Research
Allen was interested in the full range of aerodynamics research, and made contributions to the study of subsonic, transonic, supersonic and hypersonic flow. When the United States became interested in the design of ballistic missiles, Allen began research in the dynamics and thermodynamics of atmospheric reentry, as well as the effects of radiation and meteorites on space vehicles. His most significant contribution in this area was the idea of using a blunt nose for reentry vehicles, otherwise known as his "Blunt Body Theory". Earlier ballistic missiles, developed by both the United States and the Soviet Union, featured long nose cones with very narrow tips, which had relatively low drag when entering the atmosphere at high speeds. However, Allen demonstrated that a blunt body, although it had greater drag, would have a detached shock wave which would transfer far less heat to the vehicle than the traditional shape with its attached shock wave. Excessive heating was the greatest concern in the design of ballistic missiles and spacecraft, since it could melt their surface; the blunt body design solved this problem. Allen's theory led to the design of ablative heat shields that protected the astronauts of the Mercury, Gemini and Apollo programs as their space capsules re-entered the atmosphere.
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