ISS online - Earth from space in real time. Satellite communications You are a participant in the scientific program

Urgent problems are solved by a chain of space stations with an orbital period of 24 hours, occupying an altitude of 42,000 km relative to the center of the Earth... in the equatorial plane.

A. Clark, 1945.

In the Stone Age, the cohesive network worked by repeatedly repeating actions to regulate the volume of smoke emitted by the fire. The earth knew fast walkers, Little Muk became the best. The modern system uses spacecraft. The advantage of the satellite is its large coverage of the territory. The waves used are predominantly short, capable of propagating in a straight line. There is only one world - prices are different everywhere...

Prerequisites for use

The idea of ​​relaying was conceived by Emil Guarini-Foresio in 1899. The concept of indirect signal transmission was published by the German Journal for Electrical Engineering (vol. 16, 35-36). Arthur Clarke in 1945 voiced the concept of a communication system between geostationary spacecraft. The writer refused to take out a patent, denying two conclusions:

1. Low probability of the idea being realized.
2. The need to present the idea to humanity as a whole.

At the same time, the scientist indicated the coordinates of the best coverage of areas of the planet’s surface:

• 30 degrees east – Africa, Europe.
• 150 degrees east – China, Oceania.
• 90 degrees west - America.

The writer underestimated the operating frequency, expressing his intention to use 3 MHz, reducing the hypothetical reflectors (several feet).

Terrestrial microwave systems

The Anglo-French consortium, led by Andre Clavier, went further. The first successful attempts to use the microwave communications range date back to 1931. The English Channel demonstrated the transmission of information at a frequency of 1.7 GHz (modern cellular band) over 64 kilometers by stations equipped with dishes with a diameter of 3 meters, connecting Dover and Calais.

Interesting! First commercial TV channel VHF used a frequency of 300 MHz.

Historians tend to consider the Second world war the horse that took the industry to the top. The invention of the klystron and the improvement of paraboloid manufacturing technologies made an invaluable contribution. The heyday of transatlantic relations dates back to the 50s of the 20th century.

For reference! The first relay line, formed by eight repeaters, New York - Boston, built in 1947.

America and Europe have established the transmission of information by repeaters (radio communication, called relay). Commercial television broadcasting began immediately. A feature of microwave communications is the ability to accurately predict the result already at the system design stage.

For reference! Relay communication is a technology for transmitting digital, analog signals between receivers within the field of view.

Spacecraft

The first Soviet satellite (1957) carried communications equipment. Three years later, the Americans raised an inflatable balloon to an altitude of 1,500 km, which served as a passive repeater thanks to the metallized coating of the sphere. On August 20, 1964, 11 countries, including the USSR, signed an agreement to create Intelsat (international communications). The Soviet bloc followed the path of secrecy while the West made money. The Eastern Bloc created its own program in 1971.

Satellites were a real godsend, allowing us to connect opposite shores of the ocean. An alternative is optical fiber.

The military was the first to launch a dark horse along with tropospheric communications, which used the effect of wave reflection top layers. Soviet microwave communications were intercepted by the Rhyolite sky group. System developed for the CIA (USA). The device occupied a position captured by the ground beam of the Soviet relay communication, recording messages. The territories of China and Eastern Europe were controlled. The diameter of the umbrella-like reflectors reached 20 meters.

The US leadership always knew the intentions of the leaders of the USSR, listening to everything, even telephone calls. Today, satellite systems make it possible, thanks to the Doppler effect, to remotely attend any “confidential” conversations held in rooms equipped with a typical double-glazed window.

The first attempts to implement Nikola Tesla's ideas in space have been registered: wireless transmission electricity from satellite dishes. The epic started in 1975. Now the concept has returned home. Wardenclyffe Tower has long been destroyed, but the main island of Hawaii received its portion of 20 W wirelessly.

For reference! The use of space communications has proven to be an economically viable alternative to optical fiber.

Signal Features

The use of satellites is not surprising, given the above.

Transparency windows

The phenomenon of wave absorption by the atmosphere has been known for a long time. Scientists, having studied the phenomenon, concluded:

• Signal attenuation is determined by frequency.
• Windows of transparency are observed.
• The phenomenon is modulated by weather conditions.

For example, the millimeter wave range (30-100 GHz) is greatly suppressed by rain. The vicinity of the frequency 60 GHz absorbs oxygen molecules, 22 GHz - water. Frequencies below 1 GHz are cut off by galactic radiation. Temperature noise in the atmosphere has a negative impact.

This explains the choice of modern frequencies for space communications. A complete list of Ku-band signal characteristics is shown in the figure.

The C-band is also used.

Reception areas

The beam, crossing the surface of the globe, forms isotropic equivalent reception curves. Total losses are:

1. 200 dB – C-band.
2. 206 dB – Ku-band.

Solar interference can interfere with packet catching. The worst conditions lasting 5-6 days are created during the off-season (winter, autumn). The interference of the luminary provides ground station technicians with guaranteed work. During a natural phenomenon, tracking systems are turned off. Otherwise, the dishes may catch the Sun by giving incorrect commands to the onboard stabilization systems. Banks and airports receive a warning: communications will be temporarily disrupted.

