Communication with satellite. Satellite communications: operating principle, coverage area, channel characteristics and tariff plans. Features of wave addition

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Communications satellites launched into space, as a rule, enter geostationary orbits, that is, they fly at the speed of rotation of the Earth and find themselves in a constant position relative to the surface of the planet. Orbiting 22,300 miles above the equator, one such satellite can receive radio signals from one-third of the planet.

The original satellites, such as Echo, launched into orbit in 1960, simply reflected radio signals aimed at them. Improved models not only receive signals, but also amplify them and transmit them to specified points on the earth's surface. Since the launch of the first commercial communications satellite, INTELSAT, in 1965, these devices have become much more sophisticated. latest model A solar-powered satellite handles 30,000 phone calls or four television broadcasts simultaneously. The signals arrive from the antennas of the Earth-LA communication station and are received by the satellite transponder. This electronic device amplifies the signal and switches it to an antenna, which transmits it to the nearest LA-Earth communications station. To avoid interference, upstream and downstream signals are transmitted at different frequencies.

Launched into geostationary orbits, three INTELSAT satellites (left) transmit long-wave radio signals around the world. Serving the regions of the Pacific, Indian and Atlantic oceans, satellites make high-speed telephone, television and telegraph communications possible. In this regard, radio signals are lost high frequencies, since they are repelled by charged particles that make up the E and F layers of the atmosphere.

This parabolic antenna can receive even very weak signals from a satellite; most similar systems can also serve for Earth-to-aircraft communications.

INTELSAT-6

Radio signals arriving at the satellite gradually weaken over the long journey to such a level that they can hardly be transmitted back to Earth. Satellites like INTELSAT, the model of which is shown above, amplify incoming signals using solar energy. Each satellite also has a supply of solid fuel, allowing it to maintain its orbit.

In the picture at the top of the article:

1. solar battery power supply element
2. parabolic reflectors
3. parabolic reflectors
4. parabolic reflectors
5. parabolic reflectors

Like terrestrial antennas, this satellite antenna consists of a tooth-shaped device called the primary emitter and a reflective parabolic shield. Two elements of this system ensure the acceptance of incoming radio waves and the destruction of foreign waves.

Stations located on the surface of the planet communicate with INTELSAT through huge, 30-foot-wide parabolic antennas like the one shown in Fig. above.

A communications satellite can be placed in low-Earth orbit, intermediate-altitude Earth orbit, or geostationary orbit, whose altitudes above the Earth's surface are (in order) about 1000, 10,000, and 36,000 km. The first type of orbit passes below two of the Earth's radiation belts, the second type - between them, and the third - above them. Cm. ATMOSPHERE .

In geostationary orbit, a satellite makes one revolution around the Earth exactly every day. Since during this time the Earth also makes one revolution around its axis, the satellite appears stationary at the equator. The main advantage of geostationary orbit is that ground radio antennas do not need to track satellites moving across the sky; you just need to always point the antenna at one point throughout the life of the satellite. Its major drawback is the delay of about a quarter of a second between the transmission of a radio signal from one terrestrial radio station and the reception of another, which arises due to the large distances that the signal must travel.

The main advantage of a lower Earth orbit is that a less powerful launch vehicle is required to launch it into it. Because the distance from the ground radio station to the satellite is shorter, the satellite's equipment may be less powerful. However, satellites in such orbits move relative to terrestrial radio stations, so tracking antennas are needed to ensure continuity of coverage and cannot be done with just one satellite.

Technical means.

Satellite communications require three types of technical means: satellites, ground-based radio stations and launch vehicles for launch into orbit. These technical means vary somewhat depending on the type of orbit into which the communications satellite is launched.

Satellites.

