The Global Positioning System (GPS) is a navigational and accurate positioning tool. In 1973, the United States Department of Defense (DoD) developed the precise positioning tool to assist soldiers, vehicles, planes, and ships in pinpointing their exact locations around the world. Fast forward nearly forty years later and the GPS unit has become a widespread phenomenon used by all facets of society. In fact, the popularity of the GPS tool has grown exponentially, insomuch that it has been included in airplanes, boats, cars, and mobile devices. The GPS unit has become the “compass” of all outdoor recreational activities, such as hiking, fishing, and kayaking. If a GPS unit sounds limiting, think again! The scientific community has used it for weather forecasting, global climate monitoring, geological surveying, and even to measure the motion of tectonic plates during, in between, and after earthquakes.
Early mariners and travelers used the sun, stars, and landmarks to navigate to their destination. They used sextants, or astronomical instruments used to measure the angle between two observable objects, to determine the altitude between a celestial object and the horizon, therefore effectively charting the coordinates of the stars, sun, and the planets according to their natural course. Others used a compass as a navigational tool to measure the frame of reference, or cardinal directions that are stationary to the Earth's surface. In the Eighteenth century, John Harrison invented the chronometer, which allowed navigators to uncover the time in two different places at once to determine the longitude. In the 1930's, aviation stations used radio beacons, or low frequency and medium frequency transmitters, to locate airway intersections, airway stations, and airports with a span of several miles. The launch of the space race during the 1950's and 1960's marked the beginning of the GPS navigational system. In 1957, the Russians launched Sputnik, the world's first artificial satellite, which emitted radio waves that allowed researchers to pinpoint its location. This caused researchers to think they could determine a specific coordinate on Earth from a satellite in space.
In response to the Russian Sputnik discoveries, the United States Navy developed TRANSIT in the 1960's to actively track their fleet of nuclear and ballistic submarines. TRANSIT was a system that consisted of three different satellites that orbited in space; however, it had its share of problems. For instance, it had low accuracy and limited availability. During this time, the United States Air Force created their own system to pinpoint land vehicles and aircraft. Finally, the United States Navy and Air Force systems combined to create Navigation Satellite Timing And Ranging (NAVSTAR), the prototype of the modern GPS.
The NAVSTAR project remained classified until 1983, when one of the orbiting satellites caused a commercial plane to be shot down. This caused the military to declassify the project, making it available to the general public. It marked the beginning of the modern GPS system. Over the course of eight years, ranging from 1989 to 1997, twenty eight satellites were released to create a “GPS constellation.” The United States military tested this GPS satellite cluster and discovered that it had successfully established a functional navigational and positioning system. This enabled the military to identify and focus their ground assault on specific targets, which resulted in quicker victory during the Gulf War.
How GPS Systems Work
The Global Positioning System (GPS) operates from three separate segments. The first segment of the GPS system consists of twenty four satellites that continually orbits above the Earth in twelve hour orbital intervals. In layman's terms, this means that it takes each satellite approximately twelve hours to completely move around the Earth. The overseers of the GPS mainframe have divided these satellites into six different groups of four, with each group assigned a different path to follow. This creates six different orbital planes that encircle the entire Earth. Each satellite relays pertinent information about the satellite itself.
The GPS mainframe overseers use ground-based receivers to detect, decipher, and determine the satellite's position in terms of latitude, longitude, and height. The radio signals are transmitted via two different L-band frequencies, a range between 390 and 1550 megahertz. Each radio signal contains a coded sequence that scientists use to compare with the original sequence, which can be used to determine how long it takes for the radio signal to reach the Earth's surface from orbital space. Scientists can use this data to learn more about the Ionosphere and the Troposphere, or two atmospheric layers surrounding the Earth's surface. Lastly, a third radio signal is transmitted from the satellite's receivers that reveal information about the health and position of the satellite. These radio signals are sent to the GPS ground station, which houses a receiver, antenna, and an assortment of communication tools that relay the transmitted information to one of the many data centers located around the world for future processing.
Commercial manufacturers have integrated GPS systems in every facet of civilian life. The military has further advanced the GPS cluster to enhance its accuracy when decimating its targets. GPS systems are used in planes, emergency vehicles, automobiles, phones, and computers. Consumers can purchase separate GPS devices specially designed for recreational outdoor activities. Auto insurance companies have equipped vehicles to test the driver's competency and skill level behind the wheel. Other commercial uses for GPS systems include balloon tracking, business logistics, agriculture, GeoCaching, lost pets, 9/11 assistance, personal emergency devices, and roadside assistance. Environmentalists have also used GPS systems to monitor the health of the ozone layer.
GPS Educational Materials
Follow these links to learn more about the Global Positioning System (GPS):