Double-satellite remote sensing system and method based on inter-satellite laser communication and tracking and pointing integration

Abstract

The invention discloses a double-satellite remote sensing system and method based on inter-satellite laser communication and tracking and pointing integration, and relates to the technical field of space remote sensing. The system is composed of a first satellite and a second satellite which fly back and forth in the same orbital plane, and the first satellite and the second satellite are respectively provided with a multispectral camera, a hyperspectral camera and a transmission system integrating tracking and pointing, inter-satellite laser communication and multi-dimensional calibration functions. The transmission system comprises an inter-satellite laser communication load and a Beidou short message backup load, a stable laser link can be established autonomously, and tracking and pointing precision is guaranteed through three calibration modes of fixed star, satellite-ground and inter-satellite. The system transmits trigger information through an inter-satellite laser link, and realizes collaborative observation of multispectral general survey-hyperspectral detailed survey. The method comprises the steps of calibration preposition, laser link establishment, collaborative observation, calibration maintenance and the like, and supports data collaboration and emergency communication. The timeliness and observation precision of double-satellite remote sensing are improved, and the high-reliability and high-timeliness requirements of scenes such as earth surface anomaly monitoring and the like can be met.

Description

A dual-satellite remote sensing system and method based on inter-satellite laser communication and tracking. Technical Field

[0001] This invention relates to the field of aerospace remote sensing technology, and in particular to a dual-satellite remote sensing system and method based on inter-satellite laser communication and tracking integration. Background Technology

[0002] Earth observation remote sensing satellite systems are developing towards collaborative observation with high timeliness, high resolution, and high spectral resolution. Among these, collaborative remote sensing systems, composed of multiple satellites and communicating data and commands via inter-satellite links, can significantly improve the ability to repeatedly observe specific areas and the efficiency of rapid detection and detailed investigation of anomalous targets. In such systems, the performance of the inter-satellite data links directly determines the real-time performance and level of intelligence of the two-satellite collaboration.

[0003] Currently, dual-satellite or multi-satellite collaborative remote sensing systems primarily employ microwave communication as the means of inter-satellite data transmission. However, microwave communication links have inherent limitations: First, their available bandwidth is limited, making it difficult to meet the transmission rate requirements for real-time relay of high-resolution multispectral and hyperspectral remote sensing data; second, microwave antennas have wide beams, and establishing precisely oriented inter-satellite links typically requires complex initial acquisition and tracking systems, resulting in long link establishment times and making them unsuitable for fast-response collaborative observation scenarios; furthermore, traditional inter-satellite communication systems and attitude tracking systems are often designed separately, increasing system mass, power consumption, and complexity, and reducing overall reliability.

[0004] Furthermore, existing dual-satellite collaborative modes are often relatively fixed, lacking the intelligent collaborative capability to dynamically schedule tasks and route data based on real-time on-orbit status (such as satellite power, storage capacity, and satellite-to-ground link visibility). When the primary inter-satellite communication link is blocked, the system also lacks a reliable backup communication mechanism to ensure the transmission of critical commands and data.

[0005] Therefore, there is an urgent need in this field for a novel dual-satellite remote sensing system and method to solve the problems of insufficient inter-satellite communication bandwidth, slow link establishment speed, high system complexity, and poor collaborative flexibility in the existing technology, so as to achieve fast, reliable, and efficient dual-satellite intelligent collaborative remote sensing. Summary of the Invention

[0006] The purpose of this invention is to provide a dual-satellite remote sensing system and method based on integrated inter-satellite laser communication and tracking. By employing integrated inter-satellite laser communication and tracking technology, high bandwidth, rapid autonomous link establishment, and stable tracking are achieved. Simultaneously, an intelligent collaborative mechanism is constructed, enabling the two satellites to dynamically schedule their operations based on mission and resource status, ultimately achieving rapid, accurate, and efficient collaborative Earth observation.

[0007] To achieve the above objectives, this invention provides a dual-satellite remote sensing system based on inter-satellite laser communication and tracking integration, comprising a first satellite and a second satellite that fly forward and backward in the same orbital plane and work collaboratively, wherein:

[0008] The first satellite carries a multispectral camera for wide-area surveys, a first on-board processing unit, and a first transmission payload.

[0009] The second satellite carries a hyperspectral camera for detailed investigation, a second on-board processing unit, and a second transmission payload;

[0010] Both the first and second transmission payloads include inter-satellite laser communication payloads, which are used to autonomously establish and maintain a two-way laser communication link between the two satellites and to achieve high-precision beam tracking.

[0011] The first on-board processing unit is configured to: process multispectral camera data to identify targets of interest and generate observation trigger commands;

[0012] The system is configured to send the observation trigger command from the first satellite to the second satellite via the inter-satellite laser communication link, triggering the hyperspectral camera of the second satellite to conduct collaborative observation of the target area.

