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Comment by justinator | Hacker News Reader

Once all the GPS (or similar) satellites are knocked out, uh, what are you going to use now fight the war?

On either side?

And anyways, what country has the budget to knock out twenty four satellites in quick succession?

And what if this doesn't work? I'm having a hard time thinking the US Gov. doesn't have a shadow GPS constellation up there, somewhere, but I will concede this is the most wahoo part of my meanderings...

I think knocking out GPS is a rather risky move to even try.

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> what country has the budget to knock out twenty four satellites in quick succession?

The only countries between whom a war would be a globally consequential event: the United States, China, and Russia.

Actually any country with a nuclear weapon should be on that list.

And that is quite a few: Israel, UK, France, India with North Korea/Iran not that far behind.

+ Pakistan

That's not enough - you also have to be able to deliver the warhead to the satellite.

It's not very easy to do.

I understand your point, but I think your choice of words underestimates the global consequences of war.

Doesn't have to be knocked out. India developed Indian Regional Navigation Satellite System (IRNSS) because access to GPS is not guaranteed in hostile situations when its controlled by one country, as it happened to the Indian military in 1999 during the Kargil war when it was dependent on GPS and was denied access.

That's a feature, not a bug. GPS is the US-based sat. nav. system. Of course they can turn it off at will.

And of course to get around that, is to put your own sat. nav. system together.

The US military doesn't use GPS for military navigation, they use it for precisely measuring the Earth. This happens almost entirely in peacetime, so no threat to the satellites. US military navigation and guidance systems rely on INS, which is neither jammable nor spoofable, based on the GPS measurements collected in peacetime.

The US military uses very advanced and highly classified inertial navigation technology for both guidance and navigation systems pervasively. GPS was just a way to collect the data required to make inertial guidance effective. The US military has never relied on GPS for anything; the Soviets could destroy it the day it was designed, so it wasn't designed for war.

They do use GPS for military navigation, but as part of a broader suite of systems. For example, Tomahawk missiles use INS for continuous estimates, plus a combination of visual and radar terrain contour matching and GPS to correct the inertial fix. And probably a few other things they don't talk about publicly.

When they can get it, GPS reduces error, though I agree that systems are designed to be tolerant of jamming and shootdowns.

> And anyways, what country has the budget to knock out twenty four satellites in quick succession?

China and USA. Any war that they don't participate in is anyway irrelevant on the global scene.

The US Air Force has a keen interest in SpaceX with its possibility for rapid launches of reusable rockets for this and other reasons. SpaceX is hoping for less than one day turnaround with its most recent design (block 5) of its Falcon 9 rockets[1]. This design is already flying. With enough GPS satellites in storage, they could all be replaced in a week.

[1]https://spacenews.com/spacex-targeting-24-hour-turnaround-in...

There are also much simpler workarounds. Although not as precise, early cruise missiles simply used a gyroscope.

Another option would be hacking the enemie's GPS-like system. I assume we're already hard at work on that.

I imagine that the military is going to be much more effective without having to use workarounds. I doubt current munitions have extra weight dedicated to backup gyroscope navigation (could be wrong). Launching two dozen satellites has to be easier, faster, and cheaper than replacing the whole military's munitions stockpile with less effective weapons.

replying to sibling - i recall reading that ICBMs use celestial navigation.

What country? Russia or China.

They don't have to take them all out at once. Just the threat of the system going sown at any time is enough to make it unreliant.

Think of the threat to the US GPS system. To make it stick, you need to knock out most of the GPS system,

as well as the system of the US allies (EU) and if you do that, you're in hot water with those allies.

I say, good luck with that, sir.

I think 24 missiles pointed at earth targets would have more impact than some pesky satellites.

> as well as the system of the US allies (EU) and if you do that, you're in hot water with those allies.

You will already be in a lot of hot water if you're in a war with the US. The countries who have the capability of doing this have thousands of missiles. A hundred of them being used to knock out some sats is nothing.

Missile launches still involve a significant cost. Firing a missile into space is not a cheap proposition.

And again, what if it doesn't work? You can only try this one time. After that, you lose your element of surprise. Your enemy now knows the enormity of your intent to do harm. Lesson to be learned from Pearl Harbor.

Risky. Risky. Risky.

Presumably you are betting your sextant skills are better than the other guy's.

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