A satellite-ground laser communication system and a satellite-ground laser communication link establishment method

Abstract

The application discloses a satellite-to-ground laser communication system and a satellite-to-ground laser communication link establishment method, and relates to the technical field of laser communication, and alleviates the problems that the existing laser communication technology has high system complexity and cost under high-precision pointing requirements, is greatly influenced by external environment, lacks anti-interference capability, and a single light source is easy to fail and further leads to failure of the whole communication task. The satellite-to-ground laser communication system comprises a ground station and a satellite platform, wherein the ground station is provided with a ground station telescope, signal light emitting equipment, a target lamp array and a target lamp array tracking frame; and the target satellite platform comprises a target satellite, and the target satellite comprises a load camera, a satellite-borne laser terminal and a satellite laser terminal receiver. The satellite-to-ground laser communication link establishment method comprises three stages of coarse tracking, establishment of a downlink and establishment of an uplink. The method is suitable for a high-speed laser communication system between a low-orbit satellite and a ground station, and is especially suitable for link establishment in a high-dynamic and strong background interference environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser communication, in particular to the technical field of laser communication link establishment. BACKGROUND

[0002] With the surge in satellite data transmission demand, as a supplement to radio frequency communication, laser communication has the characteristics of short transmission wavelength, high frequency, etc., can carry much more data than radio frequency, and the laser signal is extremely narrow and has high antenna gain, which can effectively resist interference, so laser communication has great advantages in the problems of bandwidth size and anti-interference ability in the field of satellite data transmission. However, the small beam divergence angle of laser also brings a series of technical bottlenecks, as follows.

[0003] High-precision pointing requirements. For narrow-beam laser communication beams, the divergence angle is usually within one hundred microradians, and the satellite attitude control and ground pointing error must reach the microradian level. This directly leads to the need for high-precision attitude control and measurement equipment on the satellite, and the need for additional installation of special acquisition cameras and fast pointing mechanisms on the satellite, increasing system complexity and cost.

[0004] Environmental interference problems. The ground optical environment has strong stray light, especially in the daytime or near-ground optical station scene, and the signal-to-noise ratio is significantly affected. In the existing satellite-ground link acquisition method, if a narrow-beam laser beacon is used, the beacon pointing itself also needs high precision, otherwise it is easy to lose pointing lock. At the same time, there are problems of atmospheric disturbance and beam drift, and large speckle effect.

[0005] Single-point failure risk. The ground beacon beam is usually a single light source, and if a single point fails, it will cause the entire communication task to fail.

[0006] In summary, the existing laser communication technology has the problems of high system complexity and cost under high-precision pointing requirements, large external environmental influence, lack of anti-interference ability, and single light source easy to fail and cause the entire communication task to fail. SUMMARY

[0007] The present application alleviates the problems of high system complexity and cost under high-precision pointing requirements, large external environmental influence, lack of anti-interference ability, and single light source easy to fail and cause the entire communication task to fail in the existing laser communication technology. The present application provides the following scheme:

[0008] Scheme one, a satellite-ground laser communication system, the system includes a ground station and a satellite platform, wherein the ground station is provided with a ground station telescope, a signal light emitting device, a target lamp array and a target lamp array tracking frame; the target satellite platform includes a target satellite, the target satellite includes a load camera, a satellite laser terminal and a satellite laser terminal receiver, wherein:

[0009] The target lamp array is used for emitting a wide-beam light;

[0010] a target lamp array tracking frame, configured to drive the target lamp array to emit a wide beam light to a target satellite;

[0011] a load camera, configured to take a picture of the wide beam light emitted by the target lamp array to obtain a lamp array light spot image;

[0012] a target satellite platform, configured to adjust the attitude of the target satellite according to the lamp array light spot image obtained by the load camera, so that the target satellite points to a ground station;

[0013] a spaceborne laser terminal, configured to emit a narrow beam downlink laser signal;

[0014] a ground station, configured to receive the narrow beam downlink laser signal and emit an uplink laser signal;

[0015] a satellite laser terminal receiver, configured to receive the uplink laser signal.

[0016] Further, in an embodiment of the present application, the width D of the target lamp array is 0.3 meters, and the divergence angle of the target lamp array is 9°.

[0017] Further, in an embodiment of the present application, the target lamp is a narrowband light source, and the wavelength of the narrowband light source is 808 nm;

[0018] A band-pass filter is arranged in front of the narrowband light source, the center wavelength of the band-pass filter is 808 nm, and the bandwidth is 1 nm.

