/ GPS - Selective Availability

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FesteringSore - on 28 Nov 2016
Given that GPS is owned, operated and maintained by the US I was wondering, do they use SA top prevent its use by the jihadists?
Swig - on 28 Nov 2016
In reply to FesteringSore:

They said they wouldn't use it any more and it probably wouldn't work very well now as receivers can do Glonass and differential GPS.
FesteringSore - on 28 Nov 2016
In reply to Swig:

> They said they wouldn't use it any more

I thought the option was still there for use "against" appropriate (potentially belligerent) users.
robhorton - on 28 Nov 2016
In reply to FesteringSore:

They certainly have the ability to use SA - they did for a military exercise in Scotland a year or so back. Obviously they don't have any control over the Russian system but both can be jammed fairly easily so I suspect they would do that in practice. No idea what actually happens in Syria, for example though.
Swig - on 28 Nov 2016
In reply to FesteringSore:

It might be still there in theory. But probably not that effective if they did use it.
KevinD - on 28 Nov 2016
In reply to robhorton:

> They certainly have the ability to use SA - they did for a military exercise in Scotland a year or so back.

I thought most of those exercises used jamming and buggered it up all round.
GPS did have, at least, two variants for many years. Civvie which had some inaccuracy built in and the military variant which didnt and was more tightly restricted. I am not sure how the two were managed separated technically though.

Swig - on 28 Nov 2016
In reply to FesteringSore:

"Will SA ever be turned back on?

The United States has no intent to ever use SA again. To ensure that potential adversaries do not use GPS, the military is dedicated to the development and deployment of regional denial capabilities in lieu of global degradation."

http://www.gps.gov/systems/gps/modernization/sa/faq/#world
davidbeynon on 28 Nov 2016
In reply to FesteringSore:

SA never worked very well anyway, as there were always workarounds. Now that there is credible competition from other navigation systems it's completely pointless.

Far easier to just jam signals as required.
StuDoig - on 28 Nov 2016
In reply to robhorton:

I believe that was jamming rather than selective availability as selective availability affects the whole network rather than a small geographic area only. They carry out the same ex most years, or at least every second year (the vessel I work on is often in the jamming area and restricts our ability to work as reliant on DGPS for positioning - means we're very aware of when these exercises happen!). Though in fairness, last time I was onboard during the ex, we didn't notice a great loss in in ability to hold station on GPS.

to Op: As others have said, now that there are working alternative systems selective availability is more pointless as it isn't likely to be that effective are reducing GPS accuracy, and would most likely just end up hacking off a load of recreational users in the US.

Cheers,

Stu
robhorton - on 28 Nov 2016
In reply to KevinD:

> I thought most of those exercises used jamming and buggered it up all round.

Think you're right actually. Presumably it's pretty localised as shipping as heavily (over) reilant on GPS.

> GPS did have, at least, two variants for many years. Civvie which had some inaccuracy built in and the military variant which didnt and was more tightly restricted. I am not sure how the two were managed separated technically though.

I think the military one is encrypted and uses multiple frequencies making it harder to jam.
GrahamD - on 28 Nov 2016
In reply to FesteringSore:

How on earth would you target Jihadists as opposed to, say, local emergency services or aid workers ? Its not like they buy their GPS from a dedicated Jihadi shop.
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wintertree - on 28 Nov 2016
In reply to FesteringSore:

I don't think your average jihadist has much to loose if SA is turned on. Other people might...

I believe the US have the ability to jam other people's GLONAS systems. They were most emphatic that the EU system should use a different frequency to GPS to allow them to jam it without borking their systems. I believe there was talk of the US shooting down or otherwise borking Galileo satellites as an alternative if it wasn't made separately jamable...

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