Galileo: Europe's Version of GPS Reaches Key Phase

another random user sends this quote from the BBC: "The third and fourth spacecraft in Europe's satellite navigation system have gone into orbit. The pair were launched on a Russian Soyuz rocket from French Guiana. It is an important milestone for the multi-billion-euro project to create a European version of the U.S. Global Positioning System. With four satellites now in orbit — the first and second spacecraft were launched in 2011 — it becomes possible to test Galileo end-to-end. That is because a minimum of four satellites are required in the sky for a smartphone or vehicle to use their signals to calculate a positional fix."

Comments

Chicken::egg.

[Anonymous Coward]

Are there any consumer gear that can receive Galileo?

Re:Chicken::egg.

[_merlin]

They'll arrive. There are already devices that can receive both Soviet GLONASS and GPS (e.g. Galaxy SIII) to get better positional accuracy. Soon the new devices will receive Galileo as well, for triple redundancy and improved accuracy.

Re:Chicken::egg.

[BradleyUffner]

Are there any consumer gear that can receive Galileo?

I don't see how this could possibly be called a Chicken and the Egg type problem, as the satellites are are already in space to support consumer devices. They obviously didn't need consumer device support to get things started at all.

Re:Chicken::egg.

[Anonymous Coward]

In Asia China's Beidou/Compass should be interesting now, and we'll see how quickly the next phase comes along.

And Japan's QZSS is easily usable by GPS receivers with the right software.

Re:Chicken::egg.

[anared]

And Galileo will be the most accurate of them.

Re:Chicken::egg.

[northerner]

There are already chipsets that use multiple positioning constellations simultaneously. It won't be long until consumer gear has this as a standard feature.

The chips can receive some or all of GPS, GLONASS, Galileo, COMPASS (AKA China's Beidou or Big Dipper), QZSS (Japan) and SBAS augmentation services.

For hardware hackers, companies have put the chips into easier to use modules. Two examples are the Telit Jupiter SL869 and the uBlox NEO-7, which are even footprint compatible with each other.

Re:Chicken::egg.

[K. S. Kyosuke]

They'll arrive. There are already devices that can receive both Soviet GLONASS and GPS (e.g. Galaxy SIII) to get better positional accuracy. Soon the new devices will receive Galileo as well, for triple redundancy and improved accuracy.

It's already happened. There have been modules for GPS+GLONASS+Galileo on the market for quite some time.

Re:Chicken::egg.

[petsounds]

The iPhone 4S and 5 can use GLONASS as well. But agreed, once the Galileo project gives the thumbs-up, we should see mobile device support shortly thereafter.

Re:Chicken::egg.

[RockDoctor]

When I was looking to replace my stolen hand-held GPS in 2004, I was debating whether to get one with GPS-only, or GPS+GLONASS. Then I decided that the small amount of additional coolness factor of owning something that wasn't subject to shutdown by the US military wasn't worth the potential for doing jail time with hard-labour for being in possession of spying equipment.

That's probably not so much of an issue this decade, but I've still not replaced the "proper" GPS, because I frankly don't see the need ; my navigation is perfectly adequate without one. The wife did get us a SatNav (which uses GPS for it's position finding) for the car, and it's base maps are over 20 years out of date, illustrating the point that the important thing about a SatNav system is not one of the position-finding technology, or the route-finding algorithm, or the base map, or the "wireless updates for the safety camera database", but it is all of the components and their interactions.

(Incidentally, I object to being required to subscribe to a "safety camera database" which is a euphemism for "speed where ever you dare database" ; if we ever replace this "Road Angel" heap of shit, I'll be looking for a system without this unnecessary capability.)

Good to hear

[Sycraft-fu]

There has been far, far too many delays and political fuckery with this. I'm glad to hear it is finally going online.

Satellite navigation is just very important to everything these days (it is the primary nav method for all planes, ships, etc). Having everything rely on GPS, and thus on the budget the US chooses to spend keeping it working, is not a good idea.

This will make things much more reliable since, after an initial hissing match, the US and EU settled down and the systems play nice together and you'll be able to get devices that use both for better accuracy and reliability.

Re:Good to hear

[Grave]

Oh, the budget for GPS will pretty much never be cut until the system becomes obsoleted by something newer. The US military relies on GPS. However, the more navigation systems we have, the faster and more reliable fixes can become for civilian use.

Re:Good to hear

[Anonymous Coward]

GPS is not the primary means of navigation for airlines. It sees a lot of us in General Aviation, but not for scheduled airline service.

Re:Good to hear

[caseih]

In agriculture GPS guidance systems already have the capability of talking to Galileo when it is finished, and Glonass right now. After the military, agriculture is probably the most dependent on positioning technology these days. If GPS guidance goes down (IE our hardware has a problem), we simply cannot drive the machines. They are too wide to drive manually (my sprayer is 120 feet wide-- very difficult to drive that manually at less than 5 feet overlap even with markers) and the inputs too expensive to waste on overlaps. If GPS fails, everyone can switch to Glonass with Glonass correction signals, which should keep us going, but Galileo would offer superior accuracy and also precision. Such a switch, however, is not instantaneous. Would take weeks or months to get the firmwares updated (though the radios already are capable). And if that failed, I guess we can do terrestial positioning signals.

But it's not a matter of if GPS will fail. It's a matter of when. Maybe the US will be able to replace satellites when they die, but if not, it should be very interesting to see what happens.

Re:Good to hear

[Jane Q. Public]

" If GPS guidance goes down (IE our hardware has a problem), we simply cannot drive the machines. They are too wide to drive manually (my sprayer is 120 feet wide-- very difficult to drive that manually at less than 5 feet overlap even with markers) and the inputs too expensive to waste on overlaps."

They did it -- with the same size machines -- before GPS.

Cry me a river.

Re:Good to hear

[Anonymous Coward]

it is the primary nav method for all planes

No it isn't. Its a secondary system. Terrestrial signals are still the primary source of navigation, at least in the US. Sure, plenty of private pilots use GPS like its the primary method, but the FAA doesn't allow it by law. Its simply not reliable enough to use when peoples lives are at stack.

Second, the systems already play well together, they dont' share the same spectrum, problem solved before it existed. You can already get devices with Galileo, GLONASS as well as USGPS support.

Re:Good to hear

[Anonymous Coward]

They did?! No doubt they used to drive them without GPS, but at less than 5 feet overlap? That's very hard to believe. And how did they even know they were that accurate? Yes farm machines were invented long before GPS, but GPS and other new technology make farming much more efficient, leading to higher crop yields, lower food prices, food for more people... you know all that crap that makes us a more advanced civilization.

Re:Good to hear

[Anonymous Coward]

No they did not.
Farm machinery has grown in size and complexity over the last couple of decades. GPS is now REQUIRED for many machines.

But i know you're just arging to be a douchebag even tho you know nothing about the topic at hand.

So just foad eh?

Re:Good to hear

[Jane Q. Public]

"Farm machinery has grown in size and complexity over the last couple of decades."

Why? Are you saying it's because GPS was there? That's pretty stupid. It might be true, but it's pretty stupid.

"GPS is now REQUIRED for many machines."

Then get different machines. I still don't give a damn. You can put up some reflectors at the edge of your field and use a goddamned laser. There are about 100 ways to get around this "requirement".

And you can think I'm trying to be a douchebag all you like. What I'm doing is giving my honest opinion. If you don't like it, that's fine; ignore it. But I *DO* know something about it. I live in an area that is mostly rural, and mostly farms (where the terrain is not prohibitive, that is). So FOAD yourself.

Re:Good to hear

[R3d M3rcury]

They even drove 10 miles through the snow! Uphill! Both ways!

Re:Good to hear

[Anonymous Coward]

Then just GTFO.

Re:Good to hear

[davester666]

And without those sissy tires. All wood wheels RULE!

Re:Good to hear

[Noughmad]

Its simply not reliable enough to use when peoples lives are at stack.

Just allocate people on the heap, and we're all safe?

Re:Good to hear

[FireFury03]

Oh, the budget for GPS will pretty much never be cut until the system becomes obsoleted by something newer. The US military relies on GPS. However, the more navigation systems we have, the faster and more reliable fixes can become for civilian use.

ISTR that due to budget cuts the newer GPS satellites don't operate in polar orbits, giving poor coverage at the poles.

Re:Good to hear

[Your.Master]

You seem to have drifted into a different discussion. He was listing out as fact that many machines require GPS. You may think that's stupid, and you may correctly point out that different machines could be made to accomplish the same thing without GPS, but you aren't arguing against his point at all that it is required.

I don't actually know how true this is so I'm not taking his side per se -- I grew up in a rural area but not on a farm and haven't lived there in almost a decade, but honestly this is the first I've heard of using GPS for these purposes, even if it does make perfect sense.

Re:Good to hear

[Flytrap]

...Having everything rely on GPS, and thus on the budget the US chooses to spend keeping it working, is not a good idea.

Everything does not rely on GPS... the iPhone, for example has had support for GPS as well GLONASS since the iPhone 4S (http://www.apple.com/iphone/specs.html). The iPhone seamlessly switches between the two satellite constellations (as well as Wi-Fi and GSM triangulation) so the consumer never really knows which system is being used to provide location services). So clearly the world is not solely dependent on the budget the US chooses to spend to keep GPS working; it is dependent upon the combined budgets of the US, Russia and soon the EU and hopefully China one day.

While the separate national or regional systems result in duplication of effort and resources, the upside is that it also results in a high level of redundancy for consumers - kind of like how the Internet is a network of networks. I particularly appreciate how the newer satellite constellations, like Galileo, are offering improved accuracy at consumer level

Re:Good to hear

[Conley Index]

ISTR that due to budget cuts the newer GPS satellites don't operate in polar orbits, giving poor coverage at the poles.

Poor coverage at the poles is not a problem: If I can see the sky but no GPS satellite, I just have to figure out if there are polar bears or penguins around to know at which pole I am.

Re:Good to hear

[DerekLyons]

ISTR that due to budget cuts the newer GPS satellites don't operate in polar orbits, giving poor coverage at the poles.

You recall incorrectly - the GPS constellation has never had any birds in polar orbit, and has always provided poor coverage at very high latitudes.

Re:Good to hear

[heypete]

You recall incorrectly - the GPS constellation has never had any birds in polar orbit, and has always provided poor coverage at very high latitudes.

On a more detailed note, GPS satellites are in inclined orbits at 55 degrees. This means that a receiver at the pole would only ever see a satellite reach a maximum altitude of 55 degrees over the horizon.

While is certainly isn't as great as at lower latitudes, it's more than adequate to provide location information -- it's not like the poles have huge buildings and whatnot that would obstruct the view. I wouldn't really consider that to be "poor" coverage, but your mileage may vary.

The Russian GLONASS system has satellites in inclined orbits at 64.8 degrees as Russia is located at higher latitudes than the continental US. This can get proportionally better coverage at higher latitudes.

Galileo is planned with a 56 degree inclination.

Re:Good to hear

[peragrin]

It is simpler than that look for actual land.

The north pole has none, the south pole you can't get to by water.

Re:Good to hear

[drinkypoo]

That makes modern farming methods even more pathetic than I formerly believed. I already knew that the end result of "green revolution" farming is a failure of crop land and the creation of hard pan due to the driving around of your beloved machines, but I didn't know that you guys were dumb enough to buy something that depends on GPS when you have perfectly acceptable locations to plant terrestrial navigation beacons. Farmers are smart enough to use solar-powered electric fences even when they have power, how come they're dumb enough to use celestial navigation when they could use terrestrial?

Re:Good to hear

[q.kontinuum]

Just allocate people on the heap, and we're all safe?

But then you have to make sure to eliminate them yourself, and you must have a reference counter to prevent eliminating people anyone still needs. Just look at the over-population we are facing due to unused people running around, still allocating resources. Maybe we should move all suspects to 72930S 1100016E for some time to make sure...

Re:Good to hear

[q.kontinuum]

That was supposed to be 7 degree, 29 minutes and 30 seconds South and 110 degree, 00 minutes and 16 seconds East. Unfortunately Slashdot ate my special characters.

Re:Good to hear

[Anonymous Coward]

You can already get systems that work on the US GPS as well as also receive from the Russian system of GPS.

Re:Good to hear

[Anonymous Coward]

Maybe the US will be able to replace satellites when they die, but if not, it should be very interesting to see what happens.

What the fuck? This isn't the Imperium of Man. It's not like we figured out how to build and launch GPS satellites ages ago and then there was a great cataclysm and now the technology is lost to us forever. If a satellite dies, we build and launch another one.

Re:Good to hear

[dotancohen]

In agriculture GPS guidance systems already have the capability of talking to Galileo when it is finished, and Glonass right now. After the military, agriculture is probably the most dependent on positioning technology these days. If GPS guidance goes down (IE our hardware has a problem), we simply cannot drive the machines. They are too wide to drive manually (my sprayer is 120 feet wide-- very difficult to drive that manually at less than 5 feet overlap even with markers) and the inputs too expensive to waste on overlaps. If GPS fails, everyone can switch to Glonass with Glonass correction signals, which should keep us going, but Galileo would offer superior accuracy and also precision. Such a switch, however, is not instantaneous. Would take weeks or months to get the firmwares updated (though the radios already are capable). And if that failed, I guess we can do terrestial positioning signals.

But it's not a matter of if GPS will fail. It's a matter of when. Maybe the US will be able to replace satellites when they die, but if not, it should be very interesting to see what happens.

If 5' of overlap in unacceptable, then Glonass will not help. The military signal provides 10 meter resolution, and the civilian signal provides one quarter of that (20 meter resolution - exercise to the reader why that is one-quarter resolution). In fact, I'm surprised that you can get consistent 5 foot accuracy with GPS. You might have more overlap than you think.

Re:Good to hear

[profplump]

It's pretty common to use radio navigation in modern, large-scale agricultural machines. Whether or not it's "required" is a matter of efficiency; they all still have steering wheels, and could in theory be driven manually, but you'd pay for it in more input materials and/or lower yields, so it may not be economically viable (or may drive up food prices if it affected the entire market).

But it's probably also fair to say these same machines could be adapted to other navigation systems without a major redesign. It's possible to build small-scale navigational systems with sufficient accuracy and adapt the computer to deal with the different data set. On the other hand, that change wouldn't be instantaneous, and there would probably be new hardware required both on-board and in the field, so it's not a trivial or quick change.

Re:Good to hear

[AmiMoJo]

If the US economy implodes or the government just decided to turn GPS off for part of the world it would be wise to have a backup.

Re:Good to hear

[profplump]

Because it's free and universally available?

That's like asking why you drive on roads instead of using an ATV for all your transit needs -- you use a car because it's cheaper, easier, faster and more reliable than the alternatives. Why would you expect agribusiness to do anything different?

Re:Good to hear

[profplump]

It's pretty common to use a localization signal in agricultural radio navigation to provide much greater accuracy than is available over the air.

Re:Good to hear

[AmiMoJo]

Satellite positioning doesn't work that way. The absolute error might be 10m, but it will be fairly consistent over tens of square kilometers and several hours. For reducing overlap it's fine.

Re:Good to hear

[DerekLyons]

While is certainly isn't as great as at lower latitudes, it's more than adequate to provide location information -- it's not like the poles have huge buildings and whatnot that would obstruct the view. I wouldn't really consider that to be "poor" coverage, but your mileage may vary.

Because of the geometry of the system, accuracy in the polar regions flirts with the lower bounds of the specification and violates it at times. But for the originally intended uses/users of GPS, it's not really a problem and was an acceptable trade-off for improved coverage at lower latitudes. (People often seem to forget that GPS was intended for ships and planes - pretty much everything else is something of an afterthought.)

Re:Good to hear

[Anonymous Coward]

To be clear, the reliability of the GPS system, particularly at altitude -- where atmospheric moisture is low and the view of the sky is greater -- is actually very good, particularly when you consider the modern near-real-time feedback mechanisms now available to detect errors (from any source, be it the atmosphere, a particular bird, or the system as a whole). It's arguably more reliable than VHF navigation in such circumstances.

The problem the FAA has with it is mostly that they don't control it, and/or that it isn't 80 years old. There are cases were other nav system are more reliable (near the ground, in the rain, etc.), but there are a lot of cases where GPS is more reliable as well (high accuracy, global availability). Obviously the best solution is to use qualified inputs from as many nav systems as are available at any particular location; if/when the FAA embraces that fact all flights will be safer.

Re:Good to hear

[DerekLyons]

In fact, I'm surprised that you can get consistent 5 foot accuracy with GPS. You might have more overlap than you think.

Either that, or they have some form of local augmentation (DGPS) system. (I've heard of farmers installing them, but they aren't cheap.)

Re:Good to hear

[dunkelfalke]

That's what differential GPS (WAAS/EGNOS and local broadcasters) is for.

Re:Good to hear

[drinkypoo]

That's like asking why you drive on roads instead of using an ATV for all your transit needs -- you use a car because it's cheaper, easier, faster and more reliable than the alternatives

But using GPS as opposed to terrestrial beacons is neither faster nor more reliable.

Re:Good to hear

[K. S. Kyosuke]

Poor coverage at the poles is not a problem: If I can see the sky but no GPS satellite, I just have to figure out if there are polar bears or penguins around to know at which pole I am.

Except that there will soon be no polar bears to check. The money saved on those satellites should be either pumped into the polar bear breeding program, or into dumping more CO2 into the atmosphere to melt the North pole ice - that would allow you to check which pole you're on by checking whether your socks are wet or not. The way I know you Americans, it will be the latter. So don't forget your socks when you go on your polar expedition!

Re:Good to hear

[evilviper]

Having everything rely on GPS, and thus on the budget the US chooses to spend keeping it working, is not a good idea.

Right... Because the US almost exclusively using GPS-guided munitions, being in the process of converting the entirety of civil aviation over to GPS, and more, is a clear indication they're going to just let those GPS satellites fall out of the sky ANY TIME NOW.

If other countries want to waste their money, be my guest, but let's be honest here... Other countries are putting up their own GPS systems for MILITARY reasons, as well as political / nationalism pissing contests.

Re:Good to hear

[evilviper]

If GPS guidance goes down (IE our hardware has a problem), we simply cannot drive the machines.

If true, this is incredibly sad. The lowest-end consumer navigation units can correctly handle positioning and navigation WITHOUT GPS. While GPS is initially used to bootstrap the system, coordinates of every WiFi AP anyone has ever been in-range of has been fed into the system, and will be used if a GPS fix can't be determined, or just because a WiFi fix can be much more accurate. And if you're using an older cell phone without GPS, and a navigation product from the cellular provider, it'll fall-back on the coordinates of the cell towers in-range of your handset.

There are radio signals all around us. It's should be trivial to dump the FCC database to get the exact location and power levels of TV, FM radio, and other broadcasters, and use any trivial TV-tuner chip to determine a solid position fix without GPS satellites. If most cell phones had TV-tuners (a few in the world, have DVB-T) I'd expect this would already be in widespread use.

Re:Good to hear

[evilviper]

push human
push human
pop human

Re:Good to hear

[Anonymous Coward]

May I humbly suggest you take a heavy equipment training course that includes cranes. I have operated some for a living in the past. With skilled guidance and some supervised practice 5 out of 120 feet will become as easy as driving a pickup within the lines of the road.

It is also very fun.

Re:Good to hear

[dotancohen]

Satellite positioning doesn't work that way. The absolute error might be 10m, but it will be fairly consistent over tens of square kilometers and several hours. For reducing overlap it's fine.

Thank you, I did not realize that the error is consistent. I'll look that up, but resources are welcome.

Re:Good to hear

[dotancohen]

Would that not help if 'real' GPS goes down, as per the Grandparent's concern?

Re:Good to hear

[Anonymous Coward]

International Society for Third-Sector Research?!?

Re:Good to hear

[j-beda]

That's like asking why you drive on roads instead of using an ATV for all your transit needs -- you use a car because it's cheaper, easier, faster and more reliable than the alternatives

But using GPS as opposed to terrestrial beacons is neither faster nor more reliable.

It's probably way cheaper to buy off the shelf receivers than buy receivers and then also erect terrestrial beacons.

