It's not really an alternative to GPS. It has no idea where on earth you are, it simply accurately tracks your motion through the world but it has no idea where that motion is occurring, you have to start off with a known starting point, then it tracks your motion to work out your current location. But it is only as accurate as the accuracy of the starting point, if that's off by 400 m then so will be the result.

It's basically a very good inertial navigation system, plus this isn't the first time it's been tested it's been tested on ships and planes before.

It's not going to replace GPS for commercial purposes because there's very few scenarios where you don't have a GPS up link. But it'll be useful is in situations where that's not possible like on submarines or yeah in space. It isn't like your car is ever going to use this though.

This sounds pretty fancy.

Commercial aircraft get their location from multiple places including GPS, ground based facilities (VOR's), IRS, etc. IRS is what I'm used to calling it, but it's the same as INS, which is what this article is talking about.

It determines location by keeping track of rotation, acceleration, etc. It's often called "dead reckoning" because it just gives the best guess, and you don't know how accurate it is. There are multiple of these devices on each aircraft, and they compare their locations to the other sources and if one is drifting way further than the rest, it gets ignored. That's a very basic explanation because how it really works is way above my knowledge level.

It's very cool how these devices find their location, though. When you first boot the system up, it spends about 5 minutes measuring the rotation of the Earth. For this reason, you can't reset it when in motion. Based on what it feels it can determine your exact location on the surface of the earth.

So it thinks you're everywhere at once until you look out the window and observe your position?

Does anyone know how much more accurate this is compared to other interferometer gyroscopes like fiber-optics?

This would be a great idea for caving

Yeah won't work without stars or a reference point.

A beacon in the warp….