High temperature optical performance of MgO:Y2O3 films for space applications

Abstract

As a species we are pushing the bounds of possibility as we seek to venture beyond our solar system. With the pursuit of interstellar space comes a need for spacecraft that can reach unprecedented speeds. For this purpose, a passive gravity assist around a planet such as Jupiter has become commonplace by NASA. However, it is limited by the orbital velocity of that planet. In order to reach greater speeds, it is desirable to perform a powered gravity assist around the Sun, in which a spacecraft falls into its gravitational well and performs an impulsive burn at the perihelion. To achieve this feat, spacecraft must pass closer to the Sun than ever before withstanding temperatures exceeding 2000 K. This will require thermal barrier coatings that are both highly emissive in the infrared and highly reflective in the visible. Since development costs associated with fabricating and testing these materials at elevated temperatures can be prohibitive, models describing the high temperature optical properties of candidate coating materials can play an important role in the overall design process. This paper discusses the use of Kubelka Munk theory to model the reflectance spectra over a range of temperatures for a MgO:Y2O3 film on a tungsten substrate and demonstrates an approach for determining the efficacy of various thermal barrier coatings for passive cooling under solar loading.