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#173690 - 05/22/09 03:41 PM Re: GPS accuracy at risk in coming years. [Re: ]
BruceZed Offline
Enthusiast

Registered: 01/06/08
Posts: 308
Loc: Canada
Look at the good side, maybe Map and Compass training will pickup again.
_________________________
Bruce Zawalsky
Chief Instructor
Boreal Wilderness Institute
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#173701 - 05/23/09 12:13 PM Re: GPS accuracy at risk in coming years. [Re: Blast]
Brangdon Offline
Veteran

Registered: 12/12/04
Posts: 1201
Loc: Nottingham, UK
Originally Posted By: Blast
This doesn't seem to be that big of a deal
Agreed. It sounds like scaremongering as part of budget negotiation. You need 4 satellites for a fix, so having 24 in the aid includes a large safety margin. The implications of losing GPS are far worse for the military than for domestic use.
_________________________
Quality is addictive.

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#173716 - 05/24/09 01:01 AM Re: GPS accuracy at risk in coming years. [Re: Brangdon]
Art_in_FL Offline
Pooh-Bah

Registered: 09/01/07
Posts: 2432
GPS was developed, designed and built for military use and they remain in complete control over the system.

At little more than a flip of a switch they can turn off all non-military use. They can, and often do, insert various amounts of random error, referred to as 'dither', into any or all parts of the system. From sources in the area I hear that when major parts of the fleet come to Mayport Florida they toss in a dither of 50 to 100 meters for the Jacksonville area readings. High end GPS units, which use more satellites and fold in a considerable amount of computational power and multiple readings over time, can avoid a good bit of the error and give more consistent readings.

Considering the value we, the entire world, are getting from a defense program I wouldn't balk at the taxes paid for it. Some of you are too young to remember a time before GPS and so you might take any inconvenience or inaccuracy as a revocation of a right. I remember the many hours having to hike up hills to get to a point I could take sights on landmarks or backtrack and pace from a known point to verify I was on the right trail.

Sailors used to have to pick their way around difficult shores and a location of plus or minus ten miles was considered good. LORAN was a big step up from dead reckoning, compass and sextant but it was often both inaccurate and unreliable. Sometimes dangerously so.

All that changed with GPS. At first it was only the military but in a few years receivers got cheap and now anyone with a couple of bills can get their location with accuracy unimagined by previous generations. And, except for having to buy a receiver, they give access to this multi-billion dollar system away for free.

It is hard to overestimate how much the GPS system has saved humanity. The people who now have a reliable fix on their position when they need help. Rescuers who can go out blind in fog and storms and find people because they know where they are and where they are going. The ships that don't run aground. The thousands of people and man-hours saved. Just the reassurance and comfort of knowing for-sure where you are alone is worth quite a lot. Yes, if it came down to it, I would willingly pay for the privilege.

But be aware that if the SHTF in a big way, perhaps another world war, the civilian GPS receivers may not work. So appreciate the beauty, simplicity, and reliability of the system we have now.

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#173719 - 05/24/09 02:14 AM Re: GPS accuracy at risk in coming years. [Re: Art_in_FL]
avillageperson Offline
Stranger

Registered: 01/31/09
Posts: 7
Loc: ohio

I'm surprised no one has mentioned the competing European version called Galileo:


http://en.wikipedia.org/wiki/Galileo_(satellite_navigation)


"Galileo is a global navigation satellite system (GNSS) currently being built by the European Union (EU) and European Space Agency (ESA). The 3.4 billion project is an alternative and complementary to the U.S. Global Positioning System (GPS) and the Russian GLONASS. On 30 November 2007 the 27 EU transportation ministers involved reached an agreement that it should be operational by 2013."

Still a couple of years off.


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#173729 - 05/24/09 02:36 PM Re: GPS accuracy at risk in coming years. [Re: avillageperson]
Art_in_FL Offline
Pooh-Bah

Registered: 09/01/07
Posts: 2432
I was completely unaware of the Galileo and GLONASS systems. Thanks for the heads-up.

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#173731 - 05/24/09 03:45 PM Re: GPS accuracy at risk in coming years. [Re: Art_in_FL]
Arney Offline
Pooh-Bah

Registered: 09/15/05
Posts: 2485
Loc: California
Originally Posted By: Art_in_FL
I was completely unaware of the Galileo and GLONASS systems. Thanks for the heads-up.

The Indian government is cooperating with the Russians on Glonass. I'm not sure if they actually went through with it, but I remember reading a while back that the Indians were even going to launch some of the satellites for the Russians.

And let's not ignore yet another competing global naviation system, this time from the People's Republic of China--the Beidou Navigation System. Not yet operational, but they're actually sending the birds up.

GPS, and to a lesser extent, Galileo, get all the attention, but as we've just learned in this thread, they are not the only games in town.

