Just as the seats in a theater provide different perspectives on a performance, the different orbits of the satellites provide a perspective, each with a different purpose. Some appear to be hovering over a point on the surface, providing a constant view of one side of the Earth, while others circle our planet, sweeping over many places in a day.

Orbit types

At what altitude do satellites fly? There are 3 types of Earth orbits: high, medium and low. As a rule, many weather and some communication satellites are located on the high, the most distant from the surface. Satellites rotating in medium near-Earth orbit include navigation and special satellites designed to monitor a particular region. Most scientific spacecraft, including the NASA Earth Observation System fleet, are in low orbit.

The speed at which satellites fly depends on the speed of their movement. As we get closer to the Earth, gravity becomes stronger and the movement speeds up. For example, NASA's Aqua satellite takes about 99 minutes to fly around our planet at an altitude of about 705 km, while a meteorological apparatus 35,786 km from the surface takes 23 hours, 56 minutes and 4 seconds. At a distance of 384,403 km from the center of the Earth, the Moon completes one rotation in 28 days.

Aerodynamic paradox

Changing the height of a satellite also changes its orbital speed. There is a paradox here. If the operator of a satellite wants to increase its speed, he cannot simply start the engines to speed it up. This will increase the orbit (and height), resulting in a decrease in speed. Instead, you should start the engines in the opposite direction to the direction of the satellite, i.e., perform an action that, on Earth, would slow down a moving vehicle. This action will move it lower, which will increase the speed.

Orbit characteristics

In addition to altitude, the path of a satellite is characterized by eccentricity and inclination. The first relates to the shape of the orbit. A satellite with a low eccentricity moves along a trajectory close to circular. The eccentric orbit has the shape of an ellipse. The distance from the spacecraft to the Earth depends on its position.

The inclination is the angle of the orbit with respect to the equator. A satellite that orbits directly above the equator has zero inclination. If a spacecraft passes over the north and south poles (geographic, not magnetic), its tilt is 90°.

All together - height, eccentricity and inclination - determine the movement of the satellite and how the Earth will look from its point of view.

high near earth

When a satellite reaches exactly 42,164 km from the center of the Earth (about 36,000 km from the surface), it enters a zone where its orbit corresponds to the rotation of our planet. Since the vehicle is moving at the same speed as the Earth, i.e., its period of revolution is 24 hours, it seems to remain in place over a single longitude, although it may drift from north to south. This special high orbit is called geosynchronous.

The satellite moves in a circular orbit directly above the equator (eccentricity and inclination are zero) and stands still relative to the Earth. It is always located above the same point on its surface.

The Molniya orbit (inclination 63.4°) is used for observation at high latitudes. Geostationary satellites are tied to the equator, so they are not suitable for the far northern or southern regions. This orbit is quite eccentric: the spacecraft moves in an elongated ellipse with the Earth close to one edge. Since the satellite accelerates under the influence of gravity, it moves very quickly when it is close to our planet. When moving away, its speed slows down, so it spends more time at the top of the orbit in the farthest edge from the Earth, the distance to which can reach 40 thousand km. The orbital period is 12 hours, but the satellite spends about two-thirds of this time over one hemisphere. Like a semi-synchronous orbit, the satellite follows the same path every 24 hours. Used for communication in the far north or south.

Low Earth

Most scientific satellites, many meteorological and space stations are in a nearly circular low Earth orbit. Their slope depends on what they are monitoring. TRMM was launched to monitor rainfall in the tropics, so it has a relatively low inclination (35°) while staying close to the equator.

Many of NASA's surveillance satellites have a near-polar, highly inclined orbit. The spacecraft moves around the Earth from pole to pole with a period of 99 minutes. Half the time it passes over the day side of our planet, and at the pole it passes to the night side.

As the satellite moves, the Earth rotates underneath it. By the time the spacecraft moves to the illuminated area, it is above the area adjacent to the zone of passage of its last orbit. In a 24-hour period, polar satellites cover most of the Earth twice: once during the day and once at night.

Sun-synchronous orbit

Just as geosynchronous satellites must be above the equator, which allows them to stay above the same point, polar orbiting satellites have the ability to stay in the same time. Their orbit is sun-synchronous - when a spacecraft crosses the equator, the local solar time is always the same. For example, the Terra satellite crosses it over Brazil always at 10:30 am. The next crossing in 99 minutes over Ecuador or Colombia also occurs at 10:30 local time.

