Bush to consider shutting down GPS in extreme emergency

[Juergen Nieveler]

So you say--Where is your cost analysis?

Farmers have worked for millenia without GPS. You're claiming that they
can't work without it anymore? My brother-in-law will prove otherwise -
he's a farmer, and has never been near a GPS receiver in his whole life.

So you say--Where is your cost analysis?

Just HOW often do you need to precisely map a utility pole or oil well
in the middle of a war zone, or during a global crisis? And why is it
so important to do it with GPS instead of normal surveying equipment?

You asked what would be effected

We talked about critical, life threatening stuff...

The are many safety of life and rescue operations now using GPS.
There are certainly life threatening situations that GPS can make a
difference.

And you can bet that if human lifes depend on the service, the
operators will have contingency plans for situations when GPS isn't
working - if only because GPS receivers can break, too...

Juergen Nieveler

 

[Juergen Nieveler]

Network Synchronization.

High-density OC-48 to OC-192 SONET systems require very precise sync
systems. Single digit nanosecond systems are the norm, and they use
GPS+atomic clocks.

And what exactly would stop them from working if only atomic clocks are
available? At least for a limited time span they would keep in sync
using atomic clocks, and after that they'd still work at reduced
bandwidth.

I agree that GPS is a convenient tool to keep the clocks synched, but
that can be done by other means, too. And you can bet that major
network providers DO have contingency plans in case GPS isn't available.


Juergen Nieveler

 

[Juergen Nieveler]

No--it's much more complicated than that.

Verbose, please - how do you want to want to persuade the Pentagon to
pay for the damage they caused you by shutting down GPS?


Juergen Nieveler

 

[Juergen Nieveler]

At what cost?

In restricted waters? No additional costs, they already need pilots
anyway. Open ocean navigation is another issue, but ship crews ARE
supposed to know how to navigate without GPS, and unless the ship owner
tried to save a lot of money on training they WILL manage to go to the
right continent. There are navigation aids available besides GPS, and
the ships could use these - or if things go REALLY bad, we'd see
convoys forming up around military-GPS equipped ships.

And not to put a too fine point to it, but GPS is run and paid for by
the Pentagon - they aren't responsible for saving money for people all
over the world, are they?


Juergen Nieveler

 

[Juergen Nieveler]

Can you do that with civilian GPS?

Certainly [SNIP]
Differential GPS involves the cooperation of two receivers, one that's
stationary and another that's roving around making position
measurements. The stationary receiver is the key. It ties all the
satellite measurements into a solid local reference.

But the position of the stationary receiver has to be known - the more
precise the measurement of that point, the more precise the rest of the
measurements get. And if you got a precise reference point (or better:
two reference points), you can get the same degree of accuracy with
plain old surveying equipment.

Yes, it will take more time, and will take experienced surveyors, but
it can be done - so a shutdown of GPS wouldn't be that critical for
that line of work.

Not to mention that surveying isn't really time-critical work ;-)

Juergen Nieveler

 

[Juergen Nieveler]

Turn off all the satellites that a GPS receiver can see and then
calculate the numbers seen at all point on the earth and the DOPs
at those locations and you will find that the damage is not nearly
as *localized* as you might think. Do the calculations.

But it's also not nearly as close to a global shutdown as people seem
to think. Accuracy might be reduced, and it will take longer to get a
fix, but the system would stay up for most of the planet, with results
being better the further you get away from the affected region. As that
region will probably be a warzone anyway, there won't be that many
people requiring civilian GPS service in that area at that particular
time.

Let's face it:
a) It IS possible to shut down civilian GPS without taking down
military GPS
b) The chances of terrorists using military GPS are slim at best
c) Civilian GPS can be degraded or shut down on a regional basis
d) The world isn't going to end when that happens
e) If your company depends on GPS running 24/7, you might want to
rethink your contingency planning real soon


Juergen Nieveler

 

[Juergen Nieveler]

Don't be obtuse. You said, "because GPS is designed to calculate
positions, not to tell the time." And that is erroneous. The first
concern of a GPS receiver is time.

No it isn't. The first concern of a GPS receiver is to show you your
current position - hence the name "Global Positioning System". It uses
very precise clocks to do so, and so the feature of showing you the
current time came with the system, but GPS wasn't designed as a global
talking clock.

Juergen Nieveler

 

[Juergen Nieveler]

albeit more expensive!

But it can be done, which is my point. People enjoy the free ride while
it lasts, but if GPS wouldn't be available any more they'd find other
ways of making things work. The world wouldn't end, life would go on.


