On August 1, 1958, a few minutes before midnight, an intense flash of white light tore across the night sky illuminating everything it touched for miles around Johnston Island, a tiny atoll located smack in the middle of the Pacific Ocean. The black sky turned blue, and personnel at the air force base instinctively ducked for cover.
The source of the light was a nuclear test conducted high up in the atmosphere. It was one of two conducted under Operation Hardtack to study, among other things, the effect of the earth’s rarefied atmosphere on nuclear detonation, as well as to investigate defensive tactics against ballistic missiles. This particular test, codenamed “Teak”, was the most powerful one at 3.8 megaton—equivalent to 250 Hiroshima-grade nuclear bombs.
The fireball from Operation Hardtack “Teak”.
The high altitude of the detonation (76 kilometers) enabled the flash of light to be seen from far away. In Hawaii, 1,500 km away, a thousand startled residents called the police to report strange lights on the sky. The sky had turned from dark to yellow to orange and then red.
- “The red spread in a semi-circular manner until it seemed to engulf a large part of the horizon. A cloud rose in the center of the circle. It was quite large and clearly visible. It remained visible for about a half-hour,” a witness in Honolulu described.
Military and civilian air traffic communications were knocked out for several hours, and many trans-Pacific high-frequency communication networks that utilized the ionosphere for transmission were disrupted for up to nine hours. In distant Western Samoa, 3,200 kilometers to the south, the explosion produced a brilliant display of aurora. Astronomers at Apia Observatory measured the strength of the electromagnetic pulse (EMP) and found it to be four times stronger than any created by solar storms.
Four years later, the United States conducted another series of high-altitude nuclear tests. This time, the purpose of the tests was to study and measure the effects of nuclear detonation on the earth’s magnetic field. Mostly, they wanted to understand the effects observed during the Teak test—the EMP generated during the blasts, the strange auroras generated thousands of kilometers from the explosion, and the nature of the Van Allen radiation belts that were only recently discovered.
Known as Operation Fishbowl, the tests were conducted at a much higher altitude, in the region where satellites orbit. The first two attempts ended up in failure, and the rockets were destroyed. The third attempt, codenamed “Starfish Prime”, took off from Johnston Island on July 8, 1962, at eleven o’clock Hawaii time. The nuclear warhead the Thor rocket was carrying was rated at 1.4 Megatons.
The rocket went straight up and exploded at a height of 400 kilometers, about 36 kilometers southwest of Johnston Atoll. At the precise instant of the explosion, streetlights in Hawaii blinked out. Radios stopped working. Telephone lines went dead. Elsewhere in the Pacific, high frequency communications systems malfunctioned as a powerful electromagnetic pulse (EMP) surged through the vast region below the blast. In the minutes following the blast, a blood-red aurora spread across the horizon caused by ionization of air molecules. The visual phenomenon was intense and widespread, illuminating a large area of the Pacific.
The fireball created by Starfish Prime as seen through the cloud cover from Honolulu.
The flash created by the explosion of Starfish Prime as seen through heavy cloud cover from Honolulu.
The debris fireball of Starfish Prime stretching along Earth's magnetic field with air-glow aurora as seen from a surveillance aircraft.
At high altitudes, nuclear blasts behave differently than those closer to the ground. Near the ground, the atmosphere absorbs the tremendous amount of energy a blast releases in the form of thermal radiation, high-energy x-rays and gamma rays, fast neutrons, and the ionized remnants of the fissile materials themselves. Up high in outer space, the fireball grows larger and faster as there is no air to slow down and absorb the energy of the detonation products. A strong EMP results when gamma rays collide with air molecules in the upper atmosphere to produce fast-moving, high energy electrons that generate transient electric fields and currents. These electric fields can produce potentials of several thousand volts.
Scientists had anticipated EMP interference, but the EMP blast from Starfish Prime proved to be too powerful. There was another effect they failed to predict. A large number of charged particles did not fall down to earth or dissipate, instead they became trapped by the earth’s magnetic field and lingered in space for months, frying electronics onboard earth orbit (LEO) satellites. At least six satellites were lost to Starfish Prime, including one British and one Soviet.
The EMP mechanism for a 400 km high altitude burst: gamma rays hit the atmosphere between 20-40 km altitude, ejecting electrons which are then deflected sideways by the earth's magnetic field. This makes the electrons radiate EMP over a massive area. Because of the curvature of earth's magnetic field over the USA, the maximum EMP occurs south of the detonation and the minimum occurs to the north.
The Soviets conducted their own high-altitude nuclear tests with similarly disastrous results. On October 22, 1962, a 300 kiloton device was detonated at an altitude of 290 km. The resulting EMP fused 570 km of overhead telephone line with a current of 2,500 ampere, shut down 1,000 km of buried power cables and burned down a power plant. Although the weapons used by the Soviets had much smaller yield compared to the US tests, the damage caused by the resulting EMP was much greater because the tests were conducted over populated land mass, and at a location where the Earth's magnetic field was greater.
The following year, in 1963, both countries and a host of others signed the Partial Test Ban Treaty and agreed to end atmospheric and exoatmospheric nuclear tests. The Outer Space Treaty of 1967 banned the use of nuclear weapons in space, and the Comprehensive Nuclear-Test-Ban Treaty of 1996 prohibited all kinds of nuclear explosions whether over- or underground, underwater or in the atmosphere.
EMP weapons like Starfish Prime are no longer a real threat, believes Elizabeth Quintana, director of Royal United Services Institute, a British defense and security think tank. Space is already a hostile environment electromagnetically, with satellites and spacecraft being continuously bombarded with cosmic rays and charged particles from the Sun. Modern satellites are therefore hardened against radiation, and an EMP weapon like Starfish Prime would have little additional effect.
Besides, any aggressive nation wanting to knockout the communication system or the power grid of another could do it more easily and cheaper with conventional explosives.
“If a foreign power detonated a 100 or more kiloton in an electromagnetic attack on America, then the world is at war and there’s little strategic benefit for the aggressor to not just go ahead and nuke a city,” Matthew Gault wrote in National Interest.
“It's not that EMPs are not a threat,” military analyst Sim Tack told Vice. “It's just that—although the effect would be massive—currently they're not really a risk apart from nuclear strikes, so highlighting them as the greatest threat there is might not be entirely realistic.”
References:
# https://apps.dtic.mil/dtic/tr/fulltext/u2/a995428.pdf
# https://apps.dtic.mil/dtic/tr/fulltext/u2/a955411.pdf
# Scientific American, https://www.scientificamerican.com/article/nuclear-explosions-in-orb/
# Wikipedia, https://en.wikipedia.org/wiki/Soviet_Project_K_nuclear_tests
# BBC, https://www.bbc.com/future/article/20150910-the-nuke-that-fried-satellites-with-terrifying-results
# National Interest, https://nationalinterest.org/blog/buzz/world-wont-end-danger-emp-attack-more-fantasy-fact-94681
# Vice, https://www.vice.com/en_us/article/kwxq4v/we-asked-a-military-expert-how-scared-the-us-should-be-of-an-emp-attack-508
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