Nuclear crater depth on dense metals

[Digi5]

I had an idea for this large military space installation that was protected by a thick shell of steel at a stand-off from the main structure. The shell would be meters to tens of meters thick.

I wanted to estimate just how thick it would need to be to resist multi-megaton nuclear surface detonations, but I'm at a loss as to how to approach the problem. The only things I found through google regarding cratering were for buried explosions in soil and sand.

I tried referencing real world tests, such as the Castle Bravo (15 Mt) and Ivy Mike (10.4 Mt) tests. The Castle Bravo detonation left a crater 2 km wide and 76 m deep. The Ivy Mike detonation left a crater 1.9 km wide and 50m deep. However, those craters were formed out of soil and rock, and I'm not sure how they would scale with metals. One thing that stands out to me is that nuclear detonations leave very shallow craters relative to their width.

Essentially, I'm asking for help estimating the crater depth left by a nuclear explosion when detonated on the surface of an object. I realize that this is probably too difficult of a question to answer definitively, but any informed guesses or ball-park estimations would be appreciated.

To put a number to it: How deep would the crater be if a 10 Mt nuclear explosion detonated on a 50 meter thick steel structure?

[Elheru Aran]

...I'm not sure there's enough steel on Earth to make a *solid* shell that thick, if it's a sphere surrounding a space station or some such of even moderate size. I'm also not sure you'd even be able to get it into orbit in a timely fashion.

[Terralthra]

Even a small nuclear weapon (15 kilotons) emits ~1000 watts per cm^2 from the surface of the fireball at 2 km. That's "acetylene torch" levels of energy, and will cut through metal in much the same way, over the second or two of that level of emission. Temperature within the fireball is in the millions of degrees, and the fireball can be as small as a few tens of meters to over a kilometer. If the fireball encompasses the thickness of the steel, it will almost certainly destroy any of the structure within it, since the structure in space is stuck with radiation as the only way of shedding heat energy, I'd think.

This is a good place to start.

[Imperial528]

I plugged the data for iron into this calculator: http://www.5596.org/cgi-bin/nuke.php

It doesn't have surface detonation, but at 250m with a 10MT warhead you're looking at 22m of armor vaporized. Given the sheer amount of energy released by that and the accompanying impulse shock I expect that the blast will puncture the shell. At an impact detonation you would probably see full vaporization through the entire depth.

For steel you'd have to average the elemental composition together for the respective values required by the calculator.

...I'm not sure there's enough steel on Earth to make a *solid* shell that thick, if it's a sphere surrounding a space station or some such of even moderate size. I'm also not sure you'd even be able to get it into orbit in a timely fashion.

For a shell with an inner diameter of 500m and thickness of 50m that's just under annual steel production, which is about 1.5 billion tonnes. Prohibitively expensive but technically possible. I would suggest rock instead since it is in great abundance in space and is cheaper than steel.

[Eternal_Freedom]

Even if the blast doesn't completely puncture the shell wouldn't you get some pretty nasty spalling effects off the inner surface? Eve if those fragments don't directly hit the inner structure, they'll riccochet off the other side of the shell and back again. And some shockwaves etc through the rest of the shell too I would think.

I have a sneaky suspicion that if this were a good idea we'd have seen it present in hard SF somewhere. For defence against megaton-range missiles I think interceptors and point-defence are going to be far superior to armour.

Also, if your shell is around some important space station it will need openings in it to allow passage of stuff to and from the station, plus presumably some form of strutural connection to the station itself and station-keeping thrusters.

Finally, even if your massive armour shell can tank the nuclear hit, that's a whole lot of energy dumped into the shell, and that would mostly be x-rays/gamma rays IIRC for a nuke detonating in vacuum. Which (also) IIRC have a tendency to make metals very brittle. I think you'd also run the risks of having enough momentum imparted to the shell to push it into a decaying orbit.

[Imperial528]

Any feasible armor method would probably have it in separated plates, ideally spaced from each other both in distance from the origin and laterally along the "surface area" of the shell, bound together by an integrated flexible lattice. That way the shockwave present in one plate won't spread to the others and they will be thermally isolated as well. In a solid shell I expect the impulse shock would be enough to cause severe damage and warping across a large area from the hit, to say nothing of the secondary shocks and explosions from the iron plasma rapidly expanding in the wake of the blast.

[Eternal_Freedom]

No matter how good the armour might theoretically be, I'm pretty sure that an equivalent cost in mass and money of interceptor missiles, point-defence lasers/railguns/coilguns and associated tracking/fire control would be a much better defence for a major military space station.

