Intersatellite laser terminal capturing method without rough capturing and tracking device

Abstract

An inter-satellite laser terminal capturing method without a rough capturing and tracking device comprises the following steps: calculating and adjusting a satellite platform to a target attitude according to position information of a target satellite and the satellite and an attitude real-time value of the satellite, and determining a target value of an optical axis pointing vector at the same time; dividing the captured uncertain region (parent region) into a plurality of sub-regions, and numbering the sub-regions according to a rectangular spiral track; enabling the optical axis to point to the first sub-region for light beam scanning, detecting the light spot intensity to recognize an effective light spot, and calculating the angle pointing to the target vector according to the miss distance and the galvanometer angle; if the preset capturing frequency threshold value is reached, the scanning range is narrowed and scanning is continued; when effective light spots are detected again in the reduced scanning area, it is judged that capturing is completed, and a tracking state is switched to; and if all the sub-regions are scanned and are still not captured, ending. According to the invention, efficient and accurate capturing of the inter-satellite laser terminal under the condition of no rough capturing and tracking device is realized, and the reliability and stability of inter-satellite communication are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of spacecraft communication, and particularly to an inter-satellite laser terminal acquisition method without a coarse acquisition and tracking device. Background Art

[0002] As a new type of national informatization infrastructure, the space-based information network system has unique advantages in covering the whole region, the whole airspace and the whole sea area, and can be widely applied to multiple fields such as remote sensing monitoring, weather forecasting, ocean development and military operations. Composed of low-earth orbit constellations and medium-high-earth orbit constellations, and realizing efficient data transmission through inter-satellite laser links, it has become the mainstream technology for future space-based communication. However, the implementation of inter-satellite laser links faces technical challenges, especially the effective acquisition, alignment and tracking of light beams.

[0003] Traditional laser terminal designs include coarse acquisition and tracking devices and fine acquisition and tracking devices, and the corresponding acquisition strategies are also designed for other systems with coarse acquisition and tracking devices. Currently, there are reports on laser terminals without coarse acquisition and tracking devices. For example, the literature Riesing, Kathleen M., et al. “On-orbit results of pointing, acquisition, and tracking for the TBIRD CubeSat mission.” LASE (2023). introduced a method of using a satellite platform to achieve beam pointing and track the communication link between the satellite and the ground, but the acquisition strategy was not introduced in this literature. The literature R. Ruddenklau and G. Schitter, "Optimization of acquisition patterns for establishing inter-CubeSat optical communications," in Journal of Optical Communications and Networking, vol. 16, no. 8, pp. 814-821, August 2024, doi: 10.1364 / JOCN.518004. introduced a method of using a satellite platform to perform skip scanning in the form of a rectangular helix along a spiral in an uncertain area. Each time the satellite platform takes a step, the laser terminal performs scanning in a small range. The literature only carried out simulation analysis on the scanning pattern method, compared the acquisition probabilities under different scanning patterns, and did not give a specific acquisition strategy. The patent literature CN 116318394, "A beaconless composite scanning method for a lightweight laser communication terminal," proposed a method of composite scanning with a two-dimensional turntable and a fine tracking galvanometer. The two-dimensional turntable performs raster spiral skip scanning, and the fine tracking galvanometer performs raster scanning in a sub-region. This patent only introduced the scanning method, but its performance and stability in practical applications still need to be further evaluated and optimized.

[0004] Therefore, although significant progress has been made in the construction and application of the space-based information network system, there are still many technical challenges in the realization of the laser link and the acquisition, alignment, and tracking of the beam. Therefore, researching and developing more advanced and efficient laser terminals and their acquisition strategies is of great significance for promoting the further development of the space-based information network system. Summary of the Invention

[0005] In view of the deficiencies of the above-mentioned existing technologies, the present invention proposes a method for capturing an inter-satellite laser terminal without a coarse acquisition and tracking device, aiming to solve the problem of how the inter-satellite laser terminal can efficiently and accurately capture the target satellite without the assistance of a coarse acquisition device. The present invention solves the problem of missed scanning caused by attitude drift during large-time-scale scanning by dividing the uncertain area (parent area) into several sub-areas; solves the problem of target angle ambiguity caused by fast scanning by calculating the target angle through the detector offset + fine acquisition and tracking angle; further improves the target positioning accuracy by averaging the target angles calculated multiple times; and further improves the capture probability by reducing the uncertain area in gradient.

