A self-transpiring technology for hypersonic or reusable space vehicles using a solid material that becomes gaseous and flows through the porous outer surface to cool the surface has been patented by Boeing.
Boeing expects the technology to provide cooling over a temperature range of 600-1600ºC (1,100-2,900ºF). The solid material is held within an inner cavity between the support structure and ceramic matrix composite outer skin.
The material vaporises, sublimes or decomposes into the gas at a temperature below the maximum the outer skin can withstand. Once a gas, it transpires through the porous outer surface to cool the skin.
The patent states: "The solid material system is a non-regenerable resource, it is capable of protection for only a limited duration during a high heat flux event." But the material would be replaced between flights, it notes.