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    Re: FOGs
    From: Lu Abel
    Date: 2008 Jan 30, 16:25 -0800

    Apologies to Paul.
    As far as the mind-boggling technology, my favorite is the "lead
    balloons."   How do you create NO magnetic field inside the satellite,
    even in the presence of the earth's magnetic field?   First, you make a
    container that's super-conducting.  That prevents outside fields from
    penetrating.   But there's still a residual field inside, how do you get
    rid of that?   You take the gyros and enclose them in super-conducting
    balloons.  You then "inflate" the balloon.    Since the total "amount"
    of magnetism (layman term, I know) inside a superconducting object has
    to remain constant irrespective of the size of the object, "inflating"
    the balloon reduces the magnetic field density.   Use four concentric
    balloons and when you're done inflating all four, you've got one of the
    lowest magnetic fields ever observed, something like 10^-18 Gauss.
    George Huxtable wrote:
    > Lu Abel wrote-
    > |
    > | I am tremendously enjoying this discussion.  And thanks, Frank, for the
    > | pointer to NASA's Gravity B experiment.   Its technology is truly
    > | mind-boggling.
    > George adds-
    > Me too. I hope the thread will continue, and perhaps expand.
    > However, the link to the Gravity B experiment came from Paul Hirose, not
    > Frank. And it leads to a further question-
    > That article, http://einstein.stanford.edu/sitemap.html  , was written in
    > the future tense, describing a proposed experiment which was intended to
    > launch in 2003, and last for two years. So by now it should have
    > been-and-gone. Can anyone tell us whether it actually happened, an if so,
    > what the results were?
    > Just as Lu describes, there's a combination of technologues in that
    > experiment that is indeed mind-boggling. The bit that tickles me best is the
    > notion of floating the spinning ball within the spherical cavity, by
    > accelerating the spacecraft about, with puffs of gas, to keep it
    > centralised. That certainly puts the egg-and-spoon race in the shade.
    > =========================
    > Knowing little about the optical  versions of these gyros, I had asked- "...
    > 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?"
    > And Frank responded-
    > "No, they drift for many little reasons."
    > I would like to know a bit more than that, if anyone can tell me. What,
    > roughly is the current limit on the long-term drift of a ring laser gyro,
    > suitably "dithered"? And how does it differ from that of a fibre-optic gyro?
    > George.
    > contact George Huxtable at george@huxtable.u-net.com
    > or at +44 1865 820222 (from UK, 01865 820222)
    > or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    > >
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