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Comment by ethbro | Hacker News Reader

I don't have firsthand knowledge, but I'd be surprised if mission critical military gear uses GPS for more than a secondary / corrective role.

I can't imagine the signals play that well in a heavily-jammed environment.

High probability rough GPS fix + radar / optical terrain comparison & dead reckoning for terminal guidance seems more likely.

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I'm not sure if you consider this "mission critical" but US military drones use GPS for navigation. There have been several cases of them being captured via GPS jamming.

From what I heard, that extended to GPS spoofing.

Military GPS devices have access to more frequencies and channels that consumer devices don't have. These frequencies use anti-jamming techniques (frequency hopping using pseudo-random patterns, etc). They also have much better accuracy available to them than the consumer devices. Typical dumb jamming systems aren't really going to do much against military anti-jamming techniques and if it really is hurting comms they can send in an anti-radiation missile and blow up the jammer, no GPS needed.

Do you have a source for the better accuracy claim?

I know they turned off Selective Availability ( https://en.m.wikipedia.org/wiki/Error_analysis_for_the_Globa... ) in 2000, so not sure if it's been true since then.

From what I was reading, it seems like semi-codeless approaches to the P(y) (aka military) signal offer approximately similar accuracy to actually being in possession of the key.

Furthermore, the P(y) signal uses the same L1 and L2 frequencies as civilian devices. Which makes sense when you're designing a system with 1970s broadcast technology.

From Wikipedia, it seems like the soon-to-be-launched Block IIIA satellites are the first that will incorporate the ability to spot-beam at higher power ( https://en.m.wikipedia.org/wiki/GPS_Block_IIIA#New_navigatio... ).

A non-insignificant portion of what GP said is mumbo jumbo. The reason military usage of GPS is more accurate is most significantly due to usage of multiple frequencies (which is now available to civilian too). What you’ve stated indicates you have good sources, so I recommend trusting those and asking questions if there’s gaps rather than trusting random folks commenters (yes, guess this includes me).

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