Will nuclear ICBMs in their current form be obsolete soon? Here’s the argument:
ICBMs’ military utility is to make the cost of intercepting them totally impractical for three reasons:
Intercepting a reentry vehicle requires another missile with higher performance—the rule of thumb is an interceptor needs 3x larger acceleration than the incoming missile. This means interceptors cost something like $5-70 million each depending on range
An ICBM has enough range to target basically anywhere, either counterforce (enemy missile silos) or countervalue (cities) targets, so to have the entire country be protected from nuclear attack the US would need to have millions of interceptors compared to the current ~50.
One missile can split into up to 5-15 MIRV (multiple independent reentry vehicles) which carry their own warheads, thereby making the cost to the defender 5-15x larger. There can also be up to ~100 decoys, but these mostly fall away during reentry.
RVs are extremely fast (~7 km/s of which ~3 km/s is downward velocity) but their path is totally predictable once they enter the boost phase, so the problem of intercepting them basically reduces to predicting exactly where they’ll be, then putting something ~100 g or larger in their path. The RV’s own kinetic energy will completely destroy it.
My understanding is that sensing had historically worked like this. The launch is first detected by primitive satellites, but there are too many decoys to tell which are the warheads and the resolution is poor. Interceptors thus require extremely high performance, meaning expensive systems like thrusters for moving sideways at tens of g at the last minute, radar, and cooling systems for IR cameras; including all the fuel the interceptor masses thousands of times what it needs to.
Sensing is quickly being solved. One new generation of satellites (HBTSS) can track warheads after their booster burns out (at which point they become much dimmer), and advertises “weapons quality track for fire control” even for hypersonic glide vehicles, which are much harder to track than ICBMs. The first two were just launched last year, but it would not surprise me if hundreds will be operational soon: US has well over 1000 Starshield satellites in orbit, many equipped with radar and infrared cameras. Through SpaceX, they have the ability to launch tens of satellites per month if they needed to. China doesn’t have the boost capacity of SpaceX but they would still be able to launch 1000 sensing satellites.
The ultimate cost floor for intercepting ICBMs in the limit of perfect sensing is interceptor drones. Ukraine and Russia are in the middle of a war where most casualties are caused by drones, providing extremely high incentives to develop interceptor drones, which already have a top speed of 300 km/h, max altitude of 5 km, and basic infrared cameras at a unit cost of $1k-10k. The idea is the space-based sensors know the missile’s velocity well enough to locate the target within 100 meters with 15 minutes of warning, the drones launch to a position 3 km in front of the target and are guided into exact position by radar and their own sensors as the RVs reenter, with sufficiently low error that they never need to go above their top speed or accelerate more than 1 gee.
The other thing keeping ballistic missile defense from being practical during the Cold War was treaties like the ABM treaty, but today there are basically no active nuclear treaties between Russia, the US, and China.
The internet seems to think it’s still really hard to do missile defense against ICBMs. It seems like this was true in the Cold War but we can no longer be confident it’s true today after 40 years of peace, with Boeing and American drone manufacturers vastly less competent than SpaceX and Ukraine’s/Russia’s. My guess at why the meme has persisted is that it is highly threatening and destabilizing to advertise one’s ICBM defense capabilities. But many officials are talking openly about the predictability of ballistic missiles, and there is an arms race for other hypersonics for a reason.
My current guess is that the SM-6 and PAC-3 missiles either are already reliable or would be if the US had more practice, and if sufficient incentive exists, the cost of terminal ballistic missile defense will gradually decline as sensing improves, from the SM-6′s $5M unit cost to lower and lower cost missiles like $400k AIM-9X until one could defend every city and silo in the US or China with a fleet of 100,000 interceptor drones. This would last until there are enough hypersonic glide vehicles and cruise missiles to reestablish deterrence (because they can outmaneuver cheap interceptors). But MIRVs would never return to their previous state of heavily cost advantaging the attacker, because Russia’s state of the art ICBMs only claim to be able to carry 3 HGVs, vs 15 purely ballistic MIRVs. Also HGVs and HCMs are vulnerable in other ways.
Edit: Another option pointed out by commenters is that ICBMs are retrofitted to carry reentry vehicles with limited maneuvering ability, which could happen faster.
