Performance of Transpiration-Cooled Heat Shields for Reentry Vehicles

Abstract

This paper presents results of a system study of transpiration-cooled thermal protection systems for Earth reentry. The cooling performance for the sustained hypersonic flight and transient reentry of a blunt cone geometry is assessed. A simplified numerical model is used to calculate the transient temperature of a transpiration-cooled heat shield. The performance of transpiration cooling is assessed by calculating the overall required coolant mass for different steady-state and transient flight scenarios. Spatially and temporally optimized mass injection is presented for various flight conditions. The majority of the injection is required on the spherical nose segment of the blunted cone. Carbon/carbon composite ceramic and the ultra-high-temperature ceramic zirconium diboride are considered as wall materials. Both materials require similar amounts of coolant injection. In continuous hypersonic cruise, transpiration cooling is highly effective for flight conditions with velocities below $8\mathrm{km}·{\mathrm{s}}^{-1}$ and altitudes above 40 km. For transient reentry, transpiration cooling is most viable for the trajectories of entry velocities below $8.5\mathrm{km}·{\mathrm{s}}^{-1}$ and ballistic coefficients below $2.1\mathrm{kg}·{\mathrm{m}}^{-2}$ .