Applications of the satellites

This article describes various the applications of the satellites .

What an artificial satellite?

Different the type of artificial satellites

The satellites are generally classified into three classes :

Scientific satellite

They are dedicated to the pure Recherche in Astronomie (it is acted in fact of telescopes in orbit with more or less broad observation fields and observing the unit of the electromagnetic spectrum), in Géodésie, Géodynamique, etc They are generally single objects. If they are lost during launching, they are seldom replaced.

Applications satellite

They have a commercial application in the fields of the Météorologie, of the Observation of the Earth (known as Télédétection), of the Télécommunications, the Navigation. They generate direct incomes (communications satellite) or induced (meteorology, observation of the civil ground and soldiers, navigation, etc). Their service not having to stop, they require Redondance S in orbit and replacements by new generations. It is a truth gone of the satellites and their applications. The applications can be civil or Militaire S. Certains satellites has a Dualité application, being able to have several applications (Meteorology and Telecommunications, Military Civile and, for example, etc). One finds:

Telecommunications satellites: these satellites are used to transmit information of a point to the other of the Earth, in particular of the telephone calls or data transmission, the communications satellite and the televised programs.
Satellite of teledetection: these satellites observe the Earth, with a scientific aim (temperature of the sea, snowy coat, dryness,…), economic (natural resources, agriculture,…) or soldier. The spectrum of observation is vast, optical, radar, infra-red, ultra-violet, listening of radioelectric signals…
Satellites of positioning: these satellites make it possible to know the position of objects on the surface of the Earth, in the airs (planes, missiles) and in space.

Military satellite

Of Military use and Governmental, they can be telecommunications and of observation of the Earth or electronic listening (Satellite-espion).

The Space stations, also orbits about it around the Earth, constitute a special class, intended to be inhabited by the man, with a scientific aim and or of application.

The Space probes, intended to observe another celestial body, are not any more put into orbit around the Earth and thus lose this quality.

Telecommunications satellite

From time immemorial, the men had the vital need communicate. And since the beginning of the History, the communications did not cease evolving/moving, in time, distance and quantity from transported information. The telecommunications satellites represent for the moment the point of progress in this matter. Before the space era, no transmission of television was possible between the continents, and the few transoceanic cables which existed could convey only a few tens of phone conversations. Into a few years, the satellite changed completely gives it for television, the telephone or even Internet.

General characteristics

General operation

The communications satellite receives the signal of the ground station. It amplifies it and transmits it to a receiving station by using another wavelength. The television programs, the telephone calls, the numerical data can be thus relayed with the planetary scales.

Advantages of a satellite compared to the terrestrial communications

the telecommunications satellites are at the present time very numerous because they came to supplement and improve the possibilities of the terrestrial means of telecommunications per wire or waves which suffer from the following limitations:

Cost of installation, maintenance and the raw materials very high and strongly increasing with the length of the network.
physical Problem: the larger the quantity of information which it is possible to entrust to a wave is, the smaller the length of this wave is and less better this one is propagated on the surface of the Earth. If it is of a few meters, each obstacle likely to stop the light also stops it (mountains,…)
Exposure to the earthquakes, floods, storms and other main risks which can destroy the line.

Before the arrival of the satellites, the images coming from other continents reached us only by plane, several days after being filmed. When the satellite arrived, this one solved, in its principle even, the 3 constraints quoted above. Firstly, it is an average ideal for the transmission of information on very vast geographical surfaces. It thus has a priori a world vocation since it does not require a heavy infrastructure on the ground, which appears particularly well adapted for a country whose settlement is discontinuous. Secondly, the telecommunications satellites make it possible to communicate between two distant points without being constrained neither by the relief, nor by the curve of the Earth, on the condition of remaining in the surface of visibility of the satellite ensuring the transmission. Thirdly, the satellite does not risk anything in the case of an earthquake or of a flood and the infrastructures on the ground occupy a so small surface which the risk of damage in is strongly reduced.

Various types of telecommunications satellites

All these advantages, plus the fact that they are one of the only profitable space applications, explain certainly the expansion of the telecommunications satellites (one estimates at a thousand today the number of telecommunications satellites). The first of them was Echo 1. It was about a passive satellite since he reflected only the energy which he received. The signal was strongly decreased and it was the first and the last of the telecommunications satellites liability. As from 1962 and of TELSTAR, the satellites all are become “active”: they receive the signals, amplify them and re-emit them starting from repeaters. Their payload (see appendix IV) is composed of solar panels providing energy necessary to the amplification of the signal and the more or less directional antennas which it is necessary to direct with a high degree of accuracy towards the Earth. The terrestrial antennas must in addition imperatively be pointed with precision in direction of the satellite for the reception as for the emission. The first satellites télécoms were satellites with run (see chapter 1), i.e. they were visible only a few minutes. This low orbit was quickly given up and maintaining the majority of the telecommunications satellites (the first was Early Bird in 1965) are logically placed on an geostationary orbit (see appendix V) so that the antennas are constantly connected enters, without cuts. However today, one returns from there to the satellites to run (and even to a constellation of satellites with run) to answer the growth of the use of mobile telephonies.

Possible weakening of the signal

Certain weather and astronomical phenomena can weaken a signal (rain or solar winds). The signal is also more easily stopped by the relief in area of high latitudes (the angle ground-satellite is weaker and the “shade” is thus larger).

Two fundamental resources

A telecommunications satellite uses two limited resources: the Geostationary orbit and a reserved waveband radio (see appendix I). Except for some rare exceptions (uses of the laser for the communications submarines - satellites, for example), all the satellite communications exploit the radio waves. With the increase continues of the number of satellites, the problem of the allowance of the frequencies became extremely complex. The spectrum of the frequencies usable appears already very exploited. However, progress of the techniques of data transmission made it possible to multiply by ten the capacity of the installations and to reduce the size of the ground stations. The numerical methods of coding to the source thus involved a division by ten of the flow necessary to transmit a telephone call or a television program.

Modulation of the signal

To make so that the wave “carries” a message, the modulation is used. The process consists in modifying one or more characteristics of the radio wave (carrying) according to the type of information which one wishes to send. The opposite process, the " démodulation" , is used to rebuild the information of origin (speech, computer data or program TV) in the receiver.

In practice, the method of modulation, generally rather complex, is selected in order to optimize the performances of a satellite connection according to the type of information to be transported. Information is often coded with the transmitter in order to be able to detect and correct the possible errors due to a bad interpretation in the receiver. Similar techniques, such worked out, are used for example to protect the discs audio laser against the stripes and bad handling.

Types of covers of a geostationary satellite

A telecommunications satellite will never use all the surface which it can cover because on the periphery of this covered maximum zone, the angle formed between the ground and the satellite is too weak to be able to receive the waves emitted by the satellite. On the other hand, of the restricted covers - semi-total (scale of a continent), regional (scale of Europe) and narrow (2 to 3 average countries) - have the advantage of concentrating energy on smaller surfaces and thus of providing a stronger signal.

