Sounds interesting—the main point is that I don’t think you can hit the reentry vehicle because of turbulent jitter caused by the atmosphere. Looks like normal jitter is ~10m which means a small drone can’t hit it. So could the drone explode into enough fragments to guarantee a hit and with enough energy to kill it? Not so sure about that. Seems less likely. Then what about countermeasures − 1. I expect the ICBM can amplify such lateral movement in the terminal phase with grid fins etc without needing to go full HGV—can you retrofit such things? 2. What about a chain of nukes where the first one explodes 10km up in the atmosphere purely to make a large fireball distraction. The 2nd in the chain then flies through this fireball 2km from its center say 5 seconds later. (enough to blind sensors but not destroy the nuke) The benefit of that is that when the first nuke explodes, the 2nd changes its position randomly with its grid fins SpaceX style. It is untrackable during the 1st explosion phase so throws off the potential interceptors, letting it get through. You could have 4-5 in a chain exploding ever lower to the ground.
Interesting thought, Thomas. Although I agree with RussellThor that it seems like doing something along the lines of “just jitter the position of the RV using little retrofitted fins / airbrakes” might be enough to defeat your essentially “pre-positioned / stationary interceptors”. (Not literally stationary, but it is as if they are stationary given that they aren’t very maneuverable relative to the speed of the incoming RV, and targeted only based on projected RV trajectories calculated several minutes earlier.)
(Is the already-existing atmospheric turbulence already enough to make this plan problematic, even with zero retrofitting? The circular-error-probable of the most accurate ICBMs is around 100 meters; presumably the vast majority of this uncertainty is locked in during the initial launch into space. But if atmospheric drag during reentry is contributing even a couple of those meters of error, that could be a problem for “stationary interceptors”.)
Failing all else, I suppose an attacker could also go with Russell’s hilarious “nuke your way through the atmosphere” concept, although this does at least start to favor the defender (if you call it favorable to have hundreds of nukes go off in the air above your country, lol) insofar as the attacker is forced to expend some warheads just punching a hole through the missile defense—a kind of “reverse MIRV” effect.
Regardless, you still face the geography problem, where you have to cover the entire USA with Patriot missile batteries just to defend against a single ICBM (which can choose to aim anywhere).
I would also worry that “in the limit of perfect sensing” elides the fact that you don’t JUST have to worry about getting such good sensing that you can pin down an RV’s trajectory to within, like, less than a meter? (In order to place a completely dumb interceptor EXACTLY in the RV’s path. Or maybe a few tens of meters, if you’re able to put some sensors onto your cheap interceptor without raising the price too much, and make use of what little maneuverability you have versus the RV?) You ALSO have to worry about distinguishing real warheads from fake decoys, right? Sorting out the decoys from the warheads might be even harder than exactly pinning down an RV’s trajectory.
According to a random redditor, apparently today’s decoys are “inflatable balloons for exoatmospheric use and small darts for in-atmosphere”, plus “radio jammers, chafe, and other things designed to confuse enemy detection. With better and better sensing, maybe you could force an attacker to up their decoy game, retrofitting their missiles to use fewer, more lifelike decoys, maybe even to such an extreme extent that it’s no longer really worth using decoys at all, compared to just putting more MIRV warheads on each missile? But if decoys still work, then you need that many more interceptors.
“In the limit of perfect sensors” (and also perfectly affordable sensors), with perfect interception (against non-retrofitted, non-HGV missiles) and perfect decoy discrimination, I suppose it becomes a defense-economics balance where you are hoping that the cost of lots of small rockets is cheaper than the cost of the attacking ICBM system. These small rockets don’t have to be super fast, don’t have to go super high, and don’t have to be super maneuverable. But they do have to be precise enough to maneuver to an exact precalculated location, and you need enough of them to blanket essentially your entire country (or at least all the important cities). You are basically relying on the fact that the ICBM has to be super big and heavy to launch a significant payload all the way around the earth, while the numerous small missiles only have to fly a couple of kilometers into the sky.
