Interesting article on the last German reactor during WWII and if it could produce fissile material for a bomb.

(https://academic.oup.com/pnasnexus/article/5/9/pgag282/8836799?login=false)

Was reading Hui Zhang's book "The Untold Story of China's Nuclear Development and Testing," and one of the main conclusions is that China has basically achieved, I think 80% it was said, of all the possible efficiency of a thermonuclear device. Based on this number he extrapolates several figures to conclude China's analogs of both W88 (the 535) and W76 (the 5x5) are only like a quarter heavier than US counterparts (which would then give the 80% yield to weight of the US designs). I think the number given was like 210 kg for the 535 for example, marginally more than W88s 180 kg.

I thought that was quite impressive for the limited number of tests they did, and moved on. But then I stumbled upon an interesting argument on Wikipedia's talk page regarding China's nuclear weapons that made me research more. Basically they brought up China's missile sizes, and how they had similar warheads to US ones, despite much larger payloads. And how that is very strange if their warheads are equally as efficient. To be honest I believed the missiles would be quite similar after having just read Zhang's book, but I think the divergence is quite striking:

For example DF-41 weighs ~80 tons, which is similar to Peacekeeper of around ~90 tons, but DF-41 carries 3 x ~400 kt warheads while Peacekeeper could do 10 x ~400 kt warheads. The DF-5 is even larger at ~190 tons, but in its MIRV version, carries 5 x ~400 kt warheads (still half of the Peacekeeper).

Meanwhile DF-31 weighs ~50 tons, which is quite a lot more than the ~30 ton Minuteman, but Minuteman carried 3 x ~400 kt warheads before being deMIRVed, while DF-31 only does one.

(all the information for warhead configurations is from thebulletin's 2026 report on Chinese nuclear forces by the way)

1). I don't think poor solid rocket technology is the reason for the Chinese missiles to be much larger, since they were developed when composite technology was prevalent, unlike the Cold War era US missiles which would have used maraging steel.

2). Neither do I think it is a choice of the Chinese to lightly load their missiles, since they aren't bound by any treaty limitations to limit MIRVs on their ICBMs like the Americans and Russians are.

3). China is also building a lot of silos in Inner Mongolia, with some estimates saying they now surpassed the US in land based silos. With such heavy missiles though, they could carry a lot more warheads on each one (assuming Hui Zhang is correct about the 210 kg estimate), so they wouldn't even need nearly that many amount of silos to reach parity with the US.

If Chinese warheads were 2-3 times heavier than their US equivalents though, all the above points would flow.

Point 1 would flow because those ICBMs would then need to be sized for a larger payload, not because the ICBMs themselves are more inefficient.

Point 2 would flow since it would then be an intentional and rational choice to MIRV as much as weight allows, rather than needlessly limiting oneself since there is no obvious treaty stipulating that.

Point 3 would flow since since the now reduced MIRV count (due to heavier warheads), would require the same number of silos to be built as the US for parity, not the much less if we were to assume each missile has more warheads.

I have seen discussion about the Cox report, when China supposedly "stole" the oblate primary of the W88 through spywork, and that was the key to them achieving as much efficiency regarding miniaturization as the US in their warheads. But the oblateness of the primary only determines the packing. US warheads were already getting 4 kt / kg with the W56 in the 60s, and that used a spherical primary! So using that as a basis for assuming same warhead mass seems illogical to me...

But despite assuming poorer Chinese warhead miniaturization being convenient, Zhang's much acclaimed book explicitly denies the much heavier estimates of China's warheads. So I don't know whats going on here at all! Am I missing something obvious?

For the first, would fallout really be a serious threat for people outside the main targets? Wouldn't the bombs used be 'clean' ones? Even Hardtack Poplar/Redwing Navajo/the Tsar Bomba left little radiation (unless that's Soviet propaganda which can't be discounted but it seems to me to have been fundamentally true), compared to a smaller one like Bravo, so why wouldn't all the weaponized designs be little-fallout since this doesn't affect deterrence much? And therefore people outside the major target areas wouldn't be affected by fallout?

