New Data For Modeling Hypersonic Re-entry Into Earth’s Atmosphere: Electron-impact Ionization Of Atomic Nitrogen

摘要

Space vehicles returning to Earth from beyond orbit enter the atmosphere at hypersonic velocities (greater than Mach 5). The resulting shock front generates a high temperature reactive plasma around the vehicle (with temperatures greater than 10,000 K). This intense heat is transferred to the capsule by radiative and convective processes. Designing vehicles to withstand these conditions requires an accurate understanding of the underlying non-equilibrium high temperature chemistry. Nitrogen chemistry is particularly important given the abundance of nitrogen in the atmosphere. Line emission by atomic nitrogen is a major source of radiative heating during reentry. Our ability to accurately calculate this heating is hindered by uncertainties in the electron-impact ionization (EII) rate coefficient for atomic nitrogen. Here we present new EII calculations for atomic nitrogen. The atom is treated as a 49 level system, incorporating Rydberd levels up to n=20. Level-specific cross section are calculated using a combination of binary-encounter Bethe(BEB) and sealed-hydrogenic methods. These data have been convolved into level-specific rate coefficients and fit with the commonly-used Arrhenieu-Kooij formula for ease of use in hypersonic chemical models. These data can be readily sealed by the relevant atomic nitrogen partition function which varies in time and space around the reentry vehicle. Providing data up to n=20 also enables modelers to account for the density-dependent lowering of the continuum.