Clarification about the term "GPS Shutdown"

Yup. So GPS must remain available. Like electricity.

Fortunately, the President cannot order solar flares.

Not if you can demonstrate that there was no alternative to GPS, and
especially if you can show that GPS was deliberately sabotaged.

 

And in some applications, trying to continue without GPS is worse than
just closing up shop.

And remember: if there is a suitable contingency plan for every
civilian use of GPS, then there is also a suitable contingency plan for
every terrorist use of GPS ... in which case turning off GPS really has
no point.

 

The NAVSTAR GPS Satellites have been designed to live in the
environment of very high Solar activity.

 

You signed a contract with the power company. Where did you sign up for
GPS service?

Perhaps we shouldn't give him ideas ;-)

You don't have a contract for GPS. You can only sue somebody for breach
of contract if you HAVE a contract. Your clients have a contract with
you - but if YOU in turn don't have a contract for some vital system
for your company you'll be in trouble. And the lawyers won't accept
"Big bad government has pulled the plug" as an excuse.


Juergen Nieveler

 

How far in advance are the codes generated/sent out to the units?
Unless you got a spy directly in the department that generates the
codes, you'd still be hard-pressed to get them in time to be usefull -
for example, if the codes are broadcast to the units at 2300 every day
for the next day only, and the new code will be used starting 2400, the
spy would have to immediately get a copy, nip out of the barracks and
hand the code over to somebody who can transmit it to you - and you'd
have to immediately send it out to your troops. All in one hour...


Juergen Nieveler

 

IIRC the satelites simply stop transmitting through a section of their
orbital path - and that section is chosen for all satelites in the
constellation so that in the affected region you don't get a signal
from ANY sat, whereas in the areas around that region you simply won't
get a signal from a sat flying in the direction of that region. That
means that in the region itself GPS would be unavailable, and in the
neighbouring area performance would be degraded a bit, the closer you
get to the region the worse it would get.

I could be misremembering of course...

Juergen Nieveler

 

Then the applications are badly designed. Don't depend on something to
be available if you cannot get a written guarantee for it.

Depends on the situation at hand. If the terrorists built some cheap
home- made cruise missiles with GPS control, they would have problems
putting up an alternative on-the-fly. Sure, in the long run they could
come up with something, but their plan would be delayed, giving the
police more time to catch them.


Juergen Nieveler

 

I don't know. Ask the NSA.

If it works for the legitimate users, it will work for the spies and
their clients.

 

They are always transmitting. They have to be, since each one covers
half the planet. Additionally, it can take considerable time to
transmit instructions to the entire constellation.

Yes.

The methods envisaged don't require any change in the way the satellites
work.

 

The same place where I signed up for fire and police protection.

You don't need one.

You don't have to sue. You can treat a sabotage of GPS as force
majeure.

No, you won't.

Courts will.

 

No. Some designs require GPS, period, just as some designs require
electricity.

Why not? Even with a written guarantee, you're still in the same
situation if it becomes unavailable.

Nobody builds cheap home-made cruise missiles.

Terrorists don't really lack anything that legitimate users have. Never
underestimate your opponent. Always assume he has access to everything
that you have.

 

There have been a number of comments about 2 aspects:
1) Terrorists would get the military receiver codes, so therefor would have
GPS available and
2) You can't shut down the civilian system without running everyone out of
business.

A few additional comments from my perspective:

If a terrorist picks a GPS off the body of a dead US soldier before
recovery, we need to reduce the probability that the GPS can be used against
us. If a single individual or small group of terrorists is operating
somewhat independently of any well organized world "headquarters" (which
seems to be the case currently), it is less likely that the organization
will have the assests in place to acquire the necessary codes on a timely
ongoing basis. Having changing codes does not absolutely prevent use, but
it makes it far less likely to occur. So that makes use of civilian units
more likely.

