Here is a summary of a 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.

This doesn't seem to be that big of a deal but it is a reminder that you can't always count on technology (as if we all need that reminder).

-Blast

I havent had issues with mine, and regularly get a good +/- 3m accuracy in lightly forested areas. Sometimes accuracy drops, but most of the time it isnt bad.
My guess is they will let some go that are not "mission critical", and keep up the ones they need. Eventually, they will be replaced....our whole military runs on them now, and Garmin, as well as other manufacturers, would likely sue the government if it were allowed to deteriorate too far.

thanks for the link. I have a GPS, but I really don't ask that much out of it except for lat and long. and elevation.
I'm still not ready to be weaned off maps and compass.

Strokes the mahogany box with my Weems und Plath sextant inside.Winds my Poljot chronograph and cleans mirror on Silva compass.
Now, if they would stop changing the names of rivers, islands, cities and countries ( reading Doughty's Travels in Arabia Deserta.)

I agree you can't rely on electronics but one thing I like about my Garmin Vista HCX with the micro sd cards you can use, the maps I have both global topographical, nautical and street maps are more valuable than the gps on it. With the solar cells as emergency back ups,the maps are pretty easy to navigate with out any signal you just have to move the pointer every now and then. The GPS function is a plus of that unit, however loss of electronics is a guarantee probability that will happen. Paper copy is always a plus and Delorme has the new Topos just released which is nice to print out what I need and laminate the maps.
http://shop.delorme.com/OA_HTML/DELibeCC...p;section=10047

For what it's worth, here's a site where you can download free USGS topo maps...

The USGS Store

With a few exceptions, my Garmin Legend HCx has been very accurate and a great navigation aid, though I could easily do without it if necessary. Accuracy depends a lot on the reception - standing at the bottom of a ravine or under a heavy tree canopy is going to be a problem. IMO, the fact that my new Garmin unit still works with a good deal of accuracy even in rugged terrain with a very limited view of the sky shows just how far electronics has advanced over the years. Not to mention the mapping capability with expandable memory is pretty useful in the field.

That said, I've always considered GPS a bonus. Really handy when available but one should not grow dependent on it. I see folks who use GPS all the time when driving a car. I wonder if they could find their way anywhere any more?

I use the GPS in my car for the traffic receiver and ETA estimates. The reported AF mismanagement of the GPS satellite constellation is surprising. Hopefully they'll get it right.

I have a Garmin Nuvi 760 which is a good car only GPS, and has a traffic receiver which I have found very useful in heavy traffic and choosing the best (of bad) option driving thru LA. The other GPS I occasionally use on the road is a GPSMAP 60CSx which I just lay on the seat.

Well this could be a funding issue. Considering that GPS is a free service (provided you have a reciver) what if we add a $10 tax to everything sold that uses GPS and put the funding towards updating and maintance. Considering that almost EVERY phone, that is sold in this day in age has a GPS reciver on it, they could realy increas the budget..

but that is the rambelings of a mad man.

+10 to that!

I have plenty of shovels and access to a lab where dead bacteria have been successfully reanimated. We could probably pull this off though it might lead to a zombie apocalypse.

-Blast, who has been practicing headshots on microorganisms.

He has a point.
We already pay a "tax" for the "free" 911 service. Nothing in life is free and I really expect something like this to happen in the future to support the GPS network. Just about everything today can use the GPS system, hell, even the Alaska Marine Highway ferries use GPS guidance.
I personally expect a 10.00 GPS "fee" when you buy something, and for cell phones a 1.00 month GPS maintanance fee.

You DO understand how the GPS system - and the Air Force - and the Entire Military gets the money they need to run stuff, don't you?

You DO understand that "user fees" for things like, oh, say National Parks, has long been a mantra of those who don't like federal taxes. So call it a $10 user fee for those folks who want to use the GPS system.

Oh, and while you're at it, let's add a $10 user fee for the Interstate Highways.

Might as well add a User Fee of $10 for each time someone calls 911 - gotta keep those calls making money and it's not fair to those who don't need 911 to have to pay for it.

Oh, and I guess if we're going to pay the 911 center a user fee, then let's make sure you get billed by the call for fire services...I guess since most people's houses don't burn, that user fee would be at least $6,000.

And that's gotta bring up a whole question of keeping taxes low in so many other areas. You know, those lights on radio towers - the ones that keep planes from crashing into them? Yeah, we should charge a user fee of $5.00 a flight for people who use airplanes, and I guess radios too since people who don't listen to radios don't need the towers, so why should they pay anything.

OH! Wait, I totally forgot! Credit Card Regulations! Yeah, that just passed, and I bet that took a lot of office work and stuff. But people who don't use credit cards shouldn't have to pay for all that lawmaking stuff...so why not charge a "credit card user fee" of say $10 a year to cover the costs of keeping those companies from being more greedy.

Am I being silly? A little, but I think that it's a clear that we all certainly expect a lot for our taxes, which are - compared to the bulk of the developed world - very low.

In Finland for example, the tax on a new car is 100%. That's right. A $20,000 car has a $20,000 tax. In Denmark, income tax is 52%. Yeah, you get free college, health care, cash for each of your kids, a pension for when you're old...but you pay for it.

The situation with the Air Force isn't so much one of funding - it's poor management and that's a situation that spans the whole of the USA. We've lost the big picture, the long view, the sense of duty now for the future. The fact that we even have to question the stability of the GPS system - that's more than sad, it's terrifying, because the GPS system - hell the whole space-based engineering world - was absolutely the domain of the USA, and the best we can do these days is to fly 20 year old space craft up to fix 19 year old spacecraft. That's pathetic. This GPS story is pathetic. I'm disgusted.