A communications satellite consists of a rocket unit, which provides power, flight control and monitoring of on-board systems, and a unit of communications equipment, the purpose of which is to receive, amplify and relay signals from the Earth. Many connected satellites are stabilized by rotating around a single axis. Such a satellite, like a gyroscope, maintains its orientation in space unchanged. In addition, rotation helps maintain a uniform temperature distribution throughout the satellite. Satellites with three-axis stabilization, carried out using flywheels (gyrodynes) and low-thrust rocket engines, are also used. Three-axis stabilized satellites are somewhat more complex than spin-stabilized ones, but their solar panels can generate more electricity and their antennas are easier to point to ground radio stations. Solar panels ( cm. POWER SUPPLY BATTERY) cover the entire surface of rotating communication satellites or are located on special folding panels of triaxially stabilized satellites and convert about 20% of the energy of sunlight incident on them into electricity. The small satellite's solar panels generate approximately 1 kW of electricity, which is equivalent to the power consumed by ten 100-W light bulbs. On larger satellites in the 1990s, solar panels produced up to 10 kW.

Terrestrial radio stations.

Ground stations in a satellite communications system transmit radio signals to and receive signals from satellites. A 1990s satellite transmitter averaged approximately 20–40 watts per repeater (a device that receives and transmits a radio signal). That's a lot more power than a typical phone. cellular communication(0.5 W), but the satellite's radio signal must travel up to 36,000 km and can carry up to 1,000 telephone conversations. Therefore, a terrestrial radio receiving system must be a billion times more sensitive than a cellular telephone receiving system, which means larger antennas and very low noise receivers are needed. In the early days of satellite communications, terrestrial radio stations were equipped with huge antennas with a diameter of up to 30 m. In the 1990s, ground stations used “very small aperture terminal antennas” (VSAT) with a diameter of 1–2 m and larger antennas with a diameter of 2–10 m; Household television antennas with a diameter of 45–60 cm have also become widespread.

Launch vehicles.

The launch vehicle launches the satellite into a predetermined low-Earth orbit. With a few exceptions, almost all communications satellite launch vehicles have been developed from older intercontinental missiles ( cm. ROCKET WEAPONS) created in the 1950s. New launch vehicles appeared in the 1980s. The first launch vehicles not developed as military ballistic missiles were the American Space Shuttle (MBKA) and the Ariane rocket developed by the European Space Agency. The Shuttle was intended primarily to serve NASA's human spaceflight program, and the Ariane rocket was intended primarily to launch communications satellites. After the Challenger MBKA exploded in 1986, NASA stopped commercial launches. As a result, the Ariane system received the lion's share of contracts for launching communications satellites. In the 1990s, the Chinese Long March rocket and the Russian Proton also entered the commercial market. The path of the Long March was marked by accidents; As for the Proton, its nominal reliability (95%) and the large satellite mass (4 tons) foreshadowed its commercial success.

Launch is the point of greatest risk during the life of a communications satellite. The overall probability of a successful launch is about 90% (for specific launch vehicles it varies from 70 to 95%). Thus, on average, 10% of all launches fail and end in the loss of the satellite.

Status and development prospects.

Since the late 1990s, Comsat (Communications Satellite), which launches communications satellites in the United States, has faced the prospect of intense competition from public telephone systems. The fact is that fiber optic telephone cable provides high quality signal, does not introduce a time delay and is approximately equal in cost to satellites ( cm. FIBER OPTICS). It became clear that over time such cables for direct communication (without relays) would require lower costs than satellites. However, Comsat, whose satellite coverage spans the oceans, believed that satellites were better suited to broadcast television, voice and digital data than cable communications, except in large cities. In addition, satellite communications appear to be more cost-effective than cable communications when serving small, dispersed users, such as telephone subscribers in rural areas.

In 1976, the US Department of the Navy initiated a series of launches of Marisat communications satellites to service sea ​​vessels (cm. MILITARY SPACE ACTIVITIES), and this led to the creation of the International Maritime Satellite Organization, Inmarsat, which began operating in 1982. When Inmarsat launched more powerful satellites, they also found land users in remote areas. A market for mobile satellite communications has emerged - with mobile land objects. By the end of the 1990s it was mastered. American Mobile Satellite (AMSC) has launched a geostationary mobile communications satellite to serve North American subscribers. The Iridium company by the end of the 20th century. created a network of 20 satellites in low Earth orbits that would provide cellular mobile communications on land across the entire globe, as well as launch satellites for the same purpose into intermediate altitude orbits.