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#173752 - 05/25/09 08:23 AM Re: GPS accuracy at risk in coming years. [Re: Blast]
James_Van_Artsdalen Offline
Addict

Registered: 09/13/07
Posts: 449
Loc: Texas
Originally Posted By: Blast
...Air Force report on difficulties replacing aging GPS satelites. They are behind schedule and predict the probability of keeping a 24-satellite constellation in orbit drops below 95 percent in 2010, and could drop as low as 80 percent in 2011 and 2012.

Translation: if the AF doesn't quit screwing around, tinkering with the specs and just *build* *what* *they* *already* *know* *they* *need*, then some satellites already in-orbit might be beyond their design service life before a replacement is launched.

The AF is distracted by systems from Europe, Russia, etc, and trying to make sure theirs is "better", forgetting that nothing on overhead slides is ever as good as something in orbit and operational.

Accuracy is already great. If a lot of money is to be spent it ought to go into jamming-resistance.

Originally Posted By: Brangdon

You need 4 satellites for a fix, so having 24 in the aid includes a large safety margin.

You need 4 *over your location* for a fix. You need more in-orbit to guarantee that 4 are visible from every point on Earth at all times.

Originally Posted By: Art_in_FL

At little more than a flip of a switch they can turn off all non-military use. They can, and often do, insert various amounts of random error, referred to as 'dither', into any or all parts of the system.

Selective Availability was turned off by Presidential Order during the Clinton administration.

Simply turning the system off for civilian users in time of war turns out not to be an option. In the Iraq war DoD was woefully short on the military grade GPS units, which can decode the encrypted signals, and had to rely heavily on civilian models, which can't decode the encrypted signals. That meant no turning off civilian units or even significant degradation.

Quote:

High end GPS units, which use more satellites and fold in a considerable amount of computational power and multiple readings over time, can avoid a good bit of the error and give more consistent readings.

The key to accuracy is a stable oscillator. Better units shield their oscillator better, with better temperature insulation & compensation, etc. Propeller-heads that want to locate their antenna within a millimeter will use pairs of rubidium oscillators.

Originally Posted By: Arney

The Indian government is cooperating with the Russians on Glonass. I'm not sure if they actually went through with it, but I remember reading a while back that the Indians were even going to launch some of the satellites for the Russians.

The Russians that the best launch systems in the world: I cannot imagine why they'd spend money to build the birds and then launch on an Indian rocket.

More likely the Indians will build the satellites and the Russian contribution is launch services.

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#173754 - 05/25/09 09:14 AM Re: GPS accuracy at risk in coming years. [Re: Art_in_FL]
Tom_L Offline
Addict

Registered: 03/19/07
Posts: 690
Have to agree with Art here. GPS has really made life a lot easier in many ways. But as with most things in life, it shouldn't be taken for granted.

Right now, GPS is pretty much the only gamer in town. GLONASS, Galileo etc. all sound great, but they don't WORK just yet. Even once the system is set up it will take a while to sort out the glitches and make it economically viable.

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#173758 - 05/25/09 11:28 AM Re: GPS accuracy at risk in coming years. [Re: Art_in_FL]
Brangdon Offline
Veteran

Registered: 12/12/04
Posts: 1201
Loc: Nottingham, UK
Originally Posted By: Art_in_FL
So appreciate the beauty, simplicity, and reliability of the system we have now.
Oh, I do. I'm not disagreeing with anything you (or James_Van_Artsdalen) wrote, just commenting on the original story.

The potential for Americans to mess with their system is a big part of why we Europeans are interested in having our own system. And their generosity in, eg, switching off selective availability is part of why other Europeans see no need to pay for it. There's lots of politics involved.
_________________________
Quality is addictive.

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#173760 - 05/25/09 02:04 PM Re: GPS accuracy at risk in coming years. [Re: James_Van_Artsdalen]
Arney Offline
Pooh-Bah

Registered: 09/15/05
Posts: 2485
Loc: California
Originally Posted By: James_Van_Artsdalen
The Russians that the best launch systems in the world: I cannot imagine why they'd spend money to build the birds and then launch on an Indian rocket.

Well, it's apparently a strategic partnership, not a purely technical or civilian one. The Russians are selling some of their launch technology to the Indians, and the Indians are developing their launch capabilities, including for ballistic missiles, so there is probably interest on both sides to have the Indians participate in launching some of these birds. Plus the Russians can have the Indians shoulder some of the costs of launching these birds.

Interestingly, almost all the references to the Indians launching any of these birds are from around 2006 and then a big gap. I can only infer that things got put on hold for a while during that time. I finally found something more recent here. Still haven't launched any but it still seems to be the plan. I can't vouch for the veracity of this website, but it's not inconsistent with anything older I have run across.

Switching gears back to China's system--apparently it is generally referred to as the COMPASS system.

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