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    25 December 2011, Volume 31 Issue 6 Previous Issue    Next Issue
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    Inverse Polynomial Shape based Method for Low thrust Trajectory Design
    CHENG Xing, SHI Xiao-Ning, CUI Nai-Gang
    2011, 31 (6):  1-7.  doi: 10.3780/j.issn.1000-758X.2011.06.001 
    Abstract ( 1711 )   PDF (389KB) ( 1685 )   Save
    Shape based approach is a reverse design method by assuming a certain shape of the trajectory to find the parameters which fulfill the boundaryconditions. The inverse polynomial function provided a new shape-based method for the low thrust trajectory design and initial value selection for directoptimization solver. Coupled with the astrodynamics functions, the inverse polynomial shape-based method was derived and used to solve the low thrust transfer problem in a fixed time. The results demonstrate that the method presented is reasonable for the low trust trajectory design. Furthermore, thesolutions tend to be near optimal and are able to provide initial guess for direct optimizer.
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    Outliers-tolerant Test Algorithms for Error Models of Radar Measurement
    HU Shao-Lin, YU Hui, WANG Xiao-Feng, LOU Lin
    2011, 31 (6):  8-14.  doi: 10.3780/j.issn.1000-758X.2011.06.002
    Abstract ( 1907 )   PDF (450KB) ( 1154 )   Save
    The precision and  reliability of spacecraft navigation mainly relies on the accuracy of error models of the radar system and measurement data. For the pulse radar, a series of new test algorithms were built, including  the F- test algorithm and the outliers- tolerant F- test algorithm to test the fittness of the error models with measurement data, and the T- test algorithm and outliers- tolerant T- test algorithm to diagnose the significance of error components. These algorithms were based on the theory of statistical hypothesis test and can be used in two different cases with or without outliers in measurement data respectively. These algorithms were tested with practical measurement data from the pulse radar in tracking a spacecraft. The results show that these algorithms have good outliers tolerance and adaptation, and are available to diagnose whether the error models of radar data are correct.
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    Nonlinear Feedforward Control for Spacecraft Relative Attitude Tracking
    TIE Yu-Jia, YANG Wei, YUE Xiao-Kui
    2011, 31 (6):  15-20.  doi: 10.3780/j.issn.1000-758X.2011.06.003
    Abstract ( 1874 )   PDF (269KB) ( 1708 )   Save
    The spacecraft relative attitude kinematics and dynamics based on modified rodrigues parameters (MRP) were proposed in the presence of serious nonlinear and controller design complexity during spacecraft relative attitude tracking control. A nonlinear feedforward controller was designed using Lyapunov method. The control law can not only ensure global  asymptotic steady of close loop system, but also make relative attitude tracking errors converge to zero field speedily. By using Matlab/Simulink programming, the modeling and simulation of spacecraft relative attitude tracking were discussed. Numerical simulations are exploited to verify the effectiveness of the model and control law.
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    Modeling and Analysis of Ground Physics Experiments on Orbit Movements Around the Earth
    LI Hao-Yang, SHE Zhi-Kun, XUE Bai
    2011, 31 (6):  21-26.  doi: 10.3780/j.issn.1000-758X.2011.06.0014
    Abstract ( 1771 )   PDF (384KB) ( 1469 )   Save
    Based on the force analysis of a ground physics experiment system, a mathematical model was built. The effects of liquid resistance, propulsion and simulated gravitation on the orbit were qualitatively and quantitatively analyzed. Specifically, according to the perturbation equations of elliptic orbits, a theoretical model for the ground experiments with liquid resistance, propulsion and simulated gravitation was derived. Then, the effects caused by propulsion bias and simulated gravitation bias were qualitatively and quantitatively analyzed. Finally, numerical simulations were used to verify the results obtained by theoretical analysis.
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    On-board Optimal Nominal Trajectory Guidance Method for Lunar Pinpoint Soft Landing
    LIANG Dong, LIU Liang-Dong, HE Ying-Zi
    2011, 31 (6):  27-35.  doi: 10.3780/j.issn.1000-758X.2011.06.005
    Abstract ( 1930 )   PDF (488KB) ( 1188 )   Save
    To achieve the pinpoint soft landing (PPL) on a target landing site of lunar surface and minimize the fuel consumption, an optimal nominal trajectory on board rapid programming guidance method for lunar PPL was studied, based on the proposed guidance strategy with on board autonomous landing site selection by LIDAR. Firstly, according to the 3-D spherical nonlinear orbit dynamics model, the optimal control problem of trajectory optimization was transformed into a nonlinear program problem (NLP) by using Legendre-Gauss-Lobatto pseudospectral method. Secondly,sequential quadratic programming (SQP) method was used to solve the transformed problem. Finally,the optimal trajectory was verified by using genetic algorithm. And a method of providing initial value database for SQP on board trajectory programming by using genetic algorithm was proposed. The numerical simulation results show this methodology and strategy for optimal nominal trajectory on board rapid programming can meet the need of lunar PPL real time guidance.
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    Optimal Cooperative Rendezvous of Spacecraft Considering Locations of Capture Interfaces
    HE Zhao-Wei, SHI Peng, GE Bing, ZHAO Yu-Shan
    2011, 31 (6):  36-42.  doi: 10.3780/j.issn.1000-758X.2011.06.006
    Abstract ( 1809 )   PDF (364KB) ( 1357 )   Save
    The optimal close range rendezvous of two spacecrafts was investigated. The complete 26 state model with six degree of freedom for the rendezvouswas developed to prevent the undesired collision of spacecraft considering the attitude change, the locations of capture interfaces, and the pathconstraints. The minimum quadratic control and minimum time problems were discretized into the problem of large scale onlinear programming bymeans of Gaussian pseudospectral method, which was solved by the software package SNOPT. The influences of different initial parameters on theoptimal solutions were also analyzed. Numerical simulation results show that the time and fuel cost may be decreased with the optimal cooperativerendezvous compared with the optimal active passive rendezvous.
