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    25 April 2009, Volume 29 Issue 02 Previous Issue    Next Issue
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    Periodic Relative Motion Control Based on theθ-D Nonlinear Control Method
    Luo Jianjun Zhou Wenyong Yuan Jianping (College of Astronautic,Northwestern Polytechnical University,Xian 710072)
    2009, 29 (02):  1-7+24. 
    Abstract ( 1909 )   Save
    In order to maintain 1ong-term periodic relative motion trajectory with minimum fuel consumption,an optimal control method based onθ-D nonlinear control technique was investigated. A relative motion model,considering the J_2 perturbation and suitable for motion in general elliptic orbit,was used.Theθ-D nonlinear controI law was developed tO control the relative motion by dealing with the model of relative motion by the method of extending the state variables.The periodic relative orbit was designed based on the relative orbit elements and the mission requirements.Simulation results indicate that the proposed control method can carry out the suboptimal control of the periodic relative motion.
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    Attitude Stabilization of an Underactuated Spacecraft with Two Reaction Wheels
    Jin Lei Xu Shijie (School of Astronautics,Beijing University of Aeronautics and Astronautics,Beijing 100191)
    2009, 29 (02):  8-16. 
    Abstract ( 1957 )   Save
    Under the assumption that the total angular momentum of the system is not zero, Euler angles of the spacecraft at rest with respect to the inertial frame can not be controlled tO zero when there are only two flywheels output torque.Furthermore,the angular rate stabilization and spin-axis stabilization achieved based on the assumption can not satisfy various demands of attitude control.A kind of attitude stabilization scheme tO the most extent was firstly proposed,which was the spacecraft angular velocity stabilization as well as the spacecraft line-of-sight aiming at an arbitrarily given inertial direction.Then,the expected orientation of spacecraft with zero angular velocity was derived with a new attitude parameterization and LQR controller was designed based on the linearized system.The simulation results demonstrate that the LQR controller can achieve the expected attitude stabilization scheme,which not only satisfies the attitude control demand of the spacecraft with antennae or camera,but also enhances the reliability of the underactuated spacecraft.
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    Research on Static Stability of Lunar Lander with Legs
    Hu Yabing Sun Yi (School of Astronautics,Harbin Institute of Technology,Harbin 150001)
    2009, 29 (02):  17-24. 
    Abstract ( 1765 )   Save
    Stability margin is used to describe the static stability.The mathematical relationships between the static stability characteristics and the geometry and ubiety parameters of lunar lander with legs were derived.The effects of parametric quantitative change on static stability characteristics were analyzed.The static stability characteristics of lunar lander with three legs and four legs were compared.The results show that the lunar lander with four legs is more steady than the lander with three legs.The lunar lander with legs was designed and optimized based on these mathematical relationships and results.
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    Research on Satellite Attitude Control Problems of Zero-momentum Reaction Wheel System
    Li Pengkui Qian Shan Guo Caifa Cai Hong (National University of Defense Technology,Changsha 410073)
    2009, 29 (02):  25-32. 
    Abstract ( 3297 )   Save
    To study the problems of decoupling and eliminating precession for zero-momentum reaction wheel system,a new method to eliminate precession was put forward.The stability of zero-momentum wheel satellite,only using wheel as the executive component,was analysed.The principle which was used by the bias momentum system to eliminate precession and nutation was utilized to zero-momentum wheel system.According to the characteristic of zero-momentum reaction wheel,the magnetic control laws were improved.The proposed scheme was applied to zero-momentum wheel system to cope with its attitude control problems while non-decoupling. Numerical simulations were conducted,and the results demonstrate the feasibility and validity of the proposed method.
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    Reliability Test Methods for Seat Buffer in Manned Spacecraft
    Liu Zhiquan Man Jianfeng (China Academy of Space Technology,Beijing 100094)
    2009, 29 (02):  33-37+58. 
    Abstract ( 1764 )   Save
    The functions,principles and main failure modes of a seat buffer in manned spacecraft were introduced.A reliability model for this type of seat buffer was established. Reliability characteristic parameters of this mechanism were given.Based on the thought of characteristic parameter measurement,the reliability test methods of the mechanism were put forward.An application example of the methods was shown.By these reliability test methods,the reliability of the seat buffer in manned spacecraft was verified.
