4
$\begingroup$

So in my story, I have one side of the war using an orbital-based railgun to fire a tungsten rod at extremely high velocity onto a populated city. Let's say the tungsten rod is around one ton, and it's being fired at, oh I don't know, around 22% the speed of light (these values can be changed based on the answer I need.)

The question is this: Can a tungsten rod traveling at a high enough velocity create a large electro-magnetic pulse, similar to a standard nuclear warhead? What conditions would have to be met for a tungsten rod to create an EMP (assuming it even can to begin with?)

$\endgroup$
6
  • 6
    $\begingroup$ A mass of one ton ejected at a speed of 22 percent of the speed of light would impart a bit of velocity in the opposite direction to the space station firing it. The speed of light is 299,792.458 kilometers per second. 22 % is 65,954.339 kilometers per second. The space station only weighs 1,000 times as much as te h projectile it will be giveing a speed of 65.9543995 kilometers per second, which is 5.896 times earth's escape velocityof 11.186 kilometers per second, so the station will be pushed out of Earth orbit with the first shot and probably also shattered by the sudden impulse. $\endgroup$ Nov 7, 2021 at 5:19
  • 1
    $\begingroup$ Welcome Sturgeon. Please take our tour and refer to the help center as and when for guidance. Enjoy Worldbuilding. $\endgroup$ Nov 7, 2021 at 5:21
  • 3
    $\begingroup$ Can I ask why you want to have an EMP? The EMP of a nuclear blast generally is quite moot, as anything hit by the EMP is shortly afterwards very thoroughly destroyed. Dropping a tungsten rod with an EMP likely has the same effect. $\endgroup$
    – Trioxidane
    Nov 7, 2021 at 8:07
  • $\begingroup$ @Trioxidane The main character is an android who is so perfectly disguised that even they don't know they're an android. They're affected by severe headaches/coughing up blood from the EMP but not outright killed due to their long-ish distance from the blast. No one else around them is affected in that way. It's meant to be foreshadowing to their true nature. $\endgroup$ Nov 7, 2021 at 16:49
  • $\begingroup$ A nuclear EMP weapon would be set off in the upper atmosphere to maximize its EMP effect and minimize the blast and radiative effects. A fractional-c weapon will produce an electromagnetic pulse to some degree as it enters the atmosphere (plain meteors do so at vastly lower speeds), but I have a hard time seeing it be significant compared to the blast of plasma that would hit the ground. $\endgroup$ Nov 7, 2021 at 21:21

2 Answers 2

2
$\begingroup$

The EMP produced by a nuclear explosion has various components

The E1 pulse is the very fast component of nuclear EMP.

E1 is produced when gamma radiation from the nuclear detonation ionizes (strips electrons from) atoms in the upper atmosphere.

The E2 component is generated by scattered gamma rays and inelastic gammas produced by neutrons

If your rod is traveling fast enough$^*$ to cause nuclear fusion because of the impact with any other atom in its way, it will produce a robust flash of gamma rays as notoriously explained by Randall Munroe in his first What if, with annexed E1 and E2

The ideas of aerodynamics don’t apply here. Normally, air would flow around anything moving through it. But the air molecules in front of this ball don’t have time to be jostled out of the way. The ball smacks into them so hard that the atoms in the air molecules actually fuse with the atoms in the ball’s surface. Each collision releases a burst of gamma rays and scattered particles.

$^*$ fast enough in this context means "at a significant fraction of the speed of light"

$\endgroup$
4
  • $\begingroup$ No need of nuclear reactions, the simple collision with "a significant fraction of the speed of light" can cause enough energy for gamma ray emission. A proton moving at 22% c has a (relativistic) kinetic energy of 23.395MeV - that's higher than the energy that results in the D-T reaction (17.6MeV) $\endgroup$ Nov 7, 2021 at 7:31
  • $\begingroup$ Note a 1 ton rod moving at 22%c will never make it to the ground, it will disintegrate in the upper atmosphere. $\endgroup$
    – John
    Nov 7, 2021 at 14:54
  • $\begingroup$ @John it will never make it to the ground as a solid rod (and its rod shape will probably be pretty irrelevant), but that's somewhat different from never making it to the ground at all. $\endgroup$ Nov 7, 2021 at 21:39
  • $\begingroup$ @ChristopherJamesHuff if you slip into the pedantic lane, you may find that a 1 ton rod moving at 22%c is an improper mean to "fire... onto a populated city" I doubt that the damage can be that localized . We're speaking of 2.257e18J of energy - about one order of magnitude over the Tsar Bomba (243e15J) (read the results of that one) $\endgroup$ Nov 8, 2021 at 1:33
0
$\begingroup$

Yes.