[0019] A high-power diverging optical element is arranged in front of the narrowband light source.

[0020] The relative positions of the narrowband light source, the band-pass filter and the high-power diverging optical element are that the narrowband light source, the high-power diverging optical element and the band-pass filter are sequentially arranged along the light propagation direction.

[0021] Further, in an embodiment of the present application, the target lamp array tracking frame comprises a support component and a rotating component, the rotating component is configured to drive the target lamp array to rotate, and the azimuth angle rotation range of the rotating component is 0°-360°, and the pitch angle rotation range is 0-90°.

[0022] The maximum angular velocity of the azimuth axis of the rotating component is 30° / s, the maximum angular velocity of the pitch axis is 10° / s, the maximum acceleration of the azimuth is 10° / s 2 , and the maximum acceleration of the pitch axis is 5° / s 2 .

[0023] Furthermore, in one embodiment of the present invention, the payload camera has a field of view of 2°, a focal length of 13.3m, a pixel size of 5.5µm, and a resolution of 0.5m; a bandpass filter is disposed in front of the lens of the payload camera, the bandpass filter having a center wavelength of 808nm and a bandwidth of It is 1nm.

[0024] Option 2: A method for establishing a satellite-to-ground laser communication link, the method being implemented based on the satellite-to-ground laser communication system described in Option 1, the method comprising the following steps:

[0025] Step S1: The wide beam of light emitted by the target light array is initially directed at the target satellite, and the target satellite stares at the ground station and obtains an image of the light array spot.

[0026] Step S2: The target satellite platform performs real-time attitude deviation calculation based on the obtained light array spot image, and then uses the satellite attitude control system to adjust the attitude of the target satellite in real time to correct the attitude deviation, so that the target satellite points to the ground station and realizes coarse tracking closed loop.

[0027] Step S3: The target satellite platform performs a corresponding transformation on the coordinate system of the onboard laser terminal based on its own coordinate system, so that the onboard laser terminal is stably pointing at the ground station, thereby realizing the attitude transformation between the satellite platform and the onboard laser terminal.

[0028] In step S4, the spaceborne laser terminal transmits a narrow-beam downlink laser signal to the ground station. The ground station telescope captures the narrow-beam downlink laser signal and forms an image. Based on the position of the spot of the narrow-beam downlink laser signal in the image, the direction of the ground station telescope is adjusted so that the spot position is closer to the center of the image, thereby establishing a downlink laser communication link. Furthermore, the direction of the wide-beam light emitted by the target light array and the laser emission direction of the ground station's signal transmitting equipment are adjusted according to the spot position for precise tracking.

[0029] Step S5: The ground station's signal transmitting equipment transmits a laser signal as an uplink laser signal to the target satellite, and the target satellite captures the uplink laser signal to establish an uplink laser communication link.

[0030] Step S6: Based on the downlink establishment and precise tracking in step S4 and the uplink establishment in step S6, the satellite-to-ground laser communication link is established.

[0031] Furthermore, in one embodiment of the present invention, step S1 includes the following steps:

[0032] Step S11: The target light array tracking frame adjusts the direction of the wide beam of light emitted by the target light array to keep it always pointing at the target satellite;

[0033] In step S12, when the target satellite approaches the ground station, the payload camera is activated to capture the wide beam of light emitted by the target light array to obtain an image of the light array spot.

[0034] Furthermore, in one embodiment of the present invention, the target satellite platform in step S2 performs real-time attitude deviation calculation based on the obtained light array spot image, and the specific steps are as follows:

[0035] Step S21: Extract the relative pixel offset of the light spot in the light array using the light spot centroid extraction algorithm in the light spot image;

[0036] The relative pixel offset of the light array is the deviation of the light array from the center position in the field of view of the payload camera when the satellite is in a certain attitude;

[0037] The relative pixel offset of the light array includes: the amount by which the light spot deviates from the center x-axis. The amount of light spot deviation from the center y-axis ;

[0038] Step S22, based on the relative pixel offset of the lamp array, through

[0039]

[0040] Obtain the angular change about the x-axis of the load camera coordinate system ,in, The pixel size of the load camera along the x-axis is in millimeters. The focal length of the payload camera is in millimeters.

[0041] Step S23, through

[0042]

[0043] Obtain the angular change around the y-axis of the load camera coordinate system ,in, The pixel size of the load camera along the y-axis is in millimeters. The focal length of the payload camera is in millimeters.