Re:Good to hear

[drinkypoo]

Obviously. But the only thing off the shelf in an agricultural GPS unit is the GPS receiver module, so it doesn't have to be so. That's the route the ag industry chose.

Re:Good to hear

[j-beda]

Obviously. But the only thing off the shelf in an agricultural GPS unit is the GPS receiver module, so it doesn't have to be so. That's the route the ag industry chose.

Beyond the fact that the "GPS reciever module" is a pretty significant piece of technology with production and development costs amortized over a gizzillion other users, not installing a local transmitter likely is a whole lot cheaper and easier to support. Needing either the farmer or someone else to provide that type of "infrastructure" support when you can get it free from the GPS people is a "no-brainer".

Re:Good to hear

[drinkypoo]

Needing either the farmer or someone else to provide that type of "infrastructure" support when you can get it free from the GPS people is a "no-brainer".

Yes, someone with no brain would readily accept not being able to work the fields if they can't receive GPS signals, but other people might think that's a bit iffy.

Of course, someone with a conscience wouldn't operate that machine, which only contributes to eventual worldwide starvation.

Re:Good to hear

[Hal_Porter]

Of course, someone with a conscience wouldn't operate that machine, which only contributes to eventual worldwide starvation.

What, by harvesting crops?

Re:Good to hear

[qvatch]

Humour aside, north pole GPS is important for all those great-circle plane routes that go over the north.

Re:Good to hear

[dryeo]

Rural areas often have no WiFi, no cell coverage and no TV or radio. I was listening to a rancher talk about the same problem, the ranch itself was big enough to require hours of driving to get to the point where you switched to horse back. GPS was the only practical solution for using the 80 ft wide sprayers accurately.

Re:Good to hear

[shutdown -p now]

I recall reading in an old (Soviet) book about some then bleeding-edge agricultural techniques, and one thing they mentioned was basically burying guide cables in the fields at preset locations, so that automated equipment could just follow them. It sounds like this would be somewhat more complicated to prepare, but once in-place, more precise than GPS navigation. Of course, you'd potentially have to dig it out to re-arrange things. But then I could imagine some kind of 2D beacon grid buried with, say, the aforementioned 5 feet interval, and you could build any arbitrary navigation scheme on top of that. Power might be a problem - using wires to supply all those things might be a headache and require constant maintenance (but perhaps not, I really don't know much about that), but there are other ideas to consider, like magnetic induction...

Re:Good to hear

[shutdown -p now]

Just allocate people on the heap, and we're all safe?

So long as you don't forget to clean them up. Either some sort of mark and "sweep" garbage collection, or otherwise explicit deterministic destruction at the end of the scope assigned to that particular human, would be necessary.

Re:Good to hear

[DerekLyons]

No, because DGPS sends localized corrections to GPS, not signals that can be directly used for navigation.

Re:Good to hear

[drinkypoo]

What, by harvesting crops?

Mechanical cultivation creates hardpan, which causes poor drainage, which causes dieoff of various organic constituents of the soil. And the farming practices with which it is associated do likewise. In theory mechanical harvesting could be done without this problem but you'd basically have to lay rails for the harvesters to run on. I'm slightly surprised nobody has done this yet, but I guess tires are still cheap since oil is subsidized.

Re:Good to hear

[Anonymous Coward]

If there are polar bears around you have more pressing concerns than to find your location

Re:Good to hear

[evilviper]

Rural areas often have no WiFi, no cell coverage and no TV or radio.

Point me to one. You can go to the furthest reaches of Alaska and get (AM/MW) radio. Not to mention things like radio beacons for navigation. I've been to farmland in several states across the US, and I've not seen one where TV/radio is anything but prolific.

And I wasn't suggesting rural farms would be surrounded by WiFi APs like a city, more that a couple farmers would have them installed.

Re:Good to hear

[ultranova]

But then I could imagine some kind of 2D beacon grid buried with, say, the aforementioned 5 feet interval, and you could build any arbitrary navigation scheme on top of that. Power might be a problem - using wires to supply all those things might be a headache and require constant maintenance (but perhaps not, I really don't know much about that), but there are other ideas to consider, like magnetic induction...

If you're going to the trouble of burying wires and beacons, why not bury pipes and stationary sprinklers instead? Then you don't need drivable spraying equipment at all, just harvesters.

Re:Good to hear

[shutdown -p now]

Because it's useful for more than watering? In that book, they were proposing it for automated planting and weeding as well, for example.

Re:Good to hear

[dotancohen]

I see, thanks.

Re:Good to hear

[Cow Jones]

-- it's not like the poles have huge buildings and whatnot that would obstruct the view.

The Elder Things and the Shoggoths would disagree.

Re:Good to hear

[RevDisk]

Expensive and not a high level of implementation. So harder to find folks that install, service, etc rail cultivation systems. As rails would be out in the weather all the time, they'd wear out a lot faster than stuff that is stored during bad weather. Plus, you can rent mechanical cultivation equipment and a lot of folks do. Renting rail cultivation equipment is probably not as likely to occur.

Also, fields get tilled. I'm not sure how much of an issue hardpanning is. Erosion and groundwater contamination IS an issue.

All and all, current system is more reliable and cheaper (not just because of oil). Very unlikely to change. Not every "evil" is due to "Big Oil".

Re:Good to hear

[Muad'Dave]

The Russian GLONASS system has satellites in inclined orbits at 64.8 degrees...

That inclination reminded me of the strange-but-useful Molniya Orbit. At least three Amateur radio Satellites were launched into this type of orbit.

(The Glonass orbit is very nearly circular and the Molniya is very ellipitical).

Re:Good to hear

[caseih]

As the other poster said, we don't really need accuracy all that much. We do need precision. And Glonass can give us some, provided it's corrected with a signal like WAAS does for GPS.

Re:Good to hear

[caseih]

While this is true I would never want to drive manually like that for hours on end. Believe me operator fatigue is at an all-time low with autosteer. I can get under 5 feet myself currently, but it is super fatiguing, especially when you have to look back and watch the machine you are pulling.

I humbly suggest that crane operation and pulling a 120 foot sprayer at 10-20 mph are different things entirely! :)

Re:Good to hear

[caseih]

GPS is used for *all* farming operations. Spraying is just the best example. Everything from tillage to planting to harvesting is all done with autosteer.

We already have pipes buried and center pivots. But pivots move way too slow for spraying out of! 1000 gpm doesn't work well for spraying, even at top speed (which is about .2-.3 inches of water).

Re:Good to hear

[dotancohen]

I see, thanks.

One last question, if you don't mind: Why not use the GPS to lay a guide marker every 120', which can be later followed without satellite aid? I'm thinking along the lines of marked posts. Is the field to long to see a post on one side from the other? A laser might help in that regard, and the laser might also help in nighttime / foggy sprays as well.

cooperation between systems?

[bcrowell]

So now there's GPS, GLONASS, and Galileo. Is there going to be cooperation between the different sets of satellites, or will a given device only talk to its own set of satellites? It sucks, for example, when I'm hiking and can't get a GPS fix because I'm in a canyon with a view of only part of the sky. Ditto when all the visible satellites are near the horizon, so the vertical position's accuracy goes to hell, like a couple of weeks ago when I was at 7000' and it told me I was at 14000'. If we had a large number of satellites all in the sky at once, and could use them in any combination, it would be really cool.

Re:cooperation between systems?

[Anonymous Coward]

Basically, yes. There are receivers that use GPS and GLONASS right now, and work exactly as you hope.

Re:cooperation between systems?

[dakohli]

Yes

As we add satellites, even from different systems, the accuracy will get better. It is very cool.

Re:cooperation between systems?

[PhrostyMcByte]

Many newer smartphones built in the past 2 or so years can already use GPS and GLONASS combined. I don't see why we wouldn't get Galileo and Compass added to that mix.

Re:cooperation between systems?

[BillX]

This is interesting. What I am curious about is whether the US/EU systems are designed to be directly compatible or if this multi-system compatibility will come (as it does now for cell networks and local-area wireless networking) from receiver designers smooshing multiple separate radios (and possibly antennas) into the same die/package.

Re:cooperation between systems?

[dakohli]

So far, everything that I have read shows that it is the receiver that will do the "magic". At least we will be able to take advantage of these competing systems and get better accuracy, although I suspect that 1 metre will be good enough for any hiking enthusiast. Getting into the centimetre range will allow surveyers some pretty good accuracy.

...Why?

[Revotron]

Why is Europe spending billions to create their own GPS constellation when the US government already went through the hassle and expense? The GPS system is free and open to use by anyone with a GPS receiver. This strikes me as nothing but a political move, as if to say "We're independent and don't need America to provide anything for us". This is a completely redundant and pointless project by the EU.

Re:...Why?

[Luke_2010]

Galileo is much more precise than GPS. And that's just for starters.

Re:...Why?

[Anonymous Coward]

because US can turns off the GPS.

Re:...Why?

[sidthegeek]

Well, the US did have selective availability enabled for a while. Perhaps European civilians don't want to be affected by US decisions.

Re:...Why?

[dakohli]

Why is Europe spending billions to create their own GPS constellation when the US government already went through the hassle and expense? The GPS system is free and open to use by anyone with a GPS receiver. This strikes me as nothing but a political move, as if to say "We're independent and don't need America to provide anything for us". This is a completely redundant and pointless project by the EU.

Sigh,

It is a measure of trust. No one, trusts that the US will not screw with GPS if it would give them a military or economic advantage. Sure they say right now that they won't, but who knows what will happen in 5, 10 or 15 years in the future. And trust me, the value of an accurate navigation/timing system makes it well worth the efforts the Europeans, the Russians and the Chinese are making to field their own versions.

Why can't we all be friends?

Re:...Why?

[simcop2387]

The US also has the ability to disable GPS for certain areas and has in the past degraded the quality of data for national security reasons ( http://www.gps.gov/systems/gps/modernization/sa/ ). Though this has been changing (new satelites don't have it, though really it's just a software update), it puts pressure on other places to put up their own systems that are either compatible or at least non-interferring so that should the US ever do anything like that again, they cannot be impacted by it. It's a bit like MAD but instead of destruction, nobody can ever get degraded service (assuming enough players). This also raises the question of who should pay for it all, since with three systems now going that all work, it could let each place share only a part of the costs (eventually).

Re:...Why?

[Anonymous Coward]

You see, us Europeans know that Americans are hard working souls and as we don't pay US federal income taxes, we don't want to be US government freeloaders who have the victim mentality.

That said, if you're really that opposed to waste (and you seem like such a generous soul allowing us Europeans to use your GPS for free). I'm sure our governments can come together for a mutally beneficial agreement whereby we pay the US a nominal amount for a transfer of intellectual property as well as the ownership of the satellites. We'll then take over the running (we wouldn't want to tax your generosity any further) of the satellites. Obviously, the nominal amount would be substantially less than the cost of developing our own, because otherwise, it wouldn't be mutally beneficial.

Re:...Why?

[Jane Q. Public]

"Galileo is much more precise than GPS. And that's just for starters."

No, it isn't. It's just that unlike GPS, the precise part is open to the general public.

Also, I think OP is incorrect. The only reason for a 4th lock using GPS is to get the precision you would normally get with 3, if you were military. If the new system is open and precise, 4 sats should probably not have to be visible.

Re:...Why?

[hawguy]

Why is Europe spending billions to create their own GPS constellation when the US government already went through the hassle and expense? The GPS system is free and open to use by anyone with a GPS receiver. This strikes me as nothing but a political move, as if to say "We're independent and don't need America to provide anything for us". This is a completely redundant and pointless project by the EU.

Even as an American I can see the value in having a completely separate system for satellite navigation. Even ignoring the ability of the USA to reduce the accuracy (or completely shut off) the system, the system is still a potential single point of failure subject to software problems or a rogue agent controlling the ground stations. Much better to have a completely separate redundant system with no common elements.

Re:...Why?

[Jane Q. Public]

"Why can't we all be friends?"

Because some of those "friends" will eat your lunch.

Don't be paranoid... but don't be a fool, either.

--
Peace through superior firepower.

Re:...Why?

[Yoda222]

Why did the US spend billions to create their own HST when Gallileo build a telescope 400 years ago ? The gallileo telescope can be rebuild for 10$ and used by anyone with a least one eye.

Re:...Why?

[Anonymous Coward]

The 4th sat is for elevation. 3 to fix you in 2D. 4 to fix you in 3D.

Re:...Why?

[Anonymous Coward]

It is a measure of trust. No one, trusts that the US will not screw with GPS if it would give them a military or economic advantage.

Except you made it even easier. The US can jam these signals or destroy the satellites in orbit without harming American interests.

Re:...Why?

[Jane Q. Public]

"The 4th sat is for elevation. 3 to fix you in 2D. 4 to fix you in 3D."

No. That's with GPS, and that's after the fixes for precision that are necessary because the "high precision" part of U.S. GPS is restricted to military.

With an open system, it should require no more than 3 visible sats to fix your position in 3D.

Somebody tried to argue this point with me a couple of weeks ago, and it's simply false. You can get a rock-solid 2D position with only 2 observation points. 3 (and even just the first 2, if they are transmitting the appropriate data) can establish elevation.

Re:...Why?

[ZigMonty]

You need at least one other sat to fix you in time. The receiver doesn't have an atomic clock and so needs an extra point of data for the extra unknown.

Simple logic might win an argument, but that doesn't make you correct.

Re:...Why?

[TooMuchToDo]

Simple geometry states you need three satellites for an accurate 2D fix, and four satellites for a 3D fix, not whether you have access to the encrypted P(Y) code.

http://gis.stackexchange.com/questions/12866/gps-positioning-why-four-satellites
http://www.cmtinc.com/gpsbook/chap5.html
http://www.gpsnuts.com/mygps/gps/technical/ed.htm

Note that the final reference I list is written by someone who is a GPS analyst and has worked for the DOD on the GPS system since 1975.

Re:...Why?

[TooMuchToDo]

Selective availability can be turned on by geographic region, in order to degrade the civilian signal. This allows you to only degrade the middle-east, while still maintaining precision position determination for the rest of the world. If the US wants to deny position determination, they would just jam Galileo. I supposed the EU could always send the US a sternly worded letter if that were to occur.

Re:...Why?

[Anonymous Coward]

The way these systems tell you where you are is that each satellite sends a time signal and is on a known orbit. You might think that by doing that, each satellite gives you one distance information. Then you could interpret it as your position being on the sphere around that satellite with the radius given by the distance. Multiple satellites would give multiple such spheres and your position would be on their intersection. The intersection of two spheres is a circle. Intersect that with the surface of the Earth and you get one position. Voila, 2D fix. Unfortunately it's not that simple. One signal alone doesn't give you enough information to calculate your distance from the known satellite position, because you don't have sufficiently exact local time information. So what your GPS receiver does is take the signal from another satellite and calculate the time difference. That's why you need three satellites for a 2D fix and four satellites for a 3D fix.

Re:...Why?

[Sir_Sri]

It is political. It's a trust issue. The Europeans don't feel the US can be trusted to not just encrypt the whole damn thing for their own purposes, or fail to maintain it whatever. Relying on something you have no control over is very risky.

Re:...Why?

[Jane Q. Public]

"Simple geometry states you need three satellites for an accurate 2D fix, and four satellites for a 3D fix, not whether you have access to the encrypted P(Y) code."

Um... Duh... simple geometry doesn't apply here, because these are TRANSMITTERS THAT KNOW THEIR OWN LOCATION IN SPACE AND TIME.

Get that?

Re:...Why?

[tsa]

I bet the US is already working on finding a way to scramble Galileo and other GPS satellite signals.

Re:...Why?

[Anonymous Coward]

So?

Re:...Why?

[Jane Q. Public]

The real answer -- which I already gave earlier -- is that the additional lock is for error correction. Nothing more. It is NOT essential for location, including elevation.

Re:...Why?

[Jane Q. Public]

Nevertheless, I am still correct. The 4th sat is only for precision. It is not necessary for location.

Re:...Why?

[Jane Q. Public]

Which, by the way, your own references say very clearly.

Re:...Why?

[Anonymous Coward]

Yeah, except that jamming Galileo would provoke a vastly different response from the EU than the US turning some switches off on their own positioning system. You know, this isn't a computer game where the only thing that counts is what you can *technically* do.

Sternly worded letter? Fights happen in economy today, not on the battlefield. US citizens like to think they're safe just because no country is stupid and suicidal enough to drop bombs on them.

Re:...Why?

[Anonymous Coward]

Suppose you have three known satellite positions and you can get a signal from each of them which tells you when the signal was sent. How do you calculate your 3D position? (You have the local time, but only accurate to within a +-0.1ms error margin.)

Re:...Why?

[Anonymous Coward]

No, you're not correct. The 3D information that you'd get without the fourth satellite would be so inaccurate as to be meaningless. You need the fourth satellite for a 3D fix that puts you in the right city, let alone the right street. That's qualitatively different from "only for precision".

Re:...Why?

[Jane Q. Public]

"No, you're not correct. The 3D information that you'd get without the fourth satellite would be so inaccurate as to be meaningless. You need the fourth satellite for a 3D fix that puts you in the right city, let alone the right street. That's qualitatively different from 'only for precision'."

Then why do the military only require 3 satellite locks? Eh? Answer me that, you fucking genius.

Re:...Why?

[Anonymous Coward]

I'll take that bet, and probably win. Because they're not working on it, they've probably finished it already.

Re:...Why?

[flyingfsck]

There are also navigation systems that use geostationary satellites, e.g. Egnos and Inmarsat.

Re:...Why?

[maxwell demon]

Basically it is as follows:

The first satellite just gives a reference time. By itself, it is completely useless for positioning.
Each further satellite effectively allows you to determine one coordinate. Since you need three coordinates in order to specify a coordinate in space, you ultimately need four.

Re:...Why?

[JockTroll]

Fights that happen in economy can rapidly turn into something less palatable, especially when one of the sides has all the big sticks and no qualms at all to use them. The EU is in the middle of a darn big crisis and its "economic" power is greatly diminished. It couldn't even police its borders (the Balkans) without NATO - and with a heavy US contribution. If push comes to shove, the EU will cave in, unless they're prepared to use the French nuclear submarine "Force de Frappe" against US mainland.

Re:...Why?

[Jane Q. Public]

I am replying to you, but this is really aimed at these other dimbulbs who are arguing with me.

Listen up, folks. I don't claim to be the brightest bulb in the universe myself, but I do pretty good and I remember my recent history, which many of you seem to have (forgotten; never learned; didn't pay attention... pick your answer).

GPS has been around for a long time. But it was only pretty recently that we civilians learned about it, and it became something useful. Why? Well, that's a story.

Much of the GPS signals are encrypted, for use by the military. The high-precision part. When people saw potential for civilian use, they were somewhat dismayed, because the un-encrypted part of the signal was pretty inaccurate. Your location could only be found within a few tens of meters. Not good enough.

So a few electronics companies -- at about the same time -- came up with the idea of using a FOURTH satellite to correct the sloppy timing they got from the USUAL 3, used by the military.

And thus practical, consumer GPS was born.

But make no mistake: GPS was designed to work -- does work, still works very well -- for the military with only 3 sats visible. That is the way it was designed, that is the way it works.

So stop giving me all your theory about how it "needs" 4. You are just plain wrong.

Re:...Why?

[maxwell demon]

I think destroying the satellites would be the equivalent of a declaration of war. I'm not sure the U.S. would want to declare war on its allies.

Of course should the U.S. and Europe no longer be allies at the time that happens, then if the U.S. kills the Galileo satellites, I guess Europe's answer would be to kill the GPS satellites. Again, not exactly what the U.S. wants.

Re:...Why?

[Anonymous Coward]

You can reduce the error margin of a 3 satellite 3D fix by using more accurate clocks. That's not unique to the military signal. It's just a matter of how much money you want to throw at the problem. Qualitatively, this still means you can only get meaningful 3D position data with at least 4 satellites, because the cost of a sufficiently accurate local time signal is prohibitive, especially considering that you can get a 2D fix instead or just use a fourth satellite, because they're really not that scarce.

Re:...Why?

[Jane Q. Public]

"That's not unique to the military signal. It's just a matter of how much money you want to throw at the problem."

