A beacon-free inter-satellite laser communication bidirectional link building method

Abstract

This invention discloses a beacon-free inter-satellite laser communication bidirectional link establishment method, comprising: initializing the scanning and staring ends of the laser communication system; the scanning and staring ends of the laser communication system entering a search state and expanding the scanning beam; determining whether the staring end of the laser communication system has entered a capture state; determining whether the scanning end of the laser communication system has entered a capture state; determining whether the scanning and staring ends of the laser communication system have entered a tracking state; and the scanning and staring ends of the laser communication system entering a bidirectional locking state. The laser communication system described in this invention reduces the beacon-free search time, improves the probability of successful capture, and enhances the stability and anti-interference capabilities of beacon-free bidirectional link establishment.

Description

Technical Field

[0001] This invention relates to the field of satellite optical communication technology, specifically to a beacon-free inter-satellite laser communication bidirectional link establishment method. Background Technology

[0002] In laser communication link establishment, beaconless bidirectional link establishment is a novel method that directly utilizes signal light to replace the original beacon light in establishing a communication link. Since the divergence angle of the signal light from satellite terminals typically reaches the optical diffraction limit, only on the order of tens of microarcs, replacing the original beacon light with a smaller divergence angle using signal light simplifies the overall structure of the laser communication system and further improves system performance.

[0003] Existing technologies provide a rapid acquisition method for inter-satellite laser communication without a beacon, detailing the process of coarse tracking motor scanning and high-speed resonator beam expansion scanning at the scanning terminal. However, they do not describe the bidirectional link establishment process involving the coordinating actions of the staring and scanning ends, nor do they provide a link establishment method for the coarse tracking motor motion and the fine tracking high-speed resonator motion at both terminals after successful acquisition. Existing technologies also provide a tracking scheme for small target images, but do not explain the specific process and execution steps of coarse-fine composite tracking. Furthermore, existing technologies offer applications of deep learning methods in signal processing and detection, beacon beam tracking and aiming, and wavefront distortion detection and correction in laser communication systems. However, deep learning suffers from the problem that data processing speed lags far behind data transmission speed, and the bit error rate of neural network algorithms is difficult to meet the requirements of laser communication, making it difficult to apply deep learning in space laser communication at present. Summary of the Invention

[0004] The purpose of this invention is to provide a beacon-free bidirectional link establishment method for inter-satellite laser communication, which reduces the beacon-free search time, increases the probability of successful acquisition by the laser communication system, and improves the stability and anti-interference of beacon-free bidirectional link establishment.

[0005] To achieve the above objectives, this invention provides a beacon-free inter-satellite laser communication bidirectional link establishment method, comprising:

[0006] Step 1: Initialize the scanning and staring ends of the laser communication system;

[0007] Step 2: The scanning end and staring end of the laser communication system enter the search state and expand the scanning beam.

[0008] Step 3: Determine whether the staring end of the laser communication system has entered the capture state; when a flickering spot appears in the field of view of the staring end, the staring end enters the capture state and drives the staring end to move to the position where the spot appears.

[0009] Step 4: Determine whether the scanning end of the laser communication system has entered the capture state; when a flickering spot appears in the field of view of the scanning end, the scanning end enters the capture state and drives the scanning end to move to the position where the spot appears;

[0010] Step 5: Determine whether the scanning end and the staring end of the laser communication system have entered the tracking state; when the distance between the light spot in the field of view of the scanning end or the staring end and its communication center point is greater than the threshold, calculate the step value of the scanning end or the staring end using the two-level deviation algorithm; wherein, the communication center point refers to the centroid position of the light spot generated by the staring end and the scanning end.

[0011] Step 6: The scanning end and the staring end of the laser communication system enter a two-way locked state.

[0012] Optionally, the scanning end and the staring end of the laser communication system are two satellite terminals on different orbits.

[0013] Both the scanning end and the staring end include:

[0014] The camera determines the field of view and detects the signal light emitted from the other end;

[0015] The coarse tracking motor drive is connected to the camera signal to retrieve targets in the camera's field of view;

[0016] The PZT device is pre-aimed and connected to the coarse tracking motor drive to expand the scanning beam and use a small divergence angle signal light to replace the wide divergence angle beacon light.

