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GPS III satellites and ground station projects get even later as costs gently spiral

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I remember OCX

from my Visual Basic days. Ah, happy memories when things like security were non-existent !!!

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Remembers OCX blowing up.

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Do you have any idea how GPS works?

"Broadly speaking, in Raytheon’s words, the ground system which collates signals from the satellites to deduce the user’s location is the 'brain of the entire GPS system'."

Raytheon didn't say anything like that (okay, the actual words in the quotation marks are correct, but that paraphrasing before that isn't.) The OCX system does not "collate signals from the satellites to deduce the user's location." An individual user's GPS receiver does that. This is kind of GPS 101 here...

The link to Raytheon does a pretty good job explaining what the OCX system is for; you might want to read it again, and pay attention this time. And Wikipedia can tell you all about GPS in general...

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Re: Do you have any idea how GPS works?

Indeed, I also have to constantly correct a very prevalant myth that somehow GPS receivers "transmit your location" to the satellites involved.

Er... no. It's a passive system. Though there is some emergency transmission systems piggybacked on it, you won't use that unless you're piloting a large cruise ship. Your TomTom doesn't go telling the GPS sats "WHERE AM I?". The sats are saying "It's this time here at Sat 1, it's this time here at Sat 2, it's this time here at Sat 3" and your little box listens and then does some clever sums to work out - depending on the time differences of those satellites - where it must be on the planet (it's called triangulation, people...)

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Re: Do you have any idea how GPS works?

"where it must be on the planet (it's called triangulation, people...)"

Perfect explanation of how GPS operates! But my inner pedant won't let "triangulation" pass. "Trilateration" is the three-dimensional geometric equivalent to two-dimensional geometry's triangulation.

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Re: Do you have any idea how GPS works?

Keeeerekt! Give dah man a ceegar.

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Paris Hilton

Re: Do you have any idea how GPS works?

@Lee D and Sir Wired 1

And that, folks, is the state of today's The Register. The ole gray mare just aint what she used to be.

Even Paris misses the old days.

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Re: Do you have any idea how GPS works?

Yeah, those piggy-backed Search and Recuse payloads may have been what confused the article's author.

Indeed, after following the link in the article it was this Search and Rescue bit which caught my attention, and prompted some googling on my part.

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Re: Do you have any idea how GPS works?

In this case, I think "ground system" means the expensive military device using tactical grade GPS signals. Just to be confusing, there are ground systems at accurately known positions telling the satellites where they are.

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Re: Do you have any idea how GPS works?

As a mathematician, I would have to correct and say that trilateration is done by the measurement of distances, triangulation by the measurement of angles (there's a clue in each word!).

Though you are correct that GPS is therefore trilateration, it has nothing to do with how many dimensions you use.

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Re: "ground system"

The OCX "ground system" is just the command and control system for the GPS constellation. Whereas the previous systems were located in just a few places worldwide, this new system seems to be intended for deployment to dozens (hundreds) of locations at various capability levels. You don't want *everyone* to have the capability to turn the sats on and off and alter their orbits.

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Re: Do you have any idea how GPS works?

have you heard of SBAS...

seriously more information is not a bad thing...

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Anonymous Coward

Re: Do you have any idea how GPS works?

I do.

The ground stations help to make sure that the satellites are in correct orbit and position. Which is important so that your phone's GPS can give you a reasonable approximation.

(Its not just the number of sats you can 'see' but also the clock in your phone.) The more sats and the more accurate your clock... the more accurate your position... within a certain degree due to atmospheric conditions..

If the sats move, then your calculations are off.

There are two things you can do.

Either move the sats back in to their fixed positions or adjust the coordinates and publish them for a more accurate fix. (Assume that the sats 'wobble' what then? )

Naval navigation can combine land based radio stations with GPS to get a good fix. Aircraft can do the same too.

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Boffin

Re: Do you have any idea how GPS works?

Sorry Lee, had to down vote you.

You forget to mention that all of the clocks in the satellite are synced.

So at time T, each sat broadcasts the time and based on your distance from the geo stationary sats, the signals will arrive at different times. So that you can triangulate your position by knowing the fixed positions of the sats and the deltas in the clock signals. (All signals travel at the same speed, c. )

Its not the time differences, but the deltas for the same time signal to arrive at your location.

A small nit, but a big difference.

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The irony that they can't pin point an end date for a system they will use to pin point locations.

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Irony

It's the rocket science version of Heisenberg's Uncertainty Principle!

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GPSIII - mmm, does that mean your device gives you three possible locations for where you might be at any given time ? (just asking)

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"GPSIII - mmm, does that mean your device gives you three possible locations for where you might be at any given time ? (just asking)"

Strange you should mention that, as that's pretty much how the receivers correct their clock rate.

With four satellites in view they can calculate three possible positions, each position based on data from three satellites - since you can obviously only be in one place at a time, adjusting the clock rate to minimize the difference between the three calculated positions ensures the clock is running at the correct rate. This allows the receivers to provide accurate positioning with a cheap and simple clock chip, as opposed to needing an atomic clock.

Presumably the more satellites a receiver is tracking the more accurate this clock rate correction process is and hence the more accurate the final position calculated..

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Kernel - Thank you for that insight, it will however take me some time to tell my relatives about it.

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Anonymous Coward

I'll wait for GPS IV: The voyage home.

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FAIL

and modernizing software development processes. "

Oh dear.

Ada out, C/C++ in because it's hard to find good developers?

That's what LM told the DoD for the F35.

Then they sub contracted out a large chunk of the work to BAe.

Still, maybe they didn't do that in this case.....

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Joke

Re: and modernizing software development processes. "

<sarc> are you sure that javascript and java are now being substituted because developers are cheaper. Explains delays and bugs in F35, why not GPS ? After all if its technical and not managerial it must be easy, right ? </sarc>

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Coat

New Word Invented and Claimed...

...if GPS does go tits up and the world suddenly finds itself unable to find out where or when anything is, it'll be the:

Gonnagetlostalotalypse

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Childcatcher

All is not going well, however. Bloomberg News reports that the system, which was meant to have gone live in October 2016, will instead go live in 2022 at a cost of at least $6bn.

Not going well for whom? I'm pretty sure that Raytheon and Lockheed Martin along with the congress people they own are fine with the situation.

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IT Angle

"Not going well for whom?"

Indeed.

The way LM runs contracts its not so much "cost plus" as "cost plus plus"

or Cost+ and Cost++

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