GPS jamming ethics

[nathaniel 0]

Some satellites you talk to with regular antennas.

Think vacuum vs TV.

GPS is typically in this category so you don't have to keep track of the (non-geosynchronous) orbits of the 20 or so satellites. One of the neat parts of GPS is that all satellites broadcast on the same frequency but they encode their signals in such a way that receivers can pick them apart. The Russians made a half-hearted attempt at their own satellite navigation system called GLONASS http://www.rssi.ru/SFCSIC/english.html that sucked b/c they can't share a frequency and the Russians basically didn't allocate enough of the spectrum..not to mention not funding the project.

Nathaniel

My advice is to do what your parents did; get a job, sir. The bums will always lose. Do you hear me, Lebowski?

[AndyMan 7]

you don't do anything to the satalite itself, you just broadcast "yankee doodle" on the same frequency and with as much power as you can come up with.

It's sort of like trying to whisper to your neighbor at a Metalica concert. One signal just over-powers the other.

One question I had though, is how accurate are military GPS's? Can GPS be trusted to solely accurately deliver a weapon? Moreover, now that 'selective availability' is pretty much turned off worldwide, is there a difference in accuracy between the military units and civilian ones? How?

_Am

__

You put the fun in "funnel" - craichead.

[skycop 0]

If all this war/gps jamming stuff messes up my TV reception, I'm gonna be pissed!!!

"Just 'cause I'm simple, don't mean I'm stewpid!"

[indyz 1]

Quote

One question I had though, is how accurate are military GPS's? Can GPS be trusted to solely accurately deliver a weapon? Moreover, now that 'selective availability' is pretty much turned off worldwide, is there a difference in accuracy between the military units and civilian ones? How?

Military GPS is as accurate as civilian GPS in the US. Civilians used to get a worse signal (the time from the atomic clocks was shifted slightly, and only the military knew how to undo it). I get 32 feet with my $100 Garmin eTrex on a regular basis. That won't put bombs down ventilation shafts, but it's plenty accurate to take out a SAM site in the desert, or a large building.

[quade 4]

Quote

Military GPS is as accurate as civilian GPS in the US.

The military receivers are -far- more accurate than the civilian receivers.
For basic getting un-lost, the civilian stuff is just fine, but the military stuff is at least 10 times more accurate and -possibly- as much as 100 times more.
Yes, the military stuff -can- put bombs -exactly- on target. Maybe not 100% of the time, but damn sure often enough.

quade -
The World's Most Boring Skydiver

[indyz 1]

I should have said that military receivers are at least as accurate as civilian receivers, and that civilian receivers are now receiving an unmodified signal, so they have the potential to be as accurate as military gear.

I thought the extremely accurate stuff (less than one foot) required a fixed ground station.

[skycop 0]

Wow, another thread where I can speak with some authority!!
I'm a USAF AMMO guy on the military side for over 20 yrs.(active and reserve). I've never built a JDAM, I've shipped some kits, but never built any. I'm assuming they have coded anti-jamming features like the GBU-10/12's I have built. The press is probally making a huge deal out of nothing.

"Just 'cause I'm simple, don't mean I'm stewpid!"

[newshooter12 0]

"The press is probally making a huge deal out of nothing."
More then likely.. you're right. I find my end of "the media"... TV News. Talking about the same things over and over and over and over again so tending to jump at any little info that's thrown out there.
The whole slow news day syndrome magnified b/c like many stations mine has something like 6 hours to fill every day so the commercials don't bump into each other.
matt

[hagar 0]

What is the big deal about GPS guided bombs? There are other ways to deliver bombs. I think there will be more problems for moving ground troops, they have used GPS the last ten years and may not know the art of navigating in a desert (they have probably learned land navigation, but why practice those skills when you can pull out a GPS?).

---
PCSS #10

[rhino 0]

Quote

You don't have to decrypt a signal in order to jam it.

You couldn't be more incorrect. You have to be on the same frequency, using the same algorythms in order to jam anything.

You can't block encrypted GPS signals unless you have the encryption keys. Which change every millisecond or so..

Rhino

[LouDiamond 1]

I think everyone here , like the media, is making this into more than it really is. GPS jamming is WAAAAAAYYY on the back burner of concerns right now. Actualy, it's not even on the stove.

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[indyz 1]

Gawain is right. You just have to overpower the "good" signal with garbage.

[AndyMan 7]

You don't need the same algorhythm, just the same frequency. Just broadcast white noise on the same frequency, and you'll overpower the real signal.

_Am

__

You put the fun in "funnel" - craichead.

[nathaniel 0]

Bomb accuracy / effectiveness is a bit like Zeno's paradox. The last few meters are the most important, but the hardest to get. If you can get your bombs on target more often, you can use fewer bombs and / or smaller bombs to get the same job done. "Force multiplier" blah blah blah. Also, the better the guidance system the further away a friend needs to be from the delivery mechanism.

Inertial guidance has been around since around (pre?) WWII, but has drawbacks. For instance, small errors tend to accumulate over time / distance into big errors. German V1 + V2 bombs had almost no military value in WWII despite being fairly big since they were totally inaccurate. Modern inertial guidance systems are better but still not as good as we would like.

