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[aprssig] Fwd: TidBITS#979/18-May-09 - GPS Accuracy!

Brian B. Riley brianbr at mac.com
Tue May 19 13:42:14 UTC 2009



Begin forwarded message:

>
> GPS Accuracy Could Start Dropping in 2010
>
>   by Adam C. Engst <ace at tidbits.com>
> We've all become accustomed to using the Global Positioning System,  
> or GPS, whether via our iPhones, car navigation devices, handheld  
> GPS units, or even watch-based devices like the Garmin Forerunner  
> series. The GPS system went into full operation in December of 1993,  
> was declared a dual-use (military and civilian) system by President  
> Bill Clinton in 1996, and in 2000 had "Selective Availability"  
> removed to increase accuracy for civilian uses. It relies on a  
> constellation of between 24 and 32 medium Earth orbit satellites,  
> some of which have been operating for nearly 19 years. Unlike other  
> national satellite navigation systems, GPS serves the entire world  
> and is maintained by the United States Air Force 50th Space Wing.
>
> So far, so good, but TidBITS reader Mike Craymer, a geodesist who  
> studies the size, shape, and temporal variations of the Earth,  
> recently alerted me to a report about a possible future problem with  
> the accuracy of the GPS system. Mike and his team at Natural  
> Resources Canada use very high-end GPS receivers and special data  
> processing techniques to measure the motions of the Earth with an  
> accuracy of about 1 mm per year in their work defining and  
> maintaining the coordinate systems used in North America and in  
> contributing to the global coordinate system used by GPS. Needless  
> to say, Mike is very interested in GPS maintaining its high level of  
> accuracy.
>
> The problem is that, at the end of April 2009, the U.S. Government  
> Accountability Office released a report expressing concern about the  
> Air Force's modernization and maintenance of the GPS system.  
> Constant replacement and upgrading of satellites is necessary,  
> especially with hardware that's been operating in space for almost  
> two decades.
>
> The GAO's report draws attention to problems that the Air Force has  
> had in working with contractors to build and launch GPS satellites  
> within cost and schedule goals. Some of the problems stem from  
> government acquisition methods that didn't provide for enough  
> oversight, and added requirements that resulted in cost and schedule  
> overruns.
>
> The GAO also lays some of the blame on a series of industry mergers  
> (Boeing buying Rockwell, Boeing merging with McDonnell Douglas,  
> Boeing buying Hughes Electronics Corporation's space and  
> communications businesses) that resulted in moving the GPS work  
> repeatedly and losing knowledgeable workers.
>
> Delays in launching new satellites - the next one is scheduled for a  
> November 2009 launch, almost 3 years late - could be problematic if  
> the older hardware starts failing. The GAO has calculated - using  
> reliability curves for each operational satellite - that the  
> probability of keeping a 24-satellite constellation in orbit drops  
> below 95 percent in 2010, and could drop as low as 80 percent in  
> 2011 and 2012. And if the Air Force doesn't meet its goals for the  
> next-generation GPS III satellites, the probability drops to around  
> 10 percent in 2017. (The GPS III satellites bring with them new  
> features, including new military and civilian signals for greater  
> accuracy, particularly in urban environments, plus higher power for  
> current civilian signals, which will help existing GPS receivers.)
>
> Even if the satellite constellation drops below 24 satellites, that  
> doesn't mean GPS service will fail altogether. It does mean that the  
> level of accuracy that both military and civilian users have become  
> accustomed to - which is actually higher than promised - may degrade  
> significantly.
>
> The GAO has made recommendations for addressing the problems it  
> found in the handling of the GPS system, most notably a single  
> authority to oversee development. Apparently, while the Air Force is  
> in charge of the satellites and ground control, various other  
> branches of the military develop their own user equipment, which  
> makes for coordination problems as the technology is updated and  
> improved.
>
> Another solution may come in the form of international cooperation.  
> Although the GPS system is available worldwide, the European Union  
> has a proposed global navigation satellite system called Galileo in  
> the works, currently due to come online in 2013. Galileo is intended  
> to be a largely civilian system that wouldn't operate at the whim of  
> the U.S. government in time of military conflict, although a 2004  
> compromise makes it possible both for the United States to block the  
> Galileo frequencies and for the two systems to interoperate in the  
> future. Galileo also aims to provide greater accuracy than GPS, and  
> when combined with the next-generation GPS III satellites, could  
> improve accuracy even further.
>
> Russia and China also have satellite navigation systems, and there  
> have been discussions with the Russian government about making the  
> Russian GLONOSS system compatible with both GPS and Galileo. No  
> formal announcement has emerged from those talks, but in 2007,  
> GLONOSS was opened up for civilian use. GLONOSS has a checkered  
> history, coming online in 1995 but falling into disrepair soon  
> after, due to Russian economic troubles. Russia committed to  
> restoring the system in 2001, with a full 24-satellite constellation  
> (necessary for global coverage) in operation by 2010.
>
> From the standpoint of normal people in the United States, there's  
> nothing to do except wait and watch, and, if the opportunity  
> presents itself, make sure your elected representatives are aware of  
> the situation. If you think about how essential GPS-based services  
> have become to society at large in the years since Selective  
> Availability was abolished, you can imagine how much more important  
> those capabilities will become in the next decade.
>
> Personally, I can't imagine that the Air Force would let GPS  
> accuracy drop, especially given the military's reliance on it for  
> everything ranging from helping soldiers find their objectives in  
> the dark to accurate targeting of missiles and other precision- 
> guided munitions. If the GAO's suggestions (with which the  
> Department of Defense agrees) don't resolve the problems faced by  
> the GPS system, the Air Force may end up spending far more money to  
> patch the system on an interim basis.
>
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>

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