Science & Technology Review CONTENTS	Vol.26  No.20  2008 (Sum No. 266)
	This issue published on 28. Oct., 2008
Forward
3  Entering into a New Era of Solar System Exploration OUYANG Ziyuan
News Round
9  400 Years Later, Let's Start Again HUANG Yongming
Suggestion
10  Improving Food Security Detection Mechanism ASAP, and More GUO Yiping, YANG Ling, YE Fei
Special to S&T Review
21  Development of Technologies of Extravehicular Activities PANG Zhihao
Articles
28  Field-of-view Constrained Guidance Algorithm for -V-bar Departure LIANG Libo, LUO Yazhong, LI Haiyang, et al. Abstract: This paper investigates a guidance algorithm for -V-bar departure, with consideration of the constraints of field of view and safety distance. The constraint model is first built. By introducing a weighting factor of impulse, the multi-impulse Clohessy-Wiltshire guidance algorithm for the field-of-view angle and safety distance constraints is then designed based on the two-impulse Clohessy-Wiltshire rendezvous algorithm. The influence of the weighting factor of impulse on the number of impulses, maneuvering time and propellant consumption is analyzed. The effectiveness of the proposed algorithm is evaluated by an example. The simulation results show that the proposed guidance algorithm can well satisfy the conditions for the constraints. The number of impulses and the maneuvering time decrease as the weighting factor increases, while the relationship between the total velocity increment and the weighting factor is not apparent. Keywords:  rendezvous and departure; -V-bar departure; field-of-view angle; safety distance; Clohessy-Wiltshire rendezvous algorithm
32  Research on Attack Avoidance for Spacecraft CUI Hongzheng, HAN Chao Abstract: This paper first presents a relative motion dynamics model for two spacecraft based on relative orbit elements, with a certain precision requirement, as a starting point for further related computation and research. The main perturbation factors and the relationship between the spacecraft and the unidentified object are taken into account. The range, elevation angle, azimuth angle and their rates are to be measured by microwave radars or other instruments fixed on the spacecraft to obtain the relative position, relative velocity and relative orbit elements, and to realize relative navigation. After the determination of an unknown object's trajectory, a judgment is made by alert strategy to decide whether it is hostile or not and whether one has to avoid it or not. The avoidance orbit maneuver strategy is discussed based on relative orbit elements, with respect to the realization of keeping away from object, going with object, following object, transferring to initial orbit, etc. The relative motion, avoidance alert strategy, autonomous relative navigation and avoidance control strategy are implemented by Simulink for typical cases to show the avoidance method's feasibility. Keywords:  space dynamics; spacecraft attack avoidance; relative orbit elements; relative navigation; avoidance alert; avoidance control strategy
37  Undetermined Factor Method for Finite Element Analysis of Undetermined Beam-plate Composite Structures ZHU Zengqing, CHEN Jianjun Abstract: Probabilistic method can not be properly applied in case of small sample. To deal with such situations, the undetermined but objective information is considered, and in the finite element analysis model of space beam and plate structures the structural physical parameters and the applied loads are defined as undetermined variables. And a structure analysis method based on the undetermined factor method is proposed. From the expression of undetermined factors, the computational expressions of the structural displacement response and the element stress response are obtained. It is concluded that the confidence levels of structural responses are in direct proportion to the confidence level of each parameter. Compared to the probabilistic method, the proposed method can obtain reliable results with higher confidence levels in case of inadequate number of data or insufficient information; moreover, it is simple and easy to apply. At last, an example is given, in which the possible values and confidence levels of the undetermined structure responses are obtained. The rationality and validity of the presented method are demonstrated. Keywords:  solid mechanics; structural analysis; beam-plate  composite structures; undetermined information
