Satellite-borne laser terminal sun-synchronous avoidance method and system based on optical path switching and pointing maintenance

Abstract

The application relates to a sun-eclipse-avoiding method and system for a spaceborne laser terminal based on optical path switching and pointing maintenance, which comprises the following steps: based on satellite attitude, orbit data and laser terminal pointing data, a real-time included angle theta between a sun vector and a laser communication link vector is calculated in real time; a first protection threshold theta1 is preset, and it is judged whether physical optical path switching is started; when the real-time included angle theta is less than or equal to theta1, it is determined that it is in a sun-eclipse danger stage, and the incident optical path is switched from a communication receiver to a light shield plate area; during the optical path switching, the pointing of the laser terminal to the communication target is maintained unchanged; the real-time included angle theta is continuously monitored, and when theta is greater than theta1, the optical path is restored from the light shield plate area to the communication receiver; and after the optical path is restored, the communication link is recovered in stages based on the unchanged terminal pointing, so that the communication link is re-established. Through the cooperative mechanism of hardware optical path switching and pointing maintenance, the communication receiver is quickly protected, and the link is quickly recovered.

Description

Technical Field

[0001] This invention relates to the field of space laser communication technology, and to a method and system for avoiding solar interference on a spaceborne laser terminal based on optical path switching and pointing maintenance. In particular, it relates to a method and system for avoiding solar interference that can quickly protect optical receiving devices through optical path switching within milliseconds and quickly restore the communication link after the solar interference ends. Background Technology

[0002] Inter-satellite laser communication boasts advantages such as high bandwidth, strong security, and robust anti-interference capabilities, making it a crucial supporting technology for building satellite internet, achieving seamless global coverage, and deep space exploration. However, when a satellite reaches a specific orbital position, the sun, the satellite, and the communication target may be nearly collinear, causing sunlight to directly enter the receiving field of view of the laser communication terminal—a phenomenon known as solar interference. During solar interference, the intense solar background light power density can reach the milliwatts per square centimeter level, far exceeding that of the communication signal light. This not only causes a sharp drop in the signal-to-noise ratio, an increase in the bit error rate, and even communication interruption, but more seriously, it can burn out precision photodetectors such as avalanche photodiodes (APDs) or charge-coupled devices (CCDs), causing permanent equipment damage and severely impacting the satellite's on-orbit lifespan and mission reliability.

[0003] To address the issue of solar interference, various avoidance methods have been proposed in existing technologies. For example, patent application CN119402063A proposes a method for avoiding direct sunlight in inter-satellite laser communication. This method calculates the angle between the solar vector and the optical axis pointing vector in real time. When the angle is less than 3 degrees, it autonomously enters a solar interference avoidance mode, adjusting the terminal's pointing direction to avoid direct sunlight. Patent CN115865198B discloses an inter-satellite link solar interference avoidance and reset tracking method and system. By determining the solar interference angle, different avoidance strategies are adopted for different link types to ensure the laser terminal avoids direct sunlight. After solar interference, the terminal returns to a designated angle to re-establish the inter-satellite link. Patent application CN121000287A proposes a method for avoiding solar interference in inter-satellite laser communication by rotating the pointing vector along the direction of the solar vector's normal plane component.

[0004] However, existing technical solutions have the following common drawbacks: 1) Limited response speed: Existing solutions all rely on adjusting the pointing mechanism of the entire laser terminal to avoid interference, involving the mechanical movement of a coarse tracking turntable or gimbal. The response time is usually on the order of seconds or longer, making it difficult to quickly cut off the strong light at the moment of solar interference and effectively protect the detector; 2) Long link recovery time: After the terminal pointing is adjusted, it needs to be readjusted back to the original pointing after the solar interference ends, and the scanning, acquisition, and tracking (PAT) process needs to be re-executed. The link recovery time is usually on the order of several seconds to tens of seconds, resulting in an excessively large communication interruption time window, which cannot meet the continuity requirements of real-time communication services; 3) Complex control logic: Pointing adjustment involves complex issues such as attitude control coupling with the satellite platform, trajectory planning, and safety avoidance, which increases the control complexity and uncertainty of the system; 4) Difficult energy dissipation: When solar interference occurs, even if the terminal pointing deflects, some stray light or reflected light may still enter the system. Existing technologies have not proposed an effective solution for the absorption and dissipation of strong light energy, which poses a risk of thermal control problems; 5) Lack of pointing maintenance mechanism: Existing technologies change the terminal pointing during solar interference avoidance, which means that re-acquisition and tracking must be performed after the solar interference ends. Existing technologies have not provided an effective solution for how to maintain the pointing alignment relationship during communication interruption.

[0005] Therefore, there is an urgent need for a solar outage avoidance method that can achieve millisecond-level rapid protection, rapid recovery after the solar outage ends, and has a complete pointing maintenance mechanism and energy dissipation mechanism. Summary of the Invention

[0006] This invention aims to solve the problems of slow response speed and long link recovery time of existing spaceborne laser communication terminals during solar outage avoidance. Specifically, the technical problems to be solved by this invention include: The intense light entering the detector is cut off at the instant (milliseconds) when solar interference occurs to prevent the detector from burning out; No need to re-acquire and track after the solar outage ends, enabling rapid link recovery; During the avoidance process, maintain the terminal's pointing alignment to avoid complex control and mechanical wear caused by pointing adjustments; Maintaining pointing alignment in situations where communication is interrupted and real-time orbital data from the other party is unavailable; and It effectively absorbs and dissipates the energy of the cut-off strong light, avoiding thermal control problems.

[0007] This invention provides a method and system for avoiding solar interference in spaceborne laser terminals based on optical path switching and pointing maintenance. Specifically, it provides a method and system capable of rapidly protecting optical receiving devices through optical path switching within milliseconds and quickly restoring the communication link after the solar interference ends. This method is applicable during satellite operation, when sunlight entering the receiving field of view may cause damage to the detector. Through a coordinated mechanism of hardware optical path switching and pointing maintenance, it achieves rapid protection of the communication receiver and rapid restoration of the link.

