An Approximate Ablative Thermal Protection System Sizing Tool for Entry System Design
Author(s)
Dec, John A.
Braun, Robert D.
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Abstract
A computer tool to perform entry vehicle ablative thermal protection systems sizing has
been developed. Two options for calculating the thermal response are incorporated into the
tool. One, an industry-standard, high-fidelity ablation and thermal response program was
integrated into the tool, making use of simulated trajectory data to calculate its boundary
conditions at the ablating surface. Second, an approximate method that uses heat of ablation
data to estimate heat shield recession during entry has been coupled to a one-dimensional
finite-difference calculation that calculates the in-depth thermal response. The in-depth
solution accounts for material decomposition, but does not account for pyrolysis gas energy
absorption through the material. Engineering correlations are used to estimate stagnationpoint
convective and radiative heating as a function of time. The sizing tool calculates
recovery enthalpy, wall enthalpy, surface pressure, and heat transfer coefficient.
Verification of this tool is performed by comparison to past thermal protection system
sizings for the Mars Pathfinder and Stardust entry systems and calculations are performed
for an Apollo capsule entering the atmosphere at lunar and Mars return speeds.
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Date
2006-01
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Paper