[time-nuts] Slightly OT - GPS-Based Accurate Direction Finding

[Brooke Clarke]

Hi:

An interesting fact about gyros, independent of how they work, is that 
their Long Term Drift Rate is proportional to some power of the inverse 
of their volume.  As the sensor gets smaller the LTDR goes up as 10 ^ 4
http://www.prc68.com/I/Sensors.shtml#Gyroscopic
Ring Laser Gyros at 7E-4 deg/hour to MEMS at 1000 deg/hr.

I find the AG8 North Finding Gyro theodolite system very interesting, 
but have heard that's it's very easy to break the gyro suspension and so 
buying one used is very risky if you want to actually use it.   It uses 
a classical spinning mass gyro to find True North.  I expect it's still 
being used in places where GPS is not available, like in caves.

An old web page on North Finding:
http://www.prc68.com/I/North.shtml

Have Fun,

Brooke Clarke
http://www.PRC68.com


Jim Cotton wrote:
>
> Back in the early 1980's when attending college I worked on a single 
> axis multi-mode fiber optic
> rate gyro project that used GRIN fiber.  Back then a military three 
> axis unit based on single mode
> fiber was alleged to be a little larger than a one inch cube and cost 
> slightly less than a million dollars.
>
> We used a three inch spool for the fiber and put everything in a six 
> inch cube for a housing.
>
> The NASA contract was part of the NASP program.
>
> The company that we worked with wanted to produce a product for the 
> commercial "private
> pilot" aviation market.  I will have to ask what happened...
>
> I think the patent issue may have had something to do with it since 
> the company had a
> relationship with Litton.
>
> Jim Cotton
> n8qoh
>
> bg at lysator.liu.se wrote:
>>>>> Does anyone know how laser gyroscopes are developing?
>>>> Laser gyroscopes - as in Ring Laser Gyroscopes or as in Fiber Optic
>>>> Gyroscopes?
>>>>
>>> RLGs are a standard commercial product.  Several years back I was
>>> walking through the Honeywell plant in St Paul, MN, and they had a
>>> display case of at least a dozen RLGs that they've made over the past
>>> few decades.
>>
>> Commercial?
>>
>> US RLGs are all ITAR.
>>
>> "All types of gyros usable in the systems in Item 1, with a rated drift
>> rate stability of less than 0.5 degree (1 sigma or rms) per hour"
>>
>>     http://www.fas.org/spp/starwars/offdocs/itar/p121.htm
>>
>> Honeywell has about 2 different RLGs. Only one (gg1320) of which you can
>> make a north sensing out of. Litton (now NGC) used to do RLGs (their 
>> "zero
>> lock gyros") but I think they were on the loosing side of a patent war
>> with Honeywell.
>>
>> French Sagem do some for high end military systems. Have I missed a RLG
>> manufacturer? Almost as few vendors as in the Cesium oscillator 
>> market...
>>
>> No new RLG sensors has been announced during the last decade or two.
>>
>> -- 
>>
>>     Björn
>>
>>
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-- 
Have Fun,

Brooke Clarke
http://www.PRC68.com