I was thinking of GPS jamming as a missile defence shield of sorts, around cities and sensitive areas, to be turned on when the nation is under attack.
If our birds need GPS, the jammers could be switched off while they are in transit over the sensitive areas.
Maybe this is too much like science fiction.
There is no need for any US adversary to jam our GPS signals...We will do it for him free of charge...
GPS Selective Availability - USCG Navigation Center
The decision to discontinue SA is coupled with our continuing efforts to upgrade the military utility of our systems that use GPS, and is supported by threat assessments which conclude that setting SA to zero at this time would have minimal impact on national security. Additionally, we have demonstrated the capability to selectively deny GPS signals on a regional basis when our national security is threatened. This regional approach to denying navigation services is consistent with the 1996 plan to discontinue the degradation of civil and commercial GPS service globally through the SA technique.
Here is the scoop on GPS Selective Availability...
Information about the End of GPS Selective Availability
Selective Availability (SA) was an intentional degradation of public GPS signals implemented for national security reasons. At the direction of the President, SA was discontinued in May 2000 to make GPS more responsive to civil and commercial users worldwide. The U.S. Government has no intent to use SA again.
The Selective Availability feature degrade, or decrease the accuracy level of the public signal while keeping the military signal superior. It has to do with altering the timing clock signals transmitted to any receiver. Once the US is able to improve upon this SA feature, which is to disable the entire GPS system
ONLY WHEN THE SATELLITES ARE OVER A CERTAIN GEOGRAPHICAL LOCATION there is no need to continue using the 'old' Selective Availability feature when the 'new' one offers much more flexibility.
But if we can disable GPS regionally, who is to say that we cannot introduce errors into the signals, regionally of course, instead of disabling them? Of course we can so introduce such errors and have no doubt that such capability is already in place and tested.
What does that mean for any potential US adversary whose weapons rely on the American GPS for accuracy? What use is it to jam when the signals themselves are suspect? But how would he know that they are suspect and
WHEN did they, or would they, become suspect? How would he know that his missiles would land on empty sea instead of a US aircraft carrier? Inertial Navigation (INS) is no good against a moving target. For all he know, his missiles may return to base because they were using erroneous signals.
Selective Availability (SA) is no longer necessary. We got selective regional availability instead. Do not put all your eggs into the Russian or the Chinese baskets. Satellites do not last forever and these GPS satellites are replaced by US on a regular basis. Neither the Russian nor the Chinese have anything near the capability of the first generation of US GPS satellites...
GPS Satellite Generations
The Block IIF satellite, a generation of GPS vehicles that are planned to replace older satellites. Boeing NASSD is the prime contractor for the Block IIF, which incorporates current technology to sustain the GPS utility for military and commercial use. The NAVSTAR Global Positioning System (GPS) Joint Program Office procurement of the NAVSTAR Global Positioning System Sustainment (Block IIF) will sustain the quality GPS signal as a world-wide utility well into the next century at the lowest technical risk and acquisition and life-cycle costs. GPS Block IIF will be backward compatible with previous GPS satellite, control facilities, and user equipment. The proposed procurement for a constellation of 51 GPS Block IIF series satellites has been reduced to 33 satellites.
The American GPS was originally intended for military purposes but as long as the rest of the world continues to benefit, economically and humanitarian, from the American GPS system, and there is no doubt that a lot of money have been made and civilian lives saved, from environmental issues to agriculture, because of this technology, it will be difficult for Russia, China or even the EU to justify spending billions to develop an alternative system.