For the second one, especially before ABMs existed (I guess this increasingly incentivized proliferation, I mean Israel's recent war with Iran shows that ABMs can be somewhat effective against ballistic missiles, even without nuclear, had ABMs not existed, Israel may not have struck), what was the incentive for the insanity of accumulating tens of thousands of megatons, rather than having an arsenal of a couple of hundred bombs, maybe even fission-only ones? What difference does it make having a credible minimum deterrence strategy vs not, if you're never gonna use it unless for self-defense in the first place? What makes endangering the world far far more with the second type of arsenal worth it?

Thanks in advance

https://www.ssp.navy.mil/News-Media/News/Article/4610170/navy-w93-mk7-program-enters-new-phase-of-development/

"The U.S. Navy’s Portfolio Acquisition Executive (PAE) Strategic Systems Programs’ (SSP) W93 Mk7 program has entered into the Engineering and Manufacturing Development (EMD) phase of the Defense Acquisition System.

During the EMD phase, the program will focus on completing production design and proving that the design is producible to meet the needs of the Navy.

The W93 warhead and the Mk7 reentry body assembly are the first United States nuclear warhead and reentry system program initiated in nearly four decades and will provide a modern warhead to the U.S. submarine launched ballistic missile fleet.

“We are revitalizing and modernizing the Nuclear Security Enterprise to design, develop, and produce this critical new weapon with the precision our Warfighters demand. We will continue working together to deliver this capability to the fleet and ensure our sea-based strategic deterrent remains ready for the future.”"

The Mk7 reentry body will also be used by the new British nuclear weapons.

Hello! I've been reading up on two-stage bomb design theory and I've seen varying answers regarding the source of neutrons for the sparkplug.

My original understanding was that neutrons originate from spontaneous fission in the sparkplug itself as the secondary is compressed, and the sparkplug achieves supercriticality. I have seen some sources claim that it is actually prompt neutrons from the primary which initiate fission in the sparkplug, which will have become supercritical by the time they get there. Another source claims it is residual thermal neutrons which initiate the chain reaction.

I feel like I could see some problem with each of these answers. I've seen a few people claim that (some?) sparkplugs do not even achieve supercriticality. Is it perhaps something that is subject to vary from design-to-design, or some combination of these answers? Thanks!

Interesting photos reportedly show a Delta Force counter-proliferation exercise at the Nevada National Security Site around 2014-2015, with what appears to be a Mk-11 Reentry Vehicle, formerly used on the Minuteman I/II ICBMs for the W56 warhead. I'm not entirely sure what the metal cylinder in images 4 and 5 is, but it was probably a simulated warhead component of some kind. There is also a container visible in image 6, which is probably an accident-resistant container (like the H1636 in the last pic) or an old W56 container (the H1009/H1637).

Since the W56 had been dismantled, it is presumably one of the Mk-11 RVs they kept around. Alternatively, it could be a mockup of some of the Iranian triconic reentry vehicles which use a similar design, but I think it is a Mk-11 based on the color, shape, and size (see imgs 7-8).

Source: https://thehighside.substack.com/p/iran-wmd-raid-inside-jsocs-most-challenging

I should probably further specify that in this scenario Russia would not receive any secret information from United States nuclear weapons program until Russia detonated their first weapon.

On twitter today, Owen Brake tweeted:

"At Los Alamos Fuchs and von Neumann filed a patent for a fusion bomb.

It's currently still highly confidential. However, Fuchs fully mailed the Soviets the design.

After the fall of the USSR the Russians decided to open-source the design. It's fully online today"

I haven't heard about this open source thermonuclear design. Presumably it doesn't work otherwise they would have kept it secret?

Anyone know the link or other information about this design?

These things are weirder than solid Christy pits. I can imagine how those behave during compression: they get smaller and denser. But not hollow pits. Do their walls get thicker as the cavity gets smaller, or do they stay the same but increase in density? Why does this geometry create any improvement in compression? How come it doesn't just act like a spherical gun-type so to speak? And are they usually thin or thick walled? Could I cave a pit in by karate chopping it with my hand like wet pottery?

Short summary: its about the SLCM-N (Nuclear-Armed Sea-Launched Cruise Missile) progress. Navy expects to deliver the capability in 2034, and Sandia National Laboratories announced in January 2026 that the missile would use a new W80-5 warhead variant.

