The ALMASat Microsatellite is the first educational satellite of Alma Mater Studiorum, University of Bologna. The spacecraft, designed and manufactured following general low-cost guidelines focused mainly on affordable solutions, modular concepts and COTS components, will be inserted in orbit using a DNEPR launch vehicle. The initial conceptual design produced a first configuration of the satellite, which has been verified by finite elements analyses, in order to check compatibility with the launch vehicle requirements and to reduce the structural mass, maintaining at the same time good mechanical properties. An iterative optimization procedure has been performed, involving numerical analyses and subsequent modifications to the structure, in order to reduce material and weight. Moreover, the finite elements model has been improved introducing bolted joints, pre-stresses and increasing the overall accuracy, while optimized modeling methods have been used in order to keep the computing time reasonably small. The results of the analyses have been used to produce a first prototype of the ALMASat structure. In early July 2005, a set of vibration tests has been performed to verify the analytical and numerical methods and the whole optimization procedure. Experimental results have been compared to numerical data in order to improve the finite elements model for higher performance and precision. In particular, the tests stressed the importance of acceleration measurement. The high values measured in some critical points for electronics and payloads, forced us to modify the local geometry in order to decrease acceleration values in such stressed areas. The results of numerical spectral analyses, such as transfer function and PSD nodal response, combined with experimental results, have been useful to define the proper mechanical interfaces for each device, onboard system and payload. Most of the finite elements simulation techniques, concepts and results discussed herein are also applicable to a wide range of small satellites, designed following the same principles of modularity and affordability used for ALMASat.
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