The U.S. military GPS system was designed to work properly with only 3 visible satellites.

Put that in your pipe and smoke it, or do whatever the hell you want with it. I didn't invent the system. But I do know just a little about it.

Re:...Why?

[Gordonjcp]

Or, you know, just stop pulling the US's collective backside out of the fire in every war it gets involved in.

What is the US going to do if a European country starts jamming the US GPS system? Beg them to attack themselves? They sure as hell can't afford to attack Europe.

Re:...Why?

[dbIII]

If they are standing on solid ground or on a ship they don't care too much about elevation.
The air force on the other hand ...
So some of the military only need 3.

For the civilian stuff the more that can be seen the better to cope with the randomising that the military don't have to deal with. I think that also applies to everyone at high lattitudes, but since I don't know how high these things are and in what orbit I don't know how much of an effect getting the signal through a bit more atmosphere has.

Re:...Why?

[Anonymous Coward]

No, that's just plain wrong. It is not sufficient to know the exact time at three transmitters to get a 3D fix. You'd also need to know the exact time when the signals are received, which is a very difficult (read: costly) problem. The accuracy of the positioning information is limited by both the precision of the satellite clock signal and the accuracy of the receiver clock signal. The latter can be removed from the equations by using a fourth satellite signal, but not by providing better satellite clock signals. And you really need to stop calling people names, especially when you're so obviously out of your depth.

Re:...Why?

[Anonymous Coward]

You can't solve a four variable system (3D position and local time error) with just three equations. Perhaps you and the military think they can bomb math into submission, but that doesn't make you right, nitwit.

Re:...Why?

[Anonymous Coward]

"Why is Europe spending billions to create their own GPS constellation when the US government already went through the hassle and expense? "

Because you are broke, don't have any space-going tech anymore and because we don't trust war-mongering assholes.

Re:...Why?

[Anonymous Coward]

I just heard lots of shouting. Could you perhaps try a reasoned argument?

Re:...Why?

[Jane Q. Public]

"So some of the military only need 3."

Nice conjecture, but not correct.

3 satellites are all that are necessary to pinpoint you in any 3D position. Period.

(Technically they can only put you in 1 of 2 positions, but the other one is off in space so not very likely.)

The 4th satellite is only necessary for civilian systems to correct for timing that was very much intentionally made ambiguous for civilian receivers, since GPS was made by and for the military.

Re:...Why?

[houghi]

Please hand over your geek card if you can not understand why there are different systems. Compare it to operating systems:
There is one closed system coming from America that has a monopoly and can do whatever it likes.
Then there comes an open system from Europe that breaks that monopoly and is intended to be used by the people made for the people.
(See what I did there?)

Re:...Why?

[Anonymous Coward]

Maybe the folks at lightsquared(?) could help with that.

Re:...Why?

[bertok]

Please stop voting this guy up, while simultaneously voting down the numerous posts that are correct.

Four satellites are required because there are four unknowns, and only one measurement per satellite available, irrespective of precision or lack thereof.

Here's some quotes from Global Positioning System so we can all stop agreeing with the loudest person instead of the facts:

"About nine satellites are visible from any point on the ground at any one time, ensuring considerable redundancy over the minimum four satellites needed for a position."

"The receiver uses messages received from satellites to determine the satellite positions and time sent. The x, y, and z components of satellite position and the time sent are designated as [xi, yi, zi, ti] where the subscript i denotes the satellite and has the value 1, 2, ..., n, where n >= 4."

"Although four satellites are required for normal operation, fewer apply in special cases. If one variable is already known, a receiver can determine its position using only three satellites. For example, a ship or aircraft may have known elevation.

The time precision required for a fix of any reasonable accuracy requires atomic clocks. You can't carry atomic clocks in your pocket, they're a tad too big for that. There is no way to know the time on the satellites from the ground, because you don't know where you are, and hence how far the satellites are from you, and hence the delay added to the signals. You can use three satellites to figure out where you are, if you know what time it is, but you don't. Adding a fourth satellite in the mix lets you solve for all four unknowns in the equation. Note the exception in the wiki article applies only in some rare cases, like the GPS units used by ships, not the GPS units handed out to most military personnel.

THIS HAS NOTHING AT ALL TO DO WITH SELECTIVE AVAILABILITY.

The military encryption simply reduces the precision of the solution, it doesn't actually change the number of unknowns and hence the equations in any way. A civilian marine GPS could locate itself with just 3 satellites even with selective availability enabled, as long as it assumes that it's at 0 elevation. In all other cases, four satellites are required, even for military units.

Re:...Why?

[Anonymous Coward]

Period.

Proof by assertion? Do show us how the 100% exact time signal from three known positions determines your distance to these three positions and thereby your location. Hint: The distance to each satellite is speed of light times (time of reception - time of transmission). What's the missing information and how do you get it? Now FOAD.

Re:...Why?

[Electricity Likes Me]

"That's not unique to the military signal. It's just a matter of how much money you want to throw at the problem."

The U.S. military GPS system was designed to work properly with only 3 visible satellites.

Put that in your pipe and smoke it, or do whatever the hell you want with it. I didn't invent the system. But I do know just a little about it.

The US military system is, these days, no different to the civilian system. The system was descrambled in the 90s because it became apparent that it was just too expensive to keep building more complex and relatively low-run GPS chips for the military, when what they wanted to do was put them in bombs and things.

By and large though, even the airforce doesn't need GPS elevation data since laser altimeters are faster and very standard on all aircraft.

Re:...Why?

[Jane Q. Public]

"You can't carry atomic clocks in your pocket, they're a tad too big for that. There is no way to know the time on the satellites from the ground, because you don't know where you are, and hence how far the satellites are from you, and hence the delay added to the signals."

Proof you are a moron.

These can be CALCULATED from 3 satellites. You don't need to know them in advance, and you don't need a value from outside the satellites themselves.

Repeat: the military GPS system was designed to operate on 3 satellite locks. Sorry if your tiny brain can't wrap itself around the concept that there is more information here than simple geometry.

Re:...Why?

[Solandri]

It is a measure of trust. No one, trusts that the US will not screw with GPS if it would give them a military or economic advantage. Sure they say right now that they won't, but who knows what will happen in 5, 10 or 15 years in the future.

It has nothing to do with trust. There is nothing the U.S. or any country could do to gain the trust of other countries with a crucial technology like GPS. If Galileo had been developed first, the U.S., Russians, and Chinese wouldn't want to be reliant upon it either, so this has nothing to do with the U.S. being less trustworthy. The US-haters and the US-hater-haters are just casting it as a trust issue to troll and have something to argue about

GPS is just a technology which has become so pervasive and useful that it's become essential to modern life. And any country that's capable will want to make sure it controls anything essential which it's dependent upon. If you need a car to get to work, and you neighbor has an extra car which he says you're free to use any time, you're still gonna buy your own car. Not because you don't trust your neighbor, but because you'd feel awfully stupid if you could afford a car but didn't get one, and one day your neighbor through no fault of his own were unable to lend you his car. The exceptions (e.g. Panama and Suez canals) are only where cost or physical constraints limit the number of essentials which can be built.

And all of these systems work as accuracy enhancers and fully capable backups to each other. So it's not like a lot of duplicated effort is being put in with no gain.

Re:...Why?

[Carewolf]

No. That's with GPS, and that's after the fixes for precision that are necessary because the "high precision" part of U.S. GPS is restricted to military.

No, the obfuscation layer on GPS has been deactivated for almost a decade now. Before then you just needed a terrestrial correction signal which any GSM tower could send. The un-obfuscated signal of GPS is still a lot less precise than Galileo, though GPS planed for upgrades that would put them on par.

Re:...Why?

[jandar]

This was a kind of requirement from the beginning. USA has requested Galileo uses other frequencies so it can be jammed without damage to GPS. As the EU is timid of the USA it licked its boots.

Re:...Why?

[Jane Q. Public]

"... we can say with confidence that when we solve the navigation equations to find an intersection, this solution gives us the position of the receiver along with accurate time thereby eliminating the need for a very large, expensive, and power hungry clock. The very accurately computed time is unused in many GPS applications, which use only the location."

Note the phrase: "computed time". Not measured time.

Bozo.

Re:...Why?

[icebraining]

Redundancy improves reliability. It's the same reason why you should keep backups, even though it's a redundant copy of the data.

Re:...Why?

[Anonymous Coward]

That would fly well, yes. US bombing europe, with all the relatives, friends and distant families of countless americans there. Only in your fantasies.

Re:...Why?

[Anonymous Coward]

I hope they built in some sort of GPS emulation mode so that should Galileo be scrambled, it can use the GPS frequencies and happily churn along.

Re:...Why?

[Anonymous Coward]

For the poor souls who are going to be misguided by that Jane Q. Public troll:

To understand why that idiot is wrong, consider the reduction to 2D. There's a satellite S1 at (0, 9), the receiver is at ground level (x, 0) and looking for a 1D fix, i.e. to find x. The transmitter sends a time signal, which is 100% accurate. The signal travels one unit of length per unit of time (i.e. it reaches (0, 8) at time t1+1, for example). The receiver doesn't have a sufficiently accurate clock. According to JQP we can just calculate the local time anyway. At time t (which is unknown due to the lack of an accurate local clock), the receiver receives a signal telling it that this very signal was sent at time t1. What's the current time t and what is the receiver's position? It shouldn't be hard to see that we can't solve for t and x given just t1.

So let's add a second satellite S2 at (20,9). At time t, the receiver gets a time signal t1 from S1 and t2 from S2. What time is it and where's the receiver (i.e. solve for t and x). Now we're getting somewhere. The distance to satellite S1 is (t-t1) and the distance to satellite S2 is (t-t2), because our "speed of light" is one unit of length per unit of time. We can compare the distances from the signal delay to the geometric distances depending on x. So we have (t-t1)=sqrt((x-0)^2+(0-9)^2) and (t-t2)=sqrt((x-20)^2+(0-9)^2). Two equations with two variables (remember: t1 and t2 are given, we're looking for x and t). Let's subtract equation two from equation one. We get (t-t1)- (t-t2)=(t2-t1)=sqrt(x^2+81)-sqrt(x^2-40x+481). We got rid of t. We don't need a local clock. Was JQP right after all? No, because we needed two satellites for a 1D fix, like we need three satellites for a 2D fix (solve for x, y and t) and four satellites for a 3D fix (solve for x, y, z and t).

Re:...Why?

[the_other_chewey]

But I do know just a little about it.

Which seems to be the amount you know about everything.
That's not helpful.

GPS recievers indeed solve a 4D problem (3D space + time) which requires
4 sats. As expensive as the military units are, they may be able to bridge reception
gaps by keeping time by themselves for a while, so may for a while work with
only three sat signals.

But without a local timer with the precision of an atomic clock, that's the digital
equivalent to dead reckoning, and will only get you so far until you need your fourth
sat again.

Of course, if you are the Navy, one of your coordinates is known by default (at least
plus or minus a couple of meters), so maybe their gear is permanently set to a dedicated
2D mode. That would indeed work with 3 signals - but you still need four inputs for a 3D
position, it's just that in this case one of those inputs doesn't come from space, but from
looking out the window.

Maybe you will believe the Los Alamos Labs' GIS unit?
"If you require 3-dimensional coordinates (northerning, easting, and elevation), a minimum of four satellites is needed."

Re:...Why?

[the_other_chewey]

Note the phrase: "computed time". Not measured time.

Yes. Computed from at least four sat signals.

Bozo.

Nice sig.

Re:...Why?

[the_other_chewey]

Nevertheless, I am still correct. The 4th sat is only for precision.

No it's not.

It is not necessary for location.

Yes it is.

Quoting the Navy: "Therefore there are 4 unknowns at each timeline where a solution is computed, 3 for position and 1 for time. This is why the minimum number of satellites for a solution is 4."

Re:...Why?

[tsa]

Amazing, isn't it? As long as the European Parliament is the US's pet dog we will never be a superpower.

Re:...Why?

[dbIII]

Only three if the speed of light was instant :) The time of transmission from each satellite is not equal since they are in different places a very long way apart and timing is critical in this situation.

Re:...Why?

[tsa]

But we can jam the US's system now without any damage to Galileo, so it's a win/win situation!

Re:...Why?

[heypete]

While "selective availability" (the intentional degradation of civilian signals to roughly 100m accuracy) has been disabled for a while and the new satellites don't have the capability for implementing it, the military does indeed have separate signals for civilian and military users.

Referring to the wikipedia, the civilian signal ("C/A") is only transmitted on the L1 band at 1575.42 MHz. The encrypted precision codes (for the military) are transmitted on both L1 and L2 at 1227.60 MHz. The military signal is indeed quite a bit more accurate than the civilian signal: by itself, the civilian GPS signal is only accurate to around 3 meters. The military signal is accurate to around 30cm.

With current civilian signals only transmitted on a single frequency, receivers cannot correct for ionospheric conditions (which composes a major part of the current uncertainty in measurements) as doing so requires two frequencies. Military signals are transmitted on two frequencies so receivers can correct for ionospheric delay. The military signal is also transmitted at a much higher rate (10x the civilian rate), yielding proportional increases in accuracy.

Currently there are systems like WAAS (North America) and EGNOS (Europe) that provide augmentation in the form of corrections for ionospheric delays (and some other information, like current "health" status of the satellites). This can improve accuracy even more (my handheld civilian unit is able to compute position with an uncertainty of 2 meters). EGNOS also provides an internet feed of the augmentation data so one doesn't have to have a clear view of the geostationary satellites that provide the augmentation. WAAS only augments GPS, but EGNOS augments GPS, GLONASS, and Galileo (for what it's worth at present).

The GPS upgrades will add more detailed signals (the civilian signal will be broadcast on L1 and L2 as well as safety-of-life signal on L5 at 1176.45 MHz). The military codes will also get an upgrade as well, but that won't really matter for civilian users. With the civilian signals being transmitted on a total of three frequencies it will be possible for receivers to account for ionospheric delay and other factors. Overall, things will get considerably more accurate.

Re:...Why?

[heypete]

Is there any practical way of shooting down satellites in medium earth orbit? GPS satellites orbit around 20,000km -- that's a long way for any anti-satellite missile.

Re:...Why?

[heypete]

There are also navigation systems that use geostationary satellites, e.g. Egnos and Inmarsat.

EGNOS augments other satellite navigation systems (GPS, GLONASS, Galileo) by providing ionospheric correction data and other relevant information. It is not a full-fledged navigation system in its own right -- it cannot be used for navigation on its own.

Re:...Why?

[jo_ham]

The "high precision" part of the GPS system was opened up to the public by Clinton back when he was president. Birds launched since then lack the capability to restrict civilians to the lower quality fix.

Re:...Why?

[jo_ham]

"No, you're not correct. The 3D information that you'd get without the fourth satellite would be so inaccurate as to be meaningless. You need the fourth satellite for a 3D fix that puts you in the right city, let alone the right street. That's qualitatively different from 'only for precision'."

Then why do the military only require 3 satellite locks? Eh? Answer me that, you fucking genius.

They have accurate clocks?

I don't know, maybe I'm not a "fucking genius" enough for that to be the right answer.

Re:...Why?

[jo_ham]

"So some of the military only need 3."

Nice conjecture, but not correct.

3 satellites are all that are necessary to pinpoint you in any 3D position. Period.

(Technically they can only put you in 1 of 2 positions, but the other one is off in space so not very likely.)

The 4th satellite is only necessary for civilian systems to correct for timing that was very much intentionally made ambiguous for civilian receivers, since GPS was made by and for the military.

This is the second time you've brought this up. The US stopped deliberately degrading the signal for civilian uses years ago, mostly because it was simply pointless to keep doing it since most civvy receivers were able to overcome the problem with assisted GPS and other methods.

You are technically correct that you only require three satellites to get a 3D position but *only* if you know your local time extremely accurately. It has nothing to do with only three satellites being "deliberately bad" at positioning on civilian equipment - it's the laws of physics.

Re:...Why?

[Anonymous Coward]

What is the US going to do if a European country starts jamming the US GPS system? Beg them to attack themselves? They sure as hell can't afford to attack Europe.

We could tell Russia we'd look the other way if they needed to kick the shit out of some Eurotrash and occupy a few countries as a buffer zone like the good old days.

Re:...Why?

[jo_ham]

"You can't carry atomic clocks in your pocket, they're a tad too big for that. There is no way to know the time on the satellites from the ground, because you don't know where you are, and hence how far the satellites are from you, and hence the delay added to the signals."

Proof you are a moron.

These can be CALCULATED from 3 satellites. You don't need to know them in advance, and you don't need a value from outside the satellites themselves.

Repeat: the military GPS system was designed to operate on 3 satellite locks. Sorry if your tiny brain can't wrap itself around the concept that there is more information here than simple geometry.

My goodness. Do you want a fresh spade? You seem determined to keep digging.

Re:...Why?

[Anonymous Coward]

War isn't about practicality. So, while its a long way.. its obviously possible to get a warhead there, since you can get a satellite there. And as with any sort of destruction, disruption is easier than creation. You don't need to destroy the whole constellation; You just need enough holes to make the system useless.

Re:...Why?

[Gordonjcp]

And what's Russia going to do? Threaten to turn the gas supplies off? They need the money!

The US has spent itself into a smoking crater and the Soviet Union isn't far behind. I'd take the threat of an attack by the US seriously if they didn't have to come round here begging for equipment and soldiers every time they decide to poke some middle-eastern halfwit in the eye.

Re:...Why?

[jo_ham]

"Simple geometry states you need three satellites for an accurate 2D fix, and four satellites for a 3D fix, not whether you have access to the encrypted P(Y) code."

Um... Duh... simple geometry doesn't apply here, because these are TRANSMITTERS THAT KNOW THEIR OWN LOCATION IN SPACE AND TIME.

Get that?

They know their location in space and time, but they cannot tell you what it is before it changes. The speed of light is not instant.

You have four unknowns - x, y, z and time. You can't solve those with only three equations, unless you can make a reasonable guess about one of them, thus either you need an extremely accurate clock (an atomic one) or you need to know either x, y or z to high accuracy - laser altimeter, being at sea level, knowing a point due to a separate beacon that knows its position (eg, a phone mast or a battlefield command post with a transmitter).

There's simply no way around this. There is plenty of information about the maths behind the GPS system. You might want to check it out before you start insulting people for correcting you; it just makes you look foolish.

Re:...Why?

[Seeteufel]

The US will focus on a trade war with Asia. An interesting attrition war from which Europe and Africa would benefit a lot.

Re:...Why?

[Anonymous Coward]

You don't "shoot down" satelites, you destroy them in place. There are several methods:

1. Hit the satellite with a missile - very expensive. Not only do you need to launch the missile, but you also need an expensive guidance system.

2. Put some rocks in an orbit that intersect the satellite orbits. After a while, all satellites have holes in them. Expensive to launch, but no guidance needed.

2. Explode a nuke in space, melt several satellites in one go. Also causes interesting EMP effects over an entire hemisphere - preferably over the countries you want to mess with. Expensive, and a risk of nuclear retaliation.

4. Use energy weapons, such as lasers. Maybe not practical yet

Re:...Why?

[Anonymous Coward]

An unnecessary and pedantic point, but you can carry atomic clocks in your pocket now. Search for "Chip-Scale Atomic Clock"....

Re:...Why?

[leromarinvit]

You can't carry atomic clocks in your pocket, they're a tad too big for that.

Actually, it seems you can. And even older generations weren't that huge - certainly too big to carry in your pocket, but not impossible to mount in a vehicle, aircraft or ship. E.g. this HP 5071A which can be yours for the bargain basement price of just $27.500.

So maybe some GPS receivers can indeed get a 3D fix with 3 satellites, when combined with (or including) an atomic clock.

Re:...Why?

[Anonymous Coward]

An interesting data point from the history of Galileo.

It was originally to use a band which overlapped with the US military use of GPS. This meant if US would jam Galileo, they would jam their own military GPS band as well.

The US was of course butt-hurt, and in the end Europeans accepted to change the design.

Re:...Why?

[profplump]

Please lay out your mathematical solution to this positioning problem using only 3 birds. Until and unless you can do that you're not going to convince anyone here.

