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