Einstein's general relativity plays role in GPS time
... The GPS satellite clocks
are moving at 14,000 km/hr in orbits that circle
the Earth twice per day, much faster than clocks
on the surface of the Earth, and Einstein's
theory of special relativity says that rapidly
moving clocks tick more slowly, by about 7
microseconds (millionths of a second) per day.
....
Also, the orbiting GPS clocks are 20,000 km
above the Earth, and experience gravity that is
four times weaker than that on the ground.
Einstein's general relativity theory says that
gravity curves space and time, resulting in a
tendency for the orbiting clocks to tick
slightly faster, by about 45 microseconds per
day. The net result is that time on a GPS
satellite clock advances faster than a clock on
the ground by about 38 microseconds per day. ...
Clifford M. Will /Phisics Central/
Atomic
Time (TA): a time scale based on the hyperfine
resonance of Cesium 133.
Atomic Second is precisely, 9,192,631,770
cycles of the cesium resonance.
GPS Time: GPS time
is the basic time which the entire system (Control-Space-User)
utilizes for its time delay ranging techniques.
It is the free running time kept by the Control
Segment based upon one of the Monitor Station
Cesium clocks . It is generally considered in
units of GPS week number and seconds of week.
Satellite Time:
Each satellite broadcasts its approximation of
GPS time. This approximation is known as
satellite time. It consists of the P or C/A code
state (Z count) and the satellite clock
correction terms in the 50 BPS data stream. Each
satellite’s time is approximately (within the
SS-GPS-300 error budget) equal to GPS time.
All above further references to time are in
Coordinated Universal Time (UTC).
Coordinated Universal Time
(UTC): An internationally
agreed upon time scale which has the same rate
as Atomic Time (TA). The. UTC is corrected by
step adjustments of exactly one second, as
needed to remain within 0.9 seconds of
Astronomical Time (UTl).
The Burbau International
de L’HeureN (BIPM)
determines when step adjustments are needed.
This is the universal time used by DOD and other
precise time users.
Tomasz Widomski
