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Subject: Re: How likely is a GPS shutdown?
From: Richard Langley (lang@XXX.XXX)
Date: Wed Jan 26 2000 - 08:41:56 EST
The current SPS error budget assigns an SA error of 24 metres r.m.s to the
total user-equivalent range error (UERE). Without SA, the UERE could drop to
about 8 metres and would be dominated by ionosphere and multipath effects.
With an HDOP of 2 (a bit high for a 28+ satellite constellation), this would
lead to a 32 metre horizontal 2 d.r.m.s. (95% probability) positioning error.
At times, this error could easily be half as much and even possibly under 10
metres.
-- Richard Langley
Professor of Geodesy and Precision Navigation
On Tue, 25 Jan 2000, Craig wrote:
>What accuracy might we expect with SA disabled?
>
>Craig
>Columbia, SC 2000.01.25 2245 EST
>
>-----Original Message-----
>From: Navigation Mailing List
>[mailto:NAVIGATION-L@XXX.XXX]On Behalf Of Richard Langley
>Sent: Tuesday, January 25, 2000 22:38
>To: NAVIGATION-L@XXX.XXX
>Subject: Re: How likely is a GPS shutdown?
>
>
>On Tue, 25 Jan 2000, Tony wrote:
>
>>Richard:
>>
>>Thanks you. I believe I read several years ago that DOD also has the
>>capability of dithering the time base so that SA accuracy can be degraded
>>further if needed. Is this true? TIA
>
>Yes, DoD has the ability to adjust the SA degradation to even higher
>levels. But SA will be switched off by 2006 under presidential directive.
>The SA security measure will be replaced by in-theatre jamming.
>-- Richard Langley
> Professor of Geodesy and Precision Navigation
>
>>Tony
>>
>>Richard Langley wrote:
>>>
>>> PPS uses the encrypted P-code on both the L1 (same as civilian SPS) and
>the L2
>>> carrier. However, there are DoD single-frequency (L1) receivers and these
>>> also have SA and A/S decryption capability.
>>> -- Richard Langley
>>> Professor of Geodesy and Precision Navigation
>>>
>>> On Tue, 25 Jan 2000, Rodney Myrvaagnes wrote:
>>>
>>> >This is not quite right, although the rest of RBE's post is
>>> >right on. The military receivers that can get the encrypted
>>> >(long) word get it over another carrier than that used by
>>> >the C/A word decoded by civil receivers. There is no way
>>> >for your Walmart gps to use the military code.
>>> >
>>> >
>>> >During the Gulf War, SA was turned off because the military
>>> >had to use civilian receivers. SA was an afterthought,
>>> >applied because the civil receivers turned out to work much
>>> >better than expected.
>>> >
>>> >On Mon, 24 Jan 2000 19:09:42 -0500, Richard B. Emerson
>>> >wrote:
>>> >
>>> >> >
>>> >> > I suspect that the military has its own encrypted version
>>> >> > of GPS although this is simply a guess on my part.
>>> >>
>>> >>One of the absurdities of GPS is that during Desert Storm and Panama,
>>> >>GPS' selective availability was turned off. Thus, for a short period,
>>> >>the normally encrypted data segment (it's already there and used
>>> >>routinely) was available unencrypted. Consider, too, the error even
>>> >>with S/A enabled. A fuel-air bomb (or ammonium nitrate bomb) could
>>> >
>>> >
>>> >
>>> >Rodney Myrvaagnes J36 Gjoa
>>> >Senior Editor Electronic Products
>>> >My oyster knife is Y2K compliant
>>> >
>>>
>>>
>============================================================================
>===
>>> Richard B. Langley E-mail: lang@XXX.XXX
>>> Geodetic Research Laboratory Web:
>http://www.unb.ca/GGE/
>>> Dept. of Geodesy and Geomatics Engineering Phone: +1 506 453-5142
>>> University of New Brunswick Fax: +1 506 453-4943
>>> Fredericton, N.B., Canada E3B 5A3
>>> Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/
>>>
>============================================================================
>===
>>
>
>
>============================================================================
>===
> Richard B. Langley E-mail: lang@XXX.XXX
> Geodetic Research Laboratory Web: http://www.unb.ca/GGE/
> Dept. of Geodesy and Geomatics Engineering Phone: +1 506 453-5142
> University of New Brunswick Fax: +1 506 453-4943
> Fredericton, N.B., Canada E3B 5A3
> Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/
>============================================================================
>===
>
===============================================================================
Richard B. Langley E-mail: lang@XXX.XXX
Geodetic Research Laboratory Web: http://www.unb.ca/GGE/
Dept. of Geodesy and Geomatics Engineering Phone: +1 506 453-5142
University of New Brunswick Fax: +1 506 453-4943
Fredericton, N.B., Canada E3B 5A3
Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/
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