What functions would be disabled if the GPS satelites were knocked out?

[Faelwolf]

The GPS system in the aircraft does not let "the powers that be" know the location of the aircraft at all times. I'm sure that Search and Rescue wishes it did!

For an example pretty close to the "defector" scenario mentioned earlier: http://en.wikipedia.org/wiki/Craig_D._Button

 

TAD is a wonderful aid in keeping track of your squadmates, and I really like being able to hook the flight lead for easy reference. But Yurgon is correct, while this system makes use of GPS data, it is not a direct function of the GPS system itself. Also don't forget TACAN which can be used for navigation and air to air tracking which makes no use of GPS at all.

 

If I read this correctly, you assume that GPS transmits an aircraft's location, which to the best of my knowledge is not correct. The GPS on the aircraft (just as in a car) is merely a receiver that calculates its own position with the help of the signals it receives from multiple satellites at the same time.

 

Of course, being a modern aircraft integrated with the other units on the battlefield, the A-10C has an array of communication devices so that other friendly units can know the aircraft's location (and the aircraft can know other unit's locations, like those shown on the TAD). I'm sure several of the guys on the forum can give a lot more information on the topic, but let's simply subsume all of these devices under the term "data link", and AFAIK the A-10C's datalink capability can be switched on or off with the switch labeled SADL (situational awareness datalink) JTRS (Joint Tactical Radio System) (although just recently I read that the system behind it is not actually called "SADL" "JTRS", they just didn't re-label the switch accordingly).

 

So if a pilot wanted to defect in an A-10C he could still use GPS without using the datalink. Then again, I doubt the Warthog would be a pilot's jet of choice to defect in because it is incredibly slow compared to just about anything that would be sent to intercept it... :megalol:

 

 

 

Faking GPS signals in order to reroute GPS receivers is pretty simple and doesn't even require the GPS satellites themselves to be affected in any way. Well, I couldn't do it, but from a technical point of view it's pretty straight forward, especially with unencrypted civilian GPS. As mentioned above, the US military uses encrypted GPS which is a lot harder to break and I don't know if there are any scenarios right now to perform such an attack in the real world.

 

When a US drone went down in Iran last year, one of the theories was that the military, encrypted GPS had been jammed, which led to a fall-back to the unencrypted and thus vulnerable signal. No clue whether that's what happened or whether the drone's software even uses such a fall-back, but it sounded like a plausible explanation for hijacking a drone.

 

Edit: Leto is right, I mixed up SADL and JTRS. I wish we had a strike-through markup on the forum, or did I just not find it?

[Echo38]

INU drift is not modelled

Are you sure of this? When I do not turn on the ... whatever that unlabelled switch is on the right console, I find that my pitch ladder gradually becomes more and more tilted diagonally.

[Eddie]

Are you sure of this? When I do not turn on the ... whatever that unlabelled switch is on the right console, I find that my pitch ladder gradually becomes more and more tilted diagonally.

 

That's HARS, a backup system wich operates in case of EGI failure. It is separate from the EGI, and its drift is indeed modelled.

 

Drift for the INU portion of the EGI is not modelled.

 

That "unnamed" switch is the EGI switch. And as its name suggest, it is both the INS and the GPS in one system. In the A-10C the only time GPS is not on when the INS is on is in the case of a failure of the GPS systems. And I'm not sure such a failure is modelled in DCS.

Edited August 12, 2012 by Eddie

[amalahama]

In the A-10C the only time GPS is not on when the INS is on is in the case of a failure of the GPS systems. And I'm not sure such a failure is modelled in DCS.

 

Yep. I've just tested changing my GPS_GNSS.lua to this

 

SAT_SYS_GLONASS = 0
SAT_SYS_GPS = 1

almanac = {}
--GPS

SA_mode = false
AS_mode = false

 

But EGI still maintain a FOM of 1 for GPS in SYS/GPS, and several GPS satellites detected.

 

So unfortunately GPS almanac is not implemented in DCS:A-10C.

 

Regards!

[redfish]

Good old INS overhead fixes. I suppose it's not like we are typing in GPS synchroniser keys now. Still gotta love this sim.

