[time-nuts] Satellite Glitch Rekindles GPS Concerns

Magnus Danielson magnus at rubidium.dyndns.org
Fri Jun 19 05:40:35 EDT 2009


Brooke Clarke wrote:
> Hi again Mike:
>
> The IIR-2 satellite was launched in order to meet a deadline rather 
> than when it was truly fully operational.  The L5 module is an add on 
> and can not run at full power.  So this is not a representative of the 
> future sats.
First of all, it's the IIR-20(M). If you look at the article it has both 
variants, so I think it is just an editorial mistake.

The problem is how the L1 tracking is affected. Exactly what mecanism 
shifts the L1 signal is unclear in the material I have seen, but L1 
seems shifted. Depending on the elevation in the sky, this shift is more 
or less apparent.

Cheers,
Magnus
>
> Have Fun,
>
> Brooke Clarke
> http://www.prc68.com
>
> Mike Monett wrote:
>>   An article in NetWork World discusses performance degredation in the
>>   new Lockheed-built  GPS  IIR-2  satellite.  Apparently.  the  new L5
>>   transmissions are interfering with other signals from the satellite.
>>
>>   This reduces  the accuracy an order of magnitude, from 2 feet  to 20
>>   feet. It  should have a corresponding effect on the accuracy  of the
>>   decoded time signals.
>>
>>   The Air  Force said it has identified several parameters in  the GPS
>>   IIR-20 (M)'s  navigation  message  that   can  be  corrected  and is
>>   studying the impact these may have on military and civil GPS users.
>>
>>   Presumably, the  problem  will  be corrected in  the  12  Boeing GPS
>>   satellites currently being built that also feature the L5 signal.
>>
>>   The article  discusses  issues   such   as  delays  due  to techical
>>   problems, cost overruns, and aging of the fleet. These  could affect
>>   system performance in the future.
>>
>>   However, Col. Dave Buckman stated
>>
>>   "The issue  is  under control. We are working hard  to  get  out the
>>   word. The issue is not whether GPS will stop working. There's only a
>>   small risk we will not continue to exceed our performance standard,"
>>   he said.
>>
>>   http://www.networkworld.com/community/node/42767
>>
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