Semi-active Whole-spacecraft Vibration Isolation Technology Using Magnetorheological Damper

The launch stage is the period with most severe dynamic environment that a spacecraft will experience during its whole mission life. At the launch stage, the spacecraft is subject to severe vibrations induced by the launch vehicle, such as the steady-state aerodynamic loads, the thrust load, and shock loads at the stage separation period. Generally, a conical adapter is employed to connect the payload and the launch vehicle. The conical adapter cannot prevent the vibration energy from being transmitted into the satellite because of its high stiffness. To protect the satellite from the severe loads, a whole-spacecraft isolation system is presented recently.In this dissertation, new semi-active whole-spacecraft vibration isolation (WSVI) platform is presented for the isolation of FY-III satellite and LM-3A launch vehicle. In the WSVI, the magneto-rheological (MR) damping technique is adopted and utilized. Special bars are presented as the elastic elements, which are fixed to the upper and lower stages. An anti-shake mechanism is proposed to enhance the lateral stiffness of the isolation system. The dynamic model of the platform is established in a simple form utilizing the mode truncation method. Furthermore, the dynamic and structural parameters are optimized by introducing the genetic algorithm.The principle of high-frequency hardening, which usually occurred in conventional shear-valve MR damper, is investigated based on the lumped-parameter model and its effects on isolation are evaluated theoretically.The large dynamic stiffness in high frequency plays a negative role in isolation; therefore, a new high-frequency decoupled MR Damper is proposed and applied to WSVIP. The lumped parameter model is derived; then the energy loss in lower frequency and dynamic properties in high frequency are analyzed. The structure and parameters are given according to the isolation requirements, while maximum output force and corresponding current are determined by magnetic circuit saturation analysis utilizing FEM. Based on the existing models of MR dampers, a parameterized dynamic model for high-frequency decoupled MR damper is given based on the Bi-Sigmoid model. The high-frequency decoupled MR dampers are manufactured and then tested to verify the mathematical model. The results are compared with the experimental results of conventional MR dampers. Generally, large damping is difficult to obtain, which is needed in the WSVI system. Therefore, a new mechanism is presented for the installation of the high-frequency decoupled MR dampers in the WSVI system.Based the analyses and comparison of conventional index, including transmission ratio, vibration level difference and power flow, a weighted impact factor is proposed for performance evaluation of WSVI. The formula of the weighted impact factor is derived for the proposed WSVI system. The formula is a function of the displacement admittance. The weighted impact factor is evaluated, and then the performance of the proposed WSVI system is predicted. The results prove that, the proposed appraisal method can unify the real measurement and theoretical analysis.Based on the finite element model of the satellite-PAF system and satellite-WSVIP, the passive isolation performance with base excitation is investigated. Numerical results prove that the proposed WSVIP can perform better. Furthermore, the satellite-launch vehicle coupled system is investigated in the same way. The transfer functions between key points in the satellite and the engine are used to evaluate effects of the rocket stiffness on the isolation performance. The correlative coefficients of the launch vehicle with and without the WSVI system are evaluated; accordingly, the effects of the additional WSVI system on the dynamic characteristics of the launch vehicle are investigated.A fuzzy optimal control method is utilized for the semi-active control of the WSVI system. The state equations are firstly established, and then the isolation performances of the WSVI system is analyzed in MATLAB/Simulink, two control method are compared, i.e. the limiting optimal control and fuzzy optimal control. Furthermore, the isolation performances of the WSVI system and the conical adapter are evaluated and compared.Finally, the PAF, the proposed WSVIP and the satellite model are designed and manufactured, and then the WSVI system is assembled. The on-loop experiments of passive and semi-active WSVI are carried out. The results prove that, by utilizing the fuzzy logic control, the proposed WSVI system is effective at both low and high frequency stage, which is coincident with theoretical analysis.