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    Re: How likely is a GPS shutdown?
    From: Richard B. Langley
    Date: 2000 Jan 25, 8:38 PM

    On Tue, 25 Jan 2000, Tony wrote:
    
    >Richard:
    >
    >Thanks you. I believe I read several years ago that DOD also has the
    >capability of dithering the time base so that SA accuracy can be degraded
    >further if needed. Is this true?  TIA
    
    Yes, DoD has the ability to adjust the SA degradation to even higher
    levels.  But SA will be switched off by 2006 under presidential directive.
    The SA security measure will be replaced by in-theatre jamming.
    -- Richard Langley
       Professor of Geodesy and Precision Navigation
    
    >Tony
    >
    >Richard Langley wrote:
    >>
    >> PPS uses the encrypted P-code on both the L1 (same as civilian SPS) and the L2
    >> carrier. However, there are DoD single-frequency (L1) receivers and these
    >> also have SA and A/S decryption capability.
    >> -- Richard Langley
    >>    Professor of Geodesy and Precision Navigation
    >>
    >> On Tue, 25 Jan 2000, Rodney Myrvaagnes wrote:
    >>
    >> >This is not quite right, although the rest of RBE's post is
    >> >right on. The military receivers that can get the encrypted
    >> >(long) word get it over another carrier than that used by
    >> >the C/A word decoded by civil receivers. There is no way
    >> >for your Walmart gps to use the military code.
    >> >
    >> >
    >> >During the Gulf War, SA was turned off because the military
    >> >had to use civilian receivers. SA was an afterthought,
    >> >applied because the civil receivers turned out to work much
    >> >better than expected.
    >> >
    >> >On Mon, 24 Jan 2000 19:09:42 -0500, Richard B. Emerson
    >> >wrote:
    >> >
    >> >> >
    >> >> > I suspect that the military has its own encrypted version
    >> >> > of GPS although this is simply a guess on my part.
    >> >>
    >> >>One of the absurdities of GPS is that during Desert Storm and Panama,
    >> >>GPS' selective availability was turned off.  Thus, for a short period,
    >> >>the normally encrypted data segment (it's already there and used
    >> >>routinely) was available unencrypted.  Consider, too, the error even
    >> >>with S/A enabled.  A fuel-air bomb (or ammonium nitrate bomb) could
    >> >
    >> >
    >> >
    >> >Rodney Myrvaagnes                   J36 Gjoa
    >> >Senior Editor           Electronic Products
    >> >My oyster knife is Y2K compliant
    >> >
    >>
    >> ===============================================================================
    >>  Richard B. Langley                            E-mail: lang---.ca
    >>  Geodetic Research Laboratory                  Web: http://www.unb.ca/GGE/
    >>  Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506 453-5142
    >>  University of New Brunswick                   Fax:      +1 506 453-4943
    >>  Fredericton, N.B., Canada  E3B 5A3
    >>      Fredericton?  Where's that?  See: http://www.city.fredericton.nb.ca/
    >> ===============================================================================
    >
    
    
    ===============================================================================
     Richard B. Langley                            E-mail: lang---.ca
     Geodetic Research Laboratory                  Web: http://www.unb.ca/GGE/
     Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506 453-5142
     University of New Brunswick                   Fax:      +1 506 453-4943
     Fredericton, N.B., Canada  E3B 5A3
         Fredericton?  Where's that?  See: http://www.city.fredericton.nb.ca/
    ===============================================================================
    

       
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