[0017] The high-speed resonant mirror device for precise tracking is connected to the camera signal to achieve tracking control of signal light with a small divergence angle.

[0018] Optionally, when the staring end enters the staring waiting process, the coarse tracking motor drive device of the staring end starts from the initial position as the first search area, stays in the search area for a certain period of time to scan, and moves forward by a first field of view size to the next search area, stays again, until the search of the uncertain area is completed.

[0019] Optionally, the size of the gaze field of view is a first field of view size.

[0020] Optionally, when the scanning end is in the search state, the coarse tracking motor drive device of the scanning end completes the double-layer square spiral skip scan;

[0021] The initial position is taken as the first dwell position. The first layer of square spiral skip scan starts from the first dwell position and moves in the shape of the first square spiral. Each time, it moves by one second field of view size and stays at the position for a certain period of time to scan. When the scanning end has completed moving in the square spiral shape, it will return to the first dwell position along the same trajectory, and then the second layer of square spiral skip scan will be performed.

[0022] The second layer of square spiral skip scan starts from the first dwell position and moves by one third field of view size, so that the scanning end moves to the next second dwell position, and again uses the second dwell position as the starting point to move and scan according to the first square spiral shape, and completes the first layer of square spiral skip scan once more;

[0023] Similarly, the first layer square spiral skip scan and the second layer square spiral skip scan are performed alternately until the scanning end moves to the last stop position of the second layer square spiral skip scan and completes the first layer square spiral skip scan at that stop position.

[0024] Optionally, the second field of view size is larger than the third field of view size, so that the range of the first layer of spiral step scanning can completely cover the range of the second layer of spiral step scanning; the range of the second layer of spiral step scanning at the scanning end is equal to the field of view size at the staring end.

[0025] Optionally, during the beam expansion scanning process at the staring end, the scanning path of the pre-aiming PZT device is a square spiral skip scan, and the scanning range is the field of view size of the staring end; and the staring waiting time of the staring end in a search area is equal to the time required for the scanning end to complete the second layer of square spiral skip scan.

[0026] Optionally, during the beam expansion scanning process at the scanning end, the second field of view size and the divergence angle size of the beam expansion are the same; when the scanning end completes the second layer of square spiral skip scanning, the third field of view size and the beam expansion scanning range are the same.

[0027] Optionally, a threshold Δt2 for the disappearance time of the light spot is set in both the staring end and the scanning end. When the disappearance time of the light spot in the field of view of the staring end or the scanning end exceeds Δt2, it is determined that the light spot is lost. At this time, the end will re-enter the search state with the current position of the coarse tracking motor drive device as the initial position.

[0028] Optionally, the second-level deviation propagation algorithm is as follows: the deviation value between the position coordinates of the light spot in the field of view and the coordinates of the communication center point is converted into the rotation angle of the fine tracking high-speed resonant mirror device, and the fine tracking high-speed resonant mirror device is driven to complete the rotation angle; at this time, the fine tracking high-speed resonant mirror device deviates from its zero position, and its deviation value from the zero position is converted into the rotation angle of the coarse tracking motor drive device, and the coarse tracking motor drive device is driven to rotate and return to the zero position.

[0029] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0030] In the search phase, this invention utilizes the coordinated scanning of the pre-aiming PZT device and the coarse tracking motor drive device to effectively reduce the difficulty and time of beacon-free search, thereby improving the on-orbit link establishment efficiency of the inter-satellite laser communication system. In the acquisition phase, the coarse tracking motor drive devices at the staring end and the acquisition end move according to the position of the light spot in the field of view, causing the deviation of the light spot from its communication center point in the field of view to continuously converge, thus increasing the probability of successful acquisition by the laser communication system. In the tracking phase, a two-stage deviation propagation algorithm is used to enable the fine tracking high-speed resonant mirror device and the coarse tracking motor drive device of each terminal to cooperate in tracking, further improving the stability and anti-interference capability of beacon-free bidirectional link establishment. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the spiral skip scanning method in the beacon-free inter-satellite laser communication bidirectional link establishment method of the present invention.

