Why are artificial earth satellites needed? Types of artificial satellites

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In our VK group (vk.com/posterspbru) one of the users left the following playfully sarcastic comment:

- Monya, where are you looking?

- To the stars. You won’t believe it, there are 8000 satellites there!

- So, did it become easier to breathe?

He gave us the idea for this article.

Perhaps Monya’s friend is right - in the literal sense of the word, satellites do not help people breathe. Although this is a controversial issue, because satellites can save people from situations in which people could suffocate. Probably many of us rarely think about how much our companions influence our lives.

These are some of the applications that satellites provide us.

1. Satellites send television signals into homes, but they are also the basis for cable and network TV. In other words, no satellites - no news, no broadcasts of sports matches, no Olympics in live and so on. Satellites transmit signals from central station, which generates programs for smaller stations that transmit signals locally. All direct broadcasts are possible thanks to satellites.

2. Satellites provide telephone communications on airplanes and are often the only telephone connection for many rural regions and areas where telephone lines damaged as a result of natural disasters. Satellites also provide the primary timing source for cell phones and pagers. In 1998, a satellite failure demonstrated this dependence - 80% of pagers in the United States were temporarily silenced, National Public Radio was unable to distribute its broadcasts to affiliates and transmitted only through its website, and the CBS Evening News video was frozen and broadcast only audio.

3. Satellite navigation systems allow any user to navigate the terrain. GPS navigators are part of the modern world, whether used in private cars or for commercial or military purposes for navigation on land, sea or in the air. And by the way, GPS navigation plays a decisive role in many situations, for example, when a ship is heading towards a harbor in bad weather.

4. Satellites connect companies with suppliers, are the basis for international video conferences, provide instant credit card authorization and banking operations. Without a satellite in orbit, you will not be able to pay for goods in a hypermarket with your bank card.

5. Satellites provide meteorologists with weather data, with which they monitor not only whether it will be cloudy or sunny today, but also volcanic eruptions, hurricanes, gas leaks, and the like. Returning to the question about Monet and his friend, in some cases, satellites will help a person breathe, simply because they will warn him that a cloud of toxic gases is moving towards the place where he is. Or a satellite can rescue him at sea or on land by transmitting a beacon signal to rescue services.

Satellites are one of the main sources of data for climate change research. Satellites monitor ocean temperatures and currents. They can indicate air pollution, help organize rescue operations in disaster areas, help locate people in remote regions, transmit distress signals, etc.

6. The satellites can detect underground water and mineral springs, monitor the transfer of nutrients and pollutants from the ground to water sources, measure the temperature of land and water, measure the growth of algae in the seas and the erosion of topsoil on land. They can effectively monitor large-scale infrastructure, such as fuel pipelines, which need to be checked for leaks using satellites rather than manual labor (which would take many hours). Satellite imagery helps various industries and even you can benefit Google Earth thanks to satellites.

Satellites are of great importance to developing countries as they provide their populations in remote regions with access to data, educational information, medical information, etc. A person can receive the correct treatment only because his doctor has consulted with a more experienced colleague.

7. Space research is impossible without satellites. Telescope satellites play a critical role in understanding many cosmic phenomena.

Man-made satellites orbiting the Earth greatly influence our modern lives, although many do not realize it. To some extent, satellites help us breathe freely by providing us with data, timely assistance, and opportunities. Satellites make life safer, provide many modern conveniences, and also help broadcast entertainment and study the Earth and space.

On the outside of Sputnik there are four whip antennas transmitted on shortwave frequencies above and below the current standard (27 MHz). Tracking stations on Earth picked up the radio signal and confirmed that the tiny satellite survived the launch and was successfully on a course around our planet. A month later, the Soviet Union launched Sputnik 2 into orbit. Inside the capsule was the dog Laika.

In December 1957, desperate to keep pace with their Cold War adversaries, American scientists attempted to place a satellite into orbit with the planet Vanguard. Unfortunately, the rocket crashed and burned during takeoff. Shortly thereafter, on January 31, 1958, the United States repeated the Soviet success by adopting Wernher von Braun's plan to launch the Explorer 1 satellite with a U.S. rocket. Redstone. Explorer 1 carried instruments to detect cosmic rays and discovered in an experiment by James Van Allen of the University of Iowa that there were far fewer cosmic rays than expected. This led to the discovery of two toroidal zones (eventually named after Van Allen) filled with charged particles trapped magnetic field Earth.

