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25 October 2020, Volume 40 Issue 5 Previous Issue   
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System design and key technolongies of the GF-7 satellite
CAO Haiyi, ZHANG Xinwei, ZHAO Chenguang, XU Chi, MO Fan, DAI Jun
2020, 40 (5):  1-9.  doi: 10.16708/j.cnki.1000-758X.2020.0052
Abstract ( 83 )   PDF (5941KB) ( 68 )  
GF-7 satellite is the first 1∶10000 scale stereoscopic surveying and mapping satellite independently developed in China, and an important part of the national high resolution earth observation system. The satellite is based on the active and passive combined surveying and mapping system of “two-line array surveying and mapping + laser altimetry” and forms a series of key technologies and innovation points, such as highprecision internal/external element stability design, highprecision attitude stability control, the first X-band adaptive high-rate data transmission system, and onboard intelligent satellite management system. The capability of large scale stereoscopic mapping with little or no control points was realized. The system design of the satellite was described, and the technical innovation points were summarized such as observation system, high-precision load, attitude control, digital data transmission, intelligent satellite service, etc. The preliminary evaluation was carried out through the test results of satellites in orbit, and the satellites can meet the requirements of the 1∶10000 surveying and mapping mission.
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Dimensional stability design and verification of GF-7 satellite structure
QIAN Zhiying, LUO Wenbo, YIN Yazhou, ZHANG Ling, BAI Gang, CAI Zheng, FU Weichun, LU Qingrong, ZHANG Xinwei, ZHAO Chenguang
2020, 40 (5):  10-17.  doi: 10.16708/j.cnki.1000-758X.2020.0053
Abstract ( 56 )   PDF (4744KB) ( 22 )  
Dimensional stability is an important mission of GF-7 satellite structure design. The influence factor analysis was carried out in accordance to the demand of structural dimension stability, and then the design and verification process of structural dimensional stability was proposed according to the decomposed index. Firstly, on the basis of the structure configuration design, the structure material selection plan was determined by sensitive analysis. Then the thermal and structure design of the key component of dimensional stability, the integrated support structure, was proposed. Finally, the mean coefficients of thermal expansion of structure were obtained by thermal distorsion test, and the feasibility of the index was verified by in-orbit thermal deformation analysis using the updated finite element model of the satellite. The results show that the design of GF-7 satellite structure meets the requirements of dimensional stability index.
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Research on the application efficiency of variable coding modulation in remote sensing satellite
ZHANG Shasha, CAO Haiyi, ZHANG Xinwei, YAO Xingyu, ZHENG Xiaosong, ZHANG Yu
2020, 40 (5):  18-25.  doi: 10.16708/j.cnki.1000-758X.2020.0054
Abstract ( 57 )   PDF (3531KB) ( 22 )  
With the increasing amount of LEO remote sensing satellite observation data,the ability of data transmission has become a  factor to restrict the efficiency of satellite. Variable coding modulation (VCM) can be used to make full use of the system link margin, based on the dynamic evaluation of the satellite-ground data transmission channel conditions. And on the premise of ensuring the bit error rate and link margin, the optimal coding and modulation mode switching under the current channel conditions are carried out adaptively, so as to improve the satellite data transmission efficiency. Using this method, the efficiency of log link was simulated and analyzed. Compared with the constant coding modulation (CCM) with the same symbol rate, the transmission efficiency was increased by 42.1% on average, which can provide a reference for the design of data transmission channel of remote sending satellite.
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A disturbance mitigation method for moving appendages on spacecraft
LU Dongning, GUO Chaoyong, WANG Shuyi, CHEN Chao
2020, 40 (5):  26-33.  doi: 10.16708/j.cnki.1000-758X.2020.0055
Abstract ( 48 )   PDF (5717KB) ( 34 )  
To improve the attitude stability of the GF-7 spacecraft under disturbances from moving appendages,especially those induced by dualaxis directional antennae, a motion smoothing method was proposed and the corresponding disturbance mitigation technique was investigated. Firstly, as the attitude disturbances were usually caused by the data transmission antennae′s rapid capturing of ground targets for communications, a motion planning method with global smooth angular velocity was presented. Secondly, the general attitude dynamic equations of spacecraft with dualaxis antennae, which held true under any angular velocities, were developed and verified by comparison simulations. Then, feedforward compensation was developed and applied in the attitude control loop for reducing the disturbances from the antennae. Simulation results show that the proposed methods mitigate the disturbances of moving appendages by 90% while the antenna was working.
