March 16, 2002

9:00 PM

The Global Positioning System is now commonly used for navigation in hundreds of ways worldwide. Some very innovative things are now being done with the system beyond simply finding out where you are. However, according to this BBC story, "emerging applications are being hampered by concerns that information from the global satellite network, which is run by the United States, could be switched off or restricted in the event of a security threat." Am I the only one worried about what will happen to all the hikers, rescue services, ships, small planes and geeks that would suffer if the network is switched off?
posted by Gamecat (12 comments total)

Backup navigation systems are recommended (and used by anyone with a brain).
posted by HTuttle at 9:14 PM on March 16, 2002

Also, there's 'selective restriction' where tightly defined geographic areas are denied accurate (or any) GPS signals. This is and has been the case over Afghanistan for the last several months.

Of course, that doesn't apply to the encrypted gov't signals.

At any rate, it's unlikely they'd turn off GPS over the US unless we were actively being invaded.
posted by kfury at 9:20 PM on March 16, 2002

I didn't realise they system could be controlled in quite that detailed a manner - it certainly isn't even hinted at in the BBC article that prompted me to post the link. And having learned about the controllability, I must confess it isn't the service in the US that is concerning me. I'm sure that would be the last to go.
posted by Gamecat at 9:30 PM on March 16, 2002

Heres a Wired article from Oct 20, 2001 describing the possibility. I believe they enacted selective availability a couple weeks after that.
posted by kfury at 9:34 PM on March 16, 2002

If gps is shut off for security reasons, then yes, you will be the only person worried about hikers.
posted by Settle at 9:59 PM on March 16, 2002

oh my god! the surveyors! who will think of the surveyors?!??!?
posted by quonsar at 10:43 PM on March 16, 2002

The possibility of geek collisions -- potentially even massive geek collisions -- goes way up.
posted by coelecanth at 11:19 PM on March 16, 2002

All those geocaches... lost forever...
posted by kfury at 11:31 PM on March 16, 2002

Selective Availability doesn't "turn off" GPS, it encrypts the P 'Precision' code. The civilian C/A 'Coarse/Acquisition' code remains in place, with accuracy reduced to around 30-100m. Modern GPS systems can use 'differential' GPS by combining/triangulating multiple signals to achieve much greater accuracy without the military code, though. Any precision civilian application will probably use the differential methods or both. Moving a bulldozer might be a bad idea, but finding a hiker would still be possible.
posted by dhartung at 12:12 AM on March 17, 2002

Although the BBC article states that the final decision wouldn't be made until March 26th, the following article in today's Observer indicates that Galileo, the alternative European GPS system, has been given the go-ahead (despite strong US opposition):

'Euro satellite to be £2bn eye in the sky for blind'
posted by Owen Boswarva at 6:37 AM on March 17, 2002

yep, faa says "don't use gps for flying navigation." pilots would be safe (SHOULD be safe).
posted by tomplus2 at 8:35 PM on March 17, 2002

Selective Availability doesn't "turn off" GPS, it encrypts the P 'Precision' code.

Dhartung is pretty much correct in his description of what is happening with the P-code except that SA is not what enciphers the P-code, AS (Anti-Spoofing) is. AS is intended to prevent false GPS info from being introduced.

SA is the intentional introduction of errors into the information from the satellites. Someone equipped with the GPS cryto keys could decipher the information needed to back these errors out of the signal. There were ways around SA; the DoT was spending tons of money to get rid of the errors while the DoD was spending more tons to keep the errors in place for everyone but their own people. SA was turned off in 2000.

There's an update to this technology called Selective Availability/Anti-Spoofing Module. This module not only provides stronger encipherment of the P-code, but it also provides the capability of being very selective in who is able to use the GPS signals.

Backup navigation systems are recommended...
A primary navigation system is also recommended. GPS is not a navigation system, it's a positioning system. It tells you where you are, not how to get someplace else. The systems that provide navigation cues have other sub-systems that close the loop around the GPS info.
posted by joaquim at 12:25 PM on March 18, 2002