Bush to consider shutting down GPS in extreme emergency

It's not precise enough.

Many servers use GPS, because it is inexpensive and extraordinarily
accurate.

But the main clocks on the ground are not readily accessible, whereas
GPS is available everywhere, and it is nearly as accurate as the ground
clocks.

No. They aren't comparable because GPS is far more accurate.

Then you must cultivate greater imagination, as accuracy within tens of
milliseconds is woefully inadequate for many applications. NTP and
DCF77 are in about the same league, however.

 

That cannot substitute for applications that require GPS accuracy. A
less accurate signal is equivalent to no signal at all in some cases.

But the clocks have to be synchronized with other clocks. An atomic
clock isn't much good if it's one second off.

 

There aren't enough of those.

Nanoseconds, if you need GPS clocks.

Both time and frequency on GPS satellites are corrected for the
relativistic effects of their motion and their height in orbit
(gravitational relativistic effects). So GPS _is_ THAT accurate. It
has to be, or it won't work.

There were, but they they didn't achieve the accuracy they manage today.
Sometimes they were off by hundreds of metres.

But it's not possible to shut down GPS for a USER. You either affect
all (non-military) users, or none. Terrorists are not a separately
targetable class of users.

That's when navigation becomes more important than ever.

Nothing surprises me today.

There aren't any other satellite systems that can replace it. GLONASS
comes close, I suppose.

You can't do "contingency planning" unless there are suitable
alternatives. Without electrical power, you can't listen to the radio,
no matter what your plans.

They paid taxes, and that's the same thing.

There's no guarantee that the power will stay on or that the water
supply will be maintained, but both are always present, just the same,
and it's not unreasonable to depend on them.

If you never allow yourself to become dependent on any technology, you
never make any progress.

Which is why nobody will use it.

 

That depends. The threshold for commercial flights is higher than that
for other flights. Not being able to navigate with the usual aids on a
large number of aircraft would effectively halt many commercial
services.

If they normally use GPS, navigating by VOR may not be a practical
alternative. It might suffice to make a quick landing, but that's all.

Whom do you sue if the magnetic compass fails?

 

That's no way to run an airline.

Beyond a certain point, you stop training for certain situations,
because it is no longer practical to do so. Nobody trains for normal
commercial service with one engine not running, for example.

They do it for emergencies, not for normal operation.

 

If "for a while" is fifteen minutes, you might be right. If it's hours
or days, the problems may become very grave.

One should not assume that just because something is briefly possible in
an absolute emergency it is also practical for prolonged periods and/or
can maintain any kind of normality in other domains.

 

A jammer won't disable GPS over a 'region' nor, as suggested by the
OP, will it 'shut down GPS'.

 

The manufacturer of the compass, unless you want me to believe that the
magnetic field of the planet is going to instantly collapse

Of course, there is the theory that the magnetic poles are going to
switch sometime soon - but that's soon in geological terms, meaning
"Oh, could be tommorow, but the smart money is on some time in the next
100000 years".

But of course even WITH GPS there is still the rule that ships have to
take on pilots in restricted waters... so people don't really trust GPS
to be the sole navigation aid for commercial shipping. Makes sense, too
- GPS can tell you the position, but only the pilot will know wether
your map really is the latest edition and wether that sandbank might
have shifted.

Juergen Nieveler

 

If your atomic clock is one second off, you should call a technician.
The main purpose of atomic clocks is to simply run for years and years
WITHOUT being off, without any resetting needed.


Juergen Nieveler

 

Not because of lack of GPS, but because a lack of precise maps. Aerial
photography and the maps produced through it had at least as much to do
with better accuracy, and a good surveyor with a telescope and a
precisely defined starting point will be at least as (if not more)
accurate as a GPS receiver (civilian version).

Depends a lot on the kind of emergency. If there's a shooting war in
that region, civilian air traffic will be zero...

Pray that the Pentagon keep their fingers out of Galileo, then - of
course, not much hope of that, they'll keep trying to get control over
that as well...

There are always alternatives. With reduced performance, no doubt, but
alternatives do exist.

Only people in the US paid taxes that financed GPS.

Yes, there IS a guarantee that the power will stay on and that the
water supply is maintained. You pay money for it - it's part of the
contract you signed with your supplier.

Except for the people who DEPEND on a navigation system to be up 24/7
and without anybody fiddling with the accuracy. Galileo will be used in
future toll collection systems in Germany, for example, replacing GPS
(IF they make that system work - last news was that they'll start
running the first version in January).


Juergen Nieveler

 

And once that happens, the off-switch for GPS will be taken away from
the politicians and the military - I'd even bet that in that case the
FAA would get control over the civilian part.

Juergen Nieveler

 

You do that ONCE, at installation - the good thing about atomic clocks
is that they KEEP being accurate, you don't need to reset them that
often...


Juergen Nieveler

 

We were talking about fixed installations such as computer centers
using GPS to keep the time in this particular sub-thread. Hard as I
try, I cannot imagine why you'd need constant updates on position or
velocity for a building ;-)

Use a clock on site, then... that would be even more accurate than GPS.

It's definately not IMPOSSIBLE to do withouth GPS, don't you agree?

Juergen Nieveler

 

No. Some applications require GPS, period.

 

Why? Atomic clocks measure time intervals with precision, but nothing
automatically synchronizes them with standard time. Indeed, "atomic
clocks" are usually frequency standards that are used to drive real
clocks.

Not true. The main purpose of atomic clocks is to minimize long-term
inaccuracies in timekeeping.

 

No, you do it regularly.

You need to check their synchronization regularly. The national
agencies responsible for keeping standard time do this with each other
constantly.

 

If they had GPS, they wouldn't be hundreds of metres off. And if you
have precise maps, you don't need surveys.

Odd that surveyors are spending so much on GPS, then.

There's more than air traffic that requires navigation.

I don't expect Galileo to amount to much, especially over the short
term.

So? (Actually, all "U.S. persons" pay taxes, whether they are in the
U.S. or not.)

Is it? Where? All I see in such contracts are disclaimers.

GPS will be just as reliable. The attractiveness of zero cost will
outweigh the slim chance of interference, and the accuracy will continue
to be excellent.

I suppose the Germans will make it illegal to use GPS?

 

That has nothing to do with any lack of GPS accuracy.

See above.

 

Which is why it will be a free service for all but the most demanding users:

"Like GPS, GALILEO will be free of charge to basic users (open service).
Some applications will have to be paid for - those requiring a quality of
service which GPS is unable to provide."

"above that, with it's open service at least offering the same performances
as GPS by the time of GALILEO's deployment, GALILEO will offer also value
added services with integrity provision and, in some cases, service
guarantees, based on a certifiable system."

(from:
http://europa.eu.int/comm/dgs/energy_transport/galileo/faq/index_en.htm )

(From another post on this NG)

It is easy to come to agreement if you are one country (like the USA)!
Here we have to deal with 20 countries with different cultures and different
priorities etc. I think it is remarkable that 20 countries reached agreement
so soon (a week ago every country agreed).

The first sat will be launched end of 2005.

 

Yes. But when you first set up the clock, of course you WILL
synchronize it with the master clock in your country. From that point
on it will keep acurate time.

The difference being?


Juergen Nieveler