[0044] The present invention discloses a satellite-to-ground laser communication system and a satellite-to-ground laser communication link establishment method based on a ground-assisted target light array. This alleviates the problems of existing laser communication technologies, such as high system complexity and cost under high-precision pointing requirements; significant external environmental influence and lack of anti-interference capabilities; and the susceptibility of single light source failure leading to the failure of the entire communication mission. Specific beneficial effects include:

[0045] 1. The space-to-ground laser communication system of this invention includes a target light array, a target light array tracking frame, a payload camera, a target satellite platform, a spaceborne laser terminal, a ground station, and a satellite laser terminal receiver. This invention creatively designs the target light array, relaxing the requirements for the array's own pointing and suppressing ground stray light interference; the payload camera has a large field of view and high ground resolution, used for staring imaging of the ground light array, eliminating the need for an additional dedicated acquisition camera and rapid pointing mechanism on the satellite, effectively reducing system complexity and cost; based on this, the target satellite platform, spaceborne laser terminal, ground station, and satellite laser terminal receiver achieve full-link establishment of space-to-ground laser communication in three stages: coarse tracking, downlink establishment, and uplink establishment. The space-to-ground laser communication system of this invention helps improve the feasibility and robustness of laser communication, significantly reducing the cost of the space-to-ground laser communication system while achieving high-precision pointing. The significant cost reduction lies in the fact that using such a system eliminates the need for acquisition cameras and rapid pointing mechanisms originally required on the satellite, reducing the overall satellite mass and related equipment costs. It also replaces the ground-based beacon light transmitter equipment with a target light array, which costs several hundred yuan, while specialized transmitter equipment costs tens of thousands of yuan. Furthermore, due to the large beam divergence angle of the target light array, the initial pointing accuracy of the ground-based target light array tracking frame is reduced, thus shortening the setup time.

[0046] 2. The satellite-to-ground laser communication link establishment method described in this invention consists of three stages: coarse tracking, downlink establishment, and uplink establishment. In the coarse tracking stage, a target light array deployed by the ground station is controlled by a target light array tracking frame to emit a wide beam of light towards the target satellite. A satellite-side staring image is performed by the payload camera to calculate and correct the target satellite's attitude error, thus achieving a coarse tracking closed loop. In the downlink establishment stage, after coarse tracking is completed, the coordinate system of the onboard laser terminal is transformed accordingly, ensuring the onboard laser terminal stably points and accurately transmits downlink laser signals to the ground station. The ground station receives the downlink laser signals and performs fine tracking closed loop, thus establishing the downlink. In the uplink establishment stage, after the downlink is locked, the ground station transmits uplink laser signals to the satellite. After these three stages are completed, the entire satellite-to-ground laser communication link is established. This invention transforms the reliance on "high-precision satellite pointing" in traditional satellite-to-ground laser communication into a collaborative mechanism of "ground-based wide-beam light source assistance + satellite coarse tracking," thereby alleviating the problems of extremely small downlink laser beam divergence angle and high requirements for initial satellite pointing accuracy in existing laser communication technologies. It also solves the pain points of high cost, low robustness, and poor environmental adaptability.

[0047] The method described in this invention is applicable to high-speed laser communication systems between low-Earth orbit satellites and ground stations, especially for link establishment in high-dynamic, strong background interference environments. Attached Figure Description

[0048] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0049] Figure 1 This is a schematic diagram of the light array pointing and satellite staring as described in Implementation Method 1;

[0050] Figure 2 This is a flowchart of the satellite-to-ground laser communication link establishment method described in Implementation Method Six;

[0051] Figure 3 This is a schematic diagram of the target light array described in Embodiment 2.

[0052] Figure label:

[0053] 1-Ground station telescope tracking frame; 2-Target light array tracking frame; 3-Target light array; 4-Target satellite; 5. Ground station telescope and signal light transmitting equipment. Detailed Implementation

[0054] Various embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. The embodiments described with reference to the drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0055] Implementation Method 1: A satellite-to-ground laser communication system according to this implementation method includes a ground station and a satellite platform. The ground station is equipped with a ground station telescope and signal light transmitting equipment, a target light array, and a target light array tracking frame. The target satellite platform includes a target satellite, which includes a payload camera, an onboard laser terminal, and a satellite laser terminal receiver.

