This idea has come back up, and it could be feasible this time around because of the high launch capability and total reusability of SpaceX’s Starship. The idea is a large constellation (~30,000?) of low earth satellites that intercept nuclear launches in their boost phase where they are much slower and more vulnerable to interception. The challenge of course is that you constantly need enough satellites overhead at all times to intercept the entire arsenal of a major power if they launch all at once.
There are obvious positives and risks with this
The main positive is it removes the chance of a catastrophic nuclear war.
Negatives are potentially destabilizing the MAD status quo in the short term, and new risks such as orbital war etc.
Trying to decide if it makes nuclear war more or less likely
This firstly depends on your nuclear war yearly base rate, and projected rate into the foreseeable future.
If you think nuclear war is very unlikely then it is probably not rational to disturb the status quo, and you would reject anything potentially destabilizing like this.
However if you think that we are simply lucky and there was >50% chance of nuclear war in the last 50 years (we are on a “surviving world” from MWI etc), and while the change may be currently low, it will go up a lot again soon, then the “Pebbles” idea is worth being considered even if you think it is dangerous and destabilizing in the short term. Say it directly causes a 5% chance of war to set up, but there is a >20% chance in next 20 years without it, which it stops. In this case you could decide it is worth it as paying 5% to remove 20%.
Practical considerations
How do you set up the system to reduce the risk of it causing a nuclear war as it is setup?
Ideally you would set up the whole system in stealth before anyone was even aware of it. Disguising 30K “Pebbles” satellites as Starlink ones seems at the bounds of credibility.
You would also need to do this without properly testing a single interceptor as such a test would likely be seen and tip other nations off.
New risks
A country with such a system would have a power never seen before over others.
For example the same interceptors could shoot down civilian aircraft, shipping etc totally crippling every other country without loss of life to the attacker.
The most desirable outcome:
1. A country develops the system
2. It uses whatever means to eliminate other countries nuclear arsenals
3. It disestablishes its own nuke arsenal
4. The Pebbles system is then greatly thinned out as there is now no need to intercept ~1000 simul launches.
5. There is no catastrophic nuclear threat anymore, and no other major downside.
My guess as to how other countries would respond if it was actually deployed by the USA
Russia
I don’t think it would try to compete nor be at all likely to launch a first strike in response to USA building a system. Especially if the Ukraine war is calmed down. I don’t think it regards itself as a serious worldwide power anymore in spite of talk. Russia also isn’t worried about a first strike from the USA as it knows this is incredibly unlikely.
China
Has 200-350 nukes vs USA of ~5000
I think China would be very upset, both because it would take fewer “Pebbles” to intercept and it does see itself as a major and rising world power. I also don’t think it would launch a first strike, nor could credibly threaten to do so, and this would make it furious.
After this however it is hard to tell, e.g. China could try to destroy the satellite interceptors, say creating a debris cloud that would take many out in the lower orbits, or build thousands of decoys with no nuclear and much smaller missiles that would be hard to tell apart. Such decoys could be incapable of actually making it to orbit but still be effective. To actually reduce the nuclear threat, USA would have to commit to actually destroying China nukes on the ground. This is a pretty extreme measure and its easy to imagine USA not actually doing this leaving an unstable result.
Summary
Its unclear to me all things considered, whether attempting to deploy such a system would make things safer or more risky in total over the long term with regards to nuclear war.
Yes for sure. I don’t know how it would play out, and am skeptical anyone could. We can guess scenarios.
1. The most easily imagined one is the Pebbles owner staying in their comfort zone and not enforcing #2 at all. Something similar already happened—the USA got nukes first and let others catch up. In this case threatened nations try all sorts of things, political, commercial/trade, space war, arms race but don’t actually start a hot conflict. The Pebbles owner is left not knowing whether their system is still effective, nor the threatened countries—an unstable situation.
2. The threatened nation tries to destroy the pebbles with non-nuke means. If this was Russia, USA maybe could regenerate the system faster than Russia could destroy satellites. If its China, then lets say its not. The USA then needs to decide whether to strike the anti-satellite ground infrastructure to keep its system...
3. The threatened nation such as NK just refuses to give up nukes—in this case I can see USA destroying it.
4. India or Israel say refuses to give up their arsenal—I have no idea what would happen then.
It would certainly be nice if we could agree to all put up a ton of satellites that intercept anyone’s nuclear missiles (perhaps under the control of an international body), gradually lowering the risk across the board without massively advantaging any country. But I think it would be impossible to coordinate on this.
Brilliant Pebbles?