Business services

Telecommunications very quickly represented an important market (50 billion dollars in 2000). Several business services thus developed, as well on a world level as national:

International services

Intelsat

Intelsat is the International organization of the telecommunications satellites which joins together more than 120 countries. The first satellite of Intelsat was “Early Bird”, which ensured of the tele retransmissions between Europe and the United States.

The following generations of satellites had emission and line capacities more raised already, concentration of the power in direction of the Earth, and division of the spectrum of transmission as narrower wavebands. Thus, the first of the satellites Intelsat of fourth generation, launched in 1971, was equipped with a capacity of 4.000 vocal Circuits.

In 1980, the satellites Intelsat of 5th generation had a capacity of 12.000 vocal circuits. One in addition started to concentrate the power of the satellite on small areas of the Earth, which made dropped the prices of the reception antennas (size and smaller diameter). Brought into service as from 1989, the satellites of sixth generation could establish 24.000 simultaneous circuits. To the beginning of the year 1990, Intelsat, with 15 satellites in orbit, thus offered the widest communication system of the world, relaying 100.000 telephone telephone circuits. However, other systems also propose an international service of the same type, thus competing with that of Intelsat which was privatisé in 2001…

Official site of Intelsat

Inmarsat

International organization of the maritime satellites, Inmarsat ( International Maritime Satellite ), founded in 1979 and transformed into privately held company since 1999, covers a mobile network of telecommunications which ensures of the connections of numerical data, the telephone links and a service of transmission by telefax between boats, installations at sea and ground stations throughout the world. Moreover, this network prolongs the system of connections now by satellites used by the planes of the international lines. The telephones Inmarsat became essential in the transatlantic races, the rallys, etc They are also formidable tools for the journalists, and all the rescue squads in the event of natural disaster: thus, at the time of the great earthquake of Kobe, the connections with the outside world could be restored thanks to telephones Inmarsat. It is the same in the event of tidal wave, of volcanic eruption, flood… Inmarsat from now on will be competed with by the new constellations of satellites for the “mobiles” (Globalstar) to see even by geostationary satellites which will offer connections at low price for the countries in the process of development (ACES in Asia and EAST for Africa).

Official site of Inmarsat

Regional services

the expansion of the international systems was parallel to done the system development to the regional scales.

In Europe : The importance of the telecommunications satellites appeared very early to the European countries but it will be necessary to await a true European space cohesion to establish, in 1977, Eutelsat which will allow obtaining a true European telecommunication service independent of the world supervision. Thus, Eutelsat belongs to the achievements which allowed a greater regional cohesion between Member States of the ex-EEC. The service is based mainly on a television offer with a European service of telephony which made it possible to supplement the European ground network without enfreindre the conditions of Intelsat (always used for the communications out-Europe). It is also necessary to mention the European network of telecommunications satellites ECS (Satellite European Communication), developed by the European space agency (ESA); each one of its satellites can establish 12.600 circuits.
Arabsat :The creation of the Arab Organization of Telecommunications in 1976 corresponds to a political will of development of the regional bonds but in a different context since it was here about a programme of reinforcement of the Arab cultural identity. These last years, the commercial will however seems to have carried it on the cultural will.
Palapa :At the beginning only based on Philippines, the Palapa system gradually extended to the remainder from the countries from the ASEAN (Association of the countries of the South-East Asia) until being recognized regional system by Intelsat.

Outlines

Compete with fiberoptics

Place du satellite in Internet network

Should it be pointed out: everyone does not have access to the Internet high banc of the type ADSL. Even in a developed country, like France, a quarter of the population cannot obtain high banc. In other words, 15 million French, approximately a commune on two and one third of the private companies will remain at the edge of “the highway of information” if nothing is done to democratize the access to high banc.

One of the solutions which would be essential is a constellation of satellites, or rather a constellation coupled with a ground network (by cables). One would thus associate the advantages of the satellite, namely natural diffusion (only one satellite is enough for a whole area) worms of the mobile users in distant zones and without infrastructures terrestrial developed, by avoiding the many engineering problems inherent in this systems: the long times return ticket of the waves (effect “of echo”), errors of transmissions carrying more to consequence (considering there is more information in transit and that one directly removes this information at the time of an error) and finally a certain asymmetry (the quantity of received information is not all the time the same one as the quantity of information sent, which obliges the satellite “to store” data).

Satellite of positioning

The company of information includes not only telecommunications but also the localization and navigation. The latter is the whole of technologies which allow:

to know the position of a mobile compared to a frame of reference;
to calculate or measure the course to be followed to join another point of known coordinates;
to calculate other relevant information (distance, rate of travel, estimated hour of arrival, etc).

The frame of reference

The current satellites of géopositionnement use to be located compared to the terrestrial sphere (which is far from being perfectly spherical), system WSG841 (World Geodetic System, 1984) based on the terrestrial geoid . The punctual coordinates are given by longitude (meridian line) and the latitude (parallel) starting from an arbitrarily selected origin: the intersection of the meridian line of Greenwich with Ecuador. The latitude varies 0° with 90° northern or southern and longitude varies 0° with western 180° or is (always compared to the meridian line of Greenwich and Ecuador). Knowing the coordinates of the mobile and those of the place of destination one can then calculate (or measure on a chart) the course to be followed to join this last point. Traditionally, in fact the stars had been selected to be used as benchmarks for navigation. However, these old reference marks leave more and more the place to artificial satellites. Latitude and longitude

Advantages of a system of positioning per satellite

the satellites are not influenced by the weather conditions.
They are largely more precise and more rapids that the old navigation systems (radionavigation for example) (precision of about 15 meters with the GPS and of 1 meter with Galiléo).
the system can be used as well by mobiles evolving/moving on the level of the ground (or of the sea) as by mobiles evolving/moving in the atmosphere.
the system is much more accessible than the old means from positioning (by waves radios), which were used only on the aircraft.
the system in itself is free, it has there only the receivers which are more or less expensive (all while remaining it much less than the receivers of the old systems).

General operation

Systems with downward way

The systems of géopositionnement existing and Galiléo (see 4.2.2) function all on the same basic principle: the system consists of three “segments”: a constellation of satellites in orbits around the Earth, receivers and finally of the stations on the ground which control the satellites, are given the responsability to define their orbitography 1 and the other information repeated by the satellites themselves in the receivers.

In order to determine the position of a mobile, the principal current systems and futures (GPS and Galiléo) use (or will use) the principle of the “downward way”, i.e. the satellites have a very simple load utile2 and emit signals given rhythm by a stable ultra clock, the receiver having an instrumentation more important than the satellite itself. The satellites permanently emit microwaves (electromagnetic waves) which are propagated with speed of light and which are collected by the receivers. Knowing the speed of light propagation (+ 300.000 km/s), they can then calculate the distance which separate them from the satellite by comparing the hour of emission (included in the signal) and of reception of the wave. An error of 1 thousandths of second in calculation is transformed into an error of 300km on the ground! Therefore the satellites must contain an extremely precise atomic clock. To know its position in real-time in space with three dimensions, one needs a minimum of four satellites received permanently. Indeed, one at least needs four benchmarks to carry out a precise triangulation. Three satellites will be useful to be able to have the coordinates latitude, longitude and altitude and a fourth will be used to determine the shift between the clock of the user compared to the reference frame of time of the system of géopositionnement (it should be understood that to place an atomic clock which would be synchronized perfectly with the reference frame of time in each receiver is impossible). The triangulation thus consists in here solving an equation with 4 unknown factors which are the position in 3 dimensions plus the shift of the clock of the receiver with the hour of reference of the system. (N.B.: to know only its position in 2 dimensions, 3 satellites are enough and more than 4 satellites does nothing but increase the precision of the answer and thus of the position). In light, to obtain the coordinates of the receiver, one seeks the intersection of the circles of radius “outdistances calculated between the satellites” and of center “satellites” and one defers this intersection compared to the terrestrial geoid (the latter is known because the messages of navigation contain parameters on the orbits of the satellites).

