Saturation effects on stagnation radiative heating for the Jupiter Probe

The equations for nonequilibrium radiation transport in the stagnation ablation layer for conditions typical of entry of spacecraft into the atmosphere of a major planet are developed. The equations are simplified and shown to contain two parameters which are used to classify the radiation transfer as equilibrium or nonequilibrium. The parameter omega represents the ratio of the radiative de-excitation rate to the sum of the radiative de-excitation rate plus the collisional excitation rate. The second parameter, omega-prime represents the ratio of the radiative excitation rate, due to external radiation, to the sum of the radiative de-excitation rate plus the collisional excitation rate. Both parameters vary between zero and unity. It is shown that the population ratio of the two electronic states of a molecular band approaches its equilibrium value as omega approaches zero. When omega and omega-prime are greater than zero, the population ratio becomes greater than its equilibrium value. An order of magnitude analysis is undertaken for conditions expected in the shock layer near the maximum heating point in the entry trajectory of the Jupiter Probe. It shows that saturation effects are likely to occur in the ablation layer.