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Highprecision control technology and onorbit verification of GF-7 satellite
CHEN Chao, DING Jianzhao, WANG Shuyi, LIU Jie
2020, 40 (5):  34-41.  doi: 10.16708/j.cnki.1000-758X.2020.0056
Abstract ( 50 )   PDF (5870KB) ( 25 )  
 The performance of GF-7 satellite attitude and orbit control system (AOCS) is improved by developing new very high precision star sensor and solar array driver architecture (SADA). The precision of AOCS is improved by adopting on-board parameter calibration and low frequency compensation between satelliteground loop technologies. The result of flight test shows that the control system achieves the angular-second highprecision accuracy and the control stability is expected to be within 10-5(°)/s, which indicates the control methods are effective. Compared with other control systems of satellites, the system of GF-7 satellite is advanced in the world which has improved the ability of highprecision control of satellites in China. At the end of this paper, the development direction of GF-7 highprecision control is pointed out.
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Low-thrust transfers between librationpoint periodic orbits based on Gauss pseudospectral method
ZHOU Jing, HU Jun
2020, 40 (5):  42-52.  doi: 10.16708/j.cnki.1000-758X.2020.0057
Abstract ( 47 )   PDF (2731KB) ( 14 )  
In order to solve the problem of low-thrust orbit transfers between periodic orbits around  libration points in the three-body system, a novel shape function was constructed and a method based on Gauss pseudospectral method (GPM) was proposed. Firstly, the dynamics model of low-thrust transfers was built, a novel shape function was constructed to approximate the lowthrust transfer trajectory according to the type of initial orbit and target orbit. The approximate analytic solution for the transfer trajectory was deduced under the assumption that amplitude and phases change in the form of a polynomial to satisfy different constraints. Secondly, the optimal control problem of lowthrust transfer was discretized into a nonlinear programming problem based on the GPM, and the effective initial value of control variables of the nonlinear programming problem was obtained by solving and processing the approximate analytic solution. At last, the numerical simulation of transfers between Halo orbits around the L1 libration point of the Earth-Moon three-body system was conducted. The simulation result shows that the approximate analytic solution for low-thrust orbit transfers based on the new shape function is valid and general. The efficiency of GPM can be improved by 55%. Besides, the GPM can effectively solve the problem of lowthrust orbit transfers between periodic orbits around libration points in the three-body problem. 
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Research on autonomous navigation method for deep space exploration spacecraft in cruise phase
YE Zipeng, ZHOU Qingrui, WANG Hui
2020, 40 (5):  53-60.  doi: 10.16708/j.cnki.1000-758X.2020.0058
Abstract ( 51 )   PDF (3856KB) ( 19 )  
A method for autonomous navigation of deep space exploration spacecraft was proposed. In order to cope with the error of the spacecraft orbital dynamics model in deep space exploration, not only the radial velocity of the spacecraft relative to the sun, but also the line of sight vector of the asteroid was measured. The position information obtained by the asteroid's line of sight vector was calculated by the least squares method, and the state estimation error caused by the inexact dynamic model in the extended Kalman filter was modified by the improved information fusion method. At the same time, the observability of the model was calculated and analyzed. The simulation results show that the dependence of the algorithm on the dynamic model is significantly lower than that of the other algorithms. Under the same model precision, better result can be obtained.
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Design of point return orbit for human lunar polar exploration mission
LU Lin, LI Haiyang, LIU Jianghui, YANG Luyi
2020, 40 (5):  61-71.  doi: 10.16708/j.cnki.1000-758X.2020.0059
Abstract ( 55 )   PDF (4734KB) ( 20 )  
The optimal design of point return orbit was studied for human lunar polar exploration mission. According to the characteristics of lunar polar orbit (LPO), three return orbit maneuver schemes were proposed. Considering threeimpulse maneuver scheme, a serial orbit solution strategy from initial calculation to accurate calculation was adopted to design point return orbit. The initial orbit was obtained by establishing a novel model with threesegment two-body patched orbits based on pseudoperilune parameters to decouple the threeimpulse maneuver with the lunar escape. Two-segment orbits were matched to get precise point return orbit by using numerical continuation theory and the suggested backward and forward orbital integral model with high precision perturbation. The effectiveness and reliability of the approach proposed were demonstrated by simulation test. According to the simulation results by the method, the orbit characteristics of point return orbit were analyzed. The research conclusions can provide reference for the design of point return orbit scheme in human lunar polar exploration missions in the future.
