A Selective Availability Anti-spoofing Module (SAASM) is used by military
Global Positioning System
The Global Positioning System (GPS) is a satellite-based hyperbolic navigation system owned by the United States Space Force and operated by Mission Delta 31. It is one of the global navigation satellite systems (GNSS) that provide ge ...
receivers to allow decryption of
precision GPS observations, while the accuracy of civilian GPS receivers may be reduced by the
United States military
The United States Armed Forces are the Military, military forces of the United States. U.S. United States Code, federal law names six armed forces: the United States Army, Army, United States Marine Corps, Marine Corps, United States Navy, Na ...
through
Selective Availability
The error analysis for the Global Positioning System is important for understanding how GPS works, and for knowing what magnitude of error should be expected. The GPS makes corrections for receiver clock errors and other effects but there are sti ...
(SA) and
anti-spoofing (AS).
However, on May 1, 2000
it was announced that SA was being discontinued, along with a United States Presidential Directive that no future GPS programs will include it.
Before the advent of
L2C, AS was meant to prevent access to dual-frequency observations to civilian users.
SAASM allows satellite authentication, over-the-air rekeying, and contingency recovery. Those features are not available with the similar, but older, PPS-SM (Precise Positioning Service Security Module) system. PPS-SM systems require periodic updates with a classified "
Red Key" that may only be transmitted by secure means (such as physically taking the receiver to a secure facility for rekeying or having a trusted courier deliver a paper tape with a new key to the receiver, after which that paper tape must be securely destroyed). SAASM systems can be updated with an encrypted "
Black Key" that may be transmitted over unclassified channels. All military receivers newly deployed after the end of September 2006 must use SAASM.
SAASM does not provide any additional anti-jam capability, however, the higher data (chipping) rate of
P(Y) code can provide a higher processing gain which will provide better tracking performance in a jamming environment. Future GPS upgrades, such as
M-Code, will provide additional improvements to anti-jam capabilities.
SAASM hardware is covered with an anti-tampering coating, to deter analysis of their internal operation.
Deployment of the next generation military signal for GPS, called
M-code, commenced with the launch of IIR-M and IIF satellites, beginning in 2005. A complete constellation of 18 satellites with M-code capability is planned for 2016.
See also
*
Defense Advanced GPS Receiver
The AN/PSN-13 Defense Advanced GPS Receiver (DAGR; colloquially, "dagger") is a handheld GPS receiver used by the United States Department of Defense and select foreign military services. It is a military-grade, dual-frequency receiver, and has ...
*
Precision Lightweight GPS Receiver
The AN/PSN-11 Precision Lightweight GPS Receiver (PLGR, colloquially "plugger") is a ruggedized, hand-held, single-frequency GPS receiver fielded by the United States Armed Forces. It incorporates the Precise Positioning Service — Security ...
References
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External links
GPSworld.com article "Saving SAASM"by Robert Huffman (January 2006) - The file is not available.
Global Positioning System