[time-nuts] LORAN C shutdown

[bg at lysator.liu.se]

Hi Robert,

High performance - for me - is 'navigation grade' wrt intertial systems.
Your terminology is somewhat strange to me. 'IN' is that short for
INertial or Inertial Navigation?

There are (used to be) two basic types of intertial navigation systems;
platform systems, where a number of gimbals with help from the gyros keep
the central accelerometer platform at a constant orientation. The other
type is strapdown systems, where gyros and accelerometers are mounted
fixed within the INS box.

High performance mechanical rotating gyros are associated with platform
systems. Ring laser gyros and fiber optic gyros are typically strapdown,
which completely dominate modern navigation.

I doubt that your "cheap" FOG IN platform really is a platform system. I
also very much doubt that these FOG systems perform as well as older
mechanical platform inertial navigation systems! If you compare with
vertical gyro-types, those are for aircraft control, not for navigation.

Any IMU integrated with GPS/GNSS provides complete attitude information on
moving platforms. There are certified pure GNSS heading sensors on the
marine and other markets.

--

     Björn

> Hi Bjorn,
> This depends on what you call high performance. The normal definition
> of "high performance" in relation to IN is low drift with time. Even
> "cheap" fibre optic gyro based IN platforms can perform as well as the
> early airline standard mecanical units. GPS does not provide attitude or
> heading information (I'm ignoring specialist multi antenna differential
> set ups, these are not normal or mature systems). This information is
> needed in real time to fly the aircraft in IMC (low visibility) or on
> autopilot. Either attitude and directional gyros or an IN platform are
> still needed and IN is becoming the norm. There are also MEMS units that
> are making inroads in the light aviation market, especially in the
> USA. GPS (or to be more accurate GNSS) is only part of the system, all be
> it a very important one.
>  
>  
> Robert G8RPI.
>
>
> --- On Tue, 10/11/09, bg at lysator.liu.se <bg at lysator.liu.se> wrote:
>
>
> From: bg at lysator.liu.se <bg at lysator.liu.se>
> Subject: Re: [time-nuts] LORAN C shutdown
> To: "Discussion of precise time and frequency measurement"
> <time-nuts at febo.com>
> Date: Tuesday, 10 November, 2009, 19:29
>
>
> On the other hand... With GPS-aiding its argued that high performance
> INS-systems are not needed. The same performance will be reached with a
> low cost GPS and a mid to low performance inertial system. So I doubt we
> will have low cost high performance intertial sensors anytime soon.
>
> --
>
>    Björn
>
>> Don't overlook that laser/fiber "ring-gyros" will drop in price the
>> patents expire and the predatory pricing ends:
>>
>>     http://www.es.northropgrumman.com/solutions/mk39/assets/mk39.pdf
>>
>> As much as I have enjoyed playing with Loran-C, I would far rather
>> have a shoebox-sized, totally autonomous dead-reckoning backup, with
>> no lightning-prone antenna, than a Loran-C receiver.
>>
>> Doesn't help us timing guys, but we have Cesiums if we are really
>> serious.
>>
>> --
>> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
>> phk at FreeBSD.ORG         | TCP/IP since RFC 956
>> FreeBSD committer       | BSD since 4.3-tahoe
>> Never attribute to malice what can adequately be explained by
>> incompetence.
>>
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>
>
>
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