The only thing I can think of where that isn't the case is if the main threat is kinetic-kill weapons. The OP stated low-megaton-range nukes, but if they have powerful enough rockets to put this station in orbit in the first place, then logically they could use that for hypervelocity impactors instead.

[Digi5]

Even a small nuclear weapon (15 kilotons) emits ~1000 watts per cm^2 from the surface of the fireball at 2 km. That's "acetylene torch" levels of energy, and will cut through metal in much the same way, over the second or two of that level of emission. Temperature within the fireball is in the millions of degrees, and the fireball can be as small as a few tens of meters to over a kilometer. If the fireball encompasses the thickness of the steel, it will almost certainly destroy any of the structure within it, since the structure in space is stuck with radiation as the only way of shedding heat energy, I'd think.

It's easy to get a sense of the sort of damage a nuke would do at distance when its intensity can be compared to day-to-day analogues. It's when it starts becoming ridiculous like petajoules per m^2 that asking what happens begets huge question marks, and a picture of what happens cannot necessarily be constructed by scaling up lower intensity events. If 1 MJ/m^2 would vaporize to x depth, 1 GJ/m^2 would not necessarily vaporize to 1000x depth.

There is something I'm unclear about regarding the nuclear fireball though. For large nuclear explosions the fireball can become over a km in diameter. It is also said that the temperature of the fireball can be millions of degrees. However, it would require >600 PJ to instantly heat a 1km sphere of air to 1 million degrees, which exceeds the energy of even the tsar bomb. So what I suspect is that only the very centre of the fireball reaches millions of degrees in temperature, and that the temperature drops of steeply with distance.

I plugged the data for iron into this calculator: http://www.5596.org/cgi-bin/nuke.php

It doesn't have surface detonation, but at 250m with a 10MT warhead you're looking at 22m of armor vaporized. Given the sheer amount of energy released by that and the accompanying impulse shock I expect that the blast will puncture the shell. At an impact detonation you would probably see full vaporization through the entire depth.

For steel you'd have to average the elemental composition together for the respective values required by the calculator.

Umm, for a 10 MT explosion I'm getting 68 cm of tungsten vaporized at 250m. 2.8 meters for carbon. The "armor thickness vaporized" is in mm, not cm.

The problem I have with that calculator is, while the numbers it outputs seem reasonable enough at large distances, it breaks down at very close detonations. For example, it states that a 10 MT detonation at 1 m will vaporize 42 km's of tungsten. This is probably because it assumes an even spread of the nuke's energy throughout the mass of material in its path -- which works well enough at shallow depths, but once the depths become deep enough you have to account for inefficiencies as the vaporized matter continually absorbs more radiation, while shielding the proceeding material somewhat. Which results in a temperature gradient through the material.

i.e., The first cm of material might be millions of degrees, but a few meter down it might not even be hot enough to melt.

No matter how good the armour might theoretically be, I'm pretty sure that an equivalent cost in mass and money of interceptor missiles, point-defence lasers/railguns/coilguns and associated tracking/fire control would be a much better defence for a major military space station.

The only thing I can think of where that isn't the case is if the main threat is kinetic-kill weapons. The OP stated low-megaton-range nukes, but if they have powerful enough rockets to put this station in orbit in the first place, then logically they could use that for hypervelocity impactors instead.

I envisioned the shell of armour being used in conjunction with point-defence systems. My reasoning was that a lightly armoured structure protected primarily by point-defence systems would be highly vulnerable to high-energy lasers which could not be intercepted, and hypervelocity kinetic weapons which would be much more difficult to intercept.

If the structure was enveloped by a thick shell, however, then it would be impervious to conventional weaponry, and the only way it could be destroyed would be with high-yield nuclear weapons, which simplifies the defence of the station. However, point-defence can be saturated, and so the armour still needs to be thick enough to stop the few that can get through.

[Imperial528]

My apologies, I had accidentally input 100MT. The proper result at 250m for a 10MT would be vaporization of the upper 2.2m of the shell. At 25m it gives a result of 22m vaporized. The calculator is indeed simplistic, but I think it gives an underestimate of the damage taken at face value as it doesn't account for secondary effects. The energy required to vaporize 172,000 cubic meters of iron will melt an order of magnitude more.

Also do remember that depending on the weapon design a large amount of radiation emitted may penetrate deeply into the material, such as gamma rays.

[Eternal_Freedom]

No matter how good the armour might theoretically be, I'm pretty sure that an equivalent cost in mass and money of interceptor missiles, point-defence lasers/railguns/coilguns and associated tracking/fire control would be a much better defence for a major military space station.

