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Since most online and media depictions of EMPs run the gamut from devastating annihilation (complete with sparks shooting from every angle) to gentle shutdowns resulting in inconvenient repairs, what's the reality of small-scale EMPs used against military personnel in a vacuum or near-vacuum environment? Would this automatically be a death sentence for the affected troops (as well as leaving them potentially defenseless)? Would spacesuits and personal weapons like particle-wave or Gauss rifles be utterly destroyed or would redundant systems be possible in order to reboot their functionality?

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    $\begingroup$ Maybe the first time. The second time they will have EMP-hardened kit. We do. $\endgroup$ – AlexP Feb 24 at 2:32
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Given the hostile environment in space, preparation for EMP equivalent events is a normal consideration. For example, when a massive CME hits, many satellites have to be rebooted. In short - EMP is a common enough natural event in space that it would be a temporary inconvenience to troops that they train for regularly, independent of it being weaponized. It could prove decisive in specific military actions, buying time for attacking troops to close, but in and of itself would not be a novelty.

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EMPs can be astonishingly devastating. The EMP that was created by a test of the atomic bomb 'Starfish Prime' in the Pacific ocean blew out about 300 streetlights and disrupted telephone and radio services in Hawaii, nearly 1000 miles away from the blast. Considering that power, it's possible that this technology could be implemented, albeit on a smaller scale. I'm not sure how small or powerful such a device might be, but I think it could work. Now while some minor EMPs only temporarily disrupt the functionality of electronic equipment, more powerful, intentionally weaponized ones could easily completely overwhelm the target circuitry with high currents and would irreversibly melt/fry them. This will not be fixed by a simple reboot. The vulnerable wiring in life support and coil guns would burn out without too much of a fight, and even a small failure in one area in an electronic device has a good chance of causing critical failure down the line. Your enemy space troops are quite doomed. It would seem like an EMP based device to attack enemy troops might be feasible. However, the problem with this EMP based warfare is that it's just so easy to shield anything from an attack. Surrounding the delicate circuitry with a conductive material (or a faraday cage) prevents the pulse from penetrating any further. If such a weapon was widely available, undoubtedly essential items such as the life support on space suits and probably weapons too would be shielded. The only thing that cannot be shielded would be an antenna (you can actually shield them from electromagnetic waves, but that would ruin the point). So in conclusion, your high-power EMP could probably knock out communications, but it isn't likely to do much more than that.

Hope this helps!

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    $\begingroup$ Some sort of retractable shielding for some antennas might work, if you have some advance notice. not sure how fast EMP propogates though, so it likely wouldn't be cost effective. $\endgroup$ – Andon Feb 24 at 4:12
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    $\begingroup$ One little quibble; those telephones and streetlights would have had problems because the electrical grid acts like a huge antenna and collects a very large amount of charge. A space suit has much less wiring than an electrical grid, and those wires are much smaller, so it is likely to be less effected than the Hawaii example would suggest. $\endgroup$ – Ryan_L Feb 24 at 18:41
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What does an EMP actually do?

An electromagnetic pulse (EMP) works the same way a generator does. The magnetic pulse moves across metal and, depending on the conditions, couples energy onto the metal in the form of electricity. Said another way, when you move a magnetic field across a wire, it causes the electrons to move.

The longer the metal, the worse this is. The more conductive the metal, the worse this is. let's look at a short list of consequences and let's assume we have some zombies in front of us to deal with.

  • Wooden club: An EMP wouldn't effect this at all. Not even if you have nails in it. You're peachy safe, beat the snot out of those zombies!

  • Colt .45 revolver: if the EMP is strong enough, it'll shock you, but other than that, very little would happen to the weapon. Pick it back up and shoot the zombie in front of you.

  • M1 carbine: It doesn't take as much of an EMP to get shocked by a rifle due to the longer piece of metal. However, more-or-less the only thing you're touching that is metal is the trigger. Rather than forcing you to drop it, the EMP is more likely to cause the muscles in your finger to contract, firing off the round. Probably not a zombie in front of you, so you'll be using the rifle as a club until you can cycle the bolt.

  • Gauss rifle (aka, railgun): Gauss rifles use magnetism to accelerate a slug of some kind to breathtaking velocities. The problem is that you need coils of wire to make that happen. The coils may be small, but you have the proverbial miles and miles of wire in them — and long wires are bad when it comes to EMPs. An EMP can actually melt the magnetic coils in this sucker. So, after a good sized EMP, you have a paperweight you can throw at the nearest zombie, then you need to pull out your knife.

  • Particle-wave: see Gauss rifle. You're using magnetics to control energy flow. No magnetics after an EMP.