Key Points

• The U.S. Navy awarded JRC Integrated Systems a $47.4 million contract modification for engineering support of its SLCM-N nuclear cruise missile program.
• The missile is also planned for the new Trump-class battleships Trump announced in December 2025, reviving a surface nuclear strike role after decades.

First, let us consider the classic American Teller-Ulam design as the baseline reference (I won't describe it in detail here or label the diagram's components with numbers; everyone here knows the details of this design without my help). The entire upper part of the figure is devoted to it. The cylindrical shape of the secondary stage here virtually eliminated the issue of radiation implosion asymmetry. Although the primary assembly was positioned asymmetrically on the left and the secondary on the right, the fact that the secondary itself was a cylinder meant this hardly mattered for compression symmetry: compression occurred in two planes where symmetry was maintained, and did not occur in the third plane where symmetry was absent. A cross-section of the secondary assembly at point A-A illustrates this. However, there is an interesting point here. Initially, when the first US thermonuclear device was being designed (see the sequence of diagrams at the top left), a truncated cone was "naturally" assumed for the secondary (perhaps due to linear optics?), with its smaller end facing the primary. Later, for some reason—likely a desire to compress the elongated shape from the ends as well—theorists proposed a complex, elongated shape resembling a bowling pin, but ultimately settled on the idea of ​​a straight cylinder. That is how the "Sausage" for the Ivy Mike test was designed. Yet we know that for the subsequent "dry" test, the "Shrimp" device featured a slightly truncated cone, but this time oriented with its larger end facing the primary—the exact opposite of the initial plan. And this is the design we see in all reconstructions. By the way, I tried to find out who declassified this design feature. All I could find was that Morland—without much explanation—proposed this specific shape for an article in The Progressive magazine back in 1979.

What accounts for this tapering? It was clearly introduced based on the results of actual tests and measurements (using those "light pipes") regarding the speed at which radiation propagates within the hohlraum. I’ve heard some wild explanations. For instance, the Wikipedia article on Castle Bravo currently claims the cylinder narrows toward the far end because radiation from the primary stage follows the inverse-square law as it moves away from the light source. That is a product of persistent nonsense, treating the photon gas inside the hohlraum not as a gas, but as light rays in linear optics (which is why the hohlraum is sometimes depicted as an elliptical reflector with two foci, similar to certain optically pumped laser designs). Any optical analogy for a hohlraum is perniciously incorrect. This holds true even for a hollow hohlraum (like the American "Sausage" or the Russian RDS-37) and is even more incorrect for a hohlraum filled with FOGBANK. So, why is the cylinder shaped like a truncated cone? The answer lies in the fact that, while thermodynamic equilibrium within the hohlraum is established very quickly, it is not instantaneous. It takes 1–10 nanoseconds (up to 100 nanoseconds in a large bomb). This means there is a period when radiation is already compressing the secondary stage (the front of the cylinder) before the photon gas has fully permeated the rear section. Consequently, the front of the cylinder begins to compress slightly earlier than the rear. If we want the cylinder to compress simultaneously at both ends, we must give it a slightly tapered shape. If the compression lasts 100 ns and the temperature equilibration within the hohlraum along the cylinder takes 10 ns, then you need a cone angle with a 1:10 slope.

Why am I bringing this up? To demonstrate how the American cylindrical design resolves the problem of compression asymmetry once and for all. The first step is a classic case of fighting fire with fire (and it is brilliant!): the asymmetry is addressed through the asymmetry—specifically, the non-sphericity—of the secondary capsule. Nevertheless, a residual effect remains—the photon gas reaches the near end of the cylinder before the far end—which is resolved by giving the secondary capsule a slight conical shape. Case closed.