Curious to hear if I’m missing something major, as I’m by no means an expert here.
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
Guided artillery, like Excalibur with muzzle velocities that can exceed 1000m/s and unit costs of <$100k can be at edge of space in ~30s, perhaps faster than a missile, with ramjet variants (Nammo etc) even faster (up to perhaps 1500m/s) and it would not be that difficult to create a muti-barrel gun system for a few 10′s of millions that could fire off 10′s of low cost guided rounds in a second (with guidance and detonation signals sent from ground) to detonate when in close proximity to target.
Lasers seems pretty hopeless as a defense given clouds and ablative coatings, unless very high power and located in large numbers in space based constellations.
I think the big problem is if one or more warheads are blown up at limits of interceptor range, to blind or otherwise disable necessarily sensitive interceptor instruments. following Mirvs don’t need to be very accurate with large warheads.
And Mirvs could be very cheaply given random guidance directions during reentry to screw up defenses.
Militarised space is also a big problem. With cheap and un-monitorable space launch parking 1000 warheads in geostationary orbit (or beyond) will soon be viable for China or USA, and they can be launched in a coordinated way without warning, potentially with radar stealthing features, and give as little as 5-10s from start of re-entry to detonation for every target across the whole world and no way for local systems to know if they are just meteorites. If subs can be tracked (likely with drones or enough ocean based sensors) then decapitation 1st strikes become viable.
I also worry about space based lasers as non-nuclear first strike weapons. A day of over flights from a constellation of multi MW laser weapons that might only cost a few hundred million each—say a few $10′s of billions in total (a tiny fraction of annual military budgets) - could see a million fires lit in your country, every transformer taken out, electrical grid and internet gone, powerstations, oil and gas infrastructure wrecked. Bridge trusses melted (wrecked), ships sunk. Most heavy vehicles and locomotives incapacitated and take decades to recover from. Over a few weeks you could basically send a country back to the 17th century.
I don’t think there will ever be a viable defense to nukes given easy paths to making them tougher, faster, less detectable, and so less and less interceptable. But every other branch of military tech is getting similarly more lethal and impossible to defend against unless we all start living in caves with geothermal power sources or somesuch the necessity for a harmonious world is going to matter more and more.
Guided artillery, like Excalibur with muzzle velocities that can exceed 1000m/s and unit costs of <$100k can be at edge of space in ~30s, perhaps faster than a missile, with ramjet variants (Nammo etc) even faster (up to perhaps 1500m/s)
This is wild, I did not know that Excalibur had CEP under 1 meter or that there were artillery shells with solid-fueled ramjet engines.
You seem to believe that radars and infrared cameras can somehow distinguish between the decoys and the warheads, but they can’t. In space, no radar and no IR camera can differentiate between a conical foil balloon with a small heater inside and a reentry vehicle with a nuke.
Another problem of ballistic missile defense is that once you are dealing with nukes and not conventional warheads, you can’t afford, say, a 97% average interception rate, it must be 99.999+%[1]. To put this in context, Israel, which currently has the best BMD system in the world, couldn’t even reliably achieve 90% against Iranian MRBMs (and those are pretty unsophisticated, e. g. they lack MIRVs and decoys).
Now calculate how many interceptors your plan requires for a plausible probability of an interception with a single drone, and you will see it’s entirely unworkable. Note that both arguments are based on simple physics and math so don’t depend on the progress in technology at all.
When this seemingly waterproof probability is raised to the power of the Russian warhead count it still results in ~4% (basically 1e-5 times ~4k) of at least one RV not intercepted, and in reality hundreds of warheads will be harder to intercept than the average one you accounted for when calculating your probability. E. g., drones work poorly in bad weather, and it’s almost always bad weather above at least some of American cities
Yeah seems reasonable. I don’t think the system will ever get to 99%+ accuracy until the defense has like ASI and nanobots; my claim is mostly that the economics could shift from MAD (where the attacker is heavily cost advantaged) to something like conventional war, where each side has the ability to inflict unacceptable losses on the other but must pay a similar cost to attack and also can’t “win” with a first strike.