[0013] Preferably, the optical head serves as an optical signal transceiver and tracking actuator, comprising a coarse tracking servo turntable, an optical antenna, a rear optical path module, a beacon laser transceiver module, and a capture and tracking control module;

[0014] The processor, serving as the power supply, signal processing, and communication hub, includes a secondary power supply module, a comprehensive signal processing module, and an optical fiber power amplifier module.

[0015] Preferably, the rear optical path module includes a tracking detector and a communication detector; the tracking detector is used to convert the received spatial optical signal into an electrical signal and calculate the beam pointing angle error and tracking error; the communication detector is used to convert the spatial laser communication signal into an electrical baseband signal.

[0016] The beacon laser transceiver module includes a beacon laser and a CMOS detector. The beacon laser is used to emit beacon light for auxiliary capture, and the CMOS detector is used to receive the beacon light from the other party and realize star calibration function.

[0017] The capture and tracking control module is connected to the capture and tracking detector, CMOS detector, coarse tracking servo turntable and fine tracking unit, and is used to complete image signal processing, turntable driving, fast mirror control and capture and tracking process control.

[0018] Preferably, the integrated signal processing module is used to complete the encoding, modulation, demodulation and decoding of communication signals, generate the transmitted laser seed signal, and perform payload workflow control, telemetry and remote control, and information interaction with the satellite platform;

[0019] The fiber optic power amplifier module is connected to the integrated signal processing module and is used to amplify the emitted laser seed signal at high power.

[0020] The secondary power supply module is used to isolate and convert the primary power supply of the satellite platform into the secondary power supply required by each module inside the payload.

[0021] Preferably, the inter-satellite laser communication payload has multi-mode on-orbit calibration capability, including:

[0022] The star pointing calibration mode uses the CMOS detector to image stars and combines them with satellite attitude data to calibrate the installation matrix error between the payload body coordinate system and the satellite attitude reference.

[0023] The coaxiality calibration mode uses optical references internal to the payload or between satellites to calibrate the coaxiality error between the transmitting optical axis, the receiving optical axis, and the tracking optical axis.

[0024] The inter-satellite pointing calibration mode uses bidirectional tracking data to fit and correct pointing deviations in real time after the link is established, maintaining long-term tracking accuracy.

[0025] Preferably, the first and second transmission payloads further include the BeiDou short message communication payload, which serves as an emergency backup for the inter-satellite laser communication link. When the laser link is interrupted, it automatically or in a controlled manner switches to the short message link to transmit key instructions and status information.

[0026] The dual-satellite remote sensing method based on inter-satellite laser communication and tracking integration, implemented in the aforementioned system, includes the following steps:

[0027] Link initialization steps: After the two satellites enter orbit, the inter-satellite laser communication payload performs on-orbit unlocking, self-testing and calibration procedures to complete the initialization of pointing accuracy and optical axis consistency;

[0028] Laser link autonomous establishment steps: Based on the calibration results and orbital parameters, the two satellites autonomously establish and lock a stable inter-satellite bidirectional laser communication link through beacon light scanning, bidirectional acquisition, and coarse-fine composite tracking control;

[0029] Collaborative observation triggering steps: The first satellite uses a multispectral camera to perform wide-area imaging, identifies the target after on-board processing, generates a triggering command containing the target's location, and sends it to the second satellite in real time through the laser communication link;

[0030] Hyperspectral detailed investigation steps: After receiving the trigger command, the second satellite schedules the hyperspectral camera to perform rapid pointing and fine spectral imaging of the designated target area.

[0031] Preferably, the laser link autonomous establishment step specifically includes:

[0032] Open-loop pointing sub-step of the program: The two satellites calculate the relative pointing angle based on the orbit prediction and the calibrated installation matrix, and control the coarse tracking servo turntable to drive the optical antenna to point to the expected position;

[0033] Scanning and Acquisition Sub-steps: One satellite's beacon laser emits beacon light to scan the area; the other satellite's tracking detector captures the beacon light, calculates the error, adjusts its own pointing, and simultaneously emits a response beacon light.

[0034] Coarse and fine tracking closed-loop sub-steps: Based on the error signal of the tracking detector, both parties switch to composite axis tracking. The coarse tracking servo turntable compensates for large-range, low-frequency deviations, and the fine tracking fast-reflection mirror suppresses high-frequency micro-vibrations to achieve stable alignment of the line of sight.

[0035] Communication link establishment steps: After tracking stabilizes, both parties switch the laser to the communication wavelength, and the integrated signal processing module and the fiber optic power amplifier module work together to start high-speed data transmission.