And if you *can* do that it's worth big money, so you should file for a patent immediately.

Re:...Why?

[Anonymous Coward]

And what's Russia going to do? Threaten to turn the gas supplies off?

Umm, yes - "Russia shut off all gas supplies to Europe ... on Wednesday". http://www.msnbc.msn.com/id/28515983/ns/world_news-europe/t/europeans-shiver-russia-cuts-gas-shipments/.

Having actually turned the gas supplies off before, any threat to turn them off again would be pretty believable.

Re:...Why?

[mSparks43]

I could be wrong, but I'm pretty sure you can figure out your t from 2 satellites, as long as you know their relative position to each other.

Meaning you only need three for a full fix as long as you know where the sats are.

Re:...Why?

[jareth-0205]

No, it isn't. It's just that unlike GPS, the precise part is open to the general public.

Still a pretty good reason for launching then... since if public GPS can't be accurate... the public can't have accurate GPS...

Re:...Why?

[jareth-0205]

Selective availability can be turned on by geographic region, in order to degrade the civilian signal. This allows you to only degrade the middle-east, while still maintaining precision position determination for the rest of the world. If the US wants to deny position determination, they would just jam Galileo. I supposed the EU could always send the US a sternly worded letter if that were to occur.

You don't see the difference between the US changing the delivered accuracy of a system they own, and intentionally screwing with others (ie getting close to an act of war)?

Re:...Why?

[Anonymous Coward]

Yes, you can figure out t from two satellites if you know your location. I showed how to solve for x above, and then, with your known position, you can solve either of the original equations for t. If you don't know all of your location, then t remains dependent on the remaining variables. In the 2D reduction above, there is a hyperbola comprised of all possible positions that result in the given time difference t2-t1 between the signals from the two satellites. The points on this hyperbola are not at a constant distance from either of the satellites, so the time t can not be computed from the time difference alone.

If you have trouble visualizing the shapes of the solution spaces, which admittedly isn't easy, just remember that a system of n variables needs at least n equations for a unique solution. If this is news to you, please refresh your middle school math knowledge. More equations may not be enough if they're not independent. For example, the equation we got by subtracting equation two from equation one is dependent and doesn't add new information. But no matter how you combine equations, fewer than n equations can not provide a complete unique solution to an n-variable problem. Two separate n and m variable problems may pose as an n+m variable problem and you may be able to find a unique solution for some variables, but in the case of GPS, the problems aren't separable.

If you have information that fixes variables, the principle doesn't change. For example, if you write the problem above with variable altitude y and then decide you know that the altitude is 4, you effectively add another equation y=4 to the equation system, resulting in a three equation system of three variables. Of course you could just as well simply substitute 4 for every occurrence of y and get a two equation system of two variables. That's why having accurate local time information (e.g. from an atomic clock) allows for a 3D fix from just 3 satellites. With t fixed, it's a three variable problem and each of the three satellites contributes one equation. The remaining ambiguities result from the non-linearity of the equations and are easily solved with application knowledge.

Re:...Why?

[gnasher719]

Only three if the speed of light was instant :) The time of transmission from each satellite is not equal since they are in different places a very long way apart and timing is critical in this situation.

If the speed of light was instant, GPS wouldn't work. You would receive n identical time stamps from n satellites and would be stuck.

Re:...Why?

[mSparks43]

Don't need "your" location - just that of the sats.
time difference from 2 sats + known time difference between the two sats would allow you to solve for t (your time).
meaning you wouldn't need a 4th sat to solve for t.

Re:...Why?

[ChumpusRex2003]

No, it isn't. It's just that unlike GPS, the precise part is open to the general public.

Correct. The L5 intermediate-precision Galileo signal will be freely available to the public. However, this signal is not as precise as the GPS encrypted "precise acquisition" (aka military) signal.

The freely available L1 signal has essentially an identical format as the GPS "coarse acquisition" signal, and is therefore expected to offer broadly similar performance.

The advantage of having 2 distinct frequencies available to the public is that it is possible to correct for atmospheric dispersion. Within the ionosphere, the propagation velocity of the signals from the satellites can be altered by prevailing "space-weather" conditions; this is actually the major source of error in GPS. As different frequencies are affected differently, using a multi-frequency receiver makes it possible directly to measure this dispersion. Single-frequency receivers must either use a model based upon satellite ascension, or utilise a correction obtained from another source (e.g. DGPS or SBAS).

The galileo service plans to offer a paid-for premium service, offering another signal technically equivalent to the GPS "precise acquisition" signal, and encrypted using commercial cryptography. This service is also expected to provide high-bandwidth downlink for rapid acquisition of satellite ephemeris and differential-correction data (if conventional terrestrial based assisted GPS techniques are not available), as well as a guaranteed level of service, with guaranteed OTA alerts if a satellite malfunction is detecte, allowing a receiver immediately to drop a bad satellite rather than attempt to solve the location problem with bad data. As this signal will be transmitted on a 3rd frequency - triple frequency receivers which could perform an even more precise measurement of atmospheric signal dispersion are possible.

Re:...Why?

[TooMuchToDo]

I see the difference; I'm just saying its a very small difference.

The US has gone into sovereign nations to execute individuals we're at odds with; you think jamming a location based service is going to chill our spines?

Re:...Why?

[TooMuchToDo]

What is the US going to do if a European country starts jamming the US GPS system? Beg them to attack themselves? They sure as hell can't afford to attack Europe.

Pay Gazprom a higher rate for their gas, depriving Europe of warmth in the dead of winter.

Re:...Why?

[Anonymous Coward]

*Sigh*. Please show your work. I told you that the information from two satellites (their exact position and the exact times they sent their signals) determines your position to be on a parabola in the simpler 2D setting (a paraboloid in the real world) and that the points on the parabola (paraboloid) result in different times t even though (t-t1)-(t-t2)=t2-t1 is the same for all of these points. Since t2-t1 is the only observable information other than the positions of the satellites, you can know neither the time nor your position.

You're trying to determine the length of all sides of a triangle knowing just one length and the difference of the lengths of the two other sides. That's IMPOSSIBLE, and not just in the "nobody has done it" sense. It's a mathematical certainty that nobody will ever do it. The current time is the time at either of the satellites plus the time the signal took to get to you, which is proportional to the length of the straight line between you and the satellite. You don't know that distance. You know the time the signal would take to get from satellite 1 to satellite 2 (proportional to the distance between the satellites, which you know) and you know the difference between the times the signals from satellite 1 and satellite 2 took to get to you (again, these times are proportional to the distances to the satellites, so you only know the difference between these distances.) Lengths are durations and durations are lengths, with just a known fixed factor between them. So you know the distance between the satellite positions and the difference between the lengths of the other two sides of the triangle. That is not enough information to determine the absolute lengths of those triangle sides, and consequently not enough information to determine how much time has passed since t1 and t2.

Re:...Why?

[gregski]

"You can't carry atomic clocks in your pocket, they're a tad too big for that."

Well, that *used* to be true!

http://www.symmetricom.com/products/frequency-references/chip-scale-atomic-clock-csac/SA.45s-CSAC/

Re:...Why?

[jareth-0205]

With what, money borrowed from China? The US isn't all-powerful, they rely on the cooperation of other nations, we all do. Push it too far and they'll find out.

Re:...Why?

[bbn]

You seem to assume that you somehow know the distances to 3 satellites. But you don't. What you got is three time-signals. From that you can only infer two distances. Two is only enough for a 2D-fix.

That is what people have been trying to tell you. You need one satellite to be your time-fix.

The satellites will all send out a signal at exactly the same time. Because of the speed of light you will receive each signal slightly delayed and with a different delay for each satellite. When you receive the first signal you start your clock. You then measure time until you receive the second signal and then the third signal. It should be fairly obvious that you by this method only end up with TWO values from THREE satellites.

IF you did carry around your own atomic clock you could in theory be your own time fix. You would know _exactly_ when the satellites are going to broadcast their signal so you could start your timing clock before receiving any signal.

Atomic clocks are however big as a fridge, so nobody actually does this, not even the military.

Re:...Why?

[Anonymous Coward]

In other words, it's all about trust. You can blabber all you want, but everything you have just written is about trust.

Re:...Why?

[mSparks43]

I think you are making the mistake of thinking you know how long the signal took to get to you from each sat?

afaik, what you get is
sat1:I'm at x,y,z and the time is t
sat2:I'm at x,y,z and the time is t
sat3:I'm at x,y,z and the time is t

where the difference between the t in the message and the "real" t when you receive it is how long the message took to get there.

So two sats gets you the "real" t
and the 3rd allows you to derive your x,y,z

again, could be wrong - but afaik until you get the real t you know nothing about your position 2D or 3D.

Re:...Why?

[dbIII]

My point is the above poster doesn't understand why 3 points is not perfect.

Re:...Why?

[Anonymous Coward]

So two sats gets you the "real" t

No, it does not. It gets you the difference between the distances, nothing more. Please stop with the conjectures. You'll never see what you're doing wrong if you don't try to actually write down the solution. For starters, don't name different variables the same. The satellites transmit x1, y1, z1 and t1 for satellite 1 and x2, y2, z2 and t2 for satellite 2. If you think you can derive t from that, show us the formulas that make it happen (warning: impossible challenge, but you need to try to see the error of your ways).

Re:...Why?

[JockTroll]

During WW2 many US citizens had close relatives in Europe, since there were a great lot of first-generation immigrants. The Italian-American community was, and still is, huge. Didn't stop the US from bombing Italy to smithereens. The German-American community was, still is, huge and politically important. Didn't stop the US from bombing Germany to smithereens. Want to talk about the Japanese? Full of Nisei, a good lot of them fought - and valiantly I'd like to add - on the European front while their families were kept in concentration camps. Japan got nuked. In recent times, how many Serbs do you think live in America? Lots of them. Didn't stop the US trundling like a drunken beast over the Balkans and messing up the place. Take into account that today's bombing strategies center around precision strikes instead of city-busting raids so collateral damage is massively limited. What happens is, Europeans lose their electricity and industrial infrastructure and they either give up or learn to relive the good ol' agricultural times and forget being a "power", forever. Also, during WW2 the flag-waving, jingoistic "USA USA USA!" uberpatriotic feeling was way less extremistic than it is now. Not sorry for blasting your puppy with a shotgun.

Re:...Why?

[mSparks43]

still pretty sure you know enough to get a fairly good estimate of t from 2 sats.
Showing working would require ThinkingAboutShit(TM), which I'll leave up to people who are SureAboutShit(TM)(you).
Conjecture:
either you know t by three sats or you need 4 sats unless you have t

Re:...Why?

[mSparks43]

I'll give it a quick go though
sat 1 is x1,y1,z1, t=0
sat 2 is x2,y2,z2, t=1000ns
sat3 is x3,y3,z3, t=1000ns
you are therefore 300m further away from sat2 and sat3 than sat1
you know how far away sat1 is from sat2 and sat3 -
form a bounded tri - you now calc how far you are away from sat1 and can hence calc "real t".

Re:...Why?

[Anonymous Coward]

mSparks43 does not understand simple algebraic concepts and does not have a basic understanding of three dimensional geometry. mSparks43 does not follow instructions to show actual calculations. Recommended grade: Fail.

Re:...Why?

[Anonymous Coward]

Yes.

Re:...Why?

[RevDisk]

Why do I have the feeling you would complain if the US cured cancer and AIDS? "But they're still evil bastards who HATE folks with malaria!"

They provided a free useful service for everyone in the entire world, with no licensing fees that I'm aware of. It's a friggin clock and radio in the sky, that has been running very well since 1994 and not mucked with. "Monopoly"? No one is stopping you from putting your own clocks in the sky. You're basically upset that they built it for their own purposes, but opened it to everyone when it became obvious it was globally useful? You're complaining that a FREE system doesn't do everything YOU want, so it's evil and bad and probably kicks puppies.

Some folks would complain if you hung them with a golden rope, geesh.

That said, sure, always room for improvement. It irks the heck out of me when folks let blind prejudice block out all of the good things and focus solely on the bad. More systems are good for improved accuracy and redundancy. Sharing the cost for satellite navigation between countries is also good. As long as they all play nice with each other, I don't see any downside.

Re:...Why?

[Jane Q. Public]

"My point is the above poster doesn't understand why 3 points is not perfect."

And this is where the misunderstandings lie. I did not say it was perfect. In fact, in a number of different places in this thread I mentioned how 4 satellites are used to improve the accuracy.

However, in an ideal theoretical situation 4 would not be necessary.

Re:...Why?

[Jane Q. Public]

But there is information missing here: the locations of the satellites themselves. You are assuming the use triangulation using nothing but the timing of the signals. But there is actually more information than that.

If you know the satellite locations -- but not your own -- you can calculate your position in 3-space from only 3 points.

Each time signal gives you a semi-sphere of known dimensions. There is only one place where those surfaces will all intersect. (Technically there are two, but only one of them is on Earth.)

As I have stated elsewhere, I know that 4 are typically used to improve the timing. But it isn't absolutely necessary to get an approximate position, including altitude.

Re:...Why?

[bbn]

You already know the location of the satellites without receiving anything at all from the satellites. The orbits are well known and downloaded into your GPS device. The satellites themselves have no way of knowing their own position, they only know the same data as was downloaded into your GPS. The only principal information from the satellite is the timing of the signal. The signal also tells you the time of the day with a precision of 1 second, but you hardly need an atomic clock to know that already.

Your basic misunderstanding of the system is that you believe you that you have 3 points. But the only thing you actually got is the timing of the relative delay of reception of three signals which gives you two values to work with. From these two values you have to calculate your position and no magical tricks can somehow infer three points from 2 values.

Re:...Why?

[Jane Q. Public]

Yes. Computed from at least four sat signals.

Well, guess what? We were all wrong, to varying degrees.

My memory that the 4th signal is used just to improve accuracy was correct. However, that 4th signal is not a satellite at all, but a ground station.

Re:...Why?

[dbIII]

However, in an ideal theoretical situation

Fair enough, I wasn't considering the ideal theoretical situation (with the twist of throwing out the second point) but instead actual practical ones.

Re:...Why?

[khayman80]

"The Casimir effect is the best known example of negative energy:" [Dumb Scientist]

This is going to be one of my rare responses to your posts. Prepare to be ignored for the most part, from here on in. ... Get a clue. If you are seriously using that link as a citation, then you lose. You did not properly comprehend what it said. ... Dude. I know you are a scientist. But do you even really know what the Casimir effect is? Of course I expect you will by the time you answer (if you do). And if you do answer, I probably won't reply. But at this very moment, at the time you first read this, from what you have already stated, I suspect that you really don't know what it is. [Jane Q. Public]

Comments like these suggest that you're not really interested in studying physics. On the other hand, John Cramer's Alternate View columns inspired me to study physics in high school. In 1998, FTL Photons introduced me to the Casimir effect. In 2001, I made an offhand remark about these faster-than-light (FTL) implications to my experimental physics professor, and he asked me to give a presentation to the class.

The next comment I wrote summarized the first part of my presentation. The second part showed that virtual particles actually slow down light in the standard vacuum, because photons spend some of their time as electron-positron pairs that travel slower than "true" lightspeed. Because the Casimir effect suppresses some of these virtual particles, light actually travels faster between the plates (perpendicular to the plates) than in the standard vacuum. This is called the Scharnhorst effect.

The Casimir effect can be modeled mathematically as a negative-mass region; Hawking showed that negative energy is necessary for certain effects on WORMHOLES to take place in conjunction with such a negative mass. But he did not claim that the negative energy was supplied by it. But that does not establish a direct relationship between the two. It is a very FAR cry from equating negative energy with the Casimir effect. [Jane Q. Public]

Why are you talking about Hawking? I already pointed you to "Wormholes, Time Machines, and the Weak Energy Condition":

"The following model explores the use of the 'Casimir vacuum'[12] (a quantum state of the electromagnetic field that violates the unaveraged weak energy condition[11]) to support a wormhole..." [Morris, Thorne, and Yurtsever, 1988]

Nevertheless, Hawking's findings did not point at Casimir effect as a source of negative energy; they merely indicated that negative energy was necessary for the negative mass to have the calculated effect. Not the same thing. [Jane Q. Public]

Again, why are you talking about Hawking? You might want [1] to read "FTL Photons":

"Since the energy density of normal vacuum is defined to be zero, the vacuum between the metal plates actually becomes a region of negativ

Re:...Why?

[khayman80]

Because those fluctuations do exist in the vacuum outside the plates (which is defined to have zero energy), the energy inside the plates is actually negative. The attractive force implies negative energy between the plates because force is the negative gradient of potential energy.

A force being applied in the context of the Casimir effect is definitely a vector. It has direction. Neither a positive or negative vector implies "negative energy": it simply defines the physical direction in which the energy is directed. The coordinates are arbitrary according to vector calculus. There are circumstances in which energy can also be considered a vector, but this is not one of them. The Casimir effect is definitely a measurable vector in a particular direction, and he clear implication then is positive energy. [Jane Q. Public]

Good grief, you're arguing with the definition of potential energy. I was referring to the fact that all conservative forces can be described as the negative vector gradient of a potential energy function. Many of your statements on this topic are confusing:

A force being applied in the context of the Casimir effect is definitely a vector. It has direction. [Jane Q. Public]

Yeah, forces are vectors...

Neither a positive or negative vector implies "negative energy": it simply defines the physical direction in which the energy is directed. [Jane Q. Public]

The force vector points from a region with high potential energy to a region with lower potential energy. That's why an attractive force implies that the Casimir vacuum has less energy than the standard vacuum. No energy is "directed" anywhere because we're talking about potential energy, not calculating Poynting vectors.

"Because those fluctuations do exist in the vacuum outside the plates (which is defined to have zero energy), the energy inside the plates is actually negative."

You're trying to get my goat. Haha. That isn't what it says. According to the article, the force is negative, in relation to the chosen physical framework, which (as it clearly says in the article) merely implies that the energy is lowered when the physical substrates come together. [Jane Q. Public]

The Casimir force between two parallel conducting plates is negative/attractive. Period. More complicated geometries can have repulsive Casimir forces, but that doesn't affect the attractive force between parallel plates any more than your meaningless caveat does. Perhaps you meant to say "According to the article, the energy is negative..."

The same phenomenon can be demonstrated with magnets. No "negative energy" is implied. [Jane Q. Public]

In my

Re:...Why?

[khayman80]

I will add a tidbit that I picked up last night shortly after I wrote the above. You mentioned that since the ground state (not your exact words) of the vacuum is "defined" to be 0, then the energy must be negative. I understand that logic. The problem is that the premise is incorrect. Planck's equations, as refined by Einstein et al. in 1913, show that in fact the vacuum energy of a quantum system must always be above its "potential well", or the theoretical zero state. Thus, "zero-point" energy is NOT "defined" to be zero, but in fact is always positive, and the Casimir effect then, even using your own framework, is not "negative energy". [Jane Q. Public]

If you really did "understand that logic" then you wouldn't have written all that nonsense about vectors. Instead, you'd have skipped immediately to this point, which now implicitly acknowledges that the Casimir vacuum has lower energy than the standard vacuum.

Remember that spacetime is curved near large masses, but ~flat far away from masses where only vacuum energy is present. This implies that vacuum energy exerts ~zero gravitational force, so its stress-energy tensor must be ~zero, so the standard vacuum has ~zero energy.

If you're interested in the details, John Baez summarizes several vacuum energy density calculations. A naive quantum field theory calculation yields a vacuum energy with a mass density of +10^96 kg/m^3, which would've ripped the universe apart [1] before galaxies could form. On the other hand, general relativity and observations of our nearly-flat universe place a more rigorous upper bound at +10^(-26) kg/m^3. It seems like [2] gravity renormalizes vacuum energy to zero, within about one part in 10^122. Even though renormalization was harshly criticized at first, it's necessary to explain why galaxies (and thus humans!) exist.

