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    25 April 2021, Volume 41 Issue 2 Previous Issue   
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    Recent research advances of passive intermodulation suppression methods for aerospace microwave components
    WANG Xiaoli, CHEN Xiang, LI Jun, CUI Wanzhao
    2021, 41 (2):  1-9.  doi: 10.16708/j.cnki.1000-758X.2021.0016
    Abstract ( 111 )   PDF (2921KB) ( 36 )   Save
    Passive intermodulation (PIM) is widespread in high power microwave passive components and systems, which may cause serious interference in satellite and terrestrial communication systems. The PIM suppression technology is a key research issue in both theory study and engineering applications, and is important to solving various PIM problems. On the basis of explaining the generation mechanism of PIM, the existing PIM suppression methods and research status at home and abroad are systematically and comprehensively summarized from the aspects of process, structure, electrical design and signal processing, and the advantages and disadvantages of various suppression methods are discussed. On this basis, the subsequent development trends are analyzed. Based on traditional process structure optimization design, integrated design based on advanced manufacturing technology, contactless passive intermodulation suppression and digital signal processing to achieve PIM suppression are the important future directions, which bring new ideas and methods for PIM research.
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    Study on the thermal radiation influence of the sputtering target on the ion thruster
    GENG Hai, SUN Mingming, LUO Junhua, LIU Jiatao
    2021, 41 (2):  10-18.  doi: 10.16708/j.cnki.1000-758X.2021.0017
    Abstract ( 93 )   PDF (5614KB) ( 46 )   Save
    In order to study the thermal radiation influence of the sputtering target on the ion thruster in vacuum facility, finite element analysis was adopted to simulate the plume distribution of the thruster in vacuum chamber. Having obtained the temperature variation of the sputtering target caused by the influence of plume on the target, variation of temperature and thermal deformation of the grids caused by the increase of the sputtering target temperature were analyzed. The results show that the thruster plume can be described by a directional molecular flow model, and there was almost no energy loss in the plume diffusion process. The gas pressure in most areas of the vacuum chamber was in the range of 2×10-3 Pa to 6×10-3 Pa when the thruster was working. Under the influence of the sputtering target, the central temperatures of the accelerator grid and the screen grid were 352℃ and 440℃, and the edge temperatures were 342℃ and 411℃, respectively. The reduction of the gap between the screen grid and the accelerator grid increased from 0.560mm (without the sputtering target) to 0.585mm. The experimental results show that the temperatures at the edges of the accelerator grid and the screen grid were 364℃ and 385℃ respectively, with an error of 6% compared with the test results. The temperature test value of the plume at the rear of the sputtering target was about 50℃ higher than that in the simulation results, and the error was due to the neglection of the energy deposition of plume particles in simulation.
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    Design and optimization algorithm of GEO/IGSO hybrid regional navigation constellation
    XU Zheyu, DU Lan, LIU Zhihao
    2021, 41 (2):  19-30.  doi: 10.16708/j.cnki.1000-758X.2021.0018
    Abstract ( 23 )   PDF (6882KB) ( 18 )   Save
    The regional navigation constellation can provide the navigation ability for the users of the targeted area with the balanced cost and efficiency, and the geosynchronous orbits are some of the important orbit types to construct non-polar regional navigation constellation. A configuration method was proposed for regional navigation constellation based on GEOs (geosynchronous orbits) and IGSOs (inclined geosynchronous orbits). Firstly, a set of SSP (sub-satellite point) involved design parameters were presented and depicted especially for the symmetric constellation. And the long-term perturbations due to the earth's oblateness were induced to recalculate the mean orbital elements of the GEOs and IGSOs and propagate their orbits. Then the statistical GDOP (geometric dilution precision) of the grid points of the specific navigation service area was used as the objective function for the DE (differential evolution) optimization algorithm. Finally, taking the Indian constellation of IRNSS as an example, the presented design and optimization algorithm was verified by the constellation simulation, and various configurations and orbit types of IRNSS constellation were discussed in detail. The results show that for India and surrounding region, the 7-satellite constellation can best consider the navigation performance and construction cost; the elliptical orbit is unable to take into account the navigation performance of the northern and southern hemispheres, which is difficult to expand to global navigation constellation. This method can improve the global optimization efficiency of GEO / IGSO hybrid regional navigation constellation, and provide the number of satellites and configuration design quickly for the subsequent asymmetric constellation. 
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    Space-based networks system and adaptive dynamic resource management
    WANG Rui, HAN Xiaodong, HAN Huan, WANG Baiyan, AN Weiyu, WANG Chao
    2021, 41 (2):  31-37.  doi: 10.16708/j.cnki.1000-758X.2021.0019
    Abstract ( 17 )   PDF (5378KB) ( 17 )   Save
     Along with the continuous extension of application and the emerging of task significance, space-based networks and communication satellite constellation play more and more important roles in future network communications. The technology progresses of space-based resource management are important for assurance of instantaneity and high efficiency of operational load. In this paper, the status quo and business characteristics of space-based network are analyzed. According to the function and characteristics of resource management system of space-based information network, the dynamic resource management technology was studied, including implementation scenario, function reconstruction and resource allocation. For realtime resource allocation, an adaptive distributed resource allocation method was proposed based on first price sealed-bid (FPSB) auction game, and the corresponding allocation scheme was designed. Finally, through the simulation of space-based network scenarios, the advantages of the proposed method in improving the utilization rate of resources and system operation efficiency were proved.
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    Analysis of configuration offsetting maintenance method for LEO Walker constellation#br#
    LI Jiuyang, HU Min, WANG Xuyu, LI Feifei, XU Jiahui
    2021, 41 (2):  38-47.  doi: 10.16708/j.cnki.1000-758X.2021.0020
    Abstract ( 15 )   PDF (14175KB) ( 7 )   Save
    Aiming at the problem of maintaining the stability of Walker constellation in low Earth orbit (LEO), the factors affecting the orbit perturbation of LEO satellites and the stability of constellation configuration were analyzed. By analyzing the characteristics of the orbit perturbation and relative drift of the LEO Walker constellation, a two-bias strategy was proposed. First, the offset amount at the first offset was obtained by fitting the relative drift amount of the constellation when it was not offset. Then the relative drift after the first offset was used to obtain the second offset, eliminating the effects of residual terms. The two offsets were superimposed to greatly reduce the relative drift. The results show that the deviation of the initial parameters of the satellites in the LEO Walker constellation caused the divergence of the relative ascension of the ascending node and the relative drift of the along-track angle. The two-bias strategy can reduce the relative drift of the two constellations to less than 0.1°, which improves the effectiveness of the strategy and the stability of the constellation configuration.
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    Temperature estimation of satellite equipment without thermistor based on BP neural network#br#
    NING Dongpo, XU Zhiming, LIU Zhijia
    2021, 41 (2):  48-54.  doi: 10.16708/j.cnki.1000-758X.2021.0021
    Abstract ( 15 )   PDF (3666KB) ( 7 )   Save
    There are only a few equipments that can be installed with thermistors because of the limited sources on satellite. A BP neural network which can predict the temperature of equipment without thermistor was built based on the excellent fitting ability of BP neural network for complex nonlinear system. The temperature data acquired in thermal test through thermal couple of equipments on satellite either with or without thermistors were used to train and test the neural network. The test result shows that the temperature prediction accuracy of BP neural network is smaller than 1℃, and the temperature prediction neural network can be used to accurately predict the temperature of equipment without thermistor. Additionally, the relationship between samples and estimation errors were also studied, showing that sample diversity and large data can reduce the estimation error significantly. 
