[LEAPSECS] temporal turf wars

[Magnus Danielson]

Tom Van Baak skrev:

>> An interesting NIST document from 2000 gives insight into the turf wars

>> about precision time scales.

>>

>> http://tf.nist.gov/general/pdf/1429.pdf

>>

>> The document makes it clear that GPS time was never designed to follow

>> UTC(USNO) (and by implication, TAI).

> 

> I think you're misreading that sentence. GPS is in fact steered to

> the USNO MC which is steered to UTC. But I think the steering

> parameters are quite different between the two though. I also

> suspect there have been improvements in the past ten years.

> Demetrios can explain more, if needed.


It is certainly true that "GPS time was never designed to represent the 
DoD's precise time source, UTC(USNO)". GPS Phase I did not include 
navigation messages for time corrections or ionospheric correction model 
for that matter [1].

This was introduced at a later stage [2] as the initial system 
evaluation was completed. The GPS Program Office polled potential users 
for their needs and it was decided that adding the feature would be "a 
piece of cake" (actual words in article). UTC access through GPS can be 
dated back to 1983 (exact time is not available in my sources, but the 
articles is from 1983 and says "now".)

So the statement in the NIST article [3] is correct with other sources 
and it seems updated practices have shown that the introduced method to 
achieve it is fairly successful considering that the system was not 
specifically designed for it but certainly had good potential. The 
article is rather a report on work to improve the process, which is 
indeed what the Abstract is saying.

Thus, we can totally leave NIST vs USNO political issues out of this 
one, as it has a track record back into the early days of GPS 
development itself.

[1] A. J. Van Dierendonck, S. S. Russell, E. R. Kopitzke and M. Birnbaum 
"The GPS Navigation Message", ION Papers published in NAVIGATION, Global 
Positioning System Volume I.

[2] A. J. Van Dierendonck, W. C. Melton "Applications of Time Transfer 
Using NAVSTAR GPS", ION Papers published in NAVIGATION, Global 
Positioning System Volume II.

[3] A. Gifford "One-Way GPS Time Transfer 2000", 32nd Annual PTTI Meeting.

Cheers,
Magnus