Re: Myth of GPS Employing the Nonsense of SR and GR
- From: Eric Gisse <jowr.pi@xxxxxxxxx>
- Date: Fri, 10 Aug 2007 22:02:51 -0000
On Aug 10, 8:49 am, Koobee Wublee <koobee.wub...@xxxxxxxxx> wrote:
On Aug 10, 8:30 am, Randy Poe wrote:
On Aug 10, 11:23 am, Timothy Murphy wrote:
Although Potter's postings seem fairly nonsensical to me,
I wouldn't have thought GR was relevant to GPS?
SR, conceivably, even though I would have thought
the discepancies from Newtonian theory would be negligible in this area.
At GPS altitudes, the effect of gravitation is stronger than
the effect of relative velocity between satellite and ground station.
Though both are terms in the same GR calculation, the
gravitational term (+45 usec/day) is colloquially called "the
GR effect" and the velocity term (-7 usec/day) is colloquially
called "the SR effect".
This actually has never been verified by GPS. <shrug>
http://npoesslib.ipo.noaa.gov/IPOarchive/MAN/doc165.pdf
But it is a GR calculation that predicts this net 38 usec/day
effect. That doesn't sound like much, but to achieve the
accuracy desired from GPS, the designers like to keep the
space clocks within a few nanoseconds of the ground
clocks. A 38 microsecond drift is thousands of time too
large to support the desired accuracy, so it's not a
"negligible discrepancy".
At first, the physicists want the receiver to track only three
satellites. In doing so, yes the satellite real-time clock must be
synchronized with the ground station. However, engineers quickly
realize that if the information from four satellites is received,
there is no more need to impose such an expensive and unreliable
requirement of ground-satellite synchronization. However, all
satellite clocks must be synchronized to each other but not
necessarily the ground stations. This latter task is must simpler to
achieve. One does not need GR (all satellite on the same altitude) or
SR (all satellites moving with relatively low speed to each other) to
implement. <shrug>
http://npoesslib.ipo.noaa.gov/IPOarchive/MAN/doc165.pdf
[snip remaining]
.
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- Re: Myth of GPS Employing the Nonsense of SR and GR
- From: Randy Poe
- Re: Myth of GPS Employing the Nonsense of SR and GR
- From: Koobee Wublee
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