[0006] The technical solution of the present invention is as follows:

[0007] A method for capturing an inter-satellite laser terminal without a coarse acquisition and tracking device, characterized by comprising the following steps:

[0008] S1. Attitude calculation and adjustment:

[0009] According to the position information of the target satellite and the present satellite and the real-time value of the attitude of the present satellite, calculate the target values of the yaw angle, pitch angle and roll angle required for the satellite platform to be adjusted to the target attitude value; at the same time, calculate the target value of the optical axis pointing vector;

[0010] Adjust the body attitude of the satellite platform to converge it to the target attitude value, and calculate the real-time pointing vector of the optical axis;

[0011] S2. Optical axis pointing and capture area division:

[0012] Receive the target vector and real-time vector of the optical axis pointing, calculate the pointing vector difference, and adjust the angle of the laser terminal so that the optical axis points to the capture uncertain area, that is, the geometric center of the capture parent area;

[0013] According to the size of the capture parent area, the preset size of the capture sub-area and the capture sub-area overlap factor, divide the capture parent area into multiple sub-areas, and number and sort each sub-area according to the rectangular spiral trajectory;

[0014] S3. Beam scanning and capture:

[0015] The laser terminal uses the fine acquisition and tracking device to point the optical axis to the geometric center of the first sub-area and starts to perform beam scanning;

[0016] During the scanning process, use the acquisition and tracking detector to detect the spot intensity. When the spot intensity exceeds the preset threshold, it is regarded as a valid spot, and record the offset of the spot and the current angle of the galvanometer;

[0017] According to the offset and the galvanometer angle, calculate the angle of the pointing target vector;

[0018] If the number of captures reaches the preset threshold, calculate the average value of the effective spot extrapolated pointing target vector angle as the new center of the beam scan, and reduce the scan coverage to 1 / 4 of the current sub-region;

[0019] S4. Capture judgment and control:

[0020] Continue to perform beam scanning within the reduced scan area;

[0021] If the acquisition and tracking detector detects an effective spot again and the spot intensity exceeds the preset threshold, it is determined that the acquisition is completed and the tracking state is entered;

[0022] If no effective spot is detected within the preset capture statistical period, check whether there are still un-scanned sub-regions;

[0023] If there are un-scanned sub-regions, point to the geometric center of the next sub-region and repeat the beam scanning process in step S3;

[0024] If the capture is not completed after all sub-regions have been scanned, end this capture.

[0025] Furthermore, in the step S1, the attitude adjustment of the satellite platform is realized by the attitude control system on the satellite, and the attitude control system includes thrusters, reaction wheels or other attitude control mechanisms.

[0026] Furthermore, in the step S2, each sub-region is numbered and sorted according to the rectangular spiral trajectory. Specifically: the sub-region with the geometric center coinciding with the geometric center of the parent region is numbered 1, and then, the numbers 1, 2, 3...M are assigned to each sub-region in turn according to the rectangular spiral trajectory, where M is the total number of sub-regions divided by the capture parent region.

[0027] Furthermore, in the step S3, it also includes: setting scanning parameters for each sub-region, including the azimuth axis scanning range Xr, that is, the scanning angle range on the horizontal plane; the pitch axis scanning azimuth Yr, that is, the scanning angle on the vertical plane, the scanning step Stp, that is, the angle increment of each scan and the scanning step interval time StpTm, that is, the time interval between two scans; and setting capture parameters, including the capture spot intensity threshold Pthrh, the capture statistical period ΔTm, the capture number threshold Nthrh, that is, how many effective spot detections are required to consider the capture successful, and the capture timer CapTm, which is used to record the duration of each scan attempt.

[0028] Furthermore, in the step S3, according to the off-target amount (Δθ xmn , Δθ ymn ) and the galvanometer angle (θ fxmn , θ fymn), calculate the angle pointing to the target vector, and the formula is as follows:

[0029] θ fxdmn = θ fxmn + Δθ ymn

[0030] θ fydmn = θ fymn + Δθ ymn

[0031] In the formula, θ fxdmn is the X-axis angle of the target vector deduced by the nth effective light spot in the mth sub-region, θ fydmn is the Y-axis angle of the target vector deduced by the nth effective light spot in the mth sub-region, Δθ xmn is the X-axis miss distance of the nth effective light spot in the mth sub-region, Δθ ymn is the Y-axis miss distance of the nth effective light spot in the mth sub-region, θ fxmn is the X-axis angle of the galvanometer corresponding to the nth effective light spot in the mth sub-region, θ fymn is the Y-axis angle of the galvanometer corresponding to the nth effective light spot in the mth sub-region.

