Coordinated Attitude Control For Synthetic Aperture Radar Satellites With Performance Constraint

Synthetic aperture radar satellites formation can accomplish the imaging task under vile weather.Thus,it is an essential part of current research in the field of aerospace and plays an important role in ground imaging and monitoring geological disasters.Conventional coordinated control methods often analyze problems from the perspective of consistency,but this is different from the working mode of synthetic aperture radar.Therefore,this thesis analyzes the working model,working environment,and imaging mechanism of SAR satellites,and designs a variety of coordinated attitude controllers in consideration of actual engineering requirements and special actuators.The main research contents of the thesis are as follows:Considering the working situation and working mechanism of the synthetic aperture radar satellite formation,this thesis establishes the relevant physical model and basic concepts;defines the primary and secondary targets of the satellite formation during the attitude maneuvering,and determines the need for subsequent research on the attitude cooperative controller.In the presence of communication delay and signal transmission quantification,the reasons for using logarithmic quantizer is analyzed and explained.Using the terminal sliding mode control method and adopting behavior-based design approaches,a robust terminal-sliding-mode control scheme is designed.The terminal-sliding-mode control law has a great steady-state performance and can suppress the influence of unknown disturbance torque on each member satellite.However,since the transient performance of the controller is extremely sensitive to some control parameters,it may takes a lot of time to tune these parameters in practical applications.Also,it may not even meet the performance constraints of the task.Therefore,in order to make it easier to adjusting the control parameters and obtain a more acceptable transient performance,the fractional sliding mode surface,integral sliding mode surface and super twisting control method are combined into a fractional-order-sliding-mode controller that can easily obtain a good control performance.Note that satellites have to meet some specific task requirements to accomplish the imaging task;this paper introduces the prescribed performance theory and a simple performance function,and uses the back-stepping control method to design an attitude cooperative controller.The back-stepping control law can design performance function for each parameter of the relative attitude precisely and ensure that the relative attitude errors of each member satellite can satisfy the mission’s requirements.Then,this paper uses a quasi-sliding mode method to design a second kind of simpler coordinated attitude control scheme,which can simultaneously constrain both the Euler angle and relative attitude angular velocity of each satellite in the formation.Combining it with a back-propagation neural network,the third control law which can dynamically tune the control gains can be obtained;this controller can adjust control parameters in real-time according to the state of the system and reduce the energy consumption.Considering that in some special working environments,satellites with thrusters need to save propellant to extend their life,an improved performance function and two attitude cooperative controllers are proposed.When the improved performance function is applied,each member satellite will save a large amount of fuel and propellant without changing the steady state performance and transient performance.Considering that in practical applications,it may be impossible to obtain the continuous and arbitrarily adjustable control input,this thesis describes the control signal and the control torque through the input quantization model when multiple thrusters are used as actuators in each member satellite in the formation.When designing the controllers,it can be found that the conventional sliding mode control law may cause a serious system chattering phenomenon.Therefore,this paper reconstructs the updating law of the control signal by artificially introducing a hysteresis section,and designs a quasi-sliding-mode controller with a single-neuron structure to optimize control parameters and reduce energy consumption.Then,noticing that there are certain shortages and lacks in the hysteresis section,this paper designs an event-triggered coordinated attitude controller.The action mechanism of this event-triggered condition and the hysteresis section have certain similarities.Both of them can effectively reduce the chattering problem caused by the quantization of system input.