[Evil.Bonsai]

I think your understanding of the GPS is a little bit wrong to! A GPS satelite doesn't transmit speed nor heading nor altitude. It just continusly transmits the time (and some other stuff, which I will skip here) meassured by it's internal atomic clock. The satelite itselfe doesn't transmit your position as it doesn't know your position (your mobile phone can't be bositioned by GPS only as you don't send anything to the satelites).

The accuracy of GPS navigation depends on the number of satelites which send you their time. E.g.:

1 Satelite available: You only get the actual UTC time from the satelite. Your GPS won't do anything, as it doesn't know where it is.

2 Satelites available: Your GPS can now calculate a 2D position which maybe is prett inacurate.

3 Satelites available: Your GPS can now calculate a 3D position which is more accurate.

4 Sateelites or more available: As a GPS device normally doesn't have an atomic clock included the time meassurement is not as exact as it could be. With 4 satelites or more your GPS reciver can use the 4th (or any other of the four satelites) as a aid for more precise timing, which will allows the GPS to calculate your position more actually.

 

The calculation of the position can be explained easily (Altough it is much more difficult):

For example you have 3 satelites available, every one sends you their time. Every time has been send at exactly 08:00:00 o'clock. We recived the signals at that times:

 

1. 08:00:02 The signal traveled 2 seconds from the satelite to you.

2. 08:00:03 This signal even traveled 3 seconds.

 

As the satelites send out electro magnetic waves, which travel with the speed of light, we would be able to calculate the distance ( distance = speed * time ).

Now we know the distance from both satelites, and we somehow (I don't want to exain that here) know their possition. We can now draw two imagine lines from the satelites. Our position is at that point where both ends meet. Now we know our latheral position but not our altitude. That is the momment where the 3rd satelite comes in handy. We recived it's signal at 8:00:05 (5 second of travel). We can also calculate our distance relative to it and we also can draw that line, whic end also is at our position. Now the GPS can calculate our altitude to.

 

Heading and speed aren't transmited by the satelite as stated privously, they are just easy (easier than the calculations bevore :D ) calculations: The GPS device "thinks": One second before I have been there, now I am here, that means I hae traveled so fast in that heading.

 

 

I hope thats understandable, it is not technically perfect and I am pretty tired (1 am in the mornig, lol), but it may helps you to understand the GPS.

If somebody finds any failures in my descripiton, please corrrect me, thanks!

 

Best regards!

John

 

Any chance you could forward this to AT&T/Samsung? After they udated my phone to Android 4.0, my phones gps is fubar. They might learn something from this.

[xxJohnxx]

Any chance you could forward this to AT&T/Samsung? After they udated my phone to Android 4.0, my phones gps is fubar. They might learn something from this.

 

:megalol: Lol

 

Ever tried to leave your GPS needing application (like maps, or whatever) running for about 20 minutes? This could theoretically help, but I am not sure how it is about your phone. The reason for this:

 

...and we somehow (I don't want to exain that here) know their possition.

 

A GPS device can have a hard time finding sattelites if it doesn't know where they are.

To encounter this every sattelite sends out a so called Almanac, an information which contains an information, where to expect all the sattelites.

With that information a GPS device can reduce the search time by a high number, however a transmittion of that Almanac can take 12.5 minutes*. So if you have bad luck, you may have to wait 24 minutes to get an complete Almanac message.

 

Maybe this helps your phone in the future, but there is just one little problem:

 

Normaly the Almanac can be downloaded from the internet. A good GPS software on a phone with internet connection could do that in seconds (the message is tiny). I don't know if your mobile has an internet access neither do I know if Android contains that feature (it would be very emberassing if it doesn't, but I can't say).

 

 

*The Almanac message is not very big, however if you get something from a GPS satelitte you can expect a download speed of about 3000 bit per minute.

To see how such a thing looks like, you can download one from here.

Jump to that line:

 

Current YUMA Almanac - .alm, .txt

 

And dowload the .txt

Have a good read :D

 

Please note: I don't think that any information from that post can help you with your phone (you can give it a try thought!), but at least you have something to think about, and a little bit more to talk about:smilewink:

 

Best regards,

 

John