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    Re: Position fix by satellite observation
    From: Don Seltzer
    Date: 2023 May 26, 12:48 -0400
    On Fri, May 26, 2023 at 11:48 AM NavList Community <NavList@fer3.com> wrote:
    Maybe it's worth nothing here, too, that early Polaris missile designs depended on inertial navigation corrected by automated celestial sightings. Did the satellite system entirely replace the celestial-aided system? Or was it kept as a backup to the satellites?? Maybe your subsim friends will know? :)

    I believe that the satellite systems were intended to aid in the navigation of the submarines, prior to launch.
    Missile guidance has been by inertial instruments.  After the boost phase, a startracker is used to provide a celestial reference for correction to the IN.
    The startracker is a small telescope with a limited field of view, on a gyro stabilized platform.  Prior to launch, a suitable reference star is chosen and the platform is rotated so that the startracker telescope is pointed directly at that star.
    After the boost phase into space, a window is opened to allow the startracker to sight the reference star.  Any error in the alignment is used to correct the calculated trajectory from the IN data.

    That is how it worked through the first generations of the Trident successors of Polaris.  Whether that is true today, I do not know, and couldn't say if I did.

    Don Seltzer 
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