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25 April 2005, Volume 25 Issue 02 Previous Issue    Next Issue

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Parametric Estimation of Mixed Poisson-Gaussian Distribution Model Zhou Hongchao Zhu Jubo Wang Zhengming (National University of Defense Technology, Changsha 410073) 2005, 25 (02):  1-5.  Abstract ( 3031 )   Save According to the noise composition in CCD image, the added mix Poisson-Gaussion noise model is analyzed. Two methods are presented for parameters estimation, in which the moment estimation method can also be applicable to the condition of non-zero gaussian noise. Simulation calculation confirms that this method is more accurate. Related Articles | Metrics

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Theoretical Simulation of Infrared Radiation Fields of Satellite Shen Guotu Yang Baocheng Cai Jiguang Jiang Jin (East China Normal University, Shanghai 200062) Gao Jing (Shanghai Jiaotong University, Shanghai 200030) 2005, 25 (02):  6-10.  Abstract ( 1736 )   Save A geometry model of a type of satellites was built based on the universal framework for theoretical simulation of infrared radiation fields. By taking account of inhomogeneous background radiation and in light of the corresponding physical model, the outside surface temperature fields and the infrared radiation fields of the satellite were simulated. Related Articles | Metrics

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Launch Opportunity Analysis for Lunar Probe Yang Weilian Zhou Wenyan (Chinese Academy of Space Technology, Beijing 100086) 2005, 25 (02):  11-15.  Abstract ( 1982 )   Save To launch a lunar probe is actually a problem of rendezvous between the probe and the Moon. Since the positions of the Moon vary the lunar trajectories are different for different times of rendezvous. The relation of the right ascension and argument of perigee of the required orbit with the lunar position is derived within one lunar month. Based on this relationship the launch opportunity and launch window are discussed. Related Articles | Metrics

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The One-Dimensional Analysis of Heat and Mass Transfer Processes in Loop Heat Pipe Evaporator Xiang Yanchao Yao Wei Li Jindong (Chinese Academy of Space Technology, Beijing 100086) 2005, 25 (02):  16-21+51.  Abstract ( 2052 )   Save This paper analyzes two kinds of evaporation in loop heat pipe (LHP) evaporator, namely evaporation at porous wick surface and evaporation in the porous wick. One-dimensional calculation of heat and mass transfer processes is conducted. The results show that evaporation normally takes place at porous wick surface, and evaporation in the porous wick may possibly happen only when inlet liquid is subcooled. Moreover, variables having effects on heat and mass transfer processes are discussed, which include thickness and thermal conductance of porous wick, and sulcool of the inlet liquid. Related Articles | Metrics

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Research on Design of Nonlinear Smoothing Filter Based on Feedforward Neural Networks Sheng Shouzhao Wang Daobo Huang Xianghua ( Nanjing University of Aeronautics and Astronautics, Nanjing 210016) 2005, 25 (02):  22-25+33.  Abstract ( 1886 )   Save The design of nonlinear smoothing filter based on feedforward neural networks is discussed. The existence of the nonlinear smoothing filter and the composition of filter error variance are analyzed theoretically. The target function for training networks is given, then a new suboptimal algorithm for training networks is proposed, which has good noise suppression capability. Its reliability and advantage are illustrated through an example. Related Articles | Metrics

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Dynamics Simulation and Application of Satellites Formation Flying Lin Laixing (Beijing Institute of Control Engineering, Beijing 100080) 2005, 25 (02):  26-33.  Abstract ( 1717 )   Save Several small satellites flying in formation may constitute a virtual satellite with the performance the same as or better than a large satellite, which will open up a new application field for small satellites. The formation flying concepts and their application are firstly outlined, then the orbit dynamics of the virtual satellite is investigated. Three kinds of dynamics models are described, the model accuracies and their applications are analyzed through mathematical simulation. At last, the accuracy and the application of each mathematical model are analyzed. Related Articles | Metrics

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Study on Long-term Degradation of Solar Absorptance Properties of Geostationary Satellite Thermal Control Coatings Feng Weiquan Ding Yigang Yan Dekui Liu Xuechao Wang Wei Li Dongmei (China Academy of Space Technology, Beijing 100029) 2005, 25 (02):  34-40.  Abstract ( 1827 )   Save This paper introduces a study of 15 years geostationary environmental effects on solar absorptance degradation at outer surface of satellite, in order to supply reliable bases for thermal control design and material selection. A kind of combined low energy irradiation simulation test methods is studied. A combined low energy environment simulation test facility and a solar absorptance in-situ measuring system developed by CAST is briefly introduced. A long-term solar absorptance degradation simulation test of satellite thermal control coatings such as S781 white paint, SR107-ZK white paint, silvered F46, OSR etc is carried out on that facility. The test data for 15 years environmental effects on solar absorptance degradation of these thermal control coatings are obtained. The comparison between the simulation test and flight test are made to prove the reality of the simulation. Related Articles | Metrics

