Attitude Stabilization Control Of The Underactuated Post-Captured Combination

In the missions of active removal of space debris,disused satellites recycling,spacecraft components removal & replacement et.al,the operating targets are lack of self-controllability or even uncontrollable,due to the malfunctions on communication,mechanism or unknown parameters.After the capture of such targets,the attitude stabilization takeover control of the combination by spacecraft’s actuators is an intuitive and effective method.To achieve the attitude stability of the combination,the actuators usually need to provide the control inputs for three or more axes.However,in the long-term space missions,the actuators on the spacecraft may become ineffective that leads to the underactuated state of the system.Considering the missions’ safety and the fault tolerance of actuators,it is necessary to study the attitude stabilization control of the combinations under underactuated conditions.In addition,to the underactuated state caused by the passive failure of the actuators,in order to reduce the launch cost of the spacecraft and reduce the excess load caused by the actuators during the space operation period,it is necessary to study the attitude stabilization control of the combinations with less control actuators than common.Then,the method for desired actuators’ setting can be supported theoretically.The underactuated attitude stabilization control of the combination coalesces the characteristics of the combination control and the underactuated control,which involves following key difficulties:(1)The model that reflects the characteristics of underactuated combination is needed: the combination is an asymmetric body whose variation of the mass distribution leads to the offset of the inertia principle axis and introduces the product of inertia.Moreover,there exists a complex coupling between the underactuated axis and the attitude of the actuated axis.These characteristics should be reflected by the model simultaneously;(2)Disturbances and control.The influences of the disturbance torque component on the underactuated axis can only be compensated by the motion of the actuated axis,while the complex coupling in the combination increases the difficulty in the control law design.It is necessary to study the attitude stabilization method to compensate underactuated disturbances;(3)Complex coupling processing and parameters uncertainty control.Considering the uncertainty of the quality characteristic parameters of the underactuated composite,the control law cannot be designed directly because of the uncertainties and state variables due to the complex states’ coupling.Thus,it is necessary to study the decoupling method for uncertain terms and underactuated control problems with uncertain parameters;(4)Underactuated axis control.When the underactuated angular velocity is non-zero,according to the characteristics of underactuated control,it is necessary to stabilize the underactuated axis movement and stabilize the controlled axis motion afterwards.Due to the coupling of the dynamic model of the combined body,in order to get better control performance,it is necessary to design a faster under actuated axis stability control law with complex coupling;(5)Ground test platform selection and experimental verification.It is necessary to choose the experimental platform that can simulate the space environment to the greatest extent.Furthermore,the platform should be able to be applied to show the motion of the combined body and carry out experiments.Based on the difficulties above,the underactuated attitude stabilization control of the combination after capturing the space target is studied.The main research contents and research results are as follows:(1)The modeling of the combination after capturing the space target is studied.First,in order to eliminate the redundancy of the attitude parameters under underactuated conditions and reflect the spatial motion characteristics of the combination,the extended attitude kinematics based on the parameters in the complex plane is derived.In addition,in order to accurately reflect the coupling situation of the attitude dynamics of the underactuated combination,the moment of inertia partition matrix with the product of inertia is proposed,and the reduced underactuated attitude dynamics model of the combination is derived.It provides a model basis for theoretical analysis and control design.(2)The partial attitude stabilization control of underactuated combination is studied.A partial stability control law based on feedback control is designed for the underactuated model.The stability condition releases the full state stability to the stability of rotation around one axis,which simplifies the design process of underactuated control and avoids the periodic oscillation of the system.Then,in view of the disturbance caused by the space environment,an underactuated cascade control law based on the composite disturbance observer is designed,and the attitude stabilization control of the cascaded underactuated system with disturbance is realized for the first time.(3)The attitude stabilization problem of the underactuated combination under coupled uncertain conditions is studied.The dual linear transformation strategy is proposed to decouple and replace the coupling uncertainty,and the multiple decoupling of uncertain parameters and state variables is realized.Then,the adaptive sliding mode control law,the parameter adaptive law and the sliding mode parameter update law are designed to achieve the attitude partial stability of the combination under the coupling uncertainty.(4)The finite-time full state stabilization control of the underactuated combination is studied.In order to solve the singularity problem of the kinematic part,and to suppress the excessive amplitude of the control quantity in cascade control,an improved singular avoid kinematic control law is designed by introducing a saturation function to limit the amplitude of the control quantity.The attitude control problem of the combined underactuated combination is transformed into the attitude tracking problem,and an adaptive tracking control law of the combination is designed.Based on the research above,a full state stabilization control law is designed,and the underactuated angular velocity is proved stability in finite time.(5)The method validation for the proposed method using liquid magnetic hybrid suspended ground microgravity simulation system is studied.In view of the attitude dynamics model of the composite experimental body influenced by the complex underwater environment,the proposed full state stabilization control law is verified by simulation.The stability of the attitude angle and angular velocity of the combined experimental body is realized and validated in the ground experimental environment.The experimental results are compared with the simulation results,which further prove the availability of the method.