Friday, March 12, 2010


Another cartoon by The New Yorker regular, Roz Chast, this one from June 2003.  GPS satellites can, in fact, be this capricious.  Allow me to explain:
The GPS technology was initially developed in the 1970's.  When the Cold War ended the companies that helped the DoD create it requested that they be allowed to market the technology commercially.  The Defense Department finally agreed, but on condition that they could scramble the signal so that nobody could have locations as accurate as the military. So while the military had sub-centimeter-accurate locations, everybody else was limited to locations +/- 30 meters. Within a year of its commercial release some intrepid users had found a way to get around the scrambled signal.  After further lobbying the DoD released a more accurate commercial signal, but with a more sophisticated signal scramble so that the commercial devices could be accurate to within 10 meters.  Users cracked that signal within 6 months.  Finally the military gave up and let the same signal they had out to everybody.  They still reserve the right to scramble the signal whenever they deem it necessary, and that could cause this kind of bad behavior.  But with the launch of the European "Galileo" GNSS, and the upcoming launch of the Chinese version, what's the point?

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