Blunt Body Entry Vehicles
These four shadowgraph images represent early reentry-vehicle concepts. A shadowgraph is a process that makes visible the disturbances that occur in a fluid flow at high velocity, in which light passing through a flowing fluid is refracted by the density gradients in the fluid resulting in bright and dark areas on a screen placed behind the fluid.
In the United States, H. Julian Allen and A. J. Eggers, Jr. of the National Advisory Committee for Aeronautics (NACA) made the counterintuitive discovery in 1951 that a blunt shape (high drag) made the most effective heat shield. From simple engineering principles, Allen and Eggers showed that the heat load experienced by an entry vehicle was inversely proportional to the drag coefficient, i.e. the greater the drag, the less the heat load. Through making the reentry vehicle blunt, air cannot "get out of the way" quickly enough, and acts as an air cushion to push the shock wave and heated shock layer forward (away from the vehicle). Since most of the hot gases are no longer in direct contact with the vehicle, the heat energy would stay in the shocked gas and simply move around the vehicle to later dissipate into the atmosphere.
The Allen and Eggers discovery, though initially treated as a military secret, was eventually published in 1958.
Read more about this topic: Atmospheric Entry
Famous quotes containing the words blunt, body, entry and/or vehicles:
“He sits, strong and blunt as a Celtic cross,
Clearly used to silence and an armchair:
Tonight the wife and children will be quiet
At slammed door and smoker’s cough in the hall.”
—Seamus Heaney (b. 1939)
“All are but parts of one stupendous whole,
Whose body Nature is, and God the soul;”
—Alexander Pope (1688–1744)
“All mothers need instruction, nurturing, and an understanding mentor after the birth of a baby, but in this age of fast foods, fast tracks, and fast lanes, it doesn’t always happen. While we live in a society that provides recognition for just about every life event—from baptisms to bar mitzvahs, from wedding vows to funeral rites—the entry into parenting seems to be a solo flight, with nothing and no one to mark formally the new mom’s entry into motherhood.”
—Sally Placksin (20th century)
“Only by the supernatural is a man strong; nothing is so weak as an egotist. Nothing is mightier than we, when we are vehicles of a truth before which the state and the individual are alike ephemeral.”
—Ralph Waldo Emerson (1803–1882)