Bush to consider shutting down GPS in extreme emergency

Care to give an example?


Juergen Nieveler

 

Accurate timekeeping and navigation.

 

It's not quite that simple.

No, but it will keep pretty good time. You have to verify the
synchronization periodically.

Obvious.

 

I think this whole discussion is moot:

Did Osama et al. use high-tech weaponry the last time?
Osama knows he can't compete in the high-tech arena, so he wont.

Nope, they used box-cutters.

And while the US as usual is looking into high-tech solutions (or wanting to
turn them off) Osama is thinking up another low-tech attack, which will
succeed because the US is staring itself blind on which high-tech toy to
create, use or to disable.

 

Since satellite navigation does not have a "load" (no matter how many
users there are, the cost of operation is the same), what would a "most
demanding" user be like?

If GPS can't provide it, I wouldn't hold my breath about GALILEO
providing it.

They'll disagree on other things, rest assured.

And it will be in service by 2045.

 

Was in my post already:
"value added services with integrity provision and, in some cases, service
guarantees, based on a certifiable system"

If you emulate/copy something, you generally improve upon it (like the
Japanese did with German camera's). This is always the case with technology:
the first generation of manufacturers/adopters/users etc. has the
disadvantage when the second generation comes along.
For example: we still have hundreds of miles of copper wire for our phones.
Some emerging countries start straight away with glass fibre.

No problem: Galileo is agreed on.

2008

 

Yes, but that doesn't mean you will.

In Europe, it's more a matter of politics than technology, and politics
don't always move ahead.

But we also have electricity for our wires, whereas the developing
countries' glass fibre remains dark.

Sure, just like the euro.

 

Alan,

I'm only speculating, but if GPS satellites were temporarily
switched off for exactly as long as they can be seen from a
particular target country, then that country would lose GPS
entirely, while a country on the other side of the planet would
not notice any failure.

However, a wide belt around the target country would lack GPS
service as well. Adjacent areas would probably not be able to
use GPS, countries farther away would experience limited GPS
service, only being able to receive GPS signals from one side.

Effectively you'd deprive a wide, roughly circular area of GPS
service, but far more than half the planet's surface would still
be able to navigate by GPS, some of it with reduced accuracy and
reliability.

Hans-Georg

 

Stan,

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.

Hans-Georg

 

I don't think it's quite as simple as that. Don't forget that at
higher latitudes it's possible to see satellites which are 'on the
other side of the planet' so more than an earth hemisphere would be
affected. It would be much easier to turn off the lot!

 

It doesn't work that way. Each satellite can be seen by half the world
at any given time.

 

But it would disturb GPS reception (up to a radius of 100km according
to http://de.wikipedia.org/wiki/GPS-Jammer), as asked by the
grandparent.

 

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

 

Alan,

now you're confused. Each satellite can be seen only from less
than half of the planet's surface.

Hans-Georg

 

Think before you write.

Hans-Georg

 

Yes, I agree, which is why, in an earlier post, I posted 'As the
'footprint' for one satellite is slightly less than a hemisphere of
the earth...'

 

Alan,

not so slightly. It's quite a bit less.

OK, now we can argue about the exact meanings of slightly versus
quite a bit. -)

Hans-Georg

 

No thanks

It's a long time since I did the math and based my statement on a
rough scribble. It's interesting, though.

 

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

 

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