Bush to consider shutting down GPS in extreme emergency

[Mxsmanic]

NTP servers exist. Much easier to use than GPS, too...

A lot of NTP servers use GPS clocks.

Can easily done by radio.

Not with anything approaching the same accuracy.

REAL Surveyors don't need GPS, they can manage happily without.

Real surveyors with real jobs depend on GPS.

Anyway, overall, you're making the same mistake the President and others
are making: you either shut down everyone with by shutting off GPS, or
you shut off no one. It's impossible to shut off GPS in a way that
affects only "terrorists," and the effect on civilian society of any
perturbation in service would now be disastrous. It's an incredibly
stupid idea.

Being able to neutralize GPS in a specific, small area is much more
rational ... but it still carries with it many of the same problems
(disaster for civilian services in the area, perhaps causing more damage
than would be caused by just leaving it on and letting the "terrorists"
use it).

 

[Mxsmanic]

But AFAIK GPS isn't allowed to be the primary means of navigation ...

I'm not sure what you mean by "primary means of navigation." GPS is a
great way to navigate just about anywhere except on takeoff and landing.
It's more reliable and accurate than other methods of navigation. After
all, it was DESIGNED to be that way.

... it's only a navigation AID, commercial aircraft still need to use
VOR/ILS to navigate ...

They can use anything they want, including GPS with waypoints that don't
even exist in real life. And I don't see why anyone would use VOR for
navigation in real-world practical environments if GPS is available
instead.

This is like saying that all ships should continue to navigate with
sextants, just in case GPS fails. What good are new systems if you
never trust them as much as you did their predecessors?

 

[Juergen Nieveler]

Wow DGPS without GPS, now why didn't I think of that!?!?

It is possible, although other ways would be easier (for example using
lasers to measure the distance to the position markers).

GPS works by having various clocks tell the time to the receiver. DGPS
does the same, but with a transmitter in a KNOWN position instead of
the orbit. Use several fixed transmitters, and you don't need the
satelites any more.

But as I've written above, that would be a kludge to keep using the
DGPS receivers already installed - for geological purposes it would be
easier to use traditional surveying methods, it just wouldn't be as
comfortable because people would have to go on site to measure
distances. However, you don't really need PERMANENT measurement of the
position when the thing you're tracking is a continent moving a few
inches a year


Juergen Nieveler

 

[Juergen Nieveler]

NTP is not going to help when synchonising 2 PABX's across a 100km
10Gbit fiber link.

Whyever not?

And where do you think that main (stratum 1) NTP servers get their
time from?

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

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.

DCF77 and similar long-wave radio systems produce time accurate in the
milliseconds, GPS in nanoseconds. Not comparable.

They aren't comparable because GPS is designed to calculate positions,
not to tell the time. As a source for accurate time, DCF77 is more than
enough for just about any purpose I can imagine.


Juergen Nieveler

 

[Juergen Nieveler]

I'm not sure what you mean by "primary means of navigation." GPS is a
great way to navigate just about anywhere except on takeoff and landing.
It's more reliable and accurate than other methods of navigation. After
all, it was DESIGNED to be that way.

"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.

They can use anything they want, including GPS with waypoints that don't
even exist in real life. And I don't see why anyone would use VOR for
navigation in real-world practical environments if GPS is available
instead.

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

This is like saying that all ships should continue to navigate with
sextants, just in case GPS fails. What good are new systems if you
never trust them as much as you did their predecessors?

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

Juergen Nieveler

 

[Juergen Nieveler]

A lot of NTP servers use GPS clocks.

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

Not with anything approaching the same accuracy.

Just WHAT kind of accuracy do you need? And what for? 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.

Real surveyors with real jobs depend on GPS.

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

Anyway, overall, you're making the same mistake the President and others
are making: you either shut down everyone with by shutting off GPS, or
you shut off no one. It's impossible to shut off GPS in a way that
affects only "terrorists," and the effect on civilian society of any
perturbation in service would now be disastrous. It's an incredibly
stupid idea.

