System.Time.Clock Design Issues

Gregory Wright gwright at
Mon Feb 7 10:42:35 EST 2005

On Feb 6, 2005, at 7:18 PM, Ashley Yakeley wrote:

> In article <83fcd29a8070c7a77db3b2f01bbaac71 at>,
>  Gregory Wright <gwright at> wrote:
>> Raw GPS time (the number of seconds since the GPS epoch)
>> is broadcast  in a complicated form in the satellites' navigation
>> message,
>> along with the current number of UTC leap seconds since the GPS epoch.
>>  From the raw GPS time and the number of leap seconds UTC can be
>> calculated.
> So there's some way that the satellites get told about leap seconds 
> when
> they're announced?

Yes, the GPS satellites have the next scheduled leap second insertion
uploaded.  They begin broadcasting the new leap second count when the
scheduled leap second occurs.

The navigation messages of the GPS satellites are frequently updated
with the latest orbital parameters of the satellites, among other 
This is necessary because the gravitational perturbations of the moon 
sun, and the higher multipole moments of the Earth's gravitational field
slowly alter the orbits.


> -- 
> Ashley Yakeley, Seattle WA
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