THERMAL RESPONSE AND ABLATION CHARACTERISTICS OF LIGHTWEIGHT CERAMIC ABLATORS

This paper presents the thermal performance and ablation characteristi cs of the newly developed lightweight ceramic ablators (LCAs) in a sup ersonic, high-enthalpy convective environment. Lightweight ceramic abl ators were recently conceived and developed at NASA Ames using low-den sity ceramic or carbon fibrous matrices as substrates for main structu ral support and organic resins as fillers. These LCAs were successfull y produced with densities ranging from approximate to 0.224 to 1.282 g /cm(3). Several infiltrants with different char yields were used to st udy the effect on surface recession. Tests were conducted in the NASA Ames arc-jet facilities. Material thermal performance tvas evaluated a t cold-wall heat fluxes from 113.5 to 1634 W/cm(2), and stagnation pre ssures of 0.018 to 0.331 atm. Conventional ablators such as SLA-561, A vcoat 5026-39HC, MA-25S, and balsa wood were tested at the same heat f luxes for direct comparison. Surface temperature was measured using op tical pyrometers, and the recession rates mere obtained from the high- speed films. In-depth temperature data were obtained to determine the thermal penetration depths and conductivity. Preliminary results indic ated that most LCAs performed comparably to or better than conventiona l ablators. At low flux levels (<454 W/cm(2)), the addition of silicon carbide and polymethyl methacrylate significantly improved the ablati on performance of silica substrates. The carbon-based LCAs were the mo st mass-efficient at high flux levels (>454 W/cm(2)).