In this fifth and final part, I’m going to discuss the nuclear capabilities of North Korea, and dispel some of the myths behind their nuclear program, as well as the myths surrounding their leader, Kim Jong-un.
On April 5th, 2009, North Korea launched a satellite known as Bright Star-2 into space. Their only previous attempt at a space launch had taken place in 1998 with the failed attempt to put Bright Star-1 into orbit. By most accounts, the launch of Bright Star-2 was a failure, with the three-stage rocket failing to achieve orbit, and the satellite package crashing into the Pacific Ocean. North Korea, however, disagreed and claimed that it had indeed placed a satellite into orbit, and that it was a complete success.
Whether or not they actually achieved a stable orbit with the satellite, (spoiler alert – they didn’t) North Korea’s announcement that the launch had been a complete success was probably not hyperbole. If their intent was actually to test a rocket capable of entering space at low-earth orbit altitudes, such as the type of rocket that would be capable of delivering a nuclear weapon – the type otherwise known as an ICBM, it was indeed a success. And that is what many in the intelligence community believed it to have actually been.
At the time of the launch, North Korea was involved in what was known as the Six-party talks, a gathering of six countries whose goal was to find a peaceful resolution to concerns over the DPRK nuclear weapons program. The talks were originally in response to North Korea’s advancements in creating a nuclear program since they withdrew from the nuclear non-proliferation treaty in 2003. During the talks, North Korea had made concessions such as dismantling their lone nuclear reactor, and allowing international weapons inspectors access to their processing facilities, in exchange for international aid and an easing of sanctions put in place against them after their withdrawal from the treaty.
When the remaining countries of the six-party talks, particularly South Korea, Japan, and the United States (China and Russia being the other two) strongly condemned the Bright Star-2 missile launch, claiming it was nothing more than a test of ICBM technology, North Korea angrily removed themselves from the talks, expelled international weapons inspectors from the country, and reassembled the nuclear reactor, announcing they would resume full operation of their nuclear program.
On May 25, 2009, less than two months after the presumed ICBM test, North Korea conducted its first (successful) detonation of a nuclear device. The device was probably a fission-only bomb utilizing uranium-235 as the fissile material, and it resulted in a blast yield that was likely between 2 and 5 kilotons. Not a large explosion with regard to nuclear blast yields, but a clear message to the world that North Korea was now a nuclear power.
On February 11, 2013, North Korea conducted another successful nuclear test, this one with a blast yield in the 6-9 kiloton range, and on January 6, 2016, they conducted a fourth test (third successful test) resulting in a similar yield of 6-9 kilotons. They claimed that this one was actually a hydrogen bomb, however there is nothing to confirm that, and the low yield makes that claim dubious. There is ample evidence (the bomb was detonated much further underground than previous tests) that the DPRK expected this blast to be much larger than it actually was, making it likely they failed in an improvement they’d implemented. It seems possible, with their claim that it was an h-bomb, they’d attempted unsuccessfully to detonate a boosted fission device, and it had achieved a fission-only yield.
A fourth successful detonation was made on September 9, 2016, and this was the largest yet, with a yield estimated to be somewhere between 10 and 20 kilotons.
In order to launch a nuclear strike, North Korea (which I’ll often refer to as the DPRK – the Democratic People’s Republic of Korea) needs two things: a functional and reliable nuclear bomb, and a reliable means of delivering it to its target. I use the word “reliable” in both of those things because reliability is one of the most difficult aspects of the very technical process of building both nuclear weapons and ICBMs.
As you saw in part two of this paper, a nuclear weapon is fairly simple to build if you have the necessary amounts of a fissionable metal such as uranium-235 or plutonium-239. Uranium-235 is present in very small percentages in naturally occurring deposits of uranium-238, of which North Korea has plenty. There are several ways to separate the two isotopes, but the most common and effective method is through the use of a gas centrifuge.