[0036] Preferably, in the coarse-fine tracking closed-loop sub-step, a composite axis control strategy based on feedforward compensation is adopted:

[0037] The coarse tracking loop takes the low-frequency error calculated by the tracking detector as input and drives the servo turntable to perform low-speed, wide-range tracking.

[0038] The fine tracking loop performs windowing processing on the tracking detector signal to obtain high frame rate error, and drives the fast-reflection mirror to perform high-speed and precise calibration.

[0039] The capture and tracking control module combines real-time trajectory, attitude, and calibration parameters to generate feedforward compensation, which is then injected into the coarse and fine tracking loops to improve the tracking performance for dynamic relative motion.

[0040] Preferably, the method further includes data collaborative management and downlink steps:

[0041] The hyperspectral detailed survey data acquired by the second satellite is transmitted to the first satellite in real time or near real time via the inter-satellite laser communication link.

[0042] The onboard processing unit of the first satellite fuses the multispectral survey data and the hyperspectral detailed survey data to generate a fused product.

[0043] Based on the real-time geometric relationship between the two satellites and the ground station, the optimal satellite is dynamically selected, and the fused product or raw data is transmitted to the ground through the satellite's data transmission system.

[0044] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0045] (1) Achieved highly efficient and reliable intelligent collaborative observation: Through inter-satellite laser links and intelligent task scheduling, the survey satellites and detailed survey satellites can quickly take over the work, greatly shortening the response time from target discovery to detailed analysis, and improving the system's ability to observe dynamic targets and emergency tasks.

[0046] (2) Significantly improved the overall performance and system integration of inter-satellite links: By adopting an integrated design of communication and tracking and composite axis tracking technology, while ensuring high-bandwidth data transmission, it has achieved fast and stable autonomous link establishment and precise tracking, which simplifies the system configuration and improves reliability.

[0047] (3) Enhanced system flexibility and mission adaptability: It has dynamic mission scheduling and multi-link (laser / BeiDou) redundant communication capabilities, and can autonomously optimize the workflow according to on-board resources, link status and mission priority, effectively responding to complex space environment and changing observation needs.

[0048] (4) Improved overall data acquisition and downlink efficiency: Through load balancing and data relay between the two satellites, the data flow path was optimized, the storage and data transmission pressure of a single satellite was alleviated, thereby improving the data backhaul efficiency of the entire satellite constellation and the timeliness of ground information acquisition.

[0049] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 is a diagram of the dual-satellite operation mode of a dual-satellite remote sensing system based on inter-satellite laser communication and tracking integration according to an embodiment of the present invention.

[0052] Figure 2 is a schematic diagram of the on-board payload according to an embodiment of the present invention;

[0053] Figure 3 is a schematic diagram of the inter-satellite laser communication payload configuration according to an embodiment of the present invention;

[0054] Figure 4 is a diagram showing the spatial beam pointing control of the inter-satellite laser communication payload according to an embodiment of the present invention.

[0055] Figure 5 is a flow diagram of inter-satellite laser communication payload information in an embodiment of the present invention;

[0056] Figure 6 is a flowchart of the on-orbit operation of the inter-satellite laser communication payload according to an embodiment of the present invention;

[0057] Figure 7 is a schematic diagram of star pointing calibration according to an embodiment of the present invention;

[0058] Figure 8 is a schematic diagram of satellite-based calibration of payload pointing error according to an embodiment of the present invention;

[0059] Figure 9 is a flowchart of the satellite-based calibration process for the payload pointing error according to an embodiment of the present invention;

[0060] Figure 10 is a flowchart of the laser payload inter-satellite pointing calibration process according to an embodiment of the present invention;

[0061] Figure 11 is a schematic diagram of the BeiDou short message communication payload composition according to an embodiment of the present invention;

[0062] Figure 12 is a diagram of the overall data flow of the BeiDou short message communication payload according to an embodiment of the present invention.

[0063] Figure 13 is a technical specification diagram of the multispectral camera according to an embodiment of the present invention;

[0064] Figure 14 is a diagram showing the technical specifications of the hyperspectral camera according to an embodiment of the present invention;

[0065] Figure 15 is a flowchart of the on-orbit link establishment process of the inter-satellite laser communication payload according to an embodiment of the present invention. Detailed Implementation

[0066] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0067] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0068] Example

[0069] This embodiment takes the dual-satellite collaborative remote sensing system composed of "Muduo-1A" and "Muduo-1B" satellites from Beijing Normal University as an example. Its dual-satellite collaborative mode is shown in Figure 1.