The only thing I can think of where that isn't the case is if the main threat is kinetic-kill weapons. The OP stated low-megaton-range nukes, but if they have powerful enough rockets to put this station in orbit in the first place, then logically they could use that for hypervelocity impactors instead.

I envisioned the shell of armour being used in conjunction with point-defence systems. My reasoning was that a lightly armoured structure protected primarily by point-defence systems would be highly vulnerable to high-energy lasers which could not be intercepted, and hypervelocity kinetic weapons which would be much more difficult to intercept.

If the structure was enveloped by a thick shell, however, then it would be impervious to conventional weaponry, and the only way it could be destroyed would be with high-yield nuclear weapons, which simplifies the defence of the station. However, point-defence can be saturated, and so the armour still needs to be thick enough to stop the few that can get through.

OK then. The point still stands however, you apparently have rocket engines powerful enough to loft arbitrarily high amounts of iron/steel into orbit and/or retrieve said iron from elsewhere int he solar system - which means you also have engines powerful enough to accelerate a smaller mass to a very high speed - say, enough to build a big coilgun to shoot this station out of the sky.

Also, are you familiar with Casaba Howitzer? It's a nuclear shaped charge, or a nuclear-powered plasma cannon, depending on how you look at it (I chose the latter as it sounds cooler). I would assume that anyone attacking this station would be able to build such a weapon rather than simple omnidirectional nukes, so your thick armour shell needs to become even thicker to protect against a given yield.

Finally, I am curious as to how you envision this structure being built. Are you saying you'll have a huge spherical armour shell that's isolated from the squishy innards, but also has point-defence systems, station keeping engines etc on the surface? Because having a gap between the armour and the innards seems unnecessary if you've got lots of stuff on the exterior that needs connections to the interior - ammo/power feeds for the weapons, data links for the same and tracking systems, fuel feeds for the thrusters, a method of transferring crew and cargo. All of those represent things that shock damage can and will disable, and if you're trying to tank megaton-range nukes, shock damage is something you'll have to deal with.

[jwl]

A 10 Mt explosion vaporising 42 km of tungsten is completely impossible. Assuming a spherical distribution, you're looking at least at 260 Tt from just the latent heat of evaporation.

Regarding kinetic weapons, just because you have extremely powerful kinetic weapons doesn't mean your opponent does. Also, the base could be something like a geostationary satellite launched from a space elevator, which wouldn't be conductive towards launching kinetic weapons to geostationary orbit (but could work on firing them at lower orbits or the ground).

[Formless]

You are all forgetting a critical problem here: if this detonation goes off in the vacuum of space, there will be no fireball and no shockwave. Just a sudden and very intense flash of gamma rays and alpha particles that irradiates your target, potentially vaporizing material that is close enough (but that is very close, and point defense might shoot down such a missile). There may also be an EMP, depending on how close the blast is to Earth's upper atmosphere. But that's it, and that leads to a completely different set of considerations than the OP and several other posters here have assumed.

There is a device that has been mentioned which would be far better suited for the task at hand, however:

Also, are you familiar with Casaba Howitzer? It's a nuclear shaped charge, or a nuclear-powered plasma cannon, depending on how you look at it (I chose the latter as it sounds cooler). I would assume that anyone attacking this station would be able to build such a weapon rather than simple omnidirectional nukes, so your thick armour shell needs to become even thicker to protect against a given yield.

Actually, the Howitzer can take on a number of forms besides just the classical plasma blaster or particle cannon types. In fact, a true particle cannon might be possible if you can magnetically confine the emitted radiation for the brief moment that it goes off, but I can't imagine why you would want to do that when you can also make bomb-pumped x-ray lasers much more easily. But that's beside the point, lets talk about nuclear-kinetic weapon hybrids. This is what you want to crack open fortresses or bombard low atmosphere planets with (such as Luna and Mars). For instance, you can take advantage of the Munroe effect and use it like a souped up conventional shaped charge that skewers the target with a lance of pliable semi-liquefied metal. Another alternative, which actually originates from the US military (because of course they've considered this concept for real warheads) is a shaped nuclear explosive projectile or shotgun blast of projectiles. Basically, think of Project Orion. Now think of a one-time sacrificial pusher plate that you fire at the target with a nuclear shaped charge. Alternative designs call for barrels made of plastic for shooting smaller bullets at more conventionally sized spacecraft. The resulting projectile or projectiles could be fired at speeds in excess of 100 km per second.