Galileo

The GPS being a system developed for the American soldiers, a selective availability was envisaged. Since 1990, the civilians had access only to one weak precision (approximately 100m). May 1st, 2000, president Bill Clinton announced that it put an end to this voluntary deterioration service. However, the system can always be subjected to a jamming of the signal without the users not being informed, which makes a service far from sure of it for the activities like the guidance of the planes for example. Moreover, the majority of the new satellites are now equipped with receivers GPS in order to be able to calculate their position, which creates a situation of dependence with respect to the American army. Indeed, if each satellite is equipped with a receiver GPS, it can be allowed to create a total chaos by scrambling the emissions of system GPS! Lastly, the market of the localization by satellite is in full expansion and should represent 155 billion euros in 2020. Europe could not thus allow itself not to react vis-a-vis the American monopoly and decided to launch its own constellation of satellite of navigation: Galileo. This one will be complementary to GPS while being much more precise (precision about the meter, for 15 meters with the GPS) and exploiting 5 “channels” (particular frequency). Each “channel” will be useful to 1 in particular service, of which some will be paying. These services are:

open service (or OS for Open Service): like the free service offered by the GPS, but the precision is larger: about 1 meter. No information of integrity is assured. It is this service which will be mainly used by the private individuals;
business service (or CS for Commercial Service): in exchange of a royalty paid with the Galileo operator, it will offer many services to added-value (guaranteed service, integrity and continuity of the signal, better precision of the dating and data of positioning or the diffusion of encrypted information using 2 additional signals). In fact mainly the subscriptions with this service will ensure the financing of Galileo;
service of safety of the life (or GROUND for Safety Off Life service): it will deliver a service made safe, just and reliable, for the critical applications in the field of the safety of the life such as air transport, maritime and terrestrial;
regulated public service (or PRS for Public Regulated Service): will address itself in priority to the users fulfilling a public service mission, very dependant on the precision, quality of the signal and reliability of its transmission (emergency services, transport of dangerous matters, transport of funds, etc). As this service must be available in any time, it uses two signals with share and has several systems preventing a jamming of the signal;
research service and help (or SAR for Search And Rescue service): it will make it possible to locate the whole of the park of the beacons Cospas-Sarsat 406 MHz and to return a message of payment towards the beacons in distress. The regulation and the definition of the functions are under the load of the International Maritime Organization (OMI) and the International Civil Aviation Organization (ICAO).

With Galileo finally, one hopes for the creation of 140.000 direct uses in Europe.

Systems with rising way

Opposite: Transmitting buoy Argos

Contrary to the satellites with way going down, the satellites with way going up have a payload complexes and its emissions can be scrambled but the transmitter on the ground (or at sea, in the case of a buoy) is very simple. To make known its position and the scientific data that this one is supposed to collect, a transmitter (which can weigh less than 20 grams) transmits a message coded regularly towards space. One of the satellites of the constellation then will collect the information which will have arrived to him by uplink and will record it. The satellite can calculate the altitude of the transmitter by knowing time that the wave put to traverse the way and its position thanks to the Doppler1 effect. As soon as the satellite passes to the top of one of the 21 centers of data processing, it returns collected information which will then be analyzed by afterwards.

Applications of the systems to downward way

Military navigation

Being reserved only to the soldiers, I will not be delayed on this part since this type of application does not improve really our life. But the GPS being at the base a military project, it is clear that there are many applications in this field: it was in particular used during the programs of the war of Balkans and the second war of the Gulf to guide missiles, to guide the troops and to locate them, to have an overall good sight of the sphere of activities…

Topological statements and terrestrial motion studies

Not badly of people are unaware of that the systems of géopositionnement can play a part of prevention in certain natural disasters. Indeed of many systems are developed or are under development on Earth to supervise an active fault or to measure the deformations of a volcano. Applications in geophysics, certainly less spectacular, are they also made thanks to the GPS: the measurement of the plate tectonics, the measurement geoid,…

Measurements of the plate tectonics

To measure speed to which the terrestrial plates advanced, one made, before having system GPS, of the estimates starting from the rocks located close to the oceanic dorsals. It is noted that there are bands of rocks magnetized towards north or towards the south according to at which time they were solidified because the terrestrial magnetism changes periodic direction of manner.

The major disadvantage of this method is that it provides only one estimate calculated over geological times. Speeds of displacements present being able to be very different, it was essential to be able to measure the instantaneous speed of the current deformations.

The system using the GPS is relatively simple: at a given place, one fixes a metal stem firmly related to the rock. At the exact vertical of this one, one places antenna GPS exactly at the vertical of the center of the reference mark, with a certain height. Thanks to system GPS, one calculates with precision the position of the reference mark in space. A certain time afterwards, one starts again the operation and one calculates the rate of travel thus.

To have the deformation in a zone considered, one measures the displacement of a certain number of points distributed on the aforementioned zone.

To obtain precise measurements (about the millimetre), one is obliged to make many measurements during a certain time and simultaneously with all the reference marks of the zone. Usually, one takes a measurement every 30 seconds, during 3 days, on all the visible satellites at every moment.

That represents an average from 30.000 to 40.000 measurements per point. Obviously, the time of measurement is conditioned by the necessary precision. For a precision of a few centimetres, it is necessary to measure for one length of time of about an hour. Thanks to this technique, one could be extremely precise measurements the speed and direction of the terrestrial plates what helped the researchers to refine their models.

Results obtained thanks to process GPS: The Pacific: 10 cm/an towards NO South America: 1cm/an towards the NR Eurasia: 1cm/an towards the E Nazca: 7cm/an towards the E Africa: 2cm/an towards the NR Philippines: 8cm/an towards O The Antarctic: rotate Arabia: 3cm/an towards India-Australia: 7 cm/an towards the NR Coconut: 5cm/an towards North America: 1cm/an Caribbean: 1cm/an towards

the monitoring of a fault activates

The seisms and the phenomena related to those were the first cause of mortality in the natural disasters during last century. Unfortunately, the scientists enormously have difficulties in create a precise model to envisage the earthquakes, because they do not have a sufficiently large time of study and undergo the random effect of these events. Despite everything, many studies are undertaken in order to discover the harbingers of these catastrophes and to be able to create an effective alarm system for the populations. American was the first to consider the application of system GPS to geophysics. Mainly because of the very great risk of major seism in the state of California. In this area of the world, the sliding motion of two tectonic plates along the fault of “San Andréas” causes seisms devastators regularly. By measuring the position of points distributed on both sides of the fault, and the movements of these points during time, it is possible to chart this one precisely. The analysis of the deformation of the surface of the ground in the area of the fault gives information on the depth of the fracture, the length of the active segments, the zones where the risk of seism is most important, in short refines the models of the geologists.