Economic factors and government regulation.

The development of satellite communications is determined primarily by economic factors, although politics also plays an important role. At first, the main area of ​​application for communication satellites was voice communication, then the emphasis began to be placed on television, and by the end of the 20th century. The transmission of digital data began to develop rapidly.

The initial major economic driver for the development of satellite communications was that satellites could provide direct (no hop-on) transoceanic communications at significantly lower costs than the coaxial submarine cables installed in the 1950s and 1960s. The difference in costs was then more than tenfold, but it disappeared at the end of the 20th century. Since cable introduces less time delay, it is more suitable for voice (telephone) communications. In the late 1990s, fiber optic cable could carry almost all transoceanic telephone signals.

The late 1970s saw the explosive growth of satellite-based cable television. By the end of the 20th century. The majority of the world's population has the opportunity to receive numerous television channels, specifically provided by cable television companies, which themselves receive them through space relays of satellite communication companies. Almost two-thirds of all satellite communications, excluding Intelsat satellites, were used for television broadcasting.

In the late 1970s, private satellite networks serving a single company also began to emerge. With the advent of "very small aperture antennas" VSAT, companies were able to communicate between all their offices using antennas with a diameter of 3-6 m. Such networks were used primarily for the exchange of digital data. Even telephone conversations, as a rule, were transmitted digitally. VSAT and larger diameter antennas provided coverage in the 1970s telephone communications with villages in Alaska. In the 1990s, satellites were first used for rural telephony around the world. In some experiments, satellite relays performed the functions of extended telephone lines, and cellular - the functions of local loops.

Despite the widespread development cellular networks and the huge number of towers that continues to grow, there are still areas on the planet where the use of such technology is impossible. In these inaccessible areas, satellite communications come to the rescue.

Satellite communications - what is it and what is it for?

In fact, satellite communication is not fundamentally different from the mobile communication that is familiar to society; it performs the same functions and allows you to establish communication between phones. The fundamental difference is the scope. Where a classic mobile (cellular) phone can fail and issue the ill-fated “No Service”, notifying the subscriber that there is no nearby cellular coverage, satellite communications will fully function and will not allow you to lose contact with the outside world.

This is extremely important in those moments when the subscriber goes beyond cellular coverage, for example, on an exotic trip, to the mountains or dense jungle. Often such a connection saves lives, because only through it will it be possible to contact a group of rescuers if a person unexpectedly finds himself in a dangerous situation. Satellite communications are also used by those who are constantly traveling for work and vitally need the ability to receive or make a call at any time.

Satellite phone: main characteristics

To work with this type of communication you need a special satellite phone. They come in several types, namely: stationary and mobile. Mobile satellite phones for your appearance They resemble classic phones released in the 80-90s, but have one characteristic detail: almost always such phones are equipped with an additional, non-hidden antenna. Setting up a satellite phone is practically no different from setting up a regular phone; you only need a suitable SIM card.

Stationary options communicate with the satellite using specialized ground interface stations. You can get by with a portable version of such a station.

A number of satellite phone manufacturers and, accordingly, owners of satellite networks produce special accessories for modern smartphones, which are small cases that can turn absolutely any gadget into a satellite one. Such cases connect to smartphones using a standard charging port and have a full set of peripherals typical of smartphones, such as headphone jacks. The cases are equipped with their own battery and can charge a smartphone, that is, they act as a battery case.

The principle of operation of satellite communication

Based on the name, it is clear that a satellite phone requires communication with a satellite to operate. The satellite phone transmits the signal directly to the satellite, which, in turn, transmits it to another connecting satellite, and it then completes the process and transmits the signal to the ground interface station. Eventually the call arrives at a landline, which completes the chain.

The satellite phone is capable of operating within specific area, and throughout the entire Earth. It all depends on satellites, some of them are located close enough to the Earth and move relative to it, they allow you to cover the entire planet and make a call to any point. There are other types of satellites that are located relatively far from the globe, in geostationary orbits. Such satellites cover only specific locations, thereby limiting subscribers.