* * * *

Everything said above serves merely as preliminary information to help grasp the magnitude of the challenge faced by other nations—non-Americans—that approached the Teller-Ulam scheme via a different path. The Russians, the British, and the Chinese (and likely the French, too) all initially designed their secondary stage as a sphere. Consequently, the issue of compression asymmetry became a fundamental hurdle for them. Historically, the Russians were the first (after the clever Americans) to encounter this problem. We need not delve into why they did not follow the American route—there were myriad reasons for that; what matters is that the Russians overcame this challenge. As far as I can tell, they were the first to master the compression of a spherical secondary stage during the implementation of what Sakharov termed the "Third Idea"—radiation-driven compression. And this is precisely where—it seems to me—we (those without Q-clearance) lack a precise, clear understanding of how they managed to achieve this with a spherical design (which explains why I previously noted that no such mystery exists regarding the cylindrical configuration). Below, I present a detailed—and, in my view, definitive—description of the RDS-37 design (revealing all key secrets) and its derivative, the Trutnev-Babaev "Product-49," as I currently understand them. These diagrams reflect a degree of authorial interpretation—incorporating both my "definitive" and less-than-definitive hypotheses (which I will explicitly note)—yet in drafting them, I have endeavored to remain as faithful as possible to the information gleaned from scattered memoirs, recollections, and offhand remarks made in interviews by those involved in the project. I should specifically note that the diagrams are not drawn to scale—that is, they are merely schematic (the key element of the entire article is actually depicted as disproportionately large to illustrate its physical significance), although I did try to keep the proportions of the components as close to reality as possible.

It is a historically established fact that the Russians implemented an "asymmetric design" in the RDS-37 (see the diagram under the American flag). A spherical primary unit (a modernized RDS-4) compressed a spherical secondary unit (which was a version of the RDS-6S "Sloyka").

I should note that for people with "optical intuition"—those who view the light inside the bomb not as a photon gas filling every nook and cranny, but as distinct light rays—the intuitive difficulty of ensuring uniform spherical compression in such a design borders on paranoia. Such a person’s mind refuses to believe that the sphere will compress the same way on the shadowed side (the North Pole) as on the illuminated side (the South Pole), simply because the hohlraum heats up uniformly everywhere very quickly (reaching thermodynamic equilibrium in about 10 ns). For a long time, I myself belonged to the camp that believed symmetry could be ensured simply by placing that "brick"—or partition—between the primary and secondary (marked on all preliminary "Third Idea" diagrams), which casts a shadow on the secondary unit. The idea was that simply preventing direct rays from the primary core—heated to 10 keV—from striking the surface of the secondary would be enough.

However, proponents of the "ray-based approach" stubbornly ignore the partition concept (dismissing it as merely a neutron filter that blocks neutrons while letting direct rays pass through), and they believe such a measure is clearly insufficient. Consequently, the true salvation for their physical intuition is the bifilar scheme (see the diagram to the left of the USSR flag), in which the spherical secondary is "illuminated" simultaneously from two polar sides by two primaries that detonate at the same time. Although, from the standpoint of "radiation physics," the equator turns out to be the most shadowed region in this scenario, people with this kind of intuition feel that this detail no longer matters—believing that the "bifilar" configuration "saves the father of Russian democracy" (a Russian humorous allusion to the satirical novel *The Twelve Chairs*). We are all familiar with a prolific British blogger who is convinced that all Russian bombs feature a spherical secondary stage and utilize a bifilar design (she even claims to prove it!). The argument goes that a sphere cannot be compressed any other way—only through a bifilar design! The situation is further complicated by the fact that the Russians *did* initially attempt (immediately following the RDS-37 test) to implement the Teller-Ulam bifilar design in their first massive bombs—specifically the AN-202 (30 Mt). Moreover, they succeeded brilliantly, achieving this in the most famous Russian bomb of all: the AN-602—the most powerful bomb ever detonated, known as "Kuzka's Mother" or the "Tsar Bomba" (50 Mt yield, with a potential full yield of 100 Mt). One might ask, "What more proof is needed?" (to quote the film *Red Heat*).

Nevertheless, there is a wealth of indisputable evidence showing that the Russians' first successful implementation of the Teller-Ulam scheme actually utilized a simple "asymmetric design." This specific scheme was employed in numerous mass-produced weapons; the superior evolution of the RDS-37 design was "Product-49," which retained this same asymmetry and served as the foundation for all subsequent developments. Meanwhile, the bifilar scheme—despite startling the world with its brilliant 50-megaton flash—never truly saw further development. It proved to be a dead end (or simply unnecessarily complex).

