Exploration of a new affordable thermal protection system utilizing 2.5D silica/polysiloxane composite

Abstract

Ablative materials are used as thermal protection systems (TPS) for reentry vehicles and solid rocket motor (SRM) nozzle applications. Phenolic and cyanate ester are the state-of-the-art (SOTA) resin systems used in many of the ablative composites today, including MX-2600 (silica/phenolic) from Cytec Solvay Group. While these ablatives have worked well, more demanding requirements drive the need for affordable lightweight advanced composites capable of handling high heat fluxes with minimal mass loss. These advanced ablative composites result in lighter reentry heat shields and solid rocket motors, increasing payload capabilities of spacecraft and rockets. Molding compound made of aerospace grade 99% SiO2 fabric and polysiloxane resin showed considerable improvement over MX-2600 in ablation properties in recent studies. In order to meet increased mechanical strength demands, NASA recently developed an ablative composite using a 3D quartz woven/cyanate ester composite material designed for the Orion spacecraft. While 3D woven composites provide excellent out-of-plane mechanical and ablation properties, they are very expensive, which limits their application. This research explores needle-punched silica fabric, sometimes referred to as 2.5D, which provides similar out-of-plane mechanical benefits to 3D woven composites in a more flexible VARTM manufacturing process at a much lower cost. The needle-punched silica fabric was infiltrated with polysiloxane resin and mechanical tests were performed. The needle-punched composites showed an increase of 181% in flexural strength, 27% in interlaminar shear strength, 2% in tensile strength, and 13% in compressive strength. In aerothermal ablation tests, the 2.5D out-performed the 2D laminate in char yield, mass loss, and recession rate; and in char yield and mass loss (%), the 2.5D out-performed the industry standard MX-2600 molding compound. The increased out-of-plane strength and char yield make it a promising and affordable ablative candidate for ablation performance with enhanced mechanical properties.