This episode of Real Engineering is brought
to you by Skillshare. Home to 15,000 classes that could teach you
a new life skill. The first 500 people to sign up with the link
in the description will get a 2 month free trial. In August 2017, the Democratic People's Republic
of Korea, in it’s most provocative move to date, tested a long range intercontinental
ballistic missiles, which flew directly over the Japanese Northern Island of Hokkaido and
set sirens wailing. This is just the latest in North Korean missile
test, with the previous month's test proving the North Korean dictatorship had the capability
of reaching American soil. The engineers of North Korea have overcome
many obstacles to get to this point, but just achieving the necessary range is, thankfully,
half the battle. Today we are going to investigate the history
behind these long range weapons and why they are so difficult to engineer. An Intercontinental ballistic missile, or
ICBM, is a missile that follows a ballistic trajectory. Quite simply, the path it follows is the same
as that of a thrown or propelled projectile would take under the act of gravity. Think of it as a projectile that is thrown
extraordinarily fast and high by a relatively brief, yet powerful, rocket engine. Like many weapons of mass destruction, the
Nazis were some of the first to theorize an ICBM. “Projekt Amerika”, led by Wernher von
Braun, was a code name for a weapon being developed that could be used against New York
and other American cities during WWII. Just as the V2, which was the world’s first
long-range ballistic missile, had been used to wreak havoc on London. Luckily the war ended before it was fully
developed. but many of these same engineers were drafted
by the US and USSR after WWII to help design their first rockets, and many of these design
philosophies laid the groundwork for what we see today. These early ICBM designs were essentially
upgraded versions of the V2 bombs. The V2 was redesigned to include wings and
dubbed the A9. This would sit on top of the huge first stage,
dubbed the A10, which would boost the V2 from it’s original range of 300 kilometres, which
was enough to reach London from the Netherlands, to 5000 km, enough to reach the American eastern
seaboard from Ireland. The German engineers aimed the V2 simply by
setting a compass heading before launch, which allowed the internal guidance system consisting
of gyroscopes to keep the rocket on course while the rockets were firing. Gyroscopes allow a missile to measure its
deviation from initial flight trajectories. Spinning masses, like a gyroscope, want to
maintain the direction their axis of rotation is pointing. So if we set the axis of rotation in the direction
of desired travel, and mount the gyroscope in a frame that does not transfer the missiles
rotation to the gyro, the missile can measure that change in rotation and correct it’s
flight with control fins. The German’s controlled the range by simply
adjusting the amount of fuel in the rocket, using a slide rule to calculate the fuel needed
for a given trajectory. Although this was incredibly advanced technology
for the time, the V2s were still notoriously inaccurate, because it relied completely on
initial calculations on the ground and had no way of correcting for unexpected deviations. But London was a big target, and the Netherlands
weren’t that far away, and the Germans certainly did not care who the bombs killed. To be effective against a target much further
away would require a finer tuned guidance system, which the Germans did not have. So, incredibly, these early ICBMs were planned
to be manned. After blasting off from Europe, exiting earth’s
atmosphere, separating the first stage, reaching a max speed 10 times greater than the speed
of sound, the second stage would come hurtling back through into the atmosphere, where it
would glide to reach it’s final target. If they hadn’t already died from the heat
of re-entry the pilot would then set their final trajectory using radio guidance from
surfaced German submarines and eject. Only to be promptly killed by the force of
impact of air hitting his head and chest. This was the German’s kamikaze strategy. In an era before onboard computers and GPS
existed, developing a guidance systems was half the battle. Modern rockets use a combination of that gyroscope
based inertial guidance, satellite positioning and terrain mapping, which uses altitude maps
of the route to the target to guide the missile. You may wonder why the Germans put so much
effort into creating space age weapons, only to equip them with bombs with less power than
those they could drop from planes. Well this is arguably the hardest part of
the equation. The longer the range and the heavier the load,
the more complex the rocket. Just adding a first stage adds a significant
amount of complexity and cost to the design. Adding a massive bomb was simply not feasible
and that’s just an issue of size and weight. The German’s were limited with the type
of bomb they could use for another reason. This is a size comparison between the V2 rockets
and the two nuclear bombs dropped on Japan. Sizewise, it’s not inconceivable that these
bombs could have been integrated into the V2, but Fat man and little boy weighed 4.6
tonnes and 4.4 tonnes respectively, so weight would have been a huge issue. The V2’s warhead consisted of a 1 tonne
amatol bomb, which is a TNT based explosive. TNT’s primary advantage is its high activation
energy. Meaning it would not easily detonate from
a sudden impact shock or from heat. Even if small - lightweight nuclear bombs
existed at the time, neither America or Germany had the technology required to launch them
with a missile, because of the intense heat associated with re-entry of ICBMs would destroy
the warhead before it ever got close to the target. Re-entry vehicles typically used a combination
of blunt body design, ablative materials, heat sinks and insulating materials. Blunt body design allows the re-entry vehicle
to create a bow shock wave in front of the vehicle that keeps the super heated plasma
a little further from vehicles surface, with an insulating boundary layer of air in between. Ablative materials, like the single use Gemini
heat shield,, burn or melt and then detach from the vehicle carrying some of that super
heated plasma away and heat sinks use conductive and heat resistant materials like Beryllium
to spread some of that heat and allow it to be radiated away. The Discovery Space Shuttle used reusable
and replaceable thermal tiles and blankets, while the nose cone was a carbon-carbon composite
which acted as a heat sink. But all of these things have one thing in
common. They add bulk and mass to the design once
again. Simply put, designing a rocket capable of
launching out earth's atmosphere is arguably the easiest and most well documented part
of building an ICBM. Miniaturising nuclear bombs capable of withstanding
the journey and creating a guidance system accurate enough to hit the target is a whole
other challenge. We know North Korea is struggling with this
part of their missile program, as the re-entry of their July launch was caught on CCTV, showing
the missile burning up and disintegrating before landing in the sea off the coast of
Japan and their recent test had a similar fate. So even if North Korea have a miniaturized
Nuclear bomb, it’s unlikely it would survive the journey and when it comes to guidance,
North Korth do not have their own positioning satellites, and it’s unlikely that China
have granted them access to their high accuracy military positioning system. For now North Korea don’t pose much of a
threat to America, but if they did somehow develop an ICBM capable of carrying nuclear
weapons, despite the heavy embargoes on the country, the world has moved on since the
days of V2 bombardment of defenceless London. There are countermeasures and we will explore
them in the next video. But if you want to watch something right now
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Has anyone sent this video to North Korea?
When Kim see this video, heads gonna be rolling.
ten years ago: why north korea can't build an atomic bomb (yet)