A sun-synchronous orbit is necessary for science, as it allows sunlight to be kept on the Earth's surface, although it will change with the season. This consistency means that scientists can compare images of our planet at the same time of the year over several years without worrying about too many jumps in lighting that can give the illusion of change. Without a sun-synchronous orbit, it would be difficult to track them over time and collect the information needed to study climate change.

The path of the satellite is very limited here. If it is at an altitude of 100 km, the orbit should have an inclination of 96°. Any deviation will be invalid. Because atmospheric drag and the gravitational pull of the Sun and Moon change the orbit of the spacecraft, it must be corrected regularly.

Orbital insertion: launch

The launch of a satellite requires energy, the amount of which depends on the location of the launch site, the height and inclination of the future trajectory of its movement. To get to a distant orbit, more energy is required. Satellites with a significant inclination (for example, polar ones) are more energy-consuming than those that circle the equator. The low-inclination orbit is assisted by the Earth's rotation. moves at an angle of 51.6397°. This is necessary to make it easier for space shuttles and Russian rockets to reach it. The height of the ISS is 337-430 km. Polar satellites, on the other hand, are not assisted by Earth's momentum, so they require more energy to travel the same distance.

Adjustment

After launching a satellite, efforts must be made to keep it in a certain orbit. Since the Earth is not a perfect sphere, its gravity is stronger in some places. This unevenness, along with the attraction of the Sun, Moon and Jupiter (the most massive planet in the solar system), changes the inclination of the orbit. Over the course of its lifetime, GOES satellites have been corrected three or four times. NASA's LEOs must adjust their inclination annually.

In addition, near-Earth satellites are affected by the atmosphere. The uppermost layers, although quite rarefied, offer strong enough resistance to pull them closer to the Earth. The action of gravity leads to the acceleration of the satellites. Over time, they burn up, spiraling lower and faster into the atmosphere, or fall to Earth.

Atmospheric drag is stronger when the Sun is active. Just as the air in a balloon expands and rises when it is heated, the atmosphere rises and expands when the Sun gives it extra energy. The rarefied layers of the atmosphere rise, and denser ones take their place. Therefore, satellites in Earth orbit must change their position about four times a year to compensate for atmospheric drag. When solar activity is maximum, the position of the device has to be adjusted every 2-3 weeks.

space junk

The third reason forcing to change the orbit is space debris. One of the Iridium communications satellites collided with a non-functioning Russian spacecraft. They crashed, forming a cloud of debris, consisting of more than 2500 parts. Each element has been added to the database, which today has over 18,000 man-made objects.

NASA carefully monitors everything that may be in the path of satellites, because space debris has already had to change orbits several times.

Engineers monitor the position of space debris and satellites that can interfere with movement and carefully plan evasive maneuvers as necessary. The same team plans and executes maneuvers to adjust the tilt and height of the satellite.

The Earth, like any cosmic body, has its own gravitational field and adjacent orbits, which can contain bodies and objects of various sizes. Most often, they mean the Moon and the International Space Station. The first goes in its own orbit, and the ISS - in low Earth orbit. There are several orbits that differ from each other in distance from the Earth, relative position relative to the planet and direction of rotation.

Orbits of artificial earth satellites

To date, in the nearest near-Earth space there are many objects that are the results of human activity. Basically, these are artificial satellites that serve to provide communications, but there is also a lot of space debris. One of the most famous artificial Earth satellites is the International Space Station.

AES move in three main orbits: equatorial (geostationary), polar and inclined. The first lies completely in the plane of the equatorial circle, the second is strictly perpendicular to it, and the third is located between them.

geosynchronous orbit

The name of this trajectory is due to the fact that the body moving along it has a speed equal to the sidereal period of the Earth's rotation. A geostationary orbit is a special case of a geosynchronous orbit that lies in the same plane as the earth's equator.

With an inclination not equal to zero and zero eccentricity, the satellite, when observed from the Earth, describes a figure eight in the sky during the day.