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    Analysis of the influence of Mars surface thermal environment on spacecraft thermal control
    ZHANG Bingqiang, XIANG Yanchao, XUE Shuyan, ZHENG Kai, ZHONG Qi, ZHANG Youwei
    2021, 41 (2):  55-62.  doi: 10.16708/j.cnki.1000-758X.2021.0022
    Abstract ( 16 )   PDF (4981KB) ( 23 )   Save
    For the Mars surface exploration, the Martian atmosphere absorbs and scatters the incident solar radiation, while causing convective heat transfer between itself and the spacecraft on the surface of Mars. In the thermal design, it is difficult to directly assess the impact of the three heat transfer types (convection, radiation and heat conduction) on the spacecraft and determine the main transmission ways. Based on the investigation into the thermal environment such as Mars surface radiation and the atmosphere, the effects of radiation, convection and heat conduction on the spacecraft were compared and analyzed from the perspective of linearized heat transfer coefficient and convection-radiation ratio. The radiation heat transfer coefficient of the spacecraft surface varies with optical properties and temperature in the range of 0.3W/(m2·℃) to 1.4W/(m2·℃), and the convective heat transfer coefficient varies with the wind speed from 0.2W/(m2·℃) to 1.5W/(m2·℃). The conduction heat transfer coefficient can be controlled below 0.25W/(m2·℃). The results show that solar radiation is the main external heat source compared to Mars surface and sky radiation. Radiation and convective heat transfer on the surface of the spacecraft are two parallel transmission paths, both of which may become the main path. The heat conduction in the spacecraft is the main controllable factor of its thermal control.
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    Thermal performance equation of multilayer insulator for spacecraft
    ZHANG Yang, ZHAO Jianfeng, HAN Chongwei, ZHANG Ningli, NING Bo, DU Zhuolin, ZHAO Xin, ZHAO Qiwei
    2021, 41 (2):  63-70.  doi: 10.16708/j.cnki.1000-758X.2021.0023
    Abstract ( 43 )   PDF (2840KB) ( 47 )   Save
     The effective emissivity of multilayer insulator(MLI) is widely used in spacecraft thermal analysis and thermal design, and the empirical range of effective emissivity is 0.02 to 0.04 which is only related to numbers of layers and has nothing to do with temperature. The working condition of empirical range of effective emissivity is that the hot side temperature of MLI is within -10℃ to 50℃ and that the cold side is without solar heat flux. More condition deviation led to larger calculation deviation made by empirical range of effective emissivity.In order to solve the problem, the thermal performance equation of MLI normal heat transfer was proposed. The equation was made up of thermal radiation item and heat conduction item, and the acquisition method for the coefficient of radiation item and conduction item was described. As an example, the native 10-layer MLI was discussed, and the coefficients of the MLI were obtained,which was useful in engineering. The equation was examined in many working conditions. By using the equation, the cause of the problem was obtained, and the deviation was dropped from 20℃ to 5℃ in high and low temperature zone. The blade radiation model was well replaced by hybrid heat transfer model. Finally, the problem of how to design the operating conditions of MLI thermal balance test was briefly discussed.
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    Structural road extraction method for remote sensing image
    WANG Wenqing, HU Ruotong, HE Hao, YANG Dongfang, MA Xiaohua
    2021, 41 (2):  71-76.  doi: 10.16708/j.cnki.1000-758X.2021.0024
    Abstract ( 13 )   PDF (3950KB) ( 4 )   Save
    The road extraction of the remote sensing image plays an important role in the intelligent understanding of the ground. According to the structural characteristics of the road features, a road extraction method with structure similarity loss function and structural descriptor was proposed. Firstly, the proportion of the road is usually small in the remote sensing image, a shallow encoder-decoder based segment network with high resolution was proposed. Secondly, the structural similarity(SSIM) was introduced to the loss function and as the existing methods of road extraction network are mostly based on the comparison of the prediction and ground truth of each pixel value, the structural descriptor joined the task of road extraction as an optimization step which improves the ability of the network to make use of the structural information. Lastly, experiments on Massachusetts road dataset show that the proposed network gets the precision and F1-score up to 85.3% and 84.6%.
