GPS Briefs: Number of GPS Satellites Expanding, Jamming Threat Increases, "Wakening" Sun

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The number of GPS satellites in operation will increase over the next couple of years from 24 to 27.  Driving this increase, in part, is the need for increased GPS coverage and accuracy in Afghanistan.  That country’s deep valleys and steep mountainous terrain make GPS coverage spotty or non-existent in some areas, hampering the ability of the U.S. military to operate as needed.  The additional satellites will also benefit other users of GPS technology with the improved signals.

Read more: More Satellites Will Act as Eyes for Troops NY Times

A recent conference hosted by the Digital Systems Knowledge Transfer Network in the United Kingdom called attention to the vulnerability of GPS units to jamming.  “The strength of a GPS signal is about as strong as viewing a 25W light bulb from a satellite 10,000 miles away,” said Bob Cockshott, a director of the Digital Systems KTN. “It’s no surprise then that GPS signals are vulnerable to natural and, increasingly, criminal interruptions.”  The conference also noted that thieves are used illegal GPS jammers imported from China to help them steal cars and trucks.

Read more: Jamming of GPS signals threatens vital services – Financial Times

Earlier this month, researchers warned that the increase in solar activity will have an impact on the reliability of satellite navigation systems.  Over the next few years, the sun will build up to its peak of activity causing disruption in navigation devices.

Read more: Sat-nav devices face big errors as solar activity risesBBC News



A simulation of the original design of the GPS space segment, with 24 GPS satellites (4 satellites in each of 6 orbits), showing the evolution of the number of visible satellites from a fixed point (45ºN) on earth (considering "visibility" as having direct line of sight). The parameters used to simulate the orbits are: eccentricity (e) 0.05, inclination (i) 55º and a separation between orbits of 60º in the right ascension of the ascending node. Within each orbit, the four satellites are evenly spaced (the instant of pass through perihelion being arbitrary for the first satellite in each orbit). The orbital period of the satellites was taken to be 12 hours. The earth was considered a perfect sphere with a radius of 6400 km. The time in the animation is running about 2880 times faster than real time (half a minute representing 24 hours),as clearly seen in the rotation of earth. The simulation was created using MATLAB and converted to animated gif format using Adobe ImageReady.


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