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25 April 2007, Volume 27 Issue 02 Previous Issue    Next Issue

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Dynamics Model of Large Flexible Spacecrafts Using Active Constrained Layer Damping Control Liu Zhizhen Li Dongxu (School of Aerospace & Matherials Engineering,National University of Defence Technology,Changsha 410073) 2007, 27 (02):  1-9.  Abstract ( 1880 )   Save The simplified model of large flexible spacecraft——the hybrid system of rigid body with flexible panels which were partially bonded with active constrained layer damping treatments,was studied.By virtue of quasi-coordinates Lagrange's equations,the dynamics equations including all of the high order terms were derived.In the process of modeling,the motions of the rigid body and the active constrained layer damping plates were decribed by hybrid coordinates,the complex modulus of damping material was described by Golla-Hughes-Mctavish(GHM) model.Based on these dynamics equations,the active constrained layer damping vibration controller of the solar panels can be designed,and also,the attitude dynamics of large flexible spacecraft can be studied. Related Articles | Metrics

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Kinematic Analysis of Soft-landing Mechanism for a Lunar Probe in the Deployment Process Huang Chuanping Liu Zhiquan (China Academy of Space Technology,Beijing 100094) 2007, 27 (02):  10-16.  Abstract ( 1770 )   Save Soft-landing mechanism is the key device for a lunar probe.The deployment principle of a "four-leg" soft-landing mechanism was analyzed.Singularity of the mechanism was discussed.Constraint conditions of the mechanism without singularity were given.Kinematic equation groups for the deployment mechanism were founded.Kinematic parameters and the variation were obtained by solving non-linear kinematic equation groups with Newton-Raphson method. Related Articles | Metrics

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Design and Hardware Implementation of Virtual Channel Link Control Unit and VCDU Multiplexing Unit Zeng Lianlian Yan Chunxiang (China Academy of Space Technology,Beijing 100094) 2007, 27 (02):  17-22.  Abstract ( 1903 )   Save Presented the virtual channel control unit and VCDU(virtual channel data unit) multiplexing unit based on the AOS(advanced orbit system) recommendation,which were prepared by consultative committee of data system.They were designed to support bitstream service and VCA(virtul channel access) service and provide B_PDU(bitstream protocol data unit) construction function,VCDU assembly function,VCDU commutation function,fill generation function and delimiting function.The units were designed by FPGA(field programmable gate array),suit defferent frequences and several sources.The design amalgamates the payload datas and the platform datas,transmits the bitstream through one channel,makes the satellite more agility,more open,more available.The work on this item can saving frequency resources,sustain broad band transmission,boost up the administer ability of the satellite.It is a pre-research program and it is the implementations of advanced orbiting data systems,which are used on satellites. Related Articles | Metrics

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Method of Spacecraft Access LEO Satellite Network Yuan Jiang1,3 Wang Yu2 Meng Xin1 (1 Center for Space Science and Applied Research,The Chinese Academy of Sciences,Beijing 100080) (2 Academy of Opto-Electronic,The Chinese Academy of Sciences,Beijing 100080) (3 Graduate School,The Chinese Academy of Sciences,Beijing 100080) 2007, 27 (02):  23-28.  Abstract ( 2023 )   Save With the advance of space technology,network has become a trend for spacecraft. Spacecraft needs not only transfer data to the ground,but also share the information with each other.By building the LEO satellite network,it is easy for spacecraft to transfer and share data.However the network access method is one of challenges of the LEO satellite network.If different access methods are designed for different LEO systems,that will increase the complexity of access methods.A unified access method was proposed by using the area-routing method.It will not only simplify the access method of spacecraft,and the design of satellite network system.In addition,the access method will be independent from the satellite network design.The computer simulation result shows the feasibility of the access method. Related Articles | Metrics

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Algorithm of Determining Relative States for Computer Vision System Used During Spacecraft Rendezvous and Docking Zhu Renzhang Zhang Lei Lin Yan (Beijing University of Aeronautics and Astronautics,Beijing 100083) 2007, 27 (02):  29-35.  Abstract ( 1771 )   Save An algorithm of determining relative attitude and position between target and chase vehicles by quaternion estimation via ranges of feature points was interpreted,especially a new algorithm of solving for the ranges is presented.Also an error-transmission method was given to obtain the relative state errors from the image coordinate deviations directly,which can be used for evaluating the algorithm of determining relative state.Computational simulation results show that the precision of the algorithm provided almost reaches the theoretic values given by the error-transmission method.As to patterns of feature points,non-planar patterns(with 3 to 5 feature points) are better than co-planar patterns(with 4 feature points at least),and feature points in the base-plane should be distributed symmetrically.Among four-point co-planar patterns,square patterns are better than others. Related Articles | Metrics

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Design and Robust Analysis for Spacecraft Attitude Controller Zhou Fengqi Han Yanhua Zhou Jun (School of Astronautics,Northwestern Polytechnical University,Xi'an 710072) 2007, 27 (02):  36-41.  Abstract ( 2449 )   Save The spacecraft's attitude control system was divided into the outer loop that was angle loop and the inner loop that was angle velocity loop based on their time scales.Then the control law of each loop was designed independently using exact linearization method.In the inner loop,robust stability was analysed using small-gain theorem considering the existence of perturbation of spacecraft moment inertia. Related Articles | Metrics

