GPS receivers come in a variety of consumer formats, and today can be found in cars, watches, phones boats and planes. Major manufacturers include Trimble, Garmin and Leica, low-end, hand-held consumer units are often available at less than $100 per unit.
In late 2005, the US government introduced the first in a series of new generation GPS staellites offering new capabilities. Chief among these is a second civilian GPS signal called L2C for greater accuracy and reliability.
GPS is short for (the) Global Positioning System, a satellite navigation system developed by the US Department of Defense. A fleet of more than two dozen GPS satellites broadcasts precise timing signals to GPS receivers, allowing them to accurately determine location anywhere on Earth. In practice, this means that using a GPS device, you can find out where you are in terms of longitude, latitude and altitude.
GPS derives in part from its predecssor, the LORAN navigation system. LORAN was designed for ship and airplane navigation in the 1940s for use during World War II.
GPS has become a vital global utility, indispensable for modern navigation on land, sea, and air around the world, as well as an important tool for map-making, and land surveying. GPS also provides an extremely precise time reference, required for telecommunications and some scientific research, including the study of earthquakes.
The first experimental Block-I GPS satellite was launched in February 1978. The GPS satellites were initially manufactured by Rockwell International and now manufactured by Lockheed Martin.
In 1996, President Bill Clinton issued a policy directive declaring GPS to be a dual-use system, meaning that it could be made avilable for a wide range of civilian and military purposes.
The United States Department of Defense developed the system, officially named NAVSTAR GPS (Navigation Signal Timing and Ranging GPS), and the satellites are managed by the 50th Space Wing at Schriever Air Force Base. Although the cost of maintaining the system is significant, GPS is available for free use in civilian and commercial applications.
GPS was first made available for commercial applications in 1983, after the Soviet Air Force shot down the civilian airliner KAL 007 in restricted Soviet airspace, killing all 269 people on board.
Selective Availablity typically added signal errors of up to about 10 m horizontally and 30 m vertically. The inaccuracy of the civilian signal was deliberately encoded so as not to change very quickly, for instance the entire eastern US area might read 30 m off, but 30 m off everywhere and in the same direction. In order to improve the usefulness of GPS for civilian navigation, Differential GPS was used by many civilian GPS receivers to greatly improve accuracy.
In 1998, Vice President Al Gore announced plans to upgrade GPS with two new civilian signals for enhanced user accuracy and reliability, particularly with respect to aviation safety.