Gas Pressure and Temperature Impact on the Thermal Conductivity of Materials for Satellites, Spacecraft, and Protective Structures of Surface-Landed and Re-Entry Space Vehicles

Abstract

Thermophysical properties of protective spacecraft materials determine the heat transfer, temperature, rate of ablation, weight and safety of re-entry and planetarylanded space vehicles. In this paper, we review and analyze this problem with an emphasis on description and explanation of typical experimental results. Generally, temperature affecting the spacecraft materials can be from -200°C up to materials’ melting point (>2000°C), the gas pressure ranges from 10-6 Pa to 107 Pa. Extensive experimental data have shown that high vacuum conditions, gas pressure and temperature changes in space and during the landing and re-entry phase of spacecraft can dramatically influence (5–10 times) the materials thermal conductivity. These variations are explained using the classical (conduction, radiation, gas convection) and novel heat transfer mechanisms in the materials. The first group of heat transfer mechanisms includes the heterogeneous heat and mass transfer process in pores and cracks, including the phenomenon of gas transport (gases are produced due to gas emission, evaporation and sublimation). The grain boundary segregation and diffusion of impurities can influence the thermal conductivity of dense oxide materials and metals. The second group of mechanisms deals with phenomena that involve a mismatch between the thermal expansion coefficients of different materials. Experimental methods and analytical technique are being developed for measurement of the materials thermal conductivity and diffusivity. The experimental technique applied to studying the thermal physical properties employs either monotonic heating of samples or steady-state analysis of the involved heat transfer mechanisms