The Global Positioning System (GPS) is a satellite based navigation system originally intended for military applications. It is a network of satellites continuously transmitting coded signal as bits of information to different areas around the Earth, thus allowing the possibility of identifying different locations and position on our planet precisely, by measuring the distances between each satellite. GPS is funded, controlled and operated by the United States Department of Defense (Kaplan, 1996). The system utilizes a network of 24 satellites which orbits the earth every 12 hours, or more conveniently twice a day. This network of satellite provides specially coded radio signals that can be processed by small electronic receivers which in turn enable these receivers to calculate location, precise time and position (longitude, latitude and attitude) (Kaplan, 1996). The system is divided into various segments that work in connection with each other.
The GPS satellites, officially known as NAVSTAR (Navigator Satellite Timing and Ranging) by United States Department of Defense, was first placed placed into orbit, 12, 000 miles above the earth surface in 1978 and by 1994 a complete constellation of 24 satellites was achieved (Hoffmann-Wellenhof, 1994). By launching the satellites to a high altitude a greater coverage area is attained. Every satellite was built with at least a life span of ten years. Every now and then new satellites are built and launched to replace older and defective ones. GPS satellites are powered by solar cells and backup batteries are provided in an event a solar eclipse happens (Hoffmann-Wellenhof, 1994).s Small rocket boosters are attached to the the satellites that keep them on their track during orbit around the earth. This constellation of satellites composed the GPS Space segment.
Scattered in different locations around the world are systems of tracking stations that follow the movements of the GPS satellites. These tracking and monitoring stations composed the GPS system’s control segment also known as the ground station. There are five tracking stations located around the world- four unmanned and the other a Master control Station. The Master Control Facility is situated in Colorado at Schriever Air Force Base, formerly known as the Falcon Air Force Base (Kaplan, 1996). The Master Control station’s primary function is to control the GPS satellites by tracking them down and furnishing them with correct information. It also assures the healthy conditions and operations of every satellite.
Built on these tracking stations are devices and equipments that monitor and measure the special coded radio signals sent by the GPS satellites from space. The four unmanned stations constantly receive these coded data from the satellites and send that data to the Master station. The signals are then incorporated to orbital models of each satellite. By using the model mentioned above, the correct orbital and clock time information could be computed which then will be important in searching and calculating for locations. The Master Control Station then sends these corrected data back to the GPS satellites, and in turn the satellites convey the data through radio signal back to various electronic receivers.
The electronic receivers made up the third segment of the GPS System. These small electronic GPS receivers receive the signal from the GPS satellites and in turn convert them to useful data such as position, velocity and time estimates. GPS receivers are widely used today in different field of applications such as navigation, positioning, research and time dissemination. The primary objective and function of the GPS System is navigation using three dimensional approaches. Navigation receivers are custom built for aircraft, ships, land vehicles and for sole purpose of individual carrying. Today they have become an integral part of the government’s fight against crimes especially during surveillance and entrapment phase.
Meanwhile, the calculation of the precise location relies on the signals being transmitted by the GPS Satellites. Each GPS satellite transmit low power specially coded radio signal on different frequencies designated as L1, L2 and other names (Leick, 1995). A GPS signal is composed of three different bits of information. These bits of information are coded into the signal which travel through clouds, glass and plastic but signals found it difficult to pass through solid objects like mountain ranges. The information enclosed in the radio signal are the pseudorandom code, the ephemeris and almanac data. The pseudorandom code contained in the data distinguishes the GPS satellite that sends the signal. It serves as identification in which among the satellites is transmitting the necessary information. Through this information, the GPS Satellite sending the message is recognized. Ephemeris data on the other hand, provides the electronic receiver information of the whereabouts of the GPS satellite. It pinpoints the exact position of a satellite at any given time. The ephemeris data includes orbital information of the satellite that transmit the signal and of the remaining satellites in the constellation. It tells the satellite’s exact location which is an important aspect in order to calculate accurate position. The last data contained in the signal, the Almanac data is constantly transmitted by the 24 satellites. This data tells the status of each satellite. It tells whether damage occurs and if repairs are needed. From this data, malfunction of GPS satellites can easily be traced and troubleshooting and replacements can then be easily done. It also provides key information in determining a satellite’s position.