[0056] Target light array, used to emit a wide beam of light;

[0057] A target light array tracking frame is used to drive the target light array to emit a wide beam of light pointing towards the target satellite;

[0058] A payload camera is used to capture the wide beam of light emitted by the target light array and obtain an image of the light array spot.

[0059] The target satellite platform is used to adjust the attitude of the target satellite based on the light array spot image obtained by the payload camera, so that the target satellite points towards the ground station;

[0060] Spaceborne laser terminal unit, used to transmit narrow-beam downlink laser signals;

[0061] The ground station is used to receive the narrow-beam downlink laser signal and to transmit the uplink laser signal;

[0062] Satellite laser terminal receiver, used to receive uplink laser signals.

[0063] In this embodiment, the ground station is used to receive narrow-beam downlink laser signals, preferably through a receiving telescope or a tracking camera.

[0064] In this embodiment, the emission aperture of the spaceborne laser terminal is... The wavelength of the emitted downlink communication laser beam is 80mm. It is 1550 nanometers in size and has a divergence angle of 70 microradians.

[0065] In this embodiment, the distance between the ground station and the target light array is 5m.

[0066] The satellite-to-ground laser communication system described in this embodiment is a satellite-to-ground laser communication system based on a ground-assisted target light array, such as... Figure 1 The diagram illustrates the pointing of the light array and satellite staring. This embodiment designs a target light array, relaxing the requirements for the array's own pointing and suppressing interference from stray ground light. The payload camera has a large field of view and high ground resolution, used for staring imaging of the ground light array. This eliminates the need for a dedicated acquisition camera and rapid pointing mechanism on the satellite, effectively reducing system complexity and cost. Based on this, the target satellite platform, onboard laser terminal, ground station, and satellite laser terminal receiver achieve full-link establishment of space-to-ground laser communication in three stages: coarse tracking, downlink establishment, and uplink establishment. This space-to-ground laser communication system helps improve the feasibility and robustness of laser communication, significantly reducing the cost of the system while achieving high-precision pointing.

[0067] Implementation Method Two: This implementation method further defines the satellite-to-ground laser communication system described in Implementation Method One. In this implementation method, the width D of the target light array is 0.3 meters, and the divergence angle of the target light array is... It is 9°.

[0068] In this embodiment, the target light array consists of multiple target lights, which are preferably distributed at equal intervals, and the distance between adjacent lights is 2cm.

[0069] In this embodiment, the arrangement of the target light array is not limited to the traditional matrix (row × column) arrangement. Optional arrangements include matrix, concentric circles, radial / radial, compact hexagonal (honeycomb) arrangement, linear stripes, and random or semi-random distribution, etc.

[0070] This implementation provides one example, such as Figure 3 As shown, the target light array is arranged in a 4*5 matrix.

[0071] This embodiment further defines the target light array and provides an example of the target light array scheme. In this target light array, the wide beam light energy distribution of the target light is smooth, and the instantaneous fluctuations caused by local turbulence have less impact on overall visibility than those of an extremely narrow beam. In other words, the target light array can stably provide a detectable light source over a wider angular range.

[0072] Compared to traditional narrow-beam laser beacons, the target light array uses multiple narrow-band light sources with spectral filtering, which is compatible with the spectral response of satellite cameras and significantly compresses the background bandwidth. Therefore, the light array can still be reliably detected by the target satellite payload camera even in daylight or under strong background light conditions. It can effectively suppress stray light interference from the ground environment, thereby improving the signal-to-noise ratio of beacon detection. Furthermore, by using a wider divergence angle as the active light source, the requirements for the initial pointing of the light array itself are greatly relaxed, reducing the dependence on the initial pointing accuracy of the light source itself. This reduces the initial pointing accuracy of the target satellite from the traditional 0.2° level (field of view of the dedicated acquisition camera) to 2° level (field of view of the main payload camera), significantly relaxing the design constraints of the satellite attitude control system.

[0073] Furthermore, existing ground beacon beams are mostly single light sources. If a single point fails, the entire communication mission will fail. The target light array designed in this embodiment consists of multiple independent light sources, so that a single point failure does not affect the overall performance and enhances the system's fault tolerance.

[0074] Implementation Method 3: This implementation method further defines the star-to-ground laser communication system described in Implementation Method 2. In this implementation method, the target light is a narrowband light source with a wavelength of 808nm.

