Design of a COPV for liquid storable propellants of 4th stage VEGA launcher

摘要

This paper shows the feasibility study to manufacture the 4th stage VEGA launcher liquid propellanttanks with the filament winding technique, within the frame of the VEGA launcher evolution. Theactivity has been performed under the ESA responsibility.The 4th stage is equipped with four liquid propellant tanks, filled with UDMH and NTO. A positiveexpulsion device (bladder) provides the desired pressure level to the fluids. In the actual configuration,these tanks, and the equatorial flange to join the tanks to the main structure, are fully made of titaniumalloy.The use of composite materials with polymeric matrix, may lead to important mass saving, but thechemical compatibility problem must be faced. In the proposed design, the sealing function isaccomplished by a metallic liner, while the structural function is devoted to the filament wound material.In order to optimize the final structure, different optimization areas have been considered: a) domesshape b) metallic liner material c) composite part (winding trajectories and material) d) equatorial flangedesign (geometry and material). All the considered dome shapes have been preliminary verified withrespect to filament winding technique constraints. The selection of the best choice has been based on thestress status (obtained by simplified 3D FEM analyses). Different metallic materials, with the samecompatibility level with respect to the liquid propellants (titanium alloy, aluminium alloy, stainless steel),have been considered for the liner choice, and evaluated on the basis of their maximum deformationduring the pressurized phase. The filament winding process itself, since induces load on the liner, hasbeen taken into account for liner dimensioning. Composite materials, belonging to the carbon/epoxyfamily, have been considered for the liner overwrap, due to their specific combinations of high specificstrength and stiffness.Finally, an aluminium alloy has been selected for the equatorial flange. The developed design considersthe presence of a rubber shear ply between the flange and composite shell, with the aim of: a) to reducethe local stress peaks at the metal/composite interface b) to dampen the acceleration peaks dangerous forthe structural integrity. The proposed architecture, leads to a potential saving of the 25% of the tank shellmass.