The effects of density, thickness and heat load upon the heat shield performance of the lightweight phenolic carbon ablators named LATS (Lightweight Ablator series for Transfer vehicle Systems) were examined quantitatively for both arc-heated test and re-entry heating conditions using a one-dimensional ablation analysis code. Thermal conductivity values of the ablator were tuned based on the arc-heated test results by matching the calculated temperatures to the measured data. Main findings are: (1) For both heating conditions, the heat shielding performance of the ablator has the same tendencies with respect to parameters of the ablator density, thickness and heat load.(2) The dependency of the back surface temperature upon the ablator density is small especially for a large ablator thickness. (3) The surface recession decreases with the increase of the density. However, the mass loss increases almost linearly with the increase of the density. (4) The ablator necessary thickness, with which the maximum back surface temperature equals to the pre-determined allowable temperature value, is nearly constant as the density changes. The ablator necessary mass increases almost linearly, with the increase of the density. (5) In considering the mechanism of nearly equal necessary thickness of the ablator, it is very important that the thermal diffusivity does not vary much with different densities of the LATS ablator. (6) From the point of the reduction of the ablator weight, the selection of a lower density ablator is more advantageous than that of a higher density ablator.

The effects of heat load, ablator density, and backup structure, etc. upon the heat shield performance of the lightweight phenolic carbon ablators named LATS were investigated using a one-dimensional ablation analysis code. The ablator density was assumed to be from about 260 to 1000kg/m 3 . Heat flux time histories of a rectangular pattern were assumed, where cases of constant heating duration time and constant accumulated heat load (up to 600MJ/m 2 ) were considered. The heating level was assumed to be from 1 to 10MW/m 2 , which means that the ablator surface is in the region of diffusion control oxidation/sublimation. The materials of the backup wall are assumed to be aluminum, stainless steel and high density CFRP. Main findings are: (1) For a low heat flux q with the same heating duration time tq, the necessary thickness, with which the maximum back surface temperature equals to the pre-determined allowable temperature, is nearly constant as the density v changes. On the other hand, the necessary thickness increases largely when q is larger and v is smaller. The ablator necessary mass increases with the increase of v and q for the same tq.

The coking phenomenon within a lightweight carbon-phenolic ablator exposed to the heating environment of air is investigated. The existing one-dimensional charring ablation analysis code is modified so that the coking behavior of the ablator can be calculated as well as the thermal response behavior within a lightweight carbon-phenolic ablator. The mass conservation equations for a pyrolysis gas and carbon in the gas are given. The energy equation including the coking process is also presented. The measured density distributions of some arc-heated CFRP ablator samples are compared with those calculated by the ablation analysis code, from which good agreement is obtained. The density profiles with and without coking are compared. The effect of temperature dependency of carbon mass fraction in a pyrolysis gas in the coking equation upon the density profile is examined. The effect of heating rate upon the density distribution in an ablator is also examined. The effect of coking upon the surface recession is studied analytically and experimentally.