Research On Nonlinear Attitude Tracking Control Methods Of Ultra-low-orbit Flexible Satellite

With surveillance satellites playing an increasingly important role in the nationalstrategy as well as the ever-increasing demands of military reconnaissance missions,high-precision attitude tracking capability has become the development trend ofsurveillance satellite. This paper does some studies on the attitude tracking problem ofultra-low-orbit flexible satellites. The main contents are as follows:In the aerodynamic moment modeling problem of orbiting satellites, analyzes thenature of the atmospheric environment of the satellite’s circulating orbit and the effectsthat the main types of factors plays on. Then, with reasonable simplifications,establishes satellites’ aerodynamic torque model that can describe characteristics ofreal aerodynamic torque, and then through the establishment of specific aerodynamiccoordinate system, The expression of the aerodynamic torque was derived.As jet was used as the satellite’s actuator, analyzes the nature of severalcommonly used pulse modulators, and derived forms of static characteristic parametersof the selected PSR modulator when the input signal has a constant value. Byanalyzing the nature of the duty cycle of the modulator and comparing to PWPFmodulator, the conclusion that the PSR modulator has the same static characteristicsPWPF is got. Then in order to analyzing the dynamic characteristics of the modulator,acquires the describing function form of four kinds of fitting methods through usingmethod of solving transcendental equations, and come to the conclusion that theamplitude gain of describing function methods increases along with the frequency ofthe input signal and there exists a optimal frequency of the signal by which the PSRmodulator has the maximum phase through the analysis.As to the problem of the application of the sliding mode observer to the disturbedflexible satellites’ modal observing, theoretically derived that the modal information isobservable in the case that angular velocity of the satellite is known, and analyzes thecharacteristics of pole of the SMO with three-axis, two axis and other types ofdisturbance effects. Then design a sliding mode controller which based on slidingmode observer for the control problem of satellite attitude tracking, feasible proof ofthe control law is given. Then on the situation of the modal displacement’s informationis knowable, analyzes the performance of the sliding mode observer and establishes anextended error attitude tracking model that modal vibration is considered as controlledvariables. Then a control law that combines a sliding mode observer and an optimalsliding mode controller is designed for the proposed model, and the validity of themethod is proved.