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    Re: Turning Off the GPS
    From: Lu Abel
    Date: 2006 Apr 5, 08:31 -0700

    You are absolutely right about the EU developing EUREKA (and I can fully
    understand the EU's desire to field a system under their own control).
    But Gordon's "we need to keep our sextant skills up" note was addressed
    to the idea of *terrorists* disabling GPS, not the US government.
    As a practical matter, GPS has become deeply embedded in 21st century
    life.   For at least the past decade people have regarded the ability to
    accurately determine one's position as a new, universal utility.  That
    was one of the reasons for disabling Selective Availability.  WAAS is a
    precursor to GPS being used as a new paradigm for air traffic routing.
    In the US all new cell phones are now required to give positional
    information to 100 meters or less.  While there are a number of
    techniques for doing this (eg, triangulation), one of the most
    successful and widely adopted is embedding a GPS receiver in the cell
    phone.  GPS-based mapping systems are one of the most popular options on
    new cars.  I even have been told that John Deere is experimenting with
    driverless, GPS-directed tractors for plowing farmer's fields!  And on
    and on...
    At this point, it would be difficult for even the most paranoid US
    leader to turn off GPS.  As a specific example, I'll note that Selective
    Availability was not re-enabled after 9/11.
    Lu Abel
    Marcel Tschudin wrote:
    > Please correct me if I should be wrong: Since GPS is controlled by the
    > US military it only needs a decision from the US administration to swich
    > it off. This is, to my understanding, the reason why Europe decided to
    > set in place their own system called EUREKA.
    > Marcel
    > On 4/5/06, *Lu Abel* >
    > wrote:
    >     With all respect, Gordon, it would take a lot more technology than the
    >     terrorists have to turn off GPS much less to make it give incorrect
    >     positions.   GPS uses satellites.  One would need satellite-killer
    >     missiles to "turn off" GPS.  Only two or three countries (USA, Russia,
    >     China?) have the technology (which, BTW, includes the technology and
    >     infrastructure to track and identify the target before saying to the
    >     missile "go get 'em").  To make GPS give the wrong position would
    >     require taking over the US's GPS control centers and I'm sure the US
    >     military has put a lot of thought and effort into preventing that.
    >     There are GPS jammers available on the arms market, but they work only
    >     over a small theater of operations.  Nowhere I'd be sailing, hope you
    >     won't be there either.
    >     Last but not least, terrorists are interested in, well, terror.  I
    >     suspect they'd far rather kill a few thousand of their perceived enemies
    >     than inconvenience them by turning off GPS....
    >     Lu Abel
    >     Gordon Talge wrote:
    >      > Just for the heck of it, I wonder what would happen,
    >      > if some terrorists managed to turn off the GPS system, or
    >      > maybe even better, have it give the wrong positions.
    >      >
    >      > I have noticed that a lot of people seem to say they keep
    >      > a sextant and tables, etc, for backup. The problem that I
    >      > see with that is it takes a lot of practice to get good at using a
    >      > sextant and working out sights by hand. Someone who has
    >      > only tried out their sextant on a calm day or on the beach,
    >      > may find it hard to get a decent shot on a pitching boat
    >      > or ship, and then work out a sight where one slip of a
    >      > plus or minus, or wrong column, would make it all for naught.
    >      >
    >      > BTW,
    >      >
    >      > Has anyone seen those German films of the U-Boats during World War II
    >      > in the North Atlantic pitching and rolling? I start getting seasick
    >      > just watching it. I saw one where a German Officer was taking a noon
    >      > sight on a sub like that. They may have been the enemy, but they
    >      > sure had guts. (It took guts to stand up to them too)
    >      >
    >      > -- Gordon
    >      >
    >      >

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