[0070] (a) Dual-star platform configuration

[0071] The first satellite operates in a sun-synchronous orbit at an altitude of 500 km and an inclination of 97.4065°, flying in tandem with the second satellite in the same orbital plane. The orbital spacing can be adjusted between 500 km and 3000 km. Its onboard multispectral camera covers the full spectral band and eight multispectral bands, with a nadir resolution of 19.44 m. It features a CXP high-speed data interface with primary / backup hot backup design, and a single interface rate of 1.25 Gbps. The inter-satellite laser communication payload integrates an optical head and a processor. The optical head includes a coarse tracking servo turntable, a fine tracking fast-reflecting mirror, and an optical antenna. The processor includes a comprehensive signal processing module and an fiber optic power amplifier. The onboard processing unit of the first satellite adopts a Flash FPGA+GPU SoC architecture, supporting radiometric correction, geometric correction, and surface anomaly extraction functions, and is equipped with 4TB×2 SSD storage. The satellite platform payload configuration is shown in Figure 2.

[0072] The second satellite's orbital parameters match those of the first satellite. Its onboard hyperspectral camera covers the spectral band from 410nm to 2480nm, including 16 visible-near-infrared sub-bands and 10 shortwave infrared sub-bands. The nadir resolution is 8.88m for the visible-near-infrared band and 29.6m for the shortwave infrared band. It also features a CXP high-speed interface with primary and backup hot standby. The onboard processing unit of the second satellite has the same hardware architecture as the first satellite, supporting real-time on-orbit processing of hyperspectral data.

[0073] (II) Key Design of Inter-Satellite Laser Communication Payload

[0074] As shown in Figure 3, the inter-satellite laser communication payload includes an optical head and a processor. The optical head is the core hardware unit for realizing laser tracking and signal transmission and reception, and includes the following sub-modules:

[0075] The beacon laser transceiver module consists of an 808 beacon laser, a CMOS detector, and a beacon laser straightener. It is responsible for emitting beacon lasers to assist in inter-satellite link acquisition and receiving response beacons from other satellites through the CMOS detector.

[0076] The coarse tracking servo turntable is a two-dimensional pointing mechanism used to correct low-frequency, large-angle deviations in inter-satellite links and maintain the initial alignment accuracy of the line of sight.

[0077] The rear optical path module includes a coupling fiber, a relay receiving optical path, and a SWIR detector, which is responsible for the transmission, coupling, and detection of laser signals, and provides angle error data for tracking control.

[0078] Optical antenna: Used to reduce the size of a large-aperture space beam signal into a small-aperture space beam signal, facilitating the miniaturization of relay receiving and receiving optical paths. It expands the small-aperture laser beam emitted by the relay receiving and receiving optical path into a large-aperture laser beam, thereby compressing the beam divergence angle of the emitted beam and enabling directional transmission and reception of laser signals, suitable for inter-satellite communication distances of 500km to 3000km.

[0079] The capture and tracking control module integrates capture and tracking control software with pointing calculation and servo turntable control software. It is responsible for SWIR image signal processing, coarse tracking servo turntable drive and control, fine tracking unit drive and control, follow-up star sensor drive and control, and capture and tracking process control.

[0080] The processor provides power supply, signal processing, and power amplification support for the payload, and includes the following sub-modules:

[0081] Secondary power supply module: responsible for converting the power supply of the satellite platform into the stable voltage required by each module of the payload, ensuring the reliable operation of the payload.

[0082] Integrated signal processing module: Completes the encoding, modulation, demodulation and decoding of communication signals, generates the transmitted laser seed signal through the optical module, and performs functions such as payload workflow control, telemetry signal acquisition and transmission, remote control signal reception and execution, information interaction with the satellite platform, and optical amplifier control.

[0083] Fiber optic power amplifier module: Controlled by optical amplifier control software, it amplifies the modulated laser signal to meet the power requirements of long-distance inter-satellite transmission.

[0084] Its working principle is as follows:

[0085] The inter-satellite laser communication payload is carried on a satellite platform. The payload and the platform exchange data through an external interface. The satellite platform injects information such as ephemeris, attitude, clock and commands into the laser payload. According to the commands and workflow, the laser payload controls the optical head to complete the program tracking. With the cooperation of the payloads at both ends, it completes the rapid acquisition and stable tracking of the inter-satellite laser link. At the same time, it transmits its own status information to the satellite platform through telemetry information.

[0086] The laser payload signal processing module receives inter-satellite data sent by the satellite payload, completes data framing and encoding, generates a direct modulated laser signal through a high-power laser, collimates it into a space laser signal through an optical head, and, with the assistance of a capture and tracking system, stably illuminates the target satellite with the transmitted laser signal.

[0087] The laser payload carried by the target satellite maintains stable tracking and receiving of space laser signals through an optical system and a capture and tracking system. The laser signal first enters the coupling optical fiber, then is amplified by a low-noise optical amplifier, and finally the space laser signal is converted into an electrical baseband signal by a PIN detector. The electrical baseband signal is demodulated and decoded by the integrated signal processing module and then forwarded to the satellite platform.

