GPS, also known as the Global Positioning System, is a revolutionary technology that is reshaping our world in the 21st century. It enables us to determine our precise location on Earth at any time and in any weather condition, no matter where we are. The first GPS satellite, called GPS Block I, was launched in 1978 for experimental purposes. This was followed by nine more Block I satellites until 1988. Currently, there are 24 GPS satellites orbiting the Earth from a distance of 11,000 nautical miles. These satellites continuously transmit signals that can be detected by any GPS receiver, which allows individuals to accurately determine their location. The development and applications of GPS are constantly advancing, making it one of the most remarkable and groundbreaking advancements in history. However, it’s important to note that navigation techniques have been pursued since ancient times. Cavemen may have used stones and twigs as markers while hunting, and early mariners would carefully follow coastlines to avoid getting lost in unfamiliar seas filled with fear and uncertainty.During a time filled with danger and hope, these brave explorers fearlessly ventured into unknown territories, relying solely on the stars and knowledge gained from previous expeditions to find their way through vast expanses of water. Their courage led them to risk their lives in order to explore new lands and establish trade routes in a completely unfamiliar world. These endeavors not only laid the groundwork for future expeditions but also uncovered untapped possibilities that would greatly influence future generations.
Sailors discovered that they could navigate by using stars in the open ocean. The ancient Phoenicians used the North Star for their travels from Egypt and Crete, as recounted by Homer when Athena instructed Odysseus to keep the Great Bear on his left during his journey from Calypso’s Island. However, stars can only be seen at night and on clear nights. Advancements in navigation came later with the invention of the magnetic compass and sextant. A compass needle points north consistently, providing a constant indication of direction. The sextant uses mirrors to measure angles of stars, moon, and sun above the horizon. Initially, it only determined latitude (north or south position), while longitude (east or west position) remained a challenge.
To address this challenge, the British established a Board of Longitude in the 17th century with renowned scientists. They offered a reward of £20,000 to anyone who could determine longitude within 30 nautical miles. John Harrison’s chronometer invention in 1761 was highly accurate for its time, losing/gaining about one second per day. For centuries, sextants and chronometers were used together to determine both latitude and longitude.
In the early 20th century, radio-based navigation systems were developed and widely used during World War II by both allied and enemy ships and airplanes as technology advanced.The utilization of certain systems today comes with limitations that force users to make a trade-off between accuracy and coverage area. High-frequency radio waves offer precise location information but are restricted to small, localized areas. In contrast, lower frequency waves cover larger areas but lack accuracy. Therefore, scientists determined that positioning high-frequency radio transmitters in space was the most effective method for achieving global coverage. By transmitting encoded signals through high-frequency radio waves from space, it becomes possible to cover a large area while minimizing interference. This principle forms the foundation of the Global Positioning System (GPS). The GPS system consists of three main components: the space segment which involves 24 satellites individually orbiting 11,000 nautical miles above Earth; the user segment which includes handheld or car-mounted receivers; and the control segment consisting of ground stations spread across the world for ensuring satellite functionality. Each GPS satellite completes an orbit every 12 hours during its journey in space around Earth. These satellites possess accurate clocks for broadcasting signals along with precise time messages. The ground unit receives signals from these satellites traveling at the speed of light; however, there is still a delay in reaching the receiver despite their fast nature.By using the time difference between the sending and receiving of signals, multiplied by the speed of light, receivers can calculate the satellite’s distance. They utilize signals from four satellites to accurately measure latitude, longitude, and altitude based on signal travel time.
The GPS system can determine your location anywhere on or above the Earth, with an accuracy of about 300 feet. By using corrections calculated by a GPS receiver at a known fixed point, even greater accuracy, usually less than three feet, can be achieved. The system consists of three components – satellites, receivers, and ground control – which work together to ensure its functioning. The complete GPS space system includes 24 satellites positioned approximately 11,000 nautical miles above the Earth. Each satellite completes one orbit in 12 hours. These strategically placed satellites guarantee that we can receive signals from at least six of them at any given point on Earth for optimal position information. Moreover, these satellites have incredibly precise clocks that maintain accurate time to within three nanoseconds (0.000000003 seconds). This precision is vital as the receiver needs to calculate the duration it takes for signals to travel from each GPS satellite in order to determine its position.The first GPS satellite, along with ten developmental satellites known as Block I, was launched in 1978. Following that, from 1989 to 1993, an additional 23 production satellites named Block II were launched. The system was completed with the launch of the 24th satellite in 1994. The GPS control segment consists of unmanned monitor stations located globally, such as Hawaii and Kwajalein in the Pacific Ocean, Diego Garcia in the Indian Ocean, Ascension Island in the Atlantic Ocean, and Colorado Springs, Colorado. The master ground station at Falcon Air Force Base in Colorado Springs and four large ground antenna stations track and monitor the signals received by these satellites.