Final, dumbest thought saved for last: Aside from developing HGVs, couldn’t the ICBMs in theory overcome this defense with brute scale, by MIRV-ing to an an absurd degree? How many warheads can dance on the head of a Starship? Could you just put the entire US nuclear arsenal on a single launcher? The cost of your ICBM would essentially be zero when amortized over all those warheads, so the defense economics battle just becomes the cost of warheads vs patriots, instead of entire ICBMs vs patriots. Obviously there are many reasons why this idea is nuts:
I’m not sure how far apart different MIRVs can land, so this technique might be limited to attacking individual cities / clusters of silos.
Of course if you put your entire arsenal on one launcher, then your enemy will immediately forget about interceptors and spend all their efforts trying to sabatoge your launcher.
Going for a strategy of “we can mass-manufacture warheads cheaper than you can possibly intercept them” would quickly lead to absurd, overkill numbers of warheads that would dwarf even the most insane years of the Cold War, practically guaranteeing that any actual nuclear war would end in the classic “nobody wins” scenario of global devastation (nuclear winter, etc).
But I thought it was kind of funny to think about, and this absurd thought experiment maybe sheds some light on the underlying dynamics of the situation.
Re the dumb thought. I’ve forgotten the author, but as a teenager I was a big SciFi fan (still am actually) and read a short story with exactly this theme. Basically it was the recognition that at some point quantity >= quality. I want to say (have not fact checked myself though) that this was pretty much the USSR’s approach to fighting Germany in WWII—crappy tanks but lots of them.
(Side note, I think for whatever reason, too long a peacetime, more interest in profit than protection, the USA particularly seems to have forgotten that the stuff you use to wage a war are largely all consumables. The non consumable is the industrial base. Clearly there is a minimum cost of producing something that can do the job but much more than that is sub optimal. I am somewhat over simplifying but this also seems to be a fair characterization of where the USA-China naval relationship might be.)
Back to ICBMs, Foreign Affairs had a piece about AI’s potential impact on nuclear deterrence in general but did mention the fixed location of ICBM silos as a problem (long known and why everyone has mobile platforms). They might be considered a prime target for a first strike but the reality is they are easily monitored so the mobile platforms are the big deterrents and probably more interesting problem to solve in terms of obsoleting. But perhaps the ICBM platforms, fixed or mobile, shift to a different type role. Pure kinetic (I believe Russia did that with one of the ballistic warheads with pretty devastating results in Ukraine about a year ago) or rather than all the MIRV decoys for the armed MIRV decoys and other function for other delivery vehicles. I suspect the intercept problem with a nuclear warhead is a bit different from that of just a big mass of something dense.
So maybe perhaps obsolescence in their current function but not for some repurposed role.
Against atmospheric jitter, we have historically used ground radar, but it’s not clear to me this is even necessary depending on how much drone cameras improve. If the drone knows the exact position within 3 meters 0.5 second ahead of time (when the warhead is something like 2 km away), it won’t have enough performance to steer into the warhead, but it can throw a 1 kg explosively formed penetrator laterally at 2 km/s, which it would need to time with 0.1 ms accuracy. This would put 100 grams in each possible 1 m^2 cross section, though I’m not sure if it would work when spread out. To defeat this the warhead would either have to steer in the upper atmosphere out of range of the EFP of any available drone, or jink faster than the EFP can aim.
I thought that MIRVs were spin stabilized, but it looks like that’s not true, so in theory you could mount grid fins on them. However, any retrofit would need to handle the reentry heating which is significantly more intense than on manned spacecraft; RVs have thick ablative heat shields.
The chain of nukes plan seems possible with or without grid fins, so whether MIRVs still have cost advantage depends on the max altitude of cheap-ish terminal interceptors, which I really have no idea about.
I would expect aerodynamic maneuvering MIRVS to work and not be prohibitively expensive. The closest deployed version appears to be https://en.wikipedia.org/wiki/Pershing_II which has 4 large fins. You likely don’t need that much steering force
Sounds interesting—the main point is that I don’t think you can hit the reentry vehicle because of turbulent jitter caused by the atmosphere. Looks like normal jitter is ~10m which means a small drone can’t hit it. So could the drone explode into enough fragments to guarantee a hit and with enough energy to kill it? Not so sure about that. Seems less likely.