[0032] Figure 2 This is a schematic diagram of beam expansion scanning in the beacon-free inter-satellite laser communication bidirectional link establishment method of the present invention.

[0033] Figure 3 This is a schematic diagram of the search state at the scanning end in the beacon-free inter-satellite laser communication bidirectional link establishment method of the present invention.

[0034] Figure 4 This is a flowchart illustrating the beacon-free inter-satellite laser communication bidirectional link establishment method of the present invention.

[0035] Figure 5 This is a schematic diagram illustrating the state changes of the scanning end and the staring end in the beacon-free inter-satellite laser communication bidirectional link establishment method of the present invention. Detailed Implementation

[0036] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] In the description of this invention, it should be noted that the terms "upper," "lower," "left," "right," "vertical," "horizontal," "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 this invention and for simplifying the description, and do not indicate or imply 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 this invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0038] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0039] The laser communication beaconless bidirectional link establishment system of the present invention includes: a scanning end and a staring end; both the scanning end and the staring end include: a camera, a coarse tracking motor drive device, a pre-aiming PZT (lead zirconate titanate piezoelectric ceramic) device, a fine tracking high-speed resonant mirror device, and a control system. The scanning end and staring end of the laser communication system are terminals of two satellites in different orbits; the camera can determine the field of view and detect the signal light emitted from the other end; the coarse tracking motor drive device is connected to the camera signal and can perform large-scale, long-term retrieval of targets in the camera's field of view; the pre-aiming PZT device is connected to the coarse tracking motor drive device and can expand the scanning beam, using small divergence angle signal light to replace wide divergence angle beacon light; the fine tracking high-speed resonant mirror device is connected to the camera signal and can achieve small-range, fast, and high-precision tracking control of small divergence angle signal light; the control system is connected to the camera, coarse tracking motor drive device, pre-aiming PZT device, and fine tracking high-speed resonant mirror device, and can receive, store, and process data, and drive the camera, coarse tracking motor drive device, pre-aiming PZT device, and fine tracking high-speed resonant mirror device to move.

[0040] like Figure 4 As shown, this invention establishes a beaconless bidirectional link establishment method for laser communication based on the aforementioned laser communication beaconless bidirectional link establishment system (hereinafter referred to as "laser communication system"), comprising:

[0041] Step 1: Initialize the scanning and staring ends of the laser communication system. (For example...) Figure 5 As shown in stage 1, based on orbital satellite data, the coarse tracking motor drive devices of the scanning end and staring end of the laser communication system are randomly rotated to an uncertain region by the control system, and this position is taken as the initial position of the terminal, while keeping the line-of-sight deviation between the two terminals within Φmrad.

[0042] The control system sets the terminal velocities of two satellites with different orbits, ensuring that the scanning and staring ends of the laser communication system always move at the same speed but in opposite directions. Simultaneously, time and distance thresholds are set for the scanning and staring ends. The time thresholds include: a duration threshold Δt1ms for the light spot at both ends, and a light spot disappearance threshold Δt2s. The distance thresholds include: a distance threshold Φ1μrd between the light spot in the field of view and its communication center point, and a distance threshold Φ2μrad between the light spot in the field of view at both ends and its communication center point.

[0043] Step 2: After starting the laser communication system, both the scanning end and the staring end simultaneously enter the search state.

[0044] like Figure 5 As shown in stage 2, when the staring end enters the staring waiting process, the coarse tracking motor drive of the staring end starts from the initial position as the first search area, stays in this search area for a certain period of time to scan, and then moves forward by a first field of view size to the next search area, stays there again, and so on, until the search of the uncertain area is completed. During this time, the coarse tracking motor drive always remains at the center position of the visual axis. If the field of view size of the staring end camera is greater than or equal to the uncertain area, the coarse tracking motor drive of the staring end will not move its position.

[0045] Specifically, the size of the field of view at the staring end is a first field of view size θμrad, ensuring that all uncertain areas can be covered; and the staring waiting time t1 of the coarse tracking motor drive device in a search area is equal to the scanning search time at the scanning end.