In addition, after a seism, measurement GPS gives access to the total displacement of the ground caused by this one. This information is particularly useful for the comprehension of the fundamental mechanisms of the seismic rupture. Lastly, it is even possible to measure the position of points GPS during a seism. By calculating the position of the point to each measurement, one can literally even the point move during few tens of seconds that the earthquake lasts. If these points are well distributed, one can also even the rupture be propagated along the fault. There still, all this information makes it possible to analyze the seismic wave propagation, and the movements of the surface which result from it. This type of network is now set up around a great number of active faults of share the world: in Japan, in Indonesia, in Burma, or in Turkey. It should be recalled that 500 million people in the world lives in a seismic zone at the risk.

vulcanology

Thanks to the GPS, it is possible to supervise the deformation of an active volcano. With some points GPS judiciously placed and measured uninterrupted, one can follow day after day the deformations due to the rise of lava. These measurements are useful for the volcanologists to quantify the phenomena associated with an eruption. One can also imagine a process of prediction: the data would be sent permanently at a control center which would gather the information obtained with sensors GPS. Thanks to the preceding models establish by the latter have could thus determine at which time the situation becomes critical and which should be evacuated the zone. This system is currently tested on Etna, the Piton of the Furnace and in Martinique, with the Sulfur mine.

Civil navigation

It is the sector of applications which the general public knows best. In the survey, in fact besides the GPS is quoted initially in the applications of space research. There is of course the fact that system GPS equips more and more with cars… But the applications intended for the civilians are not limited to that solely. There exists indeed many other systems which use the GPS or the GPS coupled with another system in order to obtain a better service. The latter are extremely varied: there is in particular the agriculture of precision, with the fight against because-jacking while passing by the location of the beacons of distresses.

the agriculture of precision

The Agriculture of precision is a concept of management of the agricultural pieces. It rests on the principle of bringing the good amount, at the good place, the good moment. The agriculture of precision can be used to optimize the management of a ground on 3 levels:

environmental: the polluting pesticides, manures and other products are limited.
agronomic: one adjusts the needs for the plant to his truths needs in an extremely precise way.
economic: one increases competitiveness by increasing the output of the ground and the working time.

It requires the use of novel methods, such as the localization by satellite and data processing. The GPS is useful here in the first phase of the agriculture of precision, i.e. the control of the workspace. Thanks to the precision of system GPS and special sensors, fascinating in memory certain indications and notes of the farmer with certain coordinates taken during its work, it will be possible in the event of problem to precisely turn over on the spot. But the farmer can also note the most fertile places. Thanks to “charts of extremely precise fertilities”, obtained progressively years, it can thus decide its future policy of occupation of its pieces. If he wants to put weedkiller in order to eliminate any trace from resistance in his field, he will be able to also do it in a more productive way while avoiding passing by again where he already passed and not to forget certain zones.

Despite everything, the agriculture of precision remains a expensive tool (the cost of equipment out of computer material and software SIG, associated with the price of a GPS and a sensor of output is approximately 15000 euros) and is often reserved only to the big landowners. But one envisages a reduction in the prices in the future and thus larger a use of this system.

For “private guidance”

Receivers GPS are sold in large surfaces or equip with series the vehicles. Smallest hold in the pocket and are worth the price of a top-of-the-range electronic diary. The GPS is also used as navigation system the competitors of the rally-raids like by the hikers and other practitioners of sports in full nature.

the fishing of precision

The fishermen can, them, to locate to them (S) boat (X) with a high degree of accuracy to ensure their safety vis-a-vis the dangers of the sea (bad weather or collisions) and to increase the productivity of their activities of fishing. Without counting that the GPS can guide them during the storms and during the operations in the ports.

the guidance of the planes

One of the first applications practical of the GPS exceeding simple positioning was implemented on the airport of Chicago, one the most encumbered of of the United States. It was not a question of making it possible to the pilots to position in flight, as one could believe it, but to allow the tower of control to know constantly the position of the planes on the ground in order to manage their displacements as well as possible, the sequencing of takeoffs and to avoid the collisions, in particular the days of fog. Each plane is provided with a receiver GPS which calculates its position permanently and diffuses it by radio with the tower of control. In the tower, a computer receives these positions and posts in real-time on screen, in the field of the airport. A “radar without radar”, all in all, which makes it possible to the controllers to have all the necessary information summarized on a simple screen. And then, which does not know the autopilot on the aircraft, system which already helped many pilots in difficulties? The autopilot is not in fact an assumption of responsibility of the apparatus, coupled with a trajectory calculation guided by positions GPS in real-time!

the fight against because-jacking

It is in fact a passive process. In this case, one installs a receiver GPS under the cap of the vehicle to be protected. In case of theft vehicle, the user calls a research center which then will collect the radio message sent uninterrupted by the receiver to give its position. It then does not remain any more with the police force but to go to the residence robbers “to gather them” and recover the car.

Application of the systems to rising way

To save lives

Developed to this end, one estimates that between 1982 and 2005, the Copsas-Sarsat system made it possible to help more than 14.000 people, in majority in the maritime field.

To protect and safeguard the wildlife

While placing beacons on the wild animals such as the migratory birds, the scientists can easily observe their displacements. They can thus obtain information, normally inaccessible, necessary to the safeguard of certain protected spaces.

To know and include/understand the ocean and the atmosphere

Argos actively contributes to include/understand the oceans by collecting and treating the abundant data by 5.000 drifting buoys, 1.500 floats of deep sea, 300 anchored buoys and fixed stations. These beacons measure the atmospheric pressure, the direction and the speed of the wind, the currents of surface, etc

To supervise the volcanos

The permanent monitoring of the volcanos makes it possible to immediately detect any possible hazard for the population and the airline companies, which are sometimes brought to cross clouds of volcanic ash.

The Argos system was introduced since 1992 into networks of volcanic pre-alarm (associates sometimes with detectors GPS). Forty the 120 volcanos which account Indonesia are thus equipped with sites autonomous Argos measuring.

To measure and manage the water resources

While placing transmitters on certain rivers, one can prevent possible shortages. The Argos transmitters indeed give the rise in the level of the river. These data make it possible to better manage the exploitation of the stoppings, the cooling of the thermo plants and nuclear, etc

Satellite of observation of the Earth

The satellites of observations are one of the major components of space technology. Indeed, they correspond to a very important need for much for human activities: to have a comprehensive view of the Earth. Before the space era, the man had indeed never been able to embrace the whole of a hemisphere at a single glance. One thus needed the placing in orbit of the first space vehicles to make move back the accessible horizon and to show our planet like never we had not seen it before. Today, the satellite of observation became essential to the scientists and the industrialists as with the soldiers. It offers to each one of them a multitude of reasons to observe the Earth since space in the whole of the electromagnetic spectrum.

