The objective this thesis was to create an accurate finite element model of the FedSat satellite, verify the model through comparison of results with available test data and carry out subsequent analysis in order to prove the satellite’s structural integrity in the launch environment.
The development of a new finite element model of the Structure Model (StM) of the FedSat satellite required an iterative process of design and analysis work. The old model was not entirely representative of the satellite structure. It was converted from the ANSYS FE package to MSC/NASTRAN and compared to the current StM structure and modifications were made. Some of the modifications carried out included updating payload and platform unit masses, redefining component connectivity in some places and adding some missing structural components.
Before the characteristics of the satellite could be determined via analysis of the model, it was necessary to verify that the model sufficiently represented the physical structure of the StM. After several of the aforementioned design/analysis iterations, the model was found to experience an accuracy of over 98% with regards to its stiffness characteristics when compared with static test data for the StM. Once the stiffness of the model was sufficiently accurate, it was necessary to ensure that the mass distribution was correct. The mass distribution verification consisted of ensuring that the various unit and structural masses in the model were equal to the measured values as provided by Vipac and the Cooperative Research Centre for Satellite Systems (CRCSS).
Once the stiffness and mass distribution characteristics were considered as accurate as practically possible, a modal analysis of the modal was undertaken. This analysis was then compared to results derived from vibration testing carried out by the original FedSat designers, Space Innovation Limited (SIL). Unfortunately, the modal analysis did not compare with the test results to an acceptable degree of accuracy, though general trends in the two data sets were clearly present. An anomaly in the vibration test regime put the test data in some doubt. At this stage, it was recommended that the modal results be compared with the more recent vibration tests that were carried out early this year, once the results were available so as to verify the structure beyond doubt.
Subsequent frequency response analysis was carried out and again compared with the vibration test data. Definite trends in the data were apparent, although the FE analysis results revealed significantly higher satellite response at particular frequencies. The model displayed dangerously high responses of up to 193g’s on the Boom tip and in the +Z Panel. It was determined that such high responses would be potentially hazardous to the satellite structure and fatal to sensitive electronic equipment in the payloads and platform sensors. A more detailed static analysis was also carried out and the most critically loaded region, the baseplate, was found to experience a factor of safety of around 9 for any static loading.
Upon the submission of these results to Vipac, and comparison with their most recent vibration tests, the validity of the aforementioned concerns were recognised. Subsequent measures are currently being carried out with the formation of a team of Mechanical Engineers assigned the task of modifying the structure to implement a degree of response attenuation into the satellite structure.