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Re: How likely is a GPS shutdown?
From: Richard B. Langley
Date: 2000 Jan 26, 6:42 AM
From: Richard B. Langley
Date: 2000 Jan 26, 6:42 AM
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@LISTSERV.WEBKAHUNA.COM]On Behalf Of Richard Langley >Sent: Tuesday, January 25, 2000 22:38 >To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM >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@unb.ca >>> 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@unb.ca > 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@unb.ca 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/ ===============================================================================