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    Vision sensor design of relative pose measurement for CubeSats
    DU Ronghua, ZHANG Xingxing, ZHANG Xiang, WANG Ling
    2021, 41 (2):  77-85.  doi: 10.16708/j.cnki.1000-758X.2021.0025
    Abstract ( 13 )   PDF (6136KB) ( 13 )   Save
    Aiming at solving the close-range relative navigation problem for onorbit serving (OOS) missions of CubeSats, a vision sensor design for measuring the relative pose was proposed. In order to circumvent the complex light conditions in space, a multi-layer stereo marker was designed. The LEDs with a wavelength of 850 nm were selected as the illuminators of the stereo marker. An infrared narrow band-pass filter that only let 850 nm length waves pass was added in front of the camera lens to improve the imaging quality of the stereo marker. An iterative direct solution (IDS) was derived for the relative pose estimation. This algorithm used the depth information provided by the non-coplanar points in the stereo marker to obtain an initial relative pose. The Haralick iterative algorithm was then introduced to optimize the initial relative pose. An experiment platform with six degree-of-freedom was built to test the performance of the vision sensor. The results show that the vision sensor can overcome the interference of ambient light. The accuracy of the proposed IDS algorithm for pose estimation is better than those of the classical P3P algorithm and EPnP algorithm. 
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    Reconstruction method of regional reconnaissance elastic constellation based on improved MOPSO#br#
    WANG Hao, ZHANG Zhanyue, ZHANG Haitao, JIANG Ping
    2021, 41 (2):  86-95.  doi: 10.16708/j.cnki.1000-758X.2021.0026
    Abstract ( 99 )   PDF (3963KB) ( 42 )   Save
    A reconstruction method based on an improved multi-objective particle swarm optimization algorithm was proposed. This method reconstructed damaged constellations by combining multi-satellite launch and on-orbit satellite phase maneuver. Firstly, reconstruction indexes were selected, including coverage, reconstruction cost, reconstruction time and elasticity. Secondly, the multi-satellite launching process and on-orbit satellite phase maneuvering were analyzed, and a uniform phase strategy was adopted for remaining normal satellites in damaged constellations. In order to restore original constellation performance, considering the maximum revisit time, elasticity, reconstruction cost and time, optimization models for reconstruction time and reconstruction cost were established. Finally, a MOPSO algorithm was improved, and a population update strategy based on learning mechanism was proposed. Discrete variables were transformed into continuous variables through variable transformation, which solved mixed variable optimization problems in reconstruction optimization models. Simulation for a damaged constellation shows that the time-optimal reconstruction scheme is launching 6 new satellites combined with the uniform phase of on-orbit satellites, and the cost-optimal reconstruction scheme is launching 4 new satellites combined with the uniform phase of on-orbit satellites. The case shows that the proposed reconstruction method is effective and can provide a reference for construction of reconnaissance constellations.
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    Orbital maneuver detection method of space target based on Neyman-Pearson criterion#br#
    WANG Qingrui, ZOU Jiangwei, WU Wenzhen, CHEN Jian
    2021, 41 (2):  96-103.  doi: 10.16708/j.cnki.1000-758X.2021.0027
    Abstract ( 14 )   PDF (4921KB) ( 4 )   Save
    Orbital maneuvering detection is one of the important demands of current space surveillance activities. When the orbit maneuver of the satellite occurs under the action of low thrust maneuvers, the step mutation feature appears in the relative distance change rate between the target satellite and the accompanying satellite. Because of the measurement noise, the step mutation feature of the distance change rate is submerged in the measurement noise and is difficult to be detected. An orbital maneuvering detection method based on probabilistic decision model was proposed in this paper. The measurement noise was modeled with an independent identical Gaussian white noise distribution. It took the distance change rate as the input data for orbit change detection. Consequently, the step mutation detection problem of the distance change rate was transformed into a probabilistic decision problem. The threshold of the decision based on Neyman-Pearson criterion was generated adaptively according to the false alarm probability constraint and the fluctuation characteristic of the input data. The feasibility and effectiveness of the proposed method were verified by simulation experiments under different parameters. 