Centrifuges are actually collective farms of thousands of cylindrical centrifuges, all working to enrich uranium, either to a high enough percentage of uranium-235 to be weapons grade uranium, or to the lower percentage to be reactor grade uranium. Remember, natural uranium is about .7% U-235 and 99.3% U-238. For reactor grade uranium, you need to enrich the content to between 3-7% U-235, known as low-enriched uranium, or LEU, a process that is a relatively simple undertaking. In order to create weapons grade uranium, or HEU (high-enriched uranium) however, the U-235 content has to be a minimum of 90%, ideally closer to 95%. This is a much more laborious, time consuming, and complex undertaking.
We know the DPRK has one centrifuge collective for sure, and that it contains around 2000 individual centrifuges of a type modeled from an Iranian design. A group of non-government experts were allowed to tour it in 2010 and that gave us a lot of insight into just what type of centrifuges they have and what they’re capable of.
Here’s a screen grab I took from Google Earth that shows the centrifuge building (blue roof) and a truck I pointed out just for scale.
This is the only centrifuge building we know of, however, it is highly suspected, particularly with their allowing the group to tour the building in 2010, that the DPRK may have another, secret centrifuge, and we don’t know where that is, how big it is, or what it’s capable of.
It takes time to enrich uranium, and then it takes time for that uranium to be converted to plutonium in a nuclear reactor. North Korea has two nuclear reactors. One is an old model they got from Russia in the 1960s. It has the ability to create plutonium, but we know from infrared satellite imagery that it runs infrequently and probably not to the power level required for plutonium production. The other reactor they have is what’s known as an Experimental Light-Water Reactor, or ELWR. A light-water reactor is designed to produce electrical power, and isn’t as efficient at producing plutonium as a heavy-water reactor would be, (light water is just regular water, heavy water is deuterium, or 2H₂O, hydrogen that has two neutrons) however, the spent fuel from the ELWR can be processed to extract plutonium, something we know the DPRK has been doing under the guise of a radiochemical laboratory. I pulled a screen grab from Google Earth of the DPRK radiochemical lab that is actually used to process plutonium from the spent fuel.
All of these buildings and processing facilities are located at a place called Yongbyon, in the north part of North Korea, known officially as the Yongbyon Nuclear Scientific Research Center. Satellite images show modernization and construction of many new buildings all over that area in the last few years, easily identifiable by the new, blue roofs that show up well on the images.
So, what does all this mean? Well, North Korea likely has a stockpile of both HEU, and plutonium-239, enough to build a number of weapons. In this paper published in February, 2015 by physicist David Albright, he gives low-end, medium, and high-end projections on the number of nuclear weapons North Korea will have by the year 2020. He bases the projections on all the known and suspected factors,in addition to the unknown but possible factors, such as whether or not they have a second, secret centrifuge plant, and whether or not their ELWR is capable of running consistently and continuously. He then uses standard deviations to predict manufacturing numbers. For his medium projection, he estimates North Korea will have approximately 50 working nuclear weapons by the end of 2020.
Google Earth image of North Korea’s two nuclear reactors
The fact that they have nuclear weapons is undeniable, and the fact that they’ve been able to achieve miniaturization of those weapons is extremely likely, though there’s no actual proof of that. These weapons are almost certainly entirely fission weapons, with boosted fission hydrogen bomb technology still years away, and true two-stage thermonuclear devices even further. But still, fission weapons in the 10-20 kiloton yield size can be devastating enough to a city or military target. What matters now is, can they deliver them?
There are a number of ways of delivering nuclear weapons to their targets, but few of them are valid options for North Korea. They have no bombers to speak of, and certainly none capable of reaching any U.S. targets. The ones they do have are 70-year-old models from Russia that are slow and ponderous, and don’t have the range to even come close to Guam, let alone the U.S. mainland. In fact, they can’t even reach all of Japan with the bombers and expect to get back home. Plus, they’re fitted with old technology and would be easy to intercept or shoot down. So that’s not a real option.
They could possibly have the ability to detonate a weapon from one of the two satellites they’ve managed to put into orbit over the United States. This would result in an EMP, or electro-magnetic pulse. This would have a devastating impact on the United States power grid, and would result in serious loss of life and inability to function as a country, and many experts believe this is the most likely scenario of a North Korea nuclear attack.