[0032] Furthermore, in step S3, calculate the average value of the angles of the effective light spot deduced to point to the target vector, and the formula is as follows:

[0033]

[0034] In the formula, is the average value of the X-axis angle pointing to the target vector, is the average value of the Y-axis angle pointing to the target vector, and Ncap is the number of captures.

[0035] Furthermore, in step S4, the preset capture statistical period is determined according to the relative motion speed between satellites and the performance parameters of the laser terminal.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] 1) By dividing the uncertain area into several sub-regions and using a rectangular spiral trajectory for scanning, the problem of missed scanning caused by attitude drift during large-time-scale scanning is solved.

[0038] 2) Using the light spot miss distance measured by the detector and the current angle of the galvanometer to calculate the angle pointing to the target vector, the problem of target angle ambiguity caused by fast scanning is solved.

[0039] 3) By calculating the target angle multiple times and taking the average value, the target positioning accuracy is further improved.

[0040] 4) After capturing an effective light spot, the average value of the target vector angle is used as the center of the beam scanning, and the scanning coverage range is reduced, further improving the capture probability.

[0041] 5) The present invention solves the problem of how to efficiently and accurately capture a target satellite by an inter-satellite laser terminal without the assistance of a coarse capture device, realizes the precise alignment and capture of the target satellite, and provides reliable technical support for inter-satellite laser communication. Description of the Drawings

[0042] Figure 1 Schematic diagram of sub-region distribution

[0043] Figure 2 is a flowchart of the capture method of the inter-satellite laser terminal without a coarse capture and tracking device according to the present invention Detailed Embodiments

[0044] The present invention will be further described below in conjunction with the drawings and embodiments, but the protection scope of the present invention should not be limited thereby.

[0045] This embodiment provides a capture method for an inter-satellite laser terminal without a coarse capture and tracking device, which realizes efficient and accurate capture of a target satellite. Figure 2 is a flowchart of the capture method of the inter-satellite laser terminal without a coarse capture and tracking device according to the present invention. As shown in the figure, a capture method for an inter-satellite laser terminal without a coarse capture and tracking device includes the following steps:

[0046] Step 1: The satellite platform calculates the attitude adjustment target value of the local satellite and the optical axis pointing vector target value of the laser terminal;

[0047] In inter-satellite laser communication, to ensure that the laser beam can accurately point to and capture the target satellite, it is first necessary to calculate the attitude adjustment target value of the transmitting satellite (local satellite) and the optical axis pointing vector target value of the laser terminal, which is the basis for realizing laser communication capture and tracking. And the calculation period needs to be greater than the platform attitude control stabilization time because the attitude adjustment of the satellite platform is a dynamic process and requires a certain time to reach a stable state. If the calculation period is too short, it may cause the satellite platform to start the laser communication task before it has stabilized to the target attitude, thus affecting the accuracy and reliability of the communication.

[0048] The calculation of these attitude target values is based on the position relationship between the target satellite and the local satellite, and the real-time attitude value of the local satellite. Thus, the target attitude that the satellite platform needs to adjust to is calculated so that the laser terminal can accurately point to the target satellite.

[0049] The attitude adjustment target value of the local satellite includes (α d , β d , γ d ), that is, the yaw angle target value αd the pitch angle target value β d and the roll angle target value γ d .

[0050] The optical axis pointing vector target value, including (Az d , El d ), that is, the pointing vector azimuth target angle Az d , the pointing vector pitch target angle El d ;

[0051] Step 2: The satellite platform adjusts its body attitude to converge to the target attitude value, and calculates the real-time pointing vector of the optical axis (Az p , El p ) according to the real-time attitude value, where Az p is the real-time angle of the pointing vector azimuth, and El p is the real-time angle of the pointing vector pitch;

[0052] Step 3: After the body attitude of the satellite platform converges, transmit the pointing vector target value and the real-time value of the pointing vector to the laser terminal. The laser terminal subtracts the optical axis pointing target vector from the real-time vector to obtain the pointing vector difference where ΔAz is the difference in the pointing vector azimuth angle, and ΔEl is the difference in the pointing vector pitch angle. The fine acquisition and tracking device of the laser terminal adjusts its own angle according to the pointing vector difference to make the optical axis point to the geometric center of the acquisition uncertainty region (hereinafter referred to as the acquisition parent region);

[0053] Step 4: Inject the scanning acquisition parameters. According to the size of the acquisition parent region, the size of the acquisition sub-region, and the acquisition sub-region overlap factor, divide the acquisition parent region into M sub-regions. Number the sub-region with the geometric center coinciding with the geometric center of the parent region as 1, and then sequentially assign numbers 1, 2, 3...M to each sub-region according to the rectangular spiral trajectory. The schematic diagram of the sub-region distribution is shown in the figure. The circles in the figure represent the geometric centers of each sub-region, and the black connecting lines are the sub-region skip trajectories;

