Radiative Heating on the After-Body of Martian Entry Vehicles

This paper presents simulations of the radiative heat flux imparted on the after-body of vehicles entering the Martian atmosphere. The radiation is dominated by CO2 bands emitting in the mid-wave infrared spectral region. This mechanism has traditionally not been considered in the design of past Mars entry vehicles. However, with recent analysis showing that the CO2 radiation can be greater than convective heating in the wake, and with several upcoming and proposed missions to Mars potentially affected, an investigation of the impact of this radiation is warranted. The focus of this paper is to provide a better understanding of the impact to aerothermal heating predictions and to provide comparisons between NASA's two main radiation codes, NEQAIR and HARA. The tangent slab approximation is shown to be overly conservative, by as much as 58 percent, for most back- shell body point locations compared to using a full angular integration method. However, due to the complexity of the wake flow, it is also shown that tangent slab does not always represent an upper limit for radiative heating. Furthermore, analysis in this paper shows that it is not possible to provide a general knock-down factor from the tangent slab results to those obtained using the more rigorous full integration method. When the radiative heating is accounted for on the after-body, the unmargined total heat flux can be as high as 14 watts per square centimeter.