One of the highest was at an altitude of 540 km (335.5 mi) and used to determine the effects of the blast and radiation in the exoatmospheric environment.
The U.S. program began in 1958, with the Teak and Orange shots, both 3.8 megatons. These warheads were initially carried on Redstone rockets. Later tests were delivered by Thor missiles for Operation Dominic I tests, and modified Lockheed X-17 missiles for the Argus tests.
The USSR also did lots of these kind of tests.
EMP devastation produced:
The strong electromagnetic pulse (EMP) that results has several components. In the first few tens of nanoseconds, about a tenth of a percent of the weapon yield appears as powerful gamma rays with energies of one to three mega-electron volts (MeV, a unit of energy). The gamma rays rain down into the atmosphere and collide with air molecules, depositing their energy to produce huge quantities of positive ions and recoil electrons (also known as Compton electrons). The impacts create MeV-energy Compton electrons that then accelerate and spiral along the earth's magnetic field lines. The resulting transient electric fields and currents that arise generate electromagnetic emissions in the radio frequency range of 15 to 250 megahertz (MHz, or one million cycles per second). This high-altitude EMP occurs between 30 and 50 kilometers above the earth's surface. The potential as an anti-satellite weapon became apparent in August 1958 during Hardtack Teak. The EMP observed at the Apia Observatory at Samoa was four times more powerful than any created by solar storms, while in July 1962 the Starfish Prime test damaged electronics in Honolulu and New Zealand (approximately 1,300 kilometers away), fused 300 street lights on Oahu (Hawaii), set off about 100 burglar alarms, and caused the failure of a microwave repeating station on Kauai, which cut off the sturdy telephone system from the other Hawaiian islands [1]. The radius for an effective satellite kill for the various prompt radiations produced by such a nuclear weapon in space was determined to be roughly 80 km. Further testing to this end was carried out, and embodied in a Department of Defense program, Program 437.
There are problems with nuclear weapons carried over to testing and deployment scenarios, however. Because of the very large radius associated with nuclear events, it was nearly impossible to prevent indiscriminate damage to other satellites, including one's own satellites. Starfish Prime produced an artificial radiation belt in space which soon destroyed three satellites (Ariel, TRAAC, and Transit 4B all failed after traversing the radiation belt, while Cosmos V, Injun I and Telstar suffered minor degradation, due to some radiation damage to solar cells, etc. [2]). The radiation dose rate was at least 60 rads/day at four months after Starfish for a well-shielded satellite or manned capsule in a polar circular earth orbit [3], which caused NASA concern with regard to its manned space exploration programs.
So, to cause the kind of emp that would be needed to destroy all electronics, over a specific area would have to be low enough that it would also kill everyone.
Higher detonations would knock out satellites, including their own.
There you go debunking things with facts. Way to take the fun out or a good panic.
Then again... I guess we still have to worry about several dozen 2 megaton warheads exploded 80 km up. Seems likely some random terrorist might be able to pull that off...
“Higher detonations would knock out satellites, including their own. “
Yup, so North Korea, Iraq, Iran, Yemen, would lose all their sats!
Wait...
When looking at the initial energy necessary for the pulse to be large enough to destroy a large portion of the grid, it is necessary to have a large detonation outside the atmosphere so it converts entirely into energy.
The other fallacy some fall into is that it can be 'controlled'. A correctly built and functioning nuke will detonate as a bubble. The physics of compressibility require it. A partial detonation will not yield enough energy to perform the task, and a large, 30-40MT device will be too heavy to lift except by some of the larger rocketry.
Using multiple warheads of smaller size doesn't work either as absorption of the Gamma radiation necessary for the nuclear explosion to convert to energy gets absorbed by the other detonations, and is not 'accumulative'.
No (BTW...anyone can get educated at WIKI).
1) AGAIN: "To produce maximum coverage for the HEMP effect, a nuclear device must explode very high in the atmosphere, too far away from the earth’s surface to cause injury or damage directly from heat or blast. Also, HEMP produced by the nuclear explosion is instantaneous — too brief to start current flowing within a human body — so there is no effect on people."
So...you understand that last part? If not...I will post it again: "too far away from the earth’s surface to cause injury or damage directly from heat or blast." and "too brief to start current flowing within a human body — so there is no effect on people."
The EMP occurs 30-50 KM because that's where the gamma rays hit the atmosphere and create compton electrons. The BURST (the thing that KILLS you...is hundreds of miles up.
2) Satellite: You should have read your own WIKI article closer. The blast doesn't create a perm. damaging satellite KILL zone. A high detonation would kill sat's. But if you can pull down a country...WHO CARES? If you are a rogue country...one that doesn't have a lot of satellites to begin with...or terrorists with NO satellites (just a nuke and a scud)...who cares what happens to satellites?
Obviously the Russians don't care if they lose a few satellites (because they have a weapon to do this): "Vladimir Lukin, the former Soviet Ambassador to the United States, and former Chairman of the International Affairs Committee for the Russian Parliament, reportedly has stated that Russia currently has a capability to create a HEMP effect over the United States."
We threatened Saddam with this back in 1991. If he used his BIO/Chem...we would EMP him. Now...that is also in the One Second After" book...but if you were in the military back then (as I was and still am) at the HQ levels...you know that this threat was really given. We were told we had issued a threat to him that we would detonate a nuke 20 miles above Baghdad. That way...LOS would not damage our stuff in Saudi. No nuke effects on Iraq....but also nothing in the Baghdad area (his C&C) functioning either.
We have nukes dedicated as EMP devices in our arsenal. The are designed to burst at high atltitudes. If they didn't work...we wouldn't have them.