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The AN/MPQ-64 Sentinel is an X-band electronically steered pulse-Doppler 3D radar system used to ... (IFF) upgrade adds Mode S support with GPS M-Code capability. AN ...
A Selective Availability Anti-spoofing Module (SAASM) is used by military Global Positioning System receivers to allow decryption of precision GPS observations, while the accuracy of civilian GPS receivers may be reduced by the United States military through Selective Availability (SA) and anti-spoofing (AS). [1]
The M-code is transmitted in the same L1 and L2 frequencies already in use by the previous military code, the P(Y)-code. The new signal is shaped to place most of its energy at the edges (away from the existing P(Y) and C/A carriers). It does not work at every satellite, and M-code was switched off for SVN62/PRN25 on 5 April 2011. [29]
In a major departure from previous GPS designs, the M-code is intended to be broadcast from a high-gain directional antenna, in addition to a wide angle (full Earth) antenna. The directional antenna's signal, termed a spot beam , is intended to be aimed at a specific region (i.e., several hundred kilometers in diameter) and increase the local ...
Coarse-acquisition (C/A) and encrypted precision (P(Y)) codes, plus the L1 civilian and military (M) codes on Block III and newer satellites. L2: 1227.60 MHz: P(Y) code, plus the L2C and military codes on the Block IIR-M and newer satellites. L3: 1381.05 MHz: Used for nuclear detonation (NUDET) detection. L4: 1379.913 MHz
Few civilian receivers have ever used the P-code, and the accuracy attainable with the public C/A code was much better than originally expected (especially with DGPS), so much so that the antispoof policy has relatively little effect on most civilian users. Turning off antispoof would primarily benefit surveyors and some scientists who need ...
Like earlier GPS satellites, Block IIF spacecraft operate in semi-synchronous medium Earth orbits, with an altitude of approximately 20,460 km (12,710 mi), and an orbital period of twelve hours. The satellites supplement and partially replace the GPS Block IIA satellites that were launched between 1990 and 1997 with a design life of 7.5 years ...
Samples of three GPS satellites' orbits over a five-year period (2013 to 2018) USA-242 · USA-239 · USA-151 · Earth As of 22 January 2025, 83 Global Positioning System navigation satellites have been built: 31 are launched and operational, 3 are in reserve or testing, 43 are retired, 2 were lost during launch, and 1 prototype was never launched. 3 Block III satellites have completed ...