Then what about countermeasures −
1. I expect the ICBM can amplify such lateral movement in the terminal phase with grid fins etc without needing to go full HGV—can you retrofit such things?
2. What about a chain of nukes where the first one explodes 10km up in the atmosphere purely to make a large fireball distraction. The 2nd in the chain then flies through this fireball 2km from its center say 5 seconds later. (enough to blind sensors but not destroy the nuke) The benefit of that is that when the first nuke explodes, the 2nd changes its position randomly with its grid fins SpaceX style. It is untrackable during the 1st explosion phase so throws off the potential interceptors, letting it get through. You could have 4-5 in a chain exploding ever lower to the ground.
I have wondered if railguns could also stop ICBM—even if the rails only last 5-10 shots that is enough and cheaper than a nuke. Also “Brilliant pebbles” is now possible.
https://www.lesswrong.com/posts/FNRAKirZDJRBH7BDh/russellthor-s-shortform?commentId=FSmFh28Mer3p456yy
Interesting thought, Thomas. Although I agree with RussellThor that it seems like doing something along the lines of “just jitter the position of the RV using little retrofitted fins / airbrakes” might be enough to defeat your essentially “pre-positioned / stationary interceptors”. (Not literally stationary, but it is as if they are stationary given that they aren’t very maneuverable relative to the speed of the incoming RV, and targeted only based on projected RV trajectories calculated several minutes earlier.)
(Is the already-existing atmospheric turbulence already enough to make this plan problematic, even with zero retrofitting? The circular-error-probable of the most accurate ICBMs is around 100 meters; presumably the vast majority of this uncertainty is locked in during the initial launch into space. But if atmospheric drag during reentry is contributing even a couple of those meters of error, that could be a problem for “stationary interceptors”.)
Failing all else, I suppose an attacker could also go with Russell’s hilarious “nuke your way through the atmosphere” concept, although this does at least start to favor the defender (if you call it favorable to have hundreds of nukes go off in the air above your country, lol) insofar as the attacker is forced to expend some warheads just punching a hole through the missile defense—a kind of “reverse MIRV” effect.
Regardless, you still face the geography problem, where you have to cover the entire USA with Patriot missile batteries just to defend against a single ICBM (which can choose to aim anywhere).
I would also worry that “in the limit of perfect sensing” elides the fact that you don’t JUST have to worry about getting such good sensing that you can pin down an RV’s trajectory to within, like, less than a meter? (In order to place a completely dumb interceptor EXACTLY in the RV’s path. Or maybe a few tens of meters, if you’re able to put some sensors onto your cheap interceptor without raising the price too much, and make use of what little maneuverability you have versus the RV?) You ALSO have to worry about distinguishing real warheads from fake decoys, right? Sorting out the decoys from the warheads might be even harder than exactly pinning down an RV’s trajectory.
According to a random redditor, apparently today’s decoys are “inflatable balloons for exoatmospheric use and small darts for in-atmosphere”, plus “radio jammers, chafe, and other things designed to confuse enemy detection. With better and better sensing, maybe you could force an attacker to up their decoy game, retrofitting their missiles to use fewer, more lifelike decoys, maybe even to such an extreme extent that it’s no longer really worth using decoys at all, compared to just putting more MIRV warheads on each missile? But if decoys still work, then you need that many more interceptors.
“In the limit of perfect sensors” (and also perfectly affordable sensors), with perfect interception (against non-retrofitted, non-HGV missiles) and perfect decoy discrimination, I suppose it becomes a defense-economics balance where you are hoping that the cost of lots of small rockets is cheaper than the cost of the attacking ICBM system. These small rockets don’t have to be super fast, don’t have to go super high, and don’t have to be super maneuverable. But they do have to be precise enough to maneuver to an exact precalculated location, and you need enough of them to blanket essentially your entire country (or at least all the important cities). You are basically relying on the fact that the ICBM has to be super big and heavy to launch a significant payload all the way around the earth, while the numerous small missiles only have to fly a couple of kilometers into the sky.
Final, dumbest thought saved for last:
Aside from developing HGVs, couldn’t the ICBMs in theory overcome this defense with brute scale, by MIRV-ing to an an absurd degree? How many warheads can dance on the head of a Starship? Could you just put the entire US nuclear arsenal on a single launcher? The cost of your ICBM would essentially be zero when amortized over all those warheads, so the defense economics battle just becomes the cost of warheads vs patriots, instead of entire ICBMs vs patriots. Obviously there are many reasons why this idea is nuts:
I’m not sure how far apart different MIRVs can land, so this technique might be limited to attacking individual cities / clusters of silos.
Of course if you put your entire arsenal on one launcher, then your enemy will immediately forget about interceptors and spend all their efforts trying to sabatoge your launcher.
Going for a strategy of “we can mass-manufacture warheads cheaper than you can possibly intercept them” would quickly lead to absurd, overkill numbers of warheads that would dwarf even the most insane years of the Cold War, practically guaranteeing that any actual nuclear war would end in the classic “nobody wins” scenario of global devastation (nuclear winter, etc).
But I thought it was kind of funny to think about, and this absurd thought experiment maybe sheds some light on the underlying dynamics of the situation.
Re the dumb thought. I’ve forgotten the author, but as a teenager I was a big SciFi fan (still am actually) and read a short story with exactly this theme. Basically it was the recognition that at some point quantity >= quality. I want to say (have not fact checked myself though) that this was pretty much the USSR’s approach to fighting Germany in WWII—crappy tanks but lots of them.
(Side note, I think for whatever reason, too long a peacetime, more interest in profit than protection, the USA particularly seems to have forgotten that the stuff you use to wage a war are largely all consumables. The non consumable is the industrial base. Clearly there is a minimum cost of producing something that can do the job but much more than that is sub optimal. I am somewhat over simplifying but this also seems to be a fair characterization of where the USA-China naval relationship might be.)
Back to ICBMs, Foreign Affairs had a piece about AI’s potential impact on nuclear deterrence in general but did mention the fixed location of ICBM silos as a problem (long known and why everyone has mobile platforms). They might be considered a prime target for a first strike but the reality is they are easily monitored so the mobile platforms are the big deterrents and probably more interesting problem to solve in terms of obsoleting. But perhaps the ICBM platforms, fixed or mobile, shift to a different type role. Pure kinetic (I believe Russia did that with one of the ballistic warheads with pretty devastating results in Ukraine about a year ago) or rather than all the MIRV decoys for the armed MIRV decoys and other function for other delivery vehicles. I suspect the intercept problem with a nuclear warhead is a bit different from that of just a big mass of something dense.
So maybe perhaps obsolescence in their current function but not for some repurposed role.
Against atmospheric jitter, we have historically used ground radar, but it’s not clear to me this is even necessary depending on how much drone cameras improve. If the drone knows the exact position within 3 meters 0.5 second ahead of time (when the warhead is something like 2 km away), it won’t have enough performance to steer into the warhead, but it can throw a 1 kg explosively formed penetrator laterally at 2 km/s, which it would need to time with 0.1 ms accuracy. This would put 100 grams in each possible 1 m^2 cross section, though I’m not sure if it would work when spread out. To defeat this the warhead would either have to steer in the upper atmosphere out of range of the EFP of any available drone, or jink faster than the EFP can aim.
I thought that MIRVs were spin stabilized, but it looks like that’s not true, so in theory you could mount grid fins on them. However, any retrofit would need to handle the reentry heating which is significantly more intense than on manned spacecraft; RVs have thick ablative heat shields.
The chain of nukes plan seems possible with or without grid fins, so whether MIRVs still have cost advantage depends on the max altitude of cheap-ish terminal interceptors, which I really have no idea about.
I would expect aerodynamic maneuvering MIRVS to work and not be prohibitively expensive. The closest deployed version appears to be https://en.wikipedia.org/wiki/Pershing_II which has 4 large fins. You likely don’t need that much steering force