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The J_2 invariant relative configuration of spaceborne SAR interferometer for digital elevation measurement

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Acta Mechanica Sinica 2010年第4期26卷 643-651页

作者： Ming xu Ying-Hong Jia shi-jie xu Department of System Engineering DFH Satellite Co. Ltd. EO. Box 5616 Beijing 100094 China

A 3-craft formation configuration is proposed to perform the digital elevation model （DEM） for the distributed spacebome interferometric synthetic aperture radar （InSAR）, and it is optimized by the modified ant colony algorithm to have the best compatibility with J2 invariant orbits created by differential correction algorithm. The configuration has succeeded in assigning the across-track baseline to vary periodically and with its mean value equal to the optimal baseline determined by the relative height measurement accuracy. The required relationship between crafts＇ magnitudes and phases is formulated for the general case of interferometry measure from non-orthographic and non-lateral view. The J2 invariant configurations created by differential correction algorithm are employed to investigate their compatibility with the required configuration. The colony algorithm is applied to search the optimal configuration holding the near-constant across-track baseline under the J2 perturbation, and the absolute height measurement accuracy is preferable as expected.

关键词： InSAR Digital elevation model (DEM) J2 invariant orbit Differential correction algorithm Formation flying

Equilibrium configurations of the tethered three-body formation system and their nonlinear dynamics

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Acta Mechanica Sinica 2012年第6期28卷 1668-1677页

作者： Ming xu Jian-Min Zhu Tian Tan shi-jie xu School of Astronautics Beihang University R&D Centre DFH Satellite Co. Ltd.

This paper considers nonlinear dynamics of teth- ered three-body formation system with their centre of mass staying on a circular orbit around the Earth, and applies the theory of space manifold dynamics to deal with the nonlinear dynamical behaviors of the equilibrium configurations of the system. Compared with the classical circular restricted three body system, sixteen equilibrium configurations are obtained globally from the geometry of pseudo-potential energy sur- face, four of which were omitted in the previous research. The periodic Lyapunov orbits and their invariant manifolds near the hyperbolic equilibria are presented, and an iteration procedure for identifying Lyapunov orbit is proposed based on the differential correction algorithm. The non-transversal intersections between invariant manifolds are addressed to generate homoclinic and heteroclinic trajectories between the Lyapunov orbits. （3,3）- and （2,1）-heteroclinic trajecto- ries from the neighborhood of one collinear equilibrium to that of another one, and （3,6）- and （2,1）-homoclinic trajecto- ries from and to the neighborhood of the same equilibrium, are obtained based on the Poincar6 mapping technique.

关键词： Tethered satellites system - Formation flying.Lyapunov orbit - Homoclinic/heteroclinic connection - Equi-librium configuration

Influence of flexible solar arrays on vibration isolation platform of control moment gyroscopes

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Acta Mechanica Sinica 2012年第5期28卷 1479-1487页

作者： Yao Zhang Jing-Rui Zhang shi-jie xu School of Aerospace Engineering Beijing Institute of Technology School of Astronautics Beihang University

A high-performance vibration isolation platform （VIP） has been developed for a cluster of control moment gyroscopes （CMGs）. CMGs have long been used for satellite attitude control. In this paper, the influence of flexible solar arrays on a passive multi-strut VIP of CMGs for a satellite is analyzed. The reasonable parameters design of flexi- ble solar arrays is discussed. Firstly, the dynamic model of the integrated satellite with flexible solar arrays, the VIP and CMGs is conducted by Newton-Euler method. Then based on reasonable assumptions, the transmissibility matrix of the VIP is derived. Secondly, the influences of the flexible solar arrays on both the performance of the VIP and the stability of closed-loop control systems are analyzed in detail. The parameter design limitation of these solar arrays is discussed. At last, by selecting reasonable parameters for both the VIP and flexible solar arrays, the attitude stabilization performance with vibration isolation system is predicted via simulation.

