GPS

[mhcasey]

Anyone got any good links/books on how it works? I don't mean "there's 24 satellites and 5 have to be in view and there's this thing called RAIM and now there's WAAS..." I mean "this is technically what happens. Here is the equipment and how it works. Here's what happens if China shoot down one of the GPS satellites. etc."

I need a pretty good understanding in order to write a paper about UAVs and the Air Force's reliance (JDAMs) on GPS (and vulnerability as a result?).

[fish314]

"Global Navigation for Pilots" by Dale De Remer and Donald W. McLean (published by ASA, ISBN 1-56027031207) goes into depth pretty well. It goes so far as to tell you the frequencies that the satellites transmit on, how many BITS in each segement of the code they transmit, the inclination and altitude of satellites orbits, etc., etc., etc. Of course, only 1 chapter is about GPS, since the book is about NAVIGATION in all it's various forms (including dead reckoning, VOR/DME navigation, and celestial).

Might help you though.

[MDPilot]

http://www.aero.org/education/primers/gps/elements.html

http://www.aero.org/publications/cro...er2002/02.html

http://www8.garmin.com/aboutGPS/

[woodreau]

Of all of the military weapons that use GPS guidance, none of them use RAIM or WAAS. They use the military PPS signal. The biggest limitation to all these GPS guided weapons (from my point of view)- none of them can hit moving targets.

RAIM and WAAS are enhancements to the basic GPS signal that the aviation community needed because lives (pilots and passengers in the airplane) really are depending on that GPS signal working.

The maritime industry also uses differential GPS, but it's not as critical.

[RPJ]

Originally Posted by mhcasey

Here's what happens if China shoot down one of the GPS satellites. etc.

I need a pretty good understanding in order to write a paper about UAVs and the Air Force's reliance (JDAMs) on GPS (and vulnerability as a result?).

One does not need to destroy a satellite to deny the use of GPS signals. There are such things as localized GPS signal jammers that if PROPERLY utilized it will render the GPS signal unusable. The USAF knows a lot about this and ways to minimize the risks.

[BuickCFI]

http://www.trimble.com/gps/index.shtml

[vheissu]

Lots of information here: http://en.wikipedia.org/wiki/Gps

Since it was developed by the US Department of Defense, do other countries have use of it, or have their own satellites? Can companies in other countries develop devices to use it?

[RPJ]

Originally Posted by vheissu

Lots of information here: http://en.wikipedia.org/wiki/Gps

Since it was developed by the US Department of Defense, do other countries have use of it, or have their own satellites? Can companies in other countries develop devices to use it?

The system is owned and operated by the US, any country on earth may use the system if they have a GPS receiver. The US has a signal denial system that prevents anyone within a specific region, any region in the world dictated by the US govt, to use the GPS signal. The military PPS signal still works in those regions where active denial is taking place and only USA/allies with specific PPS GPS coded receivers can access the system.

Whenever we go to war we deny the enemy the use of GPS while our forces take full advantage of it. The only option an enemy would have would be an attempt to jam the PPS signal that is received on the ground for an area. Hence my post above, the USAF has some affective countermeasures to GPS jammers. This is one reason why the Air Force still maintains very well other targeting systems.

The only other satellite navigation/targeting system in use today is the Russian made constellation. The system is so dilapidated that only a handful of satellites even work still and the coverage area is a relatively small spot around the former USSR.

-Ryan

[RPJ]

The Russian system is called GLONASS
http://en.wikipedia.org/wiki/GLONASS

The New EU system is called Galileo
http://en.wikipedia.org/wiki/Galileo_positioning_system

The Chinese system is called Beidou
http://en.wikipedia.org/wiki/Beidou_navigation_system

The new Indian system is called Indian Regional Navigational Satellite System
http://en.wikipedia.org/wiki/IRNSS

As of 2007, USA's NAVSTAR GPS is the only fully operational global navigation satellite system.

-Ryan