[0008] The first aspect of this invention provides a method for avoiding solar interference on a spaceborne laser terminal based on optical path switching and pointing maintenance, comprising the following steps: S1. Based on the satellite attitude and orbit control system, the satellite attitude and orbit data and the laser terminal pointing data are used to calculate the real-time angle θ between the solar vector and the laser communication link vector. S2. A first protection threshold θ1 is preset, and the real-time angle θ is compared with the first protection threshold θ1 to determine whether to start physical optical path switching; when the real-time angle θ≤θ1, it is determined to be a dangerous stage of solar interference, and the incident optical path is switched from the communication receiver to the light shield area within milliseconds to cut off the strong light from the hardware level and avoid the detector from burning out. S3. During the optical path switching in step S2, the laser terminal maintains its pointing direction towards the communication target. S4. Continuously monitor the real-time angle θ. When the real-time angle is determined to be greater than θ1, the sunlight moves out of the danger zone of the receiving field of view. Within milliseconds, the optical path is restored from the sunshade area to the communication receiver. S5. After the optical path is restored, based on the terminal pointing that remains unchanged in step S3, the communication link is restored in stages according to the tracking status of the laser link when the optical path is restored, so as to quickly re-establish the communication link without having to re-execute the full-process scan capture.

[0009] Furthermore, in step S1, the real-time calculation of the angle θ between the solar vector and the laser communication link vector can be achieved through the following coordinate transformation method, including the following steps: Calculate the unit vector of the sun in the J2000.0 geocentric inertial coordinate system based on satellite orbit data; A rotation matrix is ​​constructed using the attitude quaternions provided by the satellite attitude and orbit control system to transform the solar vector into the satellite body coordinate system, thus obtaining the solar vector in the satellite body coordinate system. Obtain the pointing vector of the optical axis in the satellite body coordinate system from the laser terminal pointing mechanism; and The real-time angle θ is obtained by performing a dot product operation between the solar vector in the satellite's body coordinate system and the pointing vector in the same coordinate system. The advantages of this coordinate transformation method are high computational efficiency and the ability to directly utilize existing data from the satellite platform without requiring additional sensors.

[0010] Furthermore, in step S2, the incident light path is switched from the communication receiver to the light shield area within a millisecond time. When the light path is in the communication receiver, it can reach the communication receiver; when the light path is in the light shield area, it is physically blocked from entering the communication receiver.

[0011] Furthermore, step S2 also includes: A second protection threshold θ2 is preset, and θ > θ1. The real-time angle θ is compared with the second protection threshold θ2 to determine whether to enter the pre-interference suppression stage. The second protection threshold θ2 is based on the light intensity that the detector can withstand. When the real-time angle satisfies θ1 < θ < θ2 (when the real-time angle enters the range greater than θ1 but less than the preset second protection threshold θ2), the system determines it to be in the mild interference stage. At this time, although it has not yet reached the danger level that requires physical protection, the continuously increasing background light has begun to affect the communication quality. Therefore, the system can enable an adaptive filtering method: enter the pre-interference suppression stage to perform adaptive filtering to maintain communication. Adaptive filtering includes adjusting the center wavelength or bandwidth of the narrowband filter; or filtering out the gradually increasing background light noise through digital signal processing algorithms to maintain the stability of the communication link. This pre-interference suppression stage aims to extend the effective communication time as much as possible, postpone the occurrence of physical optical path switching, and further improve the continuity of communication.

[0012] Furthermore, the first protection threshold θ1 is determined based on the field of view of the laser communication terminal receiving optical system, the bandwidth of the optical filter, and the damage threshold of the photodetector; and / or The first protection threshold θ1 has a value range of 2° to 5°.

[0013] Furthermore, in step S3, maintaining the laser terminal's pointing direction towards the communication target unchanged includes the following steps: Under normal communication conditions, the laser terminal receives orbit data broadcast by the satellite at the communication end in real time, and calculates the pointing vector in real time based on its own attitude data and orbit data, and drives the pointing mechanism to keep it aligned. When communication is interrupted due to solar outage, and the terminal can no longer receive real-time orbit data from the satellite at the communication end, the terminal's control software starts the orbit recursion mode. Based on the historical orbit data stored before the communication interruption, it performs recursive prediction in combination with the orbit dynamics model and calculates the current position of the satellite at the communication end in real time. Based on the real-time orbit and attitude data of the local satellite, and combined with the recursively obtained position of the remote satellite, the expected pointing vector from the local satellite to the remote satellite is calculated; and The laser terminal pointing mechanism performs closed-loop control based on the desired pointing vector to maintain pointing towards the communication target. Studies have shown that using the orbital recursion method, the pointing error can be controlled within milliradians over several minutes, meeting the pointing accuracy requirements of the coarse tracking stage.

[0014] Furthermore, the orbital dynamics model is the SGP4 model or a numerical integration model.

[0015] Furthermore, in step S5, the hierarchical restoration of the communication link based on the tracking state of the laser link during optical path restoration includes the following steps: First-level recovery: When the optical path is restored, the system is still in the fine tracking and holding state, directly maintaining the fine tracking closed loop and completing communication synchronization. The recovery time is 2-10 seconds. The fine tracking and holding state is when the tracking error is <30μrad. Second-stage recovery: When the optical path is recovered, the system is in coarse tracking and holding state. First, coarse tracking acquisition is performed, and after the light spot stabilizes, it switches to fine tracking. The recovery time is 10-60 seconds. The coarse tracking and holding state is when the light spot is within the coarse tracking field of view, but the tracking error is >30μrad. Level 3 Recovery: When the optical path is restored, the system is in a target loss state, and the scanning and acquisition program is re-executed, with a recovery time of 20 seconds to 2 minutes. The target loss state is defined as the light spot leaving the field of view of the coarse tracking detector, with a pointing uncertainty > 5~10 mrad. This hierarchical recovery strategy can adaptively adjust the recovery method according to the actual link status, minimizing the recovery time while ensuring reliability.

[0016] A second aspect of the present invention provides a solar interference avoidance system for a spaceborne laser terminal based on optical path switching and pointing maintenance, comprising: The data fusion and computing unit is configured to receive satellite attitude and orbit data, as well as laser terminal pointing data (data from the satellite attitude and orbit control system and the terminal pointing mechanism), and to calculate the real-time angle θ between the solar vector and the laser communication link vector. Sun eclipse response controller module, which includes: The rapid judgment and drive unit is configured to determine whether to initiate physical optical path switching and whether to enter the pre-interference anti-interference stage based on the real-time included angle θ and a preset threshold, and to generate drive signals and cancellation signals. An optical path switching device is configured to perform physical actions to switch optical paths in response to the drive signal and the cancel signal; the optical path switching device is a turntable-type integrated flat plate structure.