Fresnel zones

Obstacles around the communication tower provoke the addition of waves, forming zones of attenuation/increase of the signal. The phenomenon explains the need for a clean space near the transceiver. Fortunately, microwaves do not have this disadvantage. Thanks to an important feature, every summer resident catches NTV+ with a plate.

Flicker

Unpredictable changes in the atmosphere cause the signal to constantly change. Fluctuations of up to 12 dB in amplitude affect a 500 MHz bandwidth. The phenomenon lasts 2-3 hours maximum. The scintillation interferes with ground stations' ability to track the satellite, requiring preventative measures to be taken.

Beam Linearity

A feature of microwaves is the rectilinear beam trajectory. The phenomenon makes it possible to concentrate power, lowering the requirements for on-board systems. Surely the initial task was espionage. Later, the antennas ceased to be narrowly focused, covering vast territories, such as Russia.

Engineers call this property a disadvantage: it is impossible to go around mountains and ravines.

Features of wave addition

There is practically no interference pattern. It is possible to significantly compress adjacent frequency channels.

Capacity

Kotelnikov's theorem determines the upper limit of the spectrum of the transmitted signal. The threshold is directly set by the carrier frequency. Microwaves, due to their high values, contain up to 30 times more information than VHF.

Possibility of regeneration

Development digital technologies paved the way for error correction techniques. Artificial satellite:

• received a weak signal;
• decoded;
• corrected errors;
• coded;
• passed it on.

The excellent quality of satellite communications has become the talk of the town.

Terrestrial antennas

Satellite dishes are called paraboloids. The diameter reaches 4 meters. In addition to the above, 2 types of relay communication antennas are available (both terrestrial):

1. Dielectric lenses.
2. Horn antennas.

Paraboloids provide high selectivity, allowing communication to be established by a beam that has traveled thousands of kilometers. A typical dish is unable to transmit a signal; higher performance is required.

Operating principle

Spy satellites were constantly moving, providing relative invulnerability and stealth surveillance. The use of peaceful technologies took a different path. Clark's concept implemented:

• The equatorial orbit is home to hundreds of geostationary satellites.
• The unshakable position ensures ease of guidance of ground equipment.
• The orbital altitude (35,786 meters) is fixed, since it is necessary to balance the force of centrifugal gravity.

The device covers part of the planet's territory.

The Intelsat system is made up of 19 satellites, grouped into four regions. The subscriber sees 2-4 at the same time.

The lifespan of the system is 10-15 years, then the obsolete equipment is replaced. The gravitational effects of the planets and the Sun reveal the need to use stabilization systems. The correction process significantly reduces the fuel life of the devices. The Intelsat complex allows position deviations of up to 3 degrees, extending the life of the orbital swarm (over three years).

Frequencies

The transparency window is limited to the 2-10 GHz range. Intelsat uses the 4-6 GHz region (C-band). The increase in load caused the transition of part of the traffic to the Ku-band (14, 11, 12 GHz). The work area is distributed in portions to transponders. The terrestrial signal is received, amplified, and radiated back.

Problems

1. Expensive start-up. Overcoming 35 thousand kilometers takes a lot of resources.
2. The signal propagation delay exceeds a quarter of a second (reaching 1 s).
3. The small angle of inclination of the line of sight of an artificial aircraft increases energy costs.
4. The reception area is not covered effectively. Gigantic spaces are devoid of subscribers. Broadcast efficiency is extremely low.
5. The transparency windows are narrow, ground stations have to be spread geographically and the polarization has to be changed.

Solutions

The disadvantages are partially eliminated by the introduction of an inclined orbit. The satellite ceases to be geostationary (see above the spy satellites of the Cold War). A minimum of three equidistant devices are required to ensure communication around the clock.

Polar orbit

The polar orbit alone is capable of covering the surface. However, several orbital periods of the spacecraft will be required. A swarm of satellites spaced around the corner can solve the problem. Polar orbits have bypassed commercial broadcasting, becoming a faithful assistant to the systems:

• navigation;
• meteorology;
• ground control stations.

Inclined orbit

Tilt was used successfully by Soviet satellites. The orbit is characterized by the following parameters:

• circulation period – 12 hours;
• tilt - 63 degrees.

Visible 8/12 hours, the three satellites provide communications to polar regions inaccessible from the equator.

Satellite phone

The mobile gadget directly catches space, bypassing ground towers. The first Inmarsat in 1982 provided access to sailors. Seven years later, a terrestrial species was created. Canada was the first to realize the benefits of equipping desert areas with sparse inhabitants. The program was followed by the USA.

The problem is solved by launching low-flying satellites:

1. The circulation period is 70..100 minutes.
2. Altitude 640..1120 km.
3. The coverage area is a circle with a radius of 2800 km.

Taking into account the physical parameters, the duration of an individual communication session covers the range of 4-15 minutes. Maintaining performance requires a certain amount of effort. A couple of US merchants went bankrupt in the 90s, unable to gain enough subscribers.

