October 26, 1962: NASA Sonic Boom Testing

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Brig Gen Irving L. Branch conducted a series of tests for Headquarters Air Force Systems Command to determine the effect of sonic booms on missile check-out equipment. The tests were to explore the possible use of the tactic against Soviet missile launch sites in Cuba. Center pilots flew a T‑38, an F-104, and an F-106 at supersonic speeds, at very low altitudes directly over the electronic launch gear with no appreciable effect on the devices.

A sonic boom is a thunder-like noise a person on the ground hears when an aircraft or other type of aerospace vehicle flies overhead faster than the speed of sound, or “supersonic.”  Air reacts like fluid to supersonic objects. As those objects travel through the air, molecules are pushed aside with great force and this forms a shock wave, much like a boat creates a wake in water. The bigger and heavier the aircraft, the more air it displaces.  The shock wave forms a “cone” of pressurized or built-up air molecules, which move outward and rearward in all directions and extend all the way to the ground. As this cone spreads across the landscape along the flight path, it creates a continu­ous sonic boom along the full width of the cone's base. The sharp release of pressure, after the buildup by the shock wave, is heard as the sonic boom.

The change in air pressure associated with a sonic boom is only a few pounds per square foot -- about the same pressure change experienced riding an elevator down two or three floors. It is the rate of change, the sudden changing of the pressure, which makes the sonic boom audible.  All aircraft generate two cones, at the nose and at the tail. They are usually of similar strength and the time interval between the two as they reach the ground is primarily dependent on the size of the aircraft and its altitude.  While some people on the ground may perceive the sound as a single sonic “boom,” many sonic booms produced from NASA’s research flights are easily heard as distinct “double” booms, similar to what was created by the space shuttle. This is the result of the two separate cones generated, at the nose and the tail of the aircraft.

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