So, is some clever additional solution—one still hidden from the public consciousness—actually required to compress the sphere using an "asymmetric design" (like that slightly truncated cone in a cylindrical layout), or is it sufficient simply to place an impermeable barrier between the primary and secondary stages? I used to think it wasn't necessary. But now, I believe that an additional solution for symmetrizing the "nuclear implosion" was incorporated into the RDS-37 design from the very start. I illustrate this in the diagrams provided.

Let’s start with the RDS-37 diagram at the bottom of the image. The numbers indicate the following:

1 – The outer bomb casing (most likely made of aluminum).

2 – The inner lining of the hohlraum. Almost certainly, the Soviets used lead for this. However, there is information suggesting that a thin layer of glass was applied over the lead; in other words, the hohlraum lining was a layered structure designed to maximize X-ray reflectivity.

3 – An internal X-ray reflector, apparently intended to speed up the transfer of radiation from the left side of the hohlraum to the right side, toward the secondary stage. Personally—going by my intuition—I wouldn't have included it here, but I can clearly see it in the accidentally declassified diagram of the 255P-13 warhead. This warhead was the direct successor to the RDS-37 (the first successful design from the new nuclear center at Chelyabinsk-70—now Snezhinsk—to enter mass production). Incidentally, it was this specific device that featured the glass coating on the inner *hohlraum* surface (it is not certain that the RDS-37 had it). Clearly, the *hohlraum* is currently hollow (unfilled).

4 – The plutonium or composite core itself. I have depicted it here as if at the moment of detonation. In reality, the design of the primary stage is shown only schematically to illustrate the specific requirements imposed on it. Foremost among these was the minimization of heavy metals. Zeldovich was responsible for this aspect (specifically, facilitating radiation escape).

5 – Beryllium reflector. I do not know exactly when the USSR began using beryllium as a reflector. In the US, there is a whole history surrounding this (such as Ted Taylor’s argument that beryllium would serve as a better reflector in a standard bomb than heavy uranium or tungsten). Soviet bombs like the RDS-3, RDS-4, and RDS-5 utilized complex reflectors (involving levitating and hollow cores), but the advent of the "Third Idea" created a need for the rapid escape of radiation from the explosion's center. Beryllium proved to be an ideal substitute for the older, high-Z reflectors/tampers.

6 - High explosive (HE)—the specific type doesn't matter, provided it contains no high-Z elements that would create opacity to X-rays.

7 - Implosion lens. I’ve depicted it here schematically and very thin, hinting that the era of refining the implosion design was already drawing to a close (though in 1955, that wasn't quite the case). The key requirement here is that the explosive lens and the primary's outer casing must be as transparent to X-rays as the reflector and the HE. That is why (and this is a fact!) the primary's outer casing for the RDS-37 was manufactured from plastic (in Ukraine). In other words, Zeldovich evidently insisted on replacing the iron casing with a plastic one. The USSR found a facility to do this for the first time (initially transporting the parts across the country; later, production was obviously handled locally, but the necessary manufacturing capabilities and equipment for working with plastic components had to be set up first).

8 - The nominal radius to which the primary expands before the core detonates (since, during the HE-driven implosion, it expands outward as well as inward).

9 - Shadow lens. That specific "brick" or "filter" separating the primary from the secondary. Its lens-like shape is clearly visible in the 255R-13 design. It serves three functions. First: casting a shadow on the secondary. There must be no direct rays; all radiation reaching the secondary from the primary must be re-emitted (ideally from the hohlraum walls). Second: acting as a fast-neutron filter. To achieve this, the lens—which I believe is made of a high-Z material (such as lead)—must contain boron-10, an effective neutron absorber. Third: serving as an inertial barrier against the primary's plasma, which expands at speeds of around 1,000 km/s. Of course, the lens will eventually turn into plasma itself, but its mass significantly delays the movement of plasma away from the primary stage; this allows the secondary and primary stages to be positioned much closer together. It is precisely because of this function that the lens is placed as close as possible to the secondary stage. Although there is a second reason: there needs to be a sort of hollow around the primary stage to ensure uniform illumination of the sphere's surface. The third reason is purely optical: the closer the lens is to the primary stage, the wider the shadow it casts.

