Alternative proposal, based on systems-engineering methods, aimed at substituting with carbon-epoxy laminates the load-bearing aluminum sandwiches employed in the structure of a small satellite

Abstract

The development process of composite structures has suffered from a lack of balance between analysis, design and the use of design methods. This study finds a solution to this matter with an alternative proposal that aims at substituting with a stiffer and lighter material the aluminum alloy originally employed in the construction of the primary structure of a micro satellite (50 kg). The structural components to be substituted are the four vertical lateral walls (VLWs) fabricated as honeycomb sandwich structures (SS). The alternative structure consists of a carbon fiber-epoxy (C-Ep) laminate whose stacking sequence is chosen so it is configured as quasi-isotropic, balanced, regular, homogeneous and symmetrical. The alternative proposal is justified from the standpoint of the feasibility of C-Ep in space applications; the reduction of the launch cost; and the enhancement of the structural performance. The first aspect is verified with a state-of-the-art review. Launch cost reduction is estimated conjecturally based on launch prices of the Ariane family of rockets. The development process of the C-Ep laminate is carried out from start to finish with an integral design process based on well-known systems-engineering (SE) methods and a structural analysis based on classic analytic and numerical approaches of thin-wall aeronautical structures. The methodological approach draws upon the Quality Functions Deployment (QFD) and the Functional Analysis (FA). Both methods allow to understand better the redesign problem and to propose a solution that ensures the satisfaction of the customer needs (i.e., launcher, structural designers, mission). The fabrication of the C-Ep laminate is accomplished with the wet lay-up process plus hot bonding with flexible heater blankets and a vacuum bag. The choice of C-Ep as the main construction material implied a reduction of 40% of mass, and a simultaneous increase of almost 12 times the bending stiffness, 4 times the buckling strength and 10 times the buckling load with respect to the all-metal VLW. Launch cost reduction could be substantial depending on the initial cost. To conclude, the hypothesis that conjectures a reduction of costs and the enhancement of the performance of the structure is proved positive on account of the simultaneous increase of the specific stiffness of the material and of the load bearing capacity of the C-Ep VLW. QFD and FA prove to be effective methods to understand and solve the redesign problem beyond the standard methods focused exclusively on analysis