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Are accurate clocks really the limiting factor in cheap Inertial Navigation?

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RoGeorge:

--- Quote from: soldar on March 26, 2019, 09:20:24 am ---
--- Quote from: RoGeorge on March 25, 2019, 06:30:13 pm ---If you have a precise clock and are allowed to look at the stars to recalibrate, than it's possible to find out the precise location.  It was a huge prize for a precise enough clock (or other method to navigate in the open sea, without following the shore line).  Many methods were presented.  One of them was looking at the star and precisely knowing the time, except there were no accurate enough clocks back then.
--- End quote ---

This is incorrect and it seems you do not understand how astronavigation works.  I am quite knowledgeable about astronav and it is quite too long and complicated to explain how it works in a short post but let us simplify and say the chronometer tells you the time at the prime meridian and the astronomical observations are an indication of the local time and the difference tells you you geographical longitude. Again, that is a huge distortion/simplification but the observations were not used to reset or calibrate the chronometer at all. That is not how it works.  If the astronomical observation was used to set or correct the chronometer then ... you wouldn't need the chronometer at all. The astronomical observation tells you local time and the chronometer tells you Greenwich time.

--- End quote ---

I never said how astronavigation works, but I admit it's all my fault for not phrasing properly what I was thinking at at that moment.  I was trying to imagine an inertial navigation where the accumulated errors are reset from time to time using astronavigation.

Please let me try again the phrase you quoted:

If you have a precise clock and are allowed to look at the stars [thus calculating the position using astronavigation instead of inertial navigation in order] to recalibrate [the position and reset the errors accumulated by the inertial navigation system], than then it's possible to find out the precise location [using mostly inertial navigation, and only rarely recalibrate the position using astronavigation, assuming most of the errors will be caused by the inertial system, and not the timekeeping system].

[New paragraph, and then the link to a documentary about how precise timekeeping enabled the possibility of astronavigation at open sea].

soldar:
Astronav does not have the precision to correct other more advanced technologies. A good navigator, with a good sextant, on a good day, on a very stable platform (not on a rolling ship), might get a fix with an error of 200 - 500 m.  Figure in bad conditions and cloudy days and it is a non-starter.

texaspyro:

--- Quote from: barry14 on March 25, 2019, 09:06:55 pm ---A quick Google search turned up a portable cesium clock introduced by Symmetricon in 2011 that is the size of a matchbox, weights 35 grams and uses 115 mw of power. It's based on work done by NIST.

--- End quote ---

And is not as good as a decent OCXO...   lower power, maybe smaller, but not as stable.  And it is not a cesium primary reference... it is like a rubidium oscillator that uses cesium... and costs a butt load 'o bucks.

texaspyro:
I use the noise from the low order bits from a MEMS INS board accelerometer, gyro, and compass data in my true random number generator.  The output from that TRNG passes every statistical randomness test.  MEMS chips are useless for anything but low precision applications.

hamster_nz:
Call me cynical, but...

Stated problem this solves: We need a technology breakthrough to know where ambulances are in tunnels!

Proposed solution #1: We need new tech for an ultra-precise time reference to enable an ultra-precise Inertial Navigation System

Proposed solution #2: We could add a CANBUS interface to the navigation system so it can read the odometer and to deduce location when GPS signal is not present

Maybe the unstated real problem: We need equivalent GPS navigation functionality for times when the GPS system is either down, cannot be trusted, or is being denied through jamming or other Electronic Counter Measures. However we also need to attract funding.

I'm slightly surprised that they haven't also mentioned it would be useful for cave and/or mine rescues...

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