It’s not obvious that decoys change the conclusion if the cost ratio is otherwise favorable enough for the defender. Suppose the interceptors cost only $30k each due to economies of scale. Decoys can be distinguished when reentry starts at about 2 minutes before impact, and if the interceptor’s speed is 300 km/h (already possible with drones) it can cover 10 km in that time, about equal to the typical spread of decoys and warheads. Supposing the defender spends 5 drones per warhead x 10 warheads / missile, this would cost them $1.5 million, while the attacker has spent something like $30 million, the cost of a Trident II. For countervalue this could be defeated by the layered attack RussellThor mentioned unless there is a higher altitude cheap interceptor, but for counterforce the attacker needs several warheads per silo destroyed so the goal is achieved.
I found both that article and this one on their more recent history a great read.
Why would anyone want to pay a fortune for a system that is expected to let ~40 warheads through (assuming ~99% overall interception rate which will require average rate of 99.99+%), about the same as the number of ICBMs the Soviet Union had in service during the Cuban Missile Crisis? Unacceptable damage is the cornerstone of the nuclear deterrence, MAD or not (there is no MAD between India and Pakistan, for example).
The RV separation distance is normally around ~100 km (even up to 300 km in some cases) not 10 km, and the decoy dispersal might be expected on the same order of magnitude. It will be easy to ramp it up BTW with a cheap modernization.
None of the US adversaries really practice counterforce targeting, so the silo protection is moot.
A blog post argues that military megawatt class lasers could reach $100 million (inclusive of all fixed costs) by 2045, because laser cost is currently halving every 4 years. In good conditions this would be able to defeat almost arbitrary numbers of any kind of missile whether they can maneuver or not. But there are huge challenges:
Adaptive optics and ultra-precise tracking tech to focus the beam to 20 cm diameter at 200 km, while slewing to track a missile at several degrees per second
Countermeasures like the spinning the RVs to distribute heat
Weather, especially thick clouds which seem completely impractical to burn through (against moving targets, this would basically mean vaporizing an entire plane of water several km^2 by 1 m^2)
Will nuclear ICBMs in their current form be obsolete soon? Here’s the argument:
ICBMs’ military utility is to make the cost of intercepting them totally impractical for three reasons:
Intercepting a reentry vehicle requires another missile with higher performance—the rule of thumb is an interceptor needs 3x larger acceleration than the incoming missile. This means interceptors cost something like $5-70 million each depending on range
An ICBM has enough range to target basically anywhere, either counterforce (enemy missile silos) or countervalue (cities) targets, so to have the entire country be protected from nuclear attack the US would need to have millions of interceptors compared to the current ~50.
One missile can split into up to 5-15 MIRV (multiple independent reentry vehicles) which carry their own warheads, thereby making the cost to the defender 5-15x larger. There can also be up to ~100 decoys, but these mostly fall away during reentry.
RVs are extremely fast (~7 km/s of which ~3 km/s is downward velocity) but their path is totally predictable once they enter the boost phase, so the problem of intercepting them basically reduces to predicting exactly where they’ll be, then putting something ~100 g or larger in their path. The RV’s own kinetic energy will completely destroy it.
My understanding is that sensing had historically worked like this. The launch is first detected by primitive satellites, but there are too many decoys to tell which are the warheads and the resolution is poor. Interceptors thus require extremely high performance, meaning expensive systems like thrusters for moving sideways at tens of g at the last minute, radar, and cooling systems for IR cameras; including all the fuel the interceptor masses thousands of times what it needs to.
Sensing is quickly being solved. One new generation of satellites (HBTSS) can track warheads after their booster burns out (at which point they become much dimmer), and advertises “weapons quality track for fire control” even for hypersonic glide vehicles, which are much harder to track than ICBMs. The first two were just launched last year, but it would not surprise me if hundreds will be operational soon: US has well over 1000 Starshield satellites in orbit, many equipped with radar and infrared cameras. Through SpaceX, they have the ability to launch tens of satellites per month if they needed to. China doesn’t have the boost capacity of SpaceX but they would still be able to launch 1000 sensing satellites.
