NavList:

There are automated star trackers for ships and aircraft, much like 
what you describe.  Description of the functionality of the ship-
borne ones can be found at the USNO site, in some of the papers 
listed by members of the observatory.

Fred

On Jul 3, 2006, at 9:13 PM, Lu Abel wrote:

>
> 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
>
> Robert Eno wrote:
>> Interesting idea.
>>
>> Let's say GPS was never invented, nor any other kind of external 
>> electronic
>> system. What would the modern sextant have looked like had it just 
>> kept on
>> undergoing improvements?
>>
>> Whatever happened to the "Sextants of Tomorrow" as described in Bruce
>> Bauer's "Sextant Handbook"?
>>
>> Robert
>>
>>
>>
>>> Seriously...it might interest an engineering class to take on the 
>>> project
>>> of
>>> redesigning a sextant for ultimate accuracy using modern 
>>> materials and
>>> techniques, as a project, with no further goal. Whether that 
>>> could then be
>>> transformed into something more....An interesting project anyway.
>>>
>>>
>>>
>>
>>
>>>
>>
>
> >


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