| Micro/nano satellite has large-scale application in many fields such as space environmental sensoring,communication and imaging observation.In this context,the demand of promoting the rapid orbital manever capability is more and more urgent.Solid rocket motors(SRMs)can be applied with advantages such as high density impulse,simple structure and reliable performance.It has a high application prospect for large constellation dispatch,deorbit at the end of life and space attack and defense.But the satellite's attitude will not stable in the existence of thrust misalignment torque of SRMs.This problem seriously affect the results of orbital manever.In this thesis,an orbital manever task using SRMs is taken as the basic research background and a new technique named mass moment control is proposed to stabilize the attitude in orbital manever.This thesis conduct a comprehensive study of the theoretical and technical problems.The main research work includes:Firstly,a mass moment attitude control system containing two orthogonal moving mass actuators is designed to steer the pitch and yaw angles,considering the attitude requirements in orbital manever and the disturbance feature of SRMs.A 8 DOF dynamic model is deduced using Newton-euler method,which consist of the system translational,system rotational and actuator translational dynamic equations.The influence of propellant combustion is also considered in the process of modeling for the first time.The moving mass could exert inertial force and coupled factor on the spacecraft,which result in a quite complicated dynamic model.Secondly,the function expressions between the actuators motion with the attitude angles,and the driving force with the actuatbelow aspacts.1)The control mechanism is obtained from the expanded formular of the thrust torqueors' displacement are established.The dynamic characteristics are deeply analyzed in:yaw and pitch control torques are generated by moving mass in Y and Z axis.And there is no coordinated control problem.2)Both the influence on attitude caused by the additional inertial tensor,inertial torque,coriolis torque,gyroscopic torque and the influence on actuators displacement caused by additional inertial force,coriolis force,gyroscopic force are analyzed with expanded formulars.3)The influence of system parameters on the steering performance is studied with several factors by simulations.These factors include the mass ratio of actuators to the whole system,the moving range and the layout parameters of actuators,and the different combustion forms and outlines of SRMs.4)Considering the problem of system vibration and channel coupling caused by moving mass,a double symmetrical actuators is proposed.Then the dynamic model is corrected.Finally the dynamic characteristics and control performance are simulated and analyzed.Results of simulations indicate that the disturbance torque and systematic coupling can be greatly reduced.This design gives a good handling performance of this mass moment control system.Thirdly,the attitude control model and actuators displacement control model are rationally simplified.And the error contrast to the complete model is analyzed by simulations.In this dissertation,two controllers are derived for the two-circuit closed-loop control.1)In order to avoid the parameter uncertainty and external disturbance in the process of combustion,a kind of dynamic sliding surface is designed to derive the global sliding mode controller,taking the pitch channel and the z-axis actuator as an example.2)A standard backstepping control technique is used to get a robust controller.At the same time a kind of dynamic surface control is introduced to solve the computer explosion problem.The stability of this controller is proved based on the Liapunov stability theory.The numerical simulation results show that the global sliding mode controller can overcome the external disturbances effectively and has strong robustness,but there are steady-state errors in both pitch and yaw channels and the overshoots are 4 and 2.6 degrees respectively.By using the dynamic surface backstepping sliding mode controller,moving masses motion can make the pitch and yaw angle stable in 0.5s,the tracking performance of instructions is excellent.Consequently after orbit manever,the deviation in the orbit coordinate frame between X axis velocity and ideal value is only 0.024m/s,better than the global sliding mode controller.Fourthly,with a view to a circumstance when there is no thrust acting on satellite,an active control method is investigated utilizing atmospheric drag for low-earth orbit satellites.Originally,via modeling of various disturbance torques and its correlation analysis with the CoM,the feasibility regarding atmospheric drag as an active external torque is discussed.Then the mass moment control model is obtained and the control mechanism is obtained.With regards to this type of underactuated system which the number of actuators are less than the system's DOF,a sliding mode controller is derived.The performance is verified through simulations,with a result that the pitch channel,roll and yaw channel can be controlled respectively to the desired attitude in 500s and 3000s,for a CubeSat of 300km altitude.The chattering of moving mass is fixed with appling continuous control method in the neighborhood of the origin.Fifthly,based on the previous theoretical research a double symmetrical actuator is developed,using brushless DC servo linear motor as the driving unit.The core chip of the mass moment computer is STM32F407 and the algorithm is programmed in the FreeRTOS real-time operating system.In order to verify the concept of mass moment control system and the performance of the prototype,a desktop demo system is developed and an attitude estimation scheme for rotating rigid body is presented utilizing accelerators and gyroscopes.Furthermore,the dynamic model of the demo system is established by Lagrange method.Ultimately a series of demonstration are carried out.The results indicate that the response time of the prototype is only about 30ms,and the attitude estimnation scheme can measure the motion of rotating rigid body in real time.Under these conditions the ? and ? angle converges in 2?3 seconds to a range of 0.2°,0.3° after turning on the mass moment control,which consequently demonstrate the mass moment control concept.This dissertation studys systematically the attitude control subsystem using mass moment control technology for rapid orbital manever satellite,extendes the application of mass moment control technology.The work of this dissertation is expected to provide certain theoretical and practical basis for promoting the application of SRMs in micro/nano satellites. |
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