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    25 June 2018, Volume 38 Issue 3 Previous Issue    Next Issue
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    Surface adjustment method of deployable cable antenna based on steepest descent algorithm
    LIU Xiao, WU Minger, ZHANG Huazhen
    2018, 38 (3):  1-7.  doi: 10.16708/j.cnki.1000-758X.2018.0022
    Abstract ( 203 )   PDF (6315KB) ( 61 )   Save

    Considering the geometric nonlinearity of cable structures and the high-degree coupling of nodal displacements, a reasonable optimization method is essential in order to improve the surface adjustment efficiency of cable antenna. The equilibrium matrix and flexibility matrix of double-layer cable-net structures were partitioned based on the topology. The gradient formula of surface error to the tensile forces of tension ties was derived in derivative form. The infinite norm of surface error gradient was used to determine the element of tension ties which has the most significant effect on the surface error. Based on the steepest descent algorithm, the negative gradient direction of surface error was chosen as the optimizing path. The surface error due to the length tolerances of cable elements is decreased by adjusting the tensile forces of tension ties. The double-layer cable-net model of AstroMesh antenna was established and some numerical surface adjustment experiments were carried out. Results indicate that the surface error after adjusting approaches zero.

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    Optimal real-time lunar soft landing using random forest
    JIANG Chunsheng, SHEN Hongxin, LI Hengnian, WANG Yong
    2018, 38 (3):  8-14.  doi: 10.16708/j.cnki.1000-758X.2018.0020
    Abstract ( 101 )   PDF (5177KB) ( 49 )   Save

    Traditional optimal trajectories for lunar soft landing can’t be calculated in real time if there’s error when spacecraft entering orbit or during the descending stage. A novel scheme was proposed to replan the trajectory in real time for the random forest model. The descending stage was modeled by three phases: deboost, descend and land. The modelcan predict the control by the state of spacecraft as the input, the lander descend slower and the error gets smaller. The simulation results show that with a 500m error in entering orbit the distances deceases to 50m after the deboost phase. This error is in the range of the training set of descend phases, so after that the position error is less than 10m and the velocity error is less than 0.01m/s, both in tolerance. Meanwhile this method is fast enough to satisfy the real time control.

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    Parametric finite element modeling and design platform for SPS
    YANG Chen, HOU Xinbin, WANG Li
    2018, 38 (3):  15-23.  doi: 10.16708/j.cnki.1000-758X.2018.0025
    Abstract ( 161 )   PDF (8564KB) ( 10 )   Save

    Due to the large dimension with multiple elements and nodes, the efficiency of finite element modeling (FEM) using traditional method is very low in dynamics and control simulation of Solar Power Satellite (SPS). The simplified model only can be assumed as rigid or rigid-flexible system, which will lead to modeling errors by this approximate simplified way. Firstly, a parametric FEM method and design platform for SPS were proposed to reduce the FEM modeling period and increase the efficiency of design, analysis and optimization. Based on planar SPS concept, the basic parameters and FEM were introduced. Secondly, the numbering rules for the nodes and elements were defined, and the process of parametric set was also presented. Based on mixed programming technology of APDL, UIDLand TCL/TK, the FEM module and design platform were both constituted. The FEM modeling can be easily realized by menus and human computer inter action interface. The FEM process and the dynamic parameters were both given through a detailed example. The validity and applicability of the proposed method can be proved.

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    Degree of freedom andsingularity analysis of the deployable truss antenna reflector
    HU Fei, SONG Yanping, HUANG Zhirong, ZHU Jialong, LIU Wenlan
    2018, 38 (3):  24-34.  doi: 10.16708/j.cnki.1000-758X.2018.0029
    Abstract ( 59 )   PDF (5904KB) ( 48 )   Save

    For the deployable truss antenna composed of tetrahedral elements, the degree of freedom (DOF) of 3RR-3RRR element and multi-element was analyzed based on the screw theory, and the complexities of the over-constraint and the singularity analysis of the structural element were reduced. Firstly, the position and characteristics of the motion pair could be expressed simultaneously by the screw theory, so the motion spinors of hinges of the 3RR-3RRR element were established, and the number of the over-constraints was solved. Secondly, according to the modified Kutzbach-Grubler formula, the DOF of 3RR-3RRR element was solved, and the singularity and instantaneity of the special configuration were analyzed. Finally, the equivalent structure method was used to simplify the network’s structure and solve the DOF of the reflector. Then the relative distance between two disks was calculated to verify the deployable coordination of the antenna. The results show that the tetrahedral element has one degree of freedom and four over-constraints, and the constraint singularity is obtained under the special position of the hinge. After networking, the reflector is a single DOF mechanism, which can be fully deployed by the control of a single drive to realize the coordination of the deployable antenna at work, and has a good application in spatial mechanism field.

