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    Re: GNSS is not immortal
    From: Steve Dunlop
    Date: 2018 Sep 25, 08:37 -0700

    Brad,

    Thank you for the carefully written reply.

    << <<Enemy action (hacking) of command and control systems>> Only in the movies.  It's possible but highly unlikely.  Please do not think of military systems as Mickey Mouse Club toys.>>

    I write software for a living and have done so since 1983.  Security and encryption are professional interests of mine.

    During my career, I have seen many carefully vetted systems that were widely thought to be unbreakable, compromised.  Pillars of secure computing like DES, MD5, and SSH have been found to be less secure than was once thought.  We've seen the extensive leaks of military data by Chelsea Manning.  We've seen the Air Force's drone command and control system brought down by an old-school virus.  Stuxnet showed us how a well-financed, motivated opponent can destroy equipment remotely in an air-gapped system.

    <<

    The prudent navigator should have multiple GPS receivers that are battery powered.  ....  Having battery GPS receivers means that you can continue your journey.  ... The backup to GPS is another GPS. >>
    I agree compeletly.
    <<Systemic (total) failure of the GPS satellite system is a low probability event.  Celestial navigation isn't a practical backup to GPS navigation, full stop.>>

    I'm not convinced on either of these points.  I believe that some sort of system-wide failure of the GNSS satellite systems, though unlikely, is worth preparing for.  (There's a separate discussion of "what constitutes failure?" that we could have; complete and long-term failure isn't the only scenario that has reprecussions)

    Whether CN is a practical backup to GNSS depends on what you're trying to accomplish.  Obviously, they aren't equivalent.  Older cruisers refer to the era "before GPS" and "after GPS" and will tell stories of the differences in what they could and could not do.

    Skilled application of traditional navigation, that is, the use of dead reckoning, pilotage, and CN, is still effective enough to continue the journey.  Absent CN, portions of the journey become unworkable -- like finding the Marquesas.  Portions of it -- like finding Miami -- become inconvenient because you're stuck showing up somewhere in the Bahamas and asking the harbormaster which island you've just arrived at.

    I'm not hoping CN will be useful to me someday.  I hope I never need it.  I have a CPR mask in my desk drawer at work, and hope I never need that, either.

    <<It is not emergency, abandon ship navigation, either. Liferafts aren't navigated anywhere anymore.  >>

    I agree with you here, as well.

       
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