Although the different bits of information contained in a signal has their own purpose, the main function of these coded signals are to allow the calculation of the time, the moment signals are transmitted from the satellites until the instant these signals are captured by the the GPS receivers on earth. Highly accurate atomic clocks are used to time these signals. The possibility of the computation of this travel time is its most important task. This travel time is also referred as the Time of Arrival. With the details of Time Arrival known, the distance between the GPS Satellite and the electronic receivers can then be computed. The satellite range is equal to the Time of Arrival multiplied by the speed of light. The computed values are important parameters that would lead to the computation of the exact location being searched.
GPS System uses the principle of triangulation to determine locations and pin point the required positions. In trigonometry and geometry, triangulation is the process of computing and finding coordinates and measuring distances of triangle sides and its angles (Kaplan, 1996). It is based on the trigonometric principle that if one side of the triangle and two angles are known, we can readily solve for the other side and the remaining angles. Through triangulation process location can be determined by measuring the radial distance and direction of the received signal from two or three different satellites (Hoffmann-Wellenhof, 1994), the measurements would then provide the range on where the exact location is. The area where these measured distances would intersect would reveal the location one is looking for. This is the basic principle on how the GPS System is designed and performs its function. But, there are other parameters which are also carefully considered in order for the system to properly conduct its task. Triangulation in GPS System is often times referred to as trilateration. It is the name applied since no angles are involved in computations.
The GPS technology operates by utilizing the satellite constellation from space as reference points of the different locations and places on earth. By measuring the distances from three different satellites as accurately as possible, preferred locations anywhere on earth can then be “triangulate”. Thus it is important to determine the exact location of satellites and to make sure that they are properly on their orbit. Through the radio signals sent by satellites to the different ground stations on earth, the exact positions of the satellites are determined. Just as discussed above, the information on the whereabouts and approximation of the exact locations of the satellites is contained inside the almanac data. The four unmanned control station constantly receives update on the satellite’s orbital data. These stations then send this orbital information to the Master Control Station. From the Master Control Facility the orbital information would be checked and data would then be uplink back to the satellite to ensure the proper locations in their orbit of each satellite. Thus, in summary the control stations must ensure that satellites are right on their orbital track by controlling their speed, altitude and location. The corrected data transmitted from the control station is the same data that the satellites would transmit back to the electronic receivers to the ground. This is the ephemeris data, which is accurate and valid up to four or six hours. Through this coded signal the distance from the satellite can be measured, since the data also contained the pseudorandom code which will identify which satellite is relaying the information.
After knowing the precise location of the satellites in space to use as reference, it is important to find out the distance or how far the satellites are away from the earth, in order to determine its position on earth. In finding out the measure of the distance of the satellites, timing is a key factor. The time on when the coded signal was transmitted and the moment it was received by the transmitter on the earth should be known. The travel time should be taken into account. As discussed before, the time is called the arrival time and by substituting it and the coded signal’s velocity to the speed formula, distance is speed multiplied by time, we can calculate for the satellites’ distances. The coded signal velocity is 186,000 miles per second (the speed of light) minus the delay it would encounter as it travels from outer space and in the atmosphere (Hoffmann-Wellenhof, 1994).
The receiver now needs to recognize this time part of the formula. Designers of the GPS system introduced a code to resolve this formula. This is the same come which distinguishes the satellite from each other, the pseudorandom code. It obtained its name from its complicated pattern which almost looks like as a random electrical noise. It is a very complicated sequence of an on and off pattern but is very integral in determining the time parameter. When a satellite generates a pseudorandom code, the transmitter from the earth tries to match the satellite’s action by generating the same pseudorandom code. The receivers analyze the pseudorandom code developed by the satellites and compare it to their own pseudorandom code. They then determine the shift or the delay needed in order to match the satellite code. This shift in time or the delay is the Arrival time, which is then multiplied to the speed of light top determine the distance. With both the satellite location and the distance of the satellite in earth known the receiver now can determine the position.