The first satellite in geosynchronous orbit is the American Syncom-2, launched into it in 1963. Today, in some cases, the placement of satellites in geosynchronous orbit is due to the fact that the launch vehicle cannot bring them to geostationary orbit.

geostationary orbit

This trajectory has such a name for the reason that, despite the constant movement, the object located on it remains static relative to the earth's surface. The place where the object is located is called the standing point.

Satellites launched into such an orbit are often used to transmit satellite television, because static allows you to point the antenna at it once and stay connected for a long time.

The altitude of satellites in geostationary orbit is 35,786 kilometers. Since they are all directly above the equator, only the meridian is named to indicate the position, for example, 180.0˚E Intelsat 18 or 172.0˚E Eutelsat 172A.

The approximate radius of the orbit is ~42,164 km, the length is about 265,000 km, and the orbital speed is about 3.07 km/s.

High elliptical orbit

A high elliptical orbit is a trajectory whose height at perigee is several times less than at apogee. Putting satellites into such orbits has a number of important advantages. For example, one such system may be sufficient to serve the whole of Russia or, accordingly, a group of states with an equal total area. In addition, HEO systems at high latitudes are more functional than geostationary satellites. And putting a satellite into a high elliptical orbit is about 1.8 times cheaper.

Large examples of systems operating on HEO:

• Space observatories launched by NASA and ESA.
• Satellite radio Sirius XM Radio.
• Satellite communications Meridian, -Z and -ZK, Molniya-1T.
• Satellite GPS correction system.

Low earth orbit

This is one of the lowest orbits, which, depending on various circumstances, can have an altitude of 160-2000 km and an orbital period of 88-127 minutes, respectively. The only time LEO was overcome by manned spacecraft was the Apollo program with the landing of American astronauts on the moon.

Most of the artificial earth satellites currently in use or ever used have operated in low earth orbit. For the same reason, the bulk of space debris is now located in this zone. The optimum orbital velocity for LEO satellites is, on average, 7.8 km/s.

Examples of artificial satellites in LEO:

• International Space Station (400 km).
• Telecommunication satellites of various systems and networks.
• Reconnaissance vehicles and probe satellites.

The abundance of space debris in orbit is the main modern problem of the entire space industry. Today the situation is such that the probability of collision of various objects in LEO is growing. And this, in turn, leads to destruction and the formation of even more fragments and details in orbit. Pessimistic forecasts say that the launched Domino Principle can completely deprive humanity of the opportunity to explore space.

Low reference orbit

It is customary to call the low reference orbit the orbit of the device, which provides for a change in inclination, height, or other significant changes. If the device does not have an engine and does not perform maneuvers, its orbit is called low Earth orbit.

Interestingly, Russian and American ballistics calculate its height differently, because the former are based on an elliptical model of the Earth, and the latter on a spherical one. Because of this, there is a difference not only in height, but also in the position of perigee and apogee.

"Man must rise above the Earth - into the atmosphere and beyond - for only in this way will he fully understand the world in which he lives."

Socrates made this observation centuries before humans successfully placed an object into Earth orbit. And yet, the ancient Greek philosopher seems to have realized how valuable a view from space can be, although he did not know at all how to achieve this.

This notion of how to get an object "into and out of the atmosphere" had to wait until Isaac Newton published his famous cannonball thought experiment in 1729. It looks something like this:

“Imagine that you placed a cannon on top of a mountain and fired it horizontally. The cannonball will travel parallel to the Earth's surface for a while, but will eventually succumb to gravity and fall back to Earth. Now imagine that you keep adding gunpowder to the cannon. With additional explosions, the core will travel further and further until it falls. Add the right amount of gunpowder and give the core the right acceleration, and it will constantly fly around the planet, always falling in a gravitational field, but never reaching the ground.

In October 1957, the Soviet Union finally confirmed Newton's hunch by launching Sputnik 1, the first artificial satellite to orbit the Earth. This initiated the space race and numerous launches of objects meant to fly around the Earth and other planets in the solar system. Since the launch of Sputnik, some countries, mostly the US, Russia and China, have launched more than 3,000 satellites into space. Some of these man-made objects, such as the ISS, are large. Others fit perfectly in a small chest. Thanks to satellites, we get weather forecasts, watch TV, surf the Internet and make phone calls. Even those satellites, whose work we do not feel and do not see, serve the military well.

