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Cloud detection methods for remote sensing images：a survey LIU Zili, YANG Jiajun, WANG Wenjing, SHI Zhenwei Chinese Space Science and Technology    2023, 43 (1): 1-17.   DOI: 10.16708/j.cnki.1000-758X.2023.0001 Abstract （1063）      PDF（pc） （3043KB）（1754）       Knowledge map     The cloud cover in the optical remote sensing images will obscure the ground information in different degrees，which causes the blurring and missing of the surface observation information and greatly affects the imaging quality of remote sensing images.Therefore，the detection and evaluation of cloud cover in remote sensing images are the basis and key to further analyze and utilize remote sensing image information.Through sufficient investigation and summary，the development trend and representative work of cloud detection methods based on remote sensing images at home and abroad since the 1990s were combed.Cloud detection methods based on remote sensing images were divided into three categories：methods based on band threshold，methods based on classical machine learning and methods based on deep learning.Besides，the public datasets at home and abroad used in the related research on cloud detection were summarized，and the accuracy of some representative cloud detection methods was compared.In addition to the vanilla cloud detection method，the cloud/fog（haze）detection，cloud/snow detection，cloud shadow detection and cloud removal methods related to cloud detection were also briefly combed.Based on the review and summary of cloud detection work above，the existing problems and future development trends of cloud detection were analyzed and prospected. Related Articles | Metrics

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Development status and prospect of satellite-based surveying YANG Yuanxi, WANG Jianrong, LOU Liangsheng, SUN Zhongmiao, XIAO Yun, MIAO Yuzhe Chinese Space Science and Technology    2022, 42 (3): 1-9.   DOI: 10.16708/j.cnki.1000-758X.2022.0031 Abstract （887）      PDF（pc） （918KB）（881）       Knowledge map    Satellite-based surveying is the main platform of global fundamental surveying, including satellite topographic survey, satellite gravimetry, satellite magnetic measuring, satellite altimetry, etc. The developments of satellite-based measuring projects have experienced “return type measuring satellite project”, “transmission type measuring satellite project” and some of “loads integration measuring satellite project”. This paper firstly reviews the development history and current situation of international satellite-based surveying projects, then analyzes the roles of China′s satellite-based surveying projects in various stages, including some existing problems. Finally, the ideas for the future development of satellite-based surveying are put forward. Related Articles | Metrics

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Space robotic manipulation: a multi-task learning perspective LI Linfeng, XIE Yongchun Chinese Space Science and Technology    2022, 42 (3): 10-24.   DOI: 10.16708/j.cnki.1000-758X.2022.0032 Abstract （735）      PDF（pc） （3443KB）（523）       Knowledge map    It is a technological development trend in recent years to apply space robot in place of spaceman to perform on-orbit service tasks. Using deep neural network controller, the learning-based space robotic manipulation has shown good potential in adaptability to the unstructured space environments and applicability in fileds such as high earth orbit, extraterrestrial planet exploration, etc. At present, a large number of studies focus on single task robotic manipulation learning problems, for either onground robots or in-space robots. From a new perspective of multi-task learning, a thorough literature review on multi-task robot learning was made, including algorithms and robotic applications therein. To further apply the state-of-the-art multi-task robot learning algorthms, main technical challenges were analyzed and suggestions on key technology development were given. The breakthrough of the above challenges will increase the overall autonomy and robustness level of the space robot system, which is expected to further facilitate the development of China′s on-orbit service towards completely unmanned autonomy. Related Articles | Metrics

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Analysis of the first stage deployment of Starlink constellation based on TLE XUE Wen, HU Min, RUAN Yongjing, YUN Chaoming, SUN Tianyu Chinese Space Science and Technology    2022, 42 (5): 24-33.   DOI: 10.16708/j.cnki.1000-758X.2022.0064 Abstract （563）      PDF（pc） （7069KB）（575）       Knowledge map     In recent years，with the rapid development of satellite technology and the increasing demand for low earth orbit（LEO）satellite broadband internet construction，the development of LEO large-scale constellations is changing rapidly.Aiming at the initial deployment of Starlink constellation，firstly，the current status of the Starlink constellation was discussed，and the altitude changes of orbiting satellites were analysed.Then，the deployment of the Starlink constellation was briefly analyzed from two aspects by utilizing the public two-line element（TLE），including satellite being launched into orbit and orbital plane distribution，and the changing rule of ascending node was given.At the same time，the ground coverage performance of the Starlink constellation was simulated and analyzed.Finally，the constellation orbital planes and phase distribution，handling of the faulty satellites，and the number of visible satellites were obtained.The results of the analysis are expected to provide reference for China′s future deployment of large-scale LEO constellations. Related Articles | Metrics

