Modeling of Glow Radiation in the Rarefied Flow About an Orbiting Spacecraft

Abstract

An approach for modeling visible glow radiation about a spacecraft in low Earth orbit has been examined. A new technique for simulation of surface chemical reactions based on the direct simulation Monte Carlo method is used. The study focuses on the sensitivity of glow radiation to the gas-phase reaction model and surface reaction cross sections in the altitude range from 140 to 200 km. Comparison of predictions for different gas reaction cross sections and surface parameters is given with the Atmospheric Explorer data. It is shown that although the radiance is increased by a factor of two when a quasi-classical model is used, the altitude dependence of the predicted radiation is the same as that obtained using the total collisional energy model. Furthermore, it is found that the ine uence of the freestream NO concentration on the total radiation is small for altitudes up to 200 km. The main contribution is the formation of NO in bow-shock gas-phase reactions. Nomenclature A = preexponential factor in the Arrhenius expression B = temperature exponent in the Arrhenius expression Ea = activation energy Fnum = ratio of molecules to simulated particles fi = number e ux of the ith species Hs = heat of absorption I = radiation intensity k = Boltzmann constant, chemical rate constant kb = desorption rate M = chemical species Ni = number of collisions of species i with species j n = number density nT = total number of surface sites P = probability S = vacant surface site So = sticking coefe cient T = temperature v = relative velocity, gas velocity Wk = weighting factor of the kth species Zij = collision frequency of species i with j D t = time step r f 3, f 4 = cross sections for glow production r T = total collision cross section s l = radiation lifetime Subscript S = surface adsorbed species Superscript ¤ = electronically excited state