Inkognito wrote:
Don’t the US routinely degrade the GPS in conflict zones?
My understanding is that the US does not degrade the GPS in conflict zones. In 2000, President Clinton signed an executive order pledging to not use Selective availability. All the new US GPS satellites do not include the SA (Selective Availability) function. SA degrades the position of the L1 frequency, but the military uses L2 and it is encrypted, so only for military usage.
Isn’t the degradation through ECM aircraft, at least that is my understanding in the UK.
That will need a very large constellation of jamming aircraft… It’s so much easier by degrading the precision at satellite level.
NCYankee wrote:
All the new US GPS satellites do not include the SA (Selective Availability) function.
I have also read that, but in what sense do the satellites “not include” SA? It’s all in software and I can’t imagine that the US can’t upload new software supporting SA if they want to.
SA is not jamming, it is the ability to reduce the accuracy of the GPS to about 100 meters. That would not block using GPS for RNP APCH to the LNAV MDA. It would make LPV or LP unusable. With other military using their own satellites, why would they bother to depend on the US satellites for their missiles or bombs. SA would deny an opponent to use the US GPS for precise targeting. The military decided that it was unnecessary for national defense to continue to support SA.
There are regular military exercises where the GPS is actually jammed so that the participants can practice in a non GPS environment. We had one off the SE coast in January while the military held their fleet exercise. These are announced in advance via NOTAM.
NCYankee wrote:
SA is not jamming,
No, it’s the satellites sending slightly incorrect information.
Hi,
SA does still exist and it’s been modified depending on the Geopolitical scenario in certain areas of the world.
Jamming is not Spoofing. Jamming will deny the use of the GPS signal (low/bad reception or not reception at all) while Spoofing will provide a “valid” signal but incorrect to the receiver unnoticed.
In a jamming scenario you can revert to non GPS scenario and you are good, in a spoofing scenario…it’s a little bit trickier. Jamming is relatively easy, Spoofing is VERY difficult, takes a lot of energy and the area is usually small.
For civil aviation, ideally there should be hybrid navigation between INS/GPS or NAVAIDS/GPS with a crosscheck and monitoring feature. RAIM is obviously necessary too. Most serious incidents with GPS in aviation are usually related to Spoofing. Neverthelessm either jamming or spoofing can cause serious damage to civil aviation since it could mean the unavailability of several RNAV, LPV, etc.. procedures.
speed wrote:
SA does still exist and it’s been modified depending on the Geopolitical scenario in certain areas of the world.
I don’t think this is accurate, at least for the US GPS system.
Early April, there were definitely GPS signal losses south of Cyprus. Not only me, but also airliners on the frequency.