[0088] The optical antenna is mounted on a two-dimensional servo turntable. By controlling the turntable, a wide range of rotation of the antenna's line-of-sight can be achieved. A piezoelectric ceramic precision tracking fast-reflecting mirror enables rapid adjustment of the transmit and receive line-of-sight. A null-point deflection scheme using a tracking detector allows for pre-aiming of the laser beam and adjustment of the transmit and receive lines-of-sight. The tracking detector detects the laser beam emitted by the other terminal, obtains the alignment error of the antenna's line-of-sight, controls the two-dimensional servo turntable and fast-reflecting mirror, corrects the line-of-sight pointing, and ensures precise alignment between the two terminals, establishing a stable laser link.

[0089] The transmission-type optical antenna system used in this application has a magnification of 5. A calibration cone reflects the emitted signal light back to the signal light receiving camera branch, achieving self-calibration. A transceiver splitter separates the signal light transmitting and receiving branches, meeting system isolation requirements. An energy beam splitter divides the received signal light into two parts: 80% is transmitted to the communication detector, and 20% is reflected to the acquisition and tracking detector. The system's operating information flow and principle are shown in Figures 4 and 5.

[0090] After the laser payload is launched into orbit, the workflow is carried out in sequence, including on-orbit unlocking, self-testing, parameter calibration, receiver and transmitter axis calibration, payload pointing calibration, and payload service communication. The payload is then reconfigured according to the testing and commissioning requirements. The process is shown in Figure 6.

[0091] (III) Multi-dimensional calibration function

[0092] Inter-satellite laser communication payloads are subject to vibration, shock, temperature changes, and stress release during satellite launch and in-orbit operation. This can cause the payload's installation zero-position to drift, resulting in pointing deviations between the inter-satellite laser communication payload and the satellite. After the satellite enters orbit, it needs to be calibrated, and this error typically varies depending on solar illumination conditions. Inter-satellite laser communication payloads offer several calibration modes, including star-pointing calibration, satellite-to-ground pointing calibration, and inter-satellite pointing calibration. The workflow for each mode is as follows:

[0093] The star-pointing calibration mode, as shown in Figure 7, is the primary calibration mode used during the initial orbit insertion phase. It involves observing stars through the CMOS detector in the beacon laser transceiver module, combining this data with satellite platform attitude data to calculate and correct the installation error of the laser payload. The laser communication payload uses attitude data output from the platform's star sensor as guidance data, pointing the receiving line of sight towards a star in the sky. The starlight is imaged onto the detector's target surface. Based on the position information of the light spot output by the detector and the star catalog information of that star, the inertial pointing of the receiving line of sight can be calculated. By comparing and analyzing the attitude measurement information sent by the satellite platform, the installation error can be measured, thus achieving pointing calibration. Since the detector can only acquire two-dimensional angle information, the calibration process requires calculating the installation error based on two-dimensional measurement data from multiple stars at different orbital positions.

[0094] In the satellite-to-ground pointing calibration mode, the laser ground station can open-loop point at the satellite and perform programmed tracking of the satellite based on guidance data, while simultaneously transmitting uplink light to cover uncertain areas of the satellite. The satellite continuously scans to correct its own optical axis error. Based on the azimuth and elevation positions of the servo turntable, the position of the precision tracking fast-reflecting mirror, the imaging error of the tracking detector, and combined with the satellite's attitude and orbit information, the payload installation error is calculated, and the payload coordinate system installation error calibration is completed. The calibration principle is shown in Figure 8, and the calibration process is shown in Figure 9.

[0095] Inter-satellite pointing calibration mode is the accuracy maintenance mode during normal mission phases. After the laser communication payload establishes a tracking link, it uses telemetry data on pointing from the two satellites, combined with data such as satellite attitude and the orbits of the two satellites, to perform real-time calibration of the payload's initial pointing deviation. The process is shown in Figure 10.

[0096] (iv) Backup communication

[0097] Both satellites carry BeiDou short message communication payloads as backup for the laser link. When the laser link is interrupted due to solar interference or atmospheric turbulence, they transmit critical data such as target position and observation commands. The main technical requirements for BeiDou short message communication are as follows:

[0098] Operating frequencies: outbound (forward) frequency (2491.75±4.08) MHz, inbound (return) frequency (1615.68±4.08) MHz;

[0099] Transmission rate: Forward receive rate 16kbps, backward transmit rate 8kbps; Bit error rate: Forward ≤10⁻⁵, backward ≤10⁻⁵;

[0100] Outgoing signal: pseudocode direct sequence spread spectrum, spread spectrum code rate 4.08 Mchip / s, convolutional (2,1,7) coding, OQPSK modulation, continuous frame information structure;

[0101] Inbound signal: pseudocode direct sequence spread spectrum, spreading code rate 4.08 Mchip / s, convolutional (2,1,7) coding, BPSK modulation, burst frame information structure;

[0102] Polarization mode: transmits with left-hand circular polarization and receives with right-hand circular polarization.

