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Research paper topic: Gps: The Future Of Navigation And Technology - 1829 words
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GPS: The Future of Navigation and Technology As we enter the 21st century, we are constantly being bombarded with new technologies. From the wireless community to operations that once took weeks to recover and now only take a day or so, our world will never be the same. Another technology that is revolutionizing the world we live in is the Global Positioning System or GPS. The first GPS satellite was called GPS Block I. Launched in 1978, it was a developmental satellite.
Another nine Block I satellites were launched through 1988. GPS is the only system today able to show you your exact position on the Earth anytime, in any weather, anywhere. There are 24 GPS satellites in orbiting the world at 11,000 nautical miles above the Earth. Ground stations located worldwide continuously monitor them. They transmit signals that can be detected by anyone with a GPS receiver.
Using the receiver, you can determine your location with great precision. GPS is one of history's most exciting and revolutionary developments and new uses for it are constantly being discovered. But before I go any farther it's important to understand a bit more about navigation. Since prehistoric times, people have been trying to figure out a reliable way to tell where they are, to help guide them to where they are going, and to get them back home again. Cavemen probably used stones and twigs to mark a trail when they set out hunting for food. The earliest mariners followed the coast closely to keep from getting lost.
When navigators first sailed into the open ocean, they discovered they could chart their course by following the stars. The ancient Phoenicians used the North Star to journey from Egypt and Crete. According to Homer, the goddess Athena told Odysseus to keep the Great Bear on his left during his travels from Calypso's Island. Unfortunately for Odysseus and all the other mariners, the stars are only visible at night - and only on clear nights. The next major developments in the quest for the perfect method of navigation were the magnetic compass and the sextant. The needle of a compass always points north, so it is always possible to know in what direction you are going.
The sextant uses adjustable mirrors to measure the exact angle of the stars, moon, and sun above the horizon. However, in the early days of its use, it was only possible to determine latitude, the location on the Earth measured north and south, from the sextant observations. Sailors were still unable to determine their longitude, the location on the Earth measured east or west. This was such a serious problem that in the 17th century, the British formed a special Board of Longitude consisting of well-known scientists. This group offered 20,000, equal to about a million of todays dollars, to anybody who could find a way to determine a ship's longitude within 30 nautical miles. The generous offer paid off.
In 1761, a cabinetmaker named John Harrison developed a shipboard timepiece called a chronometer, which lost or gained only about one second a day - incredibly accurate for the time. For the next two centuries, sextants and chronometers were used in combination to provide latitude and longitude information. In the early 20th century several radio-based navigation systems were developed, which were used widely during World War II. Both allied and enemy ships and airplanes used ground-based radio-navigation systems as the technology advanced. A few ground-based radio-navigation systems are still in use today. One drawback of using radio waves generated on the ground is that you must choose between a system that is very accurate but doesn't cover a wide area, or one that covers a wide area but is not very accurate.
High-frequency radio waves (like UHF TV) can provide accurate position location but can only be picked up in a small, localized area. Lower frequency radio waves (like AM radio) can cover a larger area, but are not a good yardstick to tell you exactly where you are. Scientists, therefore, decided that the only way to provide coverage for the entire world was to place high-frequency radio transmitters in space. A transmitter high above the Earth sending a high-frequency radio wave with a special coded signal can cover a large area and still overcome much of the noise encountered on the way to the ground. This is one of the main principles behind the Global Positioning System. GPS has 3 parts: the space segment, the user segment, and the control segment.
The space segment consists of 24 satellites, each in its own orbit 11,000 nautical miles above the Earth. The user segment consists of receivers, which you can hold in your hand or mount in your car. The control segment consists of ground stations. There are five of them, located around the world that make sure the satellites are working properly. One trip around the Earth in space equals one orbit.
The GPS satellites each take 12 hours to orbit the Earth. Each satellite is equipped with an accurate clock to let it broadcast signals coupled with a precise time message. The ground unit receives the satellite signal, which travels at the speed of light. Even at this speed, the signal takes a measurable amount of time to reach the receiver. The difference between the time the signal is sent and the time it is received, multiplied by the speed of light, enables the receiver to calculate the distance to the satellite.
