Paying for GPS? - Page 2

ukchris · 05-18-2004, 04:42 PM

Quote: Originally Posted by Falken

Ummm, Is that because it's GLOBAL positioning system?

Yep, it works everywhere, just in case they decide they want to shoot a missile up your a$$ on day...!

hijinks21 · 05-18-2004, 05:02 PM

i believe when we invdaded IRAQ this time the military had some sort of jammer they setup over the general middle easter or just iraq area so they wouldn't have to shut off the civilian GPS channel. I'm not sure.. i think i heard that somewhere.

Chairboy · 05-18-2004, 05:09 PM

The Navstar system is pretty sophisticated, they can mis-time positioning signals from the satellites when they pass over certain parts of the world so that the Civilian-band GPS units can't give accurate fixes. It's called Selective Availability and was on worldwide until near the end of Clinton's term when he had it shut off. That's why we can get GPS signals that show us on the road instead of driving two hundred feet to the left, then instantly zig-zagging to 300 feet ahead, and so on.

Nav_Attack · 05-18-2004, 05:29 PM

it was my understanding that there were 3 "levels" of GPS use, that were differentiated by the number/ring/height of satellites used... with the military (obviously) getting the most accurate satellites... pinpointing to something like within a foot... and commercial and personal use being less accurate, etc etc... cause the satellites were lower, or something..

of course, this is all based upon my (faulty) recollection of my communications engineering I class like 4 years ago.

MiniG · 05-19-2004, 03:37 AM

Thats correct, there's the 3 levels of GPS, standard (L1), dual frequency (L1,L2) and Mil spec, which uses something else.

Dual frequency GPS is much better on position, but as is to be expected much more expensive. The Mil spec stuff I beleive my old work used to make it in another part of the empire, but never got to see it myself.

Then again you can use Glonass to get a better position, don't think it's setup enough for a stand alone position, but used with GPS it'll give you a lower error.

MiniG

Ormo · 05-19-2004, 10:24 AM

All these new fangled Gee Pee Esses and carpet pooters.... Not in my day, we navigated by the stars and listened to ol' jim on his harp....

Seriosuly tho, its an ingenious system all round. Kudos to the US government for making it available. Totally understandable they retain rights of control etc.

I have a question though, as far as "military grade" GPS goes, do other countries militaries have access to it? I'm just curious, but I'd assume they'd keep it tight with maybe a few close allies allowed access...

MiniG · 05-19-2004, 01:16 PM

Quote: Originally Posted by Ormo

I have a question though, as far as "military grade" GPS goes, do other countries militaries have access to it? I'm just curious, but I'd assume they'd keep it tight with maybe a few close allies allowed access...

AFAIK trimble and ashtech make the mil grade suff as well as the normal stuff, but I'd assume it's only available to the US mil and allies.

MIniG

hijinks21 · 05-19-2004, 01:47 PM

i'd also assume their allies have it.. but if england attacks us all they'd have to do is use a new encryption

cw95403 · 05-23-2004, 08:12 PM

Now-a-days the military can't really cloud the signal and accuracy as the GPS technology is now used for aviation navigation. All major airports in the U.S. and many in other around the world have recently published GPS approaches to their runways. Wouldn't to be nice of the military to turn off the accuracy for these GPS enabled aircraft during a GPS approach in the clouds?

GezusK · 05-26-2004, 03:30 AM

I thought airports use radio beacons to guide planes in.

cw95403 · 05-26-2004, 04:03 PM

They still do. Airliners (commercial) can use either or. General Aviation aircraft (your Cessna, Piper, etc.) that are certified for IFR (Instrument Flight Rules) typically use the radio beacons, but more and more are being outfitted with GPS navigation systems in addition to the radio navigation systems.

d_sellers1 · 06-01-2004, 10:26 PM

Quote: Originally Posted by Naamanf

The government can encrpyt the signal at any time. Up intill about a year ago the signals were partly encrypted so civilian receivers did not get an accurate time signal from the sat. And yes the US tax payer is paying for the entire world to use GPS.

This is not entirely true. The government removed all encryption when I was in Korea. I remember reading the report on it in 1999 or 2000. However, with our PSN-11 PLGR's we can still put in Comsec keys so we can get encrypted messages through the GPS system. These messages are always Top Secret so I've never been able to decrypt one (and I've got a Secret clearance due to my job). I've given many classes on the PLGR to subornates and superiors. The newer civilian models are a lot nicer and have better accuracy. (+- 3m compared to +- 10m). The PLGR only has a 40x40 LCD. The civilian models also have the maps and better tracking capabilities. Plus they're a lot smaller. But they're not nearly as rugged as the PLGR. I've thrown my on the ground during a class I was given to shown its ruggedness. Didn't break it. It even worked with a cracked LCD screen. Went through the entire time in Iraq like that.

Derek

d_sellers1 · 06-01-2004, 10:30 PM

Quote: Originally Posted by cw95403

Now-a-days the military can't really cloud the signal and accuracy as the GPS technology is now used for aviation navigation. All major airports in the U.S. and many in other around the world have recently published GPS approaches to their runways. Wouldn't to be nice of the military to turn off the accuracy for these GPS enabled aircraft during a GPS approach in the clouds?

You don;t think the military can do that. Besides, the accuracy loss it not as bad as you may think. It would only make it so you will be +- 25m instead of 10m or less. Not too big of a deal. Besides, they can be locally jammed but it's usually pretty easy to avoid the jamming.

Derek

d_sellers1 · 06-01-2004, 10:38 PM

Quote: Originally Posted by hijinks21

i believe when we invdaded IRAQ this time the military had some sort of jammer they setup over the general middle easter or just iraq area so they wouldn't have to shut off the civilian GPS channel. I'm not sure.. i think i heard that somewhere.

Not true. A couple guys brought their civilian GPSs with them. They worked better and are easier to operate than our PSN-11 PLGR. Depending on the mission, I would have both of them running. The civilian models are also able to show coordinates in MGRS which is the military grid coordinate system. Fort Hood is something like 31S PV????? ?????. (I used to know the number but don't any more).

10 digits will get you with in 10m
8 digits - 100m
6 digits - 1000m
4 digits - 10,000m (basically on the right map)

Derek

PS. I don't talking about Army stuff. This is getting boring.