Thermal analysis of advanced plate structures based on ceramic coating on carbon/carbon substrates for aerospace Re-Entry Re-Useable systems

The development of reusable launch vehicles (RLV) must include a significant reduction of the payload transportation costs. One of the most expensive components of a RLV is the thermal protection system (TPS), which preserves the spacecraft from the high thermal loads during re-entry. Reusability and on-orbit environment are key parameters in TPS design, mainly as far as the adopted materials are concerned. Aim of the work is to analyze a novel TPS concept, proposing an hybrid multiscale ceramic coating - i.e., alumina-based varnish enriched by silica nanoparticles - to be applied on Carbon/Carbon (C/C) plates. The treatment is aimed at preserving the thermo-mechanical properties of the ceramic substrate from the detrimental space environment conditions, such as LEO thermal cycles, outgassing due to ultra-high vacuum, as well as Atomic Oxygen/UV irradiation. Experimental measurements of the coefficient of thermal expansion (CTE) are performed in order to evaluate the thermal stress and performance of both substrate and coating layer. Particular emphasis is devoted to evaluate the effect of coating/substrate adhesion, which may result in anomalous mechanical behavior. By the use of a robust numerical technique, known as the inverse method, heat capacity and thermal conductivity are analyzed; such approach is particularly suited to address these kind of problems, as a number of physical parameters concur for a reliable determination of material properties. The special test equipment and the regularizing algorithm for solving the heat conduction problem are described. After thermal conditioning, the integrity of coating and substrate is investigated by full morphological analysis using SEM/EDX techniques.