Scenario: EMP over the United States

[SpaceMarine93]

Let's just say some rogue state or an evil world conqueror or whatever sneaked a nuclear warhead into the upper atmosphere at a height of 400 km in the upper atmosphere, right above Continental United States, with the intention of crippling the entire country's civilian and military infrastructure without causing catastrophic physical damage or starting a nuclear war in the process.

Just curious, how powerful would the nuclear weapon have to be to create a massive electromagnetic pulse sufficiently large enough to cause extensive disruption to the US infrastructure? How much damage would it cause? What would be the effect of the disabling of America's infrastructure on both the USA and the rest of the world? How effective would it be to cripple America's armed forces and military infrastructure? What are the potential short term / long term consequences?

Note: Spoiler

In the light of recent knee-jerk reaction by the US Department of Homeland Security to a bunch of UK tourists who joked about embarking on a fun trip to "go and destroy America." and "totally in LA pissing people off on Hollywood Blvd and diggin' Marilyn Monroe up!" on Twitter, let me state that this thread about an EMP burst over the USA is proposed out of curiosity. I have nothing against the United States of America, I have no intention of doing something so ridiculously stupid as to use violence as a means of imposing an ideology as are the case of terrorists, and I possess little faith of any kind. This thread is just created for a rational discussion of a hypothetical scenario. If anyone of you Feds are monitoring this forum at this moment, please DO NOT take this thread too seriously. Everybody is too scared about getting arrested over things like this as it is.

[Mr Bean]

In before the Sheppard
The bomb would have to be bigger than any every constructed by man in order to get full US coverage and generate EMP sufficient to cover the US. Multiple warheads would be required to get real coverage and there's one massive problem with your OP.

without causing catastrophic physical damage or starting a nuclear war in the process.

Warheads designed to be used as EMP and warheads designed to nuke things look exactly the same. So unless you want to postulate that NORAD was asleep that day or were convinced that the Russians were firing warheads filled with yummy candy the fact is One fly, they all fly and your going to get nuclear war by trying to avoid nuclear war.

The is the problem with drop pods FYI so no Marine space plane because launching it's an ICBM.

[Eternal_Freedom]

Sounds like he played Call of Duty and Homefront to me.

Also, would I be correct in thinking that a high-atmosphere detonation would do nothing at all to missile subs on patrol? That gives the US a hefty second-strike retaliation against whomever launched the EMP. which is kinda the whole point of SSBN's AFAIK.

[Lord of the Abyss]

Sounds like he played Call of Duty and Homefront to me.

Or watched Dark Angel.

[loomer]

The 400KM figure is very specific, so more likely, One Second After.

The reality of it is, it wouldn't even completely shatter the US's infrastructure. There's enough hardened facilities and sites that a bare-bones replacement could be brought up in the major areas within weeks. Unless there's actual destruction of the government and certain major companies, rebuilding will be sooner, rather than later.

[Eternal_Freedom]

Would an EMP affect stuff like buried fibre optic cables? My gut says it wouldn't.

[Thanas]

What would happen is that a hot genetically engineered killing machine would do its best to save nice people. of course she will need help provided by a disabled computer nerd shutin. The two will of course fall in love.

[Shadow6]

Would an EMP affect stuff like buried fibre optic cables? My gut says it wouldn't.

Well fibre optics aren't electrical conductors, so the cables themselves wouldn't be affected. However equipment such as amplifiers and switches would be.

[dragon]

doesn't it follow an inverse law so it would rapidly lose strength. Anyway

Commercial computer equipment is particularly vulnerable to EMP effects. Computers used in data processing systems, communications systems, displays, industrial control applications, including road and rail signaling, and those embedded in military equipment, such as signal processors, electronic flight controls and digital engine control systems, are all potentially vulnerable to the EMP effect.

Other electronic devices and electrical equipment may also be destroyed by the EMP effect. Telecommunications equipment can be highly vulnerable and receivers of all varieties are particularly sensitive to EMP. Therefore radar and electronic warfare equipment, satellite, microwave, UHF, VHF, HF and low band communications equipment and television equipment are all potentially vulnerable to the EMP effect. Cars with electronic ignition systems/ and ignition chips are also vulnerable.

An EMP shock wave can be produced by a device small enough to fit in a briefcase. High Power Electromagnetic Pulse generation techniques and High Power Microwave technology have matured to the point where practical E-bombs are becoming technically feasible, with new applications in both Strategic and Tactical Information Warfare. Although much of this work is classified, it's believed that current efforts are based on using high-temperature superconductors to create intense magnetic fields. The development of conventional E-bomb devices allows their use in non-nuclear confrontations to defeat an enemy without causing loss of life.

Regardless of the method of delivery, experts agree that EMPs can be powerful enough to cripple electronic wiring and circuitry over a geographic area as large as several square miles, posing a real threat to the nation's critical infrastructure

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I know from taking military radios apart in AIT that alot of them have EMP protection but I think it's only works if the detenation is a way off. Or from low power ones closer.

edit: Heres some good info its a CRS report for congress on HEMP (high altitude EMP) and HMP (high powered microwave). Date is 2008 so not to old.

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and more info
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[Eleas]

What would happen is that a hot genetically engineered killing machine would do its best to save nice people. of course she will need help provided by a disabled computer nerd shutin. The two will of course fall in love.

And then John Savage will enter the stage and start berating recovering alcoholics. Which makes this a good future.

[MKSheppard]

Also, much of the EMP's effect depends on what exactly is being affected.

Transformers on 1,000~ km long power lines with no fusing will blow out from the voltage induced over such long lines.

As long as your computer is unplugged, you should be fine; unless the nuke is 400m from your house; at which point you're inside the primary wearpons effects.