There are different types of GPS receivers that can be handheld or installed in vehicles. These receivers detect, decode, and process signals from GPS satellites. Currently, there are over 100 different models being used. Handheld receivers are similar in size to cellphones, with newer ones even smaller. During the Persian Gulf war, U.S. armed forces personnel were given handheld GPS units weighing only 28 ounces.
To comprehend the functioning of GPS, let’s discuss its fundamental features. The system measures the distance between the receiver and satellites while providing their precise location in orbit around Earth. Essentially, if we know our exact distance from a satellite in space, we can determine our location on an imaginary sphere with that distance as its radius.
By knowing our distance from two satellites, we can pinpoint our location at the intersection of the two spheres. Adding a third measurement narrows down our location to two possible points which mathematical methods help eliminate one as unlikely for GPS receivers.The GPS system consists of satellites tracked by ground stations. Each satellite emits radio signals that a receiver uses to determine the satellite’s position and the distance between it and the receiver. By utilizing these measurements, the receiver can calculate the user’s location on or above Earth. With this understanding of how GPS works, we can now examine its practical applications in both military and civilian scenarios.
Despite its recent completion, the recently finished GPS satellite constellation has proven to be valuable for the U.S. military forces. The mobilization of troops for Desert Shield served as a wake-up call, prompting the military to work harder in preparation for Desert Storm. To ensure preparedness for future needs, Congress established a $92 million program called Simulation in Training for Advanced Readiness. This program led to the development of a revolutionary GPS-based battle simulation system known as DFIRST (Deployable Force-on-Force Instrumented Range System). Major Jeff Grant explains that this simulation involves equipping 70-ton Abrams tanks, Bradley fighting vehicles, and ground troops with DFIRST. The simulation takes place outside Boise, Idaho and utilizes off-the-shelf radio communications equipment, GPS receivers, and specially designed software. Through DFIRST, armored units engage in highly realistic combat practice to enhance their battle readiness. Inside the 70-ton Abrams tank named Charley 12, its crew receives a notification on their in-vehicle display screen that they are participating in a live distributed battlefield simulation. Charley 12 and its crew test an instrumentation system that allows combat-readiness training near their home base.GPS satellite signals are used to cover the mock battlefield, enabling Charley 12 to track movement and locate opposing troops using its onboard instrumentation. The tank’s GPS receivers monitor turret movement and aid in aiming, with processing software confirming enemy positions and firing range based on GPS coordinates and capabilities. When a hit is confirmed electronically, the target tank is alerted of imminent destruction. In June 1996, Charley 12 achieved its first victory during annual training exercises. The reliable navigation system played a crucial role in the success of U.S forces in Operation Desert Storm, allowing effective maneuverability even in challenging conditions such as sandstorms or nighttime operations.
Initially, over 1,000 portable commercial receivers were acquired for use in the Gulf region. However, due to high demand, more than 9,000 commercial receivers were used before the conflict ended. These receivers were utilized by foot soldiers and attached to vehicles, helicopters, and aircraft instrument panels. Various aircraft models like F-16 fighters, KC-135 aerial refuelers,and B-2 bombers also integrated GPS receivers.
Furthermore,GPS was employed by Navy ships for tasks including rendezvous,minesweeping,and aircraft operations.In addition to military operations and weapons systems applications,GPS has become an integral part of satellite operations.It provides highly accurate orbit data and controls spacecraft orientationThe GPS system relies on the Worldwide Geodetic System 1984 (WGS-84), which uses a coordinate system similar to latitude and longitude lines found on school wall maps. This reference system allows military units to effectively synchronize their maneuvers. Originally developed for military purposes by the Department of Defense, the GPS system has continuously found new applications.
For instance, during the construction of the English Channel tunnel, British and French crews utilized GPS receivers to ensure precise alignment. Additionally, this technology is commonly used for vehicle tracking. Fleet vehicles, public transportation systems, delivery trucks, and courier services can monitor their locations in real-time using GPS technology.
Nowadays, GPS technology is integrated into car systems to provide navigation assistance. Various car manufacturers offer optional GPS receivers that enable users to input their destination and receive turn-by-turn directions or view a detailed map on a video screen. Recent advancements have introduced features like notifying users when their turn is approaching and implementing enhanced safety measures by Lincoln-Mercury company.
