Last month the U.S. Department of Defense announced that it intends to stop procuring global positioning system (GPS) satellites with the capability to intentionally degrade the accuracy of civil signals. This capability, known as selective availability (SA), will no longer be present in the next generation of GPS satellites.
Selective availability was originally designed to enable intentional degradation of signal accuracy so that enemies could not use it to target missiles during wartime. According to some sources, the military now has other ways to deny GPS use that will not disrupt accurate use by civilian aircraft, emergency vehicles etc.
Although the United States stopped the intentional degradation of GPS satellite signals by setting SA levels to zero in May 2000, this action to permanently remove SA eliminates a source of uncertainty in GPS performance that has been of concern to civil GPS users worldwide for some time, said the DoD in a release. While this action will not materially improve the performance of the system, it does reflect the United States' strong commitment to users by reinforcing that this global utility can be counted on to support peaceful civil applications around the globe.
The decision to remove the capability from the next generation GPS satellites was approved by President Bush after a recommendation from DoD. The move coincides with the U.S. Air Force's solicitation to purchase the next generation of GPS satellites known as GPS III.
GPS is a dual-use, satellite-based system that provides accurate positioning, navigation and timing information to users worldwide. Originally developed by the Department of Defense as a military system, GPS has become a global utility. It benefits users around the world in many different applications, including aviation, road, marine and rail navigation, telecommunications, emergency response, resource exploration, mining and construction, financial transactions and many more.