Encouraged by these successes, several companies began developing and launching satellites in the 1960s. One of them was Hughes Aircraft, along with star engineer Harold Rosen. Rosen led the team that implemented Clark's idea - a communications satellite placed in Earth's orbit in such a way that it could bounce radio waves from one place to another. In 1961, NASA awarded a contract to Hughes to build the Syncom (synchronous communications) series of satellites. In July 1963, Rosen and his colleagues saw Syncom-2 blast off into space and enter a rough geosynchronous orbit. President Kennedy used new system to speak with the Prime Minister of Nigeria in Africa. Soon Syncom-3 also took off, which could actually broadcast a television signal.

The era of satellites has begun.

What is the difference between a satellite and space debris?

Technically, a satellite is any object that orbits a planet or smaller celestial body. Astronomers classify moons as natural satellites, and over the years they have compiled a list of hundreds of such objects orbiting planets and dwarf planets in our solar system. For example, they counted 67 moons of Jupiter. And still is.

Man-made objects like Sputnik and Explorer can also be classified as satellites because they, like moons, orbit a planet. Unfortunately, human activity has led to the fact that there is a great amount garbage. All these pieces and debris behave like large rockets - rotating around the planet at high speed in a circular or elliptical path. In a strict interpretation of the definition, each such object can be defined as a satellite. But astronomers, as a rule, consider satellites those objects that perform useful function. Scraps of metal and other junk fall into the category of orbital debris.

Orbital debris comes from many sources:

A rocket explosion that produces the most junk.
The astronaut relaxed his hand - if an astronaut is repairing something in space and misses a wrench, it is lost forever. The key goes into orbit and flies at a speed of about 10 km/s. If it hits a person or satellite, the results could be catastrophic. Large objects like the ISS are a big target for space debris.
Discarded items. Parts of launch containers, camera lens caps, and so on.

NASA has launched a special satellite called LDEF to study the long-term effects of collisions with space debris. Over six years, the satellite's instruments recorded about 20,000 impacts, some caused by micrometeorites and others by orbital debris. NASA scientists continue to analyze LDEF data. But Japan already has a giant net for catching space debris.

What's inside a regular satellite?

Satellites come in different shapes and sizes and perform many various functions, however, they are all basically similar. All of them have a metal or composite frame and body, which English-speaking engineers call a bus, and Russians call a space platform. The space platform brings everything together and provides enough measures to ensure that the instruments survive the launch.

All satellites have a power source (usually solar panels) and batteries. Solar panel arrays allow batteries to be charged. The newest satellites also include fuel cells. Satellite energy is very expensive and extremely limited. Nuclear power cells are commonly used to send space probes to other planets.

All satellites have on-board computer for control and monitoring various systems. Everyone has a radio and an antenna. At a minimum, most satellites have a radio transmitter and a radio receiver so the ground crew can query and monitor the satellite's status. Many satellites allow a lot of different things, from changing the orbit to reprogramming the computer system.

As you might expect, putting all these systems together is no easy task. It takes years. It all starts with defining the mission goal. Determining its parameters allows engineers to assemble necessary tools and install them in the correct order. Once the specifications (and budget) are approved, satellite assembly begins. It takes place in a clean room, a sterile environment that maintains the desired temperature and humidity and protects the satellite during development and assembly.

Artificial satellites are usually made to order. Some companies have developed modular satellites, that is, structures whose assembly allows the installation additional elements according to specification. For example, the Boeing 601 satellites had two basic modules - a chassis for transporting the propulsion subsystem, electronics and batteries; and a set of honeycomb shelves for equipment storage. This modularity allows engineers to assemble satellites from blanks rather than from scratch.

How are satellites launched into orbit?

Today, all satellites are launched into orbit on a rocket. Many transport them in the cargo department.

In most satellite launches, the rocket is launched straight up, which allows it to move faster through the thick atmosphere and minimize fuel consumption. After the rocket takes off, the rocket's control mechanism uses the inertial guidance system to calculate the necessary adjustments to the rocket's nozzle to achieve the desired pitch.

