...Everyone must keep one thing in mind. GPS is NOT a civilian system, it is built for and run by the D.O.D. All of the stand alones and computer programs are put together by private companies. The system is only 25-35 years old and everyone is still learning how to use it. Use on the roads is really new. If you were flying an airplane there are much better systems....
Just be sure to remember that it IS a D.O.D. system and they can, if they have to, encrypt the signal and EVERY gps system other than thier own would quit working....
Not really. The Global Positioning System, while originally a US military project, is considered a
dual-use technology, and is now a part of the civilian fabric worldwide. Most of the satellites that are currently up there, and all of them in the next generation of GPS, doesn't even have the capability of being encrypted.
Ground-based radar navigation systems, the LORAN and the Decca Navigator system, were developed and used during WWII. When Sputnik was launched in 1957, scientists discovered that because of the Dopler Effect and knowing their precise position on the globe, they could determine Sputnik's precise orbit by measuring the Dopler Effect. Inspiration moved the US Navy to first test 5 satellites for navigation in 1960, which provided a position update about once an hour. In 1967 the Navy developed the Timation satellite, which proved that accurate clocks coule be put in space, something that future GPS satellites would need. In the 1970's the Omega Navigation System became the first worldwide radio navigation system, based in part on signal phase comparison and on satellite data.
The Omega System was the one that was used by the military and commercial aircraft, as well as maritime shipping, for many years, right up until KAL Flight 007 was shot down in 1983 after wandering into Soviet air space. President Reagan then signed an Executive Order making GPS freely available for civilian use for the common good. The NAVSTAR satellites, which is the GPS sysem we use today, were launched between 1989 and 1993 and became officially operational in 1995. All of the originals have been replaced with more modern satellites that allow for more accurate positioning and more precise timing applications. Newer satellites with more stuff is planned for the near future (GPS III)
Selective Availability is the term used where one signal, highly accurate but encrypted, is for the military, and another signal, intentionally degraded with positional errors of up to 100 meters, for civilian use. Selective Availability was the standard, with the military using the more accurate L1 Signal and the rest of us using the intentionally degraded signal.
During the 1990-1991 Gulf War, a shortage of military GPS units, compared with the widespread availability of civilian units, caused many soldiers in the field to buy their own civilian units. The whole Selective Availability thing was based on the assumption that U.S. troops and enemy troops would have military-specification GPS receivers and that civilian receivers would not exist in war zones. In an ironic twist of fate, Selective Availability was now hindering friendly troops instead of enemy troops. So they turned it off.
If they turned it back on again, the world's GPS receivers wouldn't suddenly stop working, they'd merely be inaccurate.
After the Gulf War the FAA (among many others) wanted the military to make the change permanent, as it would save them millons of dollars a year in maintaining the radio navigation systems. Bill Clinton signed an Executive Order stating that the amout of error introduced to the civilian signal be set to zero, and that the L1 signal be unencrypted and available for civilian use. This happened in 2000. In 2005 the next generation of satellites containing a second L2C signal (the one the SIRF II and SIRF III chipsets read) went operational, and over the next couple of years yet another generation of satellites will be launched.
In theory, the Selective Availibility could be turned back on and errors introduced, but knowing the problems involved, flight and shipping safety, it's highly unlikely that it would ever happen, and the FAA and the military both say it won't, as it has worldwide implications. The specs for the GPS III satelites, in fact, do not even have the capability of encryption or Selective Availability, nor the abillity of selctive turning on or off the various Block Signals, thus making the policy of unfettered civilian access to GPS satellites a permanent one. The specific military channels of the satellites, of course, are encrypted. They include channels signals that detect nuclear detonations, among other things.
The new GPS III satellites will have four new civilian channels. And one military channel which when used with the new DAGR (Defense Advanced GPS Receiver) will detect GPS jamming signals and still maintain an encrypted lock on the satellite even when civilian units lose the signal lock. But GPS jamming only works for relatively small areas, line of sight, or within radio range. So it's not like someone can flip a switch and turn off all the GPS receivers worldwide.
My Garmin Nuvi 350 works fine for me, but it's a personal preference thing, mostly.
