NavList:

Lu,

You present some interesting ideas. These are similar to that which was
discussed in Bauer's book.

This brings to mind another concept: why can't a fully electronic sextant
such as that which you describe, be developed. Given that it costs billions
of dollars to launch and maintain in orbit, the GPS satellites, it seems to
me that the development of a self contained robo-sextant would be cheaper
and more reliable in the long run. Notwithstanding cloudy days, although I
seem to recall reading somewhere about an astro tracker that could "see" the
sun through the cloud cover.

Robert
----- Original Message -----
From: "Lu Abel" <lunav@abelhome.net>
To: <NavList@fer3.com>
Sent: Monday, July 03, 2006 9:13 PM
Subject: [NavList 456] Re: "Improved" sextants


>
> The problem is to define what kind of "improvements" are allowed in our
> sextant that "just kept on undergoing improvements."
>
> Let's start with a couple of examples of past "improvements" allowed by
> new technologies:
>
> Aluminum has replaced brass as the material of choice for sextants,
> making them lighter and easier to handle.  Cheap, pure aluminum required
> tremendous progress in metallurgy and in the technology of aluminum
> refining.  Perhaps 3/4 of a century ago someone looking for "improved"
> sextants would have demanded they remain made of brass, though.
>
> If we were having this discussion roughly 1-1/2 centuries ago, would
> someone looking for an "improved" sextant have forbidden a switch from
> verniers to drums, even though the entire history of sextants is marked
> by ever-improving high-precision manufacturing and at some point this
> allowed a switch from verniers to drums?
>
> The reason I bring this up is that we live in an age of incredible
> progress in electronics.  But traditionalists seem to eschew the devil
> of electronics, so is it excluded from technologies allowed to "improve"
> sextants?
>
> If not, the following would be trivially simple:
>
> 1. Electronic readout of sights (no more staring at verniers, just a big
> LCD display).  By the way, the mechanism needed for an electronic
> readout could trivially eliminate the bother of Index Error.
>
> 2. Electronic image stabilization.   Rock-steady bodies and horizons
> even on the smallest, bounciest vessel.
>
> 3. In fact, no traditional arm on the sextant -- just two images (one of
> the horizon, one of the sky).  Twiddle a knob controlling the latter and
> the image is brought down to the horizon.
>
> 4. Automatic height-of-eye calculation.  No, not from GPS (way too
> inaccurate) but either through ultrasonic ranging down to the ocean, or
> through an electronic barometer that's lowered to the ocean's surface
> and then brought up to the sextant.
>
> 5. Throw in a little bit of electronic knowledge about the body sighted,
> and with this and the above we go straight away from ho to Hs, no
> tedious tables, no mistakes (hmmm, do I add or subtract HP?  Is
> "off-the-arm" IE added to or subtracted from ho?
>
> 5. Last but not least, built-in logging and reduction of sights.  A
> microprocessor of far less power than is required by GPS could keep
> accurate time, log sights at the press of a button (bring body down,
> press trigger, ho and time automatically logged) and finally using a
> built-in NA, reduced.
>
> Now let's get even more radical (if the above aren't):
>
> Some satellites use "celestial" to keep themselves correctly oriented.
>  Could such star-tracking mechanisms be adapted to the "improved sextant?"
>
> In fact (although it pains my heart), is a human sight-taker necessary
> with a 21st-century sextant???   Or is it better off with an image
> processing system?   A built-in electronic almanac would know all
> available bodies at any point in time, an automated image finder would
> try to find them, for each that was visible it would bring them down to
> an automatically found horizon (heck, let's use a laser gyro and not
> even need to see the horizon, we need to see it only to get a precise
> sense of vertical and horizontal and a laser gyro could do that
> instead), and last but not least, each body would be automatically
> captured and reduced.
>
> Meanwhile, we all sit and fiddle with our GPS sets because robo-sextant
> is doing it all for us.
>
> Just some thoughts -- and my apologies to all the wonderful people on
> this list, many of who are probably very, very ill at this point...
>
> Lu Abel
>


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