After the rocket enters the thin air, at an altitude of about 193 kilometers, the navigation system releases small rockets, which is enough to flip the rocket into horizontal position. After this, the satellite is released. Small rockets are fired again and provide a difference in distance between the rocket and the satellite.

Orbital speed and altitude

The rocket must reach a speed of 40,320 kilometers per hour to completely escape Earth's gravity and fly into space. Space speed is much greater than what a satellite needs in orbit. They do not escape earth's gravity, but are in a state of balance. Orbital speed is the speed required to maintain a balance between the gravitational pull and the inertial motion of the satellite. This is approximately 27,359 kilometers per hour at an altitude of 242 kilometers. Without gravity, inertia would carry the satellite into space. Even with gravity, if a satellite moves too fast, it will be carried into space. If the satellite moves too slowly, gravity will pull it back toward Earth.

The orbital speed of a satellite depends on its altitude above the Earth. The closer to Earth, the faster the speed. At an altitude of 200 kilometers, the orbital speed is 27,400 kilometers per hour. To maintain an orbit at an altitude of 35,786 kilometers, the satellite must travel at a speed of 11,300 kilometers per hour. This orbital speed allows the satellite to make one flyby every 24 hours. Since the Earth also rotates 24 hours, the satellite at an altitude of 35,786 kilometers is in a fixed position relative to the Earth's surface. This position is called geostationary. Geostationary orbit is ideal for weather and communications satellites.

In general, the higher the orbit, the longer the satellite can remain there. At low altitude, the satellite is in the earth's atmosphere, which creates drag. At high altitude there is virtually no resistance, and the satellite, like the moon, can remain in orbit for centuries.

Types of satellites

On earth, all satellites look similar - shiny boxes or cylinders decorated with wings made of solar panels. But in space, these lumbering machines behave very differently depending on their flight path, altitude and orientation. As a result, satellite classification becomes a complex matter. One approach is to determine the craft's orbit relative to a planet (usually the Earth). Recall that there are two main orbits: circular and elliptical. Some satellites start out in an ellipse and then enter a circular orbit. Others follow an elliptical path known as a Molniya orbit. These objects typically circle from north to south across the Earth's poles and complete a full flyby in 12 hours.

Polar-orbiting satellites also pass the poles with each revolution, although their orbits are less elliptical. Polar orbits remain fixed in space while the Earth rotates. As a result, most of the Earth passes under the satellite in a polar orbit. Because polar orbits provide excellent coverage of the planet, they are used for mapping and photography. Forecasters also rely on a global network of polar satellites that circle our globe every 12 hours.

You can also classify satellites by their height above the earth's surface. Based on this scheme, there are three categories:

Low Earth Orbit (LEO) - LEO satellites occupy a region of space from 180 to 2000 kilometers above the Earth. Satellites that orbit close to the Earth's surface are ideal for observation, military purposes and collecting weather information.
Medium Earth Orbit (MEO) - These satellites fly from 2,000 to 36,000 km above the Earth. Navigation devices work well at this altitude. GPS satellites. Approximate orbital speed is 13,900 km/h.
Geostationary (geosynchronous) orbit - geostationary satellites orbit the Earth at an altitude exceeding 36,000 km and at the same rotation speed as the planet. Therefore, satellites in this orbit are always positioned towards the same place on Earth. Many geostationary satellites fly along the equator, which has created many traffic jams in this region of space. Several hundred television, communications and weather satellites use geostationary orbit.

Finally, one can think of satellites in the sense of where they "search." Most of the objects sent into space over the past few decades are looking at Earth. These satellites have cameras and equipment that can see our world in different wavelengths of light, allowing us to enjoy spectacular views of our planet's ultraviolet and infrared tones. Fewer satellites are turning their gaze to space, where they observe stars, planets and galaxies, and scan for objects like asteroids and comets that could collide with Earth.

Known satellites

Until recently, satellites remained exotic and top-secret instruments, used primarily for military purposes for navigation and espionage. Now they have become an integral part of our Everyday life. Thanks to them, we know the weather forecast (although weather forecasters are so often wrong). We watch TV and access the Internet also thanks to satellites. GPS in our cars and smartphones helps us get to where we need to go. Is it worth talking about the invaluable contribution of the Hubble telescope and the work of astronauts on the ISS?

However, there are real heroes of orbit. Let's get to know them.

