Study On Vibration Isolation Of Flexible Spacecraft Using Viscoelastic Materials

The vibration environment of spacecraft is very severe during launch. For keepingthe spacecraft safe in severe vibration environment, whole-spacecraft vibration isolation(WSVI) is applied to increase the success probability of launch. In this paper, viscoelasticmaterial (VEM) is studied, the parameters design and reliability technology are applied.The in?uence of VEM on ?exibility WSVI is studied in dynamic solution. The primaryobtained results are as follows:The lateral-longitudinal natural frequency ratio control problem of whole-spacecraftsystem is studied. The dynamic model of spacecraft and payload attaching fitting (PAF)is given. By the analytic solutions, it is proved that both to increase the height of PAF andto reduce the angle of PAF can increase the lateral-longitudinal natural frequency ratio.With no reduction of lateral natural frequency, the longitudinal natural frequency can bereduced to satisfy the requirement of actual launch.Taking the VEM as damping providing form, the multiple degree-of-freedoms(DOFs) dynamic model of vibration isolation is given and analyzed. Based on modetheory, it can be proved that the increase of VEM stiffness can cause the model loss fac-tor (MLF) saturation of vibration isolation system. By the dynamic model of vibrationisolation system, the in?uence of eccentric center of mass is discussed.Because the stiffness of VEM can cause the MLF saturation of vibration isolationsystem, a new function"mode displacement difference (MDD)", which is an inherentfeature of vibration system, is brought in this paper. By MDD, the analytic solutions ofsystem eigenvalues and the mechanism of MLF saturation are obtained. Besides, the lossfactor of VEM can also cause the MLF saturation, which is developed from the traditionaldesign technology of vibration isolation. The conclusion is provided for the design ofvibration isolator in practice.Because the spacecraft is ?exible, the finite element model is given to discuss thedynamic feature of WSVI system. By Fourier transformation, the analytic solutions oftransmissibility is obtained. By the computation of transmissibility, the performanceof isolator is obtained. The dynamic feature is analyzed at natural frequency and anti-resonance frequency. It can be proved that the displacement difference of isolator will be limited by large stiffness of VEM. The deformation of viscoelastic damper (VED) issuppressed. The MLF saturation is proved by transmissibility.By the introduction of reliability computation method of different system and com-plex system, the design method of natural frequency and damping of WSVI system withVEM are obtained. Furthermore, the optimization method is presented. By reliabilitycomputation of performance and spacecraft and launch vehicle (LV) coupled problem,the quantization method of natural frequency design is obtained. In addition, it is provedthat there must be the resonant in the coupled system of spacecraft and LV.Based on the basic study, by the test of MLF, the MLF saturation is proved by theexperiment result. The design method of VED stiffness is given in practice. The stiffnessof VEM should be designed as a little more than the critical value which is correspondingto MLF saturation. As the performance of isolator satisfies the requirement, the vibrationisolation will be improved by the failure of VEDs. Furthermore, by the redundant featureexperiment of isolator, the failure of a small amount VEDs cannot cause the failure ofisolator.