[0103] The BeiDou short message communication payload consists of an RF front-end unit, a baseband processing unit, an interface processing unit, a storage unit, and a power supply unit, as shown in Figure 11. The overall data flow of the short message payload is shown in Figure 12.

[0104] (v) Key Camera Parameters

[0105] The multispectral camera covers the panchromatic spectrum and multiple multispectral bands, with a full-spectral resolution of 4.86 μm, out-of-band response of ≤5% for multispectral bands, dynamic range ≥62.4 dB, quantization level of 12 bits, and a high-speed interface with CXP master-slave hot backup design. Its technical specifications are shown in Figure 13.

[0106] The hyperspectral camera covers multiple sub-bands from visible light to short-wave infrared, with an out-of-band response of ≤5% in the visible-near-infrared band and a signal-to-noise ratio of ≥35.87dB in the short-wave infrared band. It features a 14-bit quantization level and a high-speed interface with a CXP master-slave hot-backup design, achieving a single-interface rate of 1.25Gbps. Its technical specifications are shown in Figure 14.

[0107] II. A Two-Satellite Remote Sensing Method Based on Inter-Satellite Laser Communication and Tracking Integration

[0108] The process is shown in Figure 15.

[0109] (a) Link initialization

[0110] After the two satellites entered orbit, the inter-satellite laser communication payload immediately initiated the on-orbit unlocking process, completing the mechanical unlocking and power initialization of the optical head and processor modules. Subsequently, a self-test process was executed, checking the status of core components such as the beacon laser transceiver module, coarse tracking servo turntable, and integrated signal processing module to ensure normal operation. After passing the self-test, the star pointing calibration mode was executed first, observing the star through the CMOS detector in the beacon laser transceiver module and calculating and correcting the installation error of the laser payload using satellite platform attitude data. If star calibration was unavailable, the system switched to satellite-to-ground pointing calibration mode, using uplink optical signals from the ground laser station to detect and correct the coaxiality deviation of the receiving and transmitting optical axes, initializing the pointing accuracy and optical axis consistency to ensure that the initial pointing error was less than half of the acquisition field of view.

[0111] (ii) Autonomous establishment of laser link

[0112] Based on the calibration results during the link initialization phase and their own orbital parameters, the two satellites autonomously establish an inter-satellite bidirectional laser communication link according to the following sub-steps:

[0113] Open-loop pointing sub-step of the program: Based on the orbit prediction data and the calibrated installation matrix, the two satellites calculate the relative pointing angle of each other, control the coarse tracking servo turntable to drive the optical antenna to point to the expected position, with a pointing error ≤1mrad, and complete the initial alignment.

[0114] Scanning and Acquisition Sub-steps: The first satellite is set as the active end, and its 808nm beacon laser in the beacon laser transceiver module emits beacon light and scans in the acquisition uncertainty area according to the spiral scanning strategy; the second satellite is the passive end, and after the short-wave infrared detector in the subsequent optical path module detects the beacon light, the acquisition and tracking control module calculates the pointing error and adjusts its own coarse tracking servo turntable pointing, while controlling its own 808nm beacon laser to emit response beacon light.

[0115] Coarse and fine tracking closed-loop sub-steps: Based on the error signals calculated by the shortwave infrared detectors, both satellites transition to composite axis tracking control. The coarse tracking servo turntable performs low-speed, wide-range compensation for low-frequency, large-angle deviations ≤1Hz, while the fine tracking fast-reflection mirror performs high-speed, precise correction for high-frequency micro-vibrations from 1 to 80Hz. Combined with the feedforward compensation amount generated by the acquisition and tracking control module, stable alignment of the line of sight is achieved, with a tracking accuracy ≤5μrad.

[0116] Communication link establishment steps: Once the tracking status is stable, both satellites switch their lasers to the communication wavelength. The integrated signal processing module performs framing, RS encoding, and OOK modulation on the inter-satellite transmission data. The modulated laser signal is then amplified by the fiber optic power amplifier module and transmitted through the optical antenna to establish a high-speed inter-satellite laser communication link with a bandwidth ≥300Mbps and a bit error rate <10⁻⁻⁴. 7 .

[0117] (III) Triggering of Collaborative Observation

[0118] The first satellite activates its multispectral camera to perform wide-area imaging of the Earth's surface at a preset line frequency, acquiring raw imaging data in panchromatic and multispectral bands. The onboard processing unit performs real-time on-orbit processing on the raw data, including radiometric correction, geometric correction, and surface target identification. After identifying the target of interest, it generates a trigger command containing the target's WGS84 coordinate system latitude and longitude and observation priority. The trigger command data size is ≤1KB, and it is transmitted to the second satellite in real time through the established inter-satellite laser communication link with a transmission delay of <30min.

