Research On Dynamic Characteristics And Active Vibration Control Of Dumbbell Spacecraft

Space nuclear energy can save a lot of space for spacecraft and provide stable and lasting power supply.It is the best space energy for deep space exploration missions.However,the large amount of heat and gamma rays released during the nuclear reaction can cause great harm to human body and some instruments.A relatively safe distance between the nuclear reactor and the load module should be considered in the design of spacecraft structure.A spacecraft with an deployable truss structure is proposed.With the advantages of light weight and space saving in undeployed state,deployable truss structures have often been used to address the unique structural requirements of the space.There are a lot of truss elements,and the unfolded length can reach tens of meters.Due to its low stiffness,it is easy to be influenced by external conditions to cause low frequency vibration for a long time.Therefore,it is necessary to accurately model and analyze the mechanical properties of truss structures.In this dissertation,unfolded dumbbell spacecraft is taken as the research object.Firstly,the research object is regarded as a rigid-flexible coupling model with two rigid bodies connected by a flexible middle body.The definition of coordinate system for spacecraft dynamics modeling is completed.Based on the finite element method(FEM),the mechanical properties of unfolded truss structures are analyzed by using space bar element,including the statics and dynamics analysis.The results of the analysis are compared with those of the commercial analysis software Ansys,and the overall stiffness matrix as well as mass matrix of the truss are obtained through the relation matrix.The rigid-flexible coupling dynamics model of dumbbell spacecraft is established by Hybrid-coordinate method,and the derivation process of complex dynamics equations is given.On this basis,the vibration equation of rigid-flexible coupling dynamic model is obtained by using Lagrangian equation.Based on the unconstrained mode method to solve the frequency and mode of each order of unconstrained mode,the unconstrained mode equation model is given,and the modal analysis and dynamic characteristic analysis of the model are carried out,which lays a good foundation for the subsequent spacecraft attitude control and vibration suppression.The attitude maneuver control is carried out for the unconstrained modal model,the attitude maneuver torque is designed by the optimal control theory,the vibration generated during the Bang-off-bang control torque is analyzed,and the vibration is suppressed by the force component synthesis vibration suppression(CSVS)method.The problem of system robustness when the calculated frequency is inconsistent with the real frequency of the system is discussed and the effectiveness of the control torque with higher order robustness is verified.