The ultimate cost floor for intercepting ICBMs in the limit of perfect sensing is interceptor drones. Ukraine and Russia are in the middle of a war where most casualties are caused by drones, providing extremely high incentives to develop interceptor drones, which already have a top speed of 300 km/h, max altitude of 5 km, and basic infrared cameras at a unit cost of $1k-10k. The idea is the space-based sensors know the missile’s velocity well enough to locate the target within 100 meters with 15 minutes of warning, the drones launch to a position 3 km in front of the target and are guided into exact position by radar and their own sensors as the RVs reenter, with sufficiently low error that they never need to go above their top speed or accelerate more than 1 gee.
The other thing keeping ballistic missile defense from being practical during the Cold War was treaties like the ABM treaty, but today there are basically no active nuclear treaties between Russia, the US, and China.
The internet seems to think it’s still really hard to do missile defense against ICBMs. It seems like this was true in the Cold War but we can no longer be confident it’s true today after 40 years of peace, with Boeing and American drone manufacturers vastly less competent than SpaceX and Ukraine’s/Russia’s. My guess at why the meme has persisted is that it is highly threatening and destabilizing to advertise one’s ICBM defense capabilities. But many officials are talking openly about the predictability of ballistic missiles, and there is an arms race for other hypersonics for a reason.
My current guess is that the SM-6 and PAC-3 missiles either are already reliable or would be if the US had more practice, and if sufficient incentive exists, the cost of terminal ballistic missile defense will gradually decline as sensing improves, from the SM-6′s $5M unit cost to lower and lower cost missiles like $400k AIM-9X until one could defend every city and silo in the US or China with a fleet of 100,000 interceptor drones. This would last until there are enough hypersonic glide vehicles and cruise missiles to reestablish deterrence (because they can outmaneuver cheap interceptors). But MIRVs would never return to their previous state of heavily cost advantaging the attacker, because Russia’s state of the art ICBMs only claim to be able to carry 3 HGVs, vs 15 purely ballistic MIRVs. Also HGVs and HCMs are vulnerable in other ways.
Edit: Another option pointed out by commenters is that ICBMs are retrofitted to carry reentry vehicles with limited maneuvering ability, which could happen faster.
Curious to hear if I’m missing something major, as I’m by no means an expert here.
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
Guided artillery, like Excalibur with muzzle velocities that can exceed 1000m/s and unit costs of <$100k can be at edge of space in ~30s, perhaps faster than a missile, with ramjet variants (Nammo etc) even faster (up to perhaps 1500m/s) and it would not be that difficult to create a muti-barrel gun system for a few 10′s of millions that could fire off 10′s of low cost guided rounds in a second (with guidance and detonation signals sent from ground) to detonate when in close proximity to target.
Lasers seems pretty hopeless as a defense given clouds and ablative coatings, unless very high power and located in large numbers in space based constellations.
I think the big problem is if one or more warheads are blown up at limits of interceptor range, to blind or otherwise disable necessarily sensitive interceptor instruments. following Mirvs don’t need to be very accurate with large warheads.
And Mirvs could be very cheaply given random guidance directions during reentry to screw up defenses.
Militarised space is also a big problem. With cheap and un-monitorable space launch parking 1000 warheads in geostationary orbit (or beyond) will soon be viable for China or USA, and they can be launched in a coordinated way without warning, potentially with radar stealthing features, and give as little as 5-10s from start of re-entry to detonation for every target across the whole world and no way for local systems to know if they are just meteorites. If subs can be tracked (likely with drones or enough ocean based sensors) then decapitation 1st strikes become viable.
I also worry about space based lasers as non-nuclear first strike weapons. A day of over flights from a constellation of multi MW laser weapons that might only cost a few hundred million each—say a few $10′s of billions in total (a tiny fraction of annual military budgets) - could see a million fires lit in your country, every transformer taken out, electrical grid and internet gone, powerstations, oil and gas infrastructure wrecked. Bridge trusses melted (wrecked), ships sunk. Most heavy vehicles and locomotives incapacitated and take decades to recover from. Over a few weeks you could basically send a country back to the 17th century.
