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Underactuated spacecraft angular velocity stabilization and three-axis attitude stabilization using two single gimbal control moment gyros 被引量:6
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作者 Lei Jin Shijie Xu 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2010年第2期279-288,共10页
Angular velocity stabilization control and attitude stabilization control for an underactuated spacecraft using only two single gimbal control moment gyros (SGCMGs) as actuators is investigated. First of all, the dy... Angular velocity stabilization control and attitude stabilization control for an underactuated spacecraft using only two single gimbal control moment gyros (SGCMGs) as actuators is investigated. First of all, the dynamic model of the underactuated spacecraft is established and the singularity of different configurations with the two SGCMGs is analyzed. Under the assumption that the gimbal axes of the two SGCMGs are installed in any direction, and that the total system angular momentum is not zero, a state feedback control law via Lyapunov method is designed to globally asymptotically stabilize the angular velocity of spacecraft. Under the assumption that the gimbal axes of the two SGCMGs are coaxially installed along anyone of the three principal axes of spacecraft inertia, and that the total system angular momentum is zero, a discontinuous state feedback control law is designed to stabilize three-axis attitude of spacecraft with respect to the inertial frame. Furthermore, the singularity escape of SGCMGs for the above two control problems is also studied. Simulation results demonstrate the validity of the control laws. 展开更多
关键词 Single gimbal control moment gyro ·Undcractuated spacecraft · Angular velocity stabilization · three-axis attitude stabilization·Singularity
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Application of hybrid robust three-axis attitude control approach to overactuated spacecraft——A quaternion based model 被引量:2
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作者 A.H.Mazinan 《Journal of Central South University》 SCIE EI CAS CSCD 2016年第7期1740-1753,共14页
A novel hybrid robust three-axis attitude control approach, namely HRTAC, is considered along with the well-known developments in the area of space systems, since there is a consensus among the related experts that th... A novel hybrid robust three-axis attitude control approach, namely HRTAC, is considered along with the well-known developments in the area of space systems, since there is a consensus among the related experts that the new insights may be taken into account as decision points to outperform the available materials. It is to note that the traditional control approaches may generally be upgraded, as long as a number of modifications are made with respect to state-of-the-art, in order to propose high-precision outcomes. Regarding the investigated issues, the robust sliding mode finite-time control approach is first designed to handle three-axis angular rates in the inner control loop, which consists of the pulse width pulse frequency modulations in line with the control allocation scheme and the system dynamics. The main subject to employ these modulations that is realizing in association with the control allocation scheme is to be able to handle a class of overactuated systems, in particular. The proportional derivative based linear quadratic regulator approach is then designed to handle three-axis rotational angles in the outer control loop, which consists of the system kinematics that is correspondingly concentrated to deal with the quaternion based model. The utilization of the linear and its nonlinear terms, simultaneously, are taken into real consideration as the research motivation, while the performance results are of the significance as the improved version in comparison with the recent investigated outcomes. Subsequently, there is a stability analysis to verify and guarantee the closed loop system performance in coping with the whole of nominal referenced commands. At the end, the effectiveness of the approach considered here is highlighted in line with a number of potential recent benchmarks. 展开更多
关键词 three-axis angular rates and rotations sliding mode finite-time control approach proportional derivative based linearquadratic regulator approach dynamics and kinematics of overactuated spacecraft
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Nonlinear dynamic model and control of three-axis stabilized liquid-filled spacecraft attitude system
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作者 张龙 段广仁 张永安 《Journal of Harbin Institute of Technology(New Series)》 EI CAS 2012年第5期107-112,共6页