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Progress and prospect in planetary exploration of solar system YANG Mengfei, ZHENG Yanhong, NI Yanshuo, HUANG Xiaofeng, ZHANG Zhengfeng, XING Zhuoyi Chinese Space Science and Technology    2023, 43 (5): 1-12.   DOI: 10.16708/j.cnki.1000-758X.2023.0063 Abstract （525）      PDF（pc） （10199KB）（697）       Knowledge map    Planetary exploration is an important means of humans to understand the universe.With the continuous development of space technology，major space countries have carried out more than 100 planetary exploration activities in the solar system.Humans have realized the flyby，orbiting，lander，rover and sample return missions of solar system.Based on the implemented planetary exploration activities and upcoming missions，the main scientific issues and discoveries of planetary exploration were summarized.And the development tendency of planetary exploration was analyzed.According to the recent development plan of planetary exploration in China，a medium to longterm conceiving route and flagship mission have been proposed.It can provide support for the planning of future planetary exploration missions in China. Related Articles | Metrics

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Research of thrust measurement for space electric propulsion ZHANG Lupeng, YANG Xin, CHANG Lei, XU Qian, ZHOU Haishan, LUO Guangnan Chinese Space Science and Technology    2022, 42 (3): 25-38.   DOI: 10.16708/j.cnki.1000-758X.2022.0033 Abstract （516）      PDF（pc） （8286KB）（839）       Knowledge map     Accurate measurement of thrust is very important in the development and planning of space electric propulsion.In recent years,with the increasing of complexity and task difficulty for electric propulsion,higher requirements are put forward for the evaluation techniques and methods of thrust performance.In response to this demand,a review of the thrust measurement for space electric propulsion was presented.Measurement methods and the underlying mechanisms,technical features and applications were covered.The methods of thrust measurement can be divided into direct measurement and indirect measurement.The former mainly includes balance structure,torsional pendulum,suspension and inverted pendulum,while the latter mainly includes target and cantilever beam.The advantages and disadvantages of these measurement methods were summarized and compared,which provided a reference for developers to design the thrust measuring system.The key problems in the five segments including system design,system calibration,system response,system response measurement and calculation of thrust during the process of thrust measurement were described in detail,and the corresponding improvement methods were proposed.To serve as a reference for future thrust measurement research,suggestions were also provided by considering the development trend of electric propulsion and its demand of thrust measurement. Related Articles | Metrics

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Research progress and prospect of spacecraft reconfiguration technology PENG Qibo, WU Xinfeng, WANG Beichao, LI Shuang Chinese Space Science and Technology    2023, 43 (2): 16-31.   DOI: 10.16708/j.cnki.1000-758X.2023.0017 Abstract （503）      PDF（pc） （6523KB）（653）       Knowledge map     Spacecraft reconfiguration technology is the key technology that must be broken through for the in-orbit service of spacecraft and other major space missions，having a profound effect on the design，research and development of new spacecraft systems.Firstly，the connotation and classification of the spacecraft reconfiguration were presented.Then，the domestic and overseas research status of the technology was systematically concluded and discussed based on main structure reconfiguration and other typical technologies.Next，the system of the spacecraft reconfiguration technology was proposed based on the methods such as standardized modular design，and then application prospects were summarized in the aspects such as supporting fault elimination of spacecraft.Finally，overall research progress of the reconfiguration technology was concluded，and future development was also expected. Related Articles | Metrics

