Silicone impregnated reusable ceramic ablators for Mars follow-on missions

Abstract

New Light Weight Ceramic Ablators (LCAs) were produced by using ceramic and carbon fibrous substrates impregnated with silicone and phenolic resins. Special infiltration techniques (patent pending) were developed to control the amount of organic resin in the highly porous fiber matrices, so that the final densities of LCAs range from 0.224 to 0.30 g/cu cm. This paper presents the thermal and ablation performance of the Silicone Impregnated Reusable Ceramic Ablators (SIRCA) in a simulated Mars entry heating environment. Testing was conducted in the Ames 60 MW Interaction Heating Facility (IHF) and 20 MW Aerodynamic Heating Facility (AHF). Test results show that the ablation characteristics of SIRCA are divided into three regimes: non-receding, surface coalescent, and receding. Four different Reusable Surface Insulation (RSI) substrates were used in the production of SIRCA to determine the effect of substrate compositions on the ablation performance. SIRCA with high-purity silica fibers generally performed better at high heating rates. Samples of SIRCA were tested at heating rates ranging from 45 to 550 W/sq cm and at stagnation pressures of 0.02 to 0.47 atm. Several samples were also tested at a heating environment simulating the Mars Aerocapturing mission, which generally consists of a low heating rate and a very high heat load. Material characterizations were also conducted to evaluate the material's mechanical, thermal, and optical properties. The effective thermal conductivity of SIRCA is comparable to that of the RSI substrates, and the emissivity of the charred SIRCA was measured to be about 0.92. Several samples of SIRCA were also exposed to the same heating condition for five cycles, and no additional significant mass loss or recession was observed. (Author)