[0054] The scanning parameters within the sub-region include the azimuth axis scanning range Xr, the pitch axis scanning azimuth Yr, the scanning step Stp, and the scanning step interval time StpTm; the acquisition parameters include: the acquisition spot intensity threshold Pthrh, the acquisition statistical period ΔTm, the acquisition times threshold Nthrh, and the acquisition timer CapTm;

[0055] Step 5: The laser terminal uses the fine acquisition and tracking device to point the optical axis to the geometric center of the No. 1 sub-region, clears the acquisition statistical period ΔTm, clears the number of acquisition times Ncap, clears the acquisition timer CapTm, and starts to execute the beam scanning; starts the acquisition timer to start timing;

[0056] Step 6: Check whether the capture timer has timed out. If the capture timer has timed out, i.e., CapTm > ΔTm, where CapTm is the capture timer and ΔTm is the capture statistical period, then execute Step 13; otherwise, execute Step 7.

[0057] Step 7: Detect the spot intensity P on the tracking detector. If the spot intensity exceeds the threshold Pthrh, i.e., P > Pthrh, then the spot is valid and execute Step 8; otherwise, the detected spot is invalid in this time and execute Step 6.

[0058] Step 8: Obtain the spot deviation amount (Δθ xmn , Δθ ymn ) measured by the detector, where Δθ xmn is the X-axis deviation amount of the nth valid spot in the mth sub-region, and Δθ ymn is the Y-axis deviation amount of the nth valid spot in the mth sub-region. The current angle of the galvanometer (θ fxmn , θ fymn ), where θ fxmn is the X-axis angle of the galvanometer corresponding to the nth valid spot in the mth sub-region, and θ fymn is the Y-axis angle of the galvanometer corresponding to the nth valid spot in the mth sub-region. Use the following formula to calculate the pointing target vector angle.

[0059] θ fxdmn = θ fxmn + Δθ ymn

[0060] θ fydmn = θ fymn + Δθ ymn

[0061] where θ fxdmn is the X-axis angle of the pointing target vector calculated from the nth valid spot in the mth sub-region, and θ fydmn is the Y-axis angle of the pointing target vector calculated from the nth valid spot in the mth sub-region.

[0062] Step 9: Increment the capture count by 1. Determine whether the capture count exceeds the capture count threshold. If the capture count is greater than or equal to the capture count threshold, i.e., Ncap ≥ Nthrh, then execute Step 10; otherwise, execute Step 6, where Ncap is the capture count and Nthrh is the capture count threshold.

[0063] Step 10: Calculate the average value of the pointing target vector angles calculated from the valid spots in the mth sub-region.

[0064]

[0065] where is the average value of the X-axis angles of the pointing target vector, It is the average angle of the Y-axis of the target vector.

[0066] Step 11: Use the average angle of the target vector as the beam scanning center, and reduce the scanning coverage to 1 / 4 of the sub-region. The number of this scanning region is denoted as m 1 / 4 , keep the other scanning parameters unchanged, and perform beam scanning;

[0067] Step 12: Detect the spot intensity P on the acquisition and tracking detector sub , if the spot intensity exceeds the threshold Pthrh, that is, P sub > Pthrh, it is determined that the acquisition is completed and transferred to the tracking state; otherwise, keep the scanning state until the remote control instruction terminates this acquisition process.

[0068] Step 13: Whether the sub-region number is less than M. If the sub-region number is less than M, execute Step 14; otherwise, end this acquisition process

[0069] Step 14: According to the sub-region number, direct the optical axis to the geometric center of the next sub-region, clear the acquisition times Ncap of ΔTm, clear the acquisition timer CapTm, and start performing beam scanning; start the acquisition timer to start timing, and execute Step 6.

[0070] The acquisition method of the inter-satellite laser terminal without a coarse acquisition and tracking device in this embodiment realizes the efficient and accurate acquisition of the target satellite through fine step design and innovative technical means, and has important practical value and application prospects.