Small history of the aerial observation and space

the balloon: In the middle of last century, the balloon allowed the French photographer, Felix Tournachon, to carry out above Paris the first air photographs. But it is truly during the American Civil War (1861-1895) that the balloons became the first means of air recognition.
the plane: At the beginning of the XXe century, the plane showed all its advantages as a platform of observation of civil or military use. Nowadays, of the planes especially arranged in flying studio, equipped with rooms of catch of sight or other instruments, carry out in the whole world of the missions for the cartography, the study of the forests, town planning, espionage, the monitoring of pollution, archaeological or oil research, etc air photography provides documents of excellent quality, covering a weak surface on the ground but with a resolution of a few decimetres only. However they are there specific missions, limited in time and space, very expensive.
the artificial satellite: Appeared in 1957, the artificial satellite having of the properties (given repeated, on large extents, without constraints imposed by the political borders and low costs compared with the duration of the mission) which make an exceptional platform of observation of it became the tool of reference to observe the Earth.

Operation of the satellites of observation

General principle

These satellites rest to detection and the measure by their sensors of the electromagnetic flow of radiation coming from the zone observed. One interprets then the data by holding account of the following physical laws:

Plus the wavelength is short, plus the temperature of the object is high (Formule of Planck: Energie= (6.63  10-36)  frequency).
Each object studied (plant, house, surface of water or mass of air) emits or thinks radiation of various wavelengths and intensities depending on its state (chemical composition).

To ensure the complementarity of measurements, the scientists use several sensors specialized in a particular wavelength to study the same terrestrial phenomenon.

Classification of the various types of sensors-imageurs

According to the passivity of the system

After in the beginning being consisted photographic cameras, the current sensors are is of passive type where the signal received by the optical system is returned on detectors which transforms it into electrical signal (principle of the scanner), that is to say of active type.
the active sensor is a radar: it emits a signal, in the field of the ultra high frequencies, and records the answer returned by surfaces and the objects observed. This sensor makes it possible to emit and receive a signal whatever the atmospheric conditions and the conditions of illumination.

Active system: the embarked instrument on board satellite ERS emits a signal which is retrodiffused by the medium observed and detected by the antenna “has”. Passive system: the embarked instrument on board the satellite SPOT receives the solar radiation considered by the medium observed.

According to the spectral bands

The sensors use various spectral bands according to their mission.

According to the observation field

According to the orbit

A geostationary satellite is placed above the equator and with the same number of revolutions as the ground itself, with the result that it seems stationary from the point of view of an observer on the dry land (see appendix V). To 36.000 km of altitude, it can observe a whole hemisphere. A polar orbital satellite makes it tower of the Earth with a close relation-polar slope, meaning that it passes always exactly to the top of the axis of rotation of the Earth. The satellite passes the equator and each latitude at the same local solar time each day. The orbit of the polar satellite is much lower than an geostationary orbit and thus sees more a small portion of surface, but in with a finer detail. The two types of satellites polar and geostationary should be seen like complementary. Each category has qualities and defects that the other does not have and an ideal system of observation (a “constellation” of satellites) tries to combine the advantages of these two modes of observation.

Advantages and disadvantages of a geostationary satellite:

The satellite is visible permanently of all the points of a broad zone (a third of planetary surface). That means frequent sending of data (each minute at best), which allows a good follow-up of quickly being held event. Only one station is necessary for the maintenance of the satellite. But the polar regions are not visible and the resolution on the ground is bad. Advantages and disadvantages of a satellite in polar orbit:

It ensures a total cover and a good resolution on the ground. Synchronization with the sun produces a constant illumination for the surfaces observed thus that a maximum energy for the instruments. In spite of that, the observation continues of a particular point is impossible (although a multiple system of satellites solves the problem) and the maintenance of the satellite requires many stations on the ground.

Applications in the military field

The military satellites constituted the first shape of satellites of observation: indeed, since 1959 and within the framework of the Cold war, the United States and the USSR developed military satellites of observation, which one calls usually and wrongly “spy satellites” (the first of them was Discoverer 1). They obviously made it possible to be able to observe the military resources of the enemy in not very accessible zones in order to evaluate the danger that those were likely to represent (that was thus used as a basis for the other civil applications of the satellites of observation). All this was entirely licit considering the borders do not have any more course at an altitude higher than 80 km. The two countries thus avoided the diplomatic problems involved in the observation of the enemy starting from planes spies (U2, at the Americans). Thus, one could just like discover that the USSR had, the USA, a programme of conquest of the Moon! But more important than that, these satellites had a role stabilizing in the Cold war. Indeed, they made it possible to check the veracity of the messages of enemy propaganda: if for example the USSR affirmed to have 1000 nuclear warheads whereas the satellites could about it observe only 10, one concluded from it that the threat was less large, which rebalances the 2 involved forces (the USSR will have lost a means of pressure on the USA). That also made it possible to discover certain real threats and to remove them. The best example is the crisis of Cuba. Thanks to satellite photos, one could show the presence of intercontinental missiles on the island of Cuba in front of the United Nations what made it possible to make withdraw the threat of the island. Now, one should not hide that the military satellites also make it possible to guide missiles or to intercept telephone calls, which is definitely less positive. But the vocation first of a military satellite is used to help the soldiers, not only in the strategic sector but also on the battle field.

Meteorology

A few decades ago only, the forecasts weather were much more random than today. One of the problems was that the weather stations existed only in few places. Everywhere else, the conditions weather remained a mystery. Moreover, the meteorologists had only little retreat vis-a-vis information which they obtained and could not consequently all model. Thus, it was impossible for them to measure the temperature on the level them oceans, to observe the clouds in altitude, to know the terrestrial radiation or to follow on line the displacement of a tropical storm. Since 1962 and TIROS 1, all that is possible thanks to the satellites weather. It is little to say that they created a true revolution. The simple fact of offering a complete cover of the Earth, of day like night, literally upset all the models in situ made up since 1 century! Each system of depression or anticyclone became suddenly visible during its formation and of its evolution, thing impossible to observe from a ground station. Europe is very present there thanks to the satellites Météosat .

World Weather Day before

Since the Sixties, the appearance of the satellites strengthened the co-operation between the states belonging to the international cooperation of meteorology which joined together them in the World Weather Day before. The principal goal of the organization is to create a permanent and world service of observation of the cloudy mass.

Localization and the follow-up of the cyclones

Thanks to the satellites, the forecast of the ways of the tropical cyclones made considerable progresses. Thus for example, in 1992, at the time of the Andrew hurricane, the Meteosat images made it possible to divert the air traffic and to take the necessary measures for protection on the ground of the goods and the people. Similar examples appear each year and it is difficult to calculate the number of human lives that the forecast of the trajectory of the cyclones (which must much with the satellites) saved. Each new catastrophe however underlines the limits of the current forecasts in meteorology. The margin of progress is thus still very broad for the research centres.