From what I’ve read, and the research I’ve done, this is a definite concern, and the U.S. needs to take steps to harden our electrical grid against such an attack. However, this type of attack implies that North Korea has installed a nuclear weapon on one of its two satellites, and that seems very doubtful. They attempted to launch satellites several times unsuccessfully prior to the two recent successes, so the likelihood they risked one of their precious nukes in a package that was doubtful to achieve a successful orbit, is unlikely. I would be much more concerned about future satellite launches containing nuclear weapons than the two current satellites.
Ignoring the more extreme and unlikely methods of delivering a nuke, such as floating one over in a balloon, and launching a missile from a freighter that sails in close to the U.S. coastline, the only option left for North Korea is to develop an ICBM.
This is the most likely scenario, and the one they’ve spent the most effort achieving. It seems that the world is constantly underestimating the drive and determination of Kim Jong-un, including even the experts at my favorite website, 38north.org. If you go back through their archive of documents and articles, all the way back to 2009 as I did, you find numerous instances where they underestimated how quickly North Korea would achieve both nuclear, and missile (particularly ICBM) technology and success. There are several articles that project North Korea will not have a true and functional long-range ICBM until 2020, 2025, and even later. Yet, it seems that they’ve developed one already here in 2017, and you can read the surprise in the voices of the analysts each time Kim Jong-un achieves a stepping stone they didn’t think would be possible for many years.
If you spend enough time studying North Korea’s advancement in missile technology, you can see the incredible leaps they’ve been able to take, starting with their medium range ballistic missiles, up to their intermediate range ballistic missiles, and right up to the July 4th, 2017 launch of their first ever long-range ICBM, known as the Hwasong-14. Take a look at the state footage of that launch:
Note a couple of things: First is that Kim Jong-un is present during the unloading of the missile onto the launch platform, which shows the extent of his direct involvement in the evolution of their nuclear program. You can find pictures and video of him at all major stages of development, watching the tests closely, and consulting with the scientists directly involved. The next thing to note is that, despite the DPRK claims that this was a mobile missile launch, it was clearly not launched from the transport truck, but rather from a platform that was set up in advance. This is important because the ability to launch from a transport truck would mean that North Korea was able to forego much of the preparation time necessary to launch a nuclear warhead – preparation time that gives the United States time to notice the preparations and monitor them so as to not be taken by surprise.
Now, granted, the platform that launched the missile was some type of temporary and mobile platform; not as efficient as launching directly from the mobile truck, but still as step up from the requirement to launch from one of their two permanent launch facilities, one of which is pictured below, grabbed from Google earth.
This Hwasong-14 missile also appears to be liquid-fueled, and that’s extremely important. Liquid fuel takes a lot of time to prepare, and it can only be loaded into the missile just prior to launch. Liquid fuels need to be kept at a constant extremely low temperature, and the fuel bleeds off as it warms. Liquid fuels are also extremely volatile. Notice how slowly the truck was driving in the video? Large bumps can cause the liquid fuel to explode. If North Korea is able to convert the Hwasong-14 ICBM to a solid-fuel missile, it will become a much bigger concern, and they have proven the ability to create solid-fuel rocket motors, as evidenced by this video from last year:
Analysis of the Hwasong-14 launch of July 4th, 2017, showed that it was capable of delivering a payload of up to about 1000 – 1200 pounds all the way to the west coast of the United States. Remember, an ICBM goes into space and then has to come back into the earth’s atmosphere on its ballistic trajectory, which means that it needs a reentry vehicle to survive the extremely high temperatures when reentering the atmosphere. This reentry vehicle is going to take up much of that weight, and North Korea did test reentry vehicle technology as seen in this picture from KCTV/Reuters, modified by 38north.org:
The weight of the reentry vehicle is part of the payload, but leaves just enough for the type of nuclear device North Korea is thought to possess. And that’s a bad thing. The good thing is that the reentry capabilities of this particular missile hasn’t been tested, nor has its ability to successfully carry a nuclear payload at the extremely high speeds achieved during the ballistic portion of the missile’s flight. One little shimmy as it reenters the atmosphere, and the reentry vehicle will tumble and burn up. It typically takes years for countries to make new missiles reliable and safe, and despite the rather rapid pace of North Korea’s advancements, they can’t guarantee the success of untested and unproven missiles.