关键词： Control moment gyroscope Vibration isolationplatform Attitude control Ultra quiet platform

Dynamics and adaptive control of a dual-arm space robot with closed-loop constraints and uncertain inertial parameters

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Acta Mechanica Sinica 2014年第1期30卷 112-124页

作者： Ying-Hong Jia Quan Hu shi-jie xu School of Astronautics Beihang University

A dynamics-based adaptive control approach is proposed for a planar dual-arm space robot in the presence of closed-loop constraints and uncertain inertial parameters of the payload. The controller is capable of controlling the po- sition and attitude of both the satellite base and the payload grasped by the manipulator end effectors. The equations of motion in reduced-order form for the constrained system are derived by incorporating the constraint equations in terms of accelerations into Kane＇s equations of the unconstrained system. Model analysis shows that the resulting equations perfectly meet the requirement of adaptive controller design. Consequently, by using an indirect approach, an adaptive control scheme is proposed to accomplish position/attitude trajectory tracking control with the uncertain parameters be- ing estimated on-line. The actuator redundancy due to the closed-loop constraints is utilized to minimize a weighted norm of the joint torques. Global asymptotic stability is proven by using Lyapunov＇s method, and simulation results are also presented to demonstrate the effectiveness of the proposed approach.

关键词： Space robot Dynamics. Adaptive control Closed-loop constraint Parameter uncertainty - Kane's equation

Dynamics of a spacecraft with large flexible appendage constrained by multi-strut passive damper

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Acta Mechanica Sinica 2013年第2期29卷 294-308页

作者： Ying-Hong Jia shi-jie xu Quan Hu School of Astronautics Beihang University

This paper is concerned with the dynamics of a spacecraft with multi-strut passive damper for large flexible *** damper platform is connected to the spacecraft by a spheric hinge,multiple damping struts and a rigid *** damping struts provide damping forces while the rigid strut produces a motion constraint of the multibody *** exact nonlinear dynamical equations in reducedorder form are firstly derived by using Kane＇s equation in matrix *** on the assumptions of small velocity and small displacement,the nonlinear equations are reduced to a set of linear second-order differential equations in terms of independent generalized displacements with constant stiffness matrix and damping matrix related to the damping strut *** simulation results demonstrate the damping effectiveness of the damper for both the motion of the spacecraft and the vibration of the flexible appendage,and verify the accuracy of the linear equations against the exact nonlinear ones.

关键词： Dynamics·Motion constraints·Multi-strut passive damper·Kane's equation

Attitude control of a rigid spacecraft with one variable-speed control moment gyro

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Acta Mechanica Sinica 2013年第5期29卷 749-760页

作者： Hai-Chao Gui Lei Jin shi-jie xu School of Astronautics Beihang University

Nonlinear controllability and attitude stabilization are studied for the underactuated nonholonomic dynamics of a rigid spacecraft with one variable-speed control moment gyro （VSCMG）, which supplies only two internal torques. Nonlinear controllability theory is used to show that the dynamics are locally controllable from the equilibrium point and thus can be asymptotically stabilized to the equilibrium point via time-invariant piecewise continuous feedback laws or time-periodic continuous feedback laws. Specifically, when the total angular momentum of the spacecraft-VSCMG system is zero, any orientation can be a controllable equilib- rium attitude. In this case, the attitude stabilization problem is addressed by designing a kinematic stabilizing law, which is implemented through a nonlinear proportional and deriva- tive controller, using the generalized dynamic inverse （GDI） method. The steady-state instability inherent in the GDI con- troller is elegantly avoided by appropriately choosing control gains. In order to obtain the command gimbal rate and wheel acceleration from control torques, a simple steering logic is constructed to accommodate the requirements of attitude sta- bilization and singularity avoidance of the VSCMG. Illustrative numerical examples verify the efficacy of the proposed control strategy.