The follow-up of the epidemics

The abundant data by the Météosat satellites make it possible to anticipate the zones of propagation of the fatal diseases. Let us take the example of the malaria. The Météosat data make it possible to locate the favorable conditions with the reproduction of the mosquitos, vectors of the disease, and thus to develop a reliable alarm system facilitating the work of the health authorities. More generally, there exists a close link between the climatic conditions and the appearance of epidemics, from where importance to have precise data on the climatic conditions to establish a model allowing to envisage the zones at the risk.

Agriculture

The satellites brought to meteorology a highher degree of accuracy, with the result that data that receive the farmers are, they also, more precise. Thus, they can adapt their activities according to information weather: frozen, precipitations, fog,… to avoid a long enumeration of applications of the meteorology of precision in agriculture, here two examples which show the importance of it: - By analyzing the infra-red radiation of the Earth, satellite GOES measures, in Florida, the temperature of the ground every 30 minutes. Thus the risk of freezing, fatal with the lemon trees, is envisaged and is fought by heating with fuel oil only advisedly. The made saving rises to 45 million dollars per annum. - A company hawaïenne of production of sugar canes estimates to gain a million dollars per annum thanks to weather forecasting by satellites. Indeed, if the rain occurs less than 48 hours after one proceeded to the denshering preceding harvest, this one is lost.

Climatology

In addition to this short-term discipline that is meteorology, the satellites are also extremely useful for climatology. The latter does not have the same requirements as meteorology. One should not immediate data but data to him over one period of time much longer. The satellites of observation thus provide long series of measurements precise, total and compatible with the planetary dimension of the climatic phenomena. The climate is a “machine” comprising 3 “sectors” which interact between them: the ocean, ground and atmosphere.

Oceanography

Since 1992, oceanography was upset by the appearance of the satellites of observation of the water masses. All the models, benches with difficulty by more than one century of observations at sea, appeared vague, too old or forgery after only 10 days of operation of Topex-Poséidon! Since June 1995, oceanography has being adapted to accommodate the two modes of observation (by satellite and in situ). One arrived from there at an integrated oceanography, i.e. which not only tries to include/understand the phenomena oceanic but which can make forecasts of the evolution of the water masses. One thus uses models where the ocean evolves/moves in real-time. “Integrated” oceanography:

At sea, the satellite data make it possible to optimize fishing. By knowing, thanks to the satellite, the displacement of the cold or hot zones and the temperature of predilection of the various fish species, one can move directly on precise zones and avoid fishing too many nondesired species. By the same process, one can help the maritime police force and the scientists. One still can, by modelling the displacement of the water masses, to optimize the maritime routing (the fisherman will benefit from certain currents to use less fuel) or to better arrange the coast (3 billion human beings lives with less than 100 km of the coasts). One can also inform the people working on platforms offshore oil rig of possible agitated zones so that they can stop work in time. Altimetric satellites already make it possible to chart sea-bed by observing surface and, in the future, these same satellites will be able to detect the propagation of a vague correspondent to a tsunami and to thus inform of them the authorities which will have to take care of the system of prevention. To finish, it should be known that the oceans transport energy as much than the atmosphere. To include/understand the mechanisms which govern the oceans, it is thus to include/understand most of our climate.

Thus, El Niño (literally running of the Jesus Child, thus named because it appears shortly after Christmas) is a particular disordered state climatic, which is characterized by an abnormal rise in the temperature of the ocean. At the time of this phenomenon of enormous warm water masses move along the equator towards the East sometimes creating a rise in the sea level of more than 25 cm. El Niño involves considerable transfers of heat between the ocean and the atmosphere, at the origin of cyclones and torrential rains to the approach of the coasts of South America. Contrary, over the western edge of the Pacific where the surface water cools, the dryness dominates. The phenomenon is still very badly known scientists and the Topex-Poséidon satellite makes it possible to follow it and envisage its evolution.

Observation of the atmosphere

First of all, the satellites play a crucial role in the study of the hole of the layer of ozone. ERS-2 and Envisat in particular, make it possible to the scientists to supervise the dimension of the hole. They also make it possible to learn some more on the causes of its extension or its reduction thanks to three instruments able to study the pollutants which destroy this layer. The aerosols and the clouds are suspectés to play a great part in the climatic machine. The aerosols while diffusing and by absorbing the light or by modifying the reflective capacity of the clouds exert several effects on the climate: direct and indirect. The direct effect, or Parasol effect, results from the diffusion of the solar radiation by the aerosols and conduit to cool our planet. The indirect effect is a cooling effect. All the difficulty for the climatologists thus consists in measuring in which proportions the effects of certain phenomena play. The satellites their offer instruments to be able to improve their systems considerably. For the study of the parasol effect, it is a homonymous satellite launched on December 18th, 2004 which makes it possible to analyze the polarization and the directions of the solar radiation reflected by the Earth and the atmosphere. The researchers thus hope to discover the properties of these aerosols, their size, their distribution with the planetary scales,… the Parasol satellite also makes it possible to discover the properties of the clouds thanks to the observation of the interactions between these clouds and the aerosols. Finally, thanks to Parasol, one will be able to determine the assessment of competition between the two climatic effects: greenhouse effect and parasol effect. But another satellite, Calipso, are him able to observe the aerosols. In addition to that, it provides a vertical “cut” of the atmosphere with 30 meters of resolution. These 2 satellites form parts, like four others, of the Have-train. It is in fact a “train” of 6 satellites located on the same orbit and where each “coach” is separated from different from a few minutes. It was conceived to exploit the complementarity between 6 Franco-American satellites in the field climatic and oceanographical (for as much, each satellite is independent of different) the advantage of this kind of device is the possibility simultaneously of observing the same atmospheric phenomena at a few minutes of interval and according to various physical criteria.

Observation of the continents

The Spot satellite allows by taking in photograph phenomena like the volcanic eruptions or forest fires and to determine their impacts on the climate. Others like Cryosat and ERS, measure the variations thickness of the continental glaciers. They can detect icebergs and make safe navigation. Their measurements confirm a cast iron of the ices, all at least in the Arctic. In the next years it will be thus possible to test the cast iron forecasts of the ices within the framework of climate warming.

Satellites and climate warming

The satellites, in complement with other measures taken on Earth, thus inform us of changes observed like the rise in the average temperature of terrestrial and maritime surface, the rise in the sea level, the cast iron of the continental glaciers, the increase in precipitations and the hole of the layer of ozone. However, all the factors of the climate are not known for the moment and we do not know the climate up to what point will be modified. The satellites will have in the future to make it possible to study the impact of various phenomena and possible measurements taken to limit this climate warming. It is necessary also normally to be able “to live with” or, if possible, to anticipate the warming of planet, to have permanent aids observation total and systems of precise ultra modeling.

Major stake, the negotiations on the environment are brought to intensify in the next years. Until now, the politicians were pressed on quite fragile data when they polemized, for example, on the hole of the layer of ozone or gases with greenhouse effect. The satellites make it possible to deliver statistical data and rigorous in order to make the good decisions.