[0017] Furthermore, the optical path switching device performs a physical action in response to the driving signal to switch the incident optical path from the communication receiver to the light shield area, and performs a physical action in response to the cancellation signal to restore the optical path from the light shield area to the communication receiver.

[0018] Furthermore, the preset thresholds include a first protection threshold θ1 and a second protection threshold θ2. When the real-time angle θ≤θ1, it is determined to be a dangerous stage of solar interference. A drive signal is immediately sent to the optical path switching device to control it to complete the physical action within a millisecond time, so that the incident light path is switched from the communication receiver to the sunshade area. The real-time angle θ is continuously monitored. When it is determined that the real-time angle is greater than θ1, the sunlight moves out of the dangerous area of ​​the receiving field of view. A cancellation signal is immediately sent to the optical path switching device to control it to restore the optical path from the sunshade area to the communication receiver within a millisecond time.

[0019] Furthermore, the solar eclipse response controller module also includes: The judgment and control unit, integrated into the adaptive filtering system, is configured to activate and coordinate the adaptive filtering algorithm during the pre-interference suppression phase to maintain communication through adaptive filtering. That is, the fast judgment and drive unit can be integrated with the judgment and control unit in the adaptive filtering system into a single hardware entity, forming a unified sun-damping response controller. This controller is responsible for activating and coordinating the adaptive filtering algorithm during the mild interference phase and triggering physical optical path switching when the first protection threshold is reached, achieving integrated hardware and software control for sun-damping response, simplifying system design, and improving response speed and reliability.

[0020] The optical path switching device includes: Turntable body; Multiple through-holes are formed throughout the turntable body and configured to allow incident light to pass completely through and reach the communication receiver in non-sunlight conditions; and Multiple light-shielding areas, formed by the turntable body excluding the multiple through-holes, are configured to physically block the optical path from entering the communication receiver, ensuring the normal establishment and transmission of the laser communication link. The through-holes and light-shielding areas are alternately distributed on the turntable body. By rotating the turntable, the through-holes can be moved into or away from the optical path, thus achieving rapid switching between light-passing and light-shielding states. Specifically, the through-holes serve as the optical channel for normal communication. In non-solar interference states, they allow unobstructed, complete passage of incident signal light to reach the downstream communication receiver, ensuring the normal establishment and transmission of the laser communication link. During solar interference, the light-shielding areas are rotated into the optical path for rapid light shielding. The multiple light-shielding areas are integrated with the turntable body, rapidly transferring absorbed heat to the turntable body, and then dissipating it to the satellite's heat dissipation surface through a thermal control system, preventing localized overheating.

[0021] Furthermore, the turntable body is a flat plate structure of uniform thickness, integrally processed from lightweight and high-strength materials.

[0022] Furthermore, the turntable body undergoes black anodizing treatment to form a high-absorption-rate shading surface within the multiple shading plate areas. The shading surface achieves a solar absorptivity of 0.85~0.90 across a broad 400~1700nm spectrum.

[0023] Furthermore, the aperture of the through hole is 1.2–1.3 times the diameter of the beam to ensure that the beam passes through completely and to avoid light energy loss or diffraction interference.

[0024] Furthermore, the through hole is a through circular hole; the turntable body is driven by a micro motor and can rotate around the central axis (rotation shaft mounting hole). In normal communication mode, one through hole of the turntable body is located in the optical path; when a drive signal is received, the motor drives the turntable body to rotate by a preset angle, so that a light-shielding area enters the optical path and absorbs the incident light; when a cancellation signal is received, the motor drives the turntable body to rotate in the opposite direction, so that the through hole re-enters the optical path. This rotary integrated flat panel structure has the following advantages: First, the rotary body itself is always located in the optical path, and the switching process only involves the rotation of the rotary body, without changing the positional relationship of other optical components in the optical path. No recalibration is required after the optical path is restored. Second, the light-shielding plate area and the rotary body are an integrated structure without any connecting interface, resulting in high structural reliability. Third, the number of holes can be optimized according to terminal volume constraints and switching speed requirements, such as a 2-hole scheme (2 through holes + 2 light-shielding plate areas). Specifically, two through holes are evenly opened along the circumference of the rotary body. In non-sunlight outage conditions, the optical path is located at these two through holes. If a sunlight outage is triggered, the light-shielding plate area is rotated 90° to the center of the optical path, i.e., the switching angle is 90°, and the switching time is approximately 8-10 seconds. The 4-hole design (4 through holes + 4 light-shielding plate areas) involves four through holes evenly spaced along the circumference of the turntable body. In non-sunlight-affected conditions, the optical path lies at these four through holes. If a sunlight-affected condition occurs, the light-shielding plate area is rotated 45° into the optical path, effectively switching the angle by 45°, with a switching time of approximately 4-5 ms. The turntable structure allows for optimized hole counts based on terminal volume constraints, adapting to the engineering needs of different terminal models. The turntable body only requires drilling and localized black anodizing, eliminating the need for complex surface machining and component embedding. The process is mature, manufacturing costs are low, and it facilitates mass production. Heat absorbed by the light-shielding plate area is directly conducted through the turntable body and discharged to the satellite's heat dissipation surface via heat pipes. The heat conduction path has no interface thermal resistance, resulting in high efficiency. A thermistor monitors the temperature in real time to ensure thermal control safety.

[0025] Furthermore, a porous oxide film is formed on the aluminum alloy surface in the light-shielding plate area, with black dye embedded in the film layer, forming a high-absorption surface for a broad spectrum (400~1700 nm), achieving a solar absorptivity of 0.85~0.90. This treatment ensures a strong bond with the turntable substrate, resistance to space environment radiation, no risk of organic material outgassing, and meets the long-life requirements of aerospace applications.