[0046] like Figure 1 As shown, the coarse tracking motor drive device at the scanning end of the laser communication system adopts the square spiral skip scanning method. As shown in Formula 1, the square spiral skip scanning method involves the coarse tracking motor drive device at the scanning end moving alternately in the horizontal and vertical directions from the initial position. After each horizontal and vertical movement, the length of the horizontal and vertical movement increases by one unit dimension. The unit field of view is the distance between adjacent terminal positions during the horizontal or vertical movement of the optical communication system terminal.

[0047]

[0048] In the formula, (x next y next (x) represents the coordinates of the terminal as it moves to its next stopping position in the horizontal and vertical directions. cur y cur (x) represents the current terminal's position coordinates. step and y stepThese represent a unit dimension of movement of the terminal in the horizontal and vertical directions, respectively. motor y motor ) represents the position coordinates to which the terminal needs to be moved.

[0049] like Figure 3 As shown, when the scanning end initiates the scanning search process, the coarse tracking motor drive device of the scanning end completes a double-layer square spiral skip scan. Taking the initial position as the first dwell position, the first-layer square spiral skip scan starts from the first dwell position and moves according to the shape of a first square spiral, moving one second field of view size at a time and pausing at the current position for a certain period of time to scan. After the scanning end completes the movement and scanning according to the first square spiral shape, it returns to the first dwell position along the same trajectory, and then performs the second-layer square spiral skip scan. The second-layer square spiral skip scan moves one third field of view size from the first dwell position, causing the scanning end to move to the next second dwell position, and again starts from this second dwell position, moving and scanning according to the first square spiral shape to complete the first-layer square spiral skip scan once more. This process continues, with the first-layer square spiral skip scan and the second-layer square spiral skip scan alternating until the scanning end moves to the last dwell position of the second-layer square spiral skip scan and completes the first-layer square spiral skip scan at that dwell position. The second field of view is larger than the third field of view, so that the range of the first layer square spiral skip scan can completely cover the range of the second layer square spiral skip scan, reducing the probability of missed scans, shortening the search time, and increasing the capture probability during the bidirectional link building search process.

[0050] Furthermore, the duration of the gaze end's stay in a search area is equal to the time required for the scanning end to complete the second layer of helical step scanning, and the range of the second layer of helical step scanning of the scanning end is equal to the field of view size θμrad of the gaze end.

[0051] like Figure 2 As shown, while the coarse tracking motor drive devices at the staring end and the scanning end are operating, the pre-aiming PZT devices at both terminals are activated to perform beam expansion scanning. The pre-aiming PZT device can expand the small-angle scanning beam, making it equivalent to a large-angle beam, thereby improving the acquisition probability at the scanning end and the staring end of the laser communication system and shortening the search time.

[0052] During the beam expansion process at the scanning end, the beam expansion scanning range is θ2μrad, which is the same as the first layer square spiral skip scanning range; the second field of view size and divergence angle size are the same. The scanning time to complete one first layer square spiral beam expansion depends on the beam divergence angle θ1μrad (where θ1μrad is the maximum value of the first layer square spiral beam expansion). Figure 2The small circle diameter), the beam expansion scanning range θ2μrad, and the exposure period of the field-of-view camera. Assuming the first layer of the square spiral skip scan requires scanning x1×x1 sites, the relationship between the number of sites and the divergence angle θ1μrad and the beam expansion range θ2μrad is:

[0053]

[0054] Assuming the camera exposure time at each point during the first-layer helical skip scan is Tms, then the time required to complete one first-layer helical skip scan is...

[0055] like Figure 3 As shown, assuming the scanning end needs to scan x2×x2 dwell positions to complete the second layer of spiral skip scanning, and a third field of view size is the beam-expanding scanning range, i.e., θ2μrad, and the second layer spiral skip scanning range of the scanning end is equal to the gaze duration size θμrad, then the relationship between the number of dwell positions and the second layer spiral skip scanning range and the beam-expanding range θ2 is as follows:

[0056]

[0057] At this point, the time required to complete the second layer of the spiral skip scan is t2 = x2 × x2 × t1 ms.

