The GPS system is divided into three segments:
The Space Segment
GPS uses twenty-one operational satellites, with an additional three satellites in orbit as redundant backup.
GPS uses NAVSTAR satellites manufactured by Rockwell International. Each NAVSTAR satellite is approximately 5 meters wide (with solar panels extended) and weighs approximately 900Kg.
GPS satellites orbit the earth at an altitude of approximately 20,200Km.
Each GPS satellite has an orbital period of 11 hours and 58 minutes. This means that each GPS satellite orbits the Earth twice each day.
These twenty-four satellites orbit in six orbital planes, or paths. This means that four GPS satellites operate in each orbital plane.
Each of these six orbital planes is spaced sixty degrees apart. All of these orbital planes are inclined fifty-five degrees from the Equator.
The Control Segment
The Master Control Station (MCS) of the GPS system is operated at Schriever Air Force Base in Colorado Springs, Colorado. The United States Air Force maintains redundant Master Control Stations in Rockville, Maryland and Sunnyvale, California.
The Air Force also maintains monitoring stations in Colorado Springs, Hawaii, The Ascension Islands, Diego Garcia, and Kwajalein.
Communications with the space segment are conducted through ground antennas in the Ascension Islands, Diego Garcia, and Kwajalein.
The User Segment
The GPS user segment is any person with a GPS receiver.
วันพุธที่ 15 กรกฎาคม พ.ศ. 2552
GPS History
GPS was originally developed for the U.S. military, but is now provided as a public service for people all over the world by the U.S. government.
Deployment of the GPS system began on 22 February 1978 with the launch of the first Block I Navstar GPS satellite. Initial Operating Capability was declared in December of 1993 with 24 operational GPS satellites in orbit. Full Operational Capability was declared in June of 1995.
GPS was developed by the U.S. military to help soldiers locate their positions. Civilian access to the GPS system was guaranteed by President Reagan as a response to the communist Chinese shooting down of Korean Airline Flight KAL-007. President Reagan hoped that GPS technology would help to prevent such a tragedy from happening again.
Deployment of the GPS system began on 22 February 1978 with the launch of the first Block I Navstar GPS satellite. Initial Operating Capability was declared in December of 1993 with 24 operational GPS satellites in orbit. Full Operational Capability was declared in June of 1995.
GPS was developed by the U.S. military to help soldiers locate their positions. Civilian access to the GPS system was guaranteed by President Reagan as a response to the communist Chinese shooting down of Korean Airline Flight KAL-007. President Reagan hoped that GPS technology would help to prevent such a tragedy from happening again.
What is GPS ?
GPS is the Global Positioning System. GPS uses satellite technology to enable a terrestrial terminal to determine its position on the Earth in latitude and longitude.
GPS receivers do this by measuring the signals from three or more satellites simultaneously and determining their position using the timing of these signals.
GPS operates using trilateration. Trilateration is the process of determining the position of an unknown point by measuring the lengths of the sides of an imaginary triangle between the unknown point and two or more known points.
In the GPS system, the two known points are provided by two GPS satellites. These satellites constantly transmit an identifying signal.
The GPS receiver measures the distance to each GPS satellite by measuring the time each signal took to travel between the GPS satellite and the GPS receiver.
The formula for this is:Distance = Velocity * Time
Velocity of the GPS signal is the speed of light, approximately 300,000 Km/s.
GPS transmissions occur on a frequency of 1575.42 and 1227.60 Mhz. Both of these frequencies are within the L Band.
GPS receivers do this by measuring the signals from three or more satellites simultaneously and determining their position using the timing of these signals.
GPS operates using trilateration. Trilateration is the process of determining the position of an unknown point by measuring the lengths of the sides of an imaginary triangle between the unknown point and two or more known points.
In the GPS system, the two known points are provided by two GPS satellites. These satellites constantly transmit an identifying signal.
The GPS receiver measures the distance to each GPS satellite by measuring the time each signal took to travel between the GPS satellite and the GPS receiver.
The formula for this is:Distance = Velocity * Time
Velocity of the GPS signal is the speed of light, approximately 300,000 Km/s.
GPS transmissions occur on a frequency of 1575.42 and 1227.60 Mhz. Both of these frequencies are within the L Band.
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