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25 February 2010, Volume 30 Issue 01 Previous Issue    Next Issue

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Autonomous Time Synchronization Algorithm on Hadamard Variance Among Navigation Satellites Gu Yanan Chen Zhonggui Shuai Ping(China Academy of Space Technology,Beijing 100094) 2010, 30 (01):  1-9.  Abstract ( 2534 )   Save High-accuracy auto-time synchronization is the foundation of the navigation constellation and a key technology of auto-navigation.The accuracy of time synchronization among navigation satellites is directly affected by frequency stability of on-board atomic clocks.GPS Rubidium atomic frequency standards(RAFS) exhibit non-trivial aging and aging noise characteristics,whereas the Allan variance does not explicitly converge for the noise type of α not more than-3),and can be greatly affected by frequency drift.The three-sample variance,commonly referred as a renormalized Hadamard variance was proposed,which was unaffected by linear frequency drift,converges for α more than-5),and thus can be used for modeling noise in Rubidium frequency standards.A standard Kalman filter algorithm based on improved clock error predication model and inter-satellites measurements equations was established for practical use in on-board RAFS.System simulation results show that more precise auto-time synchronization is achieved by this method. Related Articles | Metrics

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Parameter Identification of Orbital Free-floating Space Robot Tian Fuyang Wu Hongtao Zhao Daxu Shao Bing Sun Hongli Zhu Jianying(Nanjing University of Aeronautics and Astronautics,Nanjing 210016) 2010, 30 (01):  10-17.  Abstract ( 2564 )   Save The parameter identification methods for inertial parameters of the base and unknown objects handled by manipulators on a free-floating space robot was studied.First,kinematics model of robots based on spatial operator algebra theory was obtained.Next,parameter identification of the base was studied based on the conservation principle of linear and angular momentum,then parameter identification of the unknown object handled by manipulators was considered based on the parameters of the base.Finally,the effect of the robot parameters on parameter identification was analyzed.The feasibility of the parameter identification methods was demonstrated by a hardware experiment on the ground as well as the numerical simulations. Related Articles | Metrics

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Phasing Orbit Design for Chinese Lunar Satellite CE-1 Yang Weilian(China Academy of Space Technology,Beijing 100094) 2010, 30 (01):  18-24.  Abstract ( 2603 )   Save A new concept of phasing orbit was adopted in the orbit design for the first Chinese lunar satellite.The phasing orbit established a connection between super GTO,which is inserted by the launch vehicle CZ-3A,and the trans-lunar trajectory.In order to make the conjoint orbit more accurate,the orbital perturbations caused by earth gravitational field should be taken into consideration.For doing so making use of the solution to the classical general perturbation theory is a good choice.Based on the solution,we can perform transformation between the osculation elements and the mean orbits.First transfer GTO into mean orbit,then connect it to mean phasing orbits,after that transform back to osculation one and connect with translunar-trajectory. Related Articles | Metrics

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Study of Long-distance Approaching and Companion Flying Technology Wu Huiying Chen Hongyu Yu Yong Zhao Lingfeng(Shanghai Engineering Center for Micro-satellites,Shanghai 200050) 2010, 30 (01):  25-33.  Abstract ( 2825 )   Save The orbit control technology of two long-distance satellites with similar semi-major axis,eccentric angle and inclination RAAN was analyzed.First,a new method of controlling the swing of orbit normal axis by changing the semi-major axis to adjust the change rate of RAAN was studied;secondly,the relationship between the control time and the size of relative ellipse was given;thirdly,the method of estimating the parameter of the relative ellipse by the module difference of radial vector was put forward;finally,the proposed methods were verified by the long-distance approaching and companion flying simulation of SZ-7 companion satellite and orbital module. Related Articles | Metrics

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Programming of On-orbit Service Mission for Multiple Object Spacecrafts in Coplanar Circular Orbits Ouyang Qi Zhao Yong Chen Xiaoqian (National University of Defense Technology,College of Aerospace and Material Engineering,Changsha 410073) 2010, 30 (01):  34-40.  Abstract ( 2558 )   Save In order to reduce the cost of on-orbit service,the programming of on-orbit service mission for multiple object spacecraft in coplanar circular orbits was studied.First,the mission scenario was analyzed and the mathematic model was set up.The mission programming was a bi-layer optimization problem,and the outer layer was an optimal time distribute question while the inner layer was the multiple-revolution Lambert problem.Secondly,the solving method and its corresponding step were given.The inner layer problem was solved by a scheme method and the outer layer problem by the genetic algorithm.Finally,take three object spacecrafts as example,the programming problem was solved under two conditions that the mission time was limited or not.The results validate the efficiency of the method. Related Articles | Metrics

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Study of Close-loop Hovering Method at Any Selected Position to Space Target Song Xumin Fan Li Chen Yong Li Zhi(Academy of Equipment Command and Technology,Beijing 101416) 2010, 30 (01):  41-45.  Abstract ( 2581 )   Save The method of hovering at any selected position to spacecraft target was studied.For the present open-loop method was sensitive to external disturbance and initial error,a close-loop hovering method was proposed based on the Hill equation.The simulation was performed and the method was validated.It shows that the fuel consumption of two control methods are approximate but the performance of the close-loop control is better,which can realize hovering at any selected position to spacecraft target in spite of the initial velocity error. Related Articles | Metrics

