An aerothermochemical analysis for the process of carbon-carbon composite material regression in large advanced solid-propellant rocket motors has been conducted. The analytical approach is similar in spirit to the approach of Klager, Keswani, and Kuo, with the main idea of the nozzle regression being due to the carbon chemical attack by H 2 O. The different steps of the work have consisted of the development and applications of several numerical codes substantiated by experimental results concerning the regression rate and the surface roughness of a carbon-carbon material. The calculated results show good agreement between measured data and the predicted regression when a flow transition is assumed, in the model, between a laminar boundary layer existing on the "smooth" virgin carbon-carbon material at the firing start and a turbulent boundary layer existing on the very rough ablative carbon-carbon surface during stabilized motor operation. NomenclatureB = convective transfer parameter E = activation energy h -roughness height K = constant k = kinetic energy of turbulence Le = Lewis number M = Mach number or molecular weight Pr = Prandtl number p = pressure q = heat flux density R = radial distance Re = Reynolds number r = regression r' -regression rate Sc = Schmidt number St = Stanton number T = temperature Tu -turbulence intensity ratio U = voltage u -gas velocity along nozzle surface ur = friction velocity v = gas velocity normal to nozzle surface X = mole fraction Y =mass fraction z = axial distance e = dissipation rate of turbulence kinetic energy 0 = momentum thickness v = kinematic viscosity p = density cb = mass production rate per unit surface Subscripts c = convective ch = chamber d = diffusion Presented as Paper 88-3346 at the AIAA/ASME/SAE/ASEE 24th e = edge of boundary layer g =gas / = species / k = kinetic / = liquid m = mass s = surface or sand grain T = transition t = throat w = wall 0 = initial 30 = 30% excess Superscript * = reference

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