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