See here and here
This idea has come back up, and it could be feasible this time around because of the high launch capability and total reusability of SpaceX’s Starship. The idea is a large constellation (~30,000?) of low earth satellites that intercept nuclear launches in their boost phase where they are much slower and more vulnerable to interception. The challenge of course is that you constantly need enough satellites overhead at all times to intercept the entire arsenal of a major power if they launch all at once.
There are obvious positives and risks with this
The main positive is it removes the chance of a catastrophic nuclear war.
Negatives are potentially destabilizing the MAD status quo in the short term, and new risks such as orbital war etc.
Trying to decide if it makes nuclear war more or less likely
This firstly depends on your nuclear war yearly base rate, and projected rate into the foreseeable future.
If you think nuclear war is very unlikely then it is probably not rational to disturb the status quo, and you would reject anything potentially destabilizing like this.
However if you think that we are simply lucky and there was >50% chance of nuclear war in the last 50 years (we are on a “surviving world” from MWI etc), and while the change may be currently low, it will go up a lot again soon, then the “Pebbles” idea is worth being considered even if you think it is dangerous and destabilizing in the short term. Say it directly causes a 5% chance of war to set up, but there is a >20% chance in next 20 years without it, which it stops. In this case you could decide it is worth it as paying 5% to remove 20%.
Practical considerations
How do you set up the system to reduce the risk of it causing a nuclear war as it is setup?
Ideally you would set up the whole system in stealth before anyone was even aware of it. Disguising 30K “Pebbles” satellites as Starlink ones seems at the bounds of credibility.
You would also need to do this without properly testing a single interceptor as such a test would likely be seen and tip other nations off.
New risks
A country with such a system would have a power never seen before over others.
For example the same interceptors could shoot down civilian aircraft, shipping etc totally crippling every other country without loss of life to the attacker.
The most desirable outcome:
1. A country develops the system
2. It uses whatever means to eliminate other countries nuclear arsenals
3. It disestablishes its own nuke arsenal
4. The Pebbles system is then greatly thinned out as there is now no need to intercept ~1000 simul launches.
5. There is no catastrophic nuclear threat anymore, and no other major downside.
My guess as to how other countries would respond if it was actually deployed by the USA
Russia
I don’t think it would try to compete nor be at all likely to launch a first strike in response to USA building a system. Especially if the Ukraine war is calmed down. I don’t think it regards itself as a serious worldwide power anymore in spite of talk. Russia also isn’t worried about a first strike from the USA as it knows this is incredibly unlikely.
China
Has 200-350 nukes vs USA of ~5000
I think China would be very upset, both because it would take fewer “Pebbles” to intercept and it does see itself as a major and rising world power. I also don’t think it would launch a first strike, nor could credibly threaten to do so, and this would make it furious.
After this however it is hard to tell, e.g. China could try to destroy the satellite interceptors, say creating a debris cloud that would take many out in the lower orbits, or build thousands of decoys with no nuclear and much smaller missiles that would be hard to tell apart. Such decoys could be incapable of actually making it to orbit but still be effective. To actually reduce the nuclear threat, USA would have to commit to actually destroying China nukes on the ground. This is a pretty extreme measure and its easy to imagine USA not actually doing this leaving an unstable result.
Summary
Its unclear to me all things considered, whether attempting to deploy such a system would make things safer or more risky in total over the long term with regards to nuclear war.
I think the part where other nations just roll with this is underexplained.
Yes for sure. I don’t know how it would play out, and am skeptical anyone could. We can guess scenarios.
1. The most easily imagined one is the Pebbles owner staying in their comfort zone and not enforcing #2 at all. Something similar already happened—the USA got nukes first and let others catch up. In this case threatened nations try all sorts of things, political, commercial/trade, space war, arms race but don’t actually start a hot conflict. The Pebbles owner is left not knowing whether their system is still effective, nor the threatened countries—an unstable situation.
2. The threatened nation tries to destroy the pebbles with non-nuke means. If this was Russia, USA maybe could regenerate the system faster than Russia could destroy satellites. If its China, then lets say its not. The USA then needs to decide whether to strike the anti-satellite ground infrastructure to keep its system...
3. The threatened nation such as NK just refuses to give up nukes—in this case I can see USA destroying it.
4. India or Israel say refuses to give up their arsenal—I have no idea what would happen then.
It would certainly be nice if we could agree to all put up a ton of satellites that intercept anyone’s nuclear missiles (perhaps under the control of an international body), gradually lowering the risk across the board without massively advantaging any country. But I think it would be impossible to coordinate on this.