Almasat Microsatellite structural analysis: finite element techniques, vibration tests and results correlations

The ALMASat Microsatellite is the first educational satellite of Alma Mater Studiorum, University of Bologna. The satellite, designed and built following a general low-cost guideline focused mainly on affordable solutions, modular concepts and COTS components, will be launched in 2006 by a Dnepr 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 launch vehicle requirements and to reduce 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 maintain an acceptable computational time. The results of the analyses have been used to produce a first prototype of the ALMASat structure. In early July 2005, at ENEA Casaccia Laboratory (Rome, Italy), a set of vibration tests has been performed, as verification for the analytical and numerical methods and the optimization procedure. The results of the tests have been compared with numerical data in order to improve the finite elements model for better performances 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 to modify the local geometry in order to decrease acceleration values in such stressed areas. The results of numerical spectrum analyses, such as transfer function and PSD nodal response, combined with tests results, have been useful to define the proper mechanical interfaces for devices, on-board systems and payload. Most of the finite elements simulation techniques, concepts and results herein discussed are suitable for a wide range of small satellites, designed following the same principles of modularity and affordability used for ALMASat.