Here's another, purely quantum-based, argument [3] for renormalization:

"As there is no lower energy state than the ground state, there is no energy level transition available to release the ZPE. Therefore, it can be argued that hf/2 should be dropped before integration of the quantum expression. This procedure is an example of renormalization, which basically redefines the zero of energy." [Abbott et al. 1996]

Footnotes

[1] One might assume that a large positive vacuum energy would collapse the universe just like a large amount of positive mass-energy would. This doesn't happen because in general relativity gravity depends on energy and pressure. In natural units, vacuum energy has pressure equal and opposite to its energy density. Because the stress-energy tensor has three pressure terms (for x,y,z) and only one energy density term, the negative pressure of positive vacuum energy dominates, causing the expansion of the universe to accelerate. back

[2] It's also vaguely possible that zero point energy doesn't gravitate at all

Re:...Why?

[mSparks43]

ok
simplification (drop y,z which require a 3rd point of reference)
receive from
sat1 0m, t=150,000ns
1000ns later receive
sat2 900m, t=150,000ns

gives
you are 300m further away from sat2 than sat1
therefore you are 300m from sat1
and 600m from sat2
your x = 300m
and
t when you received the first message = 151,000ns

Re:...Why?

[khayman80]

... "zero point" energy is NOT in fact zero (it is actually pretty huge)... [Jane Q. Public]

While talking with my first research advisor around 2003, I mused that it's unfortunate how the Casimir effect only supresses vacuum fluctuations with wavelengths larger than twice the spacing between the plates. Since fluctuations with shorter wavelengths have more energy, the Casimir effect only depletes a vanishingly small fraction of the vacuum energy between the plates. So I agree that a naive quantum calculation leads to a huge vacuum energy. But as I've just explained, the same theory of general relativity [1] that implies stable wormholes and the Alcubierre drive also seems to renormalize the vacuum energy to zero. So this just means that depleting vacuum energy could potentially lead to very negative energy densities.

In fact I thought it was pretty obvious to most people that the fact that "zero point" energy is NOT in fact zero (it is actually pretty huge), has been the motivation for finding ways to "Maxwell's Demon" the quantum vacuum fluctuations. There is nothing theoretically preventing it; one team this year found a possible means of exploiting it. We shall see. [Jane Q. Public]

I asked which team and you replied:

I looked again, and didn't find anything from this year. So my memory could be incorrect. [Jane Q. Public]

Agreed:

What I am curious about is: assume you get the virtual particles which then tunnel: what is the probability that they will tunnel with the same probability, then recombine properly? It seems to me (without having done the math), that there is some possibility here of ending up with a quantum Goretex, or, in other words, a Maxwell's Demon of sorts, no matter how small its effect might be. [Jane Q. Public, 2009-04-21]

Not having done the math often does lead to quantum Goretex and ironic references to Maxwell's (broken) Demon.

But there's Maclay and Forward, from 2004. There are more recent examples but I will not have time to hunt them up today. [Jane Q. Public]

Maclay and Forward 2004 [2] imagined accelerating a mirror fast enough that the dynamic Casimir effect creates real photons. A more recent example was in 2009, which imagined spinning magneto-electric nanoparticles fast enough that the centripetal acceleration created real photons. At the time, I called this device a photon drive. On page 2 of their 2004 paper, Maclay and Forward point out that more conventional photon drives would arguably be better than their propulsion system.

Granted, it's only a thought experiment,

Re:...Why?

[khayman80]

Maxwell's equations force E=0 inside perfect conductors, which means that vacuum fluctuations with a half-wavelength longer than the separation between the plates can't exist between the plates.

By the way: If you are going to refer to Maxwell's equations, you should use caution. Because often what are referred to as "Maxwell's Equations" are actually just Maxwell's simplifications of Heaviside's and Hamilton's quaternion equations, with introductions of arbitrary "constants" to cancel out inconveniences, much like Einstein's "cosmological constant". There is a good deal of modern evidence that Maxwell's attempt to simplify things may have been wishful thinking, and that Heaviside and Hamilton had it right all along. We rely much on Maxwell, but his conclusions are assumptions. Not only are they not proven, there is significant counter-evidence. [Jane Q. Public]

Good grief. Electric fields are zero in perfect conductors. I explain this fact to freshman physics students by asking: what would happen if we tried to place an electric field across a conductor? Electrons would move opposite the field, and positive electron holes would move with the electric field, exactly enough to cancel out the original field inside the conductor. Better conductors cancel out faster, so electric fields are zero in perfect conductors.

Mentioning that this fact can be derived from Maxwell's equations is meant to be helpful, because all physics students should be familiar with the first theory that emerged in a Lorentz-invariant form. In other words, Maxwell's equations were consistent with special relativity before relativity even existed. They're the basis of all radio equipment, and the correspondence principle checks that quantum electrodynamics (one of the most accurate theories in history) is identical to Maxwell's equations for large systems. If your reaction to hearing "Maxwell's equations" is to spray chaff about quaternions, you'll be disappointed to find that core classes based on junior-level Griffiths and graduate-level Jackson are almost exclusively about Maxwell's equations.

Quaternion notation is useful when desribing 3D rotations, but it's not used in electrodynamics because vector notation is more intuitive. That doesn't stop crackpots from insisting that Maxwell's equations are wishful thinking.

Physicists use Maxwell's vector equations despite the fact that we're well aware of quaternion notation. John Baez even wrote a paper on octonians. As Baez quips, if the noncommutative quaternions are like a shunned eccentric cousin, then the nonassociative octonians are like the crazy old uncle nobody lets out of the attic.

In fact, look at p542 of Griffiths 3rd edition: "Equation 12.136 combines our previous results into a single 4-vector equation-- it represents the most elegant (and the simplest) formulation of Maxwell's equations."

Page 555 of

Re:...Why?

[Anonymous Coward]

You used 2 satellites for a 1D fix (your position in the x-Dimension). That you are able to calculate t with two satellites and two variables (t and x) isn't surprising. In fact it's what has been explained here over and over again. What you claim is that you can add two degrees of freedom and need just one more satellite to solve for t. That's what you need to show.

Re:...Why?

[Jane Q. Public]

You are once again (VERY rudely, by Slashdot standards) being completely off-topic again, you once again have waited days or weeks to make arguments that I have been done with for a while and are completely off my topic list by now. If you really think I am going to go back and dig through all those long-past comments in order to argue with you, you are mistaken.

That is ONE of the reasons I have called you rude and obtuse.

But the one argument I will make is this: you ALSO insist on taking my comments out of context, and insisting that I meant something other than I did. Take the one about vectors, for example. I mentioned that it had direction (with which you apparently agreed), then objected to me mentioning the direction in which it was "directed".

This is a completely ridiculous splitting of hairs. By "directed" I simply meant it had direction. I was not proposing that it was being "directed" by anything.

" Instead, energy is removed from the vacuum itself."

And just what is it that makes you think I was arguing with anybody about that point?

Nevertheless, as I pointed out, depending on what theory you choose to follow, the positive energy density of the vacuum is anywhere from 10^-9 joules/m^3, to 10^119 joules/m^3. Anything in that range is still significantly positive.

My point was that depending on the way you do the math, sure you CAN show negative energy... but it is far from necessary. There are just as valid methods of caculation that show it as merely an absence of the positive energy elsewhere. That was all I was trying to say.

Anything else is hair-splitting on your part. YOU may not think so, but you have continually insisted on taking me too literally and picking my comments apart, then stalking me in other forums (and I suspect that you have tried to do it elsewhere, as well). And launch into this great diatribe about how wrong I am, in a situation in which you know damned well I am not interested in taking the time and effort to defend myself.

Go the fuck away, and leave me alone. Do you understand THAT? Or do I need to explain THOSE words to you, too?

Re:...Why?

[khayman80]

I emailed the Casimir motor idea to a few scientists, saying: My gut tells me that vacuum energy can't be made to do work. But I don't see an obvious, fatal problem with the following scheme. Do you?

In response, Geoffrey Landis pointed out that there will be a latent heat at the phase transition, even for type II superconductors. He uses the same reasoning that explains why magnetic fields cause latent heat. In other words, Casimir-induced latent heat will exactly cancel the net work done by the plates, which seems to forbid this free lunch...

How do they navigate now?

[Anonymous Coward]

Article did not answer: If Europeans don't have GPS yet, how do their existing sat-navs work? And why is this new system only for Europe?

Re:How do they navigate now?

[Baloroth]

Article did not answer: If Europeans don't have GPS yet, how do their existing sat-navs work? And why is this new system only for Europe?

The Europeans do have GPS, it's publicly available and "global" is in the name. There is also the Russian GLONASS, which is basically the same. The EU doesn't have it's own network, though, which is important for political reasons (and only political reasons). Although there are some technical improvements Galileo makes over GPS, they certainly don't justify a new system. It's also available for everyone, or at least will be, if it ever gets operational (again, global).

Re:How do they navigate now?

[flyingfsck]

and there are also systems that use geo stationary satellite data, for example Egnos.

Re:How do they navigate now?

[Anonymous Coward]

Egnos is an enhancement to GPS, not an independent system. Stationary ground stations monitor the effect of current atmospheric conditions on the GPS signals, and broadcast corrections via the geostationary satellite. You need a regular GPS fix first, but can roughly halve the inaccuracy if you get the Egnos signal.

There's a similar system in the US called WAAS, but it uses ground based transmitters, so covers a smaller area.

Re:How do they navigate now?

[krakass]

Close, you're thinking of DGPS. WAAS is satellite based, just like EGNOS.

Only three sats needed!

[Anonymous Coward]

You can use data from 3 satellites to get a fix.
You need a fourth one for an getting altitude.

a minimum of four satellites are required

[frovingslosh]

because a minimum of four satellites are required in the sky for a smartphone or vehicle to use their signals to calculate a positional fix.

Lets be more accurate here. A minimum of 4 satellites are required to be in the sky that can be observed at the same time from the same point on earth. Hopefully these satellites are relatively close together, because otherwise they might never all be visible at the same time. And if they are, since they are in low earth orbit they will pass by relatively quickly and only be briefly useable during each orbit. So, if the orbits are close this may allow a little bit of testing, but the "system" is still too satellite poor to be of any real use for navigation (at least unless you combine the signals with info from other U.S. or Russian satellites).

Re:a minimum of four satellites are required

[Anonymous Coward]

They are in geosynchronous orbit, something about needing to know their location I think...

Re:a minimum of four satellites are required

[Anonymous Coward]

Wrong. "23,250km-high orbit" ... GEO is 35,786 km.

Re:a minimum of four satellites are required

[Anonymous Coward]

They are in geosynchronous orbit, something about needing to know their location I think...

They are almost certainly not all in geostationary orbit. Most Global Navigation Satellite System (GNSS) satellites are not in geostationary orbits. Geostationary orbits can only be above the equator (which doesn't provide great coverage for Europe) and are also very far away from the earth (which increases the signal strength required). Wikipedia seems to indicate that the Galileo orbits are medium-earth orbits about 23,000 km above earth.

That said, for GNSS in general, there's also the possibility of non-circular orbits (eg Molniya orbit) which I believe the Indian Regional Navigational Satellite System uses.

Re:a minimum of four satellites are required

[Anonymous Coward]

Wikipedia seems to indicate that the Galileo orbits are medium-earth orbits

Not to be confused with Middle Earth Orbits, which are where we place the spy satellites used to monitor Sauron.

Re:a minimum of four satellites are required

[hawguy]

because a minimum of four satellites are required in the sky for a smartphone or vehicle to use their signals to calculate a positional fix.

Lets be more accurate here. A minimum of 4 satellites are required to be in the sky that can be observed at the same time from the same point on earth. Hopefully these satellites are relatively close together, because otherwise they might never all be visible at the same time. And if they are, since they are in low earth orbit they will pass by relatively quickly and only be briefly useable during each orbit. So, if the orbits are close this may allow a little bit of testing, but the "system" is still too satellite poor to be of any real use for navigation (at least unless you combine the signals with info from other U.S. or Russian satellites).

If you'd quoted the previous sentence: it becomes possible to test Galileo end-to-end, it'd be clear that they meant that it is possible to test the system, no one said it's a usable navigation system.

Re:a minimum of four satellites are required

[c0lo]

Wikipedia seems to indicate that the Galileo orbits are medium-earth orbits

Not to be confused with Middle Earth Orbits, which are where we place the spy satellites used to monitor Sauron.

I guess you mistake the for Middle Earth Orbs used for the same purposes.

The ones made by the Elves of Valinor in the Uttermost West, and marketed under the Palantir brand, were considered the best... until it was discovered that not only they tracked the location of its users but also subtly altered the information, in a way targeted for each particular user (very much like the targeted ads today):
1. Saruman looked through the Orthanc stone, and saw what he thought was an unassailable strength in Mordor, helping to corrupt him
2. Sauron, looking the other way with voyeuristic intent thought, thought Pippin had the One Ring
3. when Denethor used the stone, it convinced him there was no hope for Minas Tirith, driving him to suicide

Needless to say, once all of the above has been exposed, their customers lost confidence, so the production of new devices was interrupted.
It took quite a long time until the brand was resurrected and today it seems to enjoy commercial viability again.
A word of caution for the would-be consumers of their services: rumours have it that the new management team can not resist co-contracting alongside trolls if they were given an opportunity.

Re:a minimum of four satellites are required

[maxwell demon]

They didn't claim that the system was finished, or already usable for general navigation. But if all four satellites are visible at the same time, this allows to do full testing under realistic conditions, which wasn't possible with only two satellites up. That's all that is claimed.

Re:a minimum of four satellites are required

[Anonymous Coward]

Wikipedia seems to indicate that the Galileo orbits are medium-earth orbits

Not to be confused with Middle Earth Orbits, which are where we place the spy satellites used to monitor Sauron.

I guess you mistake the for Middle Earth Orbs used for the same purposes.

The ones made by the Elves of Valinor in the Uttermost West, and marketed under the Palantir brand, were considered the best... until it was discovered that not only they tracked the location of its users but also subtly altered the information, in a way targeted for each particular user (very much like the targeted ads today):

This is because they didn't use HMAC or another algorithm to ensure data integrity. With a firmware update this vulnerability is fixed.

Re:a minimum of four satellites are required

[ultranova]

Not to be confused with Middle Earth Orbits, which are where we place the spy satellites used to monitor Sauron.

Which is odd, since the Lidless Eye is located in London.

Multibillion pissing contest

[onyxruby]

Galileo is nothing but a multi-billion dollar pissing contest with the US to say "look at me, I can make my own GPS". When the continent is neck deep in an economic crisis that is miring millions of people and putting nation states on the verge of collapse, their priorities are seriously misplaced.

Seriously, there is no real benefit to this other than vanity and snubbing their noses at the United States. This has seriously got to be one of the most foolish economic decisions they have made in decades. Might as well spend billions of dollars making your own version of the Internet for the same reasons and results.

Re:Multibillion pissing contest

[timeOday]

That must be exactly what Russians think about us not wanting to use their fine space launch services indefinitely.

Re:Multibillion pissing contest

[Anonymous Coward]

You're spot-on.

This is nothing but a propaganda project for Europeans to escape reality. The idea that, after decades of parasitism, EU would become militarily independent from the USA is ridiculous! They can hardly afford this >5-gigaEuro toy, which they're building at a time of a debt crisis, and they'd need 100s of times more to be independent!

So they're getting no benefits, just costs (with debt interest), and this also goes a long way squash the potential of private satellite navigation networks from taking off...

--libman

Re:Multibillion pissing contest

[Space cowboy]

When your international reputation is at an all-time low you should expect things like this... Galileo was started way before the US popularity took a nose dive, but the last decade or so are only going to make projects like this *more* likely. To the civilised world, the US is not one of the good guys any more, they're not in "bad guy" territory yet, but they're sure headed there fast.

Basically the world no longer trusts the USA. Simple as that.

Simon.

Re:Multibillion pissing contest

[Anonymous Coward]

RU is a very different civilization, with very different geopolitical interests.

No countries in the top quarter of the Economic Freedom Index will ever have a serious conflict amongst themselves, ever.

EU (especially its best countries, like UK, NL, DE, etc) and US are largely on the same page when it comes to economic freedom and free trade, while RU remains an unstable wildcard (even more-so than CN). Some EU countries (FR, IT, etc) are major disappointments, but they're too weak to do anything by themselves. US'ians may justifiably call FR'ies "socialists", but it is a relative judgement - there's still a vast difference between them and RU.

So EU depending on US is a smart choice, but US (or anyone) depending on RU isn't.

--libman

Re:Multibillion pissing contest

[tbird81]

Yes we do. I trust the USA, much more than the unelected corrupt EU politicians.

Re:Multibillion pissing contest

[bigt_littleodd]

Your comment is short-sighted.

GPS, whether American, Russian, or EU, is first and foremost, a military asset for their respective owners.

The US military can elect to disable or cripple civilian GPS service to all devices other than their own when they deem it necessary to prevent its use by hostile forces. Presumably, GLONASS and the EU systems have the same capability.

History repeatedly shows that international political alliances vary over time. Just because we currently are at relative peace with the EU and Russia, that does not mean it will always be so in the decades to come. I'm not saying we will be in a hostile situation with either in the future, but it's not out of the realm of possibility, either.

The EU is building their own system not because they want to win a "pissing match" with the US or Russia. It would be foolish of them strategically to depend on a GPS that is under someone else's control.

Re:Multibillion pissing contest

[DNS-and-BIND]

Those evil Americans! Making their insidious GPS service available to the world for free! Bringing billions of dollars of cost savings to foreigners all over the world in the form of reduced fuel costs, increased agricultural efficiency, and time saved. They had it all planned from the beginning, those bastards!

Look, if you're going to mindlessly bash the Americans, do it right. Say something like "GPS was conceived by the perverted violent minds of the military, while our Galileo is a system of peace. Thus proving, once again, the innate superiority of Europeans over the Americans we have looked down upon ever since we kicked their sorry asses out of our own countries for having the wrong religion."

Re:Multibillion pissing contest

[Anonymous Coward]

"Nose dive"? That is bullshit from the socialist fantasy bubble! Now here's a summary of objective benchmarks by which a country's reputation can be judged...

USA is #1 in overall National Brand ranking, and #1 in international tourism receipts (in spite of really shooting itself in the foot with all the post-9/11 security theater). USA gets more foreign investment than any other country - more than twice as much as the runnerup. It has the world's most respected universities, and some of the most admired and best managed companies. USA's credit rating went down a bit under Obama, but only a handful of countries rank higher. It ranks higher among preferred immigration destinations than most of Europe (sadly too many survey respondents thought France was a romantic destination, even though most people who visit it are disappointed) (and justly behind small Economic Freedom champs like SG and NZ).

USA's reputation was at an "all-time low" shortly after the Revolution, when it was seen as a pirate nation of rootless migrants and uncivilized wilderness. USA's reputation gradually went up and up during the 19th century, leapt upward as it became a superpower and a powerful anti-colonial influence after WW1, and went further up in the civilized world after WW2 and during the Cold War.

--libman

Re:Multibillion pissing contest

[Space cowboy]

Jesus, tunnel vision much ?

Look it's nothing to do with GPS vs Galileo. It's to do with the USA, a nuclear power, declaring war left, right and center, & invading other countries basically because it can. No-one likes that; international reputation suffers, trust is lost, and consequences ensue. There's no point in getting pissy about it, you brought it on yourselves.

I don't think Europeans are innately superior. I think people are just people, wherever you are. I'm married to an American woman, whom I love dearly. I do think the USA is fucked though, the society is (IMHO) past the tipping point and heading down, and I can't see myself staying around much longer, as I've said before on this site. At some point, the money just ain't worth it.

Simon

Re:Multibillion pissing contest

[Space cowboy]

Right, I'm talking about a cop executing a handcuffed helpless suspect [warning. Graphic.] and the lack of respect for the law that "peace officers" show; about the TSA, just the very fact of its existence; about the demagoguery that passes for news and its knock-on effects on society; about the constant military action taken to divert attention from problems; about the massive debt and crippled economy; about the shameful lack of a decent for-all healthcare system; about the proliferation of lethal weapons that for some reason is enshrined in the country's constitution!, and the horrendous murder statistics that it produces; about the general sense inherent in US society that "everything's ok as long as *I'm* ok, screw you guys" ... I could go on... and on.... and on...

