A quick glance at real world anti-missile systems seems to show that they do work, but imperfectly. The problem naturally gets harder when the incoming missile is extremely high-velocity.

If your strategic calculation was "if one nuke hits us, we will be forced to retaliate in kind, and that ends badly for everyone, so let's do everything that we can to prevent the incoming strike, that way we can retaliate with sub-nuclear options" -- would nuking the nuke work?

The idea here is that a near miss wouldn't matter since the fireball would be so huge.

Assume the blast happens over uninhabited land, that nukes are not scarce, that the poltics etc isn't important here...

...is it practical?

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    Isn't the general idea to hit the enemy nuke without it going off? For example, you hit the fuel tank or the motor, forcing the missile to tumble out of the sky. Nukes normally have a pretty sophisticated detonation sequence so your scenario wouldn't work (unless intended in the story line of course) – Snow Oct 5 '16 at 15:07
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    You could just prevent the bomb from exploding, indeed, instead of blowing it up. There are a couple of ways to slow down a incoming projectile. – Yassine Badache Oct 5 '16 at 15:15
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    Depends on what is the firing mechanism and the explosion range, cost and how it is delivered. Most new strategies deploy hundreds of mini nukes which spread over the entire continent for maximum casualties all originated from a single long range missile... try to nuke all these!😱 – user6760 Oct 5 '16 at 16:48
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    Are we also ignoring the effects of EMPs and radioactive fallout from our anti-nuke nukes? (Or making use of it for the story somehow?) Those seem like a couple of big effects to consider. – HopelessN00b Oct 5 '16 at 17:21
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    To quote a sci-fi writer "'close' only counts when dealing with horse-shoe throwing and tactical nukes", but then it does count. Some reasons why being "close" may be sufficient, can be found here: en.wikipedia.org/wiki/Nuclear_fratricide – Baard Kopperud Oct 5 '16 at 20:46
up vote 58 down vote accepted

You have described 1950 era ABM's, so the short answer is "Yes, of course"

The pulse of hard radiation from the nuclear explosion could potentially fry the electronics of the incoming warhead, so the detonator does not work. The sheet of neutrons from the explosion could actually affect the nuclear material inside the incoming warhead, and of course the thermal pulse will ablate part of the incoming warhead and act like a rocket motor throwing it off course. If the explosion is close enough, the enemy warhead is simply consumed inside the fireball.

The US "Sprint" ABM deployed briefly in the 1970's, and was armed with an enhanced radiation thermonuclear warhead. Older systems like Nike or air to air missiles like Genie also used nuclear warheads (although the primary purpose was to destroy the bombers carrying the nuclear warheads, the effects of the explosion on the Russian bombs outside the immediate blast radius would be quite similar).

The downside is you are using nuclear weapons in the atmosphere in the airspace over or near your own homeland, and the enemy warheads are either disintegrating in the atmosphere (showering you with Plutonium dust), or are plunging randomly into the ground, leaving you with the task of recovering "hot" items full of nuclear warhead fuel. While much preferable than dealing with the aftereffects of a nuclear explosion vaporizing a city, it is still not an ideal solution, hence President Ronald Reagan's Strategic Defense Initiative; meant to shoot down ICBM's in the boost and mid flight stages rather than stopping warheads in the final seconds before impact.

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    Because of clustering of your own MIRVs and because of enemy EMP, many warheads were designed with non-electronic fallback detonators. I mean, still using electricity for the trigger detonators, but no small circuits. – Zan Lynx Oct 5 '16 at 16:38
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    One of the most toxic substances on Earth is the toxin from the bacterium Clostridium botulinum. Gram for gram / ounce for ounce, that is more than a thousand times as toxic as Plutonium. What do people do with it? Answer: they have it injected into their face; it is the active substance in a Botox treatment. Ask them to inject Plutonium and they would balk at the idea. Ask them to inject something more than a thousand times as toxic, and they go "Okey!". Odd that... – MichaelK Oct 6 '16 at 14:09
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    @MichaelKarnerfors Chemically, Plutonium may not be especially toxic, but the fact that it is rendered into a fine radioactive dust makes it extremely dangerous because it can easily be distributed throughout the body by inhalation or ingestion. This is pretty much how Alexander Litvinenko was killed, though by a different element. – Ryan Reich Oct 6 '16 at 16:15
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    Finally powdered plutonium is a toxic heavy metal, so should be avoided just for that reason alone, but the fact it is also radioactive provides an extra element of risk. The fate of Alexander Litvinenko, referenced by Ryan Reich in his comment should be example enough. – Thucydides Oct 6 '16 at 20:25
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    @RyanReich The isotope used to kill Litvinenko was Polonium, not Plutonium. Plutonium's decay rate is too long to do anything worse than giving you cancer a few years early. Iodine and Strontium radioisotopes are what kill you from fallout because they have shorter half-lives and more radiation damage done per unit time. Also, your body will flush Plutonium (and Polonium, not that it helped Litvinenko) but iodine gets absorbed into your thyroid, and Strontium into your bones. – kingledion Oct 7 '16 at 0:11

Keyword: One.

