Combined Thermal Management and Power Generation for Reusable Hypersonic Vehicles

The design of hypersonic vehicles is primarily driven by thermal considerations. Additionally, due to the lack of turbomachinery in these vehicles, the provision of electrical energy to vehicle systems is done almost exclusively by batteries. This paper outlines the analysis of photovoltaic cells embedded in the skin of a hypersonic vehicle to reduce the heat transfer from the hot external aerodynamic surface and the internal vehicle structure and to produce electrical energy from a portion of the thermal radiation. By treating each of the surfaces involved in the radiative exchange as coplanar surfaces in local thermodynamic equilibrium, the equations governing the transfer of thermal energy through the skin structure are derived. Two nominal refractory metals and a nominal ceramic matrix composite material are analyzed at a range of temperatures to determine the relative effectiveness of a thermophotovoltaic (TPV) skin in heat flux reduction and electrical energy generation compared to a simple skin structure. A TPV skin is shown to reduce the heat flux to the vehicle interior by more than an order of magnitude and simultaneously convert more than 10% of the external heat load into electrical energy at high temperatures.