The fuel slosh in the storage tanks affects the attitude dynamics of the liquid-filled spacecraft during orbit transferring. To describe the interactions between the fuel slosh dynamics and the spacecraft attitude dyn... The fuel slosh in the storage tanks affects the attitude dynamics of the liquid-filled spacecraft during orbit transferring. To describe the interactions between the fuel slosh dynamics and the spacecraft attitude dynamics, a novel nonlinear dynamic model for three-axis liquid-filled spacecraft is presented, and in this paper, the multi-body dynamics method is utilized. In this model, the fuel slosh is represented by the motions of an equivalent sphere pendulum, and the fuel slosh is underactuated. The proposed dynamics model meets the demand of attitude controller design of liquid-filled spacecraft. Then, a nonlinear proportional-plus-derivative (PD) type controller is designed for the proposed model based on the Lyapunov direct approach. This controller can suppress the fuel slosh and stabilize the attitude of the liquid-filled spacecraft. Numerical simulations are presented to verify the effectiveness of the proposed nonlinear dynamic model and the designed underactuated controller when compared with the conventional control scheme. 展开更多
关键词 liquid-filled spacecraft nonlinear dynamics fuel slosh underactuated control attitude control
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Axis intersection measurement of three-axis turntable with two crosshair targets 被引量:3
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作者 任顺清 马广程 王常虹 《Journal of Harbin Institute of Technology(New Series)》 EI CAS 2005年第3期250-254,共5页
In order to measure three-axis intersection error, two crosshair targets were fixed in the inner axis frame of a three-axis turntable. Also a theodolite was used to point its telescope to the targets and to measure th... In order to measure three-axis intersection error, two crosshair targets were fixed in the inner axis frame of a three-axis turntable. Also a theodolite was used to point its telescope to the targets and to measure the horizontal angles when three axes were on equi-spaced angle positions. The calculation equations of the axis intersection were deduced from the mounting position of the theodolite, positions of two targets, angular positions of three axes, and the measured horizontal angles with the theodolite. Finally, a practical measurement is carried out on a horizontal three-axis turntable and error analysis is conducted. 展开更多
关键词 Axis intersection three-axis turntable THEODOLITE error separation technology homogeneous transformation
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Misalignment Angle Calculation Accuracy Analysis of Three-Axis Stabilized Geostationary Satellite 被引量:1
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作者 Jian Shang Chengbao Liu +2 位作者 Lei Yang Zhiqing Zhang Jing Wang 《Journal of Geoscience and Environment Protection》 2017年第12期153-165,共13页
The most challenging problem of navigation in three-axis stabilized geostationary satellite is accurate calculation of misalignment angles, deduced by orbit measurement error, attitude measurement error, thermal elast... The most challenging problem of navigation in three-axis stabilized geostationary satellite is accurate calculation of misalignment angles, deduced by orbit measurement error, attitude measurement error, thermal elastic deformation, time synchronization error, and so on. Before the satellite is launched, the misalignment model must be established and validated. But there were no observation data, which is a non-negligible risk of yielding the greatest returns on investment. On the basis of misalignment modeling using landmarks and stars, which is not available between different organizations and is developed by ourselves, experimental data are constructed to validate the navigation processing flow as well as misalignment calculation accuracy. In the condition of using landmarks, the maximum misalignment calculation errors of roll, pitch, and yaw axis are 2, 2, and 104 micro radians, respectively, without considering the accuracy of image edge detection. While in the condition of using stars, the maximum errors of roll, pitch, and yaw axis are 1, 1, and 3 micro radians, respectively, without considering the accuracy of star center extraction. Results are rather encouraging, which pave the way for high-accuracy image navigation of three-axis stabilized geostationary satellite. The misalignment modeling as well as calculation method has been used in the new generation of geostationary meteorological satellite in China, FY-4 series, the first satellite of which was launched at the end of 2016. 展开更多
关键词 MISALIGNMENT Angle Accuracy Analysis LANDMARK NAVIGATION STAR NAVIGATION three-axis STABILIZATION Satellite
