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    Re: accuracy of automatic celestial navigation
    From: George Huxtable
    Date: 2002 Dec 9, 08:15 +0000

    Thank you, Paul Hirose, for another interesting insight into precise
    It seems to me that the magic of the system must lie in the nature of the
    coupling between the inertial navigation and the astronavigation, as Paul
    explains. The inertial system would slowly drift off, the astro will
    stabilise it against that drift: but the astro system must require the
    short-term stability of the inertial to stabilise its reference platform
    before it can work.
    So I don't see much prospect of that sort of technology being applicable to
    us in our small boats until the costs of inertial nav systems are brought
    down to affordable levels. And on a rough sea-surface, the disturbing
    accelerations are orders of magnitude greater than a high-altitude aircraft
    has to contend with.
    It raises yet another question. If indeed an accuracy of 15 to 30 meters
    was claimed for the system as a whole, how was that error measured and
    tested? Precise position in an airbase parking bay is one thing: in-flight
    precision in the real world is another.
    In the days before GPS, how could the instaneous position in flight be
    independently determined sufficiently accurately, for testing purposes? Is
    Loran accurate enough, and fast-responding enough? The aircraft will
    presumably pass through 15 metres in less than 30 milliseconds, so it's a
    demanding requirement.
    Fascinating stuff, but it makes the heart sink a little to observe so much
    ingenuity being applied to weapons of war.
    George Huxtable.
    George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    Tel. 01865 820222 or (int.) +44 1865 820222.

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