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