Design and manufacturing of conformal ablative heatshields

Abstract

Conformal ablators, first introduced in the early 2000s under the NASA Hypersonics Project, are a type of rigid ablative thermal protection system that uses flexible, rather than rigid, fibrous substrates. These materials are impregnated with resin in a mold to yield a part that is close to the final geometry and requires little post-process machining (a near net shape part). The lack of fiber connectivity through the thickness enables the TPS to tolerate larger strains than comparable rigid substrate ablators facilitating larger tiles and installation on most aeroshells without strain isolation. Reduced part count and simplified integration drive reductions in labor, cost and complexity –advancements which are enabling for planetary and human missions. Conformal ablators are currently fabricated using an open liquid impregnation process adapted from a technique developed for Lightweight Ceramic Ablators, such as Phenolic Impregnated Carbon Ablator, which leads to design and manufacturing inefficiencies. This work advanced a new manufacturing technique for conformal ablators, vacuum infusion processing, that reduces resin consumption and streamlines clean up. The closed process also eliminates an expensive atmosphere-controlled oven or vacuum chamber. A design methodology, centered around a simulation of the mold filling process, was developed to tailor a conformal ablative heatshield to vacuum infusion processing. A constitutive model, combining properties of individual components, was formulated to estimate the properties of the composite TPS material. The methodology leverages this model, integrated with material selection, tile layout, and the mold filling simulation, to automate a conceptual conformal heatshield design. The approach allows rapid iteration on TPS composition and manufacturing constraints.