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    On-orbit self-calibration method of non-coplanar gyros based on UDKF#br#
    ZHANG Xiaowen, LI Ji
    2021, 41 (2):  104-111.  doi: 10.16708/j.cnki.1000-758X.2021.0028
    Abstract ( 13 )   PDF (2313KB) ( 107 )   Save
    For the on-orbit calibration problem of non-orthogonal gyros, the orthogonal gyros on-orbit calibration method used in flight was improved, and the non-coplanar gyros on-orbit self-calibration method was proposed. Firstly, the attitude propagating error model of non-coplanar gyros was built, and then a UD decomposing Kalman filter (UDKF) was designed. The gyro constant bias was directly estimated, the gyro misalignment and scale factor error was estimated indirectly on orbit with star tracker and gyro measurements. When the filter was designed, in order to realize the sequential processing of measurement update, the measurement noise decoupling method was given. After filter designing, by using the vector norm constraint,the accuracy formulae were given to solve the misalignment and scale factor error from the indirect estimations. To illustrate the generality of this method, it was proved by formula derivation that the old method is a special case of this new method. In order to guide the design of calibration attitude maneuver, based on the analysis of observability, a simple rotation combination condition for system observability was given. Finally the mathematical simulation results show that this method is effective and the calibration accuracy of gyro misalignment is better than 0.01°.
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    An optimal trajectory design for lunar surface hop
    WANG Haofan, ZHANG Honghua, WANG Zeguo, GUAN Yifeng
    2021, 41 (2):  112-124.  doi: 10.16708/j.cnki.1000-758X.2021.0029
    Abstract ( 18 )   PDF (6669KB) ( 10 )   Save
    For the lunar surface trajectory design problem of hoppers, the fuel optimal trajectory for the whole hop process based on convex optimization was presented. Different from the typical method that the trajectory was designed separately firstly and then connected to a whole trajectory, it was assumed that the vertical ascent and descent time was fixed, then the constraints of the whole trajectory were divided into phases so that the constraints at each phase were convex according to practical engineering requirements. And the golden section method was used to search for the fixed ascent and descent time. The original fuel optimization problem was transformed into a second-order cone problem (SOCP) and the fuel optimal trajectory was obtained by solving this problem. In this way, an optimal solution was found for the whole trajectory design instead of a connected piecewise optimal one given by the classical method. As is shown in simulation results, when the piecewise constraints are satisfied, the fuel consumption of the piecewise convex optimization which adopts different vertical ascent and descent speed constraints is 25.7207kg and 25.3903kg respectively. On the other hand, the fuel consumption of the whole convex optimization method is only 24.9682kg, which is better than that of the piecewise convex optimization solution.
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    Disturbance rejection control for uniform scanning of space camera
    ZHANG Ai, LIN Zhe, LI Jing, LI Yinlong
    2021, 41 (2):  125-132.  doi: 10.16708/j.cnki.1000-758X.2021.0030
    Abstract ( 11 )   PDF (3124KB) ( 3 )   Save
    Aiming at the periodic disturbance during uniform scanning of space camera,the disturbance rejection of permanent magnet synchronous motor(PMSM)was studied.In order to solve the problem that traditional state observer and internal model methods are complicated with large amount of calculation,a feedforward compensation method was deduced.First,the disturbance was deduced based on the sensor output and system model.Then the feedforward compensation strategy was adopted to suppress the disturbance quickly.Compared with other suppression methods,this method is simple and has less computation.Finally,numerical simulation and experimental results illustrate that the sinusoidal disturbance is rapidly diminished after using this feedforward compensation method,and the scanning accuracy of space camera is evidently improved.
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