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    Re: FOG's, was Re: automatic celestial navigation
    From: Paul Hirose
    Date: 2008 Jan 29, 12:27 -0800

    George Huxtable wrote:
    > Nevertheless, isn't it the case that there is
    > effectively zero long-term drift in the orientation sensing of these
    > devices; quite different from the behaviour of their mechanical
    > predecessors?
    
    Unfortunately, errors are still present. The was no upward jump in INS
    performance when ring laser gyros were introduced. In fact, the most
    stable gyroscope system yet created (.0005 arc second per year) uses
    spinning spheres floating inside close-fitting vacuum chambers, similar
    to the SPN/GEANS INS arrangement. It's on Gravity Probe B:
    http://einstein.stanford.edu/sitemap.html
    
    But SPN/GEANS uses an electromagnetic motoring action to spin up its
    gyros, rather than gas jets. And the pickoff is optical rather than
    magnetic.
    
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