Satellite operators

The same laws apply in satellite communications as in cellular communications; there are a number of operators providing satellite communications services. As a rule, these are the same companies that launch their satellites into space. Each of them has its own characteristics, its own pros and cons. On this moment There are four major satellite operators, including Iridium, Thuraya, Globalstar and Inmarsat.

Operator “Iridium” and his devices

Iridium is not just an operator, but a full-fledged satellite constellation. It owns 66 satellites moving in 11 near-Earth orbits. The distance from the satellite to the earth is less than 1000 kilometers. For the user, this means that no matter where in the world he is, using the services of this operator, he will always be in touch, the main thing is to be in the open air. Even if the connection fails when trying to communicate, it is enough to wait some time and try again, since the satellites move quite quickly, and one of them will definitely fly over the subscriber in the next 10 minutes.

The Iridium satellite phone does not support other SIM cards and cannot switch between cellular and satellite communications.

Also, many people find complete anonymity in the post-Soviet space useful. The company does not have terrestrial gateway stations in Russia. This fact completely excludes the possibility of wiretapping within the country, even if the secret services take on this matter. The Iridium satellite phone is not equipped with a GPS module.

Thuraya operator and his devices

This operator has three satellites located in geostationary orbit. The distance between the satellite and the earth reaches 35 thousand kilometers. Unlike the Iridium satellites, these satellites operate only over a certain point near the equator, since they do not move relative to the planet. Roughly speaking, the Thuraya satellite phone does not function at the poles; the further the subscriber moves away from the equator, the less chance of establishing communication.

Thuraya has entered into agreements with many “terrestrial” cellular operators, thanks to which the company’s devices can work with ordinary GSM SIM cards. This allows phones to automatically switch between different types communications. At the same time, the cost of services mobile operator increases several times. At the same time, you can save on even more expensive satellite communications when there is no need for it. Thuraya phones provide Internet access at speeds of up to 8 kilobytes per second, which is quite high for satellite internet. The devices are equipped with a GPS module and constantly transmit location data to the company’s servers. On the one hand, this fact can be confusing, since the user is constantly being monitored, on the other hand, such a function can save the life of a careless traveler and extreme sports enthusiast.

Operator “Globalstar” and his devices

Perhaps the most problematic operator that provides best quality communications. In 2007, analysts conducted a study and found that amplifiers installed on satellites degrade over time, much faster than design engineers expected. The reason for this is the orbit of the satellites: they pass through the Brazilian magnetic anomaly, which has a negative effect on the amplifier.

To somehow improve their situation, Globalstar launched several spare satellites into orbit, but to this day there are problems with calls. Often the waiting time for registering online reaches 15-20 minutes, and the conversation itself lasts no more than 3 minutes.

The company produces its own devices. For example, the Globalstar satellite phone of the same name. Also on their network are devices from Erricson and Qualcomm.

Operator “Inmarsat” and its devices

The company controls 11 satellites hovering in geostationary orbit. The communications provider is focused on professional use and provides communications to law enforcement agencies, the navy (including the Russian one when domestic satellites are out of order), and so on. However, there are other business-oriented subsystems. Through the satellite system, you can make voice calls, transmit data over the Internet and issue distress signals. Not long ago, new generation satellites were launched into orbit, providing high quality communications and ISDN connections for data transmission at high speeds.

The company is not involved in developing portable solutions for ordinary people, so this is not the best choice for civilians looking for a satellite phone.

Rates

The cost of the services of the companies described above is significantly higher than the cost of GSM communications. Iridium and Thuraya work directly with their users by selling SIM cards for satellite phones.

Thuraya, for example, charges for the SIM card itself (about 800 rubles) and for the initial connection (about 700 rubles). Communication is paid per minute, on average from 20 to 40 rubles, depending on which phone the call is made to. Internet traffic is paid separately - 360 rubles per megabyte. Tariffs for international calls depend on the country receiving the call, on average from 70 to 120 rubles. Incoming calls are free.