[0026] Furthermore, the optical path switching device is connected to the satellite thermal control system, and the heat absorbed by the turntable body is discharged through heat pipes. Specifically, a miniature heat pipe is installed at the bearing seat of the fixed bracket, with one end of the heat pipe in close contact with the bracket and the other end connected to the heat pipe network of the satellite platform. The solar energy absorbed by the shading plate area is converted into heat, which is conducted through the turntable body, the rotating shaft, and the bracket to the heat pipe, and finally radiated into space by the satellite's heat dissipation surface. A thermistor is installed on the back of the turntable body to monitor the temperature of the turntable body area in real time. When the temperature exceeds the safety threshold, the system can take measures such as extending the heat dissipation cycle or switching to a backup turntable body.

[0027] The present invention has at least the following beneficial effects: 1) The present invention achieves rapid protection of the communication receiver and rapid link recovery through a coordinated mechanism of hardware optical path switching and pointing maintenance; 2) The detector protection speed is improved to the millisecond level: by adopting a physical optical path switching method, the optical path switching is completed within 8-10 milliseconds through a turntable optical path switching device, and the strong light is instantly directed to the turntable body. Compared with the second-level response of the prior art by adjusting the terminal pointing, the protection speed is improved by 2-3 orders of magnitude, which can effectively prevent the detector from burning out and ensure the safety of core components; 3) The communication interruption time is significantly shortened: by using the track recursion method to maintain the terminal pointing alignment during solar interference, the optical path is restored in stages according to the link status after restoration. The recovery time for fine tracking is only 2-10 seconds, and the recovery time for coarse tracking is 10-60 seconds. Even if the target is lost, it only takes 20 seconds to 2 minutes, which is far superior to the re-acquisition and tracking time of several minutes to more than ten minutes required by existing technologies; 4) The optical path switching device has high structural reliability: it adopts an integrated flat plate structure, and the light shield area and the turntable body are processed as a whole without any connection interface. There is no risk of vibration and loosening, and it is suitable for the severe vibration of the launch section and the micro-vibration environment in orbit. 5) The black anodized surface treatment is firmly bonded to the substrate, resistant to space environment radiation, and has no organic material outgassing issues, meeting the long life requirements of aerospace; 6) Simple processing technology and low cost: The turntable body only requires drilling and local black anodizing treatment, without complex surface processing and embedded components. The technology is mature, the manufacturing cost is low, and it is convenient for mass production in engineering; 7) Improved thermal control management: The heat absorbed by the sunshade plate area is directly conducted through the turntable body and discharged to the satellite heat dissipation surface through heat pipes. The heat conduction path has no interface thermal resistance, which is highly efficient. The thermistor monitors the temperature in real time to ensure thermal control safety; 8) Significantly improved system reliability: The decoupling design of optical path switching and pointing maintenance makes sun outage avoidance no longer dependent on complex pointing adjustment planning. It avoids mechanical wear, control errors and coupling problems with satellite attitude caused by frequent terminal pointing adjustments, improving the overall reliability and service life of the system; 9) Simplified control logic and strong engineering adaptability: The hierarchical recovery strategy based on link status can be adaptively adjusted according to the actual situation, minimizing the recovery time while ensuring reliability. The turntable structure can optimize the number of holes according to the terminal volume constraints to adapt to the engineering needs of different terminal models. Attached Figure Description

[0028] To further illustrate the above and other advantages and features of the various embodiments of the present invention, a more specific description of the embodiments of the invention will be presented with reference to the accompanying drawings. It is to be understood that these drawings depict only typical embodiments of the invention and are therefore not intended to limit its scope. In the drawings, identical or corresponding parts will be indicated by identical or similar reference numerals for clarity.

[0029] Figure 1 A schematic diagram of the overall structure of the rotary optical path switching device in some embodiments of the present invention is shown; Figure label: 1-Turntable body, 2-Through hole, 3-Rotation shaft mounting hole, 4-Light shield area. Detailed Implementation

[0030] It should be noted that the components in the accompanying drawings may be shown exaggerated for illustrative purposes and may not be to scale.

[0031] In this invention, the various embodiments are merely intended to illustrate the solutions of the invention and should not be construed as limiting.

[0032] In this invention, unless otherwise specified, the quantifiers “a” and “one” do not exclude scenarios involving multiple elements.

[0033] It should also be noted that, in the embodiments of the present invention, only a portion of the parts or components may be shown for clarity and simplicity. However, those skilled in the art will understand that, under the teachings of the present invention, the required parts or components can be added as needed for specific scenarios.

[0034] It should also be noted that within the scope of this invention, the terms "same", "equal", and "equal to" do not mean that the two values ​​are absolutely equal, but allow for a certain reasonable error. In other words, the terms also cover "substantially the same", "substantially equal", and "substantially equal to".

[0035] It should also be noted that in the description of this invention, the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not explicitly or implicitly suggest that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0036] Furthermore, the embodiments of the present invention describe the process steps in a specific order. However, this is only for the convenience of distinguishing each step, and is not a limitation on the order of each step. In different embodiments of the present invention, the order of each step can be adjusted according to the process.

[0037] The following embodiment provides a method for avoiding solar interference on a spaceborne laser terminal based on optical path switching and pointing maintenance, including the following steps: S1. Based on the satellite attitude and orbit control system, the satellite attitude and orbit data, as well as the laser terminal pointing data, are used to calculate the real-time angle θ between the solar vector and the laser communication link vector.

[0038] Specifically, the core of this step lies in fusing multi-source data to accurately calculate the angle between the incident direction of sunlight and the communication optical axis, using this as a quantitative indicator of solar interference risk. First, the satellite attitude quaternions and orbital position data published by the Attitude and Orbit Control System (AOCS) are acquired in real time via the satellite platform's bus (e.g., 1553B bus or CAN bus). Simultaneously, the precise pointing vector of the current optical axis in the satellite's body coordinate system is obtained from the pointing mechanism controller of the laser communication terminal; this is typically expressed as azimuth and elevation angles.

[0039] The real-time calculation process is as follows: First, based on satellite orbit data, calculate the unit vector S~J2000~ of the Sun in the J2000.0 geocentric inertial coordinate system. This can be done using classic solar position algorithms, such as calculating it using astronomical almanac formulas based on the Julian day at the current moment. For example, a simplified algorithm can be used: S~J2000~ = [cos(λ_sun), sin(λ_sun)] cos(ε), sin(λ_sun) sin(ε)] T , where λ_sun is the solar ecliptic longitude and ε is the obliquity of the ecliptic (approximately 23.44 degrees).

