Uncertainty Analysis of CEV LEO and Lunar Return Entries

A Monte Carlo sensitivity and uncertainty analysis is performed on CFD estimates of convective heating rate for a CEV forebody on a Low Earth Orbit entry and for the forebody of the Fire II vehicle at an entry condition similar to that experienced on a Lunar return mission. The sensitivity and uncertainty process involves generating a statistically meaningful number of calculations randomly varying the values of key input parameters about their nominal values. Correlation coefficients can be computed using a linear regression analysis to determine the fractional contribution of each input parameter to the overall uncertainty. The 2-σ and 3-σ variability ranges can also be determined. For the CEV LEO analysis, the primary contributors to the convective heating rate uncertainty were the collision integrals for the N2 - N and N2-O species pairs. The 2-σ values at the stagnation point were within 5.8% of the mean convective heating rate value. For the FIRE II analysis, the uncertainty of the convective, radiative, and total heating were determined. The range of variability for the radiative heating was less than that seen with the convective heating. The results presented in this paper represent the uncertainty in heating rate due to uncertainties in the CFD code input parameter values and don’t include the uncertainties in the basic assumptions of the physical models themselves.