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Published:November 10th, 2006 03:45 EST
Something Different in Technology

Something Different in Technology

By Yash Todi

Technology has gifted us many useful types of equipment such as the bulb, telephone, computer etc. It is advancing at such a speed that no one can tell what will happen in next two years. Scientists take help of the modern technology to make things better than they are. Technology has made life easier; however it also sometimes harms the environment.

BUT…here we are talking about something which is totally different from harming anything. We are talking about GLOBAL POSITIONING SYSTEM (GPS).

According to Microsoft, “Global Positioning System (GPS), space-based radio navigation system, consisting of 24 satellites and ground support, that provides accurate, three-dimensional position, velocity, and time, 24 hours a day, everywhere in the world, and in all weather conditions. Because the user does not communicate to the satellite, GPS serves an unlimited number of users.”

Operated and maintained by the United States Department of Defense, the Navistar Global Positioning System was initiated in 1973 to reduce the proliferation of navigational aids. By creating a system that overcame the limitations of many existing navigation systems, GPS became attractive to a broad spectrum of users. Since the earliest satellites, it has successfully proven itself in classical navigation applications; because its capabilities are obtainable in small, inexpensive equipment, GPS has fostered many new applications.

GPS is available in two basic forms: Standard Positioning Service (SPS) and Precise Positioning Service (PPS). SPS provides a horizontal position that is accurate to 100 m (109 yds.). PPS horizontal accuracy is 20 m (22 yds.). For authorized users, usually the US military and its allies, PPS also provides greater resistance to jamming and immunity to deceptive signals (antispoofing). 

GPS satellites carry atomic clocks that measure time to a high degree of accuracy. The time information is placed in the codes broadcast by the satellite so that a receiver can continuously determine the time the signal was broadcasted. The signal contains data that a receiver uses to compute the locations of the satellites and to make other adjustments needed for accurate positioning. The receiver uses the time difference between the time of signal reception and the broadcast time to compute the range to the satellite. The receiver must account for propagation delays caused by the ionosphere and the troposphere. With three ranges to three satellites and knowing the location of the satellite when the signal was sent, the receiver can compute its three-dimensional position.

To compute ranges directly, however, the user must have an atomic clock synchronized to the global positioning system. By taking a measurement from an additional satellite, the receiver avoids the need for an atomic clock. The result is that the receiver uses four satellites to compute latitude, longitude, altitude, and time.

GPS has three segments: space, control, and user. The space segment includes the satellites and the Delta rockets that launch the satellites from Cape Canaveral in Florida, United States. GPS satellites fly in circular orbits at 17,440 km (10,900 mi) altitude, each lasting 12 hours. The orbits are tilted to the equator by 55° to ensure coverage in Polar Regions. Powered by solar cells, the satellites continually orientate themselves to point the solar panels towards the Sun and the antennas towards the Earth. Each satellite contains four atomic clocks.

Since 2001, 24 production phase GPS satellites have been in operation. Replenishment satellites are ready for launch and contracts have been awarded to provide satellites into the 21st century. With its ability to enhance safety and to decrease fuel consumption, GPS will be a key component of the international aerospace system and will be used from take-off up to and including landing; cars will be using it as part of the intelligent highway system; and pilots will use it for landing aircraft at fog-bound airports. Emerging technologies of GPS include determination of the attitude of a vehicle as well as its position and the system has found broad and enthusiastic acceptance in land, sea, air, as well as space applications.