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Unfolding characteristics analysis of pentahedral deployable truss unit
PENG Xiaoyu, LIN Chengxin, YAO Qi, YANG Dongsheng, TIAN Yun
2020, 40 (5):  72-81.  doi: 10.16708/j.cnki.1000-758X.2020.0060
Abstract ( 42 )   PDF (3931KB) ( 27 )  
According to the characteristic that pentahedral deployable truss units can be combined into various types of truss structures, a pentahedral deployable truss unit was designed to solve the space onorbit assembly of large space truss structures. The pentahedral deployable truss units were used for truss structure assembly after launching into space. In order to analyze the kinematic characteristics of pentahedral deployable truss unit, the degree of freedom of pentahedral structure was analyzed based on the constrained screw theory. Kinematics analysis on the pentahedral structure was carried out by using D-H coordinate transformation method, and the kinematics equation for the deployment process was acquired. The Lagrange method was used to analyze the structure dynamics and the dynamics equation for the deployment process was obtained. Analysis results show that the degree of freedom of the pentahedral deployable unit is 1. The deduced kinematics equation result is highly consistent with the simulation results of Adams simulation software, which can fully describe the structure deployment movement process. Increasing the torsion spring stiffness has less effect on the changing trend of the parameters. The joint acceleration is related not only to the driving force of the torsion spring, but also to the joint position and the joint speed. In the late stages of deployment, the influence of position and velocity on acceleration is obvious. 
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Research on submarine positioning based on low earth orbit sparse constellation with blue-green laser
XU Weizheng, KANG Guohua, LIU Jialu, ZHANG Lei, LIU Zongqiang
2020, 40 (5):  82-90.  doi: 10.16708/j.cnki.1000-758X.2020.0061
Abstract ( 39 )   PDF (5762KB) ( 14 )  
Submarines only surface when necessary, which greatly restricts realtime communication and positioning. The blue-green laser has advantages of high penetration in deep-water and a low attenuation coefficient, which has been verified in airborne and space-borne communication with submarines. Considering the principle of GNSS signal generation, combining the integration of the blue-green laser communication ranging with the precise orbit determination of the LEO satellite, a submarine positioning algorithm based on blue-green laser was proposed. By integrating carrier phase modulation into laser communication, pseudorange measurement of the submarine was achieved, and combined with its elevation measurement, underwater positioning was realized. For the service of the Belt and Road area, especially the South China Sea region, the constellation parameters were optimized, and a sparse constellation composed of three LEO satellites was designed. The submarine remained stable within the coverage area of the constellation. It completed communication ranging and navigation message reception at least twice with the interval of 1 to 3 minutes, and performed positioning calculation with two sets of observation data, precise ephemeris and elevation measurement. Considering the accuracy of satellite orbit determination, the laser propagation error in atmosphere and seawater, simulation shows that the positioning error in X and Z direction is less than 100m, and the error in Y direction is about 100 to 150 meters, which will help improve combat capability for submarines. 
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Collaborative folding design and deployment simulations of inflatable membrane trusses
HONG Yihong, LIU Yongbing, XU Yan, ZHANG Chao, FANG Qin
2020, 40 (5):  91-98.  doi: 10.16708/j.cnki.1000-758X.2020.0062
Abstract ( 51 )   PDF (7673KB) ( 45 )  
The inflatable membrane truss structures can be used in the deployable parts and supporting structures of large inflatable membrane spacecraft. A collaborative fold design scheme of inflatable membrane truss structures was studied. Firstly, the geometric relationship of the folded state for the skin structure was formulated. To be geometrically suitable for the folded state of the skin structure, the fold scheme of inflatable truss was designed. Thus the collaborative fold design method was established and the parameterized model was obtained. Synchronous folding in both horizontal and vertical directions was realized, with a horizontal folding ratio of 2.67 and a vertical folding ratio of 8.82. Based on the improved spring-particle system, the dynamic simulation of inflatable process of the inflatable membrane truss structures was completed. The dynamic behaviors and parameters of the inflatable process were obtained. The simulation results show that deployment process is stable and reliable without any physical interference among all components. The collaborative fold design scheme is proved to be useful and can provide technical support for the engineering application of this kind of structures.
