[time-nuts] GPS backup for the stationary time and frequencyuser

jimlux jimlux at earthlink.net
Fri Oct 8 18:27:52 UTC 2010


Matthew Kaufman wrote:
>  On 10/8/2010 10:44 AM, J. Forster wrote:
>> KISS. This seems like a lot of work for not particularily good results.
> 
> I think the point is that the results are amazingly better than the 
> alternative if the medium-orbit GPS sats are all destroyed and/or 
> there's jamming coming from all over the sky.
> 
> What bothers me is that I haven't figured out yet how the WAAS satellite 
> configuration itself isn't usable as a wide-area GPS jammer. It is just 
> a bent-pipe transponder down from 6 GHz or so to L1, so if you can 
> overpower the uplink with spoofed data that interferes with reception of 
> the other satellites *and* jam the C&C channels that would be used to 
> shut the transponder off, you're able to jam a whole continent at once.

Most spacecraft have a "command loss timer" that would shut off the 
transmitter in the event that a valid command isn't received every so 
often, in case the transmitter is malfunctioning and jamming the uplink.


> 
> I'm sure this must have been considered before deployment, but I can't 
> find any references to the countermeasure(s).
> 

Maybe because WAAS is basically a civilian use system to do precision 
approaches?



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