And your point is that the "national brand" is good. Well whoopy-do. That's all right then. Phew! Glad *that*'s sorted out! .... Fuck me, it's worse than I thought :(

Simon.

Re:Multibillion pissing contest

[Anonymous Coward]

Nobody is stopping you. Please leave. Seriously.

Re:Multibillion pissing contest

[Anonymous Coward]

USA has no interest in hurting the global economy - it spends hundreds of billions a year to protect it! It won't turn off GPS just to fuck with its allies in Europe - that is insane! (Inside joke: Uncle Sam is no Ian Fraudman...)

The odds of USA ever turning off GPS due to a military threat are theoretical, and nearly non-existent in practice. I guess that scenario imagines a missile fired by al Qaeda / Iran / North Korea / etc trying to use USA's own satellites to guide it... But, why?! There are lots and lots of options for building a device to detect position - other countries' or private satellites, phase difference from terrestrial cell towers, Earth magnetic field, on-board optical recognition of the terrain, simple internal inertial sensing, target beacons, etc, etc, etc.

Cut-off switches are pointless. We need to transition to a private satellite infrastructure, and both USA and EU need to stop buying so many toys on credit and get their respective fiscal houses in order!

--libman

Re:Multibillion pissing contest

[toutankh]

Seeing how the USA are the biggest bully on the planet, it is a smart choice for no country to depend on them, even for the EU, itself made of big bullies.
The USA have already misbehaved with their "friends" and there is no reason to believe that they will not do it again. Therefore seeking independence from them is the sane thing to do.

Re:Multibillion pissing contest

[toutankh]

they're not in "bad guy" territory yet

Just speaking for myself here: they most certainly are, although discussing the reasons is out of scope and would take ages.
I get the impression that many people see the USA as a necessary evil. Apparently everybody thinks that there has to be domination by one nation over the others; in this perspective, the USA are the least bad option (alternatives such as China or Russia aren't that exciting).

Re:Multibillion pissing contest

[DNS-and-BIND]

Hm, what was the last time Congress declared war? Or are we just making shit up now?

I don't think Europeans are innately superior.
Well, a lot of your countrymen do, and they aren't shy about saying it. Try these keywords: "fat, hamburgers, Wal-Mart, fascist". That should help you become familiar with these repugnant attitudes after a bit of searching.

Re:Multibillion pissing contest

[dbIII]

Yes it is a nose dive. Years back there were rumours about rogue CIA idiots torturing people in Central America - some believed it, but most didn't, and those that did believe mostly didn't think it was standard operating proceedure. Then Baby Bush made it very clear that torture was now fully accepted as a tool and not an atrocity for the first confirmed time in the USA since the American Revolution. That's just one thing, abducting other countries citizens for torture (extreme rendition) is another, so that's a reputation loss that far exceeds Reagan's "bombing starts in 15 minutes" moment or anything Nixon ever did.
It sent a message that the US government could not be trusted to stick to the values it had for the last two centuries, so people wondered if it was going to be as untrustworthy as a place built on "might makes right" such as China or Putin's Russia. Hillary didn't help recently by demanding that agents find out the credit card details of all foreign diplomats in the USA so that they can be easily framed and pressured when needed or whatever she wanted it for.

Re:Multibillion pissing contest

[Anonymous Coward]

No. Im a EU citizen and if someone screws me over, it better be someone from the EU.
Not needing the US for that - US can screw their own citizens, thank you very much.

So, while I am not happy with the state of democracy in Brussels, I am all for independence of the US.
Including projects like Galileo. After all the (old) US administration has clearly stated to not care about the "old EU"
any more.

Re:Multibillion pissing contest

[Anonymous Coward]

Youre right on: congress did not declare war for a long time, and us has not made any prisoners of war and neither did they torture anybody.

Instead what they did is redefine a lot of words. Legal bull...

Re:Multibillion pissing contest

[Xest]

"Hm, what was the last time Congress declared war? Or are we just making shit up now?"

Note the "invading countries left, right, and centre" part of his argument too, the US has been doing this basically without a single break since World War II in one way or another, whether it's drone strikes in Pakistan, or the CIA pulling off defacto coups across the world. His point is that America spends far too much time and far too much money meddling with other nations, rather than keeping to itself, and that often leads to greater instability. Case in point, by ousting Saddam, the US removed the only credible counterbalance in the middle east to Iran, and since then Iran has been able to carry out proxy attacks everywhere from Iraq, to Lebanon, from Afghanistan, to the Philippines. They couldn't do this shit when Saddam was around, because Saddam would then be given the international blessing he needed to do the exact same thing in Iran proper. By trying to make things better for the oppressed minorities in Iraq, the US ended up making things worse for everyone in Iraq, and people in many other countris too. So when you stop avoiding the point he was making by focussing on a specific intentionally mis-used part of that, tell me, are you disagreeing that America consistently meddles in the dealings of other nations?

"Well, a lot of your countrymen do"

Well, ignoring the fact Europe is a country, what Europeans thinks is not that they have any kind of innate superiority - that's simply not in the European mindset- Europeans are simply much more rational than that, they recognise their fallibility in part because they have thousands of years of history of it to learn from. Some European nations did have this mindset- the French and British at the height of their empires for example, but as their empires fell they realise it was simply a load of bullshit. Ironically, the reason you most likely claim it is because it IS something that's in the US mindset, there's even a term for it - "American exceptionalism", it's something America hasn't, like Europe, grown out of yet.

What many Europeans do believe however, that you're getting confused with, is the fact that currently, Europe is at least governing itself just a little bit more sanely than the US, and that is what Europeans are happy to point out to you. The terms you mention are nothing more than banter, and if you believe any use of them implies some perceived superiority then it simply demonstrates that you, as an American, haven't got out of this absurd mindset that some nations and their people are simply inherently superior to others. Europeans know full well they have their problems, and this is ironically why the current global economic instabilities focus on the Eurozone's issues - because Europe is the only one really openly admitting they have a big problem and trying to deal with it, in contrast to for example America's insanely massive deficit, see here for example, and sort by worst to best, note how insanely large the US figure is in the negative compared to even the closest member on the list?

http://en.wikipedia.org/wiki/List_of_sovereign_states_by_current_account_balance

The only reason you believe there's some kind of belief about inherent superiority is because you have that mindset yourself, until you lose that you wont be able to get over this stupid idea that Europeans think they are innately superior. Believing they are doing some things better that lead to for example, lower infant mortality, longer life expectancy, higher levels of personal happiness, etc. does not in any way imply this is because of some innate superiority or belief in such.

Re:Multibillion pissing contest

[Anonymous Coward]

Hm, what was the last time Congress declared war? Or are we just making shit up now?

Whether some old men call it war or not is irrelevant. If it involves armor and troops fighting the military of a different country it's a war, and nobody sane thinks otherwise. The first definition given by Wiktionary says:

"War: Organized, large-scale, armed conflict between countries or between national, ethnic, or other sizeable groups, usually involving the engagement of military forces."

If you still don't get it: calling war something else doesn't change reality. If I called my gun a camera, it still wouldn't shoot pictures.

Re:Multibillion pissing contest

[Anonymous Coward]

Hm, what was the last time Congress declared war? Or are we just making shit up now?

I don't think Europeans are innately superior.
  Well, a lot of your countrymen do, and they aren't shy about saying it. Try these keywords: "fat, hamburgers, Wal-Mart, fascist". That should help you become familiar with these repugnant attitudes after a bit of searching.

I wish the US would have the decency to actually declare war and be honest about their agendas and motives. Right now it seems that you can't be bothered to declare war because war has rules that you have to abide by. Just Doing It instead of playing by the rules is more expedient and currently the US can get away with it. But don't think it won't have consequences.

Talking about repugnant attitudes, I think "might makes right" should have no place in modern civilization, but the vibe from the US is that both the government and a non-trivial proportion of the people (government and people are different entities, just ask anyone from Iran) share this attitude. Who gives a fuck about cheeseburgers, obesity and Wal-Mart when faced with something like this?

Re:Multibillion pissing contest

[icebraining]

Speak for yourself. I don't trust either.

Re:Multibillion pissing contest

[DNS-and-BIND]

what Europeans thinks is not that they have any kind of innate superiority - that's simply not in the European mindset- Europeans are simply much more rational than that

LOL! Read through that and see if you can spot the contradiction.

Re:Multibillion pissing contest

[jandar]

they're not in "bad guy" territory yet

They are in "bad guy" territory at the latest with Guantanamo. This incarceration and torture of people without enough evidence to start a trial is way past the limits of civilisation. If they are shocked about it like about Abu Greibh and abolish it immediately but no they continue it shameless for years after years.

Guantanamo is only the most visible tip of the iceberg. The whole war in Iraq was against international law and without any evidence of this "weapons of mass destruction" (the whole non-US world was laughing about the presentation of the pretended "facts"). Abduction and torture of foreign citizens also is not a attribute of "good guy".

I could ramble about so many "bad guy" things the USA have done lately, my keyboard would drown in the froth forming at my mouth. I'm not sure the EU would be acting better in the same position, but the USA are doing it right now in reality before our eyes.

Re:Multibillion pissing contest

[Sigg3.net]

The US is a very young child. American state of the art scientific experiments keep affirming the thesis of continental philosophy that spans 2000+ years. (Which arguably travelled from the East.)

To be fair, we should wait at least a millennium before passing judgment on the American outlook.

(I do think, though, we will see USA become SA within 150 years.)

Re:Multibillion pissing contest

[Jesus_666]

Technically it's not - being better in one thing does not imply inherent superiority. Otherwise, I'd be inherently superior to most Americans in that I'm better at German than they are while they are inherently superior to me in that their American English is better.

For the record, I don't really suvbscribe tothat rationality argument, eithar. At the very least I don't think we are inherently more rational, although we might be effectively more rational. Our advantage is that we're not a superpower. Given that people will usually do things they can get away with (depending on one's moral framework), that top politicians tend to have few scruples and that people like to believe that they aren't doing evil I think it's a reasonably safe assumption that more powerful countries will tend to be more delusional about their status in the world and the possible consequeces of their actions.

If Europe should make it to superpower status (which seems iffy given that we'll have to compete with China, India and possibly the US and Russia) we'll become just as much of an overbearing sociopath as all superpowers in recorded history have been. And boy, will we feel good about ourselves.

Re:Multibillion pissing contest

[Anonymous Coward]

Well, ignoring the fact Europe is a country

Europe is a country? As somebody who lives in a European country, I'm quite interested to know when this happened.

Re:Multibillion pissing contest

[Xest]

Oh dear, I think you're having real difficult with the rather simple word "innate".

In this context the word innate would mean that there was a belief that Europeans are born with some kind of natural superiority, the fact that I stated that Europeans tend to be much more rational and not believe in such hogwash doesn't conflict with this, because the rationality spoken about in case is a learnt trait taught into European culture through are many lessons from history we can draw on to understand why that belief is stupid. As I say, some Europeans used to have this exact belief - the British, the French, the Germans, but we also eventually learnt that wasn't true.

In contrast, many Americans do actually believe that being American gives you some kind of natural superiority, which simply isn't true. Americans have yet to learn the same lesson that Europeans have learnt in regards to this mindset, because, like the afformentioned European countries at the height of their power, they were blinkered by that power and that resulted in their eventual downfall.

So now that you understand the word 'innate' in this context, perhaps you can go back and re-read the posts in this thread and begin to understand why people are in disagreement with you and why there is no contradiction in what I said, merely a lack of understanding of a rather simple term on your part.

Re:Multibillion pissing contest

[Xest]

*facepalm*

I'm sure you knew what I meant. That'll teach me for being pedantic about the GP's post!

Re:Multibillion pissing contest

[Anonymous Coward]

We did bring it on ourselves. (Ignoring Hiroshima) We've done everything we could since the Wall went down to prove to the world that we're backsliding. As an American I fully agree with such European sentiments and so do millions of other US citizens. We have been miserably led since 1980. The Bush years were not only hell for all but our most ignorant, they were also well-disguised attacks on our basic civil liberties and economic foundations.We've also managed to ignore climate change, demonize our educators, journalists and teachers. We're heading for hell in a handbasket and most of us act as if everything is going quite well ... fully cooperating in our own decline and whistling in the dark each day.

Re:Multibillion pissing contest

[Anonymous Coward]

You're just making stuff up. Everybody knows the rest of the world hates us because of our freedom!

You just have no idea how many idiots I encounter who actually believe that the US never does anything wrong....and $diety forbid that we actually admit it when we do, because then some idiot (Romney, for instance) will run around saying he won't ever "apologize for America".

Re:Multibillion pissing contest

[onyxruby]

You perfectly made my point with your reply, and I don't think you were even trying. Without attacking a single merit of what I said, all you did was reflect 'anti-US sentiment' and failed to site a single economic reason to spend the billions of dollars Galileo will cost.

My point stands, this is nothing more than a redundant multi-billion dollar pissing contest with no real economic benefit.

Re:Multibillion pissing contest

[Seeteufel]

I wish Europe would rather develop its owns operating system (Linux, hint hint). than its own GPS. Simply because GPS seems fine to me.

Re:Multibillion pissing contest

[Anonymous Coward]

Yet the US is the only superpower. I think that says more about human nature than it does international politics.

Re:Multibillion pissing contest

[Anonymous Coward]

Can anyone help me? I can't figure out how to write a post without repeating "Simon." at the bottom of every single one, like some kind of narcissist. Yeah so I'm stupid, just help me out, would ya?

Simon.

Re:Multibillion pissing contest

[mcolom]

If we're talking about US vs europeans, pls explain to me why someone should trust those that in the last century had still colonies all over the world and started two global wars, the last one with a genocide. Sigh, I'm from Europe, but it makes me sick when someone suggests that Europe might have a moral superiority over the US.

Re:Multibillion pissing contest

[Anonymous Coward]

I give you relevant facts, and you reply with an incoherent emotional rant...

That YouTube video, though anecdotal in the grand scheme of things, only confirms my broader philosophy - governments suck. In a more capitalist society there could be no "victimless crime" nonsense like the "war on drugs", and Private Defense Agencies would actually be accountable for their mistakes. You, on the other hand, want to give the government unlimited power, including total control over your health care and a total monopoly on weapons of every kind! Read Solzhenitsyn, if not USA's gun rights advocates - an armed populace raises the cost of tyranny. The most peaceful country in Europe, Switzerland, understands this too.

As for USA's high murder statistics (which, BTW, are lower than much of Eastern Europe) - you need to adjust them by a number of factors, most importantly fertility rates. Most murders are committed by young people, of which USA has more than Europe or East Asia. USA also has a greater percentage of immigrants than almost any country Europe, particularly those that come from more violent countries. Most of the crime is caused by government prohibitionism, as well as the ineffectiveness of the law enforcement monopoly. Comparing applies to applies, US states that have similar demographics as Europe (ex. New Hampshire) are actually safer than Europe! You should also look at other crime statistics, like robberies. And, from a broad historical perspective, USA has seen far less large-scale violence than European countries did - USA's most costly wars have been to save Europe from itself!

Regarding USA's "shameful lack of a decent for-all healthcare system"... I remember the "for-all systems" back in the Soviet Union - they weren't pretty. What is most shameful is that USA's health system (pre-ObamaCare) is half-socialist, which manifests bad attributes of both worlds - the government pays for the majority of it, innovation is stifled, price competition is stifled, and costs are way too high. There's no reason why health care should be so expensive, with hospitals and doctors charging stratospheric prices that the customer never sees and health insurance companies are mandated to pay. What USA needs is free market competition in health products and services, which would immediately result in a technological revolution similar to the computer revolution of the 1990s, with prices falling far lower and benefits growing far higher than most people can currently imagine! About 90% of health care is information, and most medical tests can be done at home or in cheap competing clinics. The poor should ideally settle for private charity, but a voucher system would be a reasonable temporary political compromise.

--libman

Re:Multibillion pissing contest

[Anonymous Coward]

Sure. Reboot your computer, take a .50-caliber pistol, relaunch the Web browser, load the pistol, click the URL bar, put pistol in mouth, type in "now-thats-how-you-feed-a-troll.edu" (no quotes), press ENTER, pull trigger.

--libman

Re:Multibillion pissing contest

[Anonymous Coward]

The concept of a "superpower" is largely meaningless in a globalized inter-dependent world, because Uncle Sam (and all other mostly-capitalist countries) are very limited in what they can do militarily. (An interesting analogy is the idea of using Doom or Quake weapons IRL - pressing the trigger on the BFG would send you flying back a hundred feet while plasma ricochet and falling debris turn your body into watery hamburger.) All the major economies are so entangled that they would do almost as much damage firing at themselves as at each-other!

There are only about a dozen countries that USA could possibly go to war against, all of which are at the bottom of the Economic Freedom Index. Those countries are already at war, with their governments brutalizing their "citizens" - a military intervention by the USA would only help put an end to the violence. You can look at South Korea as an example of what happens when USA goes to war and wins, and you can look at North Korea as an example of what happens when it doesn't. Since wars cost money and are unpopular, only the countries with tangible short-term economic potential (ex. oil) or an eminent danger of aggression (ex. potential of giving WMD's to terrorists) are candidates for regime change.

There are no benefits to being a "superpower", only responsibilities and costs - USA spends 4.7% of its GDP on the military, while the world combined averages 2.2%. This means Europeans can mooch off USA's spending, enjoy the benefits of global trade (not to mention R&D, etc), stay safe, afford more welfare statism for themselves, and then have the gall to insult and bite the hand that feeds them...

--libman

Re:Multibillion pissing contest

[Anonymous Coward]

Europe's biggest claim to Linux is Linus Torvalds being a Finn, but he has moved to California in ~1996, and is now a US citizen. (I too am a naturalized US citizen, having been born in the USSR.)

The history of UNIX is rooted in AT&T research, and later corporate America, and simultaneously Berkeley, MIT (and I don't just mean that silly GNU hippie), and many other US universities. Top contributors to Linux are American corps! Many contributions also came from English-speaking countries that are culturally closer to US than the US-bashing continental Europeans. Open source projects get contributions from all over the world, but you'll find very few important FLOSS projects where European contributors dominate over North American ones.

So, if you want to make it a contest...

North America has Microsoft (still 83% of Web clients), oldest and most popular UNIXen (BSD's, MacOS X, Oracle's sunset, RedHat, etc), Commodore / AmigaOS, EMC / VMware, BeOS / Haiku, Plan9 from New Jersey, old IBM / HP / DR / Honeywell / Apple / Novell OS'es, etc, etc, etc.

Europe has Nokia, Amoeba, a few obscure UNIX-like systems (MINIX, my dear native U-NAS (Soviet BSD fork), etc), and of course Atari. (Did SAP or Ericsson ever make any noteworthy OS'es? Did I miss anything?)

The contrast is obvious.

The point is that USA (and other national champions of Economic Freedom, most of which speak English and are merely small satellites [topic.ref.pun] orbiting around USA) presently constitute the world's leading civilization, and the bulk of Europe is secondary in its aggregate merit, benefiting from diffusional ("trickle down") benefits of USA's achievements. There's nothing wrong with that, and USA has always acted benevolently toward the Europeans, but when you engage in America-bashing you are in contradiction of solid inescapable facts.

--libman

Re:Multibillion pissing contest

[Anonymous Coward]

For smaller countries, not feeling dominated is not an option. Being pushed around by a hegemonic power far away may be preferable to being pushed around by bigger neighbours. This is apparent in the incoherence of EU "foreign policy" towards the US: whenever Germany and France move too fast for the others, others break ranks to have separate negotiations with the US. The dynamic is not fundamentally different from playing your big neighbours against each other, or forming coalitions, to maintain the local balance of power.

Re:Multibillion pissing contest

[Space cowboy]

As opposed to those that committed genocide within their own country and instituted slavery for another ethnic population, you mean ?

I'm not one to visit the sins of the father unto the Nth generation, I think actions are the responsibility of the individual/entity that does them. I don't think any other approach makes sense, so I don't blame the current US citizens for what happened in historical times. I also don't blame current Europeans for actions that happened donkey's years ago...

IMHO, if you do, you either have a chip on your shoulder, or you're nuts.

Simon.

Re:Multibillion pissing contest

[Anonymous Coward]

Yes it is a nose dive.

You are parroting communist "ripe for a revolution" propaganda without the slightest comprehension of what you're saying. Here's the objective reality: all governments always use violence to gain and retain power, it's just a matter of degree. If you were to look at the big picture and graph the amount of violence, you'd see that it has been on a gradual decline.

USA has committed much violence in conquering land from the Natives (who were even more violent amongst themselves - violence in pre-capitalist cultures is unavoidable), crushing dozens of rebellions and secessionist movements you've probably never heard of (especially if you went to "public school"), and of course slavery and the Civil War (fought primarily not to end slavery but to resubjugate the South). The bloodiness of European history (including their other colonies) is orders of magnitude greater. But, as governments stabilize, their motivation for overt violence decreases, as does their ability to do things covertly - why kill when you can tax?

Years back there were rumours about rogue CIA idiots torturing people in Central America - some believed it, but most didn't, and those that did believe mostly didn't think it was standard operating proceedure.

Communists took over much of Eurasia and killed tens of millions of people through direct action, while billions of people's lives were diminished indirectly, resulting in less freedom, lower quality of life, lower life expectancy, and lower attainment. (My (grand)parents were among their victims, both directly and indirectly.) The commies want a World Revolution, and have done much to sponsor violent Communist uprisings in every part of the world, including Latin America.

USA was the only significant power that could stand in their way, propping up less tyrannical governments that offer much more respect for individual Rights. Just compare a country where anti-Communist interventionism was a success (ex. Chile - soon to be one of the world's wealthiest nations) to one where it was a total failure (ex. Cuba)... Yes, some Communists were killed in the process - revolutions aren't fought with water-guns you know. Killing an active Communist is a legitimate act of self-defense!

And, yes, there were a few innocent victims as well (perhaps 1/10,000th the number of innocent victims created by communists). If you don't want to become an "innocent victim" for either side, don't stand within a smartbomb blast radius of a commie!

Then Baby Bush made it very clear that torture was now fully accepted as a tool and not an atrocity for the first confirmed time in the USA since the American Revolution.

All governments torture when they have something to gain from it. Not all governments do it as infrequently and as by-the-book as USA does. Of course sometimes it doesn't go by the book, but still - you have to look at degrees. Base your arguments on numbers and logic, not feelings and polemic slogans. Iraq after Saddam's fall is a less torture-prone place than it was before, and in another decade the improvement will be even more significant.

That's just one thing, abducting other countries citizens for torture (extreme rendition) is another, so that's a reputation loss that far exceeds Reagan's "bombing starts in 15 minutes" moment or anything Nixon ever did.

It seems that in your version of history only recent Republican presidents engage in violence, the more recent the more evil. Many US presidents are responsible for violence on a massive scale, from Washington to Bloody Abe to Wilson to FDR and

Re:Multibillion pissing contest

[Anonymous Coward]

As opposed to those that committed genocide within their own country

The word "genocide" means the desire to kill all people based on an ethnic criteria. Actual genocides are very rare in history (there's more profit in slavery, taxation, or ransomed expulsion), and USA has never committed "genocide" of any sort!

There have been wars with some Native tribes, but there have always been tribes that weren't at war, and Native individuals who have assimilated and lived among the general USA'ian population. (If only my Jewish ancestors had historically been treated as well in Europe as the Natives had been under Uncle Sam...)

Don't get your history from monochrome Hollywood, or from left-wing race-baiting propaganda - read credible sources! You'll find many examples of European settlers and the natives getting along just fine, trading for mutual benefit, or the settlers making alliances in wars where Native tribes were fighting among themselves, etc.

Some tribes had no concept of Property Rights, and they at times broke agreements and/or raided peaceful settlers. Some settlers took revenge without distinguishing one tribe from another... Peace is a very precious thing between cultures that are so different... Cultural integration has always been difficult, in every part of the world...

and instituted slavery for another ethnic population, you mean ?

USA didn't "institute" slavery - slavery has existed in every part of the world prior to the Industrial Revolution. Europeans enslaved Europeans for thousands of years, with Feudalistic institutions lasting well into the 19th century. Read up on the Arab slave trade -- which once also enslaved Europeans, and lasted from antiquity and well into the 20th century -- and compare their accumulated enslavement count to the post-revolution United States. There has been massive amounts of slavery internally in Africa, South Asia, East Asia, and elsewhere since the dawn of time!

You mean to say that USA has perpetuated slavery, in some states, from its inception in 1776 to 1865. (With slavery being just a small fraction of the economy of those states that allowed it, and those Slave States in total only representing about a fifth of USA's GDP by 1860.) This isn't much different from the time when slavery was phased out in other Western nations, and slaves further south of the United States (Cuba, Puerto Rico, Brazil, etc) had to wait decades longer to be freed...

I also don't blame current Europeans for actions that happened donkey's years ago... [...]

The difference is that the overwhelming majority of Americans have learned from their biggest historical mistakes, while, as the recent election in France demonstrates, many Europeans have not. Germany violates Speech Rights pertaining to discussion of National-Socialism, and, equally as sadly, many today if they could would defend it...

--libman

Triangulating position

[Anonymous Coward]

I love how position is often triangulated by connecting points to form something other than a triangle.

Re:Triangulating position

[Anonymous Coward]

Triangulation is downright childs play compared to using satellites to figure out where you are. You have to take into account general relativity, atmospheric distortion and variability of gravity to get useful coordinates, and even more processing and dgps stuffs can get you down to the cm/mm range.

Re:Triangulating position

[hawguy]

I love how position is often triangulated by connecting points to form something other than a triangle.

I thought the "triangulation" name came from forming a triangle between yourself and each remote point (and depending on the accuracy you desire, there could be many remote points)

It's not that you're drawing one big triangle on a map, you're using many (or at least several) triangles to known points.

Re:Triangulating position

[Anonymous Coward]

Supposing you're right, have you ever drawn a triangle with only two points in 2-D space?

Do you really need 4-5?

[mattr]

I wonder, since you can pretty much figure out what city you are in through ordinary radio and wifi beacons, not to mention the help you could get from having a clock and a sun locator, couldn't you really use GPS on the road with just two or three satellites?

Re:Do you really need 4-5?

[BradleyUffner]

I wonder, since you can pretty much figure out what city you are in through ordinary radio and wifi beacons, not to mention the help you could get from having a clock and a sun locator, couldn't you really use GPS on the road with just two or three satellites?

Not with any kind of accuracy. the math involved in GPS calculations requires specific known timings between highly synchronized systems. Those other sources may help you get a location fix more quickly, but they aren't going to help with accuracy.

Though I am fairly sure you can get a positional fix with just 3 satellites, not 4. The 4th is required if you want altitude along with it.

Re:Do you really need 4-5?

[Anonymous Coward]

No. 3 distances are sufficient for a 3D positional fix including height. The 4th satellite is required is to sync the atomic clocks to determine the correct distance from receiver to the satellites.

Re:Do you really need 4-5?

[Anonymous Coward]

No, 2 sats give you a massive sphere of possible locations. It would be able to tell you what hemisphere you are in, maybe. 3 narrow it down to a smaller region, but still not a point in 3d space. 4 gets you to a single point 'in a perfect scenario' which isn't technically possible, so you get a fair amount of error. You start getting a good accurate position when you float about 6 overhead at good separation from each other, if several of them are to close together or near the horizon you start going to shit again.

If you want 3 meter resolution without military grade equipment you're going to want 10 or more to deal with all the various environmental factors that introduce error into the system. Its fairly difficult for a 12 channel receiver to stay accurate with all channels connected without ground based augmentations ( WAAS)

Re:Do you really need 4-5?

[feedayeen]

All the equipment you listed is either more expensive, less precise, or not global; and triangulation in 3d space does not really work that way. Using just 2 satellites, you would get a circular area of possible positions, of which 2 would intercept the surface of the Earth and most likely the other would be far from Europe, but you lose altitude measurement and consumer products using the technology will not be reliable outside of Europe. An argument can be made that 3 is sufficient and most GPS devices would be smart enough to ignore the second point ~50K miles from the Earth.

Re:Do you really need 4-5?

[bertok]

You also need to solve for time. Quartz oscillators aren't precise enough for a fix to within even kilometers, let alone meters.

Re:Do you really need 4-5?

[feedayeen]

You also need to solve for time. Quartz oscillators aren't precise enough for a fix to within even kilometers, let alone meters.

I hadn't considered that we could use the 4th signal this way... that's really quite brilliant.

Re:Do you really need 4-5?

[Anonymous Coward]

You are not thinking three-dimensionally.

One distance lets you know you are somewhere on a sphere with the centre at the satellite.
Two distances lets you know you are somewhere on a circle (the intersection between the two spheres).
Three distances lets you know you are in one of two point (the intersection between the three spheres, or rather, one sphere and a circle).

Ergo, you need four distances to know where you are.

Re:Do you really need 4-5?

[Anonymous Coward]

If you need an extra satellite in order to figure out if you are above or below the satellite's orbit you are doing it wrong (hint: if you are using GPS you are almost certainly below, your mobile phone is unlikely to work in earth orbit anyway, should you be so silly to take it with you).
As others have said, the 4th is needed to "locate" you in time.

Re:Do you really need 4-5?

[gnasher719]

I hadn't considered that we could use the 4th signal this way... that's really quite brilliant.

If you had a super precise clock, you could use GPS with only 3 receivers. 1 ns error in the clock = 30cm position error. 1 microsecond = 300 meters.

Because you don't have that super precise clock, you need four satellites. You read the time stamps from each signal, but because you don't know the actual time precisely enough, you only know "I'm x nanoseconds closer to satellite A than satellite B, and y nanoseconds further from satelitte C" and so on.

Even a single satellite would give you a rather precise clock (you know you are about 20,000 to 40,000 km away, no matter where you are, so take time stamp + 0.1 seconds, and you have 0.05 seconds precision), which is why it is quite surprising that I have to set the time on a TomTom manually. Of course with four satellites you know your time within a few ten nanoseconds.

Re:Do you really need 4-5?

[mattr]

OP of this thread here.. Thanks for your reply. Perhaps I am off base, but checking again with wikipedia I understand that the point is the user is in a locus that is an intersection of spherical surfaces, the spheres being centered on the gps satellites. If you are not carrying an atomic clock of your own, you satellite 1 for that. Then sats 2 and 3 give you an intersection locus that is a two-dimensional circle intersecting the Earth. The intersection of circle and Earth gives you two possible points you may be at. While you ought to have a sat 4 to get just one 3D point, actually instead of sat 4 you can use information you have like your elevation or inertial navigation. I was thinking that solar observation, accelerometer, wifi dictionary like google has, knowing your phone's country code, or sheer common sense would be enough to detect which of the two cities you are in. Does GPS work this way, and since wifi is not always available what would you say the resolution would be in case of 3 sats plus knowing your country and route (giving you general altitude and part of the world)?

Re:Do you really need 4-5?

[Anonymous Coward]

We actually have a project in my Numerical Analysis class about this very subject. 3 satellites wouldn't be enough due to having a undetermined system of equations that wouldn't allow for you to solve for time.

http://www.math.utah.edu/~pa/5610/tp
and the PDF that describes the project, and more specifically this problem(exercise 16) http://www.math.utah.edu/~pa/5610/tp/tp.pdf

Smartphones already use both GPS and GLONASS

[Anonymous Coward]

Once Galileo and Beidou are... what happens?

No GPS???

[Anonymous Coward]

Europe has been without GPS this whole time?! Or am I reading this wrong?

Re:No GPS???

[rbprbp]

Hint: the G in GPS means global for a reason.

Competition is never redundant

[Anonymous Coward]

Competition is never redundant, and EU is trying new things with their GPS systems.

The GPS system the US built hasn't been improved for a decade, they haven't blocked spoofing of civilian signals, yet they did for military ones. EU wants to have its own system and they'll expand the features list independently of the USA. This in turn will causes the USA to improve its system. So we'll all get more accurate GPS and less prone to spoofing and interference.

Besides, the USA is run by nutcases, what if one of those nutters decides to defund GPS because God told him to??

http://bostonherald.com/news/us_politics/view/20121006congressman_calls_evolution_lie_from__pit_of_hell
Republican Paul Broun is on the Congressional science committee BTW.

living in US, glad there's alternatives

[Anonymous Coward]

To give the US power like that is ridiculous. At any given time the US could turn off GPS systems and no one in the world would have access to them. That's a scary though considering the US's militaristic past that is borderline (or beyond) grotesque

Failzor5.

[Anonymous Coward]

BSD'S FILESYSTEM United States of users. BSD/OS worthwhile. So I

Survey quality GNSS systems

[goatbar]

Apparently, there are units available that will track 120 simultaneous channels across all the available systems (this comes from Dave Wells). Not having a unit in my possession (and never having messed with Rinex before), I'll have to take his word for it.

Triangulation vs Trilateration

[Anonymous Coward]

I would have originally insisted that the GP was correct, because I believed that GPS uses triangulation to determine location. Two intersecting lines would give a 2D position, three intersecting lines would yeild a 3D position, etc.

I clicked through your links and was confused because they have two different reasons for having 4 satellites. The first describes the geometry of four intersecting spheres, the second explains that a fourth satellite is required in order to synchronize timing for accurate distance measuring.

It appears that my assumption that GPS uses triangulation is wrong. It uses trilateration. In triangulation, you use the angle of the lines to determine where they intersect. With trilateration, it is the length of the radius (the distance to the satellite) that is used to calculate position, but the Wikipedia example diagram only requires three spheres.

So I'm still left confused and too tired to sort it all out. Is the fourth satellite a solution to a geometric problem, or a timing/measurement/accuracy problem? If it's a timing problem, why does the fourth satellite need to be the timekeeper?

Re:Triangulation vs Trilateration

[Jane Q. Public]

" Is the fourth satellite a solution to a geometric problem, or a timing/measurement/accuracy problem? If it's a timing problem, why does the fourth satellite need to be the timekeeper?"

Haha! A thoughtful and good question, and from an AC. No offense meant.

The other people in this thread would have you believe that #4 is necessary geometrically. But -- as I have been trying to explain -- that is simply false.

You are quite correct that it is a timing issue. The civilian GPS signal is not very accurate, so civilian manufacturers use a 4th satellite to correct for timing, which results in a fairly accurate position from a system that was designed (quite intentionally) to be rather rough for non-military receivers.

This was actually quite clever on their part. But it is the sole reason for the 4th satellite.

The encrypted part of the GPS signal is far more accurate. The military (well... military contractors) designed it to work robustly with only 3 satellites. There is NO geometric problem here... you are getting transmissions from 3 satellites that know their own positions in time and space... therefore you know your position. In full 3D. With only 3 satellites.

Once again: the 4th is only necessary for civilian operation, to correct for the sloppiness of the civilian-receivable GPS data. There is no geometric need for a 4th position.

Re:Triangulation vs Trilateration

[FireFury03]

If you know the distances between yourself and 3 satellites then you can trilaterate your position. However, with GPS you don't know the distances, or even the transit times (from which the distances could be trivially determined), you only know the time the signals were sent and the time offsets at which you received them (i.e. you know you got satellite A's signal Xmicroseconds after satellite B's). This is not the same as knowing the transit times, since you don't have a clock accurate enough to tell you the actual time you received the signals. So you need a 4th satellite in order to produce this extra piece of data. This is GCSE level maths - if you have 4 unknowns you need to solve 4 simultaneous equations in order to find them.

Re:Triangulation vs Trilateration

[FrangoAssado]

There is NO geometric problem here... you are getting transmissions from 3 satellites that know their own positions in time and space... therefore you know your position. In full 3D. With only 3 satellites.

That's not how I learned it, but I want to change my mind on this if you're really right. But if what you're saying is true, then what exactly is wrong with the following reasoning:

The GPS receiver gets signals from 3 satellites telling the exact time and position of each satellite at the exact moment the signal was sent. Let's call (xi,yi,zi,ti) the position ant time of satellite i (i=1,2,3), and (x,y,z,t) the position and time of the GPS receiver when the message was received. We want to find out the position of the GPS receiver, that is, x, y and z (we don't care about t).

From the data we get from the satellites, we can make an equation like this for each satellite:

sqrt((xi-x)^2 + (yi-y)^2 + (yi-y)^2) = c*(ti-t)

Where c is the speed of light, and i is the number of the satellite (i=1,2,3). This equations simply says that the time it will take for the signal to leave the satellite and reach the receiver, multiplied by the speed of light, is equal to the distance between the satellite and the receiver.

Now, we have 3 equations and 4 unknowns (x,y,z,t). Granted, we're not interested on the value of t if all we care about is position. Still, if you allow t to be free, there are an infinite number of possible values for (x,y,z) that satisfy these equations. Obviously we can discard a lot of silly values for t, like any value less than any of the ti (i.e., the time the signal was received must be later than the time it was sent), and also t can't be much more than any of the ti (i.e., we know the satellites aren't to too far from the receiver). Which means you can get a range of possible values for (x,y,z), but that's not very precise.

If you have 4 satellites, however, there's only one solution (x,y,z,t) for the system of 4 equations.

So, in the end: what's wrong with this reasoning? Or, alternatively, What extra information the GPS satellites could send that would change things?

(By the way, the method I described is -- possibly -- the easiest way to describe the problem, but not the way it's usually stated. See for example this paper for a more realistic approach)

Re:Triangulation vs Trilateration

[FrangoAssado]

Erm, I messed up the equation. It should be:

sqrt((xi-x)^2 + (yi-y)^2 + (zi-z)^2) = c*(t-ti)

That doesn't change the reasoning, though.

Re:Triangulation vs Trilateration

[fa2k]

How about if you require t1 = t2 and t2 = t3 ? Then you have five equations and four unknowns.Maybe this would break due to special relativistic effects.

Re:Triangulation vs Trilateration

[fa2k]

Oh, right, ti is the time at which the signal was sent, sorry.

Assume you know the difference in time between the receipt of the signals, you can solve for the time at which the second satellite sent the signal.
The receipt time difference
dt1i = ti' - t1'
Where t1', ti' is the time when you received the signal i, on some arbitrary clock.
Then this is the equation for t2:
t2 = c*sqrt( (x-xi)^2 + (y-yi)^2 + (z-zi)^2 ) - c*sqrt( (x-xi)^2 + (y-yi)^2 + (z-zi)^2 ) + dt12.
This second order equation in lets you solve for either x,y or z as a function of the other y and z. Now do the same for satellites 1 and 3, and 2 and 3, and you have two more equations.

  Does that make sense?

Re:Triangulation vs Trilateration

[fa2k]

Now do the same for satellites 1 and 3, and 2 and 3, and you have two more equations.

Only two equations. Strike that "2 and 3"

Re:Triangulation vs Trilateration

[FrangoAssado]

You can't set constraints to these values, they're determined by the relative positions between the satellites and the GPS receiver.

You will only have t1=t2 when the distance between the satellite 1 and the GPS receiver is the same as the distance between the satellite 2 and the GPS receiver.

Re:Triangulation vs Trilateration

[jo_ham]

How about if you require t1 = t2 and t2 = t3 ? Then you have five equations and four unknowns.Maybe this would break due to special relativistic effects.

It does. The clocks in the satellites themselves have to be continually adjusted to account for relativistic effects. That's what the GPS master ground station is for. You can't assume they are all the same.

Re:Triangulation vs Trilateration

[fa2k]

Ah bloody hell there's so much wrong in my post. I think the idea is valid, that you can use the difference of time between when the signals were received as an additional constraint. The quadratic equations have a two-fold ambiguity, so I don't know if both solutions would be physically valid, but at worst you've narrowed your position down to one of two (maybe four) points in 3D.

Re:Triangulation vs Trilateration

[FrangoAssado]

I don't understand what you're trying to say; all the signals are received at exactly the same time (which I called t). If you receive the signals at different times, than the whole thing doesn't work, because then the relative positions of the satellites will have changed -- and the whole point is to use the relative positions of the satellites to determine your position.

As for the rest of what you wrote: no amount of manipulation on the equations can change the fact that you have only 3 independent equations and 4 variables. Any equation you derive by manipulating the initial equations (by substituting variables, etc.) will not be independent, so it changes nothing.

