eli5. why isn’t the world set up to kill nukes in the air?

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Nukes in this day and age seem to me like they should effectively be obsolete. I feel like in the age of satellite observation and the idea of geo-privacy being basically null, every developed country ought to have anti icbm tech, similar to an mrap. Short of mass amounts of dirty bombs, I feel like nuclear war should be a non issue in modern times.

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A couple of things you seem to not consider.

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1: Nukelear warheads are attached to advanced missiles. The tech has continued to be developed just as the counter tech has.

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2: Nukes arn’t JUST missiles

Russia has some pretty scary nuclear torpedoes that are quite difficult to counter.

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3: Russia has a LOT of nukes.

If you manage to shoot down 9/10, there are still enough getting through to basically destroy anything they want.

ICBMs travel a lot faster than your average missile. They’re much harder to hit, particularly at altitude, and often release multiple warheads when they get closer to ground.

An icbm is vulnerable during the few minutes following its launch. After that it’s out of range of interception systems, basically most of the flight takes place in space. Interception during re-entry is also complicated as the missile travels extremely fast then splits and spread decoys.

Ballistic missiles are a tough target to hit due to their high speed. You have to maneuver an interceptor close enough to them and then set off explosives with near-perfect timing to disable the nuclear weapon inside. Some countries have figured out how to do this, and the design of nuclear missiles has been adapted to account for the defenses. Generally the method consists of detecting the launch in the boost phase with satellite assets, launching your interceptors while the ICBM is in coast phase above the atmosphere, and then intercepting the ICBM either in the coast phase or terminal phase (while it’s descending through the atmosphere towards its target).

One of the strategies used in ICBMs is to have multiple warheads in a single missile, or even have many dummy warheads interspersed. So to stop a single missile, many interceptors are needed. Even missing one warhead means a city is vaporized.

Classic ICBMs follow a ballistic trajectory, which means they don’t try to steer once the boost phase of their flight is over. Modern ICBMs have begun to include the ability to maneuver during the terminal phase of flight. This makes it much more challenging to intercept them, since they can take evasive maneuvers to dodge an interceptor or at least take a non-ballistic trajectory that your interceptor wasn’t prepared for.

Another recent method is hypersonic missiles. These are effectively missiles that no longer follow a ballistic trajectory for any phase of their flight, instead staying in the atmosphere and maneuvering continuously. With a range encompassing the entire planet, you could see how it might be a challenge to intercept them. If you detect a hypersonic missile launch, where should you launch your interceptors from? The hypersonic missile is traveling towards the west coast now, but it could turn and target the east coast relatively quickly and now you’ve wasted interceptors on the west coast, leaving yourself vulnerable to the next missile.

So, in summary, it’s what they call an arms race. People have been coming up with counter-measures and counter-counter-measures and counter-counter-counter-measures for the past half a century. The current situation is that no one has confidence they could shoot down any where near all of the other side’s missiles, and a nuclear exchange would result in mutually assured destruction for every country that participated, as well as most that don’t.