43  Architecture of Navigation and Control System of Planet Exploration Rover SONG Jinze, SHI Meiping, LI Yan, et al. Abstract: Based on the concept of human-machine interaction, a three-layer hierarchical architecture for planet exploration rover navigation and control system is proposed with consideration of drive conditions and tasks. In the architecture, a deliberation-reaction hybrid navigation and control strategy is adopted.  Various human-machine interaction mechanisms are exploited, so the competence of human operators on both planning and reaction are incorporated into the ground-based interactive planning layer, and imported into the onboard navigation system through tele-control commands, thus the human-machine intelligence integration is implemented, the movement safety and the environment adaptability of lunar rover are improved. Keywords:  pattern recognition and intelligent system; exploration rover; navigation and control system; machine learning
46  Four Impulses Minimum Time Transfer Orbit Design Using Hybrid Genetic Algorithm ZHANG Hongbo, ZHENG Wei, TANG Guojian Abstract: Transfer orbit design and optimization is a fundamental work concerning the space mission of spacecraft and the study of minimum time transfer orbit design approach is of great significance for a rapid response in space. By analyzing the physical course of four impulses orbit transfer, the orbit optimization problem is transformed to a parameter optimization problem. Accordingly, the mathematical model of multiple impulses orbit transfer is established. The hybrid genetic algorithm is chosen to optimize the transfer time, and two different hybrid structures are designed: a serial one and an embed one. In order to handle constraints flexibly, an adaptive annealing penalty function is selected. Finally, a numerical simulation is carried out to verify the effectiveness of the algorithm. The results show that the two hybrid genetic algorithms designed in this paper are efficient in solving the multiple impulses orbit transfer design problem, and especially flexible and effective in dealing with the multiple constraint optimization problem. Keywords:  orbit design; hybrid genetic algorithm; multiple constrains optimization; simulated annealing
50  Rapid Optimization of Lunar Soft Landing Trajectory Based on Generalized Lagrange Multiplier ZHAO Jisong, GU Liangxian Abstract: Soft landing is an important prerequisite of lunar exploration. Without air on the lunar surface, the velocity of lander must be reduced with thrust. The reduction of fuel consumption is a main consideration in increasing payload. So the fuel optimal lunar soft landing is an optimal control problem with variable final time.  This paper develops a rapid optimization method for lunar soft landing trajectory based on integral transformation, Generalized Lagrange Multiplier (GLM) and quasi-Newton method.  Through integral transformation, the negative angle velocity of lander corresponding to the lunar center is first introduced to replace the time in the motion equations, and the original optimal lunar soft landing problem is transformed into a fixed final integral variable optimal control problem.  Then, by direct discretization of the control variable, the fixed final integral variable optimal control problem is converted into a Nonlinear Programming (NLP) with 4th Admas predict-modification scheme for integration.  Finally, GLM is used to deal with constraints in the NLP, and the obtained unconstrained NLP is solved with quasi-Newton method. The solutions are compared with that obtained from Pontryagin's Maximal Principle (PMP). The effect of initial penalty factor on the robustness of this approach is analyzed. Simulation results show good accuracy, rapid convergence (time consumption of less than 1 s), and robustness with initial values of this approach, which means that it can used to generate an optimal soft landing trajectory through the onboard computer of the lander. Keywords:  lunar soft landing; rapid optimization; integral transformation; generalized Lagrange multiplier quasi-Newton method
55  Simulation of Errors in the Absolute Position Determination in Space Based on X-ray Pulsars GU Shuwen, WANG Anguo Abstract: The principle of the TOA (time of arrival) measurement for the X-ray pulsars was studied. Based on the TOA measurement, the model of absolute position determination in the space in SSB was established, and how to obtain the integer cycles vector was explained. The relationship between the pulse phase observation time and the TOA accuracy was shown based on the SNR. Using the simulated pulse phase data, the system of position determination in the space based on the X-ray pulsars was simulated. The result shown that there was a better resolution for searching the cycle ambiguity, and the phase observation time was important to the position determination accuracy. Keywords:  X-ray pulsar; TOA measurement; integer cycle vector; phase observation