Today, GPS technology has developed into a resource that outdates its original purpose and goal. When it was first developed designers never could have imagined its wide variety of use today, before it was ultimately intended for its application in wars. The US Department of Defense developed the system for strategic planning against rival enemies. With the system they are capable of gaining maps of their enemy’s territories. This in return would provide them better access in plotting and carrying out plans more effectively. The system also provides the military an access in tracking their enemy’s movements, which offer them great advantages to maneuver counter attacks. However, the primary reason the US Department of Defense developed the system was to have a better access in pin pointing strategic site, such as nuclear silos, technology centers, barracks and air ports and focus and concentrate their air attacks there. By blowing up such buildings a major advantage can be seized. These days the US government has allowed the public the free use of the GPS System. People have benefit from the use of the system. Doctors, fishermen, sailors, delivery drivers, fire and crime fighters have benefitted largely from it. Different fields of Application such as navigation, tracking, mapping and aviation have continually expanded and performed more efficiently with the introduction of GPS Systems in their respective field. It has become more popular with production of economically affordable electronic receivers and other GPS devices.
Aviation is a term associated with machines designed by men, such as aircrafts, which are intended for atmospheric flights. It is also used to describe activities, industries and regulatory bodies which are associated with aircrafts and flying. From the dawn of time many cultures have built devices and apparatus designed for flying. From the day the Wright brothers flew their first aircraft on December 17, 1903 the field of aviation had advanced and had grown bigger (Aranda, 2007). Through time, as technology advances aviation had encountered major developments. It has adapted to the changes brought by time.
The field of Aviation is one of the first industries that introduced GPS System and become involved with GPS applications. As early as 1978, when experimentation with GPS was starting the field of aviation has its eyes set on introducing the system to aviation (Aranda, 2007). This happens because location, speed and navigation are important disciplines in the field of flying. The system can offer variety of things that can promote safe travels on air and further increase the service of commercial flights, general and civil aviation. With regards to military aviation, it offers infinite possibilities.
There are two major categories in the field of aviation: civil aviation and military aviation. Civil aviation represents all non-military aviation. It includes commercial flights and private flying. Its major categories are general aviation and scheduled air transport. General aviation includes all the civil flight, either private or commercial. On the other hand, scheduled air transport includes passengers and cargo operating on regular scheduled routes. Military aviation as the name itself implies involve everything with regards to military. Aerial warfare, surveillance air tactical teams are example of this category of aviation. Since GPS was designed primarily for military purposes, applications of GPS devices are seen most obvious in military aviation. In designing aircrafts bound to protect and do battle for the United States, technology associated with GPS offers a major boost to the said field.
The use of GPS in aviation provides a promising result for the public. Either in civil aviation or military aviation GPS offers a lot of help. GPS on airplanes are basically devices which offers map of the route to be traveled to the plane’s destination. GPS provides mapping. This application is very helpful especially for civil aviation to ensure the quality of service and to secure the safety of the passengers on board. With the monitors providing the clear map, pilots would not have difficult time maneuvering planes. In case of emergency landings they can be capable of choosing a better site rather than doing it by presumptions. Pilots can also have accurate computations of their distance to their target destinations. GPS on airplane also included programs for auto pilot. Thus, safety of people on board will not be at risk.
For Military Aviation, mapping is essential just as in civil aviation. GPS inside jet fighters, helicopters and choppers would provide the same information, the route and destination being taken by the craft and it would provide detailed maps of sites. With GPS furnishing the necessary information, the burden on the shoulders of the military will lessen. Missions would somehow seem attainable since a good plan is prepared using the information from the GPS. Strategies are carefully laid out.
When the US Department of Defense introduced the GPS one of GPS primary role is to provide navigation information and GPS does not fail to do so. The field of aviation is not the only industry that benefits so much from these GPS applications. The shipping industry is among the fields that benefit largely from this constellation of man-made satellites. Navigation is described as the process of getting something from one location then moving to another location. With the use of GPS in aviation, airplanes’ navigation has been made easier. Navigating through clouds and disturbances has become less dangerous and risky, since computer applications exists that would provide assistance to pilots on duty. Pilots then have constant guidelines of every thing that they do. Whenever something unexpected happens, pilot can always get back on their course with system helping them to how to get back on the right track.