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Attitude Control Algorithm for Spacecraft Formation Flying Based on Network Synchronization Bi Peng Luo Jianjun Zhang Bo(Northwestern Polytechnical University,Xi′an 710072) 2010, 30 (01):  46-51.  Abstract ( 2831 )   Save In order to achieve coordinated work,the control system of spacecraft formation flying required a unified cooperative management.To enhance the cooperativity of attitude control for spacecraft formation flying,the synchronization control theory of networks was applied toattitude control of spacecraft formation flying.First,the modified rodrigues parameters(MRP) were adopted to describe the attitude dynamics of spacecraft;then,the nonlinear attitude cooperative control law was designed for spacecraft formation flying based on synchronization control algorithm of networks.Considering the differences of attitude change between the member spacecrafts,a hybrid control strategy was designed for spacecraft formation flying using hybrid control techniques.Simulation results validate the effectivity of the control method and the control law,and the hybrid control has better control characteristics compared to single feedback mechanism. Related Articles | Metrics

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Hybrid Algorithm for Distortion Compensation of Space Target High Resolution Range Profiles Du Xiaoyong Lin Xiaohong Wang Zhuang(National University of Defense Technology,Changsha 410073) 2010, 30 (01):  52-59.  Abstract ( 2253 )   Save Distortion compensation of high resolution range(HRR) profiles plays an important role in ISAR imaging of space target with high speed.Since the ambiguity function′s peaks of space target baseband echo lay on a cluster of parallel lines which contained the original,a multi-objective programming model was established based on the constraint bounds of the line cluster.After that,an analytic algorithm for velocity estimation was presented with the application of regularization principle.Furthermore,an iterative searching algorithm was applied to minimize the entropy of HRR profiles and a velocity estimator with higher precision was provided,where the proposed analytic solution was set as the initial value for iteration.Simulations demonstrate that the proposed hybrid searching strategy takes the advantages of analytic algorithm and iteration algorithm in the computational complexity and estimate precision,which can effectively estimate the velocity of space target and compensate the distortion of HRR profiles. Related Articles | Metrics

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Reliability Verification Test Methods of a Hatch for Manned Spacecraft Liu Zhiquan Xia Xiangdong(China Academy of Space Technology,Beijing 100094) 2010, 30 (01):  60-64.  Abstract ( 2597 )   Save The functions,principles and failure modes of a hatch for manned spacecraft were presented.Reliability characteristic parameters of the hatch was given.Based on the thought of measurement for characteristic parameter of the hatch,the reliability verification test method was put forward,including test method,test state,test program,failure criterion and reliability assessment method.An application example of the method was shown.By these methods,the reliability of the hatch for manned spacecraft could be verified. Related Articles | Metrics

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Experiment Study of Fluid Loop System on Manned Spaceship Huang Jiarong Fan Yufeng Fan Hanlin(China Academy of Space Technology,Beijing 100094) 2010, 30 (01):  65-71.  Abstract ( 2522 )   Save The thermal control fluid loop system technology scheme of manned spaceship was introduced,including system configure,flow chart,operating model,main technical status,and etc.All of the fluid loop experiment cases and related results were listed.Test data shows that fluid loop system has excellent temperature adjustment and adaptation ability.Further analysis of the heat transfer capability was carried out on heat exchange devices such as thermal radiator,air condenser,cold plate,and middle heat exchanger.Besides,the accumulator capability was also proved under the extreme low temperature case.The fluctuant problem of pump′s pressure head caused by gas released from fluid under extreme low pressure was also discussed.Finally,some suggestions on future fluid loop system improvement were presented. Related Articles | Metrics

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Performance Test for Image Quality Assessment Wen Yihong Yang Kai Li Bo(School of Computer Science and Technology,Beihang University,Beijing 100191) 2010, 30 (01):  72-77.  Abstract ( 2692 )   Save There are many objective methods for quality assessment(QA) in static image compression domain,but the research on assessing QA′s concidence with human quality judgements is inadequate.In order to compare their performances,an assessment method was designed.First build test image database,then obtain objective and subjective scores,finally compute all kinds of results based on the criteria.The test results prove that SSIM is more adapted than PSNR for assessing static image quality,and also verify the accurate of the proposed method. Related Articles | Metrics

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Simulation About Buffer Process of Omni-directional-type Airbag Landing Device Deng Chunyan Pei Jinhua(Institute of Unmanned Aerial Vehicle Research,Nanjing University of Aeronautics and Astronautics,Nanjing 210016) 2010, 30 (01):  78-83.  Abstract ( 2609 )   Save In order to explore landing technology of Mars lander,the omni-direction airbag landing device of Mars Pathfinder was used and the structural design and landing mathematic and mechanical model were established by use of modern FEM analysis technology.The simulation process was developed,and the important parameters including a dynamic process of whole airbag to cushion the landing,overload analysis of important structural parts,the displacement and speed changes,internal air pressure and temperature curve and the airbag structure dynamic stress distribution were obtained.The result demonstrates the good buffer property of Mars lander and engineering application of FEM simulation analysis. Related Articles | Metrics