[0075] A bandpass filter is placed in front of the narrowband light source. The center wavelength of the bandpass filter is 808 nm, and the bandwidth is... It is 1nm;

[0076] A high-power diverging optical element is placed in front of the narrowband light source;

[0077] The narrowband light source, the bandpass filter, and the high-power diverging optical element are arranged in sequence along the direction of light propagation.

[0078] This embodiment further defines the target lamp and provides an example of the target lamp scheme. The target lamp has the following effects:

[0079] (1) Light source wavelength: By selecting a light source wavelength of 808nm (near-infrared light), it is compatible with the spectral response of the satellite payload camera and facilitates light filtering. At the same time, by using an 808nm narrowband light source, the satellite camera can add a filter to compress the background stray light bandwidth from visible light (several hundred nanometers) to 1 nanometer, thereby improving the observation signal-to-noise ratio. In this way, even during the day or when the sun is close to the horizon, the light array can still be effectively detected, improving the link acquisition success rate.

[0080] (2) Bandpass filter: By setting bandpass filters in all target lamp arrays, background stray light of other wavelengths is suppressed;

[0081] (3) High-power diverging optical elements: By equipping each light source with a high-power diverging optical element, the total divergence angle of the light array can cover a range of several degrees, and the pointing accuracy requirement of the target light array tracking frame is low. It is only necessary to keep it at less than 1° to ensure that the payload camera can see the target light array.

[0082] (4) The relative positions of the narrowband light source, the bandpass filter and the high-power diverging optical element are arranged in sequence along the light propagation direction, so that the light from the light source forms a diverging beam through the diverging optical element and is filtered by the bandpass filter.

[0083] Implementation Method 4: This implementation method further defines the star-to-ground laser communication system described in Implementation Method 1. In this implementation method, the target light array tracking frame includes a support component and a rotating component. The rotating component is used to drive the target light array to rotate. The azimuth angle rotation range of the rotating component is 0°~360°, and the pitch angle rotation range is 0~90°.

[0084] The maximum angular velocity of the azimuth axis of the rotating component is 30° / s, the maximum angular velocity of the pitch axis is 10° / s, and the maximum azimuth acceleration is 10° / s. 2 The maximum acceleration along the pitch axis is 5° / s². 2 .

[0085] In this embodiment, it is preferable to use a preset scanning mode that covers the region of satellite attitude uncertainty.

[0086] This embodiment further defines the target light array tracking frame and provides an example of the target light array tracking frame scheme. The target light array tracking frame uses a program to control the target light array, ensuring that the target light array is oriented in the approximate direction of the satellite. Because the target light array has a large divergence angle, it is only necessary to ensure that the orientation error of the light array is less than 1 degree to make the light array spot visible to the satellite. Therefore, the target light array tracking frame can work in conjunction with the target light array to further address the pain points of high cost, low robustness, and poor environmental adaptability in existing laser communication technologies.

[0087] Implementation Method 5: This implementation method further defines the satellite-to-ground laser communication system described in Implementation Method 1. In this implementation method, the payload camera has a field of view of 2°, a focal length of 13.3m, a pixel size of 5.5µm, and a resolution of 0.5m. A bandpass filter is provided in front of the payload camera lens, the center wavelength of the bandpass filter being 808nm and the bandwidth being... It is 1nm.

[0088] This embodiment further defines the payload camera and provides an example. The payload camera has high ground resolution and is used to stare at the ground, ensuring coverage of the ground target light array when the satellite attitude error is within ±1°. Furthermore, to meet the high-precision requirements of satellite-to-ground laser communication link establishment, existing systems require the additional installation of a dedicated acquisition camera and rapid pointing mechanism on the target satellite, resulting in high complexity and cost. The payload camera described in this embodiment utilizes a payload camera with a large field of view and high ground resolution to stare at and image the ground light array and acquire light spot images, facilitating subsequent attitude adjustments for the target satellite and effectively reducing system complexity and cost.

[0089] Implementation Method Six: A method for establishing a satellite-to-ground laser communication link, wherein the method is implemented based on any one of the satellite-to-ground laser communication systems described in Implementation Methods One to Five, such as... Figure 2 As shown, the method includes the following steps:

[0090] Step S1: The wide beam of light emitted by the target light array is initially directed at the target satellite, and the target satellite stares at the ground station and obtains an image of the light array spot.

[0091] Step S2: The target satellite platform performs real-time attitude deviation calculation based on the obtained light array spot image, and then uses the satellite attitude control system to adjust the attitude of the target satellite in real time to correct the attitude deviation, so that the target satellite points to the ground station and realizes coarse tracking closed loop.