[0058] During the beam-expanding scan at the staring end, the scanning path of the pre-scanning PZT device is a square spiral skip scan, and the scanning range is the field of view size of the staring end. Furthermore, the dwell time of the staring end in a search area is equal to the time required for the scanning end to complete the second layer of square spiral skip scan; therefore, the staring waiting time of the staring end is x2 × x2 × t1 ms.

[0059] Step 3: Determine whether the staring end of the laser communication system has entered the capture state.

[0060] Since both the staring end and the scanning end are scanning in an uncertain region, the light spot from the scanning end will fall into the field of view of the staring end. At this time, the scanning end is still in the search state, and the beam from the scanning end briefly falls into the field of view of the staring end and then quickly leaves, causing the light spot in the field of view of the staring end to flicker.

[0061] If a spot from the scanning end appears in the field of view of the staring end, the staring end enters the capture state and ends the search state of the staring end; if no spot from the scanning end appears in the field of view of the staring end, it continues to be in the search state.

[0062] like Figure 5As shown in stage 3, when the staring end enters the capture state, the scanning end spot in the staring field is a flashing spot. The camera records the position coordinates (x, y) of the scanning end spot each time it appears and sends them to the control system for storage. The control system converts the position coordinates into the rotation angle of the coarse tracking motor drive device and drives the coarse tracking motor drive device of the staring end to move, so that the staring end reaches the position (x, y) where the spot appears, and waits for the spot to appear again.

[0063] The light spot is determined to be lost based on the light spot disappearance time threshold Δt2s. When the light spot disappears in the field of view of the staring end for more than Δt2s, it is determined that the light spot is lost. At this time, the staring end will re-enter the search state with the current position of the coarse tracking motor drive device as the initial position.

[0064] Step 4: Determine whether the scanning end of the laser communication system has entered the capture state.

[0065] When the staring end moves toward the position (x, y) where the light spot appears, the scanning end is still in the search state, causing the beam from the staring end to briefly fall into the field of view of the scanning end. Then, due to the movement of the scanning end, the light spot in its field of view disappears, causing the light spot in the field of view of the scanning end to flicker.

[0066] like Figure 5 As shown in stage 4, when a flickering spot appears at the scanning end, the scanning end will enter the capture state and end the search state. At this time, the scanning end camera will record the position (x', y') of the spot appearing at the staring end and send it to the control system for storage. The control system will convert the position coordinates into the rotation angle of the coarse tracking motor drive device and drive the coarse tracking motor drive device of the scanning end to move, so that the scanning end reaches the position (x', y') of the spot, and wait for the spot to appear again.

[0067] At this time, both the staring end and the scanning end are in the capture state, and they both reposition the coarse tracking motor drive device according to the position of the other's spot. Therefore, when the spot position in the field of view of the staring end or the field of view of the scanning end changes, the rotation angle of the motor will also be updated accordingly, so that the deviation of the spot in the field of view of the staring end and the scanning end from its communication center point (the centroid position of the spot generated by the staring end and the scanning end) will continuously converge.

[0068] Based on the duration threshold Δt1ms of the light spot at the scanning and staring ends, and the distance threshold Φ1μrd between the light spot in the field of view and its communication center point, it is determined whether the beam expansion scanning at the scanning and staring ends has ended. When the duration of the light spot exceeds Δt1ms and the distance between the light spot and the communication center point is less than Φ1μrd, the beam expansion scanning at the scanning and staring ends is stopped to reduce the deviation of the light spot from the communication center point.

[0069] If the time it takes for the light spot to disappear in the field of view of the scanning end exceeds Δt2s, the light spot is determined to be lost. At this time, the scanning end will re-enter the search state with the current position of the coarse tracking motor drive device as the initial position.

[0070] Step 5: Both the scanning end and the staring end of the laser communication system enter the tracking state.

[0071] like Figure 5 As shown in stage 5, the system determines whether to activate the high-speed resonant mirror device for fine tracking based on the distance threshold Φ2μrad between the light spot in the field of view of the scanning end and the staring end and its communication center point.

