Funds for Atomic Bomb Research Cut From Spending Bill (washingtonpost.com)

Cutting the PLYWD:

Apparently the debate on developing the Precision Low Yield Weapons Design is over. Congress has cut the funding in a sufficiently bipartisan fashion that there is little chance that next year's increased Republican majorities will revive it.

I have mixed feelings about this. On the one hand, earth penetration weapons are going to be needed in the future. On the other hand, nukes may not be the best way to go about it. There were two sets of concerns about the nukes from a technical side: they might not work (i.e., it wasn't clear that they would be able to achieve the necessary penetration) and they might kick up so much particulate material as to be very damaging to the environment.

An alternative mechanism would be the high-altitude version of the concrete bomb. Improved accuracy means that you can get by with much less firepower than in ages past. The concrete bomb is accurate enough to reliably hit a particular building, so they can take out the explosives and replace it with concrete. Simple physics does the work, with no chemistry necessary.

The earth-penetration option here is the mass driver. Scroll down on the PLYWD screen until you get to the section called "Long Rod Penetration." This explains both of the key objections to low yield nukes -- the physics suggest that it isn't possible with current materials and electronics to penetrate deeply enough to contain a nuclear explosion. Thus, they may not work, and you'll get a lot of particulate matter in any case.

But that matters only if you have to preserve the integrity of electronics or other internal structures. If you're just dropping a steel or titanium rod from orbit, you don't care about that. It can hit at a far higher velocity, and therefore can penetrate quite effectively. If you happen to know what you want to hit -- and neither a bunker nor a reactor is easy to move -- this should be quite sufficient without any explosive power. You can simply drop something heavy on it from high enough.

These same capabilities would be useful in other regards. Scroll down to "mitigation options."