[0092] Step S3: The target satellite platform performs a corresponding transformation on the coordinate system of the onboard laser terminal based on its own coordinate system, so that the onboard laser terminal is stably pointing at the ground station, thereby realizing the attitude transformation between the satellite platform and the onboard laser terminal.

[0093] In step S4, the spaceborne laser terminal transmits a narrow-beam downlink laser signal to the ground station. The ground station telescope captures the narrow-beam downlink laser signal and forms an image. Based on the position of the spot of the narrow-beam downlink laser signal in the image, the direction of the ground station telescope is adjusted so that the spot position is closer to the center of the image, thereby establishing a downlink laser communication link. Furthermore, the direction of the wide-beam light emitted by the target light array and the laser emission direction of the ground station's signal transmitting equipment are adjusted according to the spot position for precise tracking.

[0094] Step S5: The ground station's signal transmitting equipment transmits a laser signal as an uplink laser signal to the target satellite, and the target satellite captures the uplink laser signal to establish an uplink laser communication link.

[0095] Step S6: Based on the downlink establishment and precise tracking in step S4 and the uplink establishment in step S6, the satellite-to-ground laser communication link is established.

[0096] In this embodiment, the coordinate system transformation of the spaceborne laser terminal unit described in step S3 is performed accordingly. Since there is a fixed transformation relationship between the satellite platform's own coordinate system and the spaceborne laser terminal unit's coordinate system, step S5...

[0097]

[0098] Obtain the overall attitude of the spaceborne laser terminal pointing into inertial space. ,in, Let be the attitude matrix of the target satellite from its fuselage coordinate system to its inertial coordinate system. The attitude offset of the spaceborne laser terminal in the fuselage coordinate system;

[0099] During the coarse tracking phase, the satellite platform's attitude adjustment has already affected the attitude matrix. The error is very small, so at this point, it is only necessary to offset according to the known attitude. Only minor adjustments need to be made to the satellite transmitter.

[0100] In this embodiment, the precise tracking described in step S4 is achieved by the ground station detecting the spot position of the narrow-beam downlink laser signal, the detector measuring the position deviation of the downlink signal, generating feedback to drive the telescope turntable and fast-reflecting mirror to keep the received spot at the center of the ground station. By controlling the closed loop, a tracking accuracy of several micro-radians can be achieved, thereby realizing precise tracking.

[0101] The satellite-to-ground laser communication link establishment method described in this embodiment is a satellite-to-ground laser acquisition and tracking link establishment method based on a ground-assisted target light array. The target light array is initially pointed at the target satellite, the target satellite stares at the ground station, and the light array spot image is obtained. The attitude error of the target satellite is calculated and corrected based on the obtained light array spot image to achieve coarse tracking closed loop.

[0102] After coarse tracking is completed, the coordinate system of the spaceborne laser terminal is transformed accordingly, so that the spaceborne laser terminal can stably point and accurately transmit downlink laser signals to the ground station; the ground station receives the downlink laser signals and performs fine tracking closed loop to establish the downlink. At this time, the pointing accuracy of the ground station to the satellite can reach the microradian level, ensuring a stable downlink.

[0103] After downlink lock-on, the ground station transmits an uplink laser signal to the satellite. Since the ground station has corrected most errors through fine tracking, the uplink laser can successfully enter the satellite's laser receiver. The angular deviation of the ground station's telescope alignment point can be controlled to the microradian level after fine tracking. Because the downlink closed loop is stable, the ground uplink signal directly enters the satellite laser receiver. After reception by the satellite, a two-way closed loop is formed: the satellite tracks and measures the ground light array and the uplink signal, while the ground station provides feedback on the satellite's downlink signal and its own aiming system, achieving full two-way fine alignment and thus completing the full link establishment. This alleviates the problems of extremely small downlink laser beam divergence angle and high initial pointing accuracy requirements of existing laser communication technologies, and solves the pain points of high cost, low robustness, and poor environmental adaptability.

[0104] This embodiment provides an example where, when the satellite is hundreds of kilometers away from the ground station, after detecting the light array using a target satellite payload camera with a field of view of 2 degrees, the calculated attitude adjustment can rapidly reduce the pointing error from the degree level to the 0.2° level. Subsequently, the downlink laser divergence angle is approximately 70 microradians, the ground receiving aperture is relatively large, and the link signal-to-noise ratio is very high. In this embodiment, a pointing accuracy of 1 milliradian is sufficient to successfully establish a link, while the initial allowable error is increased to 2° (approximately 34 milliradians), reducing the alignment difficulty by tens of times.