[0119] (iv) Detailed hyperspectral investigation

[0120] After receiving the trigger command, the onboard processing unit of the second satellite quickly analyzes the target location information, schedules the hyperspectral camera to adjust its operating parameters, and controls the hyperspectral camera to quickly point at the designated target area, initiating detailed spectral imaging. The hyperspectral camera covers multiple subdivided spectral bands from visible light to shortwave infrared. During imaging, the integration time for the visible light channel is 472 μs, and the integration time for the shortwave infrared channel is 3630 μs. The gain is dynamically adjusted according to the target brightness to acquire detailed hyperspectral data of the target area, ensuring that the imaging accuracy meets the requirements for fine observation of surface targets.

[0121] (v) Data Collaboration Management and Downlink

[0122] After the hyperspectral detailed survey is completed, the second satellite transmits the acquired hyperspectral detailed survey data to the first satellite in near real-time via an inter-satellite laser communication link. The onboard processing unit of the first satellite fuses the received hyperspectral detailed survey data with its own acquired multispectral survey data to generate a fused observation product of the surface targets. Subsequently, based on the real-time geometric relationship between the two satellites and the ground station, the optimal satellite is determined and dynamically selected to transmit the fused product or the original multispectral and hyperspectral data to the ground station through the satellite's data transmission system, achieving efficient downlink of observation data.

[0123] When the inter-satellite laser link is interrupted due to solar interference, the two satellites automatically switch to the BeiDou short message communication payload to transmit critical information. This includes simplified coordinates of the target area (error ≤ 100m); satellite operating status (including power consumption and remaining storage); and estimated link recovery time (short message transmission delay ≤ 10s), ensuring uninterrupted collaborative observation missions.

[0124] The remaining technical features in the above embodiments can be flexibly selected by those skilled in the art to meet different specific practical needs according to actual circumstances. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims. In the above description, numerous specific details have been set forth to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to implement the present invention. In other instances, to avoid obscuring the present invention, well-known techniques, such as specific construction details, operating conditions, and other technical conditions, have not been specifically described.

Claims

1. A dual-satellite remote sensing system based on inter-satellite laser communication and tracking integration, characterized in that: The system comprises a first satellite and a second satellite that fly in tandem and work together within the same orbital plane. The first satellite carries a multispectral camera for wide-area surveys, a first on-board processing unit, and a first transmission payload. The second satellite carries a hyperspectral camera for detailed surveys, a second on-board processing unit, and a second transmission payload. Both the first and second transmission payloads include inter-satellite laser communication payloads for autonomously establishing and maintaining a bidirectional laser communication link between the two satellites and achieving high-precision beam tracking. The first on-board processing unit is configured to process multispectral camera data to identify targets of interest and generate observation trigger commands. The system is configured to send the observation trigger commands from the first satellite to the second satellite via the inter-satellite laser communication link, triggering the second satellite's hyperspectral camera to conduct collaborative observations of the target area.

2. The dual-satellite remote sensing system based on inter-satellite laser communication and tracking integration as described in claim 1, characterized in that: The optical head, serving as the optical signal transceiver and tracking actuator, includes a coarse tracking servo turntable, an optical antenna, a rear optical path module, a beacon laser transceiver module, and a capture and tracking control module; the processor, serving as the power supply, signal processing, and communication hub, includes a secondary power supply module, a comprehensive signal processing module, and an optical fiber power amplifier module.

3. The dual-satellite remote sensing system based on inter-satellite laser communication and tracking integration as described in claim 2, characterized in that: The rear optical path module includes a tracking detector and a communication detector. The tracking detector converts the received spatial optical signal into an electrical signal and calculates the beam pointing angle error and tracking error. The communication detector converts the spatial laser communication signal into an electrical baseband signal. The beacon laser transceiver module includes a beacon laser and a CMOS detector. The beacon laser emits beacon light to assist in acquisition, and the CMOS detector receives the beacon light from the other party and performs star calibration. The acquisition and tracking control module is connected to the tracking detector, the CMOS detector, the coarse tracking servo turntable, and the fine tracking unit. It is used to complete image signal processing, turntable driving, fast mirror control, and full-process control of acquisition and tracking.

4. The dual-satellite remote sensing system based on inter-satellite laser communication and tracking integration as described in claim 2, characterized in that: The integrated signal processing module is used to complete the encoding, modulation, demodulation, and decoding of communication signals, generate the transmitted laser seed signal, and perform payload workflow control, telemetry and remote control, and information interaction with the satellite platform; the fiber optic power amplifier module is connected to the integrated signal processing module and is used to amplify the transmitted laser seed signal at high power; the secondary power supply module is used to isolate and convert the primary power supply of the satellite platform into the secondary power supply required by each module inside the payload.

