Bush to consider shutting down GPS in extreme emergency

[Juergen Nieveler]

GPS timing receiver doesn't need much setup; doesn't need a
controlled environment. Works anywhere!

As long as GPS is avaible. Which isn't guaranteed, as we've learned - so
people will need an alternative. Which for this particular purpose would
be a very precise clock.

Juergen Nieveler

 

[Juergen Nieveler]

A GPS receiver with timing pulses is a hell of a lot cheap in terms of
capital expense and maintenance costs.... especially out in field where
there is no power grid.

I agree that it is cheaper - but the question was wether it was
impossible to achieve the same result without GPS. I think you'll agree
that it IS possible to use an atomic clock of your own instead of GPS
to keep acurate time, and given a threat of GPS not being available, it
would be an attractive alternative to companies who need accurate time
for busines- critical purposes. If it's business-critical, cost isn't
as much of a factor.


Juergen Nieveler

 

[Juergen Nieveler]

precision agriculture on a global scale

Slightly reduced effectiveness without GPS. And we're talking about a
minor share of farmers who actualy DO use GPS already - most don't.

precision guided ordinance

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.

precision mapping of utility poles, oil wells

The world can easily manage without that for weeks, if not months.

tracking of wildlife

See above

automobile navigation systems

Gosh, people would need to learn how to read maps again! We'll see tens
of thousands of people driving the wrong way !!!1eleven!

None of this is actually life-threatening ;-)

Juergen Nieveler

 

[Juergen Nieveler]

Switching has already begun... check back in 5-10 thousand years. If
you are curious find out how much Earth's magnetic field strength has
changed in the last few centuries.

AFAIK, it's not begun, it simply hasn't stopped. Those damn poles just
keep moving about ;-)


Juergen Nieveler

 

[Sam Wormley]

Earth is a sphere, it doesn't have "sides". Essentially, you'd set the
satelites to turn off the civilian transmitter over a certain part of
their trajectory, which would translate into a certain area of the
planet not having more than 2 active satelites over the horizon at any
given time.

Here is the current coverage of a satellite I'm currently tracking
from my location in central Iowa.
http://www.edu-observatory.org/gps/coverofPRN15.041217.16:05UTC.gif

 

[Sam Wormley]

But a single satellite isn't enough. As long as no more than 2 sats are
visible over the horizon at any given moment, using GPS is impossible
in that region. And since the horizon is different for any point on the
planet, and the satellites can be set to turn their transmitter on and
off at any given time, you can select which satellites are active and
visible over the horizon at a given plave and time.

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.

 

[Stan Gosnell]

I don't know the details, but would be very interested. The
fundamental fact, however, is that the entire justification to
have two engines is to be able to continue flying if one engine
fails. Obviously, immediately after takeoff this means that the
plane has to be able to climb slowly.

Flying a twin while knowing that it wouldn't be able to continue
after an engine failure seems undesirable to me. I'd rather have
a single then with its lower touchdown speed and much lower risk
of engine failure, generally less than 50% of that of a
comparable twin.

A twin has to be able to climb, with the gear and flaps retracted, with
the critical engine inoperative. But not at gross weight, and not at all
temperatures. It just has to be able to do it at some weight and
temperature. The flight manual has a WAT chart (weight, altitude,
temperature) that shows under what conditions the aircraft can climb
single-engine, and how fast the climb or descent will be. Few light
twins can climb single-engine at much above sea level and much above
standard temperature. Installing more powerful engines means more fuel
consumption, higher costs, etc. Everything is a compromise of some sort.

 

[Sam Wormley]

Can you do that with civilian GPS?

Certainly

DGPS is the bread and butter of the professional GPS community. Mapping,
minning, precision agriculture, survey (sub cm), and a host other applications.
See: http://www.edu-observatory.org/gps/dgps.html

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. Here's how it works:
http://www.trimble.com/gps/dgps.html
-- Trimble Navigation Ltd.

