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Comment by helsinkiandrew | Hacker News Reader

Vessels transmitting AIS data over VHF (location, speed, bearing, name, size and rate of turn of vessel etc) help other ships from colliding with it - but it can't really be relied on for tracking and I'd be amazed if any military relied on it (In a military manoeuvre I'd guess they turn it off)

Presumably the GPS was blocked/misdirected 'by some means' and this got published by the AIS systems.

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AIS is an aide to navigational safety, but cannot and is not relied upon as a sole source of data. Not every vessel is required to have it, or have redundant systems for it. As this article suggests it's not verifiable information and can be spoofed in various ways, or just switched off if you're up to no good. Various international bodies are keen to come up with standards to reduce the opportunity for spoofing AIS, but it will likely not go anywhere.

The Project Sandstone series from RUSI digs into various techniques smugglers and sanctions busters use to hide or mask illicit activity at sea.

This isn't manipulation of GPS. Anyone can send a spoofed or manipulated AIS signal, it is quite common in the wild and trivial to do.

Most military systems, and certainly all US ones, rely on inertial navigation systems, not GPS. GPS was considered unreliable for navigation when it was built, which was fine for its intended purpose.

This is patently false. Though we use Inertial, it's one component of an overall system that includes GPS.

When we have degraded GPS we have to allow for larger error margins, based on time since last positional fix. There are other systems that allow us to reset the inertial, including manual fixes, if absolutely necessary.

To say that a modern military doesn't use GPS for navigation is flat wrong.

The US does not use GPS for primary navigation and never has. It is used for small corrections within the (classified) error bounds of INS, which is already very low in state-of-the-art systems. The US largely doesn't rely on a single INS either, but uses large networks of INS and other localization technologies to significantly reduce INS error. The purpose of GPS was to provide a highly accurate model of the world, not to navigate it per se.

Some newer INS technology purportedly can reliably maintain precision within the error margin of GPS corrections for very long periods of time such that it renders GPS corrections largely pointless. The US considers this keystone technology for the military; the state-of-the-art is strictly controlled classified technology.

Last time I looked at INS the state of the art was laser gyroscopes. They were pretty good at maintaining your position, but still suffer from error buildup like any INS system. IIRC the drift became significant (more than 10m) over about a couple of hours of over-land driving. Very good by INS standards, but not something you can solely rely on.

I don't really know anything about this stuff, but recalled a quote from a reasonably trustworthy article I read recently that seems to support your position: https://www.economist.com/science-and-technology/2021/06/12/...

> even the best military-grade inertial-navigation systems, which employ lasers, but not atomic interference, drift by kilometres a day.

Though with this new fancy quantum stuff, INS-only might get more viable.

FWIW, state-of-the-art INS is not publicly available technology. No one knows what the real limits are, only that it is much less than what is available publicly. Cheap systems like guided bombs use conventional laser gyros but they don’t need to maintain their precision very long and they only accept GPS corrections within their drift error (a dozen meters?). When real precision is required, they tend to use laser guidance anyway.

The intended purpose of GPS was navigation. It is reckless to rely solely on GPS for your navigation, but it is a very important part of any modern navigation system.

>> but it can't really be relied on for tracking and I'd be amazed if any military relied on it (In a military manoeuvre I'd guess they turn it off)

I'd agree with that, so who were they trying to spoof?

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