[0040] Then, the attitude quaternion Q = [q0, q1, q2, q3] provided by the satellite attitude and orbit control system is used. T Construct the rotation matrix R~body←J2000~ from the J2000.0 inertial coordinate system to the satellite body coordinate system: R~body←J2000~ = [[q0²+q1²-q2²-q3², 2(q1q2+q0q3), 2(q1q3-q0q2)]; [2(q1q2-q0q3), q0²-q1²+q2²-q3², 2(q2q3+q0q1)]; [2(q1q3+q0q2), 2(q2q3-q0q1), q0²-q1²-q2²+q3²]] Using this matrix, the solar vector is transformed into the satellite body coordinate system, resulting in S~body~ = R~body←J2000~ S~J2000~.

[0041] The laser communication link vector, i.e., the pointing vector L of the receiving optical axis, can be directly obtained from the pointing mechanism controller of the terminal. In the satellite body coordinate system, it can be expressed as L~body~ = [cos(El)cos(Az), cos(El)sin(Az), sin(El)] T Where Az is the azimuth angle in degrees and El is the elevation angle in degrees.

[0042] Finally, the real-time angle θ between the solar vector and the laser communication link vector is calculated. In the satellite body coordinate system, the angle θ between the two vectors can be obtained through dot product: cosθ = Sbody · Lbody. Since both Sbody and Lbody are unit vectors, θ = arccos(Sbody · Lbody). This angle θ is the core parameter for judging the risk of solar interference, and its value ranges from 0 to 180 degrees. When θ approaches 0 degrees, it indicates that the sunlight is directly facing the receiving field of view, and the risk is the highest; when θ approaches 90 degrees or greater, the risk is lower. The update frequency of this calculation needs to be high enough, for example, at a rate of 50 Hz, to ensure real-time monitoring of the risk of solar interference.

[0043] S2. Preset a first protection threshold θ1, compare the real-time angle θ with the first protection threshold θ1 to determine whether to start physical optical path switching; when the real-time angle θ≤θ1, it is determined to be a dangerous stage of solar interference, and the incident optical path is switched from the communication receiver to the turntable body 1 within milliseconds to cut off the strong light from the hardware level and avoid the detector from burning out.

[0044] Specifically, this step aims to determine the severity of the solar eclipse risk through threshold judgment and take corresponding countermeasures. This embodiment sets two protection thresholds: 1. First protection threshold θ1: This corresponds to the critical value at which physical optical path switching needs to be initiated. This value is determined comprehensively based on factors such as the field of view of the laser communication terminal's receiving optical system, the bandwidth of the optical filter, and the damage threshold of the photodetector. For example, if the receiving field of view is 0.5 milliradians, considering that the angular diameter of the sun as an extended light source is approximately 0.53 degrees (approximately 9.3 milliradians), the threshold θ1 is usually set between 2 and 5 degrees. In a specific example, θ1 is set to 3 degrees.

[0045] 2. Second protection threshold θ2: The critical value at which pre-emptive anti-interference measures need to be activated, and θ2 > θ1. For example, θ2 can be taken as 8 degrees.

[0046] When the real-time angle θ satisfies θ1 < θ < θ2, the system determines it to be in a mild interference stage. At this time, sunlight has not yet directly entered the receiving field of view, but the continuously increasing background light has begun to affect the communication quality. The system can then activate an adaptive filtering method, adjusting the center wavelength or bandwidth of the narrowband filter, or using digital signal processing algorithms to filter out the gradually increasing background light noise, in order to maintain the stability of the communication link.

[0047] When the real-time angle θ≤θ1, it means that the sunlight is very close to or has entered the receiving field of view. The strong light may cause irreversible damage to the detector, and physical optical path switching protection must be activated immediately.

[0048] When θ ≤ θ1, the system determines that solar interference is imminent and physical protection is required. The fast judgment and drive unit immediately generates a drive signal, such as a 5-volt, 50-millisecond TTL high-level pulse. This signal is sent to the optical path switching device.

[0049] "Millisecond time" is defined here as less than 10 milliseconds. After receiving the drive signal, the optical path switching device must complete the physical action within 10 milliseconds to cut off the incident optical path.

[0050] In a preferred embodiment of the present invention, the optical path switching device is implemented using a turntable structure. Figure 1 This diagram shows the overall structure of the rotary optical path switching device, which includes: Turntable body 1; Multiple through holes 2 are formed through the turntable body 1 and are configured to allow incident light to pass completely through and reach the communication receiver in non-sunlight conditions; and Multiple light-shielding areas 4, formed by the turntable body 1 in addition to multiple through holes 2, are configured to physically block the light path from entering the communication receiver, ensuring the normal establishment and transmission of the laser communication link. The turntable body 1 is driven by a micro motor and can rotate around the mounting hole 3 of the rotation axis.

[0051] like Figure 1 As shown, the turntable body 1 is integrally machined from a lightweight, high-strength material (aluminum alloy 2A12) and has a flat plate structure of uniform thickness. Multiple through holes 2 and multiple light-shielding plate areas 4 are alternately arranged along the circumference of the turntable body 1. The through holes 2 are through circular holes, allowing incident light to pass through without obstruction; the light-shielding plate areas 4 are circular areas on the corresponding positions of the turntable body 1, which are black anodized to form a light-shielding surface with high absorption rate. The center of the turntable body 1 is connected to the output shaft of a micro stepper motor. Each time the motor receives a drive pulse, it drives the turntable body 1 to rotate by a fixed angle, causing the next hole or light-shielding plate area 4 to enter the light path.

[0052] In designing the diameter of the through-hole, edge diffraction effects and shading losses must be considered comprehensively. The aperture allowance coefficient k = D is defined. 孔 / D 束 The recommended value for this is 1.2-1.3. For example, for a terminal with a beam diameter of 60 mm, the diameter of through-hole 2 is 75 mm.

[0053] The estimation of the diameter of the turntable body 1 needs to consider the diameter d of the through hole 2, the number of holes n, and the installation space of the central shaft. This embodiment adopts a 2-hole scheme (two through holes 2 plus two light-shielding plate areas 4 are arranged alternately, with an adjacent switching angle of 90°). The diameter of the turntable body 1 is approximately 211 mm, and the switching time is approximately 8-10 ms. The thickness of the turntable body 1 has been optimized to 2.0 mm, and weight-reduction holes are opened in non-stress areas. The total weight of the entire device is controlled within 100 g, meeting the lightweight requirements.