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A feedback optimization access mechanism for satellite channel
DING Yi, CAO Xinyu, CHENG Zijing, LI Jie, ZHONG Qionghui, JIN Jun
2020, 40 (5):  99-110.  doi: 10.16708/j.cnki.1000-758X.2020.0063
Abstract ( 46 )   PDF (3742KB) ( 20 )  
It is urgent to improve the utilization rate of satellite channel resources and explore both efficient and feasible satellite interactive terminal access mechanism in the development of satellite communication. The disparity between the requirements for free access of satellite interactive terminal as they come and the access mechanism based on bandwidth preplanning in the current satellite communications with DVBRCS standard is emerging. Therefore, a channel feedback optimization access mechanism is proposed. The mechanism based on the signaling features of original protocol comprehensively considered the data service requirements for each satellite interactive terminal, exploratively introduced a modest incentive method and creatively constructed a dynamic negotiation feedback model to increase the access number of satellite interactive terminals and satisfy the requirements of satellite terminal ondemand access as they come. It enhanced the channel utilization efficiency, and maximized the service benefits of overall bandwidth communication as well. The experiments have proved that the bandwidth allocation feedback optimization mechanism improved the access rate by nearly one time compared with the traditional model and the algorithm took only about 0.67s with maximum number of terminal access, which could be a technical reference for the current use of satellite channels.
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Short-arc association algorithm for space target based on sine fitting
HUANG Qiushi, ZHANG Yasheng, FENG Fei
2020, 40 (5):  111-118.  doi: 10.16708/j.cnki.1000-758X.2020.0064
Abstract ( 47 )   PDF (6573KB) ( 10 )  
The star sensor is a high-precision attitude sensor with the ability to intermittently capture space targets and can be used as a space target monitoring platform. Accurately associating shortarc observations of star sensors is a prerequisite for achieving precise orbit determination of space targets. Through a large amount of observational data on the space target, it is found that the relationship between the declination and the right ascension of the space target always satisfies a sine curve with a period of 360 ° and that the peak value is related to the orbit inclination. A short arc association algorithm based on sinusoidal fitting for space targets was proposed, which avoids initial orbit determination and saves running time. In the simulation, the shortest observation time was 50s. By adding additional constraints to the dense GEO zone, it is possible to distinguish orbits with a 0.01 ° inclination difference. When the track interval is 3 h, the target association accuracy is above 90% under the three sets of noise conditions.
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Micro VLBI network for GEO satellite monitoring
ZHANG Zhibin, WANG Wei, YANG Peng, KALIUZHNYI Mykolay, MI Ligong, LI Guanghui, LI Peng, TANG Zhenghong, CUI Lang, HUANG Yong, WANG Guangli
2020, 40 (5):  119-125.  doi: 10.16708/j.cnki.1000-758X.2020.0065
Abstract ( 54 )   PDF (2483KB) ( 30 )  
According to the requirements of all-time, allweather and high precision geostationary orbit (GEO) satellite monitoring, a simple very long baseline interferometry (VLBI) observing system was developed and a micro VLBI network (MVN) including Shanghai, Duyun and Urumqi was built. Debugging in collocated stations was performed and GEO satellite named as Apstar6C was monitored by MVN, whose observing capability was evaluated. The receiving accuracy of single station without systematic errors was 2ns. The results show that the post-fit residuals of different baselines are about several nanoseconds. Moreover, the accuracy of observed GEO satellite orbit is in the level of 100m (internal and external accuracy of about 100m and 400m respectively). Unlike traditional VLBI or other GEO monitoring techniques, MVN has features including all-time, all-weather, low cost, easy deployment and convenient marketing, showing its great application value in the field of GEO satellite monitoring.
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