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Research progress and prospect of on-orbit additive manufacturing technology LIU Jie, SHI Yun, CUI Yutao, HOU Juan, ZHANG Kai, HUANG Aijun Chinese Space Science and Technology    2022, 42 (6): 23-34.   DOI: 10.16708/j.cnki.1000-758X.2022.0080 Abstract （445）      PDF（pc） （5450KB）（501）       Knowledge map    In-space additive manufacturing technology is a “space 3D” printing technology，which has attracted major attention due to its application in on-orbit manufacturing and space base additive manufacturing.The basic concepts were introduced and the progress of space on-orbit additive manufacturing technology in the world was summarized.With the requirement of space stations and on-orbit spacecraft，the significant challenge of in-space additive manufacturing was the raw materials，printing technology and equipment.This was attributed to the unique feature of the space environment，including microgravity and high vacuum，etc. Finally，based on the current development status，requirements，and possible implementation paths of in-space onorbit manufacturing technology，the development direction of in-space additive manufacturing was pointed out. Related Articles | Metrics

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Progress and prospect of lunar resources exploitation and utilization YANG Mengfei, ZOU Zhigang, WANG Weihua, YAO Wei, WANG Qinggong Chinese Space Science and Technology    2024, 44 (1): 1-10.   DOI: 10.16708/j.cnki.1000-758X.2024.0001 Abstract （430）      PDF（pc） （4467KB）（554）       Knowledge map    With the implementation of the Chang′E-5 mission in 2020，the three phases of China lunar exploration program，namely orbiting，landing and returning，have been completed.Next，the International Lunar Research Station（ILRS）will be established at the lunar south pole by 2030，and a lunar base will be planned later.It is a new era of exploitation and utilization of the Moon，in which a vast tasks should be completed.In this paper，we summarized some important progresses of investigation of lunar resources in the past，including lunar resource exploration，analysis of lunar volatiles，mineral extraction，and material construction by 3D printing of lunar regolith.Then，we proposed future tasks for the exploitation of the lunar resources.The main challenges of the Moon，such as the extreme lunar environment，unique properties of lunar regolith，and autonomous control of the process，were considered.The views in this paper can be referenced for future scientific researches and engineering tasks in the field. Related Articles | Metrics

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Progress and prospect of solar exploration in space YANG Mengfei, DAI Shuwu, WANG Ying, ZHU Chenglin, YANG Shangbin, ZHANG Yechi Chinese Space Science and Technology    2022, 42 (5): 1-10.   DOI: 10.16708/j.cnki.1000-758X.2022.0062 Abstract （413）      PDF（pc） （2853KB）（403）       Knowledge map     In order to explore the development direction of solar space exploration activities，ten typical probes were selected taking into account their implementation era，orbital design，exploration elements，technical characteristics and each mission′s result based on extensive research on solar probe missions.Scientific objectives，payloads，satellite platform characteristics and scientific achievements of the ten typical probes were analyzed.Solar space exploration progress and development trend were summarized.In general，the orbit of solar detectors has been gradually diversified，detection elements of payload have become more abundant，and the detection accuracy and resolution have been significantly improved.However，there are still a lot of problems to be solved.On the basis of analyzing the current achievements and pending problems，the development outlook of solar space exploration was proposed，pointing out that all round and multielement exploration is a feasible way to break the bottleneck of solar physics and space weather forecast. Related Articles | Metrics

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Domain control strategy for the large-scale satellite cluster LI Ning, YUE Chengfei, GUO Haibo, QIU Shi, CAO Xibin Chinese Space Science and Technology    2023, 43 (1): 18-28.   DOI: 10.16708/j.cnki.1000-758X.2023.0002 Abstract （395）      PDF（pc） （6485KB）（484）       Knowledge map    In large-scale satellite constellations，single node management and control will lead to poor system connectivity and high dependence on ground resources.A distributed domain control strategy for satellite constellations with hierarchical management，intradomain autonomy and dynamic maintenance was proposed.Firstly，both the static index and dynamic index to measure the governability were defined.According to the newly-defined indexes，a multi-factor weighted cluster head selection method was proposed.Then，based on the selected cluster head node，a cascading optimal initialization algorithm of the cluster was established.Aiming at dynamic maintaining of the established cluster control structure，an event-triggered dynamic time slice domain control method was proposed.Finally，control simulation result of the proposed method in the case of LEO large-scale satellite constellation verifies the effectiveness of cluster head selection，cluster initialization and long-time maintaining.The number of satellites which were managed through ground station was reduced to 14%.High dependence on ground resources was resolved. Related Articles | Metrics