[0072] When the distance between the light spot in the field of view of the scanning end and its communication center point is greater than Φ2μrad, the fine tracking high-speed resonant mirror device of the scanning end is activated, and the step value of the fine tracking high-speed resonant mirror device is calculated using the second-level deviation algorithm.

[0073] The second-level deviation propagation algorithm is as follows: The control system converts the deviation between the position coordinates (x', y') of the light spot in the scanning end's field of view and the coordinates of its communication center point into the rotation angle of the fine-tracking high-speed resonant mirror device, and drives the fine-tracking high-speed resonant mirror device to complete this rotation angle. At this time, the fine-tracking high-speed resonant mirror device deviates from its zero position. The control system converts the deviation between the fine-tracking high-speed resonant mirror device and its zero position into the rotation angle of the coarse-tracking motor drive device, and drives the coarse-tracking motor drive device to rotate and return to the zero position. At the same time, the process of converting the deviation between the light spot and its communication center point into the rotation angle of the fine-tracking high-speed resonant mirror device, driving the fine-tracking high-speed resonant mirror device to rotate to this angle, and driving the coarse-tracking motor drive device back to the zero position is repeated again, so that the deviation between the light spot in the scanning end's field of view and its communication center point continuously shrinks and converges.

[0074] Meanwhile, when the distance between the light spot in the field of view of the staring end and its communication center point is greater than Φ2μrad, the staring end activates the high-speed resonant mirror device for fine tracking and uses a two-level deviation algorithm to calculate the step value of the high-speed resonant mirror device for fine tracking, so that the deviation value between the light spot in the field of view of the staring end and its communication center point continuously shrinks and converges.

[0075] If, during the tracking process at both the staring and scanning ends, the spot disappears from the field of view at either the scanning or staring end for more than Δt2s, the spot is determined to be lost. In this case, both the scanning and staring ends will re-enter the search state with the current position of the coarse tracking motor drive as the initial position.

[0076] Step 6: The scanning end and the staring end of the laser communication system enter a two-way locked state.

[0077] As the deviation between the light spot in the field of view of the staring end or the scanning end and its communication center point continues to decrease, the light spot in its field of view will change from flickering light to continuous light. When the light spots in the field of view of both the staring end and the scanning end are continuous light, both the scanning end and the staring end lock their respective light spots, completing the beaconless bidirectional link establishment process of laser communication.

[0078] In summary, this invention utilizes a pre-aiming PZT device to scan and expand the small divergence angle signal light, replacing the wide divergence angle beacon light acquisition, in order to complete the spatial search process in the bidirectional link establishment of the laser communication system; and by coarse tracking motor drive device, it improves the acquisition probability and reduces the search time; at the same time, this invention uses a two-stage deviation propagation algorithm to improve the stability and anti-interference of bidirectional link establishment.

[0079] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A beacon-free inter-satellite laser communication bidirectional link establishment method, characterized in that, include: Step 1: Initialize the scanning and staring ends of the laser communication system; Step 2: The scanning end and staring end of the laser communication system enter the search state and expand the scanning beam. When the scanning end is in the search state, the coarse tracking motor drive device included in the scanning end completes the double-layer square spiral skip scan; The initial position is taken as the first dwell position. The first layer of square spiral skip scan starts from the first dwell position and moves in the shape of the first square spiral. Each time, it moves by one second field of view size and stays at the position for a certain period of time to scan. When the scanning end has completed moving in the square spiral shape, it will return to the first dwell position along the same trajectory, and then the second layer of square spiral skip scan will be performed. The second layer of square spiral skip scan starts from the first dwell position and moves by one third field of view size, so that the scanning end moves to the next second dwell position, and again uses the second dwell position as the starting point to move and scan according to the first square spiral shape, and completes the first layer of square spiral skip scan once more; Similarly, the first layer square spiral skip scan and the second layer square spiral skip scan are performed alternately until the scanning end moves to the last stop position of the second layer square spiral skip scan and completes the first layer square spiral skip scan at that stop position. Step 3: Determine whether the staring end of the laser communication system has entered the capture state; when a flickering spot appears in the field of view of the staring end, the staring end enters the capture state and drives the staring end to move to the position where the spot appears. Step 4: Determine whether the scanning end of the laser communication system has entered the capture state; when a flickering spot appears in the field of view of the scanning end, the scanning end enters the capture state and drives the scanning end to move to the position where the spot appears; Step 5: Determine whether the scanning end and the staring end of the laser communication system have entered the tracking state; when the distance between the light spot in the field of view of the scanning end or the staring end and its communication center point is greater than the threshold, calculate the step value of the scanning end or the staring end using the two-level deviation algorithm; wherein, the communication center point refers to the centroid position of the light spot generated by the staring end and the scanning end. Step 6: The scanning end and the staring end of the laser communication system enter a two-way locked state.