Fast impacts produce EMPs. This is most relevant for impacts on spacecrafts because there are fast moving object out there.

Characterizing Electromagnetic Pulses from Hypervelocity Impact Plasmas

Abstract: Projectiles that strike targets with enormous speeds will vaporize and ionize the material, producing a rapidly expanding plasma. Experiments measure electromagnetic pulses EMPs from sufficiently fast impacts, and the responsible physical mechanism is still not understood. We suspect that EMPs associated with meteoroid impacts are responsible for some spacecraft anomalies and failures.

emp cartoon

This paper covers the trouble a big impactor like a comet (or your rods) would cause, including EMPs.

https://www.jumpjet.info/Emergency-Preparedness/Disaster-Mitigation/Air/Comet_and_Asteroid_Threat_Impact_Analysis.pdf

Electromagnetic Pulse An Electro-Magnetic Pulse (EMP) is produced by a nuclear explosion. Analogously an EMP may be generated from the energy release from an asteroid/comet impact. Of the impact effects described within this paper, this effect is theoretical and has the least level of certainty attached. If this effect materializes, I would expect a high altitude bolide explosion to produce an EMP to a far greater range than a surface impact.

Impacts from projectiles produce E3 EMPs. Nuclear explosions do too in addition to E1 and E2. The E3 is more like a shower of charged particles.

https://en.wikipedia.org/wiki/Nuclear_electromagnetic_pulse

The E3 component is different from E1 and E2. E3 is a much slower pulse, lasting tens to hundreds of seconds. It is caused by the nuclear detonation's temporary distortion of the Earth's magnetic field. The E3 component has similarities to a geomagnetic storm caused by a solar flare.[26][27] Like a geomagnetic storm, E3 can produce geomagnetically induced currents in long electrical conductors, damaging components such as power line transformers.[28]

Unsurprisingly, EMP strength is proportional to impact energy.

Electromagnetic properties of impact-generated plasma, vapor and debris

Typical studies of kinetic energy warheads focus on lethality as a function of impactor momentum or energy as they couple mechanically to the target. At high enough energies, however, additional physical processes come into play [6]. Vaporization plays an important role and a partially ionized plasma can form (Figure 1). Impact-generated plasma, charged debris and magnetic fields have been characterized by laboratory hypervelocity impact experiments and are shown to be more abundant … In this study, we have demonstrated that the amount of plasma, electrostatic charge and the magnitude of the resulting currents and electric fields have near linear dependence on impactor mass and near cubic dependence on the impact velocity

Lots of other things affect a surface EMP. Dust plasma plays a bigger role than in space. I found allusions to angle of impact and projectile composition (alkali metals = more EMP?). Heady stuff.

An idea I had was of a giant lightning strike following the path of an impactor like this. Lightning is the most common source for EMPs. The plasma trail from the incoming impactor would make a path through the insulating atmopshere for charge to equalize between earth and sky. A God-grade bolt like this would be a veritable pillar of fire and itself make some good EMP.


But here is something that could be useful for your story. EMPs famously shut down all electronic things so when you are playing Command and Conquer you can stroll in with the defensive turrets inactive, or if you are robbing a casino the security does not work. But EMPs can propagate along powerlines.

https://en.wikipedia.org/wiki/Nuclear_electromagnetic_pulse

The geomagnetic storm–like E3 pulse from Test 184 induced a current surge in a long underground power line that caused a fire in the power plant in the city of Karaganda.

I learned about the origin of the moniker "Starfish Prime" reading about this Soviet nuclear test! In any event, your android is near power lines and so is affected by a transmitted EMP at a distance. I like the idea of the EMP being the main goal of the attack. Your impactor is made of rubidium and converts to plasma in the sky over the target maximizing the zone of the EMP. The idea is that then (just like C&C) ground forces can walk in unopposed.

Unfortunately your ground forces were gathered under high power lines supplying the city and so were also largely incapacitated, along with your android.

$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .