Global Positioning System Essay, Research Paper

Global Positioning System

Global Positioning System or GPS is better known as “a satellite based radionavigational system developed and operated by the U.S. Department of Defense (DOD). Global positioning system permits land, sea, and airborne users to determine their three-dimensional position, velocity, and time twenty-four hours a day, in all weather, anywhere in the world with a precise and accuracy far better than other radionavigation systems available today or in the foreseeable future.” (Navcen) The Global Positioning System was designed for two services. One being, the Standard Positioning System and the other being the Precise Positioning System. Furthermore, space, control, and the user are all segments that consist of the Global Positioning System. Global Positioning System in my opinion is one the greatest inventions are government every designed, and as you will see the ability that GPS has for everyone.

Global Positioning System provides two levels of service, the Standard Positioning Service, and the Precise Positioning Service. ” The Standard Positioning Service or SPS is a positioning and time service which is available to all GPS users on a continuous, worldwide basis with no direct charge.” (Tycho) The SPS is provided on the L1 frequency, which then will code a navigational message. The SPS accuracy is 100-meter horizontal, 156-meter vertical, and 340 nanoseconds time, and in total the SPS is ninety-five percent accurate. (Utexas) The Department of Defense also degrades this service so those consumers can use this service.

Secondly, the Precise Positioning Service or PPS ” is a highly accurate military positioning, velocity and timing service which is available on a continuous, worldwide basis to users authorized by the U.S. PPS is the data transmitted on GPS L2 frequency. Precise Positioning Service was designed primarily for U.S. military use. It is denied to unauthorized users by the use of cryptography. Precise Positioning Service is available to U.S. and allied military and U.S. Federal Government users.”(Tycho) The PPS accuracy is 22-meters horizontal, 27.7-meter vertical, and 100 nanoseconds time. (Utexas) As you can see the PPS has better accuracy then the SPS since it was ultimately designed for government use only.

Another system of Global Positioning System is the three segments. The first is the Space segment. “The space segment consists of 24 operational satellites in six circular orbits 20,200 km above the earth at an inclination angle of 55 degrees with a twelve hour period. The satellites are spaced in orbit so that at any time a minimum of 6 satellites will be in view to users anywhere in the world. The satellites continuously broadcast position and time data to users throughout the world.” (Navcen) These satellites send radio signals from space to earth so that we can read the correct data.

The next is the control segment, which is main part of this operation for this to work. The control segment consists of five Monitor Stations, and they are in Hawaii, Kwajalein, Ascension Island, Diego Garcia, and Colorado Springs. There are also three ground antennas located in Ascension Island, Kwajalein, and Diego Garcia. The Master Control Station is located at Schriever Air Force Base in Colorado. (Utexas) ” The Monitor Stations passively track all satellites in view, accumulating ranging data. This I information is processed at the Master Control Station to determine satellite orbits and to update each satellite’s navigational message. Updated information is transmitted to each satellite via the Ground Antennas.” (Tycho)

Last of the three segments is the user. ” The User Segment consists of the receivers, processors, and antennas that allow land, sea, or airborne operations to receive the GPS satellite broadcasts and compute their precise positions, velocity, and time.” (Navcen) Users figure their position on the earth by measuring their distance from the group of satellites in space. The satellites are actually precise reference points. The measurements collected from the four satellites are processed to solve for the three dimensions of position, velocity, and time. (Tycho) As you can see, the three dimensions are the primary function of GPS. GPS receivers are made for aircraft, ships, ground vehicles, and for individual to carry by hand. Furthermore, GPS has also been used in the research of measuring atmospheric parameters, land surveying, Geophysical exploration, mapping, and geodesy. One example that currently still uses GPS is Loejack, which is a recovery system for stolen automobiles. As of April 27, 1995, GPS has been fully operational for all of its component and services.

Even though GPS is a breakthrough in U.S. technology, everything has some kind of flaw or problem. The GPS errors are a combination of noise, bias, and blunders. “Noise errors are the combined effect of PRN code noise and noise within the receiver noise. Bias errors result from selective availability and other factors, and Blunders can result from receiver errors from either software or hardware failures.” (Utexas) Unfortunately all errors can not be fixed, but the Department of Defense is trying new things daily to either fix or update their systems to better the system.

The GPS system ranges from a variety of costs. Small civil SPS receivers can be purchased for around $200. For receivers that store information the price of those is considerably higher between $2000-5000. Of course, the lower the price the less accuracy the unit will have. The receivers can be classified by:

Low-cost =100-meter accuracy

Medium-costs =1-10 meter accuracy

High-cost =1 mm to 1 cm (Utexes)

As you can see Global Positioning System is a high tech device, that is taking us into the new millennium. The capability that GPS has can be helpful to people all over the world, either by boating, driving, or airborne. The Global Positioning System is funded by and controlled by the U.S. Department of Defense so new ideas and better satellites will come, and eventually GPS will be everywhere. Today, in some automobiles you can find a GPS system as an option installed into the dashboards. Furthermore, GPS is a geographer’s tool that is only going to make it easier to get information, and to learn more about the earth.