Landsat satellites have been photographing the Earth since the early 1970s, and they hold the record for observing the Earth's surface. Landsat-1, known at one time as ERTS (Earth Resources Technology Satellite), was launched on July 23, 1972. It carried two main instruments: a camera and a multispectral scanner, built by the Hughes Aircraft Company and capable of recording data in green, red and two infrared spectra. The satellite produced such gorgeous images and was considered so successful that a whole series followed it. NASA launched the last Landsat-8 in February 2013. This vehicle carried two Earth-observing sensors, the Operational Land Imager and the Thermal Infrared Sensor, collecting multispectral images of coastal regions, polar ice, islands and continents.
Geostationary Operational Environmental Satellites (GOES) circle the Earth in geostationary orbit, each responsible for a fixed portion of the globe. This allows satellites to closely observe the atmosphere and detect changes weather conditions which can lead to tornadoes, hurricanes, flooding and lightning storms. Satellites are also used to estimate precipitation and snow accumulation, measure the extent of snow cover, and track the movement of sea and lake ice. Since 1974, 15 GOES satellites have been launched into orbit, but only two satellites, GOES West and GOES East, monitor the weather at any one time.
Jason-1 and Jason-2 played a key role in the long-term analysis of Earth's oceans. NASA launched Jason-1 in December 2001 to replace the NASA/CNES Topex/Poseidon satellite, which had been operating above Earth since 1992. For nearly thirteen years, Jason-1 measured sea levels, wind speeds, and wave heights in more than 95% of Earth's ice-free oceans. NASA officially retired Jason-1 on July 3, 2013. Jason-2 entered orbit in 2008. It carried high-precision instruments that made it possible to measure the distance from the satellite to the ocean surface with an accuracy of several centimeters. These data, in addition to their value to oceanographers, provide extensive insight into the behavior of global climate patterns.

How much do satellites cost?

After Sputnik and Explorer, satellites became larger and more complex. Take TerreStar-1, for example, a commercial satellite that would provide mobile data service in North America for smartphones and similar devices. Launched in 2009, TerreStar-1 weighed 6,910 kilograms. And when fully deployed, it revealed an 18-meter antenna and massive solar panels with a wingspan of 32 meters.

Building such a complex machine requires a ton of resources, so historically only government agencies and corporations with deep pockets could enter the satellite business. Most of the cost of a satellite lies in the equipment - transponders, computers and cameras. A typical weather satellite costs about $290 million. A spy satellite would cost $100 million more. Add to this the cost of maintaining and repairing satellites. Companies must pay for satellite bandwidth the same way phone owners pay for cellular communication. This sometimes costs more than $1.5 million a year.

To others important factor is the startup cost. Launching one satellite into space can cost from 10 to 400 million dollars, depending on the device. The Pegasus XL rocket can lift 443 kilograms into low Earth orbit for $13.5 million. Launching a heavy satellite will require more lift. The Ariane 5G rocket can launch an 18,000-kilogram satellite into low orbit for $165 million.

Despite the costs and risks associated with building, launching and operating satellites, some companies have managed to build entire businesses around it. For example, Boeing. The company delivered about 10 satellites into space in 2012 and received orders for more than seven years, generating nearly $32 billion in revenue.

The future of satellites

Almost fifty years after the launch of Sputnik, satellites, like budgets, are growing and getting stronger. The United States, for example, has spent almost $200 billion since the start of the war. satellite program and now, despite all this, it has a fleet of aging devices waiting to be replaced. Many experts fear that building and deploying large satellites simply cannot exist on taxpayer dollars. The solution that could turn everything upside down remains private companies like SpaceX and others that clearly will not suffer bureaucratic stagnation, like NASA, NRO and NOAA.

Another solution is to reduce the size and complexity of satellites. Scientists at Caltech and Stanford University have been working since 1999 on a new type of CubeSat, which is based on building blocks with a 10-centimeter edge. Each cube contains ready-made components and can be combined with other cubes to increase efficiency and reduce stress. By standardizing design and reducing the cost of building each satellite from scratch, a single CubeSat can cost as little as $100,000.

In April 2013, NASA decided to test this simple principle with three CubeSats powered by commercial smartphones. The goal was to put the microsatellites into orbit for a short time and take a few pictures with their phones. The agency now plans to deploy an extensive network of such satellites.