Iridium immediately offers global tariffs and sells them in packages, on an advance payment basis. The price for the basic package is 7,500 rubles, which includes 75 minutes of communication. There are other packages designed for corporate users, the number of minutes in these reaches 4000 or more.

Satellite phone numbers in Russia, like cell phones, start with +7 (location code) and a seven-digit number. International number includes full code countries - +8816 265 and so on.

SATELLITE CONNECTION

At the last MAKS-2001 salon, behind the thunder of demonstration flights by Russian pilots, satellite projects attracted the attention of only a limited circle of visitors. Nevertheless, today it is the cutting edge of applied research in the field of new technologies in the creation of missile defense (ABM), nanotechnology and microsatellites. Moreover, if missile defense and nanotechnology are the area of ​​activity of leading companies in developed countries, then the creation of microsatellites is affordable way entry into space for all countries striving to keep up with advanced countries.

Communication system of the Rubin-2 satellite

The creation of new global satellite systems such as Iridium and Globalstar led to the development of the production of satellites in large series. Today, communication systems are deployed in space, in which the number of satellites is measured in dozens. The technology for producing and launching satellites is becoming increasingly improved. In 2007, NASA plans to launch 98 satellites using one rocket. This experiment will help solve a key problem in magnetospheric physics - constructing a quantitative scheme for the development of a magnetospheric substorm. Details of this program can be found at stp.gsfc. nasa.gov/magcom.htm.

The most important issues when launching microsatellites are issues of control and communication, or rather, data transmission (telemetry) from the spacecraft. If for satellites in circular, polar orbits with an altitude of up to 1000 km, you can get by by simple means, then with satellites moving away over distances of several thousand kilometers, communication becomes a key problem. For a microsatellite weighing 10-20 kg and a power plant power of no more than 15-20 W, ensuring stable communication using simple means seems to be a very difficult task. And here the techniques and experience of organizing terrestrial cellular communications in combination with satellite communication systems are quite suitable. An obvious step in this direction is the use of Globalstar and Orbcomm systems for communication with microsatellites. It is precisely these “connected” experiments that are included in the microsatellite program, carried out by leading American universities with money from the US Air Force (see www.nanosat.usu.edu).

At MAKS-2001, one of these microsatellites, Rubin-2, was presented by OHB-Systems (www.fuchs-gruppe.com/ohb-systems), part of the Fuchs Gruppe and which has been working on spacecraft for about 10 years. The first result of its activities was the small satellite Sapphire. “Rubin-2” is the result of a continuation of these works and is aimed at performing a whole series of technological and communications experiments. The program for creating the Rubin-2 microsatellite has interesting indicators: from the start of development to launch - 10 months, the mass of the satellite is only 30 kg, it is planned to launch using a Dnepr conversion rocket together with other microsatellites. The satellite has a triaxial orientation that includes a magnetic ring system and six solar sensors. In cooperation with the Italian company Carlo Gavazzi (www.carlogavazzi.com), the satellite will be equipped with a new type of solar panels, an electric micromotor, a GPS receiver, new lithium-ion batteries, and a laser mirror.

The Orbcomm system was chosen as the main communication scheme for the Rubin-2 microsatellite. It allows you to solve two problems at once - to provide global communication with a microsatellite and to get rid of the need to create your own ground-based infrastructure for monitoring and controlling the satellite. The economic benefits of this approach are obvious, and the use of the Internet guarantees the reliability of execution of control commands. In addition to the Orbcomm terminal, the satellite has a Safir-m packet communications system, which has already been tested on previous microsatellites manufactured and launched by OHB-Systems several years ago. The figure shows a diagram of connected experiments on the Rubin-2 microsatellite. The main control channel operates through the Orbcomm system, service information is reset via a packet channel at a speed of 9600 bps.

In conclusion, it should be noted that OHB-Systems is closely connected with Russian organizations conducting experiments in space. In previous years, the company carried out a number of joint experiments with OKB MPEI; it has its own office in Moscow. The plans of all space organizations include an increasing number of microsatellite developments. This fully applies to both Germany and Russia, and it is logical to expect that they will soon appear collaborations in this direction. Let's see what will be presented at MAKS-2003.