For deeply penetrating or destroying a target such as this one with a nuke, assuming that radiation is somehow insufficient to soft kill the target you should probably consider the shaped penetrator or the shaped projectile type Howitzers depending on how close you expect to be able to get the bomb to the structure. A plasma lance against a target with an iron shell "tens of meters thick" would probably just push it backwards like Project Orion intended for them to do. The situation basically describes a nuclear rocket burning against a nickle iron asteroid * for, oh, a tenth of a second or so. If this is anything like regular shaped charges, then the lance design will have better penetrating characteristics at very close distances, but the projectile will be useful from waaaaaaay farther away (again, hundreds of kilometers with little chance of point defense being able to react). I would prefer the projectile launcher personally, because there will be structural damage beyond just the penetration such as cracking of the space station's metal shell that could extend far beyond the crater, and vibration could destroy interior structures that are shock sensitive. You don't have to put a hole in it to crack it open, but you may decide otherwise if you have some plot for getting a bomb up to point blank range despite point defenses. At that point, you might not even need a thermonuclear device to get the job done. Either way, I'm sure there is more information out there for cratering effects due to impact of arbitrary sized projectiles than from nuclear devices. Especially nuclear devices in space.

---

* In fact, if you want to be gracious to the OP its most probable that such a fortress would be constructed by hollowing out a large captive metallic asteroid. This could even pay for itself by using the extracted ore in other projects. There. Your construction problem is solved, but I doubt you would leave such a massive structure in a close orbit with Earth. You could very well use it to end all life on Earth simply by dropping the damn thing on a continent.

[Imperial528]

You are all forgetting a critical problem here: if this detonation goes off in the vacuum of space, there will be no fireball and no shockwave. Just a sudden and very intense flash of gamma rays and alpha particles that irradiates your target, potentially vaporizing material that is close enough (but that is very close, and point defense might shoot down such a missile). There may also be an EMP, depending on how close the blast is to Earth's upper atmosphere. But that's it, and that leads to a completely different set of considerations than the OP and several other posters here have assumed.

This is a nitpick but I have been working from the vacuum perspective the entire time; the calculator I offered presumes a vacuum. I have only brought up impulse shock, which would occur given any particularly energetic impact or blast or radiation burst affecting the material.

The calculator can also somewhat simulate Casaba-esque shaped weapons by changing the weapon shape parameter in steradians.

A 10 Mt explosion vaporising 42 km of tungsten is completely impossible. Assuming a spherical distribution, you're looking at least at 260 Tt from just the latent heat of evaporation.

This is a limitation of the calculator as the closer distances make the assumptions behind the math break down. Above 100m detonation distance it seems to work just fine.

For those looking for estimates of radiation exposure, there is this calculator (http://web.archive.org/web/200702050843 ... /nukes.xls) that runs in excel. It is meant for atmospheric detonations but has a page on radiation-optimized warheads.

I should note to the OP that all such calculators will be simplistic, and they will all break down at extremes, because it is very difficult to predict the exact effects of a nuclear weapon, especially in a vacuum. There's a lot of math involved and assumptions that don't always hold true depending on the situation, which can be hard to take into account.

If you have the educational background you're welcome to put together a better calculator, but as far as the "people whose hobby consists of designing spaceships that lob nukes at each other" this is the best I've been able to find other than rules of thumb and simple magnitude estimations.

[Sea Skimmer]

I had an idea for this large military space installation that was protected by a thick shell of steel at a stand-off from the main structure. The shell would be meters to tens of meters thick.

I wanted to estimate just how thick it would need to be to resist multi-megaton nuclear surface detonations, but I'm at a loss as to how to approach the problem. The only things I found through google regarding cratering were for buried explosions in soil and sand.

1 thick layer will just never work, well not unless by tens of meters you mean tens of tens of meters, then sure. The shock effect would just blow off the back and gut the station anyway. It's not enough to just stop the radiation, you've got to deal with all of the nuclear energy somehow, an enormous amount of tungsten doped fiberglass might give better results then steal for example, in part simply because it would be thicker for the mass, and standoff matters. As does progressive energy absorption.

For a practical effect you'd want a lot of layers and void spaces and crumple zones, in fact ideally you would completely flood the space between two steel layers with water, and have nothing but the water pressure connecting the two halves around the entire shell of the station. This would require expansion joints and similar fiddly bits, but I mean, yeah I hope we can make that work if were even dreaming of building this. This would then mean the entire interior is protected by a passive water shock absorber.

I tried referencing real world tests, such as the Castle Bravo (15 Mt) and Ivy Mike (10.4 Mt) tests. The Castle Bravo detonation left a crater 2 km wide and 76 m deep. The Ivy Mike detonation left a crater 1.9 km wide and 50m deep. However, those craters were formed out of soil and rock, and I'm not sure how they would scale with metals. One thing that stands out to me is that nuclear detonations leave very shallow craters relative to their width.

