| With the increasing number of spacecraft launches around the world,especially the mass launch of various small satellites and micro-nano satellites into orbit in the past two decades,the number of failed spacecraft in orbit is increasing.Since these derelict spacecraft are no longer controllable or have insufficient self-recovery capability,they will pose a great security threat to spacecraft on orbit or ready for launch.Therefore,how to remove these failed spacecraft has become a hot issue in the field of aerospace engineering nowadays.The failed spacecraft,under the long-term action of various environmental disturbances in space,will generate large rotational angular velocity and be in a fast tumbling state.In order to control the fast free rolling spacecraft,the first problem that needs to be solved is how to deconvolve it,so that its rotational angular velocity can meet the capture and control requirements.To address this difficult problem,based on the autonomous control of the space robot manipulator,this paper proposes the installation of a flexible despun brush at the end of the robotic arm to despun the failed flexible spacecraft,and conducts an in-depth study on the dynamics modeling of the despun space robot,the despun mechanism and strategy,and the despun control problem.Firstly,the dynamic model of the unstable flexible spacecraft is carried out to analyze and study its spin and nutation motion characteristics,so as to lay the theoretical foundation for the follow-up research on the despun mechanism and strategy.Based on the ANCF plate and shell unit,the dynamics modeling of the flexible solar sail is carried out to establish the attitude dynamic model of the flexible spacecraft in the tumbling state,and then reveal the rotational motion characteristics of the spacecraft containing flexible sails and the law of its angular velocity deceleration.At the same time,since the motion state information of the space non-cooperative spacecraft cannot be obtained directly by the space robot,a visual non-contact sensing system is utilized to observe the motion state of the non cooperative target and then these state information is introduced into the despun control system design,while high requirements on their accuracy and real-time performance are required.To this end,a flexible spacecraft motion state estimation method based on the traceless Kalman filter is proposed,which enables the estimation error of the non cooperative target to converge quickly.Secondly,for the despun scheme of the space despun robot on the free tumbling flexible spacecraft,the despun mechanism and strategy based on the flexible despun brush are studied,and the optimal planning method of the robot ic arm tip motion trajectory is given to meet the space despun manipulation requirements.Based on the ANCF rope unit,a model of the flexible despun brush at the end of the robotic arm is established.And then combined with different touching modes of the brush for dynamics simulation and analysis,the despun mechanism of the flexible brush is revealed and a reasonable despun strategy is given.According to the capture requirements of the failed flexible spacecraft,an acceptable despun index is designed,and then the design parameters and despun strategy of the flexible despun brush are optimized.On this basis,a seven-degree-of-freedom redundant robotic arm dynamic model is established based on the Lagrange equation.Since the contact collision between the flexible despun brush and the failed spacecraft occurs during the deceleration process,which will have a collision impact on the space robot and then affect its stability control,a self-motion optimization of the despun process of the space redundant manipulator is carried out based on the attitude undisturbed zero-space.In addtion,the traditional Jacobi matrix pseudo-inversion method is difficult to achieve flexible selection of optimization targets,and the intelli gent optimization algorithm has disadvantages of large computation and difficult stable convergence,therefore online real-time planning is difficult to achieve.To this end,the velocity-level inverse-solve method is used to convert the motion trajectory of the robot arm end in Cartesian space into the planning trajectory in joint space.A motion trajectory planning method with minimum base reaction force is proposed,based on which the joint motion velocity is optimized by the weighted minimum parametric method,and the joint driving torque is optimized based on the zero-space method.Eventually,he optimal motion trajectory of the robot arm end considering the interference of the flexible despun brush is obtained.Finally,for the problem of despun control of a non-cooperative flexible spacecraft in space,an incremental robust optimal controller with quadratic performance index is designed under the condition that the system dynamics model parameters and the collision impact disturbance are uncertain.The simulation shows that the method can effectively and quickly track the planned optimal motion trajectory of the target during the despun process provided by the space despun robot with flexibel brush,while minimize the energy consumption of the despun process.On this basis,the despun control is carried out for the failed spacecraft with pure spin motion and additional nutation free motion respectively,and the effectiveness of the methods of non-cooperative spacecraft motion state estimation,robotic arm end motion trajectory planning and space despun robot robust control are systematically verified,which can enable the space robot to despun unstable rolling targets. |