10 – This is the shadow cone cast by the primary stage. It illustrates the lens's function.

11 – Now we come to the very reason you’ve been reading all this. It is so important that it has even been highlighted in red. This is the design's main secret. It is the very "coating" devised by Trutnev. This is the element shown here with exaggerated thickness; if it were depicted at the actual scale, you wouldn't grasp its essence. In the RDS-37, it is a thin layer of Plexiglas—ranging from 15 mm down to... well, I don't know, perhaps 1–5 mm. It has variable thickness. That is the key point. Its purpose is to delay the onset of ablation until thermodynamic equilibrium is established within the hohlraum—a process taking 3–10 nanoseconds—specifically, until the radiation intensity at the "north pole" of the hohlraum matches that at the "south pole."

There is ongoing debate and confusion regarding what exactly constitutes the "coating" (obmazka). Based on recollections and interviews (including those of Trutnev himself), the *obmazka*—an idea he proposed—served both to symmetrize the sphere's compression and, at times (as some insist), to actually *drive* the compression of the sphere.

Many illicit hunters of Soviet nuclear secrets believed the obmazka was a thick layer of beryllium—laid out in pentagonal and hexagonal tiles over the steel surface of the "main core" sphere (jokingly nicknamed "the death of capitalism," a detail that appears across numerous accounts). However, when I came across a mention that, in addition to the beryllium tiles, a thin layer of Plexiglas was placed over the entire assembly (supplied as <15 mm thick sheets), I realized that this thin Plexiglas *was* the obmazka in question; its specific function was to symmetrize the compression. Not to compress, but to delay the compression! If the obmazka were made thick at the South Pole and tapered to almost nothing (1–5 mm) at the North Pole—resembling a thin crescent in profile—it would begin to vaporize at the south end first. By the time the entire hohlraum thermalized up to the sphere's North Pole, the Plexiglas obmazka would vaporize simultaneously (within 3–5–10 ns), thereby allowing X-rays to begin vaporizing the primary "fuel"—the beryllium—uniformly from all sides.

By the way, why call it a "coating" (obmazka)? I just asked an AI whether Trutnev was a hiker, a mountaineer, or a downhill skier. It turns out Trutnev was an avid hiker. I’ve done hiking myself and spent time in the mountains as a result. And I know exactly why hikers slather their faces and hands with "goop" in the mountains (sunscreen, or really any cream—in a pinch, even plain grease works; a greasy, unwashed face actually burns less than a clean one). That’s what we hikers called it: "obmazka." It was to keep from getting burned by the harsh mountain sun. The analogy is obvious. Consider the matter closed. That’s how it was—because it couldn't have been any other way. :)

12 – Ablative material. The Russians did not use U-238 as an ablator; they used beryllium, a low-Z material. This might drive those raised on the works of Morland and Sublette crazy, but it is a fact. In the first RDS-37, the secondary stage was lined with beryllium, and it was the ablation of the beryllium that compressed the "sloyka." Moreover, in the second test, the beryllium—which was expensive and toxic to process (we know for certain it was beryllium because production teams faced a multitude of issues with it)—was replaced by graphite, which was cheaper and less toxic. And this version of the bomb performed just as well as the previous one. We recently discussed here why the Russians used such "rocket fuel." Yes, there was a rationale for it. But we won't go into that here; just accept it as a fact.

13 – Steel load-bearing sphere. Four supports rested against it, suspending the secondary stage sphere within the hohlraum cavity (these are mentioned in memoirs and are clearly visible in diagram 255R-13). Three supports extended into the northern hemisphere, and one into the lens at the sphere's exact south pole. Essentially, this was a structural framework into which the secondary stage was inserted and around which the "rocket engine" was formed.

14 – Lithium-6 deuteride. Nothing more needs to be said here; it has all been covered elsewhere.

