Development and Validation of SACRAM: A Swiss Approach to the Computational Response of an Ablative Material

Future space exploration missions foresee high-speed entries into planetary atmospheres. These latter imply extreme thermal conditions to which the space vehicle is exposed to, and require an appropriate thermal protection system (TPS). The interest of the scientific community in modelling and testing of materials that compose the TPS has hence greatly increased over the past few years. Since a complete set of material properties is not available in open literature, it is difficult to numerically rebuild experiments. The inter-code comparison exercise proposed by the AF/SNL/NASA Ablation Workshop aims to give a baseline platform for ablation code calibration, with a complete set of material and gas properties. SACRAM 1.0 is a one-dimensional, finite-volume code that solves transient mass and energy continuity equations for a carbon-resin composite material that undergoes pyrolysis and charring. Mass loss is calculated integrating Arrhenius laws, with the hypothesis that all decomposed solid material is transformed into gas, and no closed pores appear. The solid mass conservation law translates therefore in a conservation of the porosity. Darcys law is used in the momentum conservation equation to determine gas velocity in the pores. Time integration is performed with an implicit method, and non-linarites are treated with NewtonRaphson iterations. Thermal non-equilibrium between gas and solid phases, formulation of pyrolysis gas as a multi-species entity and internal radiative heat transfer are under development and will be implemented in SACRAM version 2.0. SACRAM will also help to increase European scientific interest and activity in the field of ablation, where currently US presence in primary. In fact in the session dedicated to this exercise at the 4th AF/SNL/NASA Ablation Workshop (1-3 March 2011, Albuquerque, New Mexico), out of the fourteen research groups that presented their results, only two were from European countries