[0054] In normal communication mode, a through-hole 2 of the turntable body 1 is located in the optical path, and incident light reaches the communication receiver through this through-hole 2. When a drive signal is received, the motor drives the turntable body 1 to rotate 90°, causing a light-shielding plate area 4 to enter the optical path. The incident light is absorbed by the black anodized surface of the turntable body 1, thus providing physical protection for the communication receiver. Since the turntable body 1 itself is always located in the optical path, the switching process does not change the positional relationship of other optical components in the optical path, so there is no need for recalibration after the optical path is restored.

[0055] Black anodizing creates a porous oxide film on the aluminum alloy surface, with black dye embedded within the film, forming a highly absorbent surface across a broad spectrum (especially the visible to near-infrared band), achieving a solar absorptivity of 0.85~0.90. This treatment ensures a strong bond with the turntable substrate, resists space environment radiation, and eliminates the risk of organic material release.

[0056] S3. During the optical path switching in step S2, the laser terminal maintains its pointing direction towards the communication target.

[0057] Specifically, this step is crucial for achieving rapid recovery. Under normal communication conditions, the laser terminal receives orbit data broadcast by the satellite from the other end in real time, and calculates the pointing vector in real time based on its own attitude and orbit data, driving the pointing mechanism to maintain alignment. When a communication interruption occurs due to a solar outage, the terminal can no longer receive real-time orbit data from the other satellite.

[0058] At this point, the terminal's control software initiates the orbit recursion mode: based on historical orbit data stored before the communication interruption (rather than a single data point), it performs recursive predictions using the orbital dynamics model, calculating the current position and velocity of the receiving satellite in real time. Using multiple sets of historical data as initial recursive values ​​effectively suppresses the impact of single-point measurement errors on prediction accuracy and extends the effective pointing duration.

[0059] Commonly used orbital recursion models include SGP4 (Simplified General Perturbations 4) and numerical integration models. SGP4 is an industry-standard method for prediction based on two-line orbital elements (TLE). It is fast and suitable for real-time onboard calculations, with position errors ranging from hundreds of meters to kilometers within a few minutes. Numerical integration models predict orbits by solving the differential equations of satellite orbital dynamics, offering higher accuracy. These include the Adams-Cowell method, the Runge-Kutta series (RK4, RKF4(5), RK8), and the Bulirsch-Stoer method, which can be selected based on the onboard computing capabilities.

[0060] Taking low-Earth orbit satellites as an example, using the SGP4 model for orbit recursion, the position error within 30 seconds is approximately 100-150 meters, corresponding to an angular error of approximately 0.023-0.035 mrad at an inter-satellite distance of 4300 km; the position error within 5 minutes is approximately 1-2 kilometers, corresponding to an angular error of approximately 0.23-0.47 mrad. This indicates that even within minute-level solar interference, the orbit recursion error can still be controlled within the coarse tracking field of view (typically 5 mrad).

[0061] Based on the real-time orbit and attitude data of its own satellite, and combined with the recursively derived position of the peer satellite, the terminal calculates the desired pointing vector from its own satellite to the peer satellite. The pointing mechanism performs closed-loop control based on this desired pointing vector to maintain pointing towards the target. Since the error in orbit recursion accumulates over time, the pointing mechanism in this step actually performs continuous pointing updates based on the recursively derived orbit, which can minimize pointing deviation to the greatest extent.

[0062] S4. Continuously monitor the real-time angle θ. When it is determined that the real-time angle is greater than θ1, the sunlight moves out of the dangerous area of ​​the receiving field of view and the optical path is restored from the turntable body 1 to the communication receiver within milliseconds.

[0063] Specifically, during the solar interference avoidance period, the angle calculation in step S1 and the comparison judgment in step S2 continue. As the satellite moves, the angle θ between the solar vector and the communication link vector gradually increases. When θ exceeds the preset first protection threshold θ1 (e.g., 3 degrees), it means that the sunlight has moved out of the danger zone of the receiving field of view. At this time, the fast judgment and drive unit immediately generates a cancellation signal (e.g., a 0-volt low level or a reverse pulse). This signal is sent to the optical path switching device, controlling it to perform a reverse rotation, so that the through-hole 2 re-enters the optical path. This recovery action also needs to be completed within milliseconds, i.e., less than 10 milliseconds, so that the optical path can be restored to normal as soon as possible.

[0064] S5. After the optical path is restored, based on the terminal pointing that remains unchanged in step S3, the communication link is restored in stages according to the tracking status of the laser link when the optical path is restored, so as to quickly re-establish the communication link without having to re-execute the full-process scan capture.

[0065] Specifically, since the laser terminal maintains its pointing towards the communication target through orbit recursion in step S3, the signal light from the target satellite will fall within a certain range of the receiving field of view at the instant the optical path is restored. However, the orbit recursion error accumulates as the duration of solar interference increases, causing the laser link to be in different tracking states when the optical path is restored. To address this, the present invention designs a hierarchical recovery strategy based on the link state, taking corresponding recovery measures according to the tracking mode (fine tracking hold, coarse tracking hold, target loss) at the time of optical path restoration.

[0066] Level 1 Recovery: Precise Tracking and Status Maintenance When the duration of the outburst is short, the orbital recursion error is small, and the pointing deviation is still within the fine tracking field of view, the system remains in a fine tracking closed-loop state after the optical path is restored. According to the on-orbit test data of satellite-to-ground laser communication, the SG10-1 terminal achieved rapid acquisition and stable tracking of the satellite-to-ground bidirectional beam, with a tracking accuracy better than 5 microradians.

[0067] 1) Pointing uncertainty: <0.5 mrad (typical value for fine tracking field of view); 2) Recovery Mode: Maintains precise tracking loop without the need for re-capture; 3) Recovery process: The fine tracking system uses a high-bandwidth fast-reflection mirror (control frequency up to 800 Hz) to stabilize the light spot at the center of the detector; the communication receiver completes the automatic gain control (AGC) establishment and clock data recovery (CDR) locking; 4) Recovery time: 2-10 seconds.