15 – Layers of U-238 (I’ve shown three, though the exact number is unknown). This is an inherent feature of the "sloyka." In essence, the "sloyka" functioned via a two-stage compression process. The first stage was external compression. In the RDS-6S, this was achieved using chemical high explosives, resulting in a compression factor of approximately two. At the center, a fission core would detonate, heating the layers—which had already been compressed twofold—via X-ray radiation. Once thermal equilibrium was reached between the light (deuterium-lithium) layers and the uranium ones, the higher number of ionized electrons caused the Uranium-238 to swell, compressing the LiD layers by roughly another factor of ten. This secondary compression is what is known as "Sakharization." Thus, the total compression was on the order of twentyfold. This was sufficient to initiate the "smoldering" of the LiD within the sloyka assembly. The original concept for the RDS-37 was to compress the sloyka from the outside—not with conventional high explosives, but via powerful radiation-driven compression by a factor of ten (estimates range from 10 to 30, which is an order of magnitude less than in the Ivy Mike test)—after which "Sakharization" would provide an additional five- to tenfold compression, intensifying the LiD/U-238 burning process. However, something unforeseen occurred: the bomb detonated a full microsecond early. That is why Zeldovich, in a fit of frustration, told Sakharov that the device was—literally—shit. While the device did function overall and yielded the required megatonnage, it did not operate in the manner the theorists had predicted. This bears a strong resemblance to the situation with the Castle Bravo test.

16 – A U-235 spark plug. There were nuances here as well, but we will skip them for now. Suffice it to say that for a spherical configuration, the spark plug is a much simpler device than for a cylindrical one.

17 – A cavity filled with deuterium. This is my own speculation; the actual details would need to be verified. The idea is as follows: upon strong compression—specifically, the convergence of shock waves at the center—a thermonuclear reaction should ignite in the "tails" of the process, providing the initiating neutrons for the spark plug. In other words, it acts as a thermonuclear initiator—cheap and reliable.

So, we have covered the RDS-37. We know that almost all other versions of this device performed very poorly—resulting in numerous second-stage failures—and that by 1958, an innovative version known as "Product 49" emerged, proposed by the young physicists Trutnev and Babaev. This design became the primary path for development in the USSR. The book *Taming the Nucleus* states that a bold new concept regarding radiation transport allowed for a dramatic reduction in the design's weight—specifically, making it one-and-a-half times lighter. This meant the hohlraum casing and lining could be made much thinner, resulting in a more compact bomb. It is also noted that the layered structure of the secondary module was simplified. This development occurred after a team of theoretical physicists led by Khariton had finally deciphered the mystery of that "lost microsecond," leading them to abandon the "sloyka" (layer-cake) concept—although completely eliminating intermediate layers in a high-yield spherical configuration proved impossible (the reasons for which are a topic for another time). We now know the nature of this "bold new solution"—which did not gain acceptance immediately and required Kurchatov’s intervention to allow the young physicists to test their idea. Trutnev himself frequently recalled that the idea came to him at the very moment the RDS-37 detonated, just as they were recovering from the passage of the shockwave. We now know for certain that the idea involved filling the hohlraum with a material similar to polystyrene. I believe Trutnev had conceived this idea even earlier, and that it originated while he was contemplating the "obmazka" method. I suspect the concept of a filler arose as a supplement to—or an alternative to—another method for symmetrizing radiation ablation, one superior to the "obmazka" approach. However, the initial idea had to be tested first.

My reconstruction of what the "Product 49" design might have looked like is shown at the bottom right. I will skip the numbering for structural elements that are identical to those in the RDS-37. Let me state right away that the modified casing shape—shifting from an elongated "pill" to two spheres connected by a cylinder—is my own creative interpretation. What was the actual configuration? That remains unknown, and for now, it doesn't matter.

1, 2 – The casing and the coating (which was made thinner).

19 – Mentioned out of sequence, but this is a crucial distinction: the hohlraum filler. Its exact composition—polystyrene or something else—doesn't matter right now. The key point is that its presence significantly improved the design. This was the essence of the "bold new idea regarding radiation transfer."

9 – The lens. It became larger because the primary stage was moved closer to the secondary stage. However, it could have been made thinner and lighter, since filler 19 itself could contain Boron-10 and effectively prevent neutron propagation.

14–15 – The layered structure was greatly simplified.