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A Three-Axis Robot Using a Remote Network Control System 被引量:1
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作者 Min-Chie Chiu Tian-Syung Lan Ho-Chih Cheng 《Engineering(科研)》 2010年第11期874-878,共5页
For the petroleum industry, to reduce the risk of a gas explosion in dangerous working areas, the use of explosion-proof equipment such as air-driven devices which are free from explosions becomes essential. Moreover,... For the petroleum industry, to reduce the risk of a gas explosion in dangerous working areas, the use of explosion-proof equipment such as air-driven devices which are free from explosions becomes essential. Moreover, for the purpose of saving manpower, a remote operation using a robot via a visual monitoring system and a network is used. However, to overcome the drawback of costly manpower and to improve safety in explosion-prone zones, a three-axis robot using a remote network control system is proposed. In this paper, the three-axis robot can be monitored online via the USB protocol. Furthermore, it also can be remotely manipulated via the TCP/IP protocol by clicking the command of the VB interface on the client pc. Consequently, the remote-control three-axis robot can not only work for people in severe and dangerous circumstances but also can reduce the cost of manpower. 展开更多
关键词 three-axis ROBOT REMOTE NETWORK MONITORING
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IMPROVED QUANTITATIVE FEEDBACK THEORY TECHNIQUE AND APPLICATION TO THREE-AXIS HYDRAULIC SIMULATOR 被引量:1
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作者 YU Jinying ZHAO Keding CAO Jian 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2006年第3期383-386,共4页
In order to meet tracking performance index of three-axis hydraulic simulator, based on classical quantitative feedback theory (QFT), an improved QFT technique is used to synthesize controller of low gain and bandwi... In order to meet tracking performance index of three-axis hydraulic simulator, based on classical quantitative feedback theory (QFT), an improved QFT technique is used to synthesize controller of low gain and bandwidth. By choosing a special nominal plant, the improved method assigns relative magnitude and phase tracking error between system uncertainty and nominal control plant. Relative tracking error induced by system uncertainty is transformed into sensitivity problem and relative tracking error induced by nominal plant forms into a region on Nichols chart. The two constraints further form into a combined bound which is fit for magnitude and phase loop shaping. Because of leaving out pre-filter of classical QFT controller structure, tracking performance is enhanced greatly. Furthermore, a cascaded two-loop control strategy is proposed to heighten control effect. The improved technique's efficacy is validated by simulation and experiment results. 展开更多
关键词 three-axis hydraulic simulator Quantitative feedback theory(QFT) Cascaded two-loop
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The Impact Study of Three-axis Servo System Interference Torque based on Virtual Prototype
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作者 YIN Jian WU Jian-dong +1 位作者 YU Jin-jiang HU Liang 《International Journal of Plant Engineering and Management》 2016年第4期217-230,共14页
The three-axis servo system with the core of gyro stabilization is the foundation to realize its function, and a key technology of the seeker devolopment. In order to reduce the costs, improve the efficiency of resear... The three-axis servo system with the core of gyro stabilization is the foundation to realize its function, and a key technology of the seeker devolopment. In order to reduce the costs, improve the efficiency of research and devolopment, a new method that instead of physical prototype by virtual prototype was proposed. Adams and MATLAB/simulink are used to establish the mechanical dynamics model and controller model of the three-axis servo system. The simulation data which was processed and analyzed is compared with test data, to determine the control parameters of the virtual prototype and improve the accuracy of the model, and test the multiple condition simulation,which can provide a reference for practical production.The simulation results verify the feasibility of the models. 展开更多
关键词 three-axis servo system virtual prototype co-simulation of Adams and simulink mass unbalancetorque
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Efficient cache replacement framework based on access hotness for spacecraft processors
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作者 GAO Xin NIAN Jiawei +1 位作者 LIU Hongjin YANG Mengfei 《中国空间科学技术(中英文)》 CSCD 北大核心 2024年第2期74-88,共15页
