My need is precision time, nothing else. Before GPS, ships navigated=20 knowing the time and the sun angle. I know where I am at, so with a precise clock, I can=20 obtain the sun angle. It seems to me that there would be little reason to shut the time=20 service off, which only needsONE bird. --Bob A On 4/19/2013 7:27 AM, RussellMc wrote: >> 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 The only place success comes before work is in the dictionary. VINCE LOMBARDI --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .