> AI may make it possible to build a virtually perfect missile defense against ICBMS
Massed ICBM defense is a matter of sheer volume - with the current GMD system the US can throw enough exoatmospheric kill vehicles (and THAAD to handle the leftovers) to counter a handful of re-entry vehicles from a smaller nuclear power like North Korea or Iran. Not hundreds (vs China) or thousands (vs Russia) that you would see in a peer-level nuclear exchange where everyone has multi-megaton MIRVs, decoys, and SLBMs with much shorter flight times.
Some fantasy future AI with the right sensors may perfectly track all of that sub-orbital mayhem. Without an enormous fleet of thousands of kill vehicles to actually defend against that threat, and the logistics to keep that fleet operational, it can do nothing about it. Building and supporting that sort of strategic defense is obscenely expensive, and as such it remains a Reagan-era fever dream.
Things have changes since the Raegan era. There are a couple of elements to ICMB defense:
1) If you can strike the the ICBM's before the MIRV's separate, you only need a fraction of the number. To do this, you need to already have the interceptors (or whatever else used to shot them down) in orbit before the ICBM's launch.
Independently of AI, Starship is making it much cheaper to place objects in orbit, and can help with this. (Though it could trigger a first strike if detected, it might be possible to hide interceptors within Starlink satellites, for instance.)
2) Coordination and precision. This is what wasn't in place at all in the 80s. I'm old enough to remember when this was going on, and labelled impossible. I still remember thinking, back then: "This is impossible now, but will not remain impossible forever".
Whether it applies to interceptors already placed in orbit, novel weapons such as lasers, typically also placed in orbit or interceptors intended to stop reentry vehicles one faces a coordination problem with time restrictions that makes it very hard for humans or even traditional computer algorithms to solve properly.
This, more than the volume, was the fundamental showstopper in the 80s (the willingness to pay was pretty significant).
Now, with AI tech, plenty of known options open up, and an unknown number of things we didn't think of yet, could also open up.
Accuracy and coordination is the most fundamental one. Here AI may help distribute the compute load into satellites and even independent interceptor vehicles. (Both by making them more autonomous and by improving algorithms or control systems for the dumber ones.)
But beyond that, AI may (if one side achievs a significant lead) also a path to making manufacturing large numbers much cheaper, meaning one could much more easily scale up enough volume to match whatever volume the enemy can deploy. Also, with more advanced tech (allowed by ASI), interceptors can potentially be made much smaller. Even a pebble sized chunk of metal can stop most rockets, given the velocities in space. The hard part is to make them hit the target.
Basically, what I'm saying is that whoever has ASI first may at minimum get a time window of technological superiority where the opponent's ICBM's may be rendered more or less obsolete.
In fact, I think the development of the Poseidon by Russia was a response to realizing decades ago that ICBM's would eventually be counterable.
However, AI tech will possibly even more suitable for detecting and countering this kind of stealthy threats. Just like it is currently revolutionizing radiology, it will be able to find patterns in data from sonars, radars, satellites etc that humans and traditional algorithms have little chance to detect in time.
Massed ICBM defense is a matter of sheer volume - with the current GMD system the US can throw enough exoatmospheric kill vehicles (and THAAD to handle the leftovers) to counter a handful of re-entry vehicles from a smaller nuclear power like North Korea or Iran. Not hundreds (vs China) or thousands (vs Russia) that you would see in a peer-level nuclear exchange where everyone has multi-megaton MIRVs, decoys, and SLBMs with much shorter flight times.
Some fantasy future AI with the right sensors may perfectly track all of that sub-orbital mayhem. Without an enormous fleet of thousands of kill vehicles to actually defend against that threat, and the logistics to keep that fleet operational, it can do nothing about it. Building and supporting that sort of strategic defense is obscenely expensive, and as such it remains a Reagan-era fever dream.