Thus, with GPS devices provided on board inside the planes, pilots’ tasks are easier. Included on GPS on board are programs which enable the pilot to control the plane more effectively. Programs that tell where the plane is headed are integrated. With these applications, airplanes that are moving out of their tracks would be reduced. Often times the event mentioned before is the cause of some terrible airplanes’ disasters. Collisions between airplanes are often the drastic aftermath of miscalculations. These miscalculations can be avoided with the help of the GPS devices. Another program integrated in the system is the application that tells how far the airplane to its target and original location. Through these, expected time of arrival would be known. Ground control can always determine if something wrong has transpired on the plane that causes the delay. Also the program includes a set of operations that tells the altitude the plane is traversing. Thus a pilot can readily recognized if the plane is getting off track to its destination. He could also concur if troubles occurred or malfunction of engines happened since the plane is starting to loose grounds and is moving in a lower height. Adjustments of the airplane settings can then be quickly done that would prevent a possible accident from happening.
Tracking is another important application GPS brings to the aviation field. If navigation is the process of moving things from different locations into a new location, tracking is described as monitoring these movements. The application of tracking is effectively viewed in delivering goods. In delivering important goods across continents, tracking device placed on board provides the people of the expected time of arrival of these packages. They can determine if goods reached their designated locations. These applications are very important for businesses that provide delivery service, such as the postal service. Since their main concern is that service delivered to the people, tracking equipments provide them status of the whereabouts of the different goods. Tracking device also provide security for people aboard airplanes. Through this GPS device, they are assured that their planes would not be lost. Ground control can monitor the planes activities and in case of emergency, authorities can pinpoint their exact location.
For military aviation, GPS on board allows them to track down movements of enemy troops viewed from above. Some planes are even equipped with cameras to photograph and record the movements. This provides them time to take necessary precautions. Also, utilizing tracking devices on military planes provides pilot clear information of aerial boundaries and territories between them and their enemies. Thus, safety of pilots is also enhanced. When in missions, lost of airplanes can easily be recognized and looking for those missing planes can easily be performed.
The importance of GPS in aviation is none more reflected than its effect in military planes. With the continuous advancement in technology, new planes and aircrafts are being manufactured. The design exclusively built for each aircraft functions. In designing the new models of aircrafts GPS contributes to their development. GPS system is used to simulate pre test of these newly manufactured aircrafts. Flight environment is simulated using the software information and representative data from network of the twenty four satellites. Also the aircraft’s GPS hardware is exercised in controlled environment to collect data relating to the operation of the aircraft’s code and it’s susceptibility to interference and dynamic conditions (Curtis Hay, 2006). The tests done during simulation flights are critical for weapon validation and navigation trial of aircrafts. In addition, the government is able to cut down expenses. The rising cost of aircraft’s fuel and test range expenses no longer pose a problem. Safety of pilot that would conduct the test flight outside the simulation is also achieved. Using GPS simulation data gathered will not vary compare to in flight test that would be conducted outside. Simulation test offers a controlled variable that would is not achievable during in flight test because of flight dynamics and atmospheric effects.
GPS another role in military aviation is the manufacturing of Unmanned Aerial Vehicles (UAVs). UAVs are simulated by computer systems with GPS application on the forefront of these programs. An embedded GPS navigation system, allows the flight of UAVs. Orders are executed just as a pilot getting his orders from his superiors, the only difference orders are encoded to computer systems. On September 28, 2005 UAVs test flights were conducted, at the Naval Air Warfare Center Weapons Division in China Lake, California (McAdam, 2006). They were designed to fly and perform their specific functions at altitude of 30, 000 ft and above. UAVs are designed to perform tasks which manned aircrafts could not accomplish. These tasks are those which pose grave threats to pilots due to the extremity of conditions. With this latest development, risk of loss of human lives when piloting airplanes is reduced. The GPS on board ensure the UAVs navigation and targeting accuracy as good or maybe even better compared to manned aircrafts.