Claims

1. An intersatellite laser terminal capture method without a coarse tracking device, characterized in that: The steps include: S1. Posture calculation and adjustment: According to the position information of the target satellite and the current satellite and the real-time attitude value of the current satellite, the target values ​​of the yaw angle, pitch angle and roll angle required for the satellite platform to adjust to the target attitude value are calculated; at the same time, the target value of the optical axis pointing vector is calculated; Adjusting the satellite platform's main body attitude to make it converge to the target attitude value, and calculating the real-time pointing vector of the optical axis; S2. Optical axis pointing and capture area division: Receive the target vector and real-time vector pointed by the optical axis, calculate the pointing vector difference, and adjust the angle of the laser terminal so that the optical axis points to the capture uncertain area, that is, the geometric center of the capture parent area; According to the size of the captured parent area, the preset size of the captured sub-area and the overlapping factor of the captured sub-area, the captured parent area is divided into a plurality of sub-areas, and each sub-area is numbered and sorted according to a rectangular spiral track; S3. Beam scanning and capture: The laser terminal uses a precision tracking device to point the optical axis to the geometric center of the first sub-area and starts to perform beam scanning; During the scanning process, the spot intensity is detected by the tracking detector. When the spot intensity exceeds the preset threshold, it is regarded as a valid spot, and the off-target amount of the spot and the current angle of the galvanometer are recorded. According to the miss distance and the galvanometer angle, the angle of the vector pointing to the target is calculated; If the number of captures reaches the preset threshold, the average value of the vector angle of the effective spot pointing to the target is calculated as the new center of the beam scan, and the scan coverage is reduced to 1 / 4 of the current sub-area; S4. Capture judgment and control: Continue to perform beam scanning within the reduced scanning area; If the tracking detector detects a valid light spot again and the light spot intensity exceeds the preset threshold, it is determined that the capture is completed and the tracking state is switched; If no effective light spot is detected within the preset capture statistics period, check whether there are any unscanned sub-areas; If there is an unscanned sub-region, point to the geometric center of the next sub-region and repeat the beam scanning process of step S3; If all sub-areas have been scanned but the capture is not completed, the capture is terminated.

2. The intersatellite laser terminal capture method without a coarse tracking device according to claim 1, characterized in that: In step S1, the attitude adjustment of the satellite platform is achieved through an attitude control system on the satellite, which includes a thruster, a reaction wheel or other attitude control mechanisms.

3. The intersatellite laser terminal capture method without a coarse tracking device according to claim 1, characterized in that: In step S2, each sub-area is numbered and sorted according to the rectangular spiral trajectory. Specifically, the sub-area whose geometric center coincides with the geometric center of the parent area is numbered 1, and then, each sub-area is assigned a number 1, 2, 3...M in sequence according to the rectangular spiral trajectory, where M is the total number of sub-areas divided by the captured parent area.

4. The intersatellite laser terminal capture method without a coarse tracking device according to claim 1, characterized in that: The step S3 also includes: setting scanning parameters for each sub-area, including the azimuth axis scanning range Xr, that is, the scanning angle range on the horizontal plane; the pitch axis scanning azimuth Yr, that is, the scanning angle on the vertical plane, the scanning step Stp, that is, the angle increment of each scan and the scanning step interval StpTm, that is, the time interval between two scans; and setting capture parameters, including the capture spot intensity threshold Pthrh, the capture statistical period ΔTm, the capture number threshold Nthrh, that is, the number of valid spot detections after which the capture is considered successful, and the capture timer CapTm, which is used to record the duration of each scanning attempt.

5. The intersatellite laser terminal capture method without a coarse tracking device according to claim 4, characterized in that: In step S3, according to the off-target amount (Δθ xmn , Δθ ymn ) and the galvanometer angle (θ fxmn ,θ fymn ), calculate the angle of the target vector using the following formula: i fxdmn =θ fxmn +Δθ fmn i fydmn =θ fymn +Δθ ymn In the formula, θ fxdmn is the X-axis angle of the target vector calculated by the nth effective spot in the mth sub-area, θ fydmn Δθ is the Y-axis angle of the target vector calculated by the nth effective spot in the mth sub-area, xmn is the X-axis miss distance of the nth effective spot in the mth sub-area, Δθ ymn is the Y-axis miss distance of the nth effective spot in the mth sub-area, θ fxmn is the X-axis angle of the galvanometer corresponding to the nth effective spot in the mth sub-area, θ fymn The Y-axis angle of the galvanometer corresponding to the nth effective light spot in the m-th sub-area.

6. The intersatellite laser terminal capture method without a coarse tracking device according to claim 5, characterized in that: In step S3, the average value of the vector angle of the effective light spot pointing to the target is calculated, and the formula is as follows: In the formula, is the average X-axis angle of the target vector, is the average Y-axis angle of the target vector, and Ncap is the number of captures.

7. The intersatellite laser terminal capture method without a coarse tracking device according to claim 1, characterized in that: In step S4, the preset capture statistics period is determined according to the relative motion speed between satellites and the performance parameters of the laser terminal.

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