Whether large or small, future satellites must be able to communicate effectively with ground stations. Historically, NASA relied on radio frequency communications, but RF reached its limit as demand for more power emerged. To overcome this obstacle, NASA scientists are developing a two-way communication system using lasers instead of radio waves. On October 18, 2013, scientists first fired a laser beam to transmit data from the Moon to Earth (at a distance of 384,633 kilometers) and achieved a record transmission speed of 622 megabits per second.

Modern human life is already unthinkable without artificial earth satellites, since with their help we monitor the weather and make its forecast, satellites provide people with communications over long distances, with the help of satellites people conduct unique and various studies in space, which is basically impossible to do on Earth . But the life history of the satellite is not yet 60 years old. The first artificial Earth satellite was launched in the USSR on October 4, 1957, exactly 56 years ago. On this moment There are a huge number of different satellites flying around our planet in different orbits, performing various jobs. So what kind of satellites serve humans?

Satellites providing communications are probably the most popular type of satellite operation and, so to speak, the most obvious, because at high altitudes the signals received and emitted by the satellite can be received at points on earth located at a considerable distance from each other. With the help of communications satellites, we watch TV shows, talk on the phone, and access the Internet.

Satellites that provide navigation on earth. Surely, many have heard about GPS navigation, with the help of which a person can determine the location of certain objects with great accuracy. This is exactly the job that satellite navigators do. Using GPS navigators built into Cell phones, PDAs and car computers, anyone can determine their location and plot routes taking into account road signs, search for the houses and streets they need on the map, etc.

The next most popular satellite is a weather satellite, which monitors changes in Earth's weather and studies the climate of our planet. It is thanks to weather satellites that weather forecasters make their weather forecasts.

Of course, the military could not miss such a great opportunity to spy on each other from space. As they say, I sit high and look far away. Spy satellites can take photographs of objects on Earth high definition, listen to communication systems, carry out surveillance, etc.

Satellites are also indispensable assistants for scientists in their scientific research. Research satellites study the Earth's magnetic field and radiation conditions; they are used by surveyors, cartographers and other specialists. A particular type of research satellites are biosatellites, on which scientists conduct their experiments and solve various problems. technical problems astronautics, etc.

And of course, in their research, satellites are used by astronomers who can observe distant galaxies and other space objects from space, while the earth’s atmosphere does not distort the signals received from space. One of the most famous astronomical satellites is the famous Hubble Telescope.

Telecommunications satellites are typically placed in geostationary orbit (GEO). which is a circular orbit with an altitude of 35,786 kilometers above the Earth's equator and follows the direction of Earth's rotation. An object in GEO has an orbital period equal to its rotation period, so to observers on the ground it appears stationary and occupies a fixed position in the sky.

Satellites in GEO allow constant communication , transmitting radio frequency signals from fixed antennas. These signals are not very different from those used in terrestrial broadcast television transmissions and are typically 3 to 50 times higher in frequency. The signal received by the satellite is amplified and transmitted back to Earth, allowing communication between points located thousands of kilometers apart.

A special property that makes geostationary satellites extremely attractive is their ability to transmit information. The relayed signal can be received by antennas anywhere within the satellite's coverage area, comparable to the size of a country, region, continent or even an entire hemisphere. Anyone who has a small antenna 40-50 cm in diameter can become a direct user of the satellite.

A satellite operating in geostationary orbit does not need any engine and its stay in Earth orbit can last for many years. Friction from the thin upper atmosphere will eventually slow it down and cause it to sink lower and eventually burn up in the lower atmosphere.

If a satellite is launched with more fuel, it moves faster and its orbital radius is larger. A large orbit means that the satellite's angular motion around the Earth is slower. As an example, the Moon, located 380,000 km from Earth, has an orbital period of 28 days.

Low-Earth orbit (LEO) satellites such as , many science and observation satellites operate at much lower altitudes: they orbit the Earth in approximately 90 minutes at altitudes of several hundred kilometers.

Telecommunications satellites can also be on LEO, being visible from any location for 10-20 minutes. To guarantee the continuity of information transmission in this case, the deployment of dozens of satellites will be necessary.