60  Real-time Attitude Control for Gravity Gradient Micro-satellite HAN Jianbin, WANG Xinsheng Abstract: Gravity gradient micro-satellite is a kind of satellite that orientates itself with respect to the earth using gravity gradient moment. Before reaching the state of the stability of gravity gradient, active control is required for the micro-satellite to complete gravity gradient capturing and dumping of the angular velocity. In view of the dynamics of the gravity gradient micro-satellite, a mathematical model of the micro-satellite in a body fixed frame is proposed. The magnetic torque is chosen as the executor which has a small mass and needs a low power. The magnetic torque is adjusted with the local geomagnetic intensity and the micro-satellite will obtain the active control torque. According to the result of mathematical simulation, the real-time on-board computer is used in the hardware-in-loop simulation. The result of semi-physical simulation shows that the method can be used for the gravity gradient micro-satellite. Keywords:  control of spacecraft; gravity gradient; semi-physical simulation; magnetic torque
65  Doppler Instantaneous Frequency Simulation of Radar Echo Signal LU Jiuming, LIANG Jianguo Abstract: The radar echo signal is a non-stationary time-variable signal, and its instantaneous frequency is an important parameter in the echo signal received by radar receiver, by which the moving information of the target can be obtained in space. Its mathematical basis is analyzed with respect to Doppler instantaneous frequency in the radar echo signal processing. Its signal frequency spectrum peak value changes with time variation. The performance parameter of the Doppler instantaneous frequency is simulated by the time-frequency analysis method, the associated distribution information in the time domain and frequency domain is obtained, which can easily be used to catch the moving data of target in space, and therefore, to detect and track the moving target in space. Keywords:  instantaneous frequency; moving target, time-frequency analysis, Doppler radar signal
69  UWB Radar Signal Design Based on High Resolution Range Profile ZHANG Jindong, WANG Haiqing, ZHU Xiaohua Abstract: The detection performance can be improved by designing related radar signals to maximize the energy of echoes according to the target impulse response. A new method based on phase-coded ultra-wideband signal is proposed in this paper in order to optimize the transmit-receiver waveform design by fully exploiting power of the transmitter to enhance output.  The signal to Interference plus Noise Ratio(SINR) is increased for a fixed transmitter by transmitting more energy.  To realize the poly-phase-coded ultra-wideband radar signal design based on High Resolution Range Profile(HRRP) of the target, a target function is first built for optimization calculation and then a new Constant-Module Conjugate Gradient(CM-CG) algorithm is used. Simulation results show that the poly-phase-coded radar signal derived by this algorithm approaches the optimal waveform and the method enjoys fast convergence and small computation amount. Keywords:  signal and information processing; waveform design; UWB radar signal; conjugate gradient
72  Fast Image Matching Based on Hill-climbing YAN Yuzhuang, WANG Yiping, HUANG Xinsheng Abstract: For a high speed system, a fast image matching algorithm based on Hill-climbing search is presented. By analyzing the correlative surface of NNPROD, a heuristic searching algorithm is defined for multi-climbers to climb the hill according to their priorities to ensure the global optimization. The paper also proposes three schemes to improve the speed of image matching, they are: adaptive adjustment of the climber's step, calculation of the correlative coefficient according to samples of the images, and a strategy of combining the Hill-climbing and Layered-searching. The experimental results show that the algorithms presented enjoy an excellent performance. Keywords:  hill-climbing; fast algorithm; layered-searching; image matching; NNPROD method
