| Global Positioning System (GPS) | | | | provide two different signals that provide |
| | | | different accuracies. Coarse-acquisition (C |
| Originally designated the NAVSTAR (Navigation | | | | A) code is intended for civilian use, and is |
| System with Timing And Ranging) Global | | | | deliberately degraded. The accuracy using a |
| Positioning System, (GPS) was developed by | | | | typical civilian GPS receiver with C/A code |
| the US Department of Defense to provide | | | | is typically about 100 meters. The military's |
| all-weather round-the-clock navigation | | | | Precision (P) code is not corrupted, and |
| capabilities for military ground, sea, and | | | | provides positional accuracy to within |
| air forces. Since its implementation, the GPS | | | | approximately 20 meters. Numerous on-line |
| system has also become an integral asset in | | | | tutorials on how GPS works and its |
| numerous civilian applications and industries | | | | applications are available, including those |
| around the globe, including recreational uses | | | | at the University of Texas and Rentec |
| (e.g. boating, aircraft, hiking), corporate | | | | International. GPS systems satellites are |
| vehicle fleet tracking, and surveying. | | | | controlled at the GPS Master Control Station |
| | | | (MCS) located at Falcon Air Force Base |
| The GPS system employs 24 spacecraft in | | | | outside Colorado Springs, Colorado. The |
| 20,200 km circular orbits inclined at 55 | | | | ground segment also includes four |
| degrees. These spacecraft are placed in 6 | | | | active-tracking ground antennas and five |
| orbit planes with four operational satellites | | | | passive-tracking monitor stations. |
| in each plane. All launches have been | | | | |
| successful except for one launch failure in | | | | GPS receiver technology has developed by |
| 1981. The full 24-satellite constellation was | | | | leaps and bounds over the last few years. |
| completed on March 9, 1994. | | | | GPS receivers were initially the size of a |
| | | | suitcase with the antenna the size of a kid's |
| The first eleven spacecraft (GPS Block 1) | | | | blow up swimming pool. Over time, the system |
| were used to demonstrate the feasibility of | | | | has been developed into a civilian friendly |
| the GPS system. The orbit inclination used | | | | program, and GPS receiver technology has |
| for these satellites was 63 degrees, | | | | miniaturized as well. Automobile GPS |
| differing from the 55 degrees used for the | | | | receivers are the size of a deck of cards. |
| operational system. The Block 2 spacecraft | | | | The gps receiver used in hand held devices is |
| began the operational system. The Block 2A | | | | not much larger than a small cell phone. |
| spacecraft (A = Advanced) were a slight | | | | Many newer cell telephones have a GPS |
| improvement over the Block 2. | | | | receiver integral in their hand set. As |
| | | | manufacturers develop the GPS receiver, they |
| The Global Positioning System (GPS) was | | | | will have to work through display, power use |
| designed as a dual-use system with the | | | | and dexterity limitations. An individual |
| primary purpose of enhancing the | | | | will need a screen with a size that can be |
| effectiveness of U.S. and allied military | | | | viewed from any angle and at a reasonable |
| forces. GPS is rapidly becoming an integral | | | | distance. The GPS receiver is generally |
| component of the emerging Global Information | | | | always on while in use, so managing power |
| Infrastructure, with applications ranging | | | | will continue to be an on going problem. The |
| from mapping and surveying to international | | | | ability to push the small buttons will limit |
| air traffic management and global change | | | | just how small a GPS receiver can be. As |
| research. The growing demand from military, | | | | touch screens develop and other input systems |
| civil, commercial, and scientific users has | | | | are introduced, we will see the GPS receiver |
| generated a U.S. commercial GPS navigation | | | | continue to change in appearance and use. |
| systems equipment and service industry that | | | | |
| leads the world. Augmentations to enhance | | | | Author: John B. Whitsell |
| basic GPS services could further expand these | | | | |
| civil and commercial markets. | | | | Making Tracks GPS |
| | | | |
| GPS systems receivers use triangulation of | | | | Information referenced from NASA and USCG |
| the GPS satellites' navigational signals to | | | | data. |
| determine their location. The satellites | | | | |