31–40 of 52 posts
The evidence shows that the contrary. Has a plane ever gone down from “electronic warfare?” If a motivated adversary know you have a defence, they will find a way around it, meaning you can only go so far in defence
Earlier quoted context omitted.
Radio goes through and reflects off things, including aircraft. GPS signals are incredibly weak, and even if an aircraft attenuates or reflects 99.9% of the signal, a ground based system will nearly always be able to overpower it. It can be as simple as reflecting off the tail section of the aircraft.
Incredibly weak is correct and even bordering on understatement. They are below the noise floor by about 50dB (which is a logarithmic scale, so is a factor of 100,000x).
For the past 10 years I've been travelling to Russia occasionally. Normally during a flight I like opening up my GPS app to check the location, altitude and speed of the aicraft. About a year ago I noticed that shortly after crossing Russias border the GPS stopped working. Initially I thought it was a glitch, but after a few flights it became obvious that something was going on, probably the signal was baing jammed.…
GPS isn’t the only navigation tool. INS is pretty accurate if you zero it correctly, and VOR is good enough to keep to a specific airway.
A perfect use case for public key cryptography. Digitally sign the GPS coords!
For the past 10 years I've been travelling to Russia occasionally. Normally during a flight I like opening up my GPS app to check the location, altitude and speed of the aicraft. About a year ago I noticed that shortly after crossing Russias border the GPS stopped working. Initially I thought it was a glitch, but after a few flights it became obvious that something was going on, probably the signal was baing jammed.…
RNAV (or aRea Navigation) based on VOR-DME has been a thing since (at least) the 1970's. You put in a waypoint based on a radial and distance from a navaid, and then the box in the cockpit would Do Math so you could follow a track to/from that virtual navaid.
Bendix even made a cute little box for small airplanes in the 1980's that allowed you to pre-store up to 4 (or 10) such waypoint-frequency tuples and cycle through them to approximate a straight path from your origin to destination, using navaids near (but not on) your route. Given the service volume of a typical VORs, the 10 waypoints could enable a flight segment of over 2,000 km before you needed to enter more waypoints.
Around the same time, the flight management systems in airliners began to have navaid databases, allowing you derive lat/lng from the angle and distance. They could even auto-select the best local navaid to use. That enabled DME-DME area navigation, which has ~10x better precision than VOR-DME.
The flight management systems in modern airlines of course still have these databases and support navigation by ground-based navaid.
Russia still operates their version of LORAN (Chayka), too, so that's another option. By the 1980's, LORAN receivers were pretty well automated and directly produced lat/lng outputs. LORAN has worse accuracy than GPS, about ~400 meters, but is still good enough to get you to the airport.
And, as several other people have mentioned, virtually all airliners continue to carry an INS.
A perfect use case for public key cryptography. Digitally sign the GPS coords!
Perhaps I just don't understand how this works all that well, but shouldn't it be easy to defeat GPS spoofing when you're 30,000+ feet in the air? Presumably the spoofed GPS signals are all coming from the ground, or close to it. I would think it would work to use a semi-directional antenna that is on top of the aircraft, pointing upward. Even an antenna that has a 180-degree field of view should reject fake GPS sign…
Earlier quoted context omitted.
Incredibly weak is correct and even bordering on understatement. They are below the noise floor by about 50dB (which is a logarithmic scale, so is a factor of 100,000x).
It still blows my mind that gps even works given how far below the noise floor it is. I am very far from being any sort of expert in radio theory but my layman understanding is that the receiver "knows" exactly what a gps signal should look like and somehow magically uses that to extract the data out of the noise. It is one of those absolutely genius aspects of modern life, and we tend to just take for granted
Fortunately I only saw this afterwards, otherwise I would have been worried.
(obviously we didn't actually make this detour)