5. The dual-satellite remote sensing system based on inter-satellite laser communication and tracking integration as described in claim 1, characterized in that, The inter-satellite laser communication payload has multi-mode on-orbit calibration capabilities, including: a star pointing calibration mode, which uses the CMOS detector to image stars and combines them with satellite attitude data to calibrate the installation matrix error between the payload's coordinate system and the satellite's attitude reference; a coaxiality calibration mode, which uses optical references internal to the payload or between satellites to calibrate the coaxiality error between the transmitting optical axis, the receiving optical axis, and the tracking optical axis; and an inter-satellite pointing calibration mode, which, after the link is established, uses bidirectional tracking data to fit and correct pointing deviations in real time to maintain long-term tracking accuracy.

6. The dual-satellite remote sensing system based on inter-satellite laser communication and tracking integration as described in claim 1, characterized in that: The first and second transmission payloads also include the BeiDou short message communication payload, which serves as an emergency backup for the inter-satellite laser communication link. When the laser link is interrupted, it automatically or under control switches to the short message link to transmit key instructions and status information.

7. A dual-satellite remote sensing method based on inter-satellite laser communication and tracking integration, executed in the system described in any one of claims 1-6, characterized in that, Includes the following steps: Link initialization steps: After the two satellites enter orbit, the inter-satellite laser communication payload performs on-orbit unlocking, self-testing, and calibration procedures to initialize pointing accuracy and optical axis consistency; Laser link autonomous establishment steps: Based on the calibration results and orbital parameters, the two satellites autonomously establish and lock a stable inter-satellite bidirectional laser communication link through beacon light scanning, bidirectional acquisition, and coarse-fine composite tracking control; Collaborative observation triggering steps: The first satellite uses a multispectral camera to perform wide-area imaging, and after on-board processing to identify the target, it generates a trigger command containing the target's location and sends it to the second satellite in real time through the laser communication link; Hyperspectral detailed investigation steps: After receiving the trigger command, the second satellite schedules its hyperspectral camera to perform rapid pointing and fine spectral imaging of the designated target area.

8. The dual-satellite remote sensing system based on inter-satellite laser communication and tracking integration as described in claim 7, characterized in that: The laser link autonomous establishment steps specifically include: Open-loop pointing sub-step: Based on orbit prediction and the calibrated installation matrix, the two satellites calculate the relative pointing angle and control the coarse tracking servo turntable to drive the optical antenna to point to the expected position; Scanning and acquisition sub-step: One satellite's beacon laser emits beacon light to scan the area; the other satellite's tracking detector acquires the beacon light, calculates the error, adjusts its own pointing, and simultaneously emits a response beacon light; Coarse and fine tracking closed-loop sub-step: Based on the error signal from the tracking detector, both satellites switch to composite axis tracking. The coarse tracking servo turntable compensates for large-scale, low-frequency deviations, and the fine tracking fast-reflecting mirror suppresses high-frequency micro-vibrations, achieving stable alignment of the line of sight; Communication link establishment sub-step: After tracking stabilizes, both satellites switch their lasers to the communication wavelength, and the integrated signal processing module and the fiber optic power amplifier module work together to initiate high-speed data transmission.

9. The dual-satellite remote sensing system based on inter-satellite laser communication and tracking integration as described in claim 8, characterized in that: In the coarse and fine tracking closed-loop sub-steps, a composite axis control strategy based on feedforward compensation is adopted: the coarse tracking loop uses the low-frequency error calculated by the tracking detector as input to drive the servo turntable to perform low-speed, wide-range tracking; the fine tracking loop performs windowing processing on the tracking detector signal to obtain high frame rate error, and drives the fast-reflection mirror to perform high-speed, precise correction; the acquisition and tracking control module combines real-time trajectory, attitude, and calibration parameters to generate feedforward compensation, which is injected into the coarse and fine tracking loops respectively to improve the tracking performance for dynamic relative motion.

10. The dual-satellite remote sensing system based on inter-satellite laser communication and tracking integration as described in claim 7, characterized in that: The method also includes data collaborative management and downlink steps: the hyperspectral detailed survey data acquired by the second satellite is transmitted to the first satellite in real time or near real time through the inter-satellite laser communication link; the multispectral survey data and the hyperspectral detailed survey data are fused by the processing unit on the first satellite to generate a fused product; based on the real-time geometric relationship between the two satellites and the ground station, the optimal satellite is dynamically selected to transmit the fused product or raw data to the ground through the data transmission system of the satellite.

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