See: http://www.edu-observatory.org/gps/dgps.html

 

[Stan Gosnell]

I don't disagree. And the FAA will certainly commission non-prec.
approaches. But I don't think they will pay for the lighting required
to commission a prec. approach (CAT I) where none existed before
unless the airport pays for that end of the improvment. There may
also be cases where existing lighting meets the lighting requirement.
There may also be cases where existing obstructions make it impossible
to cert. a prec. approach and that airport will have to be content
with non-prec.

It's the FAA's job to pay for those. A tax is collected on every
passenger who boards any airliner and put into the airport trust fund to
pay for this. Certainly not every airport will get a precision approach,
but more are coming. And the lighting isn't necessarily required for a
precision approach - only to get the approach minima down to the lowest
possible. It's possible to have a precision approach to a runway with no
approach lights. The minima will be higher, of course, but it's still
better than an NDB approach that only gets the aircraft into the general
vicinity of the airport, or even a non-precision GPS approach that
encourages 'dive and drive' techniques. Precision GPS approaches are
coming.

 

[Sam Wormley]

With GPS, there is no such statement, and thus no chance to stop a
politician from switching it off. For all we know, civilian access to
GPS could be stopped today, without any of us being able to protest
against it - it's a Pentagon-owned system, so the Pentagon decides what
to do with it, PERIOD.

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

 

[Sam Wormley]

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

Time dissemination
http://www.edu-observatory.org/gps/time.html

 

[Robertwgross]

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

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.

---Bob Gross---

 

[Stan Gosnell]

I won't look those up, but plaase feel free to cite where a twin can
be cert. without being able to climb on a single engine at gross
weight on a standard day. As I recall the min. climb rate is 100 ft.
min in that condition (which is scary enough).
At 4000' at 30C at gross weight I can understand a piston single
having difficulty...

Well, you need to look them up. The only requirement in Part 23, normal
and commuter aircraft, is that the aircraft demonstrate the ability to
climb with the critical engine inoperative, gear and flaps retracted.
There is no specification of weight, temperature, or rate of climb. The
manufacturer must provide a WAT chart to show the conditions where it can
climb. That's it. The US Codes of Federal Regulations are available at
http://tinyurl.com/3n7tx. Title 14, Aeronautics and Space, are at
http://tinyurl.com/6j27s. The various parts are a click away. Or if you
don't trust tinyurls, you can start at http://ecfr.gpoaccess.gov.

 

[Sam Wormley]

Slightly reduced effectiveness without GPS. And we're talking about a
minor share of farmers who actualy DO use GPS already - most don't.

So you say--Where is your cost analysis?

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 world can easily manage without that for weeks, if not months.

So you say--Where is your cost analysis?

See above




Gosh, people would need to learn how to read maps again! We'll see tens
of thousands of people driving the wrong way !!!1eleven!

You asked what would be effected

None of this is actually life-threatening ;-)

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

 

[Gabriel Ebner]

Can you do that with civilian GPS?

Surely, you just need to be around a DGPS reference station.

 

[Sam Wormley]

But you agree that this can easily be done WITHOUT GPS, and that it
actually will be a bit more acurate than GPS, albeit more expensive?

albeit more expensive!

 

[Sam Wormley]

Surely, you just need to be around a DGPS reference station.

DGPS doesn't work without GPS...
http://edu-observatory.org/gps/dgps.htm

 

[Sam Wormley]

As long as GPS is avaible. Which isn't guaranteed, as we've learned - so
people will need an alternative. Which for this particular purpose would
be a very precise clock.

Nothing in life is "guaranteed" except death. Critical infrastructure like
GPS needs to be on all the time.

 

[Sam Wormley]

But it means that people will manage without GPS in restricted waters -
because they already do.

At what cost?

 

[Juergen Nieveler]

Nothing in life is "guaranteed" except death. Critical
infrastructure like GPS needs to be on all the time.

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


Juergen Nieveler