| The GPS satellite system for navigation was | | | | military, they did include some capabilities |
| designed in the 1970s by the U.S. Department | | | | that could be useful for the civilian |
| of Defense. It started out as a global | | | | community. The GPS satellites transmit |
| navigation system for military land-based and | | | | encrypted signals, which only the military |
| air vehicles, with some limited use for the | | | | has access to. The satellites also transmit |
| civilian population. But today, the tables | | | | non-encrypted signals, which can be detected |
| have turned - there are more GPS receivers | | | | in both military and civilian GPS receivers. |
| used by civilians than by the military! | | | | The civilian signal is referred to as the C/A |
| | | | code signal (Coarse Acquisition). |
| Back in the 70's, the military employed a | | | | |
| variety of navigation systems such as LORAN | | | | A key parameter that describes GPS capability |
| (acronym for Long Range Radio Navigation), | | | | is positioning accuracy, which simply put, is |
| VOR (acronym for VHF Omni-directional Radio) | | | | the accuracy of the GPS receiver user's |
| and OMEGA, and a need was felt for a more | | | | position computed in the GPS receiver. GPS |
| accurate navigational aid which would be | | | | system developers initially did not expect |
| functional all day, all year and everywhere | | | | the civilian signal to provide position |
| on Earth, irrespective of day or night or | | | | accuracy comparable with those obtained by |
| weather conditions. The military's needs were | | | | the military signals. However, the designers |
| to navigate its airplanes, tanks and | | | | soon realized that the civilian GPS receivers |
| personnel reliably. At that time, the U.S. | | | | could employ several newly developed |
| Navy and the Air Force were in the pursuit of | | | | algorithms that could improve the position |
| developing systems that would meet such | | | | accuracy obtained in civilian GPS receivers |
| requirements with programs such as Transit | | | | dramatically. In order to limit the |
| satellite system, Timation satellite system | | | | positional accuracy of civilian GPS |
| and Project 621B. The Department of Defense | | | | receivers, they implemented degradations of |
| eventually formed a Joint Program Office | | | | the civilian GPS signal before being |
| (JPO), which consolidated the developments to | | | | transmitted by the GPS satellites. The |
| date in to what we know today as the Global | | | | degradation capability is referred to as |
| Positioning System (GPS). | | | | Selective Availability (SA). SA limited |
| | | | position accuracy in GPS receivers to ~50 |
| The first GPS satellite was launched in 1974, | | | | meters. However, by late 1990s, President |
| and the GPS satellite constellation was | | | | Clinton having realized the benefit of GPS to |
| declared fully operational in 1994. The | | | | the civilian community, ordered SA |
| satellites were/are designed and built by | | | | degradation to be removed. With the removal |
| Rockwell International, Boeing and | | | | of SA, the doors opened up for civilian users |
| Lockheed-Martin. | | | | to use GPS for automotive tracking for |
| | | | driving assistance, fleet management, |
| Though GPS was designed by the DOD for the | | | | ……. |