Simulation of total equilibrium shock-layer radiation for three typical entry body shapes

An approximate comparison has been made of the total equilibrium shock-layer radiation for three potential Martian entry body shapes at 0°, 45°, and 90° angles of attack. This assessment was performed by conducting radiation measurements in a shock tube, and shock-shape measurements in a shock tunnel. With these data, radiation results were extrapolated to a trajectory condition for the full-size vehicles using a simplified analytical model based on the assumptions that the shock layers are both optically and geometrically thin. The efficacy of the extrapolation method was tested by comparing the zero angle of attack extrapolated results of the shock tube to radiation measurements obtained in ballistic range and to theory. The agreement was found to be satisfactory for the blunt cone and Apollo shapes, but because of a lack of range data and because the theory may not be valid for the tension shell, no comparison could be made for that shape. The ratio of the radiation generated by the Apollo to that generated by the blunt cone in the wavelength region from 0.35 to 1.3 n is approximately 3 at zero angle of attack, whereas that of the tension shell to the Apollo is more than 5. Local radiation distribution measurements were performed in the shock tube for a blunt 60° halfangle cone, using a model instrumented with fiber optics. Agreement was obtained to within a factor of 2 to 5 with the uniform-infinite slab shock-layer theory using NASA Ames spectral data. The effect of pressure on the total equilibrium radiation was determined over a limited range for the blunt cone at zero angle of attack.