The Global Positioning System: A Shared National Asset by Aeronautics and Space Engineering Board, National Research

By Aeronautics and Space Engineering Board, National Research Council Staff

The worldwide Positioning approach (GPS) is a satellite-based navigation approach that used to be initially designed for the U.S. army. despite the fact that, the variety of civilian GPS clients now exceeds the army clients, and lots of advertisement markets have emerged. This ebook identifies technical advancements that might improve army, civilian, and advertisement use of the GPS. numerous technical advancements are prompt that may be made to reinforce the final process functionality.

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However, the accuracy without SA greatly depends on the condition of the ionosphere at the time of observation and user equipment capabilities. Page 4 The NRC committee believes that the principal shortcoming in a denial strategy, regardless of the level of SA, is the difficulty that military GPS receivers currently have in acquiring the Y-code during periods when the C/A-code is unavailable due to jamming of the L1 signal. The implementation of direct Y-code acquisition capability, as recommended in Chapter 3, would provide the optimal solution to this problem.

Military receivers with the appropriate encryption keys can eliminate the effects of SA and obtain an accuracy of approximately 21 meters (95 percent probability). 42 MHz. 3 DGPS is based upon knowledge of the highly accurate, geodetically surveyed location of a GPS reference station, which observes GPS signals in real time and compares their ranging information to the ranges expected to be observed at its fixed point. The differences between observed ranges and predicted ranges are used to compute corrections to GPS parameters, error sources, and/or resultant positions.

Improvement Implementation Strategy Because of the relatively long life time of GPS satellites (5 to 10 years) and the length of time required to replace the total constellation of 24 satellites, opportunities for introducing enhancements and technology improvements to the system are limited. Figure 1 shows the current plan for satellite replacements. According to the GPS Joint Program Office, current plans for the Block IIF contract include 6 short-term and 45 long-term "sustainment" satellites.

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