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Guest Paul Lamble

Selective Availability

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Guest Paul Lamble

This is really two questions.

 

Suppose the U.S. were involved in some localized military engagement somewhere in the world. The Gulf War is a good example. In that case, would Selective Availability be turned on again? For the duration of the matter, would we civilians temporarily lose the 10 meter accuracy we now enjoy?

 

Second question, I read that the Russians had begun developing a system of GPS satellites of their own. Seems like I saw that at the GPS display at the Smithsonian. Does anyone know if this was ever established? Did their system ever get off the ground? Is it comparable to the one we use? Is it more or less accurate?

 

These kinds of questions just keep me up at night!

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Guest alwaller

I believe it is called "Glonast" or very similar. And yes it is fully operational with commercial receivers available to use it. We have one at work (NASA) that tracks all the US and Russian Satellites at the same time. Receiver manufacturer is Ashtech

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Guest alwaller

FOLLOW UP POST

 

Found this in a search...

 

Ashtech makes GPS+GLONASS receivers. However, they are for

surveyors, and so will be expen$ive. Also, the GLONASS system

is in very poor health, and Russia has no money to heft the

replacement satellites (which fly for only two years each).

They are desperately trying to sell stakes in the system to

outsiders in order to revive it. Meanwhile, the system is

crumbling away.

 

Ashtech was gobbled up by Magellan in 1998, who in turn

is owned by Orbital. I have no idea what name you'll find the

GPS+GLONASS products under...the first thing new marketing

people do after a merger is rename everything.

 

GNSS is the new European satnav system. GNSS-1 is

supposed to be up by 2002, and is basically a gigantic land-

and space-based diff system for GPS and GLONASS. The ESA is

running the show. GNSS-2 is planned for 2010 and will be

entirely civilian, though that doesn't mean as much in Europe

as it does here.

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Guest peter

First question:

It's very unlikely that SA would be reactivated. Prior to it being turned off, the military conducted extensive tests of local jamming/spoofing that would deny the enemy use of GPS in the battle area while leaving it available for the US forces. So GPS might well be unavailable in the conflict area but unaffected elsewhere. At this point there are so many commercial interests relying on accurate GPS that the political pressure against turning on SA would be immense.

 

Second question:

Yes, the Russians established the GLONASS system and there are a few GPS receivers that also work with signals from those satellites (I think they're all very expensive though). There is not a full constellation of GLONASS satellites and they have reliability problems. My impression is that accuracy falls somewhere between 'GPS with SA' and 'GPS without SA' when you have enough sats overhead to compute a solution.

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Guest jeremy

As I can see it, there are two logical reasons why SA was turned off (and is 99.999% likely won't be turned on again) -

 

1. We were going the way of differential GPS anyway, which would render SA basically useless.

 

2. The US government has a better location-based system that is more reliable and hard to block. Still classified, I'd wager.

 

I'd go for #2. Or a combination of GPS and new technology that is redundant in case the signals for GPS are jammed (possible?) in battle.

 

Jeremy

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Guest ScottJ

That, and TERCOM and other technologies are becoming so good that an enemy wouldn't NEED GPS to effectively target a weapon anyway icon_smile.gif

 

Scott

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Guest ScottJ

That, and TERCOM and other technologies are becoming so good that an enemy wouldn't NEED GPS to effectively target a weapon anyway icon_smile.gif

 

Scott

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Guest bubba232

Just a side note. I thought I read somewhere that Japan/Asia is close to their own GPS system? Anyone else know about this? I can't remember where I read it.

 

S.

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Guest Nomad

I can understand the idea of SA, but I don't think it's very practical. If we (the public) have heard of the technology, you can bet every military in the world has their own version of it! So, while Asia may be close to a public GPS system, I gurantee the Asian militaries have been using one for years. And, as far as SA goes, if our military could get around it, I'm sure every other significant military could too. I'm not saying the militaries are equal in all aspects, but the things that YOU and I have actually heard about are so common place taht everyone has it. The real secrets are in the technologies that the public has never heard about. In summary, I'm just saying that the miltray did away w/ SA b/c they realized it was pointless...b/c everyone else had their own way around it. So, they decided to let the public in on the fun too. So, what we consider to be cutting edge technology (GPS units that can get w/in 10 meters) they are extremely outdated in military terms.

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Guest Moun10Bike

t face="Verdana, Arial" size="2">Originally posted by Nomad:

So, while Asia may be close to a public GPS system, I gurantee the Asian militaries have been using one for years.


 

The NavStar constellation (the one our GPS units use) cost $12 billion to implement, plus there are the maintenance costs. Very few countries can afford that kind of outlay. There likely really are only two systems (NavStar and Russia's GLONASS).

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