Observation of the earth resources

The cartography

The cartographers particularly appreciate the aptitude of a satellite to cover instantaneously the vast surfaces, even most inaccessible by terrestrial way, and to be able to renew the observation with the request. The first applicants of precise charts are ONG which work after the passage of a natural disaster (small a spin-off with Angleur is specialized in the preparations of such charts) because much of country in the world are low in geographical information. The charts of the Third World countries, when they exist, are often incomplete and old. Spot in addition makes it possible to draw up a total assessment of the damage and to follow the evolution of the situation from day to day. The Spot satellites in particular were very requested at the time of the tsunami which touched Asia at the end of 2004 and in 2005, at the time of the succession of hurricanes in the United States. In the industrialized countries, this demand for precise charts is often explained by studies on certain public achievements (roads, stoppings,…). The charts in 3D obtained thanks to the radars also make it possible to the telephone operators to better be able to locate their antennas. Lastly, the archeologists could discover old tombs in Egypt, hidden on sand, thanks to these same images radars which could chart the relief in lower part of sand.

Prospection for minerals

Each mineral has its clean electromagnetic “print”. It indeed will absorb or reflect parts of the luminous spectrum different according to its chemical composition. Thus, of iron will not be represented same manner on “a photo” catch by a satellite-radar as of cobalt. It thus does not remain any more with the prospectors but to check on the ground if there exists a seam and if it is exploitable.

Agriculture

Same manner that each mineral has its clean electromagnetic “signature”, each plant will have a different “signature” according to its nature or the fact that it is healthy, in growth or patient. One can thus establish charts of the cultures, follow their evolution, distinguish variations of their physical status (partners with the appearance of a disease or a lack of water) and estimate harvests (by combining information of the images with data obtained in addition, in particular on the ground).

Environment

By monitoring deforestation, pollution, the erosion of the grounds,… the satellites of observations allow an overall monitoring of the Earth, facilitating the comprehension and the control of these phenomena and playing a moderating part in the destruction of the natural resources. The satellites can thus know the water reserves, determine the impact of such or such activity on the environment… They can also determine the medical condition of the vegetation after an ecological catastrophe and supervise the impact of certain human achievements.

Prevention of the natural risks

The possibility of programming certain satellites of observation makes it possible to quickly acquire images on the affected areas by a catastrophe. Thanks to this information, updatable quickly, it is possible to place at the disposal of the helps recent information. The satellite also makes it possible to draw up a total assessment of the damage and to follow the evolution of the situation from day to day. The Spot satellites in particular were very requested at the time of the tsunami which touched Asia at the end of 2004 and in 2005 and at the time of the succession of hurricanes in the United States.

Technology transfers

If it is par excellence an industrial branch of industry where the innovation is the key word, it is well the space sector. Space is indeed the place of form of the grey matter. Nothing astonishing so that the space system development results in the advent of new technologies, products and services of great quality and who if, certainly, is more numerous, has an high added value.

In the time of the pioneers, all was to be invented. It was of course necessary to imagine, develop, to conceive, qualify a whole of powerful technologies for a new world: powerful and reliable systems of propulsion to free itself from the terrestrial attraction, vessels the acceleration proof terrible and incredible variations in temperatures, satellites and payloads ready to function in an extreme environment bathing in a permanent microgravity…

But each time, one found and one always finds in the schedule of conditions, various constraints: that of the reliability of the system first of all. It is indeed difficult to go to repair a satellite once this one placed in orbit. That of the weight then, because of the high costs of launching and of the limits of power of the launcher.

Performance, reliability and drive out with the superfluous kilos: the originators of space engines have always at the head this triple forced. A leitmotiv which has which pushed the researchers and industry to design new materials unceasingly, new systems.

Other techniques come from the manned flights. For them other constraints related to the effect on the organization of the space medium - weightlessness and the elevated level of radiations are added. The effects of weightlessness are especially made feel on the level of the muscles (atrophies), the bones (decalcification) and the blood system (surge of blood to the head,…). “Remedies” thus have being worked out to counter these problems.

Developed with blow of important investments, these space techniques find a new life today.

Applications of the manned flights

The International space station (ISS) was initially created with a scientific aim. The applications of the manned flights thus touch primarily the fields of fundamental sciences of the chemistry, the physics and the biology which need weightlessness to carry out certain experiments. These last are prepared on Earth and are carried out in Space. The scientists then interpret the results of these experiments. Thus, thanks to weightlessness, of the purer crystal samples could be produced. These crystals are semiconductor or superconductive and have applications in multiple fields of electronics (thanks to them, more data can be sent at the same time). However, it should be specified that the ISS is not a space factory and that thus the elaborate products are not marketed, nor even marketable because of their price. If the ISS helps mainly fundamental sciences today, it does not remain about it less than certain technologies developed to help the astronauts to face the space environment are used sometimes today elsewhere. For example, disposable the breeches layers were invented for the first spationauts, who needed materials absorbing inside their combination… More seriously, measurements taken to make it possible to the spationauts to evolve/move in a hostile environment benefit the firemen today. In another field, work completed to ensure the protection of the spationauts against food poisoning made it possible to go further in the conditioning and the hygiene of food. Space technology initially conceived to sterilize water thanks to two electrodes at the time of the space missions of long lives is used today in certain swimming pools to avoid the use of chlorine. Another application which one does not suspect of his space origin is the smoke detector, developed in the Skylab orbit station launched in 1973. Another application which can save lives and which finds its origin within the framework of the Apollo program is the raft of help which can inflate in 12 seconds.

The manned flights find especially applications in the field of medicine. Like known as in the intro, several remedies and techniques were developed to counter the undesirable effects of the “evil of Space”. Thus, the remote support or teleprocessing, born for the needs for the space flight, is used with the monitoring and the care of people with reduced mobility or alive in isolated places. This technique is especially used in the United States. Like the remote monitoring, the holter was developed to be able to follow the cardiac rhythm of the astronauts during the vol. This electrocardiogram equips today all the cabinets with cardiology. To face the phenomenon of decalcification of the bones, of the techniques of evaluation of the osseous density contributed to the development of instruments used to study the osteoporosis. Always in the imported techniques of the manned flights, of the robot-like apparatuses of assistance to the astronauts are used today to help the handicapped people. A last discovery in the study of the gaseous exchange in the lungs at the time of long stay in Space by professor Païva, physicist at the medical college at the Erasme hospital of the ULB, allowed the development of special clothing (of which the name is Mamagoose) to fight against the sudden death of the infant.

Various applications

In addition to the applications of the manned flights, we will now see an outline of technologies and materials transferred from space research towards other fields, classified in “various” because they are very heteroclite and it is consequently impossible to operate a logical classification. They are here by no means a complete listing but simple examples.