GPS bombs are usually inertial guidance bombs (like someone posted above) except every once in a while they reset the inertial guidance system with GPS. This reduces the cumulative effects of inertial guidance errors. Satellite constellations are like the holy grail of planet-wide navigation. When they work, anyway.

Nathaniel

My advice is to do what your parents did; get a job, sir. The bums will always lose. Do you hear me, Lebowski?

[rhino 0]

WROOOOONG!!!!!!! Try again...

[nathaniel 0]

I don't think he's totally wrong. Such a technique would work against civilian GPS. Certainly the military uses civilian GPS receivers in addition to military grade ones.

Nathaniel

if you want technical detail about the civilian side I encourage you to read the .pdf I posted a link to above. It has a whole appendix on the vulnerabilities of civilian GPS, natural and man-made.

My advice is to do what your parents did; get a job, sir. The bums will always lose. Do you hear me, Lebowski?

[Guest]

As in "I'm gonna cram some RF into that satellite".

Ain't hard. ASAT would be even better if it weren't so difficult and expensive.

"The mouse does not know life until it is in the mouth of the cat."

[AndyMan 7]

Quote

WROOOOONG!!!!!!! Try again...

Unless they've invented a new kind of radio signal, any kind I know of can be overpowered.

GPS isn't spread spectrum, I don't think. I believe it broadcasts on a known frequency. Known frequencies can be locally overpowered - cheaply and easily.

Is there something special about GPS that prohibits this? IE, like spread spectrum?

_Am

__

You put the fun in "funnel" - craichead.

[Guest]

Probably some SHF version of Have Quick (synchronized freq hopping).

"The mouse does not know life until it is in the mouth of the cat."

[Gawain 0]

Quote

WROOOOONG!!!!!!! Try again...

If you are broadcasting encrypted signals across say, 5MHz of spread spectrum (800-805MHz), then in order to jam it, I simply need to broadcast a more powerful noise, in the same area, in the same spectrum. Hell, if my signal is strong enough, I won't even have to use the whole spectrum.

Now, if I want to try and translate that into misleading information (i.e. not jamming, but intercepting and retransmitting) then you need to break the encryption which is a fruitless task.

So I try and I scream and I beg and I sigh
Just to prove I'm alive, and it's alright
'Cause tonight there's a way I'll make light of my treacherous life
Make light!

[billvon 3,090]

>You couldn't be more incorrect. You have to be on the same
>frequency, using the same algorythms in order to jam anything.

No you don't. All you have to do is put out enough power to swamp the original signal. You could do it with a spark gap transmitter and LC filter with enough power. (1900's technology.)

>?You can't block encrypted GPS signals unless you have the
> encryption keys. Which change every millisecond or so..

You sure can. We designed several encrypted secure communications devices. They are as easy to jam as any other device - easier, since the encryption generally requires some overhead which either makes it harder to reaquire the signal or effectively reduces your Eb/No.

[billvon 3,090]

>Yes, the military stuff -can- put bombs -exactly- on target. Maybe
>not 100% of the time, but damn sure often enough.

You can definitely do that with DGPS. Accuracies down to a millimeter are possible - DGPS systems are used to track movements in faultlines. DGPS is even easier to jam though and you need a reference station on the surface.

[billvon 3,090]

>I fully expect the US would employ GPS "jamming" by degrading or
> turning off the GPS signal should iraq bombard the continental US
> with GPS guided bombs...

Not sure they would, given what havoc that would wreak with air travel, ocean naviagtion, cellphones, communications systems etc.

In any case, I think an invasion of the US by the Iraqi air force, and their subequent use of GPS guided munitions, ranks pretty low on the threat scale. And if we are worried about something like a Korean Taepodong II making it to the US - by the time we see it coming I think it will be too late to turn off GPS.

Interesting note - most OEM GPS's shut themselves down if their speed exceeds about 600 knots, to prevent their use in missiles.

[Gawain 0]

Quote

something like a Korean Taepodong II making it to the US - by the time we see it coming I think it will be too late to turn off GPS.

Wouldn't we know the moment they launched it? Say 30 minutes launch to impact, assuming it's GPS guided (doubtful anyway), we wouldn't be able to flip the switch in time?

So I try and I scream and I beg and I sigh
Just to prove I'm alive, and it's alright
'Cause tonight there's a way I'll make light of my treacherous life
Make light!

[billvon 3,090]

>Wouldn't we know the moment they launched it?

We'd know shortly after they launched it, but they've launched missiles before; the question is how long it would take us to determine that it was headed in our direction and was really going to make it here. Heck, the last missile they launched _was_ in our direction, but its range was limited, and it didn't get much farther than Japan.

>Say 30 minutes launch to impact, assuming it's GPS guided (doubtful
>anyway), we wouldn't be able to flip the switch in time?

If we knew it was coming I think we could shut things down in time. But coordination is always the issue with this stuff. You have to get a ground station to send messages to _all_ the GPS satellites, and they are only overhead once every 90 minutes or so. You'd need ground stations all over the planet to shut it down in a short time (10 minutes?) or at least three space-based relay satellites (like the TDRS satellites.) As far as I know we don't have anything like that for the GPS constellation.