Thermal response and ablation characteristics of lightweight ceramic ablators

The paper presents the thermal performance and ablation characteristics of the newly developed lightweight ceramic ablators (LCAs) in a supersonic, high-enthalpy convective environment. Light-weight ceramic ablators were recently conceived and developed at NASA Ames using low-density ceramic or carbon fibrous matrices as substrates for main structural support and organic resins as fillers. These LCAs were successfully produced with densities ranging from approx0.224-1.282 g/cm exp 3 . Several infiltrants with different char yields were used to study the effect on surface recession. Tests were conducted in the NASA Ames arc-jet facilities. Material thermal performance was evaluated at cold-wall hat fluxes from 113.5-1634 W/cm exp 2 and stagnation pressures of 0.018-0.331 atm. Conventional ablators such as SLA-561, Avocat 5026-39HC, MA-25S and balsa wood were tested at the same heat fluxes for direct comparison. Surface temperature was measured using optical pyrometers and the recession rates were obtained from the high speed films. In-depth temperature data were obtained to determine the thermal penetration depths and conductivity. Preliminary results indicated that most LCAs performed comparably to or better than conventional ablators. At low flux levels ( < 454 W/cm exp 2 ) the addition of silicon carbide and polymethyl methacrylate significantly improved the ablation performance of silica substrates. The carbon-based LCAs were the most mass efficient at high flux levels ( > 454 W/cm exp 2 ).