*This message was transferred with a trial version of CommuniGate(tm) Pro*
Cougarjack@aol.com wrote:
> *This message was transferred with a trial version of CommuniGate(tm) Pro*
> Not quite of the significance you might think...
>
> The GPS constellation consists of 2 totally separate systems, Precise
> Positioning System (PPS) and Standard Positioning System (SPS). PPS is
> available to the US Military only, and is rumored to have real time,
> sub-centimeter accuracy in all 3 axis' (Yes, GPS does do 3D and is starting
> to make pressure based altimeters obsolete). SPS, the system available to
> the rest of the world, is said to have accuracy "within several meters" and
> was added to the system late in the design phase, the intention being to
> replace a quickly degrading LORAN-C system and to help justify/defray the
> cost of the constellation in an era of decreasing defense spending. One
> well known trouble with SPS (at least among fishermen) is that its
> repeatability (ability to locate the same spot, such as some under sea topo
> feature) is poor at best when compared to LORAN-C, having something to do
> with postioning being triangulated from different combinations of constantly
> moving satelite, rather than the fixed land based stations in LORAN-C. Add
> to this Selective Availability (SA), which was intended as a facility that
> could be switched on in a time of military emergency to further degrade the
> accuracy of SPS, theory being the degradation of the SPS signal to the point
> where it was useless, strategically speaking.
>
> As the LORAN-C network continued to crumble and the Coast Guard had several
> budget scares that could have resulted in the plug being pulled prematurely
> on the LORAN-C network, the Coast Guard, with significant support of the
> private sector, began design and constuction of a network of land based
> differential beacon stations to cover our coastal and inland waterways.
> These differential beacons, now mostly completed, receive SPS, analyze it
> and transmit a correction factor. Specially equipped receivers, referred to
> as Diffential Global Positioning System (DGPS) receivers, receive the
> correction factor as well as the positioning data from the constellation and
> are able to resolve it in real time, displaying significantly more accurate,
> but more importantly, more reliably repeatable positioning data. This is
> not a global strategic issue, as it just covers the continental US at this
> time.
>
> Now, back to the subject at hand, SA. SA was never intended to be left on
> all of the time, rather it was to be switched on in times of crisis. Its
> first big showing was during the Persian Gulf conflict. Apparently, a
> significant number of our troops were not equipped with PPS capable
> receivers, and after several incidents of troops getting lost in the desert,
> civilian SPS receivers started showing up in the theater, but guess what,
> with SA switched on, SPS was virtually useless. At some point, the decision
> was made to turn off SA and widely distribute the much cheaper and readily
> available SPS units. All of that being said, its really no big deal that
> they are canning SA, is it?
>
> So, we
> really don't have anything more than we started out with and we still
> don't have the military only PPS.
>
> ===Mil-Veh is a member-supported mailing list===
> To unsubscribe, send e-mail to: <mil-veh-off@uller.skylee.com>
> To switch to the DIGEST mode, send e-mail to <mil-veh-digest@uller.skylee.com>
> To reach a human, contact <help@uller.skylee.com>
This archive was generated by hypermail 2b29 : Thu Jun 01 2000 - 22:37:10 PDT