The introduction of GPS applications to the field of aviation is a fine example of how men strive to improve his way of living and his quality of life and the things around him. With the limitations the human body imposes, men continue to look for mediums that will compensate these limitations that surround him. Men constantly search for ways and varieties of techniques that would equipped him with the tools needed in his everyday living. The vast advancement and development of technology through the years attest to men’s continuous search of better living condition. These improvement, however are not for reasons of luxury. Many times these changes are brought about to yield better output and to elevate working and living condition of men.
With the use of GPS in aviation, a door has been opened to man. Limitless possibilities and infinite options have been unfolded. Things we thought impossible for once are slowly being realized. Gone were the days when accidents in air flights and travels are regular occurrence due to pilot’s error. Unmanned air crafts are slowly being developed to reduce death and loss of pilots and crew in case of disasters. In an event of a very dangerous mission, where environment condition are too harsh and extremes for man to handle, these unmanned aircrafts would serve their purpose and GPS technology is in the forefront of these developments. Flights are made much safer with computer applications providing assistance to aircraft personnel. Navigation of flights can be monitored, and once an aircraft is gone missing and an emergency rises, rescue operations can then be easily mobilized knowing the plane’s coordinates. The application of GPS in aviation has provided people with confidence in flying. With the system, fear of flying is slowly being conquered.
Precautionary measures and procedures are several reasons of GPS integration to aviation. The anxiousness of an accident happening and the fear of lost of loved ones are very difficult to deal with. The assurance of a much secured air travel, hassle and worry free are several factors why the field of aviation has been constantly pushing in adapting GPS technology in their system. The necessary precautions the system provides greatly reduced the risk of flying. The burden of the uncertainty of travel on air is decreased.
Security is attained with the use of these applications not only by prevention of untoward accidents but also from terrorists who are planning of using air crafts as weapon for attacks on buildings and establishments at ground. Since a program is running that would automatically check the plane’s altitude and return the plane to its original height and path, it would be difficult for attackers to set new course for the planes to take. Ground control can also track their path and can monitor if change of original destination is taken. Thus, they can easily alert the authorities.
On the manufacturer’s point of view on the other hand, introduction of the system to aviation poses various challenges to provide people with better products. They have become eagerly excited to intensify their researches further. The thought of providing the public with better quality service in a cost effective manner was fulfilling enough for them. Also, we could infer that pride somehow plays a role for introduction of GPS to aviation. In an effort to prove that the launching of the satellites and the project itself was worth all the billions the government had spent, DOD has applied the system to different disciplines and did not limit the use of the system for military matters. The use of GPS technology also reveals how superior American technology is. From the launching of the 24 satellites up to the simulation, designs and test flights of new aircrafts, one would be mesmerized of this technology. Thus by utilizing it to various fields and discipline it brings fame and honor to the people.
GPS has become an integral part of Aviation. It is remarkable to see that it seems GPS technology is tailor fit in the field of Aviation. Although, aviation was not the primary reason for the existence of the GPS technology and the constellation of the satellites, no one can deny the great impact it has done in the field of aviation. It may be even fitting to say that the future of aviation is the technology the GPS offers. Although it has been around and used by aviation as early as the first satellite was launched, it is only lately that major steps are being taken and made that mark great improvements in the field of aviation.
As days pass, researches are continuously being worked on by engineers and scientist. The field of aviation will continue to boom with the GPS technology around. Aviation industries have yet to harness the great potential the GPS technology brings. But they are working on it and for the next few years vast advancement in the field of aviation will be attain.
References
Aranda, N. (2007). A Brief History of GPS in Aviation [Electronic Version]. EzineArticles Retrieved July 27, 2007 from http://ezinearticles.com/?A-Brief-History-of-GPS-in-Aviation&id=500920.
Curtis Hay, C. F., Greg Gerten (2006). Modeling and Simulation for Navigation System Testing. GPS World
Hoffmann-Wellenhof, B. H. L., and J. Collins. ( 1994). GPS: Theory and Practice. New York: Springer-Verlag.
Kaplan, E. D. (1996). Understanding GPS: Principles and Applications. Boston: Artech House Publishers.
Leick, A. (1995). GPS Satellite Surveying: New York: John Wiley & Sons. .
McAdam, L. (2006). Robotic Fighters Coming in on GPS GPS World.