But if you want to play with GPS equations, I suggest reading the paper I linked to. It has the equations that are actually used by GPS devices; what I wrote is a simplified version just to show an overview of how the process works.

Re:Triangulation vs Trilateration

[gnasher719]

I don't understand what you're trying to say; all the signals are received at exactly the same time (which I called t). If you receive the signals at different times, than the whole thing doesn't work, because then the relative positions of the satellites will have changed -- and the whole point is to use the relative positions of the satellites to determine your position.

Not a big problem, if the times are close together. If you receiver four signals at t, t + 1 microseconds, t + 2 microseconds, and t + 3 microseconds, then even the last satellite has only moved for 3 microseconds, just a few centimetres.

Re:Triangulation vs Trilateration

[FrangoAssado]

Right, in practice it doesn't matter. In practice, there are all lots of sources of errors, and if you try to naively solve the system of equations I wrote, you'll find no exact answer, because of these errors. And that's not even considering that, depending on the relative positions of the satellites, the equations might not even be independent (e.g. if all satellites are in the same plane, which is very unlikely, but can happen). The best you can do is to find the best approximation (i.e., the point that most closely satisfies the equations). A good way to do that is discussed in the paper I linked to.

Re:Triangulation vs Trilateration

[Jane Q. Public]

"You can't set constraints to these values, they're determined by the relative positions between the satellites and the GPS receiver."

But this is what everybody keeps forgetting: it isn't just a timing (distance) signal. You have more information than that. The relative positions of the satellites themselves are known.

Remember that the solution to each of the timing equations is not a line or a circle, but a surface. At the intersections of the 3 surfaces, you may technically have an infinite number of solutions, but in practice they will all fall within a certain range.

Granted, you will improve your accuracy with more satellites (and as you say, if they were all in a plane relative to you, that would introduce complications.) But my point was that as a practical matter it is theoretically possible with only 3... within certain limits of course. Many here seem to think I did claim it was perfect, but I have explicitly stated several times now that you will clearly get better results with 4.

Re:Triangulation vs Trilateration

[Jane Q. Public]

"You can't set constraints to these values, they're determined by the relative positions between the satellites and the GPS receiver."

Additional information:

My memory was roughly correct about the civilian "4th fix" to improve the accuracy of GPS. But it wasn't perfect. What I did not realize -- or remember -- is that this 4th input is typically a ground installation (the U.S. Coast Guard maintains a nationwide set of longwave transmitters), which sends out a corrective signal. So it is in fact used by the military. I must assume that the situation is similar in Europe and other places.

So the discussion involving whether 4 satellites are necessary is rather moot, since their positions are actually calculated precisely by ground-based stations, and the 4th, ground-based signal(s) correct for variances.

Re:Triangulation vs Trilateration

[FrangoAssado]

But this is what everybody keeps forgetting: it isn't just a timing (distance) signal. You have more information than that. The relative positions of the satellites themselves are known.

Did you see the paper I linked? It uses exactly this idea (the relative positions of the satellites) to do the calculations, completely eliminating the need to worry about time. Still, this reduces the number of equations from 4 (one for each satellite, involving position and time) to 3 (involving only position). But if you begin with only 3 satellites, you end up with 2 equations involving only position, which consists of 3 variables (x,y,z). So, I still don't understand how you can calculate the position of the receiver with only 3 satellites.

About differential GPS: from what I understand, you still need 4 satellites in addition to the ground station. The ground station just broadcasts the difference between the signals received from the satellites and the signals you'd get if there were absolutely no errors (it can do that because it knows its exact location and also the trajectories of the satellites). This information can then be used by GPS receivers to correct their readings and improve accuracy. That's still not perfect, because the corrections are exact only at the exact position of the ground station; so the farther you are from the station, the worse the correction gets (still, Wikipedia suggests that the corrections are still useful hundreds of miles away from the ground station).

It's interesting to note that initially, differential GPS was used to completely bypass the signal degradation that was built in the GPS system (the satellites used to intentionally introduce random errors in their time signals, a "feature" called "selective availability"). The differential GPS correction was so successful that "selective availability" became pointless, and in 2000 the US decided to stop degrading the GPS signal.

Re:Triangulation vs Trilateration

[Anonymous Coward]

The three equations from the timing difference, which do not depend on the local time anymore, are not independent. Two of them give you all the information you can get from them. The third does not add more information because combined with the other two it ends up saying 0=0, i.e. a tautology. Sit down with a piece of paper and a pen and do the math. Put three satellites where you want them, calculate the time it takes for their signal to arrive at a chosen location and try to derive that location from just the known satellite positions and the time differences between the three signals. It is impossible, and anyone with an elementary understanding of algebra can see that it is impossible, but if you can't see it yet, perhaps you need to go the hard way and attack an impossible problem.

I don't know why you insist on explaining something that is obviously and - in the absolute mathematical sense - provably wrong. Also note the difference between accuracy and precision. You need the accurate local time, which is a much more difficult problem than having precise local time information. A clock with 100 microsecond accuracy is exceptionally good. A good quartz timer is much worse. Light travels 30 kilometers in 100 microseconds. You do not get usable 3D location information without 4 satellites. It is not a matter of "improving accuracy". A 3D signal without a fourth satellite or an extraordinarily accurate local clock is useless.

Re:Multibillion pissing contes

[Serious Callers Only]

The EU sees the US as far less trustworthy than you do, and expects to come into conflict with it again - war is unlikely but economic and policitical spats are quite common between the two. In addition to that galilleo lets them have greater accuracy than the US will allow with GPS, and ensures that they don't have a strategic dependency on the US in space.

Strange how myopic and solipsistic the view from the US is sometimes.

Satellites are being replaced

[dutchwhizzman]

GPS satellites are already being replaced. So far, three IIF sats have made it into orbit. As usual with US military operations, things happened late and extremely over budget, but things are happening and the chance that the system fails due to not enough operational sats is rather small.

scientific reasoning?

[dutchwhizzman]

Just quoting someone else without knowing what you are talking about doesn't make you right. Come up with scientific reasoning using trigonometry and publicly available specs for GPS to prove your point, or keep your mouth shut, please.

Triangulation (without altitude) works with three points if you have one unknown transmitter and three known receivers. This is the other way around. Using just two receivers would give you two possible locations, without altitude. The other way around, in a real life situation with moving sats and a round planet, you need more data sources to get anything near to accurate results. It may very well be that given enough time, you can get somewhat accurate lat/long information from just 3 transmitters, but you'll be suffering to get altitude positioning correct if they are all in more or less the same horizontal plane. The trajectories of GPS sats are such, that you will in practice need more than three sats to accurately determine your position and still have global coverage with less than 30 sats orbiting the planet.

So in theory, using one location and stationary sats, aided with other navigational means, you may be able to get lat/long with just 2 sats and alt with 3, but in practice, you need 4.

Re:scientific reasoning?

[Jane Q. Public]

It doesn't work by "triangulation", dimbulb.

Jesus, spare me.

Re:scientific reasoning?

[gnasher719]

Just quoting someone else without knowing what you are talking about doesn't make you right. Come up with scientific reasoning using trigonometry and publicly available specs for GPS to prove your point, or keep your mouth shut, please.

People who think they know everything are pretty annoying to those who actually do :-)

GPS doesn't use triangulation. There is no way for a receiver to determine what direction a satellite signal is coming from.

The satellite has an atomic clock. It transmits a time signal at 1 MHz frequency (but because of doppler effect you receive each satellite at a different frequency, which is why non-assisted GPS takes so long to work when you turn it on: It doesn't know where and when it is, so it doesn't know at which frequencies to expect signals, so it has to scan they whole band around 1 MHz for multiple very weak signals). The signal is digital, and a good receiver detects edges of the signal with 10 ns precision.

So the receiver gets n timestamps from n satellites with good precision. The other bit of information that it has is the exact path that each satellite is following and where it should be at any moment in time. A single timestamp gives you the real time within 0.1 seconds (making the assumption that you are on earth), and that gives you the satellite positions within a kilometer (since they are moving at finite speed), so you can position your n satellites in space roughly.

Now if you had time within a few nanoseconds, each timestamp would tell you within a few meters your distance from one satellite (and you would now know the satelitte position with very little error as well). But you don't have that time. So you take two timestamps, and you know "the distance to satellite A is x meters more/less than the distance to satellite B". One satelitte - you have nothing. Two satellites - you know you are on some curved plain. Three satellites - you are somewhere on some curved line. Three satelittes plus assuming you are on the surface of the earth - there are two points where you could be. But climb on a ladder, and you get it wrong. Four satellites - you know where you are.

Difference between general theory and practice

[jandar]

With 3 satellites there are 2 possible solutions to the equations. Since we know we are on earth and not in space one solution can be discarded. So in theory 4 satellites are required in practice not.

Re:Difference between general theory and practice

[Jane Q. Public]

"With 3 satellites there are 2 possible solutions to the equations. Since we know we are on earth and not in space one solution can be discarded. So in theory 4 satellites are required in practice not."

I mentioned this myself elsewhere. But as you of course know, one of those solutions is clearly nonsense, so there is no ambiguity.

Re:Difference between general theory and practice

[jandar]

"With 3 satellites there are 2 possible solutions to the equations. Since we know we are on earth and not in space one solution can be discarded. So in theory 4 satellites are required in practice not."

I mentioned this myself elsewhere. But as you of course know, one of those solutions is clearly nonsense, so there is no ambiguity.

This exactly what I said: one solution is nonsense. Your explanation I have read only afterward otherwise I hadn't wrote mine.

Re:Multibillion pissing contes

[Anonymous Coward]

GPS has a civilian and military accuracy. In order to get the military accuracy (and bomb the correct buiilding) you have to have the greenlight from US command. Ths US also has a limited ability to reduce the accuracy dramatically in selected zones. Europeans do not want to rely on a system that can be turned off whenever it fits US agenda.
 
This is not about a EU-US war, this is about the ability to have an independent diplomatic and military stance. I do believe that this is in America's best interest : it allows a diplomatic roleplaying game of good cop/bad cop.

Let's go one satellite at a time...

[Sanians]

Let's go one satellite at a time...

First satellite: You know approximately what time it is because the satellite tells you. You know the position of the satellite, and all of the other satellites, because it tells you in its signal. However, you don't know how far away the satellite is because you don't know the difference in time between when it sent its signal and when you received it. Thus, while one satellite tells you a lot, it does nothing at all to narrow down your position.

Second satellite: Now you know the difference in time between when you heard the two satellites, and thus, you know how much further you are from one of them than you are from the other. So in 3D space, you can use this information to narrow down your position to a point that lies on a sphere. This sphere intersects the earth, forming a circle. Thus, you know a lot of place where you might be, but you still really don't know much.

Third satellite: Now you're able to cut that huge sphere down to a circle. Where this circle intersects the earth, are two points. One point is flying around at high speed, the other relatively stationary. Thus, you kind of know where you are now. ...but only kind of. While the earth is a sphere and we intersected that with a circle to get two points, the places on the earth you might be aren't an infinitely thin mathematical sphere. There's thousands of feet of elevation in which you might exist. ...and worse than that, even if you don't care to know your elevation, the intersection of that circle with the atmosphere isn't straight up and down -- it's at some bizarre and slowly changing angle -- thus you can't ignore it because it isn't just your elevation you don't know, but rather, you're equally uncertain about your latitude and longitude. You know your position to within a mile or so, but if you want to be more accurate than that, you need to either know your elevation or find another satellite.

Fourth satellite: That circle of possible locations is now narrowed down to two points. One is flying randomly through space, the other is near earth. You don't even need to find an intersection with the surface of the earth, unless by some odd chance you're having difficulty figuring out which of those two points is you.

Fifth satellite: No longer any questions, you know exactly which point is you. ...but still, the math is only narrowing you down to about a 10 ft. radius...

Sixth satellite: ...and so it's nice to have some additional data to average together for a slightly more accurate result.

Seventh satellite: ...and it's nice to have some spares for when some become obstructed by trees or tall buildings.

Re:Let's go one satellite at a time...

[the_other_chewey]

That's a fantastic explanation, thank you for writing this.
Bookmarked for future use.

Re:Let's go one satellite at a time...

[Anonymous Coward]

It would be a nice explanation. Unfortunately it's not correct. It's all good until this part:

Second satellite: Now you know the difference in time between when you heard the two satellites, and thus, you know how much further you are from one of them than you are from the other. So in 3D space, you can use this information to narrow down your position to a point that lies on a sphere.

The set of points such that the difference between the distances to the two satellites is constant isn't a sphere. How to see this? Any point in space that satisfies the condition can be rotated around the axis through the two satellites. Since this doesn't change the distances to the satellites, the rotated point still satisfies the condition. The connection between the satellites is an axis of symmetry of the point set. There is one point on the axis which satisfies the condition: If the distance between the satellites is d, the point at distance d/2-a/2 from the first satellite is at distance d/2+a/2 from the second satellite and thus satisfies the condition. Since there are other points that satisfy the condition, the suspected sphere can't have radius 0. Together with the symmetry this tells us that there has to be a second point on the axis that satisfies the condition, but there is no such point, so the set of points can't be sphere. (Special case: a=0, you get the same time signal from both satellites at the same time. This puts you on a plane perpendicular to the axis halfway between the satellites.)

So what is the shape of the point set satisfying the condition? It's a hyperboloid.

Re:Let's go one satellite at a time...

[Anonymous Coward]

Good explanation, for the case when the receiver doesn't have its own atomic clock.

If you have an atomic clock though, things gets easier.

One satellite: You know where it is (it says so) and from the timing difference you know how far from it you are. So you have a spherical shell. If you know you're on a boat (one of the few mobile platforms big enough to bring an atomic clock with negligible effort) then it gets even better. The shell intesects the sea as a ring, you're somewhere on that ring. The ring is usually enormous. If you wait for a while, the satellite moves. The new ring interesect the old one in only two places. So one satellite might do - if you're on a ship and have time to wait.

Two satellites: Both satellites gives you spheres, they intersect as a ring. Most of the ring moves wildly - if you aren't in space then you know you're on the small part of the ring that doesn't move at satellite speed. Even better if you're on a ship, the ring intersect the sea in two places and only one place stands still.

Three satellites: You get two positions, you usually go for the one that doesn't move around at orbital speed. If you actually are in space, you go for the position that best matches the acceleration you undergo. One of the spots will likely be very wrong, with an unrealistic trajectory.

Four satellites usually resolve any ambiguity. Unless you have a "bad constellation", such as all the satellites lying on a line. Which is a good reason for wanting much more than four birds up there. Using a gps in a canyon sometimes force you to see only satellites on a line - and you get wild inaccuracy even though you have five or six satellites visible.

Re:Let's go one satellite at a time...

[Anonymous Coward]

Third satellite: Now you're able to cut that huge sphere down to a circle. Where this circle intersects the earth, are two points. One point is flying around at high speed, the other relatively stationary.

I still have a track from 1992 where my GPS receiver recorded me moving at 1200 km/h in Cameroun instead of 5 km/h walking in Amsterdam. I guess this explains what mistake it made.

Re:Let's go one satellite at a time...

[Anonymous Coward]

Like others have mentioned, 4 Satellites are required as you end up with a under-determined system of equations and cannot solve for time.

See exercise 16 for a mathematical explanation. http://www.math.utah.edu/~pa/5610/tp/tp.pdf

GPS is scheduled for scheduled airline service

[Anonymous Coward]

GPS is not the primary means of navigation for airlines. It sees a lot of us in General Aviation, but not for scheduled airline service.

But it will be, "soon".

http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/

The FAA Global Navigation Satellite System (GNSS) Program Office provides satellite (GPS) based positioning, navigation, and timing (PNT) services in the United States to enable performance-based (RNP/RNAV) operations for all phases of flight from en route, terminal, approach, and surface navigation. PNT services are an essential enabler required to overcome the deficiencies in today's air traffic infrastructure and support implementation of the Next Generation Air Transportation (NEXTGEN) system for the United States' National Airspace System (NAS). The FAA's plan to provide PNT services requires implementation of two GPS augmentation systems, the Wide Area Augmentation System (WAAS) and the Ground Based Augmentation System (GBAS). Both systems improve the accuracy, availability, and integrity needed to support continuous all-weather use of GPS as a primary means of navigation and automated dependent surveillance (ADS-B) within the NAS.

"GPS as a primary means of navigation ... Within the NAS".

OMG, Russian rockets in our hemisphere!

[Shag]

Quick, notify JFK, Romney, Limbaugh, and whoever's hosting "Coast to Coast" these days.
This calls for derp-rage.

It will be just like Europe

[Anonymous Coward]

As opposed to its US counterpart, the Galileo network is slated to only work when it feels like it, so generally not in the summer months. Additionally, some of the other satellites are going to have to constantly bail the others out or risk them taking out the whole network.

Money isn't everything, but it's close

[Anonymous Coward]

Ask yourself: Why do European countries give in to US military requests so much, despite citizen disapproval? Quid pro quo. Military technology, bases, the big missile defense shield program flow to Europe. It pays for those things with military support for arbitrary wars that keep the money flowing into the military and defense industry on both sides of the pond.

Don't think for one second that there is a good guy to be found on either side.

Problem is...the US hasn't learned it isn't in their best interests to push their agenda or go to war all the time. Given what is more likely, the US would definitely attack Europe if it had an economic incentive to do so. Russia would do the same for pride despite itself.

What could the EU do? Just sit in committees for the over site of the Lunch scheduling office and declare it's ideas unhealthy while Rome burns around them.

Incorrect.

[Anonymous Coward]

In agriculture GPS guidance systems already have the capability of talking to Galileo when it is finished, and Glonass right now.

No. Wrong. Please never say that again.

These satnav devices are receivers. Only. No data is ever sent from them to the satellites. Instead, the chips triangulate position based on clock data received through transmissions from these satellites in known orbits.

I have interacted with more than one person who required over 10 minutes to be convinced that these systems could work without the device "talking to" the satellites. I just would like to do whatever I can to avoid the spread of this misinformation, if only to avoid having more of these wearying discussions with ignorant people.

Thanks for pointing that out...

[Sanians]

I really suspected it wasn't a sphere, but my brain power wasn't able to imagine what the correct shape would be, so I'm happy to finally know.

Still, absent that mistake, the explanation is essentially correct. Second satellite makes the set of possible locations a 2D surface, third satellite reduces it to a line of some sort, fourth cuts that down to two possible points, etc. So three satellites still isn't sufficient for a 3D fix.

launched on a russian rocket since arianne and the

[KingBenny]

esa have no real failproof record. i'm paranoid again i know but if they can't deliver a payload into orbit without external help where did the tek for a global tracking system come from ????

Re:Good to hear..Yah, and when it fails???

[rhalstead]

Unfortunately the US chose to have no ground based back up to GPS and I assume the EU will go the same way. One major Coronal Mass Ejection (CME), severe meteor storm, or even EMP and we'll all be without navigation signals. We (in the US) had an ideal back up in the new Enhanced, or E-Loran, but that was scrapped and the equipment (including antennas) immediately destroyed. Non Directional Beacons (NDBs) which are very simple, but require a little skill and practice to use are already being phased out and the VORs are also scheduled to be decomissioned. Many airports, at least through class C require GPS for instrument approaches. If we are going to get hit by a major CME I hope it's before they get all the ground based backups decommissioned. One other point: Beyond a certain point additional satellites gain you little in accuracy. My question is why do people with consumer devices want more accuracy? With the current number of US satellites it can tell you where you are on a taxiway within 15 to 20 feet and that is without the additional, high accuracy ground based augmentation transmitters. GPS is not infallible. It has failed for a few hours a couple of times. It is also not immune to interference, or even strong signals a few channels off to the side, or even farther. Fly or drive in the SW US and you'll see what I mean. It is not a good system for putting all your eggs in one basket.

Thanks for pointing that out...

[Sanians]

I posted this yesterday, but somehow posted it in reply to my own message by mistake.

Naive Tossers

[Anonymous Coward]

Top comments on this one are by a bunch of naive tossers who failed to comment on the sole reason this system is going up in the air: Control of the system in case of war.