Keeping Cool: System shows promise for better thermal protection of hypersonic vehicles
DOI: 10.1063/10.0039841
Keeping Cool: System shows promise for better thermal protection of hypersonic vehicles lead image
Hypersonic vehicles travel faster than Mach 5, which is more than 3,800 miles per hour. The space shuttle, for example, returns from orbit at nearly Mach 25. With this kind of speed comes heat, on the order of thousands of degrees, so an effective thermal protection system (TPS) is key for the design of such a vehicle. Existing systems are limited, though, and often present uncertainties or succumb to material stresses, even with the most advanced materials.
Monroe et al. explored electron transpiration cooling (ETC) — when electrons are emitted from “thermionic” materials to impart a cooling flux onto their surfaces — for use in a hypersonic vehicle TPS.
“With a thermionic material placed at the vehicle’s tip to carry away heat with emitted electrons, our TPS recycles electrons downstream to be recirculated through a battery-powered onboard circuit,” said author Kalvin Monroe. “In essence, the system converts the thermal energy at the vehicle’s hottest point into electrical current in the flow around the vehicle and converts it back to thermal energy downstream where temperatures are cooler.”
For the difficult task of quantifying ETC performance, the researchers developed a model that can gauge all the TPS components and, compared to previous studies that only modeled emission, better estimate surface cooling in hypersonic environments. The model identified material and sizes for the TPS that can maximize thermionic cooling for a given hypersonic flight condition.
“We hope these results motivate and inform future studies of ETC, which is applicable beyond hypersonic vehicles,” said Monroe. For example, chamber walls in tokamak fusion reactors also experience extreme heating and can potentially benefit from ETC systems.
Source: “Electron transpiration circuits for hypersonic leading edges,” by Kalvin Y. Monroe, Marcel P. Georgin, and Iain D. Boyd, Journal of Applied Physics (2025). The article can be accessed at https://doi.org/10.1063/5.0297243 .
