What is GPS?
GPS is an abbreviation of the initials of the words “Global Positioning System” in English, which means Global Positioning System.
Uses of GPS
GPS was developed by the United States in 1978 for military purposes as a result of projects initiated to determine the location of submarines and boats.
The control of the system is in the US Department of Defense. This system contain 11 satellite and it was only used by the US military.
In 1983, a Korean civilian plane accidentally entered US waters without permission and the consequences of the dropping of this plane enabling the civilian use of GPS.
The US increased the number of satellites to 24 in 1993. These 24 satellites were divided into the following, 21 active, 3 backup. With the increase of the areas to be covered in the earth, the number of satellites was increased to 27 by “Expandable 24” project in 2011.
To do this, 24 satellites were deployed by placing 6 satellites instead of 3 satellites. Today 31 satellites are active, including 12 BLOCK IIR, 7 BLOCK IIR (M) (modernized versions of BLOCK IIR) and 12 BLOCK IIF.
Orbits of GPS Satellites
The GPS satellites move around our 20200 km orbit around the Earth in 12 hours. To GPS satellites to work correctly, their orbits must be stable. A small deflection in the orbit is causing millions of deviations in the world.
They correct their position with the powerful motors attached them. These satellites are solar powered systems but they use the fuels when they do not see the sun’s rays.
Because of the main task of these satellites which is the transmission of the positioning signal, they consume their fuels.
When GPS satellites complete their life, they are sent to the space and replaced with new ones. Their lifetime has increased with advancing technology.
The project, which began with 7.5 years of life suits, has risen to 12 years of life in the satellites sent in 2010. After that, they will have a satellite system that will be sent after 2016 and 15 years of life.
Location Finding With Phone or Navigation Devices
When we want to use GPS from our phone or navigation devices, our device needs to receive position signals from at least 3 satellites. The signals sent from the satellite are circular propagation.
The combination of 2 circles is located at 2 points and points to this position. The intersection of 3 circles is a single point and points to a single position.
However because of the signal difference is received at a time, the position is exactly determined by a reference 4th satellite. So they are moving any point of the earth to cover at least 4 satellites.