Weight and dimensions characteristics are continuously improving. Globalstar offers proprietary smartphone software that uses Bluetooth to pick up the signal from a relatively bulky satellite receiver.

Satellite phones require a powerful receiving antenna, preferably a fixed one. They equip mainly buildings and transport.

Operators

1. ACeS covers Asia with a single satellite.
2. Inmarsat is the oldest operator (1979). Equips yachts and ships. With 11 aircraft, the company is slowly expanding into the market. mobile devices, with the help of ACeS.
3. Thuraya serves Asia, Australia, Europe, Africa, Middle East.
4. MSAT/SkyTerra is an American provider using equipment equivalent to Inmarsat.
5. Terrestar covers North America.
6. IDO Global Communications is in the dormant stage.

Networks

Commercial projects are limited.

GlobalStar

GlobalStar is a joint brainchild of Qualcomm and Loral Corporation, later supported by Alcatel, Vodafone, Hyundai, AirTouch, Deutsche Aerospace. The launch of 12 satellites was disrupted; the first call took place on November 1, 1998. The initial cost (February 2000) was $1.79/min. Having undergone a series of bankruptcies and transformations, the company provides customers in 120 countries.

Provides 50% of US traffic (over 10,000 calls). Operation is supported by ground repeaters. There are 40 in total, including 7 that accommodate North America. Territories without terrestrial repeaters form a zone of silence (South Asia, Africa). Although the devices regularly plow the heavenly heights.

Subscribers receive American phone numbers, excluding Brazil, where the code is +8818.

List of services:

• Voice calls.
• Positioning systems with an error of 30 km.
• 9.6 kbit/s packet Internet access.
• Mobile communication CSD GSM.
• Roaming

The phones use Qualcomm CDMA technology, excluding Ericsson and Telit, which accept traditional SIM cards. Base stations are forced to support both standards.

Iridium

The provider uses a polar orbit, providing 100% coverage of the planet. The organizers went bankrupt, the company was revived in 2001.

This is interesting! Iridium is the culprit behind night sky flares. Flying satellites are clearly visible to the naked eye.

The company's fleet includes 66 satellites using 6 low-orbit trajectories at an altitude of 780 km. The devices communicate using the Ka-band. The lion's share was launched by former bankrupts. As of January 2017, 7 units were updated. Regeneration continues: the first group (10 pieces) flew away on January 14, the second on June 25, the third on October 9.

This is interesting! The Iridium 33 satellite rammed the Russian Kosmos 2251 on February 10, 2009. Celestial debris is flying over Siberia today.

The company continues to provide services to 850 thousand subscribers. 23% of profits were paid by the state. The cost of a call is 0.75 – 1.5 dollars/min. Callbacks are relatively expensive at $4/min (Google Voice). Typical areas of activity of employers:

1. Oil production.
2. Marine fleet.
3. Aviation.
4. Travelers.
5. Scientists.

The inhabitants of the Amundsen-Scott South Pole Station asked to convey special gratitude. The company everywhere sells call packages lasting 50-5000 minutes. The validity of the first ones leaves much to be desired, the expensive ones (5000 minutes = 4000 dollars) remain operational for 2 years. Monthly renewal – $45:

• 75 minutes cost $175, use period is 1 month.
• 500 minutes – 600-700 dollars, period of use – 1 year.

Phones

Former owners supplied customers with telephone sets from two manufacturers:

Motorola 9500 became the companion of the company's first commercial trial. The mobile shockproof version 9575, which is still in use today, was born in 2011, supplemented with a GSM emergency call button and an advanced location interface. The device sets up a Wi-Fi hotspot, allowing users of ordinary smartphones to send emails, SMS, visit the Internet.

Kyocera equipment has been abandoned by the manufacturer. Models are sold by resellers. KI-G100, based on a GSM phone with a frequency of 900 MHz, is equipped with a suitcase equipped with a powerful antenna that picks up broadcasts. The ability to receive SMS is ensured; only certain models (9522) can send messages. The SS-66K is equipped with an atypical ball antenna.

1. 9575 shockproof, a waterproof phone, equipped with a dustproof housing. Withstands temperatures from minus 20 to plus 50 degrees Celsius.
2. 9555 – equipped with a built-in headset, a USB interface, and an adapter for an RS-232 serial port.
3. 9505A is a hefty brick-shaped gadget. Equipped with a native RS-232 interface.
4. SS-55K released in limited edition. Incredible size, sold by eBay resellers.

The company's other equipment included:

1. Pagers.
2. Payphones.
3. Equipment for yachts and aircraft.

Buoys

Floating buoys, reminiscent of a tsunami tracking system, are capable of receiving/transmitting short messages. The interface will allow you to use the functionality of a branded phone that refuses to pick up satellites.

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, nothing radically different from what is usual for society mobile communications Satellite is no different, 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 regular phone, you just 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 provide communications to security forces, the navy (including the Russian fleet 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 connection for data transfer 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 communications 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 the full country code - +8816 265 and so on.

Amateur radio communications with the ISS and via AMSAT satellites

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