[0068] Second-level recovery: Coarse tracking maintains status When the duration of the obstruction is prolonged, the orbital recursion error accumulates, and the pointing deviation exceeds the fine tracking field of view but remains within the coarse tracking field of view, the system enters the coarse tracking hold state after the optical path is restored. The coarse tracking system uses mechanisms such as a turntable, has a large field of view (on the order of milliradians), and is responsible for introducing the light spot into the field of view of the coarse tracking detector.

[0069] 1) Pointing uncertainty: 0.5 mrad - 5 mrad (typical value for coarse tracking field of view) 2) Recovery mode: First, coarse tracking and capture, then switch to fine tracking. 3) Recovery Process: The system first enters coarse tracking mode, adjusting the turntable to guide the light spot into the field of view of the coarse tracking detector. After the light spot stabilizes, it automatically switches to fine tracking mode to complete high-precision alignment and communication synchronization. According to research on beaconless inter-satellite laser communication systems, the average scanning acquisition time of the coarse-fine composite scanning method is less than 20 seconds, and the acquisition probability is greater than 95%.

[0070] 4) Recovery time: 10-60 seconds. It depends on the magnitude of the pointing deviation. Recovery is faster (10-20 seconds) when the deviation is close to the fine tracking field of view, and slower (30-60 seconds) when the deviation is close to the edge of the coarse tracking field of view.

[0071] Level 3 Recovery: Target Lost Status When the duration of the daytime interference is long, the orbital recursion error is large, and the pointing deviation exceeds the coarse tracking field of view, the system is in a target loss state after the optical path is restored, and the scanning and acquisition procedure needs to be re-executed. However, thanks to the orbital recursion pointing maintenance in step S4, the initial pointing uncertainty at this time (5-10 mrad) is much smaller than the initial uncertainty when re-acquiring after terminal deflection in the prior art (which may reach 50-100 mrad).

[0072] 1) Pointing uncertainty: 5 mrad - 10 mrad (outside the coarse tracking field of view) 2) Recovery Mode: Re-execute the scan capture. 3) Recovery Process: The system searches for the target signal within the uncertainty domain according to a predetermined scanning trajectory (such as helical scanning). Beacon-free scanning acquisition studies show that, within an uncertainty domain of approximately 10 mrad, the average scanning acquisition time can be controlled within 20 seconds to 2 minutes. Once the target signal is acquired, the system sequentially enters coarse tracking and fine tracking modes to complete the link establishment.

[0073] 4) Recovery time: 20 seconds to 2 minutes. This depends on the size of the uncertainty domain and the scanning strategy. Optimized coarse-fine combined scanning methods can significantly shorten the acquisition time.

[0074] Example estimation based on Walker constellation Taking a typical Low Earth Orbit (LEO) Walker constellation as an example, assuming a total of 300 satellites, 30 orbital planes, an orbital altitude of 550 km, a phase factor of 1, and an adjacent satellite distance of approximately 4300 km within the same orbital plane, the solar interference angle threshold (solar angular radius + receiving field of view) is approximately 5.15 mrad (0.295°) based on orbital kinematics analysis, and the satellite angular velocity is approximately 1.1 mrad / second.

[0075] Based on the orbital recursive model (SGP4 or UKF), the pointing uncertainty after different daytime outage durations can be estimated.

[0076] Estimates show that under this Walker constellation, most solar outage events (10-15 seconds) fall under Level 1 recovery, with link reconstruction completed within 10 seconds. When the outage lasts 5-10 minutes, it may enter Level 2 recovery, with a recovery time of 15-30 seconds. Even if the outage lasts for 30 minutes, the pointing uncertainty can still be controlled within 3.5 mrad (still within the coarse tracking field of view), and the recovery time does not exceed 60 seconds. This fully demonstrates the effectiveness of the pointing maintenance method and hierarchical recovery strategy based on orbit recursion in this invention.

[0077] Through the above steps S1 to S6, the method provided in this embodiment realizes millisecond-level physical optical path switching protection when solar outage occurs, and hierarchical rapid recovery based on orbit recursive pointing maintenance and link status after solar outage ends, effectively solving the problems of slow response and long interruption time in the prior art.

[0078] The decoupled collaborative mechanism of optical path switching and pointing maintenance in this invention differs from existing technologies that avoid solar interference by adjusting the terminal's pointing (software / mechanical avoidance). This invention innovatively proposes to decompose solar interference avoidance into two decoupled collaborative actions: "optical path switching" and "pointing maintenance." During solar interference, a physical optical path switching device instantly guides the strong light to the beam terminator, achieving hardware-level millisecond-level protection; simultaneously, the terminal's pointing towards the communication target remains unchanged through a track recursion method. This decoupled design allows the acquisition and tracking process to begin immediately after the optical path is restored following the end of solar interference, significantly shortening the link recovery time.

[0079] This invention proposes a rotary optical path switching device, employing an integrated flat panel structure. The rotary body 1 has alternating through-holes 2 and light-shielding plate areas 4. The light-shielding plate areas 4 are absorption surfaces formed directly on the corresponding positions of the rotary body 1 through black anodizing, eliminating the need for openings or embedded components. The rotary body 1 remains within the optical path; the switching process involves only the rotation of the rotary body 1, without altering the positional relationships of other optical components in the optical path. Recalibration is unnecessary after the optical path is restored. The integrated structure eliminates connection interfaces, offering advantages such as high structural reliability, simple processing, excellent heat conduction efficiency, and good adaptability to various spatial environments.

[0080] This invention proposes a method to maintain the terminal's pointing towards the target during solar outages by using historical orbit data stored before the outage and combining it with an orbital dynamics model for recursive prediction. This method solves the problem of existing technologies failing to maintain pointing during communication outages, allowing communication to be restored after the solar outage ends without the need for re-acquisition and tracking or with only minor adjustments. Research shows that using the orbital recursion method, the pointing residual can be controlled to around 0.5 milliradians, and the acquisition time can be shortened from more than 8 minutes to less than 15 seconds.

[0081] This invention proposes a tiered recovery strategy based on the duration of solar interference: For short-duration interference, the recursive error is small, allowing direct entry into fine tracking with a recovery time of several seconds to tens of seconds; for medium- to long-duration interference, the recursive error accumulates, requiring coarse tracking before fine tracking, with a recovery time of tens of seconds to minutes; for long-duration interference, the recursive error may exceed the coarse tracking field of view, requiring rescanning and recapture, but the recovery time is still significantly shortened. This tiered strategy balances reliability and recovery speed.