2. The beaconless inter-satellite laser communication bidirectional link establishment method according to claim 1, characterized in that, The scanning end and the staring end of the laser communication system are two satellite terminals with different orbits. Both the scanning end and the staring end include: The camera determines the field of view and detects the signal light emitted from the other end; The coarse tracking motor drive is connected to the camera signal to retrieve targets in the camera's field of view; The PZT device is pre-aimed and connected to the coarse tracking motor drive to expand the scanning beam and use a small divergence angle signal light to replace the wide divergence angle beacon light. The high-speed resonant mirror device for precise tracking is connected to the camera signal to achieve tracking control of signal light with a small divergence angle.

3. The beaconless inter-satellite laser communication bidirectional link establishment method according to claim 2, characterized in that, When the staring end enters the staring waiting process, the coarse tracking motor drive device of the staring end starts from the initial position as the first search area, stays in the search area for a certain period of time to scan, and moves forward by a first field of view size to the next search area, stays again, until the search of the uncertain area is completed.

4. The beaconless inter-satellite laser communication bidirectional link establishment method according to claim 3, characterized in that, The size of the field of view at the gazing end is a first field of view size.

5. The beaconless inter-satellite laser communication bidirectional link establishment method according to claim 1, characterized in that, The second field of view is larger than the third field of view, so that the range of the first layer of spiral step scanning can completely cover the range of the second layer of spiral step scanning; the range of the second layer of spiral step scanning at the scanning end is equal to the field of view at the staring end.

6. The beaconless inter-satellite laser communication bidirectional link establishment method according to claim 2, characterized in that, During the beam expansion scanning process at the gaze end, the scanning path of the pre-aiming PZT device is a square spiral skip scan, and the scanning range is the field of view size of the gaze end; and the gaze waiting time of the gaze end in a search area is equal to the time required for the scanning end to complete the second layer of square spiral skip scan.

7. The beaconless inter-satellite laser communication bidirectional link establishment method according to claim 1, characterized in that, During the beam expansion scanning process at the scanning end, the second field of view size and the beam expansion divergence angle size are the same; when the scanning end completes the second layer of square spiral skip scanning, the third field of view size and the beam expansion scanning range are the same.

8. The beaconless inter-satellite laser communication bidirectional link establishment method according to claim 2, characterized in that, A threshold Δt2 is set for the duration of the light spot disappearance in both the staring end and the scanning end. When the duration of the light spot disappearance in the field of view of the staring end or the scanning end exceeds Δt2, the light spot is determined to be lost. At this time, the end will re-enter the search state with the current position of the coarse tracking motor drive device as the initial position.

9. The beaconless inter-satellite laser communication bidirectional link establishment method according to claim 2, characterized in that, The second-level deviation propagation algorithm is as follows: the deviation value between the position coordinates of the light spot in the field of view and the coordinates of the communication center point is converted into the rotation angle of the fine tracking high-speed resonant mirror device, and the fine tracking high-speed resonant mirror device is driven to complete the rotation angle; at this time, the fine tracking high-speed resonant mirror device deviates from its zero position, and its deviation value from the zero position is converted into the rotation angle of the coarse tracking motor drive device, and the coarse tracking motor drive device is driven to rotate and return to the zero position.

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