Advanced manufacturing of titanium propellant tanks for space applications part 1: tank design and demonstrator manufacturing

Satellite propellant tanks are mostly built from titanium alloys using expensive forgings, which have a long lead time and require significant amounts of machining. The propellant tank components are then welded using fusion-based welding techniques like electron beam or tungsten inert gas welding, that can cause loss of joint strength due to imperfections produced during solidification. To reduce the manufacturing time and associated costs, an alternative method of tank manufacturing has been developed. This study describes the application of a casting technique to manufacture tank end domes and the cylindrical sections using titanium alloy Ti-6Al-4V. The domes and cylindrical parts are machined to the required geometry and welded together using Friction Stir Welding. The microstructure and mechanical performance of the tank parts was evaluated and compared to that of a conventionally manufactured tank. Although there was a slight degradation in weld elongation, the fracture toughness and the stress corrosion cracking properties were quite similar before and after welding. The fabrication of propellant tank components using the casting technique has offered typically five times lower cost and two-third reduction in lead time when compared to the forging and forming process route.