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1. A fadeout of radio communications due to ionospheric disturbances.
Blackouts are most common in, but are not restricted to, the arctic. An arctic blackout may last for days or even weeks during periods of intense auroral activity. Past experiments with high-altitude nuclear detonations have produced blackouts and artificial auroras over the subtropics .
2. A fadeout of radio and telemetry transmission between ground stations and vehicles traveling at high speeds in the atmosphere caused by signal attenuation in passing through ionized boundary layer (plasma sheath) and shock wave regions generated by the vehicle.
3. A vacuum tube characteristic which results from the formation of a dielectric film on the surface of the control grid.
A negative charge, accumulated on the film when the grid is driven positive with respect to the cathode, affects the operating characteristics of the tube.
4. A condition in which vision is temporarily obscured by a blackness, accompanied by a dullness of certain of the other senses, brought on by decreased blood pressure in the eye and a consequent lack of oxygen, as may occur, e.g., in pulling out of a high-speed dive in an airplane. Compare grayout, redout.


This article is based on NASA's Dictionary of Technical Terms for Aerospace Use