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    Study on heatflux density/ stratified temperature/carbonization layer of hypersonic vehicle
    YANG Kaiwei, ZHANG Yang, LIANG Huan, ZHANG Lisong
    2018, 38 (3):  33-39.  doi: 10.16708/j.cnki.1000-758X.2018.0024
    Abstract ( 219 )   PDF (3723KB) ( 76 )   Save

    Limited by the capacity of the test equipment, the ground wind tunnel can’t fully simulate the near space thermal environment of the hypersonic vehicle. The longtime high temperature heat sensor was installed on the surface of the aircraft. For the first time in china, the characteristics of heat flux density time-varying data and boundary layer transition in the hypersonic vehicle above Ma 12 was obtained. The measured heat flow value is the same as the theoretical prediction value, and the deviation is less than 20%. Theoretical calculation of the internal temperature of resin based composites is higher than actual value, by the method of adding physical property parameters with temperature variation and the thermal conductivity in the heat conduction differential equation of resin matrix. And the internal stratified temperature and thickness of carbonization layer were calculated. Compared with the measured results, the deviation between the calculated value and measured result is less than 70℃, but the calculated value is higher than measured result and the maximum deviationis 275~320℃, when the thermal conductivity and physical property parameters with temperature variation are not considered.

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    A method ofcalculatingintegraltimefor off-axis remote sensing camerabased on equivalent focal plane
    WU Bin, SUN Yanping, YIN Huan, ZHU Jun, LU Chunling, BAI Zhaoguang
    2018, 38 (3):  40-44.  doi: 10.16708/j.cnki.1000-758X.2018.0033
    Abstract ( 183 )   PDF (4035KB) ( 84 )   Save

    At present, most of the in-orbit and in-producing optical remote sensing satellites are equipped with off-axis remote sensing cameras. In order to ensure the view axis imaging at the nadir, the camera needs to pitch a certain angle to compensate for the off-axis angle. As a result, there will be an angle between the focal plane and the horizontal plane of nadir when imaging by push broom and it will lead to an inaccurate integral time. An accurate method of calculating integral time based on equivalent focal plane was proposed. This method constructed an equivalent focal plane parallel to the horizontal plane of nadir. By establishing a strict geometric model, the pixel size corresponding to the real time of electric charge moving was calculated and thus the accurate integral time was obtained. Simulation experiments show that this method can increase the calculation accuracy of the integral time by 1.2%, and it will improve the image quality in orbit.

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    Weighted discriminator function based tracking method forbinary offset carrier signals
    YAN Tao, WANG Ying, QU Bo, WANG Guoyong, LEI Wenying, BIAN Lang
    2018, 38 (3):  45-53.  doi: 10.16708/j.cnki.1000-758X.2018.0034
    Abstract ( 141 )   PDF (10109KB) ( 14 )   Save

    To remove the ambiguity threat and maintain the outstanding code tracking performance of binary off set carrier (BOC) signals, an unambiguous tracking method based on weighted discriminator function (WDF) was developed. The WDF combined the noncoherent early minus late power (NELP) discriminator with the sub carrier phase cancellation technique (SCPC) discriminator to generate a discriminator function without false lock points for BOC signal tracking. Regarding BOC (10,5) signal, the simulation results show that compared with SCPC, pseudo correlation function based unambiguous delay lock loop (PUDLL) and symmetrical pulse ambiguity removing (SPAR) successively, the proposed WDF has2.5dB, 5.5dB and 8.3dB improvement in terms of code tracking error. The multipath errors of WDF method are reduced to 60.4%, 32.8% and 38.0%, respectively. Therefore, the proposed WDF is an effective BOC signal unambiguous tracking method without standing performance.

