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