Stealth Attitude Control Method For Flexible Spacecraft

With the continuous development of radar detection technology,the continuous improvement of radar detection range and accuracy,and the continuous improvement of radar networking system,in the modern war offensive and defensive confrontation,correspondingly,aircraft need higher stealth performance to avoid radar detection.In this paper,under the background of known launching point position and three radar positions,the necessary basic coordinate system is established,and the concept of aircraft and radar line-of-sight angle(LOS angle)is introduced.According to this LOS angle,the limited condition of aircraft stealth is given.Besides,according to the Three Cosine Theorem,the horizontal component and vertical component of LOS angle are obtained,then the equations can be given by introducing the LOS angle component into the coordinate system through the transformation relationship.The transformation relationship of coordinate system mainly includes the transformation relationship among spacecraft,launching point and radar detection system with radar LOS being in the projection relationship of missile coordinate system.Introduce the LOS deflection component and the nonlinear equations are established.Then,the attitude angle of the aircraft relative to the first radar is obtained by Newton iterative method,and then the attitude angle relative to the second and third radars and the inertial system of the launching point are obtained.At the same time,according to the obtained attitude angle,the realized deflection angle of the aircraft relative to the three radars is inversely calculated to verify whether the realized deflection angle is within the limited stealth range.In modern wars,with the renewal of aircraft,higher requirements are put forward for the stealth performance,speed,accuracy,range and maneuverability of aircraft in order to win modern wars,which all point to the characteristics of large lengthen diameter ratio of aircraft.In this paper,a space vehicle with an aspect ratio of 40 is taken as the research object.Due to flexible vibration,the inertial components installed on the aircraft fuselage will affect the measurement accuracy of attitude angle,thus affecting the stability and control accuracy of the control system.Firstly,the dynamic equation and kinematic equation of rigid-body aircraft is given,by which the model of rigid-body aircraft is established here.Then,based on the finite element analysis theory,the aircraft is simplified to a simple beam model,and the stress analysis of the micro-element is carried out.As for the influence of flexibility effect on attitude angle of aircraft in space,this paper only considers the thrust of attitude control engine in space.Based on this thrust,the flexibility model is established by using the assumed modal method.Finally,the flexible vibration is transformed into additional attitude angle and simulated.Based on quaternion,by selecting PD control law as the control strategy and introducing error quaternion,the error quaternion kinematics equation is established and the attitude tracking PD controller is designed in this paper.Then,the switching logic of attitude control engine under PD control law is designed by pulse width modulation(PWM)method,and the trajectory simulation of aircraft is carried out and analyzed.Finally,the influence of flexibility effect on aircraft,the effectiveness of stealth effect of aircraft and the effectiveness of PD control law are verified.