It varies with yield, and the underlying rock strata, the layers of which tend to refract the blastwave back upwards, which also forces it further out. But generally crater size and volume doesn't scale up rapidly with yield because no matter how big the yield is the original nuclear burst still happened at just one point no more then a few feet across. So sure the yield is high, but it takes a while for all that energy to radiate out, and the fireball is basically just wasting most of it being hot for a couple minutes, in a place where everything was already destroyed.

Also nuclear craters actual damage depth is much greater then the apparent crater. Firstly because a lot of debris fall back into the crater, including boulders that might weigh hundreds of tons, and secondly because a large zone of plastic deformation will exist past the true crater limit that's been buried by debris. This is all true of high explosive induced craters too. If you bury a nuke slightly it will make a crater about the same width and depth.

To put a number to it: How deep would the crater be if a 10 Mt nuclear explosion detonated on a 50 meter thick steel structure?

It would blow the whole thing in over a considerable radius I'd reckon. The tamping effect of the direct hit would be tremendous against solid metal. How wide the hole will be would depend on how its actually built, actually pouring a 50m thick slab would be both less then ideal and basically implausible with any amount of technology because of how absurdly long you would have to wait to sloooowly let the plate cool at the foundry when you made it. Something like a metal honeycomb made from six inch thick plates would be more effective at holding up. Notional solid metal this thick though certainly would resist say, a 10kt nuke with no problem.

[Digi5]

Finally, I am curious as to how you envision this structure being built. Are you saying you'll have a huge spherical armour shell that's isolated from the squishy innards, but also has point-defence systems, station keeping engines etc on the surface? Because having a gap between the armour and the innards seems unnecessary if you've got lots of stuff on the exterior that needs connections to the interior - ammo/power feeds for the weapons, data links for the same and tracking systems, fuel feeds for the thrusters, a method of transferring crew and cargo. All of those represent things that shock damage can and will disable, and if you're trying to tank megaton-range nukes, shock damage is something you'll have to deal with.

The outer shell is completely separate from the internal station. They each have their own engines, power supply, staff, etc. The station simply maintains its position within the cavity of the shell, which itself is mostly empty, and can accommodate a limited number of other ships within itself. The purpose of the station would be a military headquarters, housing high-ranking staff.

There are asteroids such as 16 Psyche within the asteroid belt that are composed primarily of nickel and iron. Such asteroids should provide the bulk of materials necessary for the construction of the shell. Excavation and construction would be on-site within vicinity of the asteroid, which should should minimize the mass of materials that needs to be sourced from elsewhere. The final orbit of the shell is heliocentric between Earth and Mars, and since it was constructed within the asteroid belt, the delta-v required to get it to its orbit shouldn't be too much -- although admittedly, the actual energy and reaction mass required would be quite immense due to its mass.

However, the setting is in the distant future. No FTL travel, but with prolific colonization of the solar system in the form of space colonies, centuries long terraforming of planets, prolific construction of electromagnetic space-launch systems, as well as cheap and abundant fusion power. So they would presumably not be strangers to large undertakings.

Actually, the Howitzer can take on a number of forms besides just the classical plasma blaster or particle cannon types. In fact, a true particle cannon might be possible if you can magnetically confine the emitted radiation for the brief moment that it goes off, but I can't imagine why you would want to do that when you can also make bomb-pumped x-ray lasers much more easily. But that's beside the point, lets talk about nuclear-kinetic weapon hybrids. This is what you want to crack open fortresses or bombard low atmosphere planets with (such as Luna and Mars). For instance, you can take advantage of the Munroe effect and use it like a souped up conventional shaped charge that skewers the target with a lance of pliable semi-liquefied metal. Another alternative, which actually originates from the US military (because of course they've considered this concept for real warheads) is a shaped nuclear explosive projectile or shotgun blast of projectiles. Basically, think of Project Orion. Now think of a one-time sacrificial pusher plate that you fire at the target with a nuclear shaped charge. Alternative designs call for barrels made of plastic for shooting smaller bullets at more conventionally sized spacecraft. The resulting projectile or projectiles could be fired at speeds in excess of 100 km per second.

Casaba Howitzers are something that gets brought up a lot when it comes to nuclear weapons. However, considering that the original concept was highly hypothetical and much of the information on it are still classified, it's unclear whether it not it actually works. This page would suggest that experiments were not so successful. Maybe. The author isn't really sure either.

As for nuclear shaped charges similar in principle to conventional shaped charges, wouldn't that require the weapon to be extraordinarily bulky? My understanding is that in a nuclear shaped charge the wavefront of the explosion is shaped to collapse a liner and accelerate it to high velocities. However, that would necessitate that the intensity is low enough to not just vaporize the liner, which requires distance.

