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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.
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