Imagine that you are an aeronautical engineer in the later 1950s. You have been given the task of designing an atmospheric entry vehicle—in those days it would have been an intercontinental ballistic missile. (Later, in the early 1960s, interest also focused on manned atmospheric entry vehicles for orbital and lunar return missions.) You are well aware of the fact that such vehicles will enter the earth’s atmosphere at very high velocities, about 7.9 km/s for entry from earth orbit and about 11.2 km/s for entry after returning from a lunar mission. At these extreme hypersonic speeds, aerodynamic heating of the entry vehicle becomes very severe, and is the dominant concern in the design of such vehicles. Moreover, you are cognizant of the recent work performed at the NACA Ames Aeronautical Laboratory by H. Julian Allen and colleagues wherein a blunt-nosed hypersonic body was shown to experience considerably less aerodynamic heating than a sharp, slender body—contrary to some popular intuition at that time. (This work was finally unclassified and released to the general public in 1958 in NACA Report 1381 entitled A Study of the Motion and Aerodynamic Heating of Ballistic Missiles Entering the Earth’s Atmosphere at High Supersonic Speeds.) Therefore, you know that your task involves the design of a blunt body for hypersonic speed. Moreover, you know from supersonic wind tunnel experiments that the flowfield over the blunt body is qualitatively like that sketched in Figure 1.1. You know that a strong curved bow shock wave sits in front of the blunt nose, detached from the nose by the distance δ, called the shock detatchment distance.