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HISTORY
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The Global Positioning System (GPS) is a US-owned utility that provides positioning, navigation, and timing services.
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In the context of the Cold War, in response to the launch of Sputnik by the Russians in 1957, the Americans worked on a program to enable the terrestrial positioning of mobile devices using radio emissions from a satellite. Thus, in 1960, the US Navy made the first concrete use of satellites for land positioning. The NAV.S.T.A.R-G.P.S (navigation system time and ranging - Global Positioning System) system was then designed, financed and developed in 1973 by the United States Department of Defense for strictly military use. The first satellite was launched in 1978. The system was declared operational in 1995, with 28 satellites in near-circular orbits around the Earth at an angle of 55° to the equator and 60° to each of the other orbits at an altitude of 20200 km. They go around this orbit in 11 hours and 58 minutes. There are currently 30 active satellites.
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Commercially, GPS has been very successful and has led to numerous developments in a wide range of fields: maritime, land and air navigation, tracking of commercial fleets (boats, aircraft, trucks), route monitoring and tracing, and route relevance assessment. The integration of "GPS chips" in smartphones is increasing the number of domestic and individual uses. In the scientific field, the precision of location and synchronization makes it possible to develop and exploit new applications: geodesy, synchronization between atomic clocks, study of the atmosphere, etc.
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SCIENCE
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Today the constellation of 30 satellites is composed of different generations (all transmitting the same signals): 7 from the IIR block (1997-2004), 7 from the IIR(M) block (2005-2009), 12 from the IIF block (2010-2016) and 4 from the III block.
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- ` `IIR block : They can transmit messages to each other without any ground contact, allowing system operators to communicate with satellites that are inaccessible to them in direct communication. They are equipped with three rubidium atomic clocks. Twenty-one Block IIR satellites have been launched, the last on 17 August 2009. The last eight are designated IIR-M (Modernized) because they transmit a new civilian code (L2C) on the L2 frequency and new military codes (M) on the L1 and L2 frequencies.
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- ` `IIF block : These satellites were built by Boeing and are 12 in number, the first in the series was launched in May 2010, the last in February 2016. These satellites transmit a new civilian signal on the L5 frequency, which allows the start of dual-frequency position calculations.
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- ` `III block : These satellites transmit the new civilian signal (L1C) on the L1 frequency.
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Obviously, each new generation takes over all the signals of the previous one. |
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