1 thick layer will just never work, well not unless by tens of meters you mean tens of tens of meters, then sure. The shock effect would just blow off the back and gut the station anyway. It's not enough to just stop the radiation, you've got to deal with all of the nuclear energy somehow, an enormous amount of tungsten doped fiberglass might give better results then steal for example, in part simply because it would be thicker for the mass, and standoff matters. As does progressive energy absorption.

For a practical effect you'd want a lot of layers and void spaces and crumple zones, in fact ideally you would completely flood the space between two steel layers with water, and have nothing but the water pressure connecting the two halves around the entire shell of the station. This would require expansion joints and similar fiddly bits, but I mean, yeah I hope we can make that work if were even dreaming of building this. This would then mean the entire interior is protected by a passive water shock absorber.

Would multiple thin layers spaced apart be a significant improvement over a single thick layer? For example, instead of one 50m layer you have 10 5m layers spaced 5m apart. Spaced armour tends to be effective against projectiles, but I wondered if it would just be a liability against nukes. My decision to use steel was because iron is relatively abundant in the solar system in comparison to elements like tungsten. Although I wonder if steel production is really worth it, or if it would be better to just use iron.

The water filler for the armour is a good idea though.

It would blow the whole thing in over a considerable radius I'd reckon. The tamping effect of the direct hit would be tremendous against solid metal. How wide the hole will be would depend on how its actually built, actually pouring a 50m thick slab would be both less then ideal and basically implausible with any amount of technology because of how absurdly long you would have to wait to sloooowly let the plate cool at the foundry when you made it. Something like a metal honeycomb made from six inch thick plates would be more effective at holding up. Notional solid metal this thick though certainly would resist say, a 10kt nuke with no problem.

Are you saying the explosion would blow a hole through the steel structure through mechanical stress? In a similar fashion that conventional explosions blow a hole through a brick wall? Of course, I always assumed that some degree of mechanical damage would occur due to shock effects, but I also assumed that the primary damage mechanism would be thermal in nature.

So a metal honeycomb totally 50m in thickness would only be able to resist nukes in the low kt range? I admit I didn't expect it to be that low.

[Patroklos]

On the nuclear shaped charge, the liner (by which I assume you mean the X-ray opaque casing)only has to exist a few milliseconds longer than the channel filler, which in turn only has to last as long as whatever you are using for the jet material which is often tungsten in my reading.

Essentially you have a nuke surrounded by a shell of said X-ray opaque material. Nuke explodes and the casing forces all the X-rays through a hole in the casing with a channel filler like berrilyum. Result is heat, which then encounters the tungsten which is turned into a plasma jet and sent towards your target.

The practical issues with this is the jet has relatively low velocity and a significant dispersion angle. There are theoretical ways to improve both and this is where the arguing starts.

On another note, encountering such a think hunk of steel in space is just begging for some bremsstrahlung action. Fire up the particle beams!

[Digi5]

On the nuclear shaped charge, the liner (by which I assume you mean the X-ray opaque casing)only has to exist a few milliseconds longer than the channel filler, which in turn only has to last as long as whatever you are using for the jet material which is often tungsten in my reading.

Essentially you have a nuke surrounded by a shell of said X-ray opaque material. Nuke explodes and the casing forces all the X-rays through a hole in the casing with a channel filler like berrilyum. Result is heat, which then encounters the tungsten which is turned into a plasma jet and sent towards your target.

The practical issues with this is the jet has relatively low velocity and a significant dispersion angle. There are theoretical ways to improve both and this is where the arguing starts.

On another note, encountering such a think hunk of steel in space is just begging for some bremsstrahlung action. Fire up the particle beams!

No, I was referring to something a bit different than the classical description of a Casaba Howitzer. An alternative method of directing the energy of a nuclear explosion is to utilize wave shaping to produce a jet of material in a similar fashion as conventional shaped charges. Although it requires something inbetween the nuclear charge and the liner to act as a working fluid.


I am highly sceptical of this description of Casaba Howitzers on project rho, however:

Remember that in the vacuum of space, most of the energy of a nuclear warhead is in the form of x-rays. The nuclear device is encased in a radiation case of x-ray opaque material (uranium) with a hole in the top. This forces the x-rays to to exit only from the hole. Whereupon they run full tilt into a large mass of beryllium oxide (channel filler).

The beryllium transforms the nuclear fury of x-rays into a nuclear fury of heat. Perched on top of the beryllium is the propellant: a thick plate of tungsten. The nuclear fury of heat turns the tungsten plate into a star-core-hot spindle-shaped-plume of ionized tungsten plasma. The x-ray opaque material and the beryllium oxide also vaporize a few microseconds later, but that's OK, their job is done.

