Ablating Material

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An Ablating Material is a material, especially a coating material, designed to provide thermal protection to a body in a fluid stream through loss of mass.

Ablating materials are used on the surfaces of some reentry vehicles to absorb heat by removal of mass, thus blocking the transfer of heat to the rest of the vehicle and maintaining temperatures within design limits. Ablating materials absorb heat by increasing in temperature and changing in chemical or physical state. The heat is carried away from the surface by a loss of mass (liquid or vapor). The departing mass also blocks part of the convective heat transfer to the remaining material in the same manner as transpiration cooling.

It should be noted that use of ablating material for heat shields has two significant drawbacks: first, the mass of the material must either be carried throughout the mission (at an attendant penalty to payload capacity) or must be installed immediately before reentry (adding greatly to complexity and raising safety concerns if, for whatever reason, the installation fails) and, second, the coating is a single-use component, making it unattractive as an option on reusable vehicles.

References

This article is based on NASA's Dictionary of Technical Terms for Aerospace Use