[time-nuts] "The GPS navigation is the weakest point,"

[Jim Lux]

On 12/15/11 2:06 PM, Jim Palfreyman wrote:
> Fascinating.
>
> I can picture setting up a bunch of transmitters in the hills to send out
> strong GPS-like signals to mimic the real thing. I suppose you could
> control those signals to fool the device it is somewhere else. That bit is
> very clever - you'd have to adjust the signals taking into account current
> positions of all current satellites. Smart bit of work there.
>
> But it would also need incredible timing. Even a few ns out and it wouldn't
> work. So how do you set up fantastic timing at different locations of
> transmitters throughout a country. Well you've blocked the GPS - so that's
> no good.
>
> It would require local atomic clocks (good ones) at each location.
>
> Do they have access to such things? Maybe I'm being naive.
>
> Jim
>
>


This would be insanely difficult to do. and hmm.. do you think that the 
antenna on the drone is pointing UP (towards the GPS constellation) or 
down (towards jammers?).  The only people pointing antennas down are 
ones experimenting with precision landing systems and pseudolites or 
people doing bistatic radar using GPS as illuminators.

As Jim points out you have to time the signals very carefully, and think 
about what the jamming signals needs to look like... you have to (very 
accurately) know where the victim is (so that you can broadcast your 
spoofing signals with the correct timing so that they arrive at the 
victim within a fraction of chip.. Let's see now, that UAV is covered 
with radar absorbing material, and the shape is such that it probably 
has a radar cross section of a few square centimeters.  How will you 
know where it is accurately enough to generate that spoofing signal 
(say, within a meter).


And, of course and it has to start synced with the real GPS signal so it 
can pull it off gradually)

Oh, and you need to be able to encrypt the fake GPS signal (assuming 
that the UAV is using a P/Y capable receiver).

AND, your "spoof trajectory" has to be carefully designed so that it's 
not too different from what the UAVs internal IMU is telling it.  After 
all, a failure of GPS or IMU is something they design for, so they're 
always cross checking  (just like human pilots do..   Hey, GPS is 
reading 500kts and I'm in a Piper Cherokee... I think the GPS on the blink)



Nope.. UAV engine quits, it goes into "glide to the ground doing the 
least damage" mode... UAV ditches in a gravel and sand covered field 
(with which much of eastern Iran is covered).


Even LightSquared, idiotic and pernicious as it may be, would have a 
hard time bringing down a UAV.