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    Re: Air Force One sextant?
    From: Robert VanderPol II
    Date: 2021 May 19, 20:09 -0700


    Frank suspected that there would be a bunch of alternatives to GPS, CelNav among them as, I presume, the ultimate fallback.

    Don S. brought up inertial nav.  INav is fine when there secondary systems to correct for drift or if the time from last fix is relatively short.  As I understand it IN drifts at 0.25-1.0nm/hr depending on the stability/vibration of the carrier vehicle and the accuracy of the particular equipment being used.  Distance traveled does not directly impact final accuracy,  time and stability/vibration do.  My guess is that after 5hr or so CelNav would provide a statistically better location than IN. At that point IN is regularly updated with CN and location uncertainty becomes CN uncertainty plus a small amount to account for drift since last CN fix.

    Bob II

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