[time-nuts] Satellite Glitch Rekindles GPS Concerns
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.
> Have Fun,
> Brooke Clarke
> 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.
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