wrote:
IIRC, President Clinton decreed that the GPS system be made available
for public use. But that was not its original purpose, nor is it now
its first priority. If the DOD wants to take it off line for testing,
that's their prerogative.

I have no time to track down appropriate references, but this is not
correct. Part of the negotiation that resulted in the executive order
involved the DOD giving up the right to do routine area denial
exercises, in exchange for a significant portion of the funding for GPS
upgrades being moved to the civilian budget. In particular,
"operational" use of GPS for safety critical civilian uses was delayed,
in order to provide the military adequate time to develop appropriate
jamming technology. That period has been over for a number of years.
GPS approaches are in routine use. ADS-B is being deployed nationwide.
Cellphone E911 systems are dependent on GPS. Railroad signaling
systems are now heavily GPS based. The DOD no longer has the
"prerogative" to deny GPS within the US whenever they feel like it. Of
course, the US military is no longer accountable to anyone except Donald
Rumsfeld, so I don't expect anyone to particularly care, until a
GPS-related accident results in a major loss of life.

And, people wondered why the Europeans felt the need to build their own
civilian positioning system...