Re: Inertial Navigation ???

From:         Doug Holik <drholik@prodigy.net>
Date:         26 Apr 2000 11:46:26 -0700
Organization: Prodigy Internet http://www.prodigy.com
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brian whatcott wrote:

> In article <u0k8j6g3dt.fsf@orville.dfrc.nasa.gov>, pkearn@eircom.net says...
> >.....
> >Now with GPS - the NAV systems can be updated even when out in the
> >Atlantic/Pacific where DME may not be available.  Which i suppose is
> >''re-zeroing'' itself.
>
> >The B737 Flight Managment Computer uses DME/DME cross-bearings to
> >confirm its location when it knows that it has 2 DME's to work with.

GPS alone can not be used to update an INS fix because there is no
cross check available, that is the same reason why they are having
such a hard time geting GPS certified for low visibility approaches,
because of the nature of the system, error checking is impossible
without some other navigational aid.  You are correct about IRS's
updating their position.  When an IRS can lock on to 2 vor's it will
triangulate its position and update itself.