Manufacturing a 3D stitched highly unitized PRSEUS-based conformal propellant tank: Lessons learned

Abstract

Lightweight cryogenic propellant tanks are critical components of space launch systems and next-generation supersonic or hypersonic aircraft using liquid hydrogen or liquid oxygen as propellants. In recent years, NASA has made significant efforts to develop reusable cryogenic propellant tanks like those developed during the X-33/VentureStar program. However, mechanical/bolted connections, penetrations and joints in the tank wall, and gaps/holes were some of the major causes of the premature failure of the X-33 tank. This study demonstrates the manufacturability of a novel and more efficient conformal tank by using advanced 3D stitched composite technology and fabrication methods. Through-thickness stitching enables the design of conformal tanks with uninterrupted load paths between skin, stringer, and frame elements by maintaining structural continuity. A one-third scale externally stiffened carbon/epoxy composite tank was manufactured using the Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) panel construction. Complex preform assemblies were selectively stitched and built without the need for exacting tolerances and accurately net molded using resin infusion in a single oven-cure operation using high-precision outer mold line tooling. The resulting structure is a one-piece unitized assembly with seamless co-cured interfaces. The details of tool design, preform construction, stitching procedures, and infusion methodologies are described in the paper.