A notable portion of cachelines in real-world workloads exhibits inner non-uniform access behaviors.However,modern cache management rarely considers this fine-grained feature,which impacts the effective cache capacity... A notable portion of cachelines in real-world workloads exhibits inner non-uniform access behaviors.However,modern cache management rarely considers this fine-grained feature,which impacts the effective cache capacity of contemporary high-performance spacecraft processors.To harness these non-uniform access behaviors,an efficient cache replacement framework featuring an auxiliary cache specifically designed to retain evicted hot data was proposed.This framework reconstructs the cache replacement policy,facilitating data migration between the main cache and the auxiliary cache.Unlike traditional cacheline-granularity policies,the approach excels at identifying and evicting infrequently used data,thereby optimizing cache utilization.The evaluation shows impressive performance improvement,especially on workloads with irregular access patterns.Benefiting from fine granularity,the proposal achieves superior storage efficiency compared with commonly used cache management schemes,providing a potential optimization opportunity for modern resource-constrained processors,such as spacecraft processors.Furthermore,the framework complements existing modern cache replacement policies and can be seamlessly integrated with minimal modifications,enhancing their overall efficacy. 展开更多
关键词 spacecraft processors cache management replacement policy storage efficiency memory hierarchy MICROARCHITECTURE
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An impact sensitivity assessment method of spacecraft based on virtual exterior wall
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作者 Runqiang Chi Yuyan Liu +1 位作者 Diqi Hu Baojun Pang 《Defence Technology(防务技术)》 SCIE EI CAS CSCD 2024年第1期142-157,共16页
The impact sensitivity assessment of spacecraft is to obtain the probability of spacecraft encountering the OD/M(orbital debris or meteoroid),which is a prerequisite for survivability assessment of on-orbit spacecraft... The impact sensitivity assessment of spacecraft is to obtain the probability of spacecraft encountering the OD/M(orbital debris or meteoroid),which is a prerequisite for survivability assessment of on-orbit spacecraft.An impact sensitivity assessment method of spacecraft based on virtual exterior wall was proposed to improve the computational efficiency.This method eliminates determination of the outermost surface elements of the spacecraft before generating the debris rays,which are assumed to originate from a non-concave virtual wall that completely wraps the spacecraft.The Dist Mesh method was adopted for the generating of the virtual wall to ensure its mesh quality.The influences of the sizes,mesh densities,shapes of the virtual wall on the efficiency and accuracy were considered to obtain the best combination of the size and mesh density of the wall and spacecraft.The results of this method were compared with those of S3DE(Survivability of Spacecraft in Space Debris Environment),BUMPER,MDPANTO,ESABASE2/Debris to verify the feasibility of the method.The PCHIP(Piecewise Cubic Hermite Interpolating Polynomial)was used to fit the size vs.flux relationship of the space debris to acquire the impact probability of OD/M with arbitrary size on the spacecraft. 展开更多
关键词 Sensitivity OD/M spacecraft Virtual exterior wall
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Decoupling Algorithms for the Gravitational Wave Spacecraft
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作者 XueWang Weizhou Zhu +4 位作者 Zhao Cui Xingguang Qian Jinke Yang Jianjun Jia Yikun Wang 《Computer Modeling in Engineering & Sciences》 SCIE EI 2024年第7期325-337,共13页
The gravitational wave spacecraft is a complex multi-input multi-output dynamic system.The gravitational wave detection mission requires the spacecraft to achieve single spacecraft with two laser links and high-precis... The gravitational wave spacecraft is a complex multi-input multi-output dynamic system.The gravitational wave detection mission requires the spacecraft to achieve single spacecraft with two laser links and high-precision control.Establishing one spacecraftwith two laser links,compared to one spacecraft with a single laser link,requires an upgraded decoupling algorithmfor the link establishment.The decoupling algorithmwe designed reassigns the degrees of freedomand forces in the control loop to ensure sufficient degrees of freedomfor optical axis control.In addressing the distinct dynamic characteristics of different degrees of freedom,a transfer function compensation method is used in the decoupling process to further minimize motion coupling.The open-loop frequency response of the systemis obtained through simulation.The upgraded decoupling algorithms effectively reduce the open-loop frequency response by 30 dB.The transfer function compensation method efficiently suppresses the coupling of low-frequency noise. 展开更多