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Intelligent program synthesis framework and key scientific problems for embedded software YANGMengfei, GUBin, DUANZhenhua, JINZhi, ZHANNaijun, DONGYunwei, TIANCong, LIGe, DONG Xiaogang , LIXiaofeng Chinese Space Science and Technology    0, (): 1-7.   DOI: 10.16708/j.cnki.1000-758X.2022.0046 Abstract （389）      PDF（pc） （2052KB）（297）       Knowledge map    Program synthesis is an effective way to improve the efficiency of software development and the quality of software，and it is one of the most challenging problems in computer science.Firstly，the research status and existing problems of program synthesis methods were reviewed.Secondly，the concept of software IP（intellectual property）and an embedded software intelligent synthesis development method based on software IP（IP based embedded software intelligent synthesis，IPESIS）with its framework were proposed.Finally，the key scientific problems and main research contents that IPESIS needs to solve were discussed.IPESIS describes software requirement at a higher level of abstraction by defining the domain requirement description language，reduces the program search space with software IP as the granularity，and uses machine learning and other artificial intelligence technologies to automatically synthesize programs.It is expected to break through the limitations of existing methods，and then realize the transition of embedded software development from manual programming to software IP research and development plus intelligent synthesis based on software IP. Related Articles | Metrics

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Application and development of high-precision Hall electric propulsion technology LIU Qi, MAO Wei, HU Peng, WEI Yanming, HU Yanlin, LI Yong, BIAN Bingxiu, LIU Xuhui Chinese Space Science and Technology    2023, 43 (2): 1-15.   DOI: 10.16708/j.cnki.1000-758X.2023.0016 Abstract （348）      PDF（pc） （8062KB）（403）       Knowledge map    Under the application background of modern global communication and navigation，the abilities of precise orbit prediction and real-time orbit control of satellite platforms request better performances such as thrust accuracy and resolution ratio，so it is significant to construct high-precision electric propulsion system.According to the survey of the space application demand and the research status of electric propulsion technology，it is demonstrated that the output accuracy of thrust under current technology can not satisfy requirements of missions such as the high-precision continuous navigation，the real-time drag compensation of super low orbit satellites and imaging during the movement of high-resolution remote sensing satellites.Taking the Hall effect propulsion system as the research object and focusing on the technical difficulties of high-precision electric propulsion system，the research status at home and abroad was depicted，the development trends and the research routes of the key techniques were analyzed and discussed from the aspects of electric thruster technology，mass flow control technology，power supply and control technology as well as testing technology.The future focal directions of research and development were suggested for high-precision electric propulsion technology. Related Articles | Metrics

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Review of flexible tensioned thin-film deployable antennas ZHOU Xiaotao, MA Xiaofei, LI Huanxiao Chinese Space Science and Technology    2022, 42 (4): 77-91.   DOI: 10.16708/j.cnki.1000-758X.2022.0055 Abstract （315）      PDF（pc） （14136KB）（292）       Knowledge map    The flexible tensioned thin-film deployable antenna is a kind of large-scale deployable antenna with wide application prospects，which integrates flexible electronics，flexible thin-film material，flexible structure and flexible deployable technology.The antenna has the characteristics of lightweight，high spreading ratio，high gain，and flexible beam，which can effectively meet the special needs of remote sensing，communication and deep space exploration satellites.The characteristics and current status of research on flexible tensioned thin-film deployable antennas were described；a survey of the antennas in terms of materials，structures and applications was carried out to provide an overview of the existing structural forms；the basic theory and comprehensive test methods of the development of the thin-film antennas were summarized；the key technical problems to be solved in the development of the large deployable space antennas were discussed in the context of specific engineering problems，and the technical development trend of the thin-film antennas was further analyzed. Related Articles | Metrics

