IIRC, the GPS isn't really "shut down" it's encrypted to ensure authorized use only.
I could be wrong but I'd swear that was what I was taught in 1992 when I first trained on the GPS.
GPS has some intentional noise introduced into its signal to limit the accuracy of receivers - a cheap GPS unit would be able to say "I'm within a 100-foot circle of here". Military gear had the capability of removing the noise, so GI's could be "here" within a much smaller circle of error.
In 2000 or so, the military removed the noise from the signal so everyone could be "here", closer together.
BTW, GPS stands for "gets people somewhere".
It is ALWAYS encrypted. The Military would have no problem shutting down only the parts civilians can decode while retaining all the other parts.
"IIRC, the GPS isn't really "shut down" it's encrypted to ensure authorized use only.
I could be wrong but I'd swear that was what I was taught in 1992 when I first trained on the GPS."
Essentially correct.
Prior to Desert Storm, Commercial GPS capability was limited to something on the order of 10 +/- meter accuracy. THis provision and control measure could be re-introduced, providing military applications with the required 1 meter +/- accuracy
And it can be done in stages. AFAIK, the precision "code" is available to all right now. That can be encrypted so that only military users can get the most accurate position information needed for weapon guidance. Others can still get lower quality position information.