LEO telecommunications systems may require 48, 66, 77, 80 or even 288 satellites to provide the required services. Several of these systems have been deployed to provide communications for mobile terminals. They use relatively low frequencies (1.5-2.5 GHz), which are in the same range as the frequencies used in mobile networks with GSM. The fact that for of this type satellites do not require any expensive transmitting and receiving devices - a plus for them: no careful tracking of the satellite is necessary in this case. In addition, low altitude minimizes signal travel time delay and requires less transmitter power to establish communications.

An Earth satellite is any object that moves along a curved path around a planet. The Moon is the original, natural satellite of the Earth, and there are many artificial satellites, usually in close orbit to the Earth. The path followed by a satellite is an orbit, which sometimes takes the shape of a circle.

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To understand why satellites move the way they do, we have to go back to our friend Newton. exists between any two objects in the Universe. If not for this force, a satellite moving near the planet would continue to move at the same speed and in the same direction - in a straight line. However, this rectilinear inertial path of the satellite is balanced by a strong gravitational attraction directed towards the center of the planet.

Orbits of artificial earth satellites

Sometimes the orbit of an artificial Earth satellite looks like an ellipse, a squashed circle that moves around two points known as foci. The same basic laws of motion apply, except that the planet is at one of the foci. As a result, the net force applied to the satellite is not uniform throughout the orbit, and the satellite's speed is constantly changing. It moves fastest when it is closest to Earth - a point known as perigee - and slowest when it is furthest from Earth - a point known as apogee.

There are many different satellite orbits of the Earth. The ones that receive the most attention are geostationary orbits because they are stationary over a specific point on the Earth.

The orbit chosen for an artificial satellite depends on its application. For example, live broadcast television uses the geostationary orbit. Many communications satellites also use geostationary orbit. Other satellite systems, such as satellite phones, can use low-Earth orbits.

Likewise, satellite systems used for navigation, such as Navstar or Global Positioning (GPS), occupy a relatively low Earth orbit. There are also many other types of satellites. From weather satellites to research satellites. Each will have its own orbit type depending on its application.

The actual Earth satellite orbit chosen will depend on factors including its function, and the area in which it is to serve. In some cases, the Earth satellite's orbit can be as large as 100 miles (160 km) for a LEO low earth orbit, while others can reach over 22,000 miles (36,000 km) as in the case of a GEO low earth orbit.

The first artificial earth satellite

The first artificial earth satellite was launched on October 4, 1957 by the Soviet Union and was the first artificial satellite in history.

Sputnik 1 was the first of several satellites launched by the Soviet Union in the Sputnik program, most of which were successful. Satellite 2 followed the second satellite in orbit and also the first to carry an animal on board, a female dog named Laika. Sputnik 3 suffered the first failure.

The first earth satellite had an approximate mass of 83 kg, had two radio transmitters (20.007 and 40.002 MHz) and orbited the Earth at a distance of 938 km from its apogee and 214 km at its perigee. Analysis of radio signals was used to obtain information about the concentration of electrons in the ionosphere. Temperature and pressure were encoded over the duration of the radio signals it emitted, indicating that the satellite was not perforated by a meteorite.

The first earth satellite was an aluminum sphere with a diameter of 58 cm, having four long and thin antennas ranging from 2.4 to 2.9 m in length. The antennas looked like long mustaches. The spacecraft received information about the density of the upper atmosphere and the propagation of radio waves in the ionosphere. Instruments and sources electrical energy were housed in a capsule that also included radio transmitters operating at 20.007 and 40.002 MHz (about 15 and 7.5 m wavelength), the emissions were made in alternate groups of 0.3 s duration. Ground telemetry included temperature data inside and on the surface of the sphere.

Because the sphere was filled with pressurized nitrogen, Sputnik 1 had its first opportunity to detect meteorites, although it did not. The loss of pressure inside, due to penetration to the outer surface, was reflected in the temperature data.

Types of artificial satellites

There are artificial satellites different types, shapes, sizes and play different roles.