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Ion beam characteristics of iodine RF ion thruster optical system ZHANG Yuanzhe, HAN Xianwei, YANG Zhenyu, LU Haifeng, TAN Chang Chinese Space Science and Technology    2022, 42 (6): 115-124.   DOI: 10.16708/j.cnki.1000-758X.2022.0090 Abstract （312）      PDF（pc） （5836KB）（245）       Knowledge map    Based on the particlein cell（PIC）method，a numerical simulation on iodine RF ion thruster optics system was carried out to analyze characteristics of ion beam.Besides substantial I+，ionization products of iodine contain a little multivalent ions including I2+，I2+，I3+.Comparison of ion beam characteristics′ simulation results with and without addition of multivalent ions obtained spatial distribution of ions，potential distribution，phase space distribution，beam current and divergence angle.The results show that the program can simulate the motion of ions in optics system properly.With addition of multivalent ions，plasma potential increases and saddle point potential declines，though the variation range of the whole potential distribution is limited.The charge-to-mass ratio of the ion group increases slightly with addition of multivalent ions，therefore beam current increases and divergence angle declines a little.Both thrust and specific impulse increase slightly through theoretical analysis.When the plasma density in discharge chamber increases to about 2.4×1017m-3，the optics system reaches the limit of beam extraction，and extracted beam current decreases instead of increasing with proceeding increase of plasma density.The simulation results can provide a reference for design of RF ion thruster optics system. Related Articles | Metrics

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Retro-directive microwave power beam steering technology for space solar power station DONG Shiwei, HOU Xinbin, WANG Xin Chinese Space Science and Technology    2022, 42 (5): 91-102.   DOI: 10.16708/j.cnki.1000-758X.2022.0070 Abstract （311）      PDF（pc） （11662KB）（236）       Knowledge map    Microwave power transmission（MPT）design and demonstration are key jobs in development of space solar power station（SSPS）in China，while retro-directive microwave power beam steering is a primary part of MPT.Research on retro-directive microwave power beam steering was conducted under the prerequisite that the power transmitting array was with an ideal profile.The position and attitude errors of structural modules had seldom been considered of the power transmitting array in space environment.With respect to the four-phased missions of SSPS development in China，the influence of position and attitude errors on power density at the rectifying array and beam steering error was investigated.After the software retro-directive microwave power beam steering was preliminarily demonstrated，software retro-directive beam steering based on phase compensation was proposed，aimed at correcting the position and attitude errors of array modules.The correction effect was simulated and analyzed.The proposed software retrodirective beam steering based on phase compensation has remarkable correction ability for the position and attitude errors of array modules.This article presents guidelines for MPT system design and assembly. Related Articles | Metrics

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Forthcoming development trend of spaceborne SAR technology for earth environment monitoring DENG Yunkai, ZHANG Heng, FAN Huaitao, YU Weidong, WANG Yu, TANG Xinming, GE Daqing, XU Feng, LIU Guoxiang Chinese Space Science and Technology    2023, 43 (2): 32-46.   DOI: 10.16708/j.cnki.1000-758X.2023.0018 Abstract （304）      PDF（pc） （20989KB）（315）       Knowledge map    Focusing on the problems in the microwave remote sensing earth observation in terms of information dimension，inversion accuracy，observation efficiency and system architecture，several future spaceborne SAR technologies for comprehensive environmental monitoring were discussed based on the research achievements of the national key research and development program which was named as “Earth Environment Monitoring with Advanced Spaceborne Synthetic Aperture Radar”.In terms of ultra-large-width SAR imaging，a design scheme of segmented gradual variable pulse repetition frequency（PRF）sequence and a low-oversampling variable PRF data processing algorithm based on optimal linear unbiased estimation were proposed to realize large-scale wide-area spaceborne SAR imaging across blind areas.In terms of high-sensitivity SAR imaging，an intermediate-frequency digital beamforming（DBF）efficient on-board real-time processing architecture and a rapid generation algorithm for weighting factors were proposed，and the 16-channel airborne data were used to verify that the image signal-to-noise ratio was increased by about 11.2dB.In terms of multi-polarimetric SAR imaging，a compact polarization decomposition algorithm and a hybrid full-polarization azimuth ambiguity suppression method were proposed respectively，which were verified in the P/L band airborne flight test.In terms of high-precision interferometric SAR technology，a tomographic SAR processing method based on an improved phase compensation scheme was proposed，and the P-band full-polarization tomographic SAR data was used to verify that the forest height retrieval accuracy was better than 0.9meters.In terms of comprehensive environmental monitoring constellation architecture design，for wide-area surface elevation，surface deformation，wave spectrum energy，ocean current velocity，and biomass applications，a high-resolution wide-range SAR satellite solution with a quality factor of 100 was  completed，and the performance was greatly improved compared with in-orbit SAR satellites. Related Articles | Metrics