Of course, the launch and operation of satellites has led to problems. Today, with over 1,000 active satellites in Earth orbit, our nearest space district is busier than a major city during rush hour. Add to that non-working equipment, abandoned satellites, pieces of hardware, and fragments from explosions or collisions that fill the skies along with useful equipment. This orbital debris, which we are talking about, has accumulated over the years and poses a serious threat to the satellites currently circling the Earth, as well as to future manned and unmanned launches.

In this article, we will crawl into the guts of an ordinary satellite and look into its eyes to see views of our planet that Socrates and Newton could not even dream of. But first, let's take a closer look at how, in fact, the satellite differs from other celestial objects.

is any object that moves in a curve around the planet. The Moon is a natural satellite of the Earth, and next to the Earth there are many satellites made by human hands, so to speak, artificial. The path followed by the satellite is an orbit, sometimes taking the form of a circle.

To understand why satellites move in this way, we must visit our friend Newton. He suggested that the force of gravity exists between any two objects in the universe. If this force did not exist, satellites flying near the planet would continue their movement at the same speed and in the same direction - in a straight line. This straight line is the inertial path of the satellite, which, however, is balanced by a strong gravitational attraction directed towards the center of the planet.

Sometimes a satellite's orbit looks like an ellipse, a flattened circle that goes around two points known as foci. In this case, all the same laws of motion work, except that the planets are located in one of the focuses. As a result, the net force applied to the satellite is not distributed uniformly throughout its path, and the speed of the satellite is constantly changing. It moves fast when it is closest to the planet - at the point of perigee (not to be confused with perihelion), and slower when it is farthest from the planet - at the point of apogee.

Satellites come in all shapes and sizes and perform a wide variety of tasks.

• Meteorological satellites help meteorologists to predict the weather or see what is happening with it at the moment. The Geostationary Operational Environmental Satellite (GOES) is a good example. These satellites usually include cameras that display the Earth's weather.
• Communications satellites allow telephone conversations to be relayed via satellite. The most important feature of a communications satellite is the transponder, a radio that receives a conversation on one frequency, then amplifies it and transmits it back to Earth on a different frequency. A satellite usually contains hundreds or thousands of transponders. Communications satellites are usually geosynchronous (more on that later).
• Television satellites transmit television signals from one point to another (similar to communication satellites).
• Scientific satellites, like the once Hubble Space Telescope, carry out all kinds of scientific missions. They watch everything from sunspots to gamma rays.
• Navigation satellites help aircraft fly and ships sail. GPS NAVSTAR and GLONASS satellites are prominent representatives.
• Rescue satellites respond to distress calls.
• Earth observation satellites are noticing changes, from temperature to ice caps. The most famous are the Landsat series.

Military satellites are also in orbit, but much of their operation remains a mystery. They can relay encrypted messages, monitor nuclear weapons, monitor enemy movements, warn of missile launches, listen to land radio, and carry out radar surveys and mapping.

When were satellites invented?

Perhaps Newton launched satellites in his fantasies, but before we actually accomplished this feat, a lot of time passed. One of the first visionaries was science fiction writer Arthur C. Clarke. In 1945, Clark suggested that a satellite could be placed in orbit in such a way that it would move in the same direction and at the same speed as the Earth. So-called geostationary satellites could be used for communications.

Scientists did not understand Clark - until October 4, 1957. Then the Soviet Union launched Sputnik 1, the first artificial satellite, into Earth's orbit. "Sputnik" was 58 centimeters in diameter, weighed 83 kilograms and was made in the shape of a ball. Although it was a remarkable achievement, the content of Sputnik was meager by today's standards:

• thermometer
• battery
• radio transmitter
• nitrogen gas that was pressurized inside the satellite

On the outside of the Sputnik, four whip antennas were transmitting at shortwave frequencies above and below the current standard (27 MHz). Tracking stations on Earth picked up a radio signal and confirmed that the tiny satellite had survived the launch and was successfully on 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, in a desperate attempt to keep up with their Cold War adversaries, American scientists attempted to put a satellite into orbit along with the planet Vanguard. Unfortunately, the rocket crashed and burned down at the takeoff stage. Shortly thereafter, on January 31, 1958, the US repeated the USSR's success by adopting Wernher von Braun's plan to launch the Explorer-1 satellite with the U.S. redstone. Explorer 1 carried the instruments to detect cosmic rays and found, 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 in the Earth's magnetic field.