One of these safety features is the RESCU system that allows users to tap on an ambulance icon during emergencies. This activates a voice-activated cell phone call connecting them with the Westinghouse Emergency Response Center while drivingThis center uses GPS technology to dispatch emergency services based on location information. GPS is not only important for car systems but also crucial for quickly locating response vehicles during emergencies. It has been instrumental in rescue missions like Scott O’Grady’s rescue in Bosnia. Many industries rely heavily on GPS receivers, including mapping and surveying companies, wildlife management organizations, ozone monitoring agencies, and those involved in tracking major oil spills. Additionally, archaeologists, explorers, and even recreational activities like golfing utilize GPS technology for various purposes. Golf carts equipped with GPS systems provide precise location information and details about the course. Kathy Speight from Skylinks emphasizes the importance of knowing how far you want to hit your next shot in golf as it helps determine the appropriate club selection. The Skylinks computer system attached to the cart offers real-time position information on the course with one-yard precision. It also provides caddie-like details such as distance to hazards and holes and suggestions on when hitting long is more advantageous than hitting short.
In the past, players had to manually search for sprinkler heads and measure distances from those markers. However, with Skylinks technology, users can conveniently access information and determine yardage without any hassle. They can even use the cart as a reference point by parking it near the ball. The GPS antenna on the cart receives signals from satellites, allowing the computer to calculate its latitude and longitude on Earth. To improve accuracy levels further, Skylinks has developed a solution that involves placing an antenna on top of the cart to receive radio signals from a more precise GPS station at the clubhouse. By integrating this data, Skylinks creates a system that is 100 times more accurate than standard mobile GPS devices. Ultimately, the position of the cart is combined with the Smart Map program through an onboard computer, enhancing navigation capabilities for golfers using Skylinks technology.
According to Richard Beckmann of Skylinks, the Smart Map is a comprehensive survey of all aspects of the golf course including tees, greens, fairways, and sandtraps. This mapping system allows golfers to determine their position in relation to other features on the course. Additionally, the Smart Map program provides information on the next hole as the golfer completes the current one. The Skyranger, an RF radio link, enables continuous monitoring of each cart from the clubhouse. This monitoring system helps the manager keep track of the pace of play on the course. Beckmann explains that the Skyranger allows them to closely examine specific holes and identify any issues. Cars displaying a red symbol indicate a problem that requires attention from the pro-shop manager. Thus, by accessing the alarm screen, necessary actions can be taken for specific cars.
The GPS system was developed by the US Department of Defense to provide accurate navigation and positioning. It includes satellites and ground receivers. To determine the position of a ground receiver, four satellites are required. The first three satellites help determine the position, while the fourth synchronizes the time clock of the receiver with the atomic clocks of the satellites. Various methods can accurately correct for measurement errors that arise. The Department of Defense intentionally introduces “noise” into the system to prevent misuse by potential enemies. GPS time keeping is crucial for regulating international communications, computer networks, banking transactions, bank time locks, and scientific experiments. However, the specific problems that non-compliant GPS receivers may encounter during the roll over are not clearly stated by most manufacturers.
The GPS receiver may encounter issues with locating the GPS satellites, leading to a complete malfunction. Alternatively, it might take an unusually long time, possibly up to two hours, to locate the satellites. Upon successfully locating the satellites, the receiver may or may not provide accurate dates, times, or positions. While it may display an accurate position, the date could be mistaken by as much as 19 or 20 years. Additionally, the displayed position may not be correct. There have been suggestions that certain receivers will experience specific problems during week 0, but they should function normally after that period. The GPS clocks will face similar problems concerning dates and time.
The potential of GPS is boundless, only limited by your imagination. As the technology progresses, countless new applications will emerge. The GPS satellites, akin to crafted stars in the sky, will guide you seamlessly throughout the 21st century.
BIBLIOGRAPHY
1. Thompson, Steven D. An Introduction to GPS, (Every Man’s Guide To Satellite Navigation). ARINC Research Corporation, 1994
2. “The Untold Story of CALCM: The Secret Weapon Used In The Gulf War”.
3. GPS World January 1998, Page 17
4. Dana, Peter H. GPS Users Overview. Available on-line at www.utexas.edu/dept/grg/gcraft/notes/gps/gps
5. Available information on-line at the United States Coastguard Navigation Center
6. GPS Joint Program office. ICD-GPS-200: GPS Interface Control Document. ARINC Research Corporation