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Multi-satellite responsive inspection mission planning with multiple constraints PENG Chenyuan, ZHANG Jin, YAN Bing, ZHOU Hongxi, LUO Yazhong Chinese Space Science and Technology    2022, 42 (3): 39-48.   DOI: 10.16708/j.cnki.1000-758X.2022.0034 Abstract （303）      PDF（pc） （4964KB）（308）       Knowledge map    Multi-satellite responsive inspection mission refers to the fact that multiple target satellites appear unknown, and the inspection service platform carries out orbit transfer within a short period of time, and carries a number of sub spacecraft to perform overflight inspection on the targets. For mission planning of this kind of problem, the platform phasing strategy based on coplanar maneuver was firstly presented and a screening calculation model of inspection window satisfying the constraints of illumination and maneuvering ability was established. Secondly, a greedy search and multiround planning method was proposed to determine the task assignment scheme and inspection order. Finally, this method’s effectiveness was tested under high precision orbit model and it was compared with hybrid en-coding genetic algorithm. In the example, the optimization effect of this method is slightly better than that of hybrid en-coding genetic algorithm and the efficiency is about 227 times of the latter, which indicates that greedy search algorithm and multiround planning method are more suitable for solving this problem efficiently. Related Articles | Metrics

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Opportunities and challenges of longdistance high-capacity continuous wireless power transmission LI Ming, DONG Shiwei, SHI Dele Chinese Space Science and Technology    2023, 43 (3): 1-13.   DOI: 10.16708/j.cnki.1000-758X.2023.0033 Abstract （294）      PDF（pc） （1058KB）（383）       Knowledge map    Long-distance high-capacity continuous wireless power transmission（WPT）is one of the candidate routes to realize space-based solar power exploitation and carbon neutrality.Firstly，the application demands and development opportunities were introduced with specific technical requirements for practical applications of long-distance high-capacity continuous WPT.Secondly，the international state-of-the-art research progress was reported.Then technical challenges were discussed，with respect to development trend and application needs.And toward these challenges，development suggestions were proposed. Related Articles | Metrics

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LEO constellation configuration design method with constant trajectory of subsatellite points ZHANG Yasheng, JIA Lu, YU Jinlong, LIANG Shuang Chinese Space Science and Technology    2023, 43 (3): 116-122.   DOI: 10.16708/j.cnki.1000-758X.2023.0044 Abstract （291）      PDF（pc） （5014KB）（350）       Knowledge map    An analytical design method for the LEO constellation configuration with constant trajectory was provided，where all satellites share a common subsatellite trajectory and the trajectory is fixed.The constellation configuration was coded with two parameters，the regressor and the number of satellites.Firstly，based on the idea of average orbital elements，an analytical model of repeat ground track orbit design was established under the condition that the harmonic order of the Earth’s non-spherical perturbation band is J4.Secondly，according to the relative motion law of the satellite and Earth，the analytical formula satisfying the common trajectory condition was established.Finally，the constellation configuration design model of the LEO constant trajectory constellation was constructed by combining the concept of repeat ground track orbit design and common trajectory design.The ultimate simulation results show that the configuration design method meets the design expectation，which verifies the effectiveness of this configuration design method.The constellation configuration is characterized by simple form，easy maintenance，and wide coverage.It guarantees the consistency of orientation between the space system and ground system，which greatly reduces the complexity of satellite-ground system cooperation. Related Articles | Metrics