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Comment by chiph | Hacker News Reader

How would it navigate? GLONASS signals won't penetrate the water to the depths mentioned. The 1.6 and 1.2 Ghz bands it uses won't even go through 1 meter of seawater [0] A star tracker would also be worthless. An inertial reference might be "good enough", as in "close enough for nuclear war"

[0] https://www.researchgate.net/figure/Radio-wave-attenuation-b...

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Instead of thinking of this like a missile, instead think of it like a submarine. Submarines don't use star tracking, they use inertial navigation systems to inform dead reckoning. This accumulates error over time, but my impression is they work a lot better than you might expect.

> Instead of thinking of this like a missile, instead think of it like a submarine

I'm former Air Force, so that sort of comes with the territory. Sorry. :)

You also don't need perfect accuracy for something that is a weapon of last resort with a 1km blast radius and 500,000 km^2 fallout radius.

This is very much a solved problem, for several decades now. US and Russian naval submarines routinely patrol for thousands of miles over weeks or months, without surfacing.

https://en.m.wikipedia.org/wiki/Submarine_navigation

It's not mentioned in the article, but I believe US subs also have a long-tether communications buoy that can float to the surface, but not expose itself vertically, to communicate with satellites. I would be surprised if it did not also have a GPS antenna.

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