As incredible as that can appear, the code-bars were designed in an original manner by NASA to ensure the follow-up of the million parts which the space engines comprise. Coding by code-bars is henceforth used by almost all those which have something to sell. This system facilitates the automatic management of stocks. Certain refractory brakes in composite are derived from the space technique in this field. Always in the automobile field, did you know that they are the accelerometers and the technology of the bolts pyrotechnics developped at the point for the launchers which start the airbags today? Memory-shape alloys are henceforth used in the hospitals not to make swivel the solar panels of satellites but to maintain well in place two pieces of a fractured bone. Lastly, when you have coffee in a thermo®, you use a space product! It is necessary defer us behind 45 years, with the launching of the passive satellite of Echo telecommunication (see chapter 2). The envelope of this enormous balloon, of more than 30 meters in diameters, consists of a sheet of figure made reflective by the radio waves thanks to a fine layer of aluminum particles. It is the firm King-Seeley Thermos which took again the properties of this composite to make the Thermos bottles of them: lightness and reflection of the infra-red waves by which heat is dissipated. Lastly, one counts among these materials derived from space research many fireproofed composites or from the chemically treated fabrics which use the manufacture of cloths, the pieces of furniture, the interior walls of the submarines, the uniforms of the people who handle dangerous matters and clothing of the racing drivers.

Thousands of other applications under development or are already used in our daily life, like athletic shoes, powerful ultra solar panels, the medical imagery, the auricular thermometer, the parabolic aerial,…

Conscious of this capacity of innovation, the ESA launched the TTP (Technology Transfert Programs). It is a question of putting the assets of space research at the range of other branches of industry, with the service of the needs for the company. In a little more than 10 years, the technology transfers space European led to nearly 150 new terrestrial applications.

Employment in the space sectors

In Europe

In America

In Asia

In Oceania

In Africa

Appendices

Bands used in telecommunications

The principal bands used (frequency of rise/frequency of descent) are the following ones:

the band L (1,6/1,4 GHz), reserved for the mobile communications. Constituting the waveband least prone to the atmospheric disturbances, it is used by mobile terrestrial small stations (terrestrial boats, vehicles and planes).
the band C (6/4 GHz), very employed by the hundreds of active satellites in orbit.
band X (8/7 GHz), reserved for the military applications;
the band Ku (14/12 GHz), used also much, mainly by great fixed ground stations;
the band Ka (30/20 GHz), used commercially for the first time in 2004 by the Canadian telecommunications satellite Anik F2.

Characteristics of the systems of teledetection

Transit

Name: Satellite Navy Navigation System (or Transit)

 Manufacturers: the American army.

 Dates: Transit was the first space system of navigation operational. He was declared operational as from 1964 for American Defense and in 1967 for the civil activity. He ceased being exploited in 1996, the relay being taken by system GPS.

 to answer which waitings? : One needed for the American navy a precise to guide its underwater ballistic missiles, accessible system whatever the weather conditions

 Segments: - On Earth: 3 stations. - In Space: 6 satellites on a polar orbit of 1000 km altitude.

 Limiting: - controlled by soldiers, therefore the signal can be scrambled at any moment without the user not knowing it. - relatively low altitude decreases the duration of visibility of the satellite with the result that the exploitation is very discontinuous. - the receivers which have too an high speed of displacement (planes) cannot use this system.

GPS

GLONASS

 Name: Total' naya NAvigatsionnaya Sputnikovaya Sistema (total system of navigation by satellite).

 Manufacturers: the Russian army.

 Dates: The first launching in 1982, truly operational in 1995 but for a time relatively runs because of the lack of budget from which suffers the Russian space agency. One however noted these last years an renewed interest of Vladimir Poutine for Glonass.

 to answer which waitings? : Idem that for the GPS.

 Segments: - On Earth: 5 stations but only in Russia. - In Space: 24 satellites out of 3 orbits of 19.100 km altitude but of which only 12 can really still function correctly.

 Limiting: - outdatedness of the system, not enough of satellites to provide a planetary cover. - contrary to the GPS, that remains a strictly military system.

GALILEO

 Name: Galileo.

 Manufacturers: The ESA (european space agency). Civil project.

 Dates: Launching of the first satellite “test” Giove-A on Thursday, December 29, 2005. The system could be used in 2008 and will be completely operational in 2010.

To answer which waitings? They are multiple: to place at the disposal of the users a civil, precise system and integrates, making it possible to know their position in real-time, to open a market estimated at 250 billion euros (!) at least for an investment of 3.2 billion euros, to create according to the estimates of the EU 100.000 new jobs and especially to become independent of the United States in this field. It is thus little to say that one awaits much Galileo.

 Segments: - On Earth: 2 principal stations located in Europe and a score of others located everywhere else in the world. - In Space: 33 satellites out of 3 circular orbits to 24.000 km of altitude including 1 of reserve on each orbit.  Limiting: it will be completely active only in 5 years. it problem of the possible military use is outstanding.

Argos

Established since 1978 by the co-operation between the USA and France, Argos consists of 6 satellites in heliosynchronous polar orbit and of more than 15.000 beacons on the whole of the Earth. Its goal is to ensure the localization and the data acquisition for the study of the environment.

COSPAS-SARSAT

Cospas-Sarsat results from an international cooperation with an aim of improving research operations and rescue on totality of the sphere by providing information of alarm and localization. It is operational since 1982. The Cospas-Starsat transmitters start either by inertia with the impact, or by immersion, or manually when that is possible.

DORY

The purpose of the system Dory developed by the CNES, is to allow the fine determination of orbits as well as the localization of beacons. It constitutes an alternative to the GPS in the localization of the satellites on their orbit.

3 laws of Kepler and various orbits

The mission of a satellite or any space vehicle forces to him to describe a well defined trajectory. It is necessary thus that it can join it and to be maintained there. It must also preserve a certain orientation compared to the Earth and with the Sun. This attitude enables him to receive sufficient solar energy, to carry out catches of sight under the desired conditions or to communicate with the Earth. For each mission thus a type of quite precise orbit corresponds. It as should be added as a satellite is subjected to the 3 laws formulated by Kepler, like any space object. It is not thus enough with the launcher to leave the terrestrial attraction: it is necessary to take account of these 3 laws:

Law I: the orbit with the shape of an ellipse whose hearth is in the center of the Earth; the circle is in fact a particular case of the ellipse whose two hearths are confused in the center of the Earth. Law II: The satellite moves all the more quickly as it is close to the Earth; in precise term, the line which joint the center of the Earth to the satellite always sweeps an equal surface in a given time interval. Law III: the square of the period of rotation of the satellite around the Earth varies like the cube length of the main roads of the ellipse. If the orbit is circular, the main roads are then the radius of the circle.

the geostationary orbit (or of Clarke) is a particular case of the third law. It corresponds in fact at an altitude of 36.000 km because it is at this altitude that the period of the satellite corresponds exactly to the period of the Earth (either 23 hours, 56 minutes and 4 seconds). Seen Earth thus, a satellite located at this altitude does not appear to move: it is thus the perfect orbit for the telecommunications satellites and certain satellites of observation (weather) which must cover a stable zone.

the heliosynchronous orbit is a low orbit whose plan preserves a constant angle with the direction Ground-Sun. The heliosynchronous orbits make it possible to obtain one hour solar local constant with the passage in a given place, which determines a constant illumination and a sweeping of almost all the surface of the sphere, the orbit being quasi polar. These characteristics make of it an ideal orbit for satellites of observation of the Earth.

the polar orbit is a low circular orbit (between 300 and 1000 km of altitude often) which with the characteristic to be tilted in such a way that the object on this orbit passes closest to the poles to each “sweeping” of terrestrial surface.

Notes and references of the article

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