Here’s an excerpt from an article written last month by John Schilling on 38north.org, about the future capabilities of the Hwasong-14.
Thus, we expect there will eventually be more than just a single warhead under the shroud. But it probably won’t be multiple warheads, at least not for a decade or more. Multiple warheads of the size North Korea has displayed and can plausibly build today, along with reentry vehicles to carry them, simply wouldn’t fit. To put multiple warheads inside that fairing, at a weight that would still allow intercontinental reach, North Korea would have to develop a lightweight nuclear warhead comparable to the W-68 warhead of the US Poseidon missile. It took the United States almost 15 years to go from building the sort of nuclear weapons North Korea has today to the W-68. And while the North Korean missile program has been conducting tests at an accelerated pace, they have conducted only two nuclear tests in the past four years. So perhaps in 2030 we will see a multiple-warhead Hwasong-14, but probably not before then.
Keep in mind, as I mentioned earlier, 38north has been wrong about the capabilities of North Korea and their advancement abilities before, but it seems that at the very least, we don’t have to worry about multiple warheads (MIRVs) on a North Korean ICBM anytime soon.
The difficulties of designing a vehicle that can survive the heat and friction of reentry was shown in the next test. On July 28th, 2017, North Korea launched another missile, thought to again be the Hwasong-14, but this time with a larger second stage, powered by a higher thrust-producing engine. This missile flew for 45 minutes, and reached an altitude of more than 2000 miles. Now, this is WAY up into space. As a comparison, the International Space Station orbits earth at an altitude of about 250 miles, so this missile flew well past what would be considered low-earth orbit. Based on that high apogee, the range of the missile was calculated to be somewhere north of 6000 miles, which caused great consternation in the media as they reported that North Korea now had a missile that could reach Chicago, and possibly as far as New York. This is somewhat accurate, but, as President Trump might say, actually “fake news.” Yes, it’s true that in a perfect simulation, with a perfect ballistic arc, the missile could have flown that far. However, it didn’t have the weight of a warhead, and it didn’t survive reentry into the atmosphere.
Video taken from a Japanese television station weather camera which looks west into the Sea of Japan, catches the missile as it reenters the atmosphere. This was a night test, and so the reentry vehicle is clearly seen glowing as it begins to heat up from the reentry friction. Here’s the footage:
Although it’s grainy, analysis of the footage clearly shows that the reentry vehicle is breaking up as it falls through the atmosphere, which means that if it had contained a nuclear weapon, the weapon would not have survived the reentry and would not have exploded. North Korea clearly has more work to do to actually produce a reliable nuclear delivery system that can target the United States mainland.
That doesn’t mean that they can’t target other U.S. assets though. Guam is clearly within reach, and they have numerous ways to target U.S. allies such as South Korea and Japan. And, North Korea is certainly capable of making threats to do just that. Preemptive strike threats are nothing new to them, in 2010 alone they threatened preemptive nuclear strikes twenty times.
So, missile technologies aside, why shouldn’t we fear them?
Mostly because, despite what the media loves to report, North Korea is not a “hermit nation,” and Kim Jong-un is not an “unpredictable madman.” North Korea watchers are mostly in agreement that Kim Jong-un acts in unpredictable ways, but with a predictable path. He’s very aware of the capabilities of the United States, and he’s very aware of what a nuclear strike against U.S. interests and U.S. allies would mean. Above all else, he’s extremely motivated toward self-preservation, both for him and for his regime, much like his father was before him, and his grandfather was before his father.