关键词 Gravitational waves spacecraft laser acquisition decoupling algorithms dynamical model optical axis control
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Development of Fault Diagnosis System for Spacecraft Based on Fault Tree and G2 被引量:4
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作者 纪常伟 荣吉利 《Journal of Beijing Institute of Technology》 EI CAS 2002年第4期444-448,共5页
Some ideas in the development of fault diagnosis system for spacecraft are introduced. Firstly, the architecture of spacecraft fault diagnosis is proposed hierarchically with four diagnosis frames, i.e., system level,... Some ideas in the development of fault diagnosis system for spacecraft are introduced. Firstly, the architecture of spacecraft fault diagnosis is proposed hierarchically with four diagnosis frames, i.e., system level, subsystem level, component level and element level. Secondly, a hierarchical diagnosis model is expressed with four layers, i.e., sensors layer, function layer, behavior layer and structure layer. These layers are used to work together to accomplish the fault alarm, diagnosis and localization. Thirdly, a fault-tree-oriented hybrid knowledge representation based on frame and generalized rule and its relevant reasoning strategy is put forward. Finally, a diagnosis case for spacecraft power system is exemplified combining the above with a powerful expert system development tool G2. 展开更多
关键词 spacecraft fault diagnosis fault tree hierarchical diagnosis model G2
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Optimal reorientation of underactuated spacecraft using genetic algorithm with wavelet approximation 被引量:5
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作者 Xinsheng Ge Liqun Chen 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2009年第4期547-553,共7页
The optimal attitude control of an underactuated spacecraft is investigated in this paper. The flywheels of the spacecraft can somehow only provide control inputs in two independent directions. The dynamic equations a... The optimal attitude control of an underactuated spacecraft is investigated in this paper. The flywheels of the spacecraft can somehow only provide control inputs in two independent directions. The dynamic equations are formulated for the spacecraft under a nonholonomic constraint resulting from the constant time-rate of the total angular momentum of the system. The reorientation of such underactuated spacecraft is transformed into an optimal control problem. A genetic algorithm is proposed to derive the control laws of the two flywheels angle velocity inputs. The control laws are approximated by the discrete orthogonal wavelets. The numerical simulations indicate that the genetic algorithm with the wavelet approximation is an effective approach to deal with the optimal reorientation of underactuated spacecraft. 展开更多
关键词 Underactuated spacecraft REORIENTATION Attitude control Genetic algorithm WAVELET
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Attitude maneuver of liquid-filled spacecraft with a flexible appendage by momentum wheel 被引量:6
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作者 Dan-Dan Yang Bao-Zeng Yue +2 位作者 Wen-Jun Wu Xiao-Juan Song Le-Mei Zhu 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2012年第2期543-550,共8页
Attitude maneuver of liquid-filled spacecraft with an appendage as a cantilever beam by momentum wheel is studied. The dynamic equations are derived by conserva- tion of angular momentum and force equilibrium principl... Attitude maneuver of liquid-filled spacecraft with an appendage as a cantilever beam by momentum wheel is studied. The dynamic equations are derived by conserva- tion of angular momentum and force equilibrium principle. A feedback control strategy of the momentum wheel is ap- plied for the attitude maneuver. The residual nutation of the spacecraft in maneuver process changes with some chosen parameters, such as steady state time, locations of the liq- uid container and the appendage, and appendage parame- ters. The results indicate that locations in the second and fourth quadrants of the body-fixed coordinate system and the second quadrant of the wall of the main body are better choices for.placing the liquid containers and the appendage than other locations if they can be placed randomly. Higher density and thicker cross section are better for lowering the residual nutation if they can be changed. Light appendage can be modeled as a rigid body, which results in a larger residual nutation than a flexible model though. The resid- ual nutation decreases with increasing absolute value of the initial sloshing angular height. 展开更多