Nobody said that we would shut down the civilian system for days - no scope
of time was mentioned in the report of the administration remarks I read.
It may well be that the intent is to be able to shut off the civilian system
for only as long as a dire emergency exists. For example, a terrorist is
using GPS to guide a plane to target. This GPS outage might last an hour or
two at most. The reason the administration wishes to create such a policy
statement is to recognize the importance of GPS and the consequences of a
GPS outage. Granted, there might be significant consequences to any length
of outage, but surveyors going out of business would not be one of them.
For those applications (timing related) where any loss of GPS signal would
be locally catastrophic, I am quite sure the operators of those systems have
a backup plan or already have their bags packed. While GPS is very much a
utility, it is also a very new one and no reasonable person with a mission
critical need for specific timeing data would use GPS (or any other system)
without a fallback plan.

My main point is that the debate on this group seems to be conducted at the
extremes - "we will shut down the system forever and have to navigate by the
stars" or "the willing accomplice of the terrorist empire will prove
military codes instantly, so what's the point in shutting down the civilian
side only?" I suggest that this policy is not about absolute risk
containment. It does reduce the liklihood that our own assets can be used
against us. Having such a policy in place may discourage terrorists from
using civilian GPS since they know there exists a contingency plan to
minimize the effectiveness of their attack. There will be no period of
uncertainty where someone in Washington pauses in confusion with a finger on
the "off" switch. So as a terrorist, perhaps you pass up GPS and look for a
better way to procede. Given that they are so bent on being martyrs,
delivering a "dirty nuke" via pickup truck to downtown USA would probably be
a reasonable and more likely alternative. We learned that often there is not
time to dispatch a fighter plane if there is a highjacking and someone has
to be consulted. We need a plan in place real time to deal with fast
unfolding dire emergencies. Yes there are economic and social risks
involved in executing the plan, but the expectation is that the consequences
of not doing it would be far worse.

 

GPS jammers can disturb the signal up to a radius of 100km.

 

How would he use it against us? Just plug it into the "GPS receiver"
slot in his waiting cruise missile?

It takes hours to shut it down, and hours to start it back up (all the
satellites have to pass over the right spots).

The system cannot be shut off that quickly.

Long enough to guide a few dozen civilian aircraft into the side of a
mountain. With casualties like that, who needs a terrorist?

People dying on aircraft might well be one of them, however.

Many new technologies don't work without GPS--GPS made them possible.
There is no fallback plan for these technologies, so if you depend on
them (and you can't avoid depending on them forever), you must have GPS.

The extreme is in suggesting that it's a practical idea at all. Today
it makes no more sense than turning off all the electricity in the
country. You don't shut off public utilities just because some nut has
a bomb.

The off switch takes hours to flip, so it doesn't matter.

 

The majority of the posts to this thread are pure unadulterated BS.

 

Code dissemination is classified.

 

I'd be surprised that the codes are not administrated remotely. Some
higher level of authority can selectively re-key all the other receivers
to shut out any lost equipments.

Jack

 

The reason phased transmission isn't used is that each satellite's
footprint is almost a whol hemisphere.
http://www.edu-observatory.org/gps/GPS_BeamPattern.jpg

 

Why shouldn't they stop transmitting for half an hour on their path,
each at different times? You need more than one sat over the horizon
for GPS to work, and simple trigonometry could make sure that for a
given point in space and time no active sats are visible, even though
for another point hundreds of miles away there ARE sats visible at the
same time, because they don't have the same horizon.


Juergen Nieveler

 

You can supply your own electricity - quite easy, just buy a diesel
generator. Not as easy for GPS...

No. If you have a written statement that something will be available
24/7, and it isn't, you have a reason to complain. Not so for GPS.

There's that guy in New Zealand who doesn't agree with you...

Using GPS still makes things easier for them - sure, you could use
optical guidance instead of GPS, but that would require a transmitter
in the missile, which uses more energy than a GPS receiver.


Juergen Nieveler