If Kim Jong-un ever feels that the United States is about to make a strike against him in a decapitation attempt where he feels he has nothing to lose, he will likely launch whatever weapons he can. But that is again due to his self-preservation instincts. Other than that scenario, he knows the consequences of an actual strike. He also knows he can rattle his sabers and make all the threats he wants, safe in the knowledge that the American people, and the world in general, would never tolerate a first strike against him or his country, despite his verbal grandstanding and blow-hard announcements. In short, he’s no different from the teenage bully who struggles to get away from his friends who are, “holding him back,” while he shouts insults. All bluster, secure in the knowledge that as long as he toes the line without crossing it, he’s safe.
Last week, Kim Jong-un threatened to launch two ICBMs into the waters off Guam, and Donald Trump responded by threatening to shoot down the missiles. Trump also made threats against the country itself: From CNBC
“North Korea best not make any more threats to the United States,” Trump told reporters, speaking slowly and deliberately with his arms crossed in front of him. “They will be met with fire and fury like the world has never seen. He has been very threatening … and as I said they will be met with fire, fury and frankly power, the likes of which this world has never seen before.”
He later doubled down on that statement, saying that against the likes of the Kim regime, it might possibly not have been a strong enough stand, following that up with vague statements about what he meant, saying, “You’ll see,” when asked for clarification.
The left-media had a field day with these statements of course, stating that Trump had “threatened nuclear war,” and that he had escalated the situation to unacceptably high levels of danger. However, as we’ve seen, North Korea does not have the capability to launch any real attack. Yes, they could possibly launch a nuclear missile at Guam, but that would be the end of Kim Jong-un, if not of North Korea itself.
Not only would that mean a massive retaliation, it’s unlikely the missile would be a success anyway. The United States has a pretty good missile defense network, which I’ll discuss in a bit, and Kim Jong-un is very aware of that fact.
So what was Kim’s response to Trump’s statements? Did he launch his missiles toward Guam? Did he escalate the situation and bring the Korean peninsula to the brink of nuclear war as the alarmists and sensationalists predicted with their outraged shouts? No. He backed down, away from the edge of the cliff, which came as no surprise to those outside the north who watch him and know him best. A quote from 38north’s Robert Carlin on August 15th.
The North Korean report that Kim Jong Un has said he will wait and see what the United States does before deciding whether or not to order execution of a plan to envelope Guam with four Hwasong-12 missiles signals a decisive break in the action. This is no mixed message. It is exactly how the North moves back from the edge of the cliff. It’s classic, and anyone paying attention could have seen it coming.
This is not a question of parsing the precise language Kim used. It’s the act itself that speaks volumes. Put that together with the fact that the regime hadn’t been mobilizing the population for imminent crisis over the preceding four or five days, and you get a familiar North Korean dance move. Didn’t Kim say he was just giving the Americans a little more time? Of course! He’s not going to say “I surrender” or “I’ve decided that launching missiles would be a bad idea.” This way he can project the aura of the one still in control of the situation, of the one who scored the victory, of the one who kept the region from descending into war. He can be seen as the one who has the whip hand.
Not to turn this into a blog where I support Trump and his moves, because I don’t; most of them have been complete disasters. However, these statements by him were spoken in a language that Kim Jong-un was able to understand. Neither Trump nor Kim have any experience in diplomatic speech and carefully crafted statements. His regime doesn’t speak “diplomatese.” Remember, they made 20 preemptive nuclear strike threats in 2010 alone!! Kim Jong-un only understands the language of force, and Trump delivered that message to him very convincingly, in a way that caused him to step back while still attempting to save face. Accidentally or intentionally, Donald Trump spoke to Kim Jong-un in a way that he’s not used to being spoken to, and in language that he understood and feared. Trump is much more unpredictable than Kim Jong-un is, and no doubt his advisors warned him that he wasn’t dealing with a pushover in the White House, and Kim is the one who chose deescalation.
Now, let’s discuss some of the United States defenses against a missile strike. Obviously, we have enough nuclear weapons with high enough yields to turn the entire country into a smoking pothole and make South Korea an island nation, so retaliation for a nuclear strike is our biggest deterrent, but not only that, we have actual defensive capabilities against any initial strike Kim Jong-un may make.