关键词 Liquid-filled spacecraft Appendage Attitude maneuver Momentum wheel Steady state time Residual nutation
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Chaotic attitude and reorientation maneuver for completely liquid-filled spacecraft with flexible appendage 被引量:7
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作者 B. Yue Department of Mechanics, School of Science,Beijing Institute of Technology, 100081 Beijing, China 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2009年第2期271-277,共7页
The present paper investigates the chaotic attitude dynamics and reorientation maneuver for completely viscous liquid-filled spacecraft with flexible appendage. All of the equations of motion are derived by using Lagr... The present paper investigates the chaotic attitude dynamics and reorientation maneuver for completely viscous liquid-filled spacecraft with flexible appendage. All of the equations of motion are derived by using Lagrangian mechanics and then transformed into a form consisting of an unperturbed part plus perturbed terms so that the system's nonlinear characteristics can be exploited in phase space. Emphases are laid on the chaotic attitude dynamics produced from certain sets of physical parameter values of the spacecraft when energy dissipation acts to derive the body from minor to major axis spin. Numerical solutions of these equations show that the attitude dynamics of liquid-filled flexible spacecraft possesses characteristics common to random, non- periodic solutions and chaos, and it is demonstrated that the desired reorientation maneuver is guaranteed by using a pair of thruster impulses. The control strategy for reorientation maneuver is designed and the numerical simulation results are presented for both the uncontrolled and controlled spins transition. 展开更多
关键词 Nonlinear attitude dynamics Attitude reorientation maneuver Control strategyLiquid-filled spacecraft
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Characteristic Model-based Discrete-time Sliding Mode Control for Spacecraft with Variable Tilt of Flexible Structures 被引量:5
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作者 Lei Chen Yan Yan +1 位作者 Chaoxu Mu Changyin Sun 《IEEE/CAA Journal of Automatica Sinica》 SCIE EI 2016年第1期42-50,共9页
In this paper, the finite-time attitude tracking control problem for the spacecrafts with variable tilt of flexible appendages in the conditions of exogenous disturbances and inertia uncertainties is addressed. First ... In this paper, the finite-time attitude tracking control problem for the spacecrafts with variable tilt of flexible appendages in the conditions of exogenous disturbances and inertia uncertainties is addressed. First the characteristic modeling method is applied to the problem of the spacecraft modeling. Second, a novel adaptive sliding mode surface is designed based on the characteristic model. Furthermore, a discrete-time sliding mode control (DTSMC) law, which makes the tracking error converge into a predefined bound in finite time, is proposed by employing the parameters of characteristic model associated with the sliding mode surface to provide better performances, robustness, faster response, and higher control precision. The designed DTSMC includes the adaptive control architecture and is chattering-free. Finally, digital simulations of a sun synchronous orbit satellite (SSOS) are presented to illustrate effectiveness of the control strategies as well as to verify the practical feasibility of the rapid maneuver mission. © 2014 Chinese Association of Automation. 展开更多
关键词 Flexible structures NAVIGATION ORBITS spacecraft
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Controllability of Spacecraft Attitude and Its Application in Reconfigurability Analysis 被引量:4
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作者 YANG Hao MENG Qingkai JIANG Bin 《Transactions of Nanjing University of Aeronautics and Astronautics》 EI CSCD 2019年第2期189-196,共8页
We review the controllability research on spacecraft attitude based on nonlinear geometry control theory.The existing studies on attitude controllability are mostly concerning the global controllability and small time... We review the controllability research on spacecraft attitude based on nonlinear geometry control theory.The existing studies on attitude controllability are mostly concerning the global controllability and small time local controllability(STLC).A presentation of study methods and connotation in both aspects is briefly carried out.As a necessary condition of reconfigurability,the controllability of the faulty attitude control system is studied.Moreover,two reconfigurability conditions based on controllability results that consider the actuator faults for a pyramid configuration spacecraft are provided. 展开更多