[0082] While some embodiments of the present invention have been described in this application, those skilled in the art will understand that these embodiments are merely illustrative. Numerous variations, alternatives, and improvements will arise in those skilled in the art under the teachings of this invention without departing from its scope. The appended claims are intended to define the scope of the invention and thereby cover methods and structures within the scope of the claims themselves and their equivalents.

Claims

1. A method for avoiding solar interference in a spaceborne laser terminal based on optical path switching and pointing maintenance, characterized in that, Includes the following steps: S1. Based on satellite attitude, orbit data and laser terminal pointing data, calculate the real-time angle θ between the solar vector and the laser communication link vector. S2. Preset a first protection threshold θ1, and compare the real-time included angle θ with the first protection threshold θ1 to determine whether to start physical optical path switching; When the real-time included angle θ≤θ1, it is determined to be a dangerous stage of solar interference. Within a millisecond time, the incident light path is switched from the communication receiver to the sunshade area. A second protection threshold θ2 is preset, and θ > θ1. The real-time included angle θ is compared with the second protection threshold θ2 to determine whether to enter the pre-interference anti-interference stage. When the real-time included angle satisfies θ1 < θ < θ2, it is determined to be a mild interference stage, and the pre-interference anti-interference stage is entered to perform adaptive filtering to maintain communication. Adaptive filtering includes adjusting the center wavelength or bandwidth of the narrowband filter; or filtering out the gradually increasing background light noise through digital signal processing algorithms to maintain the stability of the communication link. S3. During the optical path switching in step S2, the laser terminal maintains its pointing direction towards the communication target. S4. Continuously monitor the real-time angle θ. When the real-time angle is determined to be greater than θ1, restore the optical path from the light-shielding area to the communication receiver within milliseconds; and S5. After the optical path is restored, based on the terminal pointing that remains unchanged in step S3, the communication link is restored in stages according to the tracking state of the laser link when the optical path is restored, so as to re-establish the communication link. In step S3, maintaining the laser terminal's pointing direction towards the communication target unchanged includes the following steps: When communication is interrupted due to a sudden outage, and the terminal is unable to continue receiving real-time orbit data from the other satellite, the orbit recursion mode is activated. Based on the historical orbit data stored before the communication interruption, combined with the orbit dynamics model, a recursive prediction is made to calculate the current position of the other satellite in real time. Based on the real-time orbit and attitude data of the local satellite, and combined with the recursively obtained position of the remote satellite, the expected pointing vector from the local satellite to the remote satellite is calculated; and The laser terminal pointing mechanism performs closed-loop control based on the desired pointing vector to maintain pointing towards the communication target; In step S5, the hierarchical restoration of the communication link based on the tracking state of the laser link during optical path restoration includes the following steps: First-level recovery: When the optical path is restored, the system is still in the fine tracking and holding state, directly maintaining the fine tracking closed loop and completing communication synchronization. The recovery time is 2-10 seconds. The fine tracking and holding state is when the tracking error is <30μrad. Second-stage recovery: When the optical path is recovered, the system is in coarse tracking and holding state. First, coarse tracking acquisition is performed, and after the light spot stabilizes, it switches to fine tracking. The recovery time is 10-60 seconds. The coarse tracking and holding state is when the light spot is within the coarse tracking field of view, but the tracking error is >30μrad. Third-level recovery: When the optical path is restored, the system is in a target loss state and the scanning and acquisition program is re-executed. The recovery time is 20 seconds to 2 minutes. The target loss state is when the light spot leaves the field of view of the coarse tracking detector and the pointing uncertainty is >5~10mrad.

2. The method for avoiding solar interference in a spaceborne laser terminal based on optical path switching and pointing maintenance according to claim 1, characterized in that, In step S1, the real-time calculation of the angle θ between the solar vector and the laser communication link vector includes the following steps: Calculate the unit vector of the sun in the J2000.0 geocentric inertial coordinate system based on satellite orbit data; A rotation matrix is ​​constructed using the attitude quaternions provided by the satellite attitude and orbit control system to transform the solar vector into the satellite body coordinate system, thus obtaining the solar vector in the satellite body coordinate system. Obtain the pointing vector of the optical axis in the satellite body coordinate system from the laser terminal pointing mechanism; as well as The real-time angle θ is obtained by performing a dot product operation between the solar vector in the satellite's body coordinate system and the pointing vector in the satellite's body coordinate system.

3. The method for avoiding solar interference in a spaceborne laser terminal based on optical path switching and pointing maintenance according to claim 1, characterized in that, The first protection threshold θ1 is determined based on the field of view of the laser communication terminal receiving optical system, the bandwidth of the optical filter, and the damage threshold of the photodetector; and / or The first protection threshold θ1 has a value range of 2° to 5°.

4. The method for avoiding solar interference in a spaceborne laser terminal based on optical path switching and pointing maintenance according to claim 1, characterized in that, The orbital dynamics model is either the SGP4 model or a numerical integration model.

5. A spaceborne laser terminal solar interference avoidance system based on optical path switching and pointing maintenance, characterized in that, The spaceborne laser terminal solar outage avoidance system, used to implement the solar outage avoidance method based on optical path switching and pointing maintenance as described in any one of claims 1-4, comprises: The data fusion and computing unit is configured to receive satellite attitude and orbit data and laser terminal pointing data, and to calculate the real-time angle θ between the solar vector and the laser communication link vector. Sun eclipse response controller module, which includes: A rapid judgment and drive unit is configured to determine, based on the real-time included angle θ and a preset threshold, whether to initiate physical optical path switching and whether to enter the pre-interference anti-interference stage, and to generate drive signals and cancellation signals; and The judgment and control unit, integrated into the adaptive filtering system, is configured to activate and coordinate the adaptive filtering algorithm during the initial anti-interference phase to maintain communication through adaptive filtering; and An optical path switching device is configured to perform a physical action to switch optical paths in response to the drive signal and the cancel signal; the optical path switching device is a rotary integrated flat plate structure. The optical path switching device includes: Turntable body; Multiple through-holes are formed throughout the turntable body and configured to allow incident light to pass completely through and reach the communication receiver; and Multiple light-shielding areas, formed by the turntable body other than the multiple through holes, are configured to physically block the light path from entering the communication receiver.

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