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Frequency Domain LMS Based Adaptive Beamforming Algorithm Zhang Xiaofei Xu Dazhuan (Nanjing University of Aeronautics & Astronautics, Nanjing 210016) 2005, 25 (02):  41-46+58.  Abstract ( 2300 )   Save Frequency domain LMS based adaptive beamforming algorithm is presented in this paper. The received signal of array antennas is analyzed, which shows that different DOAs correspond to different frequency, and the received signal is the addition of different spatial frequency signals, Which is the foundation of frequency LMS beamformer. This novel adaptive beamforming algorithm uses FFT as the preprocessing, and uses LMS algorithm to implement adaptive beamforming in frequency domain. Fast fourier transformed signal has a better decorrelation and leads to better convergence of LMS. Theoretical analysis and simulations demonstrate that this algorithm converges faster than the conventional adaptive beamforming algorithm, and it has the better performance. And this algorithm is robust to coherence source. Finally the algorithm is less complex and can be implemented easily, and it can be used widely. Related Articles | Metrics

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Preliminary Design and Characteristics of Vertical Soft-landing Trajectory to the Moon Lin Shengyong * Li Zhuji ** He Xingsuo * (*Northwestern Polytechnical University, Xi'an 710072) (**Aerospace System Engineering of Shanghai, Shanghai 201108) 2005, 25 (02):  47-51.  Abstract ( 1845 )   Save A patched-conic technique is used to formulate the mathematical model of vertical soft-landing trajectory to the moon. Some formulas of preliminary design of transfer orbit from the earth to the moon are derived. The characteristics of the trajectory are presented by simulation. The analysis results can serve as a guidance for preliminary trajectory design. Related Articles | Metrics

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Constellation Optimum Design of Satellite Positioning System Based on MEO and GEO Satellites Chu Haibin Zhang Naitong Gu Xuemai (Harbin Institute Technology, Harbin 150001) 2005, 25 (02):  52-58.  Abstract ( 2141 )   Save In this paper, the characteristics of “Beidou” satellite positioning system are analyzed. The idea of “Beidou” GEO satellites combined with some MEO satellites constellation to perfect Chinese regional satellite positioning system is put forward. The details of general satellite constellation opimization method are presented, and the comparison of different design ideas and different orbital constellation concepts is given. Through simulation and comparison, among those design schemes, 2 GEO plus some MEO satellites scheme is chosen to be the final optimized one. With respect to the chosen constellation cover performance, the PDOP characteristics are calculated. Related Articles | Metrics

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Research on GALILEO/SINS Integrated Navigation System Hua Bing Liu Jianye Xiong Zhi (Nanjing University of Aeronautics & Astronautics, Nanjing 210016) Liu Hong (Air Force Aeronantics University, Changchun 130000) 2005, 25 (02):  59-64.  Abstract ( 1724 )   Save According to the feature of GALILEO system, this paper focuses on the GALILEO/Strapdown Inertial Navigation System (SINS)pseudo range integrated navigation mode. This paper analyzes and builds GALILEO error equation, and the error mode and Kalman Filter equation of GALILEO/SINS pseudo range integrated navigation system is given. In order to verify the validity of the integrated navigation system designed, the covariance analysis method is used in virtual simulation to study the performance of the integrated navigation system. The results of virtual simulation show that the GALILEO/SINS pseudo range integrated navigation system can increase accuracy validity. Along with the improvement of GALILEO, this system will have a bright application prospect. Related Articles | Metrics

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Design of A Scheme of Robust Estimation Applied on Net of Inter-Satellite Measurement Zhang Yan (National University of Defense Technology, Changsha 410073) Zhang Yulin (The Academy of Equipment Command & Technology, Beijing 101416) 2005, 25 (02):  65-71.  Abstract ( 1805 )   Save Navigation algorithm for constellation autonomous navigation using inter-satellite measurement is discussed. Considering the characteristic of autonomous system, the algorithm must be provided with ability to check fault points and resist gross errors. Therefore, a scheme of robust estimation based on robust least square estimation and applied on net of inter-satellite measurement is designed in this paper by analyzing the characteristic of net of inter-satellite measurement. According on the difference of influence imposed on residual by fault points and gross errors of observation, the method of processing step by step is put forward. Compared several general schemes of robust estimation by examples, the result shows that!the scheme of robust estimation designed in this paper is effective. Related Articles | Metrics