| What is a GPS ? (beginning) The GPS (" Total Positionning System " or " total system of
localization ") is a very useful electronic apparatus, even essential under certain conditions, which allows orrienter and to be geographically on a card thanks to a network of satellites surrounding the ground.
The most popular tool for a forwarding of great scale is certainly the compass, but with the North Pole the latter is not of any utility since the magnetic pole completely puts out of order the magnetized needle of the compass. It is thus necessary to find other apparatuses of orientation. In addition to the traditional card of state major, the GPS is an essential apparatus in this situation. 
HISTORICAL (beginning)
Initially the project was called ? NAVSTAR ? (navigation timing and ranging). At request of American army which wish have an apparatus him allow to know without delay their co-ordinate with some meter near but also to can locate with precision its fighter, its tank and its missile in all point of the sphere. Concept NAVSTAR is the result of the studies undertaken in 1965 by the Air Force and the American navy. Here the dates which marked the realization of the project :- 1965
- First concept- 1972
- Preview study of feasibility
- 1974/1979
- Validation of the concept (1st shooting in February 1978)- 1979/1986
- Evaluation and development- 1986/1994
- Operational installation. (Phase stopped between January 1986 and February 1989). Launchings of the satellites ? BLOCK II ? in fact started only in February 1989.
The accident which has occurred on January 24, 1986 with the shuttle ? CHALLENGER ? delayed the placing in orbit of the first satellites
of the operational configuration. Moreover persons in charge of the project decided to give up the shuttle like launcher with the profit of rockets ? MLV DELTA II ?, which obliged to make certain installations. Launchings then began again in 1989. 24 then 28 satellites will turn out of 6 orbits of or they will emit coded signals intended for the GPS.
ORGANISATION (beginning) Project NAVSTAR is coordinated by an office interarm?. The ? Joint Programm Office ? (JPO) whose seat is located in Los Angeles in the buildings of " Space Division ". This last depends on "? System Command ? of the Air Force of the United States.The JPO is composed of the representatives:
Armies and arranges taking part in the program, that is to say the ? US NAVY ?, the ? US ARMY ?, the ? US AIR FORCE ?, the bodies of the Navy, - ? US COEAST GUARDS ?, the cartographic agency of defense and the department of transport. This last is charged to make sure that the interests of the future civil users are taken into account.
- Countries of the organization of ? NATO ?
OBJECTIVE (beginning) With the origin the GPS was conceived in order to provide to the forces armed a system with location total and very good precision. The similar systems of time (SATNAV, etc) did not have the availability and the security necessary for their operational
exploitation in the armed forces. It very quickly posed the problem of the accessibility of the service, indeed of many civil applications could want to resort to this system and it was not conceivable to leave the service in free access has everyone, any country attacker then which can use it has its profit. Dice the beginning the USA wanted to secure the total control when has the exploitation of system GPS, but did not want to exclude the
civil applications, one has then to imagine the following compromise: - a service of high degree of accuracy reserved to the militairex it is mode ? PPS ? (Precise Positioning System)
- a second service with the degraded possibilities (env 100M) to which would have acc? any person provided with a receiver, it is mode ? SPS ? (Standard Positionning System).
Mode ? PPS ? fully exploiting the system for a precision of less than 10 meters and the mode " SPS " which using an electronics simplified is subjected has a voluntary degradation of the satellite signals for an accuracy of 100 meters approximately. The access to mode ? PPS ? being played on electronic level of the receiver and the codes of corrections of satellite degradations the USA thus secured the total maitrise of the military aspect of the
project, and made a beautiful gift with the civil ones. HOW IT WORKS (beginning) We will simplify to the maximum the complicated process of operation of the GPS. What it should be known it is that the GPS is a small radio operator receiver which synchronic with 2, 3, 4 or more satelittes to give information on the geographic position or it is. Like
the system of triangulation used during the last war (1939-45) to find the pirate transmitters, the GPS be a receiver which receive some information of several satellite (in general 3 or 4) and calculate with precision the time put to receive the information since each one of satellite. According to the position or one himself find, the response time be more or less length (I you reassure, it himself act here that of some thousandth of one second...) and in compare the deadline for
reply of 3 or 4 satellite, the GPS will be able to determine with precision the place or it is.To increase the precision of the GPS, one will be able to sometimes wait several minutes to several hours to extrapolate information received from various satellites, and since the ground turns, the many satellites will give even more information to the GPS. the internal computer of the GPS will compile the data to provide a maximum of very precise information. But the precision is reserved for
applications the specialized like land surveying or certain applications scientific to calculate to 3 millimetre close the displacement of the continents or the exact position of the magnetic North Pole.
10,000 TIMES MORE PRECISE THAN THE GPS ! (beginning) In 1983 the GPS functions with 8 satellites. At the
Berne Institute of astronomy the Institute of astronomy of Bern, a young scientist, Ivo Bauersima, Czech refugee, theoretically calculate how to be useful itself of the GPS. Its equations make it possible to obtain a precision 10,000 times higher than that which offers the soldiers, on the condition of reconstituting the orbit of satellites GPS except for a few
centimetres. This requirement requires to compare information of several receiving stations GPS in various points of the sphere. With the sight of these equations, the idea of a vast international network germinates in the spirit of several scientists parmis which, the Swiss astronomer Gerhardd Beutler. While spending one year in Canada, participant in many seminars (thanks to its control of German, English and French), Ivo benefits from it to promote his
project. In August 1989, in Edinburgh, the scientists organize themselves, so that organizations as prestigious as NASA take part in the project and melt the ? International GPS Service ? (IGS).June 21, 1992, the IGS starts one period of tests during 2 years with a score of 20 receiving stations. The precision of the trajectories of the satellites is 50cm and gives to the GPS a precision few
centimetres! Strong this success without fault, the network of receiving stations passes quickly to 50, then does not cease increasing. Today, more than 200 stations distributed out of 5 continents give invaluable information which make it possible to calculate with a very high degree of accuracy the displacement of the terrestrial plates, the real position of the magnetic North Pole, the situation of the pig iron and cast iron of the ices to the two poles, etc.
The precision of the orbits sat?itaires is now 3 centimetres and allows the GPS a precision few milimeters. Japan was equipped with a single network GPS in the world. This country counts more than 1000 receiving stations, that is to say one all 30km. This network made it possible to determine that the island of Japan moves on average of 50 millimetres per year. The GPS is also able to measure the quantity of water vapor contained with the
top of it in stratosphere... The GPS thus gives also invaluable information on the weather ! The IGS specifies today that the position of the Poles varies from 10 meters to the wire of time due to the axis of the ground which moves and the position of the poles is given with a precision of 3 mm !
Sme good links... (beginning) Example of a small GPS, easy to use,
simple and not too expensive. |
