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Subject: Re: accuracy of automatic celestial navigation
From: Robert Eno (enoid@XXX.XXX)
Date: Sun Dec 08 2002 - 12:52:50 EST
Hello Mr. Geers,
Have you an address, internet or snail mail, to where one can direct a
request for reprints? This sounds like very interesting stuff.
Robert Eno
----- Original Message -----
From: Glenn Geers <dgeers@XXX.XXX>
To: <NAVIGATION-L@XXX.XXX>
Sent: Saturday, December 07, 2002 5:08 PM
Subject: Re: accuracy of automatic celestial navigation
> On Sat, 7 Dec 2002 05:18 pm, you wrote:
>
> The algorithms used in STELLA have been published. The author is George
Kaplan
> former head of the Astronomical Applications Department at USNO. I have
the
> full set available (have to dig them out). The USNO will provide reprints
of
> the papers that aren't available on the web. It's pretty neat stuff. The
> algorithms take the motion of the vessel into account and can provide very
> high (30m) accuracy.
>
> Also of interest: Polaris subs of the 60's carried an automatic astro-nav
unit
> that they used to reset their inertial systems from time to time. Most
auto
> systems use infrared optics so they can track stars during the day.
>
> Regards,
> Glenn
>
>
> > On Friday, December 6, 2002, at 04:05 PM, George Huxtable wrote:
> > > For those of us that sail our small craft out at sea, my opinion is
> > > that if we can achieve a precision of 2 min, we are doing pretty well.
> > > What do others think?
> >
> > I would agree. 2 nmi at sea is very decent; on land we should be able
> > to get to 1/2 mile or better.
> >
> > On land I recently took a string of shots using a Tamaya Jupiter
> > sextant with a 7X scope. I shot the sun mid afternoon over a period of
> > 20 minutes. (This was on the coast of Oregon at a beachhouse on the
> > water.) I used a Garmin GPS in averaging mode to determine my actual
> > position to 15 feet or so. The resulting intercepts in nmi are
> > interesting to analyze. Because my assumed position is known to within
> > 15 feet, these can be taken as errors in my sights. Here they are in
> > order:
> >
> > 0.91
> > -0.06
> > 0.59
> > -0.05
> > 0.22
> > 0.55
> > 0.22
> > -0.28
> > -0.53
> > -0.57
> > -0.77
> > -0.03
> > -0.19
> > -0.11
> > -0.43
> > -0.62
> > 0.27
> > 0.24
> > 0.44
> > 0.25
> >
> > The mean of the intercepts is a mere 0.0025 nmi -- very good -- but the
> > individual readings varied over a 1.68 nmi range -- not so good.
> >
> > When we are "warming up" and we haven't used our sextants in a while I
> > find that the first shots are often in greater error than later sights.
> > This is in fact the case with this set of shots shown above: the worst
> > error came from the very first sight. Therefore I have found that it
> > is wise throw out the the first reading or two, or at least to discount
> > them.
> >
> > Other experiments I have done:
> >
> > I took five shots in my backyard using the same sextant and an
> > artificial horizon and got a 1.27 nmi range of errors and a mean error
> > of 0.644 nmi.
> >
> > I took fourteen shots in my backyard using a Tamaya Venus (not nearly
> > as powerful of scope) and an artificial horizon and got a 4.3 nmi range
> > of errors but a mean error of -0.45 nmi because of the greater number
> > of sights taken.
> >
> > And for my finale, one afternoon I used six different sextants in my
> > backyard and I took a total of 46 sights using an artificial horizon.
> > I got an 11.2 nmi range of errors with a mean error of
> > -1.23 nmi.
> >
> > From this the statistical nature is shown to be very useful: although
> > any one shot could be in error up to almost a mile, a series of shots
> > averaged does indeed improve accuracy to very good levels; STELLA
> > appears to do this, and thus an automated system is very appealing.
> >
> > Dan
>
>
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