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    Aliased Noise of Optical Sampling Imaging System for Space Remote Sensing
    JIANG Wei, CHEN Shi-Ping
    2011, 31 (6):  43-49.  doi: 10.3780/j.issn.1000-758X.2011.06.007
    Abstract ( 1752 )   PDF (413KB) ( 1024 )   Save
    In order to exactly calculate the ratio of  aliased noise in optical sampling imaging system for space remote sensing and analyze the influence of the system parameters,all leading noise sources were statistically modeled with an experimental scene model,and a noise calculating model including aliased noise was brought forward. By using this model,the ratio of aliased noise power was calculated with a spaceborne high resolution camera imaging system parameters,and the situations with different λF/p and different scene were simulated. The results show that the ratio of aliased noise is high in a spaceborne high resolution camera imaging system,and the aliased noise can be reduced by increasing λF/p.
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    A Novel AOS Virtual Channels Scheduling Algorithm with Broad Applicability
    TIAN Ye, NA Xin, GAO Xiao-Ling, LIU Qing-Li
    2011, 31 (6):  50-57.  doi: 10.3780/j.issn.1000-758X.2011.06.008
    Abstract ( 1750 )   PDF (502KB) ( 1096 )   Save
    A novel virtual channel dynamic scheduling algorithm with broad applicability in advanced orbiting systems is proposed, which can overcome the shortcoming of the dynamic priority scheduling algorithm based on VC urgency. First, the virtual channel urgency and the frame urgency are estimated separately, and then a weighted coefficient is used to combine them into a new transmission urgency function of virtual channel, which is used to make scheduling decisions. By choosing different weighted coefficients, the proposed algorithm can meet the data transmission requirements of various source models of AOS. Theoretical analysis and simulation experiments show that the proposed algorithm can achieve better performance than the dynamic priority scheduling algorithm based on VC urgency.
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    Robust Timing and Frequency Synchronization under Multipath Fading Channel for Orthogonal Frequency Division Multiplexing  Systems
    LIU Cheng-Zhen, JIN Peng-Jia, WU Xue-Ying
    2011, 31 (6):  58-64.  doi: 10.3780/j.issn.1000-758X.2011.06.009
    Abstract ( 1794 )   PDF (403KB) ( 1110 )   Save
    A synchronization scheme for  orthogonal frequency division multiplexing (OFDM) systems based on a novel training sequence was proposed. The training sequence consists of only one centrosymmetric OFDM symbol with two identical parts to  achieve reliable timing and frequency accuracy in the time domain. After coarse timing and fractional frequency synchronization  achieved, a successful estimation was declared for both channel path timing and integer frequency offset by IFFT algorithm which can largely reduce the computational load of the algorithm. For fine timing synchronization, a metric called signal to interference ratio  (SIR)was devised. Based on this metric, a fine timing synchronization method was developed to improve the timing precision. Comparison of the proposed fine adjustment algorithm and conventional synchronization algorithms by using computer simulation illustrates  that the method is more robust to multipath and pseudo multipath.
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    Experimental Investigation of a Negative pressure Loop Heat Pipe with a Flat Plate Evaporator
    CHEN Bin-Bin, LIU Wei, LIU Zhi-Chun, LI Huan, YANG Jin-Guo
    2011, 31 (6):  65-72.  doi: 10.3780/j.issn.1000-758X.2011.06.010
    Abstract ( 1763 )   PDF (499KB) ( 1581 )   Save
    A negative pressure copper methanol loop heat pipe (LHP) with a flat plate evaporator was designed for solving the heat dissipation problem of electronic devices with high heat flux. The investigation indicates that this LHP has high capacity of heat dissipation, which is able to start up with or without gravity assistance. When head load is 160W, the evaporator wall temperatures, are 85.8 °C, 66.3 °C and 64.6 °C at three gravity tilt angles of 0°, 18° and 30° respectively. The whole start period of the LHP is divided into three stages,including heat stage, pre start up stage and after start up stage. At low heat load period, the temperature oscillation phenomenon of the LHP occurs. With the gravity tilt angle increasing, both the evaporator wall temperature and the thermal resistance decrease. At the gravity tilt angle of 30° and heat load in the range from 10W to 160W, the LHP thermal resistance lies between 4.97 °C/W and 0.39 °C/W.
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    Dynamical Simulation of Tethered Subsatellite Based on Ritz′s Method
    FENG Jie, XIAN Yong, LEI Gang
    2011, 31 (6):  73-80.  doi: 10.3780/j.issn.1000-758X.2011.06.011
    Abstract ( 1734 )   PDF (489KB) ( 1077 )   Save
    Considering the tether′s mass, elasticity and deformation,the emphasis of the dynamical simulation problem for a tethered subsatellite is to solve the non-linear partial  differential equations.To establish the continuous mode functions, the dynamical models were built by Mankala method based on Newton's theorem and generalized Hook′s laws. The continuity of the numerical results was achieved via linear compounding of mode technique with polynomial shape functions by Ritz′s method. Hence, the complicated partial differential equations were transformed to ordinary differential equations. Based on the sub-satellite′s free deployment from the steady balance position and 5 degrees out of the plane, the numerical simulations were conducted. The simulation results show slight bending and other basic dynamical characteristics during tether′s swing and free deployment. Meanwhile, the calculation efficiency of Ritz′s method is low.
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