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Development of Refill Friction Stir Spot Welding (RFSSW) for skinstringer-frame stiffening of Al-CuLi cryogenic tanks



Organisational Unit
19 December 2023

Duration: 18 months


The competitiveness of the Ariane launchers is constantly challenged by the need for agile solutions with the best performance/costs ratio. The recent overall need for reusable space booster/launcher have significant consequences on the designs compared to the existing tank architectures requiring both higher performances aluminium alloys and internal stiffening patterns. This renders obsolete the smooth AA2219 cryogenic tanks traditionally used in Europe for first stages in favour of Al-Cu-Li alloy barrels with integrated stiffeners for future European launchers like ArianeNext as well as smaller alternatives. Yet, as those Al-Cu-Li alloys are expensive and poorly weldable by fusion, if stiffeners larger than 50mm in height are needed such material performance gains would be hindered by the mass penalty of the traditional mechanical fastening method needed to assemble those stiffeners to the skin. Refill Friction Stir Spot Welding (RFSSW) is a solid-sate welding process identified as a promising potential candidate for assembling such large internal stiffeners onto shallow-machined barrels. RFSSW should also reduce the assembly cost, which should contribute towards offsetting the higher expected material procurement costs. Despite the fact that the technology is well studied for 7XXX aluminium aircraft fuselages, the applicability of RFSSW to Al-Cu-Li alloys in cryogenic environments has not been reported. Furthermore, replacing mechanical fastened joints with spot welds will most likely impact the way the tanks are designed thus requiring preliminary data to anticipate the upcoming design studies for the next generation of European launchers. Consequently, regarding the benefits that this technology may allow for improved competitiveness of the European Space Industry and given the low TRL of the solution, the ESA funding would provide vital support to mature RFSSW for cryogenic applications and ease the transfer to the European spacecraft industry.

Contract number
OSIP Idea Id
Related OSIP Campaign
Open Channel
Main application area
Generic for multiple space applications
Development of Refill Friction Stir Spot Welding (RFSSW) for skinstringer-frame stiffening of Al-CuLi cryogenic tanks