关键词： Attitude control inverse Nonholonomic system Generalized dynamic Small-time local controlla- bility - Stabilization Variable-speed control moment gyro

Controllability of an underactuated spacecraft with one thruster under disturbance

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Acta Mechanica Sinica 2012年第3期28卷 838-847页

作者： Dong-Xia Wang Ying-Hong Jia Lei Jin Hai-Chao Gui shi-jie xu Department of Guidance Navigation and ControlSchool of AstronauticsBeihang University100191 BeijingChina

For an underactuated spacecraft using only one thruster, the attitude controllability with respect to the or- bit frame is studied in the presence of periodical oscillation disturbance, which provides a preconditional guide on de- signing control law for underactuated attitude control sys- tem. Firstly, attitude dynamic model was established for an underactuated spacecraft, and attitude motion was described using the special orthogonal group （SO （3））. Secondly, Liou- ville theorem was used to confirm that the flow generated by the drift vector of the underactuated attitude control system is volume-preserving. Furthermore, according to Poincar6＇s re- currence theorem, we draw conclusions that this drift field is weakly positively poisson stable （WPPS）. Thirdly, the suffi- cient and necessary condition of controllability was obtained on the basis of lie algebra rank condition （LARC）. Finally, the controllable conditions were analyzed and simulated in different cases of inertia matrix with the installed position of thruster.

关键词： Underactuated spacecraft Periodical oscilla-tion disturbance. Controllability. Weakly positively poissonstable ~ Lie algebra

Response of Lymphocytes to Radiation in Untreated Breast Cancer Patients as Detected with Three Different Genetic Assays

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Biomedical and Environmental Sciences 2008年第6期21卷 499-508页

作者： JIAN-LIN LOU ZHI-JIAN CHEN JIANG WEI JI-LIANG HE LI-FEN JIN shi-jie CHEN WEI ZHENG shi-jie xu Institute of Environmental Medicine Medical College Zhejiang University Jiaxing 310058 Hangzhou Zhejiang China The First Affiliated Hospital of Medical College of Jiaxing University Jiaxing 314001 Zhejiang China

Objective To detect the response of lymphocytes to radiation in untreated breast cancer patients with three different genetic assays. Methods Blood samples were collected from 25 untreated patients and 25 controls. Each blood sample was divided into two parts： one was irradiated by 3-Gy X-ray （irradiated sample）, the other was not irradiated （non-irradiated sample）. The radiosensitivity of lymphocytes was assessed by comet assay, cytokinesis-block micronucleus （CBMN） assay and 6-TG-resistant cells scored （TG） assay. Results The baseline values of micronucleated cell frequency （MCF） and micronucleus frequency （MNF） in the patients were significantly higher than those in the controls （P〈0.01）, and 3-Gy X-ray induced genetic damage to lymphocytes in the patients increased significantly as compared with that in the controls as detected with the three genetic assays （P〈0.01）. The proportion of radiosensitive cases in the patient group was 48% for the mean tail length （MTL）, 40% for the mean tall moment （MTM）, 40% for MCF, 44% for MNF, and 48% for mutation frequencies of the hprt gene （Mfs-hprt）, respectively, whereas the proportion of radiosensitive cases in the control group was only 8% for all the parameters. Conclusion The difference in the lymphocyte radiosensitivity between the breast cancer patients and the controls is significant. Moreover, there are wide individual variations in lymphocyte radiosensitivity of patients with breast cancer. In some cases, the radiosensitivity of the same patient may be different as detected with the different assays. It is suggested that multiple assays should be used to assess the radiosensitivity of patients with breast cancer before therapy.

关键词： Micronucleus assay Comet assay hprt gene mutation Radiosensitivity Breast cancer

A new control law based on characteristic exponent assignment for libration point orbit maintenance

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Acta Mechanica Sinica 2010年第3期26卷 495-500页

作者： Jian Wei·shi-jie xu Laboratory 504,School of Astronautics, Beihang University,Beijing 100191,China Laboratory 504 School of Astronautics Beihang University Beijing China

A new method is developed for stabilizing motion on collinear libration point orbits using the formalism of the circular restricted three body *** about the collinear libration point orbits yields an unstable linear parameter-varying system with periodic *** the variational equations,an innovative control law based on characteristic exponent assignment is introduced for libration point orbit maintenance.A numerical simulation choosing the Richardson’s third order approximation for a halo orbit as a nominal orbit is conducted,and the results demonstrate the effectiveness of this control law.

关键词： Circular restricted three body problem Variational equations Libration point orbit maintenance Characteristic exponent assignment