  • Space suit: This is more complex. The basic functions of the space suit (e.g., keeping oxygen in and the vacuum out) won't be hurt at all because most of the suit has very little metal and what is metal is (in today's tech) aluminum. Now, aluminum does conduct electricity fairly well, but it stinketh mightily when it comes to coupling energy, which is why you don't often see it used in generators. So, basic functions are OK. The computer systems controlling oxygen flow might be fried — maybe. Hollywood makes it look like everything electronic is blown by an EMP. The reality is that while all those copper traces will couple energy, they're small and the largest chunks of them are the ground-plane and power-plane — and those are connected to the power supply. Therefore, the real question is how much energy can the power supply (aka, battery) absorb and how quickly? My point is, it actually takes a pretty good sized EMP to hurt operating electronics (or even cars) and it isn't the electronics that are usually the first to go, it's the batteries and power supplies.

Yeah, but how much EMP can all those things take?

Unfortunately, that's an answer that's well outside the scope of this site because EMP size will depend on (a) the specifics of the device or piece of equipment we're talking about, (b) the surrounding geology, and (c) the nature of the device creating the EMP.

(b) is important because an area that's electrically grounded well (for example, the "earth" has a negative charge) will absorb a ton of the energy from the pulse. Said another way, you need a stronger pulse over a large body of water than you do in a desert.Citation Needed

(c) is important because EMPs are no different than any other magnetic or electrical effect. The pulse width, magnitude, and the slope of the leading and following pulse edges all contribute to how damaging the pulse is. A really narrow, very sharp, low-magnitude pulse may cause a shock but probably wouldn't seriously damage anything. A massive magnitude, very wide pulse (almost regardless of the slope of the pulse edges) will pretty much melt anything metal (if you understand integration, the amount of energy is the volume under the curve &mdash big volume = bad). However, really shallow edge slopes can mitigate a lot of harm.

Think of it this way. A shallow but fast-moving wave can knock you around, but usually won't kill you. A tidal wave will sweep aside almost everything in its path. But a wave (almost regardless of how big it is) that gently builds to its peak and then gently recedes, won't damage a lot of things. (Those were imperfect metaphors, but they'll do).

So, why do people fear EMPs?

It's not the equipment that's the problem (well, remember that long wires like power lines are a huge problem), it's all the electromagnetic signals in the air that we depend on that's the problem. A good sized EMP will disrupt an entire nation's communications network because all that energy is washing around in the air. It may not damage antennae, etc., but you'll lose pretty much all forms of modern communication if you experience one.

And, worst of all are hard drives. Indeed, all magnetic storage media is incredibly susceptible to EMP — and there's next to nothing you can do to stop it. You can enclose them in Faraday cages, but those cages are only as useful as they are grounded — and if the EMP is affecting the natural-earth ground plane, then your Faraday cage is worthless. You can kiss most of the nation's data goodbye.

Fine, fine, but how can I really protect myself?

You can coat things in metal and connect that metal to something that can absorb energy. Remember when I said a Gauss rifle is basically a lump of metal after an EMP? OK, coat the shell of the gun in highly conductive metal (aka, a Faraday cage) and connect that metal to the negative terminal of the weapon's power supply. Now you have the same problem as the space suit: if the power supply can absorb the energy, the weapon will continue to work (perhaps after a re-initialization, raising the voltage on the negative terminal won't hurt the weapon, but it will stop its operation until the voltage drops again).

So you can protect yourself — to a degree. Honestly, your enemy is always able to build a bigger EMP, so protection is valuable, but limited.

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    $\begingroup$ ...but those cages are only as useful as they are grounded — and if the EMP is affecting the natural-earth ground plane, then your Faraday cage is worthless.... Not sure I agree with this. The whole point of a Faraday cage is that there is no net field inside the cage. A spike in the ground level may fry devices outside or connected to the cage, but unless there's an earthing cable directly connected to the drives inside the cage, they should remain unaffected. $\endgroup$ – nzaman Feb 24 at 12:21
  • $\begingroup$ How bad can Aluminum be at coupling? They use it as squirrel cages in motors... $\endgroup$ – Harper - Reinstate Monica Feb 24 at 15:56
  • $\begingroup$ With electricity, there's no aether, there's no absolute reference for zero. If you energize a soldier and his gun and the dirt he's standing on to 20kv above where he was before, there he is. As long as the whole gun is equally biased, which is likely if it's metal, the gun don't care. It's like a bird can hop from phase wire to phase wire on a 20kv line. $\endgroup$ – Harper - Reinstate Monica Feb 24 at 16:02
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    $\begingroup$ @JanHudec, Please forgive me, but I'll bet my EE degree against yours. Of course Faraday cages need to be grounded. An ungrounded Faraday cage is an antenna. $\endgroup$ – JBH Feb 24 at 21:34
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    $\begingroup$ @Eth, bear in mind that a fair number of nuclear test detonations have been performed in the presence of armed military personnel. I've never heard of a bullet discharging due to the EMP from any detonation, including the Tsar Bomba. If you were close enough for the EMP to affect the bullet, you'd be killed by either the radiation or the blast. But, that suggests you need something bigger than 50MT to cause a bullet to fire. There just isn't a lot of gun to couple the energy. Remember that wire length is important. Most motors use lengths measured in hundreds of meters. $\endgroup$ – JBH Feb 26 at 17:47

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