WHOLE SPACECRAFT VIBRATION ISOLATION: A COMPARISON OF PASSIVE VS. SEMI-ACTIVE ISOLATION DESIGNS

The launch phase is the harshest mechanical environment a spacecraft experiences through its lifetime. The severity of the vibrations during the launch phase poses a serious challenge for the design of the spacecraft which generally contains many sensitive electronic components. The need to guarantee the launch survival of the spacecraft has instigated a significant amount of research in the field of vibration isolation of the whole spacecraft, which resulted in development of various passive vibration isolation systems and their widespread use since two decades ago. The present study is aimed to analyze the feasibility of implementation of semi-active vibration isolation system instead of a passive one and to compare its potential benefits in attenuating the vibrations transmitted to the sensitive components of the spacecraft during the launch phase. First, the passive system has been studied and a methodology for design optimization of the multi-degree of freedom system in frequency and time domain has been formulated. The optimized passive system is then used as a baseline to compare the performance of the optimal passive isolator with that of a semi-active system. Semi-active control strategies based on Skyhook (SH) and combined Skyhook and Acceleration Driven Damping (SH-ADD) have been utilized to control the damping of the isolator between spacecraft and launch vehicle to attenuate vibration. The results showed that while semi-active system has a significant advantage over passive system to attenuate vibrations when the excitations are harmonic or narrow band, the results are not as promising when broadband random excitation, which is a realistic model of the excitations that the spacecraft experiences during launch, is considered. This calls into question the practical effectiveness of the semi-active system to be used in whole spacecraft vibration isolation system. Further research work with experimental tests are required to verify if semi-active systems can have a practical application in whole spacecraft isolation system.