[0105] Implementation Method Seven: This implementation method further defines the satellite-to-ground laser communication link establishment method described in Implementation Method Six. In this implementation method, step S1 includes the following steps:

[0106] Step S11: The target light array tracking frame adjusts the direction of the wide beam of light emitted by the target light array to keep it always pointing at the target satellite;

[0107] In step S12, when the target satellite approaches the ground station, the payload camera is activated to capture the wide beam of light emitted by the target light array to obtain an image of the light array spot.

[0108] The implementation further defines step S1 and provides an example of it. Step S1 uses the target light array tracking frame to adjust the target light array to point at the target satellite. As long as the orientation error of the light array is less than 1 degree, the satellite can see the light array spot, without the need for extremely high pointing accuracy. When the target satellite approaches the ground station, the payload camera takes a picture of the light array to obtain an image of the light array spot, which provides a basis for subsequent attitude adjustment of the target satellite. Moreover, the payload camera has a large field of view and high ground resolution. Compared with the dedicated acquisition camera and fast pointing mechanism used in the prior art, the payload camera effectively reduces the system complexity and cost.

[0109] Implementation method eight is a further limitation on the satellite-to-ground laser communication link establishment method described in implementation method six. In this implementation method, the target satellite platform in step S2 performs real-time attitude deviation calculation based on the obtained light array spot image. The specific steps are as follows:

[0110] Step S21: Extract the relative pixel offset of the light spot in the light array using the light spot centroid extraction algorithm in the light spot image;

[0111] The relative pixel offset of the light array is the deviation of the light array from the center position in the field of view of the payload camera when the satellite is in a certain attitude;

[0112] The relative pixel offset of the light array includes: the amount by which the light spot deviates from the center x-axis. The amount of light spot deviation from the center y-axis ;

[0113] Step S22, based on the relative pixel offset of the lamp array, through

[0114]

[0115] Obtain the angular change about the x-axis of the load camera coordinate system ,in, The pixel size of the load camera along the x-axis is in millimeters. The focal length of the payload camera is in millimeters.

[0116] Step S23, through

[0117]

[0118] Obtain the angular change around the y-axis of the load camera coordinate system ,in, The pixel size of the load camera along the y-axis is in millimeters. The focal length of the payload camera is in millimeters.

[0119] The implementation further defines step S2, providing an example of the real-time attitude deviation calculation scheme described in step S2. Specifically, step S2 involves using a satellite attitude control system to adjust the attitude of the target satellite. This means the target satellite uses the attitude deviation as feedback to initiate an attitude control algorithm to adjust its attitude. As the attitude control system operates, the satellite attitude error... It will rapidly decay to zero, achieving precise coarse alignment. During this process, the payload camera continuously monitors the position of the light array to form a closed-loop control: error feedback is continuously used to correct the attitude until the light array spot is centered on the payload camera. The satellite attitude control accuracy is approximately 0.2°. Its attitude stability is 0.00035° / s, which far exceeds the requirements for coarse aiming.

Claims

1. A satellite-to-ground laser communication system, characterized in that, The system includes a ground station and a satellite platform. The ground station is equipped with a ground station telescope and signal light transmitting equipment, a target light array, and a target light array tracking frame. The target satellite platform includes a target satellite, which comprises a payload camera, an onboard laser terminal, and a satellite laser terminal receiver. Target light array, used to emit a wide beam of light; A target light array tracking frame is used to drive the target light array to emit a wide beam of light pointing towards the target satellite; A payload camera is used to capture the wide beam of light emitted by the target light array and obtain an image of the light array spot. The target satellite platform is used to adjust the attitude of the target satellite based on the light array spot image obtained by the payload camera, so that the target satellite points towards the ground station; Spaceborne laser terminal unit, used to transmit narrow-beam downlink laser signals; The ground station is used to receive the narrow-beam downlink laser signal and to transmit the uplink laser signal; Satellite laser terminal receiver, used to receive uplink laser signals.

2. The satellite-to-ground laser communication system according to claim 1, characterized in that, The target light array has a width D of 0.3 meters and a divergence angle of 0.3 meters. It is 9°.