76  Combat Effectiveness Evaluation for Satellite Navigation System with Missile Precise Strike Capability DONG Chengxi, WU Dewei Abstract: In order to evaluate quantitatively the navigation satellite combat effectiveness with missile precise strike capability, an information support function of satellite navigation system for missile operation is used, together with the performance index configuration. The function relationship between performance parameter and combat effectiveness index is analyzed, especially, with respect to missile precise strike. The simulation shows that satellite navigation system will play an important part in improving precise strike capability of missile, which will also provide food of thought in theory for further system combat applications. Keywords:  satellite navigation system; missile precise strike; combat effectiveness; evaluation
79  Design of Variable Structure Tracking Control for a Class of Discrete-time System SHAO Lei, LEI Humin, TANG Zhili Abstract: As a new method to estimate the uncertainty, a variable structure tracking controller is proposed to deal with a class of discrete-time system with unmatched uncertainties.  Taking advantage of the multiple sliding surfaces and the philosophy of backstepping, the proposed method defines multiple sliding surfaces by auxiliary reference signals, designs a controller based on the philosophy of backstepping, and makes use of the estimation of the uncertainty to reduce the influence of the uncertainty.  A detailed stability analysis of the whole system is presented. The proposed control method is applied to the control of a nonlinear missile under unmatched uncertainties, and the simulation shows the effectiveness of the proposed method. Keywords:  navigation, guidance and control; discrete-time variable structure control; backstepping; unmatched uncertainties
83  An Accurate Detection System for Missile MMW Synthetic Aperture WANG Benqing, LI Xingguo Abstract: Synthetic aperture technology applied to missile passive MMW detection system can make up for the shortcoming that a passive detection system cannot give target range, thus can greatly improve the system performance. This paper first discusses the near range MMW synthetic aperture technology, showing that its chief characteristic is the quadratic phase compensation factor in imaging formula that can compress impulse response of the point source and improve the amplitude; and then presents the principle of synthetic aperture passive ranging under near range conditions. In near range, there are spherical wave radiations and the wave front curvature of the spherical wave is inversely proportional to propagation distance, which can be used to estimate the quadratic phase compensation factor rate so as to obtain the wave front curvature, and the range. Bi-orthogonal Fourier Transform algorithm is adopted for passive ranging, which can efficiently estimate FM rates of multi-linear FM signals. Keywords:  signals and information processing; MMW radiometer; synthetic aperture; passive ranging
87  Simulation of Three-point Ballistics for Shipborne Guided Shell SUN Dongyan Abstract: By analyzing the actual battle conditions, an interrelated reference frame and the main mathematical model used in the simulation are established. Based on basic battle procedures, the simulation flow chart is given in detail. With certain initial conditions, the three-point ballistics is simulated with Visual C++ and Matlab, and the mathematical model is validated by analyzing the simulation results. Some work that has to be carried out further and the application prospect in tactics are discussed. Keywords:  ship borne; guided shell; three-point ballistics; simulation
Reviews
92  Several Problems on Control of Modern Aerocraft HUANG Lin, DUAN Zhisheng, YANG Ying
99  Notes on Reviews in Chinese Science Abstracts
Science Reports
102  NASA in Retrospect and Prospect GONG Guer
Commentary
104  Joseph Henry: Discoverer of Self-induction Phenomenon CHEN Jun
105  Where Is the Bound Within Which One Could be Flexible? WU Yishan
106  However Brilliant, NASA Has Real Problems HUANG Yongming
107  Books Appraisal
Editor-in-chief's Thoughts
109  How Do Young Scientists Achieve Success: A Prologue FENG Changgen
To the Workplace
112  Opportunities are Created by YourselfCHENG Jiwei
113  Career
117  Global Jobs
Special Columns
8  Cover Story: Space Witnesses the Footsteps of Chinese People HUANG Yongming
8  Sci-Tech News Ranking for the Second Half of September
11  Voice of Scientific Community
12  Half-month News Briefs
14  International Journal Highlights
15  Domestic Journal Highlights
16  Scientific Community Briefs
18  Guidance for Contributors to S&T Review
100  Digest of Chinese Newspapers and Journals
101  Events
108  Readers' Letters WANG Dong, WANG Xiaokun, HUANG Kai, et al.
110  Entertainments