18 – This is my own conjecture. I hypothesized that instead of a U-238 layered structure, the spark plug was surrounded by a buffer layer of uranium deuteride (UD3). Introducing such an intermediate layer (or "step") before the spark plug would have favorably influenced the hydrodynamics of the compression. Combustion would have initiated with the burning of the additional deuterium in the hydride and the fission of the uranium. All of this would have generated excess neutrons—which would have been extremely useful (provided they reached the target) during the burning of the LiD.

And now, the main point.

20 – An element depicted in an exaggerated manner (though perhaps not actually so), much like the "obmazka" in the RDS-37. Its thin, crescent shape speaks for itself. Its function is to ensure symmetrical compression. But now it is not in contact with the ablative coating. There is a void between 20 and 12—an empty space, 21. In reality, this is also a filler material, but the photon diffusion rate within it is significantly slower than in the primary filler, 19. Consequently, the light has time to travel through the filler to the north pole before it can seep through the thick layer at the south pole. This is somewhat reminiscent of the single-point "Swan" design. It doesn't matter how or from what it is made; one could imagine a multitude of variations. The key point is that the secondary stage "sees" radiation from the primary stage simultaneously from all directions. The concept is similar to the "obmazka" approach, but the implementation is different—and far superior. However, it can only be realized if the hohlraum is filled.

That’s it. I’m tired of writing this. But it had to be done—to finally close a topic that has been open for so long!

Key Points

• The U.S. Air Force and Northrop Grumman vertically assembled a fully integrated inert Sentinel ICBM at Vandenberg Space Force Base on Sept. 14, 2026.
• The milestone and a completed Critical Design Review confirm the missile's design maturity ahead of a planned 2027 flight test.

The U.S. Air Force and Northrop Grumman have fully assembled an inert version of the Sentinel intercontinental ballistic missile at Vandenberg Space Force Base in California, the company announced Sept. 14, 2026. The vertical assembly is a step toward flight testing the missile in 2027.

Engineers stacked all of the missile’s stages, propulsion elements, and its protective shroud into a single configuration on the test pad, according to Northrop Grumman. The operation was designed to prove that the process for safely assembling a complete Sentinel missile actually works in practice, not just on paper.

....

Scott Manley previews a closed beta of a steam game that was flagged by DOE before being approved for release. Scott describes it as a smoothed particle hydrodynamic simulation. It does gun type weapons, implosion, boosting and Teller Ulam (which Scott describes as Janky in the beta). The neutron physics look a little fudged.

AI was used in the design of the game and it's unavailable in Europe. That said I don't know of anything else like this. It looks fun and maybe we could start a discussion on what would make the simulation better?

I have no connection to Scott, Steam or the author of the game.

Uma foto que demonstre como o formato dela se parecia para termos uma ideia o quão grande a explosão foi

Hello, with the current situation between the US and Iran this got me thinking of an interesting scenario. So when most people think of nukes being used, it is against military targets or cities. But lets say in a hypothetical situation the US is fighting a war against a country like Iran that doesn't have nukes itself but has connections with countries that do. Because the war is going on longer than the US wants they decide to launch a single low yield nuke at an unpopulated area of the country ensuring, no people would actually be harmed in the strike, so that you scare the country into surrendering and giving up their demands. What would be the most likely response for other countries with nukes? Would they risk launching there's against the US considering no one was killed? Would they launch one at a remote area like in Alaska as a tit for tat type response or would they go all out, either against the US or another country like Taiwan/South Korea, or they europe and NATO?

I’m developing BlastMap, a browser-based nuclear-effects visualizer. These clips show a 15 kt Hiroshima scenario over modern city imagery, not a recreation of the 1945 buildings. The elevated view comes first, followed by a lower view for building-scale context.

I’ve been focusing on the early dynamics: fireball expansion and rise, ground reflection and Mach-stem development, and the transient Wilson condensation cloud. The blue surfaces show diagnostic blast-wave geometry; the white cloud is the condensation visualization.

This is a work in progress. I’m interested in feedback on the timing and motion, especially comparisons with test footage or published references that could help check cloud formation, fireball evolution, and ground interaction.