[ntp:questions] National time standard differences
mills at udel.edu
Fri Feb 19 18:51:16 UTC 2010
They believe it now. From Chapter 13 in the new edition:
"A GPS clock moving at 3.882 km/s at an altitude of 20,135 km runs
slower than TCG by 7.2 microseconds per day due to time dilation and by
14.5 microseconds per day due to redshift. Since proper time comparisons
can only be done in a coordinate frame,
(GPS - TCG)ECI - (TT - TCG)ECI = GPS - TT
is the time of the GPS clock relative to the TT clock. Thus, the GPS
clock runs (14.5 + 7.2) - (60.0 + 0.1) = -38.4 microseconds per day
slower than the TT clock. The net rate 38 microseconds per day
“blueshift” is programmed in the spacecraft before launch."
The background is in a papers by Nelson, et al, and Pettit, and cited in
the book. However, the values shown above were independently verified by me.
Hal Murray wrote:
>>Bender claims that the GPS engineers did not believe that GR was real,
>>and had a software switch which they could use to eliminate the General
>>Rel corrections in the GPS.
>Does anybody have a good URL for that?
>I've heard it before, but it's so crazy that it seems more like
>a good urban legend.
>My best guess is that the switch was there so they could run
>the experiment to test/verify relativity. I think they ran without
>the corrections for a few weeks and got wonderful data.
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