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> so in the event of a war the DOD can disable the civilian signal as the M code will work standalone, hence a third party nation cannot rely on GPS. They also
by eiaoa 8y ago
> so in the event of a war the DOD can disable the civilian signal as the M code will work standalone, hence a third party nation cannot rely on GPS.
They also had the option in older satellites of turning on selective availability, which would degrade the civilian location service from 5-meter to 100-meter accuracy without affecting the military service. Purportedly newer GPS satellites don't have the option anymore.
https://en.wikipedia.org/wiki/Error_analysis_for_the_Global_Positioning_System#Selective_availability https://en.wikipedia.org/wiki/Error_analysis_for_the_Global_...
- rangibaby 8y ago> Purportedly newer GPS satellites don't have the option anymore. That does sound suspiciously like something the military would want you to believe
- vlovich123 8y agoSelective availability was defeated a very long time ago so no reasons to doubt that the military gave up on it. Pretty sure they're just using an encrypted transport for the military signal so they can do whatever they want to civilian GPS wholesale without impacting the military. However, I'm not sure how that will work since it underpins our entire economy from logistics to air travel. On the other hand, at the point the military is disabling civilian GPS probably the economic impact is less of a concern.
- labcomputer 8y agoIt's worth mentioning here that SA-less Block IIF (and newer) satellites came after "codeless" and "semi-codeless" techniques were publicly-known. Those allow a receiver to use the encrypted P(Y) code to obtain a precise position fix without any knowledge of the encryption key. There are probably other, newer ways to prevent an adversary to use the GPS signal, but there is little reason to doubt that SA is gone.