Continued Optimization of Low-Density Foam-Reinforced Ablatives for High-Velocity, High Heat Flux Earth Return Missions, Phase II

In previous work for NASA, Ultramet and ARA Ablatives Laboratory developed and demonstrated advanced foam-reinforced carbon/phenolic ablators that offer substantially increased performance under high heat flux conditions and reduced weight relative to conventional ablators. The two-piece structure consisted of an ablative-filled foam front surface backed by Ultramet's previously established and highly insulating aerogel-filled foam. Arcjet testing was performed at NASA Ames Research Center to heat flux levels exceeding 1000 W/cm2, with the results showing a significantly reduced ablation rate compared to conventional chopped fiber ablators, and ablation behavior comparable to FM5055 at just one-third the density. It is apparent that the foam helps retain the char layer by physical reinforcement and/or that the network of interconnected passages allows pyrolysis gases to escape with less disruption of the char layer. In Phase I, Ultramet teamed with ARA Ablatives for ablative infiltration of Ultramet foams and Materials Research and Design for ablation analysis, to continue optimization of foam-reinforced ablatives by focusing on two primary areas. The ablator formulation infiltrated into the foam was successfully modified to increase heat flux capability consistent with NASA Earth return requirements (1500-2500 W/cm2 or higher). The density can be varied as needed to meet heat flux requirements while minimizing weight. In addition, a single-piece foam structure was demonstrated, rather than separate ablative- and aerogel-filled foam sections. In Phase II, the lightweight hybrid ablator will be optimized for a specific NASA mission, material and structure requirements will be predicted through modeling, and performance will be demonstrated through high heat flux testing at NASA ARC and the Air Force LHMEL-II facility. Scaleup potential will be demonstrated through fabrication of a heat shield module suitable for construction of large modular heat shields.