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Mechanical Analysis and Verifying Test of Sealing Situation at Orbicular Seal Joint Zhou Xin Pang Hewei Liu Hongyang (China Academy of Space Technology,Beijing 100094) 2007, 27 (02):  42-46.  Abstract ( 2283 )   Save The orbicular seal joint was widely used in the propulsion system of satellites. Its sealing mechanism was studied,and the important effect of the plasticity for metal seal was discussed.The nonlinear finite element method was applied to analyze plasticity problem and contact problem at the assembly process,the relation between tightening torque and sealing situation was provided.The validity of analysis method was verified by test. Related Articles | Metrics

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Multi-Grade Faulty Diagnosis Design of Small Satellite Yao Min Zhao Min (Nanjing University of Aeronautics and Astronautics,Nanjing 210016) 2007, 27 (02):  47-51+58.  Abstract ( 2003 )   Save A faulty diagnosis system based on multi-grade fuzzy neural network was presented which uses a multi-grade method to diagnose the fault of small satellite.In this multi-grade diagnosis a fuzzy clustering method was used in the first grade to estimate which module works abnormally.In the second grade fuzzy radial basis function neural network(RBFNN) was used to confirm which component or part was error.At last an experiment was done with this faulty diagnosis method according to a small satellite faulty simulation system .An experiment was done with this faulty diagnosis method according to a small satellite faulty simulation system at last.The result of the diagnosis shows no difference with the fault set beforehand in the simulation system.The result indicates that in a small satellite faulty diagnosis system,this multi-grade method can improve the integration and accuracy of the system,and greatly reduce the complexity of calculation in the process of the diagnosis. Related Articles | Metrics

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Algorithms for the Single Access Link Scheduling Model of Tracking and Data Relay Satellite System Chen Yingwu Fang Yanshen Gu Zhongshun (National University of Defense Technology,Changsha 410073) 2007, 27 (02):  52-58.  Abstract ( 2535 )   Save Mission planning & scheduling of tracking and data relay satellite system(TDRSS),which to support task plan making of TDRSS scientifically,was a main content of space resource management.One of the most important characteristics of single access link scheduling of TDRSS lies in that there was time windows constraint between tracking and data relay satellite(TDRS) and user spacecraft. Tasks could only be completed within the given time windows.The scheduling model was formulated based on reasonable assumptions and constraint programming method.The model was solved with genetic algorithm based on path representation of valid genes.On the basis of a limited experiment,it is obseroed that the algorithm was very effective in obtaining near-optimal solutions. Related Articles | Metrics

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Influence of Low Angle of Attack on the Flowfield Characteristics of an Axisymmetric Parachute in Terminal Descent Jiang Chongwen Cao Yihua Su Wenhan (Beijing University of Aeronautics and Astronautics,Beijing 100083) 2007, 27 (02):  59-65+71.  Abstract ( 1965 )   Save According to the characteristics of parachute,based on 0-thickness assumption of canopy,axisymmetric assumption of parachute,and steady assumption of flowfield,a fluid dynamics computational model was established.By solving RNG(Renormalization Group) k-epsilon turbulence N-S Equations over low angle of attack range of 0~5°,the numerical simulation result was in good agreement with the relative experiments.It was found that the direct connection of saddle point in the axisymmetric parachute sectional flowfield of 0° angle of attack was unstable.With the increase of angle of attack,the types and connection models of singular point will be changed.Limit cycles will appear in the vortex ring near the parachute surface.Also new saddle points and a nodal point will appear in the section flowfield.With the further rising of angle of attack,the area of limit cycles will decrease until limit cycles disappeared.The nodal point will change into a half-node and attach to the parachute surface.The results indicate that the topological structures of sectional flowfield of an axisymmetric parachute at low angle of attack accord with topological rules. The gained evolvement rules of the flowfield characteristics of an axisymmetric parachute in terminal descent here may lay foundation for further investigating parachute flow mechanism and fluid-structure coupling. Related Articles | Metrics

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Adaptive Diagonal Loading Beamforming Algorithm Zhang Xiaofei Zhang Shengnan Xu Dazhuan (Electronic Engineering Department,Nanjing University of Aeronautics & Astronautics,Nanjing,210016) 2007, 27 (02):  66-71.  Abstract ( 2989 )   Save Sampling matrix inversion beamforming technique(SMI) has the worse performance in the small snapshot number and high signal-noise-ratio.Diagonal loading technique can suppress noise beamforming for the small eigen value,and improve the beamforming aberration.But loading value is hard to solve.An adaptive diagonal loading beamforming algorithm is proposed in this paper.The algorithm loads adaptively diagonal matrix to enhance the algorithm robostness,according to the eigen structure of the received signal covariance matrix.Simulation results reveal that the algorithm has the better beamforming performance than conventional adaptive beamforming algorithm in the lower,middle and high signal-noise-ratio(SNR),and it has the better performance in the small snapshot number.So it has robust characteristic and the better performance.Finally the algorithm is no more complex and can be implemented easily,and it can be used widely. Related Articles | Metrics