Henri Wilson wrote:
On Tue, 07 Aug 2007 22:52:25 +0200, "Paul B. Andersen"
wrote:

Tom Potter wrote:

[..]

As the satellites take about 12 hours
(43200 seconds) to orbit the Earth,
and the ephemeris data takes about .006 seconds
to reach the receiver, this means that
the GPS receiver knows where the
satellite is to an accuracy of about one part in
43000 / .006 = 71600000 parts,
even without clock and ephemeris corrections.

Considering that the Earth is about
24,000 miles or 126,000,000 feet in circumference,
this amounts to a sphere of uncertainty of about
1.76 feet at sea level.
!!!! :-O

Paul, out of words

Here is a quote I found:

"Inspection of the differences
between UTC/TAI and the phase of each NAVSTAR
GPS clock enables the USNO to identify GPS clocks that
require particular frequency-rate control corrections. Use of
this knowledge enables the USAF to adjust frequency rates of
selected GPS clocks. Currently the USAF uses an automated
bang-bang controller(3) on frequency-rate."

....seems to make your previous claims look pretty stupid, eh Paul?

How so?
I bet you don't even know what the author is talking about
Where is the "automated bang-bang controller"?
Which frequency is adjusted with this controller?
I know the answer.
Do you?
If you read the document from where you quoted the above, you might find out.
(But probably not. It is not well explained.)
http://www.agi.com/downloads/support...k_Analysis.pdf
or:
http://tinyurl.com/yoru3y

I will however admit that the quoted part is easy to misunderstand.
(And you read it out of context, didn't you?)
It is indeed very confusing.
What the hell is "frequency-rate"? :-)

If you really want to learn what is adjusted with a "bang-bang controller", read this:
ftp://igscb.jpl.nasa.gov/igscb/resou...97tech_rpt.pdf

BTW, I can quote too:
http://tycho.usno.navy.mil/ptti/1995/Vol%2027_10.pdf

Because the GPS frequency standards are physically inaccessible,
reliability is very important for system integrity. Each GPS-satellite
contains four frequency standards (two cesium and two rubidium).
In order to meet the required mission lifetime of 7.5 years,
each of the four clocks should be expected to operate within
stability specifications for approximately two years. ...


This is among my "previous claims".
Does it look pretty stupid? :-)

I will throw you a straw, though.
The above is true for Block II and Block IIA satellites,
but is not strictly true for Block IIR satellites.
The first IIR was launched in 1997, so the GPS was operated
for 20 years with physically inaccessible frequency standards.
Now about half of the satellites are II/IIA and half are IIR.

Paul