Bush to consider shutting down GPS in extreme emergency

[Mxsmanic]

Whyever not?

It's not precise enough.

From a vial of caesium, usually - at least the servers NTPx.PTB.DE do.

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

GPS isn't the time base of the planet - on the contrary, the satellites
get their time corrections from the main clocks on the ground.

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.

They aren't comparable because GPS is designed to calculate positions,
not to tell the time.

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

As a source for accurate time, DCF77 is more than
enough for just about any purpose I can imagine.

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.

 

[Mxsmanic]

Contingeny planning for loss of GPS signal should include operating links at
lower efficiency/bandwidth to account for less accurate synchronization.

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

If that's not good enough, then alternate high accuracy time sources exist that
embed atomic clocks.

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

 

[Mxsmanic]

Use the ones that have their own atomic clock, then.

There aren't enough of those.

Just WHAT kind of accuracy do you need?

Nanoseconds, if you need GPS clocks.

Besides, not to put a too fine point to it, GPS isn't THAT
accurate unless it gets corrected regularly, the clocks
on the satelites drift because of the speed they're moving at.

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.

So there weren't any real surveyors before GPS was invented?

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

It's possible to shut down GPS for a REGION.

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.

And as that region is
going to be affected by disaster anyway (otherwise GPS wouldn't have
been shut down), all the stuff you mentioned won't really be that
important for people in that region.

That's when navigation becomes more important than ever.

I doubt anybody would shut down GPS globally for no reason at all...

Nothing surprises me today.

but maybe it would be a nice idea for those people who think they
depend on GPS to do some contingency planning?

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.

There is no guarantee
for the users of GPS, and never has been, that the service will be
maintained for any amount of time - people might rely on it, but as
they didn't sign a contract for it or pay for it they don't have any
legal rights to require GPS to keep working for them.

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.

It will be different with Galileo, because that WILL be a commercial
service, complete with service agreements and monthly bills.

Which is why nobody will use it.

 

[Mxsmanic]

"Primary" means "If this stops working, we can't go anywhere". If the
GPS receiver breaks on a commercial plane, the plane won't be grounded.

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.

They can use GPS anytime they want, but they still have to make sure
that they can navigate by VOR.

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.

Who do you sue when your tanker runs aground because of a faulty GPS
signal?

Whom do you sue if the magnetic compass fails?

 

[Mxsmanic]

All certified twin engine aircraft can fly, indeed climb at gross weight, on one
fully functional engine and pilots train for the eventuality regularly.

That's no way to run an airline.

Training is always acceptable. Including training for a non GPS world.

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.

Airlines tend to do most engine out (and other emergency) training procedures in
the simulator to keep most of the airplanes in revenue service... and not expose
them to training accidents.

They do it for emergencies, not for normal operation.

 

[Mxsmanic]

So GPS is important-agreed-but the world will NOT end
if the sat signals are off for a while.

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.

 

[Alan White]

A jammer.

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

 

[Juergen Nieveler]

Whom do you sue if the magnetic compass fails?

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

 

[Juergen Nieveler]

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

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

 

[Juergen Nieveler]

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

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).

That's when navigation becomes more important than ever.

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

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

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...

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.

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

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

Only people in the US paid taxes that financed GPS.

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.

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.

Which is why nobody will use it.

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

 

[Juergen Nieveler]

The FAA rather desperately wants to get away from
the requirement to maintain obsolete equipment at thousands of
locations all over the US. Eventually it will.

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

 

[Juergen Nieveler]

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

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

 

[Juergen Nieveler]

er, no. GPS provides 3 independant products in the receiver:
Position, Velocity and Time (PVT). They all come from the same
signals of course, but they are arrived at seperately. The
cornerstone for all of them is time.

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 ;-)

There are things that reuqire finer timing than a long wave system can
deliver.

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

 

[Mxsmanic]

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

No. Some applications require GPS, period.

 

[Mxsmanic]

If your atomic clock is one second off, you should call a technician.

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.

The main purpose of atomic clocks is to simply run for years and years
WITHOUT being off, without any resetting needed.

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

 

[Mxsmanic]

You do that ONCE, at installation ...

No, you do it regularly.

... the good thing about atomic clocks
is that they KEEP being accurate, you don't need to reset them that
often ...

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

 

[Mxsmanic]

Not because of lack of GPS, but because a lack of precise maps.

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

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).

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

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

There's more than air traffic that requires navigation.

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...

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

Only people in the US paid taxes that financed GPS.

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

Yes, there IS a guarantee that the power will stay on and that the
water supply is maintained.
Where?

You pay money for it - it's part of the contract you signed
with your supplier.

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

Except for the people who DEPEND on a navigation system to be up 24/7
and without anybody fiddling with the accuracy.

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.

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).

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

 

[Mxsmanic]

But of course even WITH GPS there is still the rule that ships have to
take on pilots in restricted waters ...

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

... so people don't really trust GPS to be the sole navigation
aid for commercial shipping.

See above.

 

[Vincent van der Laan]

Which is why nobody will use it.

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)

The greatest threat to Galileo is Europe.

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.

 

[Juergen Nieveler]

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.

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.

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

The difference being?


Juergen Nieveler