To measure precise latitude, longitude, and altitude, the receiver measures the time it took for the signals from four separate satellites to get to the receiver. The GPS system can tell you your location anywhere on or above the Earth to within about 300 feet. Even greater accuracy, usually less than three feet, can be obtained with corrections calculated by a GPS receiver at a known fixed location. To help you understand the GPS system, let's take the three parts of the system - the satellites, the receivers, and the ground control - and discuss them in more detail. Then we will look more closely at how GPS works. As I said before, the complete GPS space system includes 24 satellites, 11,000 nautical miles above the Earth, which take 12 hours each to go around the Earth once (one orbit). They are positioned so that we can receive signals from six of them nearly 100 percent of the time at any point on Earth.
You need that many signals to get the best position information. Satellites are equipped with very precise clocks that keep accurate time to within three nanoseconds - that's 0.000000003, or three billionths, of a second. This precision timing is important because the receiver must determine exactly how long it takes for signals to travel from each GPS satellite. The receiver uses this information to calculate its position. The first GPS satellite was launched in 1978. The first 10 satellites were developmental satellites, called Block I.
From 1989 to 1993, 23 production satellites, called Block II, were launched. The launch of the 24th satellite in 1994 completed the system. The GPS control, or ground, segment consists of unmanned monitor stations located around the world. They are in Hawaii and Kwajalein in the Pacific Ocean; Diego Garcia in the Indian Ocean; Ascension Island in the Atlantic Ocean; and Colorado Springs, Colorado. A master ground station at Falcon Air Force Base in Colorado Springs, Colorado, and four large ground antenna stations that broadcast signals to the satellites. The stations also track and monitor the GPS satellites.
GPS receivers can be hand carried or installed on aircraft, ships, tanks, submarines, cars, and trucks. These receivers detect, decode, and process GPS satellite signals. More than 100 different receiver models are already in use. The typical hand-held receiver is about the size of a cellular telephone, and the newer models are even smaller. The hand-held units distributed to U.S. armed forces personnel during the Persian Gulf war weighed only 28 ounces.
So you can more easily understand some of the scientific principles that make GPS work, let's discuss the basic features of the system. The principle behind GPS is the measurement of distance between the receiver and the satellites. The satellites also tell us exactly where they are in their orbits above the Earth. It works something like this: If we know our exact distance from a satellite in space, we know we are somewhere on the surface of an imaginary sphere with radius equal to the distance to the satellite radius. If we know our exact distance from two satellites, we know that we are located somewhere on the line where the two spheres intersect.
And, if we take a third measurement, there are only two possible points where we could be located. One of these is usually impossible, and the GPS receivers have mathematical methods of eliminating the impossible location. We know that the GPS system consists of satellites whose paths are monitored by ground stations. Each satellite generates radio signals that allow a receiver to estimate the satellite location and distance between the satellite and the receiver. The receiver uses the measurements to calculate where on or above the Earth the user is located.
Now that you have an idea about how the GPS functions, let's see how we can put it to work for us. As you might imagine, GPS has many uses in both military and civilian life. Although the GPS satellite constellation was completed only recently, it has already proved to be a most valuable aid to U.S. military forces. The mustering of forces for Desert Shield sent a wake-up call to U.S.
military forces. With an average of only 39 days of training each year, National Guard and reserve troops had to work double time to prepare for Desert Storm's offensive thrust. To ensure that an adequate number of reservists would be ready if the need should again arise, Congress established the $92 million Simulation in Training for Advanced Readiness program. From this sprang a revolutionary GPS-based battle simulation system. Major Jeff Grant explains that the battle simulation uses 70-ton Abrams tanks, Bradley fighting vehicles, and ground troops. All of the vehicles and personnel are equipped with the Deployable Force-on-Force Instrumented Range System (DFIRST).
Maj. Jeff Grant pointed out that simulation takes place outside Boise Idaho. By combining off-the-shelf radio communications equipment and GPS receivers with specially developed software, DFIRST enables armored units to conduct highly realistic combat practice to improve their battle readiness. Inside the 70-ton Abrams tank, these block letters glow softly on the in-vehicle display screen, informing the crew of Charley 12 that it is now operating in a live distributed battlefield simulation. Departing from traditional training methods in which combat units travel to remote locations for two or three weeks of maneuvers, Charley 12 and its four-man crew are testing an instrumentation system that enables company-sized units to conduct force-on- force combat-readiness training on ranges near their home base.
From 12,000 miles above the arid terrain, GPS satellite signals cast a net encompassing every inch of the mock battlefield. Using on-board instrumentati ...
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