> This came up in a conversation related to solar tracking. Will the
> military shut off
> ALL of the GPS services, or just positioning, during a wartime footing?
>
> How about time/date services?

First casualty is to change to "selective availability"
Accuracy drops substantially.
This was the mode the system ran in fr many years when first introduced.
AFAIR this was done for 'Desert Storm'.

I do not know if it is done, but you could shut it down regionally so
that a portion of the globe was without service. How small and well
defined you could do this would be "interesting".
A very determined person could gain useful information from two
satellites and possibly from one.

Russia operates a GPS system (GLONASS*) that (memory says) uses polar
elliptical orbit satellites as in that orbit shape they are in the
high poleward part of their orbit for the  majority of the time.
Usefulness diminishes as you go southward. If they transmit around the
whole orbit you MAY get some use from low altitude satellites in the
southern hemisphere.



          Russia

___________________

http://en.wikipedia.org/wiki/Satellite_navigation

http://en.wikipedia.org/wiki/Global_Positioning_System

Says:

           Initially, the highest quality signal was reserved for
military use, and the signal available for civilian use was
intentionally degraded (Selective Availability). This changed with
President Bill Clinton ordering Selective Availability to be turned
off at midnight May 1, 2000, improving the precision of civilian GPS
from 100 meters (330 ft) to 20 meters (66 ft). The executive order
signed in 1996 to turn off Selective Availability in 2000 was proposed
by the U.S. Secretary of Defense, William Perry, because of the
widespread growth of differential GPS services to improve civilian
accuracy and eliminate the U.S. military advantage. Moreover, the U.S.
military was actively developing technologies to deny GPS service to
potential adversaries on a regional basis.[18]

__________________

GLONASS

http://en.wikipedia.org/wiki/GLONASS

         iPhone 4S, iPad Mini and HTC provide GPS & GLONASS capability.

         GPS and phone baseband chips from  ST-Ericsson, Broadcom and
Qualcomm support GLONASS in combination with GPS.
--=20
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