Ablative materials

The functional requirements of the ablative heatsliield must be well understood before selection of die proper material can occur. Ablative heatshield materials not only protect a vehicle from excessive heating, they also act as an aerodynamic body and sometimes as a structural component (2,3). Intensity and duration of heating, thermo structural requirements and shape stability (4,5), potential for particle erosion (6), weight limitations (7—10), and reusability (11) are some of the factors which must be considered in selection of an ablative material. 

Heating Facility and ES3 Aero Heating Facility, NASA/Ames. Numbers on die curves indicate stagnation pressure P in MPa —, ballistic entry,-, lifting 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Heatsliield thickness and weight requirements are determined using a thermal prediction model based on measured tliemiopliysical properties. The models typically include transient heat conduction, surface ablation, and charring in a heatsliield having multiple sublayers such as bond, insulation, and substructure. These models can then be employed for any specific heating environment to determine material thickness requirements and to identify the lightest heatsliield materials. 

Whis = density x insulative layer thickness = f(pk/Cv, T8tructure, Tsurface ) and lVtct = unit weight of heatshield = density x thickness = TTabl + TTills. 

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