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    Research on the Ground Simulation Test Platform for Control System Based on CAN Bus
    Yang Xixiang Zhang Weihua Xiao Kai (National University of Defense Technology,Changsha 410073)
    2009, 29 (02):  38-45+52. 
    Abstract ( 1902 )   Save
    The ground simulation test evaluation was conducted for the small satellite and launch vehicle control systems transmitting data with CAN bus.Based on the two-stage bus network composed of CAN bus and Ethernet,the ground simulation test evaluation platform for satellite and launch vehicle control system was established,and the solutions for software and hardware of the bus nodes were proposed,and the analogue scheme for built-in test was designed.The simulation result shows that the signal of satellite control system,the operation of bus,the control cycle and network time delay can be appropriately analyzed with this platform.The research provides theoretic reference and technology support for the alternative evaluation,control and test study of the satellite and launch vehicle control systems.
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    Magnetic and High-frequency Electromagnetic Field Analysis in Electron Cyclotron Resonance Thruster
    Yang Tielian Yang Juan Mao Genwang Xia Guangqing (College of Astronautics,Northwestern Polytechnical University,Xian 710072)
    2009, 29 (02):  46-52. 
    Abstract ( 1773 )   Save
    Electron cyclotron resonance thruster has the advantages of cathodeless operation, high specific impulse and simple structure which make the thruster very attractive for deep space exploration.Its discharge chamber is the key component,in which the working media of electron cyclotron resonance plasma is produced.The magnetic and high-frequency electromagnetic field in the chamber are very important for thruster startup and stable operation.Hence the numerical simulation and analysis of the fields are very important.Three models with different materials of l Ocm discharge chamber for magnetic and high-frequency electromagnetic field calculation were established with finite element analysis software.With the models,the field distribution was calculated and analyzed.The results show that the location of electron cyclotron resonance surface in each model is appropriate,but the soft ion style is better.The electron cyclotron resonance surface overlaps the maximum microwave electric field region,through which the plasma was formed reliably.
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    Analysis of Positioning Accuracy of Dual-Satellites Passive Location Algorithm Aided Digital Map
    Xu Ang Fan Shiwei Zhang Yong (Beijing Tracking&Communication Technical Institute,Beijing 100094)
    2009, 29 (02):  53-58. 
    Abstract ( 1909 )   Save
    The positioning method based on WGS-84 ellipsoid model using dual-satellite TDOA/FDOA measurements was discussed,and the positioning error caused by target zero-height assumption was analyzed.The results show that if the target'S height is more than 1 km,digital map should be used tO improve accuracy.The positioning precision using digital map was analyzed by many simulation results.The research shows that this method is reasonable.At last,the influence of digital map's height accuracy was analyzed.
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    Analysis on the Influence of Natural Convection during Melting of Phase Change Material
    Jian Lujing Zhang Jiaxun Li Jindong (China Academy of Space Technology,Beijing 100094)
    2009, 29 (02):  59-64+71. 
    Abstract ( 2141 )   Save
    In order to analyze the influence of natural convection during the melting process of phase change material(PCM),the two dimensional unsteady single-phase governed equations were built and simulations were conducted with SIMPLE method for the melting process in a square cavity heated from below and cooled from above.The characteristics of temperature and flow fields varied with time were studied.The results show that natural convection increases the effective heat conductivity of liquid PCM.With the solid-liquid interface moving upwards,the effect of natural convection is enhanced and the flow patterns change continually.
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    Study of the Time-Space Bench Transformation of Mars Probe Orbital Motion Modeling
    Wei Jian Xu Shijie (School of Astronautics,Beijing University of Aeronautics and Astronautics,Beijing 100083)
    2009, 29 (02):  65-71. 
    Abstract ( 1952 )   Save
    The theoretical research and engineering practice of Mars exploration need a systematic series of time—space transformation coordinate systems tO describe the orbital motion of Mars probes.During the Mars exploration missions,the relative motion information of the probe around the Mars should be presented.However,the Earth—based ground tracking and control can only provide the relative motion information of the probe around the Earth.In order to solve this problem,definitions of several Mars—centered coordinate systems were given,and computation methods of the transformation matrices between different coordinate systems were introduced.In the end,the numerical simulation of the Mars probe's orbit dynamics based on the time-space bench put forward in this paper was carried out.The results were compared with those obtained from based on STK.The comparison between the results demonstrates the validity of the time space transformation system.
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