I received this message today through the corporate network.

Since leaving New Orleans, presently in Galveston Bay headed to Houston; I've noticed 10m (normal) to 100m (not good) accuracy.

Normally, our units provide 2m accuracy.

More likely at that moment in time you were within view of a high number of GPS satellites. That's one reason I really like the newer high sensitivity receivers -- more satellites are in view.

DGPS may provide a solution for keeping GPS accuracy reasonable (within 1-5m CEP with a < 100km baseline) which will be somewhat better than the satellite based WAAS or EGNOS PRN as long as the baseline is within a suitable range to the ground station. DGPS receivers such as the CSI MBX3 are pretty expensive and bulky so here is a link to a home brew solution for a low cost solution;

http://web.abnormal.com/dgps/bix1/ (makes for a nice home electronics project )

Your GPS model will need RS232 port comms rather than USB though to recieve the RTCM-SC104 message.

Even the cheap Garmin eTrex Units can have improved accuracy by ensuring WAAS or EGNOS PRN is enabled for differential accuracy as long as the firmware is up to date. But I don't think the eTrex models have HDOP and velocity filtering though or even the ability to discard any satellite PRN below a certain angular height above the horizon.

To determine the accuracy of your GPS you will need some software such as 'SA Watch' and run your GPS for around 24-48hrs whilst logging the GPS data on a PC. This will give you an extremely accurate position of you location i.e. less than a few decimetres using statistical averaging.

http://www.huntting.com/sawatch/

My Garmin GPS V has an "average" function. Turn it on and let it run, and the location info refines itself over time.

A bit off topic but having to do with sats.

I was talking to someone at the FAA in D.C. He told me that the Air Force does not want to put SAR-SAT on the two birds that they where going to. I do not know if tis is a move on there part but I have known the person who gave me the info for 50 years I do believe that the info is true.

I had some interesting results with the 'SA Watch' and Google Earth software used in conjuction with a Garmin eTrex Camo GPS SW ver 3.7 (Discontinued but with the latest firmware).

The Garmin eTrex is the older standard chipset and not the high sensitivity H or HC models etc.

WAAS (EGNOS in Europe) was enabled and the NMEA 0183 output (4800,8,N,1) was selected. The eTrex was situated on a south facing window sill and could observe only half the sky with some large trees obscuring the southerly view. So not the best sky view. The Garmin eTrex was still able to view 6-7 SVs (many of them to the North which was obscured so considerable multipath must have been at play). The EGNOS PRN was detected and DGPS positional computations were being carried out by the eTrex unit. (typically the error estimation by the eTrex was typically around 3-6 metres with SA view showing a CEP @ 95% around the same value. Not bad considering the poor sky view)

The Garmin eTrex supports the NMEA 0183 sentences GPGGA, GPGLL, GPGSA, GPGSV, GPRMB, GPRMC, GPRMT, GPVGT, GPWLP, GPBOD

None of these message sentences in the NMEA format indicate the Datum as indicated in the NMEA sentence reference i.e GPDTM

http://www.tronico.fi/OH6NT/docs/NMEA0183.pdf

This is where there appears to be a problem with the eTrex unit. When ever the Datum is changed a significant error may occur if the eTrex is communicating its position to another device if the other electronic mapping/recording/navigational device isn't aware of a datum change by the eTrex GPS.

Initially the eTrex was set to the OSGB36 datum for UK Ordnance Survey - the eTrex generated a stable 8 digit grid reference accurate to 10m, which was spot on (excellent considering this is about as accurate as any 1:25,000 scale mapping work would ever require and considering the poor sky view and multipath error that must have been occurring)

What wasn't so great was when I went to use Google Earth (which I assume uses the WGS84 datum) with the eTrex using the OSGB36 datum. The position was consistently out by 90m to the east. At first I was at a loss as to what was happening, then realised the difference must be down to the difference in the Google Earth WGS84 datum and the OSGB36 datum. As soon as I reconfigured the Datum on the eTrex to the WGS84 datum, the Google Earth pinpointed the window on my house on the aerial photo.

If Garmin aren't going to include the $GPDTM output message when the eTrex talks to another device application such as external electronic mapping applications then I would have expected the output NMEA sentences to have remained referenced to the WGS84 datum. So if using your eTrex in conjuction with Google Earth on your 3G enabled netbook, you need to ensure that the eTrex has the WGS84 datum selected. As always make sure that both your map and GPS are using the same Datum, whether the map is paper or electronic. This is probably more important than losing a couple of SVs in the next 5 years from the constellation where general navigation work is required. Survey work, now that might be a whole different ball game.


Edit - An update on the eTrex Camo accuracy





The blue portion in the Observed GPS horizon is the actual sky view and the orange portion would have been subject to multipath error. As you can see there wasn't a good view of the sky and the accuracy has suffered as a result. Most of the observed measurements 72% had an HDOP > 2.0

Actual accuracy is around 20 metres CEP @ 95% rather than the earlier assumption of 3-6 metres. Again I still would actually consider this to be an excellent result considering the poor HDOP due to the limited sky view and the inherent multipath errors.

Look at the good side, maybe Map and Compass training will pickup again.

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.

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.

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.

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.

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.


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.


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.


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.


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.

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.

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.

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.

With all the other weapon systems that rely on GPS I can not see the Air Force letting it degrade much. Do you think this may be some internal politics to try and keep the administration from cutting there budget or perhaps the whole program?