THAAD – Terminal High Altitude Area Defense
This missile defense system is designed to shoot down ballistic missiles while they’re on their way down, during what’s known as their terminal phase, hence the “Terminal” in THAAD. The missile is capable of mach 8 speeds, and can intercept missiles nearly 100 miles above the earth’s surface. Now, these missiles shoot down the short and medium range ballistic missiles that might be fired at South Korea and Guam, but do not shoot down intercontinental ICBMs with their significantly higher speeds. Their deployment in Guam and South Korea however, does allow early warning radar of any ICBM fired toward the continental U.S., which allows our other missile defense assets more time to track the incoming warheads.
Patriot system – In particular, PAC-3
This system is designed to shoot down ICBMs, and has incredible ability to determine which warheads are armed in the event of a final stage that deploys decoys along with the actual warhead carrying ordnance, or in a multi-rocket launch where some are pure decoys. These systems are deployed at military bases along the west coast, as well as Guam, Hawaii, and other potential target areas. It’s an incredible defensive weapon, and you can read more about it HERE.
Aegis Ballistic Missile Defense System
The United States has 30 of these Aegis systems on cruisers and destroyers split between the Atlantic Ocean and the Pacific Ocean. These have some of the most advanced radar and tracking capabilities today, and are capable of shooting down a ballistic missile prior to it beginning its reentry stage. It even has the ability to shoot down a satellite from low-earth orbit, mitigating fears that North Korea might deploy a satellite containing a nuclear weapon meant to cause an EMP. This ability was proven in February 2008 when an Aegis-equipped ship in the Pacific destroyed a U.S. satellite that was failing and in a degrading orbit, over fears its radioactive payload may contaminate land areas when it reentered the atmosphere. Pretty amazing technology that could come in handy if North Korea launches more satellites.
Ground-Based Midcourse Defense (GMD) System
This system, our best defense against long-range ICBMs, is currently deployed at Vandenberg Air Force Base in California, and at Fort Greely in Alaska. It has the ability to shoot down ICBMs while they’re in the space portion of their flight, outside of the atmosphere. These interceptor missiles are three-stage, solid fuel rockets that sit in underground silos. They’re 55 feet long, and can intercept even the fastest long-range ICBMs. Here’s a picture of one being loaded into a silo at Fort Greely.
These defensive systems, along with a few others I’m leaving out, and near-future technologies that will likely consist of space-based platforms which will be able to target, track, and shoot down missiles entirely out of the atmosphere, make it difficult for nations like North Korea to actually convincingly threaten the United States and our allies.
If North Korea decided to fire a long-range ICBM toward the mainland of the United States, a lot of things would have to go right for them to be successful. First, the missile would have to launch correctly, something they’ve thus far only been able to achieve at a rate of about 50%. Next, the missile would have to be able to hit a target, something that even with the “close is good enough” theory of nuclear explosions, is not easy to accomplish. For example, it’s thought that many of their successful missile launches have landed as much as 10-50 miles from the intended landing area. Next, the missile would have to survive reentry, something they’ve not yet accomplished with any of their long-range ICBM tests. Next, the warhead would have to work. This is something I didn’t discuss, but the forces that act on a missile and reentry vehicle during the flight portion are extreme, and nuclear devices have to be built to withstand those forces, something that requires an enormous amount of testing to accomplish — testing North Korea hasn’t yet done.
Next, the U.S. would have to miss with every attempt to shoot the missile down. We can intercept ballistic missiles with a success rate of well over 50%. Now, if North Korea fires ten or fifteen missiles at a time at the U.S., some containing actual warheads, and some as decoys, we’re going to miss a few, guaranteed. But let’s be clear, the U.S. is going to certainly fire all 40-some GMD interceptors, along with a bunch of Patriots and THAAD missiles at these things, so it would take a lot of ICBMs at the same time to get one through, something North Korea is not capable of doing as of yet.
So, what happens if they somehow manage to beat the odds and successfully land and detonate a nuclear warhead on a U.S. city? Well, if you happen to live there, it’s going to suck for you. The nukes they have, in the 10-20 kiloton range, will have a destruction radius of around one mile. If you live within that one mile radius of the detonation point, you’ll likely die instantly. Outside of that, as long as you’re somewhat protected, such as being indoors, you’ll probably survive. Depending on the altitude at which it explodes, there may be some radioactive fallout, so you’ll want to not be downwind of the explosion point.
