RC filter circuits, Σ-Δ ADCs, and median / Kalman filter combination algorithms; on the digital side, dual-core lock-step circuits, ECC circuits, triple-mode redundancy circuits, watchdog circuits, and scrubbing refresh circuits. Therefore, at the circuit level, through analog filtering, sensor redundancy, triple-mode redundancy of digital phase-locked loops, median / Kalman filter combination algorithms, and layout hardening, the propagation and accumulation of SET / SEU are suppressed.

[0078] Therefore, the integrated protection structure provided in this embodiment ensures radiation protection effectiveness while taking into account thermo-mechanical stability and the security of the domestic supply chain, providing a reliable and feasible engineering implementation path for spaceborne high-precision time and frequency systems.

[0079] Example 3

[0080] This embodiment provides a specific implementation plan for a spaceborne OCXO radiation-resistant and micron-level debris-integrated protection structure.

[0081] The protective structure consists of: an outer 5mm thick PE layer, a middle 1.5mm thick aluminum alloy layer, and an inner 5mm thick PE layer, with a total surface density of 13.55kg / m³. 2 .

[0082] Device selection: AS32A401 MCU (dual-core lockstep, SEL≥75), AS32S601 FPGA (TMR / ECC), ASP3605 DC / DC (SEL-immune), domestic MRAM (SEU-resistant).

[0083] Circuit reinforcement: The analog end uses 4 redundant sensors + RC filter + Σ-Δ ADC + median filter + Kalman filter; the digital end uses dual-core lockstep, ECC, TMR, watchdog timer and scrubbing.

[0084] Verification Example 1

[0085] This verification example verifies the impact resistance of the integrated protective structure provided in Example 3.

[0086] The integrated protective structure provided in Example 3 is a debris protection armor designed for the threat of space debris within 1 mm in low-altitude near-Earth orbit. To verify its impact resistance, a space debris target test was conducted: a 2 mm thick aluminum alloy backplate was placed behind the armor to simulate a satellite compartment, and projectiles were launched at a speed of 7-10 km / s toward the backplate. The projectiles were aluminum alloy balls (φ0.8 mm) or steel balls (φ0.5 mm). The standard for passing the test was that the backplate was not damaged (i.e., the backplate was not penetrated).

[0087] The verification results are as follows: SEL threshold ≥ 75 MeV·cm 2 With a particle size of / mg, a TID ≥ 100 krad(Si), and no penetration of the debris target backplate, the protective structure showed no failure during thermal vacuum cycling tests (temperature range -40°C to +85°C, 10 cycles). Therefore, the protective structure can effectively block micron-sized debris and has long-term on-orbit reliability.

[0088] In summary, this application provides an integrated radiation protection structure for spaceborne OCXOs that combines radiation resistance with micron-level debris protection. By sequentially stacking an outer high-density polyethylene layer, a middle aluminum alloy layer, an inner high-density polyethylene layer, and an aluminum-based PCB or SiC circuit board from the outside in, a locally enclosed protective structure integrating radiation resistance, debris protection, and thermal management is constructed. Combined with device selection and circuit reinforcement, a composite radiation-resistant structure is integrated. From material selection and stacking sequence to functional synergy, this application systematically solves the technical challenges of existing solutions being unable to provide precise localized protection for OCXOs and simultaneously meeting the special requirements of thermal stability, vibration suppression, and radiation immunity for OCXOs.

[0089] The technical features of the above embodiments can be combined in any way (as long as there is no contradiction in the combination of these technical features). For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described; these embodiments not explicitly written should also be considered to be within the scope of this specification.

[0090] The present application has been described in a relatively specific and detailed manner above through general descriptions and specific embodiments. It should be understood that, based on the technical concept of the present application, several conventional adjustments or further innovations can be made to these specific embodiments; however, as long as they do not depart from the technical concept of the present application, the technical solutions obtained by these conventional adjustments or further innovations also fall within the protection scope of the claims of the present application.

Claims

1. A spaceborne OCXO radiation-resistant and micron-level debris-integrated protection structure, characterized in that, The device comprises, from the outside to the inside, an outer high-density polyethylene layer, a middle aluminum alloy layer, an inner high-density polyethylene layer, and a circuit board for supporting the OCXO circuit. The outer high-density polyethylene layer is used to absorb debris cloud energy and cooperate in shielding space radiation. The middle aluminum alloy layer is used to break up micron-sized debris. The inner high-density polyethylene layer is used to dissipate debris kinetic energy and shield secondary radiation. The circuit board is an aluminum-based PCB board or a SiC substrate that can improve thermal conductivity and resistance to neutron activation.

2. The spaceborne OCXO radiation-resistant and micron-level debris integrated protection structure according to claim 1, characterized in that, The outer high-density polyethylene layer has a thickness of 5 mm, the middle aluminum alloy layer has a thickness of 1.5 mm, the inner high-density polyethylene layer has a thickness of 5 mm, and the total areal density of the protective structure is 13.55 kg / m³. 2 .

3. The spaceborne OCXO radiation-resistant and micron-level debris integrated protection structure according to claim 1, characterized in that, The aluminum alloy layer accounts for 25% to 35% of the total mass, and the high-density polyethylene layer accounts for 65% to 75% of the total mass.

4. The spaceborne OCXO radiation-resistant and micron-level debris integrated protection structure according to claim 1, characterized in that, A flexible thermally conductive interface material or gradient transition layer is provided between the middle aluminum alloy layer and the outer high-density polyethylene layer to alleviate thermal stress. A flexible thermally conductive interface material or gradient transition layer is provided between the middle aluminum alloy layer and the inner high-density polyethylene layer to alleviate thermal stress.

5. The spaceborne OCXO radiation-resistant and micron-level debris integrated protection structure according to claim 1, characterized in that, The OCXO circuit includes radiation-hardened electronics with a single-event latch-up threshold ≥37 MeV·cm⁻¹. 2 / mg, total ionization dose ≥30 krad(Si).

6. The spaceborne OCXO radiation-resistant and micron-level debris integrated protection structure according to claim 5, characterized in that, The radiation-resistant electronic devices include: a radiation-resistant RISC-V MCU, an FPGA, a SEL immune power supply, and an ECC memory.

7. The spaceborne OCXO radiation-resistant and micron-level debris integrated protection structure according to claim 6, characterized in that, The OCXO circuit has a redundancy and error correction reinforcement circuit structure, which includes: the analog end adopts multiple redundant sensors, RC filter circuit, Σ-Δ ADC, and median filter and Kalman filter combined algorithm circuit; the digital end adopts dual-core lockstep circuit, ECC circuit, triple-modulus redundancy circuit, watchdog circuit and scrubbing refresh circuit.

8. The spaceborne OCXO radiation-resistant and micron-level debris integrated protection structure according to claim 1, characterized in that, The outer high-density polyethylene layer, the middle aluminum alloy layer, and the inner high-density polyethylene layer are stacked in sequence to form a closed protective cavity for wrapping the circuit board.

9. The spaceborne OCXO radiation-resistant and micron-level debris integrated protection structure according to claim 1, characterized in that, The SiC substrate is made of metallized circuits using direct copper plating or active metal brazing processes, and the surface is treated with chemical nickel plating / immersion gold plating.

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