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You don’t need very many kg delivered to target if it’s plutonium. The SDI program had the idea was that if you parked enough defensive weaponry in orbit then maybe mutually assured destruction wasn’t something you had to worry about. The only problem was that getting all that mass into orbit was prohibitively expensive.

Then the deputy director of the program met a young man named Elon Musk, and the rest is history.

by amluto5 hours ago|

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I don’t think plutonium is the right comparison. Plutonium is expensive, and nuclear bombs are neither cheap nor particularly useful for doing things like attacking 10k different targets in some foreign country.

I’m imagining a launcher in a spacecraft that kicks out a bunch of payloads, one at a time, out the back, into orbits with perigee on or before the ground. (An LLM calculates the needed delta-V at under 200m/s, which is likely quite manageable with a small mass driver-style launcher or a very small rocket.) The payloads will lose a bunch of energy to the atmosphere, but all the remaining energy is kinetic energy delivered directly on target, assuming that you can inexpensively aim the thing at a target. Look up “Rods From God” on Wikipedia — you don’t even necessarily need any explosives.

So the question becomes: how economically can one build the guidance systems, avionics packages, and whatever heat shielding is needed to survive reentry?

(Cold War-era ICBMs with MIRV payloads are sort of in this category, but they treated launch vehicle as disposable, which means that the launch would be far more expensive but the reentry system could likely be a bit simpler as the payloads could be launched from a launch vehicle on a non-recoverable orbit. And it appears that Russia has attacked Ukraine with a MIRV-equipped missile with non-nuclear payloads, so there is precedent.)