Uncertainty Analysis of Air Radiation for Lunar-Return Shock Layers

By leveraging a new uncertainty markup technique, two risk analysis methods are used to compute the uncertainty of lunar-return shock-layer radiation predicted by the High-temperature Aerothermodynamic Radiation Algorithm (HARA). The effects of epistemic uncertainty, or uncertainty due to a lack of knowledge, are considered for the following modeling parameters: atomic-line oscillator strengths, atomic-line Stark broadening widths, atomic photoionization cross sections, negative-ion photodetachment cross sections; molecular-band oscillator strengths, and electron-impact excitation rates. First, a simplified shock-layer problem consisting of two constant-property equilibrium layers is considered. The results of this simplified problem show that the atomic-nitrogen oscillator strengths and Stark broadening widths in both the vacuum ultraviolet and infrared spectral regions, along with the negative-ion continuum, are the dominant uncertainty contributors. Next, three variable-property stagnation-line shock-layer casts are analyzed: a typical lunar-return case and two Fire 11 entry-vehicle cases. For the near-equilibrium lunar-return and Fire 1643 s cases, the resulting uncertainties are similar to the simplified case. Conversely, the relatively nonequilibrium 1636 s case shows significantly larger influence from electron-impact excitation rates of both atoms and molecules. For all cases, the total uncertainty in radiative heat flux to the wall due to epistemic uncertainty in modeling parameters is +/- 30% as opposed to the erroneously small uncertainty levels (+/- 6%) found when treating model parameter uncertainties as aleatory (due to chance) instead of epistemic (due to lack of knowledge).