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Comment by nathanfig | Hacker News Reader

Uhh so the author is saying that missiles designed to go faster will actually be slower because of drag? Is there a source on that claim or is it just speculation? I'm imagining someone at DARPA reading this and thinking, "Drag! Of course! That's why our missiles keep going so slow! If only we had thought of that!"

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The drag argument is that ballistic missiles spend a fair amount of time above the atmosphere, and that hypersonic missiles don't. Such that in the end, the ballistic missiles get there faster.

The article, though, doesn't mention that the arc trajectory of ballistic missiles means they are spotted faster: https://www.economist.com/sites/default/files/images/print-e...

That’s a great visual! Thanks for sharing. One thing to note from the article is these hypersonic weapons will generate insane amounts of heat which will show up on satellite imagery so they’re not as stealthy as that visual purports. Additionally, they’re powered by the same type of rocket boosters as an icbm so the same type of early launch detection system would still work to alert the moment a missile has been launched.

For ground based targeting radar at the destination at least. Not sure how relevant this is with satellite based radar or infrared detection systems.

The article, though, doesn't mention that the arc trajectory of ballistic missiles means they are spotted faster.

But such missiles are nowadays - as far as I know - primarily detected via infrared from space and not radar stations near the target which turns the atmospheric trajectory into a disadvantage due to heating of the vehicle which is also mentioned in this article.

I wonder if this fact is connected to the advances in anti-satellite weapons in recent years.

They aren't designed to go faster than ballistic missiles, they are designed to go faster than cruise missiles, and just overall very fast for something moving in the atmosphere. On a space scale they aren't very fast, about a sixth of LEO orbital velocity.

Hypersonic missiles are faster than cruise missiles but slower than ballistic missiles and confusing the two is a common mistake in the popular press when talking about how fast hypersonic missiles are.

In terms of ground speed, yes, but in terms of flight time, no. ICBMs are also easily identified and tracked compared to low flying cruise missiles. Hypersonic weapons are essentially shorter range cruise missiles. How do you defend against these? The narrative is that as long as nuclear weapons are prolific, anything that sidesteps deterrence is a threat to the species.

The good news is that this doesn't seem like it affects submarines significantly. So the defending nation should still have second-strike capability, making it unwise to initiate an attack.

Speaking of, imagine someone sending a satellite full of "ICBM" to space, covertly enough. How do you identify what it is? It's even harder than finding submarines if there's enough "chaff" launches. Dead Hand is a toy in comparison. You have no chance to intercept as the delay is too short and speeds are orbital. Better hope your spies know which satellites are weapon platforms.

Cruise missiles are already extremely hard to defend against, in as much as doing so requires the defender to identify all nearby ships, submarines, airplanes and other covert launch points. (ECM is not good enough, SAM also has no chance. Cannons and interceptors have low chance of spotting these as well.) Hypersonic version does not bring all that much to the table there, if anything.

Maybe by Anti-Neutrino detection?

> Uhh so the author is saying that missiles designed to go faster will actually be slower because of drag?

He isn't. He's saying the drag creates a large heat signature which makes them vulnerable to existing detection techniques.

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