I think the satellites have caesium clocks now but that is only from memory. The reason they need to be adjusted fairly frequently is due to the satellites propensity to fall back to earth - i.e. their orbits decay over time making the satellites closer to earth and hence the signal travel time less. They 'correct' the clock on the satellite for so many weeks / months and then boost the satellite back up into its original orbit and start again. They do it this way because of the high cost of boosting the satellite back up and the limited fuel on board.
Ian ______________________ Ian W. Wright Sheffield UK On 24/11/2010 02:27, Jon Elson wrote: > Przemek Klosowski wrote: >> On Tue, Nov 23, 2010 at 1:14 PM, Jon Elson<el...@pico-systems.com> wrote: >> >> >>> The GPS system has atomic clocks accurate to some insane level like one >>> second in 10,000 years. They have to periodically adjust the clocks for >>> relativistic >>> effects. >>> >> NIST runs the master clocks for the system from Boulder, and keeps >> improving them. The most recent generation uses single Aluminum ion, >> and is accurate to 1s in over 3 billion years. > Right, and the clocks on board the GPS satellites are periodically reset > from the NIST master > clocks. The time standards carried on board the satellites are not this > accurate, but are still > Rubidium atomic clocks, and WAYYY more accurate than anything us mere > mortals can > afford. At least, that is the way the system used to be set up, there > might have been updates > since. > > Jon > > ------------------------------------------------------------------------------ > Increase Visibility of Your 3D Game App& Earn a Chance To Win $500! > Tap into the largest installed PC base& get more eyes on your game by > optimizing for Intel(R) Graphics Technology. Get started today with the > Intel(R) Software Partner Program. Five $500 cash prizes are up for grabs. > http://p.sf.net/sfu/intelisp-dev2dev > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > > > ----- > No virus found in this message. > Checked by AVG - www.avg.com > Version: 10.0.1153 / Virus Database: 424/3274 - Release Date: 11/23/10 > > ------------------------------------------------------------------------------ Increase Visibility of Your 3D Game App & Earn a Chance To Win $500! Tap into the largest installed PC base & get more eyes on your game by optimizing for Intel(R) Graphics Technology. Get started today with the Intel(R) Software Partner Program. Five $500 cash prizes are up for grabs. http://p.sf.net/sfu/intelisp-dev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