In practice you will have a big problem when you try this--interceptor #1 engages inbound nuke #1 and destroys it. Fine.

30 seconds later inbound nuke #2 sails through the area of ionization and isn't intercepted because the interception radar can't see through the ionized area.

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    Why is this being downvoted? – Délisson Junio Oct 6 '16 at 2:53
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    I didn't downvote this but the answer seems pretty enigmatic to me. What does it mean destroys it? Does the interceptor#1 explode in proximity to nuke#1 or maybe it just rams it? Where does the ionization comes from? What is Ionized, air or some other material that got out during collision? Why wouldn't we see both nuke#1 and nuke#2 and intercept them at the same time? In my opinion the answer as it is now needs improvement. – Sok Pomaranczowy Oct 6 '16 at 8:52
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    I believe I understand what this answer is suggesting: that: (a) you can successfully prevent the first inbound nuke from getting through, but (b) the air explosion from your own interceptor nuke would create a lot of ionizing radiation and charged particles in the air that would result in a rather large radar blind spot, greatly hindering your targeting efforts to shoot down further inbound nukes. At least, I think that's what Loren is saying. Loren, your answer would probably be better if you fleshed it out a bit more, adding more explanation. – type_outcast Oct 6 '16 at 9:27
  • @wingleader This answer does not currently have any downvotes. – Michael Kjörling Oct 6 '16 at 11:14
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    I think Loren's post is pretty clear. The enemy uses a tactic that renders defensive radars ineffective and drops the 2nd warhead right down the pipe. – Tony Ennis Oct 7 '16 at 0:38

would nuking the nuke work?

Yes. This is basically the same idea as what Mythbusters tried with guns and grenades. Assuming there is nothing you want to keep within the (potentially combined) blast radius, using a nuclear weapon to destroy a nuclear weapon would work. However...

...is it practical?

No. It's kind of the difference between using a bullet to stop a grenade and a grenade to stop a grenade. Why would you spend between 2.00 and 200.00 USD on a grenade when you could spend between 0.21 and 0.32 USD on a bullet that does the same job just as well? You don't need an explosive to destroy a nuke. A kinetic kill vehicle is all you need, which is, coincidentally, exactly how the US handles missile defense.

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    Something tells me its not a coincidence – Ryan Oct 5 '16 at 15:47
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    @iAdjunct I've read parts of Wikipedia. It's a big place, after all. Which part did you have in mind? – Frostfyre Oct 5 '16 at 19:31
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    @iAdjunct Given that there is a 50 year gap between the acquisition programs for these two weapon systems, you just can't compare the prices, even adjusting for inflation. Also, the capability gap between the weapons is vast. The Minuteman cannot make course adjustments during takeoff. How could you ever expect to hit an incoming missile with it? I think you are the one being misleading. – kingledion Oct 6 '16 at 2:13
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    Not really worth my time having a conversation here about stuff I studied a lot in college. Carry on. – iAdjunct Oct 6 '16 at 2:43
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    I believe current kkvs have a hit probability in the singular digit probability space, especially when the incoming missile is equipped with either MIRVs or ABM countermeasures... hence you will have to deploy many to have any reasonable sense of security. – Doomed Mind Oct 6 '16 at 8:12

It's not practical, because you would fry your satellites.

While nuking a nuke would certainly work, so far as destroying the other nuke is concerned, you would almost definitely destroy some of your satellites in doing so. ICBMs don't travel close to the Earth, instead taking high arcing ballistic paths hundreds of miles above the ground. Your best option for hitting a nuke with another nuke would be to hit it at a high altitude, where the detonation of your nuke wouldn't harm the target of the enemy nuke. Of course, detonating a nuclear bomb at a high enough altitude over your country that it won't damage ground installations puts another important asset at risk: satellites.

High altitude nuclear tests have been done, in fact, back in the 60s before we agreed to ban the detonation of nukes in space. Even at that point in time, the tests that were done inadvertently damaged several US satellites. We now have far more satellites in space, and have become significantly more reliant on them than we were in the 1960s. Knocking out a few of these satellites with an anti-missile would make anti missile nukes, while possible, extremely impractical.

Note: this is not suggesting that nuclear interceptors are worse than getting nuked, just that they're worse than conventional interceptors.

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    Although, a few tens of millions of dollars is nothing compared to a few entire states. – wizzwizz4 Oct 5 '16 at 19:26
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    It's worth noting that a high-altitude explosion would damage everyone's satellites irrespective of owner, not just your own - even if we discount the Kessler syndrome, which would be the real bummer here. – John Dvorak Oct 5 '16 at 19:37
  • @JanDvorak: right. I wonder how problematic nukes would actually be so WRT Kessler syndrome – they'd vaporise anything close enough, and merely disable / melt / deflect further away satellites, so I'd suspect it's in the long run actually less disastrous than conventional explosions (which would shatter satellites to thousands of dangerous particles). – leftaroundabout Oct 5 '16 at 20:34
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    I am not clear why disabling satellites makes saving the lives of potentially millions of people "not practical". Downvoted. Aside from the obvious ethical issue it has a notable practical one as well - You can win (or at least survive) a war without hunks of metal in space that emit non-harmful electromagnetic radiation on command; you can't do either without people. – GrinningX Oct 5 '16 at 22:14
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    @GrinningX It's possible to do the same thing without using nukes. While nukes might be better than nothing, arming your interceptors with conventional explosives would be easier, cheaper, and have fewer damaging side effects. – ckersch Oct 6 '16 at 13:12

Anti ICBM's exist already. The SM-3 Anti-ballistic missile. I knew someone who worked on it. It is a non-explosive missile that uses optical guiding to hit incoming nukes with insane accuracy. The payload is essentially a lump of metal that hits the nuke, disabling it, and not activating the explosion.

We used a modified SM-3 to knock that failing satellite down safely a few years back:

https://en.wikipedia.org/wiki/USA-193

I know this doesn't directly answer your question about an anti-nuke-nuke, but it is a viable means to prevent a nuke from making landfall, and thus could be important to your worldbuilding.

Yes, easily. We can actually take out most ICBMs using conventional explosives. I would be willing to bet we have a quick nuke drop warhead as a fallback if the conventional ones fail.

The trick is what kind of nuke to use and what altitude.

The nuke to use is an "enhanced" a.k.a "neutron bomb." The "enhanced" is a bit of misdirection. All fusion devices emit 99%+ of their energy as neutrons. To convert the neutrons into blast and heat and in general make a big explosion, you have to wrap them in a dense, neutron absorbing material like lead, polypropylene etc.

It's a myth that fusion nukes are highly destructive in space. With no atmosphere or ground to convert neutrons to heat and blast, you just get a rather large quick flashbulb for radiant effect. Space itself, even near earth space has so much volume that you have to be within something like 30km for a 1 megaton device to generate a killing pulse. (Intensity falls with the square of distance, remember.) On the surface, a 30km radius is massive, in space its a blip.

Neutrons don't kill other nukes by primarily heat, blast or frying the electronics. Instead, they transmute the isotopes within the enemy device, altering the critical ratios of those isotopes such that the device can never go critical. (Although, if close enough, the neutrons will cause heating in isotopes and blow it apart right there and some electronics can be fried by neutrons.)

So, the best point of intercept is above the atmosphere i.e. 90miles/140km or higher. The really important satellites are in geosynchronous orbit at 25,000miles/40,000km, so they're safe from any interception blast.

Intercepting above the atmosphere also prevents the blinding effects of ionized atmosphere noted by others. Even that may not matter as the enemy will be tracked by multiple sensors deployed on the ground, airborne and from high satellites, all of which will be transmitted to the interceptor which can otherwise fly blind. The ecological and other ground effects are minimal. With little blast or heat, there is little plasma and thus little EMP.

The real utility of an interceptor system is that it introduces immense uncertainty in calculating the success for an attack. Nobody really knows how all the factors in a nuclear attack will combine to produce what output. The interceptor system might substantially fail in a real attack or it might wipe out the attack completely. In the latter case, you've done nothing but p*ss off the targeted polity.

That uncertainty was a big part of the Reagan's Star Wars mojo back in the 80s that helped bring the Soviets down. The Soviets had long planned on being able to launch a devastating first strike and then absorb a much smaller counter-strike. The maybe-it-will-work,-maybe-it-won't Star Wars talk, threw that out the window.

Active defense is the new hotness at all levels. The Israels' are knocking individual artillery rounds out of the sky and pre-detonating RPGs. Interceptors in one form or another, and at all levels are here to stay.

  • "Active defense is the new hotness at all levels." Not really, it's as old as the hills. Every decade from the 1950s has had its flirtation with interceptor weapons. Nike, Sprint, SDI and its successors. Eisenhower predicted in 1959 the Soviet Union would collapse in thirty years. Experts on the Soviet system in late 1970s and early 1980s thought it would fall soon. SDI made the USSR collapse? No, it's a myth. – a4android Oct 7 '16 at 7:22

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