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    Block compression of remote sensing image based on data-hiding#br#
    CUI Tao, ZHOU Quan, LI Jun, HU Yanlang
    2018, 38 (3):  54-59.  doi: 10.16708/j.cnki.1000-758X.2018.0031
    Abstract ( 139 )   PDF (4805KB) ( 56 )   Save

    At present, JPEG2000 and other image compression methods are limited by the compression multiple, which can not meet users’ real-time transmission requirements for mass remote sensing data. Therefore, the amount of data generated by high-resolution remote sensing images needs to be further reduced to meet the spatial transmission requirements of remote sensing image data. Aiming at this situation, a method for block compression of remote sensing image based on data-hiding was proposed. By using the similarity of image blocks, the reference image blocks and similar image blocks were determined. The numbers of similar image blocks are hidden in the reference image blocks, and only the reference image block is subjected to JPEG2000 compression. The standard image library was used as the sample image to simulate. The experimental results show that this method can reduce the amount of data before the image compression by 1/3 and increase the compression ratio of the sample image by 1.5 times.

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    An optimization-based pointing strategy design of plume impingement detumbling technology#br#
    LIU Yuqi, PAN Yi, LI Qiang
    2018, 38 (3):  60-68.  doi: 10.16708/j.cnki.1000-758X.2018.0032
    Abstract ( 192 )   PDF (7134KB) ( 8 )   Save

    In view of on-orbit capturing for free-tumbling uncooperative targets, to de-tumble the target using plume impingement force will improve the safety and feasibility of capture mission. The pointing strategy is required under the circumstance that the solar array norm is inclined from spin axis. Pointing strategy design is blank still. The optimization of pointing strategy will benefit the accuracy and efficiency of the system. A parametric plume impingement model was built, then a working condition was proposed based on typical targets, and the sensitivity of de-tumbling torque to relative position and attitude was given. Finally, by designing the target function, the model of pointing strategy was built. Simulations show that the pointing strategy is suitable for situations that solar array slopes at an angle with desired torque, and the accuracy is improved to 10 degrees with a relatively large torque. The method is feasible for spin target with a rotation of solar panel relates to spin axis and the target with nutation motion, and the research will support service vehicle’s control system design.

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    Optimal station keeping of geostationary satellites by electric propulsion
    KUAI Zhengzhong, SHEN Hongxin, LI Hengnian, HE Qingbo
    2018, 38 (3):  69-75.  doi: 10.16708/j.cnki.1000-758X.2018.0027
    Abstract ( 216 )   PDF (5162KB) ( 58 )   Save

    Considering the longer control arc of electric propulsion and the no longer applied assumption of impulse, a linear time-varying model for dynamics of geostationary satellite by perturbations and an optimization method for long-term control strategy were derived. A high-precision dynamical model of mean orbital elements was introduced based on equinox orbital parameters, which is highly consistent with STK-HPOP model. An optimization model considering overall orbit east-west and south-north control, and an optimization solving method based on sequential quadratic programming were proposed. In the simulation example, the problem of station keeping within 4 weeks for geostationary satellites configured with two thrusters was studied. The results show that the proposed method could be used to optimize the long-term station keeping control strategy.

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    Research on multi-source information fusion task scheduling of space-based information port#br#
    WANG Zhi, DENG Changlin, GUO Wei, ZHU Weige
    2018, 38 (3):  76-84.  doi: 10.16708/j.cnki.1000-758X.2018.0028
    Abstract ( 149 )   PDF (8220KB) ( 19 )   Save

    To achieve multi-source information fusion in the space-based information port, the data can be transmitted and processed on the satellite, and the transmission time of receiving and distributing data in the data center can be reduced. It can improve the timeliness of information acquisition. Considering the high timeliness requirement of task and the limited resources of the space-based information port, a multi-source information fusion task scheduling problem was proposed. By analyzing the task flow of multi-source information fusion and resource characteristics of the space-based information port, a multi-source information fusion task scheduling model was established to minimize the task completion time, and a multi-machine circular insertion (MCI) algorithm was designed to solve the model. Simulation results show that compared with the Johnson list algorithm, the algorithm can reduce the task completion time by 10.8%, and the running time of the algorithm is about 1/20 of the genetic algorithm, which proves that the algorithm can meet the high timeliness of task scheduling of space-based information port.

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