However, all of these difficulties combined makes a scenario so unlikely that I’m much more concerned with things like the advancement of artificial intelligence that I feel is a real threat to all of mankind. Nuclear war with North Korea might be a concern in the distant future, when their capabilities improve dramatically, but as for now and the foreseeable near future, dying in a nuclear attack from North Korea is not something we should be spending much time worrying about.
If you want to read more about nuclear weapons and just how they work, be sure to check out parts 1-4 of this article.
Bibliography and sources:
Many of my sources are actual links in the article. The ones I didn’t specifically link to are listed below.
Geneticist James Crow study: http://www.rerf.jp/news/pdf/residualrad_ps_e.pdf
Radiation effects of Hiroshima and Nagasaki: http://www.atomicarchive.com/Docs/MED/med_chp22.shtml
Radiation effects on humans: http://www.atomicarchive.com/Effects/effects15.shtml
Halifax Explosion: wikipedia.com/halifax_explosion
Firestorms from nuclear explosions: http://www.atomicarchive.com/Effects/effects11.shtml
National Nuclear Security Administration: https://nnsa.energy.gov/aboutus
Yield to weight ratios: http://blog.nuclearsecrecy.com/wp-content/uploads/2013/12/yield-to-weight-trends.png
Design of Fat Man and Little Boy: https://web.stanford.edu/class/e297c/war_peace/atomic/hfatman.html
Alex Wellerstein – Asst professor of STS Stevens Institue of Technology: http://blog.nuclearsecrecy.com/about-me/
Nuclear physics of atomic bombs and thermonuclear devices http://www.barryrudolph.com/pages/atomic.html
Hydrogen bombs lecture: http://work.atomlandonmars.com/h-bomb-lecture/Wellerstein-HydrogenBombLecture-Slides.pdf
Harvard PhD dissertation of Alex Wellerstein on secret patents for the atomic bomb: http://alexwellerstein.com/atomic_patents/
A guide to nuclear weapons from the nuclear weapons archive: http://nuclearweaponarchive.org/
History of the atomic bomb in WWII: http://nsarchive.gwu.edu/nukevault/ebb525-The-Atomic-Bomb-and-the-End-of-World-War-II/
Nuclear proliferation article: https://www.nobelprize.org/educational/peace/nuclear_weapons/readmore.html
Discovery Channel – Ultimate explosions – Tsar Bomba https://youtu.be/aMYYEsKvHvk
Declassified CIA Soviet Atomic Energy program report: https://www.cia.gov/library/readingroom/docs/DOC_0000843187.pdf
Project Crossroads atomic testing: https://www.osti.gov/opennet/manhattan-project-history/Events/1945-present/crossroads.htm
Lots of technical nuclear information – used extensively: http://nuclearweaponarchive.org/Nwfaq/Nfaq4-1.html#Nfaq4.1
Analysis of North Korea – weapon design and rocketry analysis http://www.38north.org/
Institute for science and international security report on North Korea’s lithium-6 production http://isis-online.org/isis-reports/detail/north-koreas-lithium-6-production-for-nuclear-weapons
Command and Control – Nuclear weapons, the Damascus Accident, and the Illusion of Safety – book by Eric Schlosser
Defusing Armageddon: Inside NEST, America’s secret nuclear bomb squad – book by Jeffrey T. Richelson
hppt://wikipedia.org/ numerous pages dealing with nuclear weapon design, production, and testing, as well as nuclear physics.
Hydronuclear testing – http://www.globalsecurity.org/wmd/intro/hydronuclear.htm
Future Directions in the DPRK’s Nuclear Weapons Program – Feb. 2015 paper by David Albright http://www.38north.org/wp-content/uploads/2015/09/NKNF_Future-Directions-2020.pdf
Hundreds of blog posts about North Korea, their nuclear program, and their missile technologies, along with related analysis and projections were used estensively, and can be found by visiting www.38north.org/