3. The satellite-to-ground laser communication system according to claim 2, characterized in that, The target light array includes multiple target lights, each of which is a narrowband light source with a wavelength of 808nm. A bandpass filter is placed in front of the narrowband light source. The center wavelength of the bandpass filter is 808 nm, and the bandwidth is... It is 1nm; A high-power diverging optical element is placed in front of the narrowband light source; The narrowband light source, bandpass filter, and high-power diverging optical element are arranged in sequence along the light propagation direction.

4. The satellite-to-ground laser communication system according to claim 1, characterized in that, The target light array tracking frame includes a support component and a rotating component. The rotating component drives the target light array to rotate. The azimuth angle rotation range of the rotating component is 0°~360°, and the pitch angle rotation range is 0~90°. The maximum angular velocity of the azimuth axis of the rotating component is 30° / s, the maximum angular velocity of the pitch axis is 10° / s, and the maximum azimuth acceleration is 10° / s. 2 The maximum acceleration along the pitch axis is 5° / s². 2 .

5. The satellite-to-ground laser communication system according to claim 1, characterized in that, The payload camera has a field of view of 2°, a focal length of 13.3m, a pixel size of 5.5um, and a resolution of 0.5m; a bandpass filter is set in front of the lens of the payload camera, the center wavelength of the bandpass filter is 808nm, and the bandwidth Δλ is 1nm.

6. A method for establishing a satellite-to-ground laser communication link, characterized in that, The method is implemented based on the satellite-to-ground laser communication system according to any one of claims 1-5, and the method includes the following steps: Step S1: The wide beam of light emitted by the target light array is initially directed at the target satellite, and the target satellite stares at the ground station and obtains an image of the light array spot. Step S2: The target satellite platform performs real-time attitude deviation calculation based on the obtained light array spot image, and then uses the satellite attitude control system to adjust the attitude of the target satellite in real time to correct the attitude deviation, so that the target satellite points to the ground station and realizes coarse tracking closed loop. Step S3: The target satellite platform performs a corresponding transformation on the coordinate system of the onboard laser terminal based on its own coordinate system, so that the onboard laser terminal is stably pointing at the ground station, thereby realizing the attitude transformation between the satellite platform and the onboard laser terminal. In step S4, the spaceborne laser terminal transmits a narrow-beam downlink laser signal to the ground station. The ground station telescope captures the narrow-beam downlink laser signal and forms an image. Based on the position of the spot of the narrow-beam downlink laser signal in the image, the direction of the ground station telescope is adjusted so that the spot position is closer to the center of the image, thereby establishing a downlink laser communication link. Furthermore, the direction of the wide-beam light emitted by the target light array and the laser emission direction of the ground station's signal transmitting equipment are adjusted according to the spot position for precise tracking. Step S5: The ground station's signal transmitting equipment transmits a laser signal as an uplink laser signal to the target satellite, and the target satellite captures the uplink laser signal to establish an uplink laser communication link. Step S6: Based on the downlink establishment and precise tracking in step S4 and the uplink establishment in step S6, the satellite-to-ground laser communication link is established.

7. The satellite-to-ground laser communication link establishment method according to claim 6, characterized in that, Step S1 includes the following steps: Step S11: The target light array tracking frame adjusts the direction of the wide beam of light emitted by the target light array to keep it always pointing at the target satellite; In step S12, when the target satellite approaches the ground station, the payload camera is activated to capture the wide beam of light emitted by the target light array to obtain an image of the light array spot.

8. The satellite-to-ground laser communication link establishment method according to claim 6, characterized in that, Step S2 describes the target satellite platform performing real-time attitude deviation calculation based on the obtained light array spot image. The specific steps are as follows: Step S21: Extract the relative pixel offset of the light spot in the light array using the light spot centroid extraction algorithm in the light spot image; The relative pixel offset of the light array is the deviation of the light array from the center position in the field of view of the payload camera when the satellite is in a certain attitude; The relative pixel offset of the light array includes: the amount by which the light spot deviates from the center x-axis. The amount of light spot deviation from the center y-axis ; Step S22, based on the relative pixel offset of the lamp array, through Obtain the angular change about the x-axis of the load camera coordinate system ,in, The pixel size of the load camera along the x-axis is in millimeters. The focal length of the payload camera is in millimeters. Step S23, through Obtain the angular change around the y-axis of the load camera coordinate system ,in, The pixel size of the load camera along the y-axis is in millimeters. The focal length of the payload camera is in millimeters.

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