Interstage 2-3 of vega c launcher: composite grid structure technology

The Interstage 2/3 is the structure that interfaces the Z40 second stage with the Z9 third stage of the new VEGA-C launch vehicle. The design concept developed for this structure is a “composite GRID architecture” which consists in a regular and rather dense system of interlaced hoop and helical unidirectional ribs completed with a thin outer skin with a secondary structural role. Interlaced ribs determine a fiber volumetric fraction that, except for the nodal regions, is usually lower than standard applications in composite material. Despite this, the typical mechanical properties are sufficient to design highly efficient solutions for heavily-loaded structures. The developed manufacturing process is based on the automated parallel winding of dry carbon fiber tows followed by liquid resin infusion under vacuum bag. The combination of a suitable design method and manufacturing process turns out to be very appealing to produce lightweight and low cost composite grid structures for space applications. This paper shows the general aspects inherent to the technology development and the design definition of the new VEGA C Interstage 2-3.