Weather satellites help meteorologists predict the weather or see what is currently happening. A good example is the Geostationary Operational Environmental Satellite (GOES). These earth satellites typically contain cameras that can return photographs of Earth's weather, either from fixed geostationary positions or from polar orbits.
Communications satellites allow the transmission of telephone and information conversations via satellite. Typical communications satellites include Telstar and Intelsat. The most important feature of a communications satellite is the transponder, a radio receiver that picks up a conversation on one frequency and then amplifies it and retransmits it back to Earth on a different frequency. A satellite typically contains hundreds or thousands of transponders. Communications satellites are usually geosynchronous.
Broadcast satellites transmit television signals from one point to another (similar to communication satellites).
Scientific satellites, such as the Hubble Space Telescope, carry out all kinds of scientific missions. They look at everything from sunspots to gamma rays.
Navigation satellites help ships and planes navigate. The most famous are the GPS NAVSTAR satellites.
Rescue satellites respond to radio interference signals.
Earth observation satellites checking the planet for changes in everything from temperature, forest cover, to ice cover. The most famous are the Landsat series.
Military satellites The Earths are in orbit, but much of the actual position information remains secret. Satellites could include encrypted communications relay, nuclear monitoring, surveillance of enemy movements, early warning of missile launches, eavesdropping on terrestrial radio links, radar imaging, and photography (using essentially large telescopes that photograph militarily interesting areas).

Earth from an artificial satellite in real time

Images of the earth from an artificial satellite, broadcast in real time by NASA from the International Space Station. Images are captured by four cameras high resolution, insulated from freezing temperatures, allowing us to feel closer to space than ever before.

The experiment (HDEV) on board the ISS was activated on April 30, 2014. It is mounted on the external cargo mechanism of the European Space Agency's Columbus module. This experiment involves several high-definition video cameras that are enclosed in a housing.

Advice; put the player in HD and Full Screen. There are times when the screen will be black, this can be for two reasons: the station is passing through an orbital zone where it is at night, the orbit lasts approximately 90 minutes. Or the screen goes dark when the cameras change.

How many satellites are there in Earth orbit 2018?

According to the index of objects launched into outer space maintained by the United Nations Office for Space Affairs outer space(UNOOSA), there are currently about 4,256 satellites in Earth's orbit, up 4.39% from last year.

221 satellites were launched in 2015, the second most in a single year, although it is below the record number of 240 launched in 2014. The increase in the number of satellites orbiting the Earth is less than the number launched last year because satellites have a limited lifespan. Large communications satellites last 15 years or more, while small satellites such as CubeSats can only expect a service life of 3-6 months.

How many of these Earth orbiting satellites are operational?

The Union of Scientists (UCS) is clarifying which of these orbiting satellites are working, and it's not as much as you think! There are currently only 1,419 operational Earth satellites—only about one-third of the total number in orbit. This means there is a lot of useless metal around the planet! That's why there's a lot of interest from companies looking to capture and return space debris, using methods such as space networks, slingshots or solar sails.

What are all these satellites doing?

According to UCS, the main objectives of operational satellites are:

Communications - 713 satellites
Earth observation/science - 374 satellites
Technology demonstration/development using 160 satellites
Navigation & GPS - 105 satellites
Space science - 67 satellites

It should be noted that some satellites have multiple purposes.

Who owns the Earth's satellites?

It is interesting to note that there are four main types of users in the UCS database, although 17% of satellites are owned by multiple users.

94 satellites registered by civilians: they are generally educational institutions, although there are other national organizations. 46% of these satellites have the purpose of developing technologies such as Earth and space science. Observations account for another 43%.
579 belong to commercial users: commercial organizations and government organizations that want to sell the data they collect. 84% of these satellites are focused on communication services and global positioning; of the remaining 12% are Earth observation satellites.
401 satellites are owned by government users: mainly national space organizations, but also other national and international bodies. 40% of them are communications and global positioning satellites; another 38% is focused on Earth observation. Of the remainder, the development of space science and technology accounts for 12% and 10%, respectively.
345 satellites belong to the military: again the focus here is communications, Earth observation and global positioning systems, with 89% of the satellites having one of these three purposes.

How many satellites do countries have?

According to UNOOSA, about 65 countries have launched satellites, although the UCS database only has 57 countries recorded using satellites, and some satellites are listed with joint/multinational operators. The biggest:

USA with 576 satellites
China with 181 satellites
Russia with 140 satellites
The UK is listed as having 41 satellites, plus participates in an additional 36 satellites operated by the European Space Agency.

Remember when you look!
Next time you look at the night sky, remember that between you and the stars there are about two million kilograms of metal surrounding the Earth!