Uncertainty and Sensitivity Analysis of Thermochemical Modeling for Titan Atmospheric Entry

Abstract

A Monte Carlo uncertainty and sensitivity analysis technique is presented to i) identify the major sources of uncertainty in the thermochemical models used for aerothermal analysis, and ii) track the propagation of these uncertainties through the system into the predicted quantities of interest, such as the vehicle heating, shock layer properties, etc. The technique is applied to the aerothermal analysis of Titan aerocapture, where CN shock layer radiation is the dominant source of vehicle heating. Several hundred model input parameters, including reaction rate constants, vibration-chemistry coupling parameters, vibrational relaxation times, and transport properties, are independently sampled over their range of uncertainties, and the vehicle heating is determined probabilistically. A massively parallel, axisymmetric CFD (Data-Parallel Line Relaxation) code was used to make the several thousand runs needed to statistically describe the variability in the heating predictions. It is found that major contributions to the uncertainty in the predicted heating originates from the uncertainties in the rates of N2 dissociation by H atom impact, and some atomic exchange reactions: N2+H→NH+N and N2+C→CN+N.