The tungsten plasma jet hits square on the Orion drive pusher plate, said plate is designed to be large enough to catch all of the plasma. With the reference design of nuclear pulse unit, the plume is confined to a cone of about 22.5 degrees. About 85% of the nuclear device's energy is directed into the desired direction, which I think you'd agree is a vast improvement over 1%.

It seems to imply that in a Casaba Howitzer, the radiation case of uranium is able to somehow deflect all the x-rays towards the beryllium oxide filler, resulting in a transference of the vast majority of the nuke's energy into the resulting plasma jet.

First of all, the thin uranium case could not deflect the intense amount of x-rays produced by the nuclear detonation with such frightening efficiency. If it could, all you'd have to do is coat your spacecraft in uranium and it'd suddenly have incredible resistance to nukes in space, as it could bounce most of the x-rays impacting it harmlessly off into space. The uranium would absorb most of the x-rays and be vaporized very quickly.

There is also the matter of thermodynamic losses throughout each step of process from nuclear detonation to plasma jet. A certain percentage of the x-rays and other particles produced by the nuclear detonation will be absorbed by the beryllium oxide, which then has to heat up the tungsten or whatever you're using for your jet.

It probably works in the sense that it'll produce a jet of plasma. It's also probable that it's more efficient than the original Orion Drive where the radiation of a nuclear detonation is made to directly impart momentum onto a pusher plate. However, the resulting will still only contain a small percentage of the nuke's energy. 85% efficiency is completely insane.

[Sea Skimmer]

Casaba Howitzers are something that gets brought up a lot when it comes to nuclear weapons. However, considering that the original concept was highly hypothetical and much of the information on it are still classified, it's unclear whether it not it actually works. This page would suggest that experiments were not so successful. Maybe. The author isn't really sure either.

They definitely work, and it would basically break physics if they didn't, its only a materials choice and WTF are you trying to do issue. The actual point is limited given mans proven ability to build literally tens of thousands of warheads for the shit of it and put hundreds of them on a single mobile platform. A high explosive shaped charge isn't going to couple more then 50% of the energy into the jet, and its going to be much less with any viable fission-fusion design (pure fusion would be much easier) and if you've already achieved skin-skin contact with a nuclear warhead your going to hit it with most of that energy anyway over a slightly larger radius. But that's also sensitive to actual weapon geometry, since on a missile or free ball bomb the actual nuke isn't literally in the nose, its at least a few feet back.

Conversely just a few feet of penetration make a nuke something silly like 9 times more effective against bunkers then a placed on the surface burst. The end effects are very sensitive to the original conditions, and that issue that the nuke blast always begins at one point.

That's also just a reason to fire multiple warheads. What are we morons? Shoot more!

As for nuclear shaped charges similar in principle to conventional shaped charges, wouldn't that require the weapon to be extraordinarily bulky? My understanding is that in a nuclear shaped charge the wavefront of the explosion is shaped to collapse a liner and accelerate it to high velocities. However, that would necessitate that the intensity is low enough to not just vaporize the liner, which requires distance.

The way the nuclear shaped charge works is you surround the warhead with a material that absorbs X-rays and then reemitts its own X-rays when that causes it to nuclear induced combust violently, and those X-rays are channeled into your flyer plate style shaped charge warhead. Except the flyer plate gets vaporized too, but the mass, and that's important, is indeed projected into a warhead jet. Notionally narrow jet type cones WOULD be possible with a nuclear shaped charge, but if you understand the actual different roles of flyer plates vs jets vs EFP slug styles it comes down to the nuclear-jet having no actual point. Because nothing is going to exist that can directly withstand any of these when propelled by an ATOMIC BOMB that also unleashed a cloud of fast neutrons to further weaken any nearby material.

So you'd functionally just use a flyer plate with little or no angle if you want a standoff attack. At skin-skin range it's not going to make a huge amount of difference, not at megaton yields. The most lethal type of warhead would be a nuke that penetrates just a few feet into the target, accepting deep penetration as unlikely due to the gee shock involved. But if the warhead core is already within the target the result will pretty much be a crater in metal just like you'd get a damn crater in rock from a surface burst.

Would multiple thin layers spaced apart be a significant improvement over a single thick layer? For example, instead of one 50m layer you have 10 5m layers spaced 5m apart.