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

Being able to neutralize GPS in a specific, small area is much more
rational ... but it still carries with it many of the same problems
(disaster for civilian services in the area, perhaps causing more damage
than would be caused by just leaving it on and letting the "terrorists"
use it).

I doubt anybody would shut down GPS globally for no reason at all...
but maybe it would be a nice idea for those people who think they
depend on GPS to do some contingency planning? 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.

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


Juergen Nieveler

 

[Alan Browne]

Juergen Nieveler writes:




Being required to have other means of navigation on board doesn't mean
that the usual means of navigation are not vital. Many two-engine
planes can fly on one engine, but that doesn't mean that it's acceptable
to shut down one engine.

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

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

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.

Cheers,
Alan

 

[Sam Wormley]

It is possible, although other ways would be easier (for example using
lasers to measure the distance to the position markers).

GPS works by having various clocks tell the time to the receiver. DGPS
does the same, but with a transmitter in a KNOWN position instead of
the orbit. Use several fixed transmitters, and you don't need the
satelites any more.

But as I've written above, that would be a kludge to keep using the
DGPS receivers already installed - for geological purposes it would be
easier to use traditional surveying methods, it just wouldn't be as
comfortable because people would have to go on site to measure
distances. However, you don't really need PERMANENT measurement of the
position when the thing you're tracking is a continent moving a few
inches a year


Juergen Nieveler

Methinks you might benefit from this....
http://www.trimble.com/gps/index.html
http://www.trimble.com/gps/dgps.html
http://www.edu-observatory.org/gps/tutorials.html
http://www.edu-observatory.org/gps/dgps.html

 

[Alan Browne]

Many airports have *only* GPS approaches.

Only airports that could not afford other approaches, or couldn't meet the
technical requirements for other approaches installation requirements. At that,
most of these are non precision approaches as to have higher levels of precision
would require more expensive runway environment lighting ... required so that
the pilot can recognize the runway environment at minimums.

 

[Alan Browne]

Mxsmanic wrote:

Either shutting off GPS has no effect on civilian navigation, in which
case it sure won't have any effect on terrorist navigation, or shutting
off GPS is disastrous for civilian navigation, in which case it is also
disastrous for terrorist navigation.

GPS provides a simple, low cost, relatively easy to integrate means of guidance.
What makes it an "enabling technology" for many things that didn't exist
before (your words, other posting) makes it an enabling technology for terrorists.

Unammned aerial vehicles have been around for a very long time. But GPS as an
enabling technology (as well as cheap, powerful CPU's and other sensors) has
been instrumental in the explosive growth of UAV's over the past 10 years.

Sponsor countries that have made a variety of effective weapons systems would
have little problem marrying drones and GPS with weapons. Verilly, once
developed and delivered, they could deploy from within the US, Canada, Mexico,
the Carribean or even from a ship. Throwing safety aside, they could fly it at
relatively low altitude (say 300'), no transponder and escape most (if not all)
primary radar coverage (which is in dwindling use).

Of course, one needs to detect the threat to even consider turning off GPS.

Cheers,
Alan

 

[Vincent van der Laan]

Either shutting off GPS has no effect on civilian navigation, in which
case it sure won't have any effect on terrorist navigation, or shutting
off GPS is disastrous for civilian navigation, in which case it is also
disastrous for terrorist navigation.

very good point.

 

[Alan White]

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

As the 'footprint' for one satellite is slightly less than a
hemisphere of the earth and up to twelve of them can be received at
any particular locality how do you disable reception for a region?

 

[Alan Browne]

"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.

Primary means "first". Sole-means means only. The only "sole means" GPS that
exists is "sole-means oceanic" where there is nothing but the GPS receiver for
navigation. When near land, VOR, DME, NDB, LORAN, etc. are used.

An aircraft in such a configuration would likely use GPS as Primary all of the
time, with the NAVAIDS as secondary when near land. When away from land it
would be GPS only. (Requiring pre-takeoff predictive RAIM to assure minimum
coverage for the whole flight).