关键词 CONTROLLABILITY spacecraft ATTITUDE CONTROL geometry CONTROL theory fault.tolerant CONTROL
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Analytical method for the attitude stability of partially liquid filled spacecraft with flexible appendage 被引量:4
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作者 Yulong Yan Baozeng Yue 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2017年第1期208-218,共11页
In this paper, the attitude stability of liquid-filled spacecraft with flexible appendage is investigated. The motion of liquid sloshing is modeled as the spherical pendulum, and the flexible appendage is approached b... In this paper, the attitude stability of liquid-filled spacecraft with flexible appendage is investigated. The motion of liquid sloshing is modeled as the spherical pendulum, and the flexible appendage is approached by a linear shearing beam. Nonlinear dynamic equations of the coupled system are derived from the Hamiltonian. The stability of the coupled system was analyzed by using the energy-Casimir method, and the nonlinear stability theorem of the coupled spacecraft system was also obtained. Through numerical computation, the correctness of the proposed theorem is verified and the boundary curves of the stable region are presented. The increase of the angular velocity and flexible attachment length will weaken the attitude stability, and the change of the filled ratio of liquid fuel tank has a different influence on the stability of the coupled spacecraft, depending on the different conditions. The attitude stability analysis of the coupled spacecraft system in this context is useful for selecting appropriate parameters in the complex spacecraft design. 展开更多
关键词 Liquid-filled spacecraft Energy-Casimir method Flexible attachment Stability analysis
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Experimental Study of Vacuum Ultraviolet Radiation Effects and Its Synergistic Effects with Atomic Oxygen on a Spacecraft Material-Polytetrafluoroethylene 被引量:5
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作者 赵小虎 沈志刚 +1 位作者 邢玉山 麻树林 《Chinese Journal of Aeronautics》 SCIE EI CAS CSCD 2004年第3期181-186,共6页
Polytetrafluoroethylene (Teflon), a widely used spacecraft material, isstudied to investigate the vacuum ultraviolet (VUV) effects and its synergistic effects with atomicoxygen (AO) in a ground-based simulation facili... Polytetrafluoroethylene (Teflon), a widely used spacecraft material, isstudied to investigate the vacuum ultraviolet (VUV) effects and its synergistic effects with atomicoxygen (AO) in a ground-based simulation facility. The samples before and after the experiments arecompared in appearance, mass, optical properties and surface composition. The reactioncharacteristics of Teflon are summarized and the reaction mechanisms are analyzed. The followingconclusion can be drawn: at the action of VUV the Teflon sample surface is darkened for theaccumulation of carbon; and when the sample is exposed to AO, the carbon is oxidized and thedarkening surface is bleached; the synergistic effects of VUV and AO may cause the erosion of Teflonmore severe. 展开更多
关键词 Polytetrafluoroethylene spacecraft material vacuum ultraviolet radiation atomic oxygen synergistic effects ground-based test
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Orbit Design for Twin-spacecraft Space VLBI 被引量:3
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作者 ZHANG Cheng WU Xia +1 位作者 ZHENG Jianhua WU Ji 《空间科学学报》 CAS CSCD 北大核心 2015年第4期502-510,共9页
Space Very Long Baseline Interferometry(S-VLBI) is an aperture synthesis technique utilizing an array of radio telescopes including ground telescopes and space orbiting telescopes.It can achieve much higher spatial re... Space Very Long Baseline Interferometry(S-VLBI) is an aperture synthesis technique utilizing an array of radio telescopes including ground telescopes and space orbiting telescopes.It can achieve much higher spatial resolution than that from the ground-only VLBI.In this paper,a new concept of twin spacecraft S-VLBI has been proposed,which utilizes the space-space baselines formed by two satellites to obtain larger and uniform uv coverage without atmospheric influence and hence achieve high quality images with higher angular resolution.The orbit selections of the two satellites are investigated.The imaging performance and actual launch conditions are all taken into account in orbit designing of the twin spacecraft S-VLBI.Three schemes of orbit design using traditional elliptical orbits and circular orbits are presented.These design results can be used for different scientific goals.Furthermore,these designing ideas can provide useful references for the future Chinese millimeter-wave S-VLBI mission. 展开更多
关键词 VLBI TWIN spacecraft ORBIT design
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