Juergen Nieveler

 

[Sam Wormley]

Let's face it:
a) It IS possible to shut down civilian GPS without taking down
military GPS
b) The chances of terrorists using military GPS are slim at best
c) Civilian GPS can be degraded or shut down on a regional basis
d) The world isn't going to end when that happens
e) If your company depends on GPS running 24/7, you might want to
rethink your contingency planning real soon

But at what cost?

 

[Sam Wormley]

Wow! You can measure a point with a horizontal accuracy of less than
10mm?


Can you do that with civilian GPS?

Certainly [SNIP]
Differential GPS involves the cooperation of two receivers, one that's
stationary and another that's roving around making position
measurements. The stationary receiver is the key. It ties all the
satellite measurements into a solid local reference.

But the position of the stationary receiver has to be known - the more
precise the measurement of that point, the more precise the rest of the
measurements get. And if you got a precise reference point (or better:
two reference points), you can get the same degree of accuracy with
plain old surveying equipment.

Yes, it will take more time, and will take experienced surveyors, but
it can be done - so a shutdown of GPS wouldn't be that critical for
that line of work.

Not to mention that surveying isn't really time-critical work ;-)

But at what cost?

 

[Sam Wormley]

And what exactly would stop them from working if only atomic clocks are
available? At least for a limited time span they would keep in sync
using atomic clocks, and after that they'd still work at reduced
bandwidth.

I agree that GPS is a convenient tool to keep the clocks synched, but
that can be done by other means, too. And you can bet that major
network providers DO have contingency plans in case GPS isn't available.

And the cost?

 

[Sam Wormley]

No it isn't. The first concern of a GPS receiver is to show you your
current position -

That's a naive understanding--GPS was design to provide position,
velocity and time. PVT solutions.
http://edu-observatory.org/gps/gps_books.html

 

[Sam Wormley]

But it can be done, which is my point. People enjoy the free ride while
it lasts, but if GPS wouldn't be available any more they'd find other
ways of making things work. The world wouldn't end, life would go on.

And my point is at what cost?

 

[Sam Wormley]

And since you can't get a guarantee on the uptime of GPS, you'd be well
advised to plan for outages.

GPS
Internet
Electricity
Medical Care
Food production and dissemination
Telephone service
Fuel
Water
Air

We try to make each as robust as we can.



etc.

 

[Mxsmanic]

I'm asking for a practical non-navigation example of timekeeping that
requires nanosecond-accuracy.

Why are you excluding navigation?

You keep evading that question.

Why are you evading navigation? Why do you only allow applications that
require "nanosecond accuracy"?

Ironically, synchronizing atomic and other clocks is one of the
applications that requires nanosecond accuracy.

 

[Mxsmanic]

I agree that GPS is a convenient tool to keep the clocks synched, but
that can be done by other means, too.

No, it can't. Before GPS, certain types of synchronization couldn't be
done.

 

[Mxsmanic]

Many microsecond and better clocks have been available on the commercial market
for 30 years or more.

A thousand times worse than nanosecond accuracy. That's the difference
between being on the center stripe of the runway and being in town.

 

[Mxsmanic]

Slightly reduced effectiveness without GPS.

As I recall, the difference is significant. It had to be, to justify
the installation of the equipment.

And we're talking about a
minor share of farmers who actualy DO use GPS already - most don't.

What percentage of them are using GPS?

Which is the reason why the US Military wants to shut it down in the
first place, excpet for their own PG systems - which would still work,
as only the civilian part would be turned off.

The only problem is that there are thousands of other applications that
use GPS, and guiding a missile is a trivially insignificant application
in comparison.

And if aircraft have contingency plans for flying without GPS, why
wouldn't missiles have the same?

 

[Mxsmanic]

Just HOW often do you need to precisely map a utility pole or oil well
in the middle of a war zone, or during a global crisis?

A lot. They are both strategic infrastructure and assets.

And why is it so important to do it with GPS instead of normal
surveying equipment?

GPS is much faster and more accurate, and it requires less training and
experience.

And you can bet that if human lifes depend on the service, the
operators will have contingency plans for situations when GPS isn't
working - if only because GPS receivers can break, too...

And you can bet that if terrorists are planning a major attack, they're
going to make sure that it cannot be foiled just by turning off GPS.

I don't understand the doublethink that holds that turning off GPS could
somehow have a huge impact on terrorism but only a minor impact on
civilian uses. The fact is, the impact on both would be the same, and
since there are lot more civilians than terrorists, the overall result
is a major loss for the civilian world.

 

[Mxsmanic]

No it isn't. The first concern of a GPS receiver is to show you your
current position - hence the name "Global Positioning System".

The quintessence of GPS is accurate timekeeping, which is essential to
accurate navigation. That is just as true now as it was centuries ago
when marine navigation drove the development of accurate chronometers.