Starfish Prime made those effects known to the public by causing electrical damage in Hawaii, about 1,445 kilometres (898 mi) away from the detonation point, disabling approximately 300 streetlights, triggering numerous burglar alarms and damaging a microwave link. This demonstrated that the effects of a high-altitude nuclear explosion were much larger than had been previously calculated. In July 1962, the US carried out the Starfish Prime test, exploding a 1.44 Mt (6.0 PJ) bomb 400 kilometres (250 mi 1,300,000 ft) above the mid-Pacific Ocean. The larger scientific community became aware of the significance of the EMP problem after a three-article series on nuclear EMP was published in 1981 by William J. The high-altitude nuclear tests of 1962, as discussed below, confirmed the unique results of the Yucca high-altitude test and increased the awareness of high-altitude nuclear EMP beyond the original group of defense scientists. In spite of these many differences, the unique EMP results were dismissed as a possible wave propagation anomaly. Also, the polarization of the Yucca EMP signal was horizontal, whereas low-altitude nuclear EMP was vertically polarized. The Yucca EMP was initially positive-going, whereas low-altitude bursts were negative-going pulses. In that test, the electric field measurements from the 1.7 kiloton weapon exceeded the range to which the test instruments were adjusted and was estimated to be about five times the limits to which the oscilloscopes were set. The first openly reported observation of the unique aspects of high-altitude nuclear EMP occurred during the helium balloon-lofted Yucca nuclear test of the Hardtack I series on 28 April 1958. In spite of this many records were lost because of spurious pickup at the time of the explosion that paralyzed the recording equipment." : 53 During British nuclear testing in 1952–1953, instrumentation failures were attributed to " radioflash", which was their term for EMP. The official technical history for that first nuclear test states, "All signal lines were completely shielded, in many cases doubly shielded. ĭuring the first United States nuclear test on 16 July 1945, electronic equipment was shielded because Enrico Fermi expected the electromagnetic pulse. The magnitude of the EMP and the significance of its effects were not immediately realized. The fact that an electromagnetic pulse is produced by a nuclear explosion was known in the earliest days of nuclear weapons testing. Effects of a HEMP device depend on factors including the altitude of the detonation, energy yield, gamma ray output, interactions with the Earth's magnetic field and electromagnetic shielding of targets. In military terminology, a nuclear warhead detonated tens to hundreds of miles above the Earth's surface is known as a high-altitude electromagnetic pulse (HEMP) device. The term "electromagnetic pulse" generally excludes optical (infrared, visible, ultraviolet) and ionizing (such as X-ray and gamma radiation) ranges. The specific characteristics of a particular nuclear EMP event vary according to a number of factors, the most important of which is the altitude of the detonation. The resulting rapidly varying electric and magnetic fields may couple with electrical and electronic systems to produce damaging current and voltage surges. For other types, see Electromagnetic pulse.Ī nuclear electromagnetic pulse ( nuclear EMP or NEMP) is a burst of electromagnetic radiation created by a nuclear explosion. This article is about nuclear-generated EMP.
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