Sole means oceanic is a very reasonable risk with two or three GPS receivers.

Cheers,
Alan

 

[Alan Browne]

NTP is not going to help when synchonising 2 PABX's across a 100km
10Gbit fiber link.

And where do you think that main (stratum 1) NTP servers get their
time from?

Contingeny planning for loss of GPS signal should include operating links at
lower efficiency/bandwidth to account for less accurate synchronization. This
should be part of the network emergency plan. It should be tested. It should
be part of training. It should be part of scheduled exercises.

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

Cheers,
Alan.

 

[Alan Browne]

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

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.

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

There are things that reuqire finer timing than a long wave system can deliver.
More to the point, using a single outside references at a distance away means
that all receivers believe the time is different. You could correct each
receiver according to its distance from the xmtr, but unfortunatley diurnal,
geography and weather effects would skew this badly at these low freq's. GPS
receivers at widely different locations can be sync'd much more accurately... as
well as providing microsecond or better accuracy at each receiver.

Cheers,
Alan

 

[Stan Gosnell]

Only airports that could not afford other approaches, or couldn't meet
the technical requirements for other approaches installation
requirements. At that, most of these are non precision approaches as
to have higher levels of precision would require more expensive runway
environment lighting ... required so that the pilot can recognize the
runway environment at minimums.

Almost all the expenses are borne by the FAA. The FAA is solely
responsible for navigation aids. And the trend is to GPS. NDBs are no
longer being maintained, and are being decommissioned at a rapid rate.
LOMs are becoming rare. And precision GPS approaches are now a reality,
if the proper equipment is installed in the aircraft. The approaches are
being published. GPS approaches are far more accurate than VOR
approaches, and the horizontal accuracy is at least as good as ILS
localizers. 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.

 

[Steven Shelikoff]

As the 'footprint' for one satellite is slightly less than a
hemisphere of the earth and up to twelve of them can be received at
any particular locality how do you disable reception for a region?

A jammer.

Steve

 

[Stan Gosnell]

An aircraft in such a configuration would likely use GPS as Primary
all of the time, with the NAVAIDS as secondary when near land. When
away from land it would be GPS only. (Requiring pre-takeoff
predictive RAIM to assure minimum coverage for the whole flight).

Sole means oceanic is a very reasonable risk with two or three GPS
receivers.

I do it all the time with one GPS. There are something over 5,000 oil
and gas production platforms in the Gulf of Mexico, and more are being
added all the time. We fly instrument approaches to them using GPS, down
to weather minimums of 200' ceiling and .6NM visibility. We're required
to have 2 VOR receivers installed and operational, because of
bureaucracy. The number of VOR transmitters in the Gulf of Mexico is
exactly zero. Disable GPS, and the oil production grinds to a crawl.
Certainly we can fly using a clock and a compass, but when you're
carrying a dozen or so passengers to a rig 200NM+ out there, something a
little more accurate is needed. The dozens of supertankers which
navigate this maze daily, each carrying millions of barrels of crude oil,
also need something a little more accurate than a sextant and a compass.
When a supertanker collides with a natural gas production platform, with
a few dozen wells at several thousand PSI pressure, nothing good results.

 

[Stan Gosnell]

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

This just isn't so. We lost an aircraft a few years back because it
couldn't maintain altitude with one engine inoperative. You need to read
CFR Title 14, Parts 23, 25, 27, and 29. Maybe it's so in the Great White
North, but not in the US.

 

[John W Montgomery]

Lets' remember the basics in this technical world! We still look at the dock when we steer our ships. We still use buoy lights and fog horns. We still look out the window when we fly. We still know how to use the rotating beacons at every airport. And come on-if the cell phone don't work we would look for a payphone. We are human-we adapt and survive around obstacles not thru them! So GPS is important-agreed-but the world will NOT end if the sat signals are off for a while.