Talk:Global Positioning System/Archive 8: Difference between revisions

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== External links modified ==

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*Added archive https://web.archive.org/web/20080916123933/http://www.armscontrol.org/documents/mtcr to http://www.armscontrol.org/documents/mtcr

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Cheers.—[[User:InternetArchiveBot|'''<span style="color:darkgrey;font-family:monospace">InternetArchiveBot</span>''']] <span style="color:green;font-family:Rockwell">([[User talk:InternetArchiveBot|Report bug]])</span> 23:29, 12 June 2017 (UTC)

== External link is spreading lies ==

This link 11:

http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html

is claiming wrongly, that:

The engineers who designed the GPS system included these relativistic effects when they designed and deployed the system. For example, to counteract the General Relativistic effect once on orbit, the onboard clocks were designed to "tick" at a slower frequency than ground reference clocks, so that once they were in their proper orbit stations their clocks would appear to tick at about the correct rate as compared to the reference atomic clocks at the GPS ground stations. Further, each GPS receiver has built into it a microcomputer that, in addition to performing the calculation of position using 3D trilateration, will also compute any additional special relativistic timing calculations required [3], using data provided by the satellites.

In reality, there was only one short experiment described here:

http://www.phys.lsu.edu/mog/mog9/node9.html

At the time of launch of the first NTS-2 satellite (June 1977), which contained the first Cesium clock to be placed in orbit, there were some who doubted that relativistic effects were real. A frequency synthesizer was built into the satellite clock system so that after launch, if in fact the rate of the clock in its final orbit was that predicted by GR, then the synthesizer could be turned on bringing the clock to the coordinate rate necessary for operation. The atomic clock was first operated for about 20 days to measure its clock rate before turning on the synthesizer. The frequency measured during that interval was parts in faster than clocks on the ground; if left uncorrected this would have resulted in timing errors of about 38,000 nanoseconds per day. The difference between predicted and measured values of the frequency shift was only parts in , well, within the accuracy capabilities of the orbiting clock. This then gave about a validation of the combined motional and gravitational shifts for a clock at earth radii.

My comment:

To sum it up, general relativity is not needed to run GPS, it could be possible to use it as confirmation for general relativity, but this are two separate things.

Another citation from the second link:

At present one cannot easily perform tests of relativity with the system because the SV clocks are actively steered to be within 1 microsecond of Universal Coordinated Time (USNO). <!-- Template:Unsigned IP --><small class="autosigned">—&nbsp;Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/212.5.215.61|212.5.215.61]] ([[User talk:212.5.215.61#top|talk]]) 12:09, 19 June 2017 (UTC)</small> <!--Autosigned by SineBot-->