Finding Ablation Rates via Temperature Measurements from the Mars Science Laboratory

Abstract

The determination of the ablation rate for thermal protection systems on atmospheric entry is a difficult task, but can have significant implications in terms of safety and heat shield design. Ablation sensors of various kinds can be used to measure ablation directly, but in the event of a failure of these sensors, the use of thermocouples imbedded in the heat shield for determining the ablation rate is somewhat more difficult. A numerical model was developed as part of this research to determine ablation rate as a function of temperature using measurements from the Mars Science Laboratory Entry, Descent, and Landing Instrumentation Mission, which took place in 2012. The numerical model accounts for ablation as well as temperature-dependent thermal conductivity and volumetric heat capacity. A temperature-dependent ablation rate is calculated simultaneously with the heat flux for each time step of data acquisition. Regularization is provided for the heat flux calculation through the use of cubic splines. A significant reduction in the residual values between the mathematical model and the measured temperatures was obtained when accounting for ablation and refined temperature-dependent thermal properties. In some cases, the standard deviation of the residuals was reduced by 70% or more, indicating a greatly improved conformance of the mathematical model to the measured temperatures when accounting for ablation.