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  • There's been a lot of talk, confusion and fear lately surrounding North Korea, and

  • ICBMs or Intercontinental Ballistic Missiles.

  • On an individual level, like there's not a whole lot that I can do about North Korea

  • but sometimes it helps to

  • understand the things that we're like

  • kinda freaked out by, so we wanted to talk about how these weapons of mass destruction work,

  • why they're so difficult to engineer, and why they're so dangerous

  • Missiles are guided, rocket-propelled weapons and ICBMs are the longest-range missiles out there.

  • They can travel at least 5,500 kilometers (about the distance between New York and London). Some designs can go twice as far or even farther.

  • ICBMs can also carry warheads, the toxic or explosive stuff that makes them especially dangerous

  • and a big concern these days is having an ICBM that carries nuclear warheads.

  • Over the last few years North Korea has been testing missiles that can go farther and farther

  • and on July 4th they launched their first test ICBM

  • and they've already followed up with a second on July 28th.

  • Experts say that, well, it doesn't seem like they've completely figured out how to make functional ICBMs;

  • they are getting closer.

  • Now the US and Russia have had ICBMs since the late 1950s,

  • but building them is really hard.

  • It's literally rocket science.

  • At the core of the problem is a trade-off between mass and distance.

  • If you want a missile to go really far, it's easier if it weighs less,

  • but you need fuel to propel it those long distances,

  • and the warhead is pretty big too which means it kind of has to weigh a lot,

  • so you need to engineer your way out of the problem and find a balance.

  • That's led weapons designers to build ICBMs

  • with multiple stages instead of just one fuel tank and set of engines.

  • They work a lot like the rockets we use to get the space.

  • Missiles with multiple stages lift off of the blast from the main stage or booster.

  • But, once that fuel is spent that part of the missile with the heaviest engines that produce the most thrust can be let go.

  • The lower mass then makes it easier for the rest of the missile to accelerate

  • and travel farther propelled by engines and fuel in higher stages.

  • Multiple stages can really extend the missile's range by gradually sloughing off some of the weight,

  • but the nuclear warheads they're designed to carry are still very heavy.

  • They're made out of enriched uranium or plutonium; some of the heaviest elements, so weapons engineers try to nuclear warheads as tiny as possible.

  • We're talking several hundred kilograms instead of a thousand

  • That's known as miniaturization.

  • Less material usually means a smaller, lighter weapon,

  • but there are ways to organize metals and other unstable materials to make the reactions extremely powerful.

  • I'm not going to get into too much detail about this for obvious reasons,

  • but one of the most space efficient designs is a thermonuclear

  • weapon; one that uses a fission reaction and then triggers a secondary fusion reaction.

  • Fission reactions release energy by splitting atoms,

  • basically, neutrons it kicked out of the nucleus of an unstable atom hit another nuclei

  • setting off a chain reaction that releases lots of heat and X-Rays.

  • When you build your weapon the right way that release of energy can set off a secondary fusion reaction which releases energy

  • by putting atoms together and producing more neutrons,

  • and if there's more uranium or plutonium wrapped around the fusion fuel the fusion reaction can trigger more fission,

  • using up more material and releasing even more energy.

  • The combination of fusion and fission makes a really powerful bomb

  • Nuclear weapons are so destructive because messing with subatomic particles can unleash a lot more energy

  • then just breaking chemical bonds like typical explosives do.

  • More energy means more immediate destruction

  • plus there's the ionizing radiation that can damage tissue and cause radiation sickness.

  • While the basics of designing a compact thermonuclear bomb have actually been well known for more than half a century,

  • which is why I'm able to talk about it right now,

  • putting all these engineering strategies into practice is a lot easier said than done.

  • You have to make the materials and figure out how to trigger

  • the fusion reaction and keep the chain reaction going through as much material as possible.

  • And even if you stick with a simpler bomb that only uses fission

  • you'd need to keep it tiny and keep those reactions going instead of just fizzling out.

  • To make an ICBM you have to do all that and then send the missile into space and back.

  • And another huge challenge for missile engineers is re-entry through the Earth's atmosphere.

  • Even though other ballistic missiles go into outer space,

  • ICBMs have it the hardest because they're traveling so fast when they're coming back into Earth's atmosphere,

  • at more than 21,600 kilometers an hour, and when you re-enter the atmosphere that fast

  • you generate lots of heat like even above the surface of the sun temperatures, it definitely melts metal,

  • so without some kind of protection these missiles would just disintegrate before reaching the ground.

  • One way to protect the warhead is to have a big, bulky re-entry vehicle that slows it down before it hits the lower denser parts of the atmosphere,

  • Where the heating gets to be the most intense, but big and bulky feeds into the weight issue.

  • We talked about before and it's harder to hit a target with this slower type of design.

  • Engineers can build heat shields that are relatively lightweight and are designed to break up during reentry

  • These chunks carry away the superheated gases and heat from the surface of the missile,

  • keeping things relatively cool, but this can also raise new challenges for getting the missile to where you want to go.

  • It's hard to use computer models to predict how an object might veer off course when pieces of it are burning off,

  • especially because they can burn off unevenly, and that's even harder for missiles like

  • ICBMs that spend a lot of time in the atmosphere because tiny trajectory errors can get compounded over longer distances.

  • So because ICBMs travel so far and fast, everything is harder.

  • You need it to have powerful engines and survive the atmosphere,

  • but you also need it to be as lightweight as possible,

  • and of course you need to be able to aim the thing and modelling a missiles trajectory is its own huge challenge.

  • It takes a lot of work and engineering and brainpower all for something incredibly dangerous that pretty much everyone agrees should never be used.

  • To be clear, we're pretty sure that North Korea doesn't have working thermonuclear ICBMs yet,

  • but they might someday.

  • As more countries make destructive weapons,

  • it's easy to feel powerless or afraid but it can help to at least

  • understand the technologies that humans are using to threaten each other, and we do have ways to protect ourselves

  • against the threat of an ICBM which we will get into in a future episode in the meantime

  • Don't freak out too much,

  • and thank you for watching this episode of Scishow News.

  • If you'd like to see our other episodes about the science of nuclear weapons or if you're interested in learning about more things in science,

  • generally you can go to youtube.com/SciShow and subscribe

There's been a lot of talk, confusion and fear lately surrounding North Korea, and

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