I don’t think there will ever be a viable defense to nukes given easy paths to making them tougher, faster, less detectable, and so less and less interceptable. But every other branch of military tech is getting similarly more lethal and impossible to defend against unless we all start living in caves with geothermal power sources or somesuch the necessity for a harmonious world is going to matter more and more.
This is wild, I did not know that Excalibur had CEP under 1 meter or that there were artillery shells with solid-fueled ramjet engines.
Not range but height. You blow up a warhead high enough the drones can’t intercept it, and all the drones below fall out of the air
You seem to believe that radars and infrared cameras can somehow distinguish between the decoys and the warheads, but they can’t. In space, no radar and no IR camera can differentiate between a conical foil balloon with a small heater inside and a reentry vehicle with a nuke.
Another problem of ballistic missile defense is that once you are dealing with nukes and not conventional warheads, you can’t afford, say, a 97% average interception rate, it must be 99.999+%[1]. To put this in context, Israel, which currently has the best BMD system in the world, couldn’t even reliably achieve 90% against Iranian MRBMs (and those are pretty unsophisticated, e. g. they lack MIRVs and decoys).
Now calculate how many interceptors your plan requires for a plausible probability of an interception with a single drone, and you will see it’s entirely unworkable. Note that both arguments are based on simple physics and math so don’t depend on the progress in technology at all.
If you are interested in the topic, I strongly recommend reading on the Soviet response to SDI for more expensive anti-ABM options that were considered but ultimately not pursued: https://russianforces.org/podvig/2013/03/did_star_wars_help_end_the_col.html
When this seemingly waterproof probability is raised to the power of the Russian warhead count it still results in ~4% (basically 1e-5 times ~4k) of at least one RV not intercepted, and in reality hundreds of warheads will be harder to intercept than the average one you accounted for when calculating your probability. E. g., drones work poorly in bad weather, and it’s almost always bad weather above at least some of American cities
Yeah seems reasonable. I don’t think the system will ever get to 99%+ accuracy until the defense has like ASI and nanobots; my claim is mostly that the economics could shift from MAD (where the attacker is heavily cost advantaged) to something like conventional war, where each side has the ability to inflict unacceptable losses on the other but must pay a similar cost to attack and also can’t “win” with a first strike.
It’s not obvious that decoys change the conclusion if the cost ratio is otherwise favorable enough for the defender. Suppose the interceptors cost only $30k each due to economies of scale. Decoys can be distinguished when reentry starts at about 2 minutes before impact, and if the interceptor’s speed is 300 km/h (already possible with drones) it can cover 10 km in that time, about equal to the typical spread of decoys and warheads. Supposing the defender spends 5 drones per warhead x 10 warheads / missile, this would cost them $1.5 million, while the attacker has spent something like $30 million, the cost of a Trident II. For countervalue this could be defeated by the layered attack RussellThor mentioned unless there is a higher altitude cheap interceptor, but for counterforce the attacker needs several warheads per silo destroyed so the goal is achieved.
I found both that article and this one on their more recent history a great read.
Why would anyone want to pay a fortune for a system that is expected to let ~40 warheads through (assuming ~99% overall interception rate which will require average rate of 99.99+%), about the same as the number of ICBMs the Soviet Union had in service during the Cuban Missile Crisis? Unacceptable damage is the cornerstone of the nuclear deterrence, MAD or not (there is no MAD between India and Pakistan, for example).
The RV separation distance is normally around ~100 km (even up to 300 km in some cases) not 10 km, and the decoy dispersal might be expected on the same order of magnitude. It will be easy to ramp it up BTW with a cheap modernization.
None of the US adversaries really practice counterforce targeting, so the silo protection is moot.
A blog post argues that military megawatt class lasers could reach $100 million (inclusive of all fixed costs) by 2045, because laser cost is currently halving every 4 years. In good conditions this would be able to defeat almost arbitrary numbers of any kind of missile whether they can maneuver or not. But there are huge challenges:
Adaptive optics and ultra-precise tracking tech to focus the beam to 20 cm diameter at 200 km, while slewing to track a missile at several degrees per second
Countermeasures like the spinning the RVs to distribute heat
Weather, especially thick clouds which seem completely impractical to burn through (against moving targets, this would basically mean vaporizing an entire plane of water several km^2 by 1 m^2)