Vibration Analysis and Testing of a Satellite Structure during it’s Launch and In-flight Stages

The success of a Satellite Launch mission takes into account many factors into consideration with a long planning and a designing procedure. Each phase of the launch vehicle in-flight from launch to reaching the target destination in space is precisely designed and executed. During this process of actually designing a satellite launch the effect of vibrations and its inherent failure and damage mechanics are closely looked upon. When analyzing the vibrations affecting the launch vehicle and the satellite in the pay-load, we closely look at what type of external forces affect the satellite varying from Acoustic pressures, structure-borne vibrations to Aerodynamic excitation. This analysis is provided in the initial part of this thesis with a detailed insight to random vibration. Following on, the author moves to the critical topic of vibration testing of the satellite under the previously analyzed external excitation. The forces experienced by the launch vehicle is mainly multi directional while having free boundary conditions. However, in the existing analysis of vibration testing, most of the test methods use single or bi-axial excitation with a high impedance fixture with no attention to the load path. Hence, the current test methods fail to indicate the actual failure modes as observed in-flight and hence will eventually result in high factors of safety driving the production costs higher. After an in detail industrial case study, the author identified a new novel method as suggested in \cite{Daborn} as a solution for vibration testing of critical structures in Aerospace applications. This method is analyzed in-depth and a comparison between the exiting testing methods is made. Physical Vibration Testing, as mentioned above is very important to understand the behavior of structures under different loading conditions. However, the advancement of computer technologies and methods of numerical discretization has paved way towards computer based mechanical simulations to properly analyze the dynamic characteristics of structures under consideration. The author looks closely to these methods as a step away from physical vibration testing. Using the software's ANSYS APDL,ANSYS MECHANICAL and MATLAB, the behavior of satellite under different loading conditions is studied. A special attention is given to the critical components of the satellite which are the solar panels and the satellite antenna. These components are modelled using ANSYS MECHANICAL and various mechanical simulations are done which include modal analysis, harmonic analysis and random vibration analysis. The obtained results reveal valuable information about the frequency levels where the designed structure indicate resonance and hence this data can be used in the design process of the space vehicle with the satellite in the pay-load to avoid these resonances by making structural modification or by using vibration isolation. In addition to this analysis, a detailed comparison was made to understand the best set estimate of the frequency response function in relation to noise and errors in the input and output. This step was crucial when designing the MATLAB operations to convert the obtained time-domain data to indicate the behavior in the frequency domain with a high level of accuracy.