Yes. But remember if you still have 50m thick armor, your total armor envelope is now much bigger, because those outside layers cover more area, so the total armor mass will go up a lot. But even without allowing mass increase spaced armor will work better. Honestly if you look at all the armor in history, its pretty common to use composite and layered armors. That includes warship armoring, belt and deck protection commonly used layers for maximum effect, and ironclads all used huge amounts of wooden backing for their iron armor precisely to spread and absorb shock. Otherwise all the iron bolts would break even if the armor plates did not fail at all. Tanks started using spaced armor in 1941 and never stopped since.

Spaced armour tends to be effective against projectiles, but I wondered if it would just be a liability against nukes. My decision to use steel was because iron is relatively abundant in the solar system in comparison to elements like tungsten. Although I wonder if steel production is really worth it, or if it would be better to just use iron.

For the trouble it would take to make the iron it would be silly not to directly convert it into steel, obtaining the needed carbon in space isn't going to be the problem. Too many other activities will already be generating a carbon surplus.

Iron would also greatly increase the chance of remote parts of the station simply cracking up from the hit. Close in to the blast, yeah, be about the same resistance steel can ever hope to offer. Also neither is a good neutron absorberr in a basic form, but you could alloy in materials which are.

The downside of spaced armor is the outer layers can be damaged easier. So what you want is a somewhat stronger outer face, and then a large number of thinner layers, then whatever your inner citadel structure is, which is going to need some kind of shock insulation to have any chance of not just killing everyone human inside from the shockwave transmitting through the structure.

Are you saying the explosion would blow a hole through the steel structure through mechanical stress?

Yeah. At 10 megatons it'd probably do so. Steel is worth a lot more then rock, but not that much more. And even if it didn't make a full hole it'd certainly crater it, and backspall it, because steel by nature is not able to distort enough over the scale required to absorb that kind of force instantaneously. This is the giant flaw of one thick piece of armor, all failure is focused on the backface. This tends to want to cause the whole thing to shear when that shockwave refracts back.

IN real life when you overmatch armor enough, it just massively fails. This is a velocity dependent thing. The slowest things the fission nuke releases move at over a thousand times the velocity of any high explosive detonation. Every time an atom splits in fission your getting some heavy fragments and two or three neutrons moving at that kind of speed, some much faster. Those mass carrying particles are devastating close in. That's why they can ignite fusion in the first place! Fusion boosting doesn't add fission fragments naturally, but it releases a higher percentage of energy in neturons in the first place.

In a similar fashion that conventional explosions blow a hole through a brick wall? Of course, I always assumed that some degree of mechanical damage would occur due to shock effects, but I also assumed that the primary damage mechanism would be thermal in nature.

Nope, nuclear weapons don't release much energy directly as heat. Ina fission explosion most of the original energy release, 80% IIRC, is released as kinetic energy of the fission fragments. Only a tiny amount is released as instantaneous gamma rays, which in an atmosphere will quickly start turning into heat. Everything else has some kind of physical mass and either needs to decay from striking atmosphere or its own instability, or will go on to sustain the chain-reaction in the case of some of the fission neutrons. Fusion energy is released differently, but still creates mass carrying debris. I a high yield fission-fusion bomb the official rule of thumb is 90% of energy is from fusion.

The whole reason a nuclear fireball forms from an atmopsheric burst is all the neutron radiation and fission fragments aren't going all that far before they are stopped and decay, making more and more heat and gamma rays in a concentrated area. In space that doesn't happen, so it's all going to hit the target together with maximum intensity possible.

You really don't want to get hit like that.

So a metal honeycomb totally 50m in thickness would only be able to resist nukes in the low kt range? I admit I didn't expect it to be that low.

I'm somewhat it could resist that and suitable structure under it would survive with people not dead. What it's upper limit would be for protecting against 'several' higher yield hits, I dunno, it wouldn't be amazing though.

I can't see 50m of anything solid doing jack to absorb the shock wave effect of a megaton nuke.. Cheyenne Mountain is under 2000ft of granite, and still not expected to withstand any high yield direct hit on the mountain, and that's with everything inside shock mounted on springs that weigh a thousand pounds each. That ring you get from tapping on metal? Even if it didn't fail a 50m plate is just going to vibrate like that, at nuclear blast intensity.

A huge amount of water + voids strikes me as being a much better idea, but basically anything is better then being solid unless you are in fact thousands of feet thick. Hollowing out existing space rocks is really the way to go if you can find suitable ones at that point, you can start the tunneling work while your still moving them into the desired orbit.

Also realistically if anyone is going to fire something as big as 10 megaton bomb in the first place they'd probably make it even bigger in turn. It does not strike me as a good design point limit for a super expensive space installation. What if the enemy sends a 35 megaton bomb? Still not three stages but way more powerful yet again.