Daniel B. Leiser

Reaction Cured Borosilicate Glass Coating for Low-Density Fibrous Silica Insulation

The Space Shuttle Orbiter, shown in Fig. 1 will be the world’s first reusable space vehicle. Basic to the development of such a vehicle is the requirement for a heat shield that can survive multiple reentries into the earth’s atmosphere at temperatures up to 1400°C. For the majority of the orbiter’s surface, a material was required that had good insulative properties, could survive temperatures up to 1260°C, and would be extremely light weight. It would also be required to survive large temperature gradients (>1000°C/cm) and severe thermal shock resulting from the entry environment (Fig. 2). The convective heating environment which occurs during the vehicle’s entry is unique in that it can result in chemical interactions between the high-temperature gases and the solid surface. These interactions cause an abnormally high vaporization rate to occur among the less refractory compounds present in a heat-shield surface (1). Therefore, the stability of the heat shield in this type of environment is critical to the success of the vehicle.

Lightweight TUFROC TPS for Hypersonic Vehicles

*† A standard lightweight fibrous thermal protection system, such as RCG-coated tile, used as a wing leading edge or nose cap, would be susceptible to excessive recession during reentry. To avoid recession and maintain the outer mold line in wing leading edge applications, the temperature capability of such a system would need to be increased to 1900-2000 K. TUFROC (Toughened Uni-piece Fibrous Reinforced Oxidation-resistant Composite) is a new two-piece TPS developed at NASA Ames. It has a higher temperature capability (1970 K) than the highest temperature capability (1750 K) tile insulation currently available, a TUFI (Toughened Uni-piece Fibrous Insulation) treated AETB (Alumina Enhanced Thermal Barrier). The temperature capability of TUFROC extends the possible application of a fibrous insulation to the wing leading edge and/or nose cap on a hypersonic vehicle. The lightweight system comprises a treated carbonaceous cap composed of ROCCI (Refractory Oxidation-resistant Ceramic Carbon Insulation), which provides dimensional stability to the outer mold-line, while the fibrous base material provides maximum thermal insulation for the vehicle structure.

Characterization of the thermal conductivity for Advanced Toughened Uni-piece Fibrous Insulations

Advanced Toughened Uni-piece Fibrous Insulations (TUFI) is discussed in terms of their thermal response to an arc-jet air stream. A modification of the existing Ames thermal conductivity program to predict the thermal response of these functionally gradient materials is described in the paper. The modified program was used to evaluate the effect of density, surface porosity, and density gradient through the TUFI materials on the thermal response of these insulations. Predictions using a finite-difference code and calculated thermal conductivity values from the modified program were compared with in-depth temperature measurements taken from TUFI insulations during short exposures to arc-jet hypersonic air streams. 16 refs.

Development of a Catalytic Coating for a Shuttle Flight Experiment

*† ‡ § ** A spray-on coating was developed for use on the Space Shuttle wing tiles to obtain data that could be correlated with computational fluid dynamics (CFD) solutions to better understand the effect of chemical heating on a fore-body heat shield having a turbulent boundary layer during planetary entry at hypersonic speed. The selection of a spray-on coating was conducted in two phases: Phase I, screening tests to select the catalytic coating formulation; and Phase II, surface property determination using both arc-jet and side-arm facilities at NASA Ames Research Center. Comparison of the predicted surface temperature profile over a flat-plate with measured values obtained during arc-jet exposure (Phase I study) was used to validate the surface properties obtained during Phase II.