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

The era of satellites has begun.

What's the difference between a satellite and space junk?

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

Man-made objects such as Sputnik and Explorer can also be classified as satellites, since they, like the moons, revolve around the planet. Unfortunately, human activity has led to the fact that a huge amount of garbage appeared in the Earth's orbit. All these pieces and debris behave like large rockets - revolve 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 as satellites those objects that perform a useful function. Fragments of metal and other trash fall into the category of orbital debris.

Orbital debris comes from many sources:

• The rocket explosion that produces the most junk.
• The astronaut relaxed his arm - if an astronaut is repairing something in space and misses a wrench, that wrench is lost forever. The key goes into orbit and flies at a speed of about 10 km/s. If it hits a person or a satellite, the results can 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 launched a special satellite called LDEF to study the long-term effects of space debris impacts. Over the course of 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 in Japan there is already a giant network for catching space debris.

What's inside an ordinary satellite?

Satellites come in all shapes and sizes and perform many different functions, but they are all basically the same. All of them have a metal or composite frame and a body that 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 arrays allow batteries to be charged. The latest 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 an onboard computer to control and monitor various systems. All have a radio and an antenna. At a minimum, most satellites have a radio transmitter and receiver so that 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 not an easy task. It takes years. It all starts with defining the purpose of the mission. Determining its parameters allows engineers to assemble the right tools and install them in the correct order. Once the specification (and budget) is approved, the assembly of the satellite begins. It takes place in a clean room, in a sterile environment that maintains the correct 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 that can be assembled to allow additional elements to be installed according to the 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 not from scratch, but from a blank.

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 launches directly upwards, which allows it to pass through the thick atmosphere faster and minimize fuel consumption. After the missile takes off, the missile's control mechanism uses the inertial guidance system to calculate the necessary adjustments to the missile's nozzle to achieve the desired tilt.

After the rocket enters the rarefied air, at a height of about 193 kilometers, the navigation system releases small rackets, which is enough to flip the rocket to a horizontal position. After that, 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 velocity is much greater than what a satellite needs in orbit. They do not escape the 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 blown into space. If the satellite moves too slowly, gravity will pull it back towards Earth.

The orbital speed of a satellite depends on its height 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 rotate at a speed of 11,300 kilometers per hour. This orbital speed allows the satellite to make one pass 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. The geostationary orbit is ideal for meteorological and communications satellites.

In general, the higher the orbit, the longer the satellite can stay in it. At low altitude, the satellite is in the earth's atmosphere, which creates resistance. At high altitude, there is practically no resistance, and a satellite, like the moon, can be in orbit for centuries.

Satellite types

On the ground, all satellites look the same - shiny boxes or cylinders adorned with solar panel wings. But in space, these clumsy machines behave very differently depending on the flight path, altitude and orientation. As a result, the classification of satellites becomes a complex matter. One approach is to determine the orbit of the vehicle relative to the planet (usually the Earth). Recall that there are two main orbits: circular and elliptical. Some satellites start in an ellipse and then go into a circular orbit. Others move in an elliptical path known as the "Lightning" orbit. These objects typically circle north-south across the Earth's poles and complete a full circle in 12 hours.

Polar-orbiting satellites also pass through 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 polar orbit. Since polar orbits give 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 in 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 move close to the Earth's surface are ideal for observational, military and weather information gathering purposes.
• Medium Earth Orbit (MEO) - These satellites fly from 2,000 to 36,000 km above the Earth. GPS navigation satellites work well at this altitude. The approximate orbital speed is 13,900 km/h.
• Geostationary (geosynchronous) orbit - geostationary satellites move around the Earth at an altitude exceeding 36,000 km and at the same rotational speed as the planet. Therefore, satellites in this orbit are always positioned to the same place on Earth. Many geostationary satellites fly along the equator, which has created a lot of "traffic jams" in this region of space. Several hundred television, communications and weather satellites use the geostationary orbit.

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

Known satellites

Until recently, satellites have remained exotic and top-secret devices used primarily for military purposes for navigation and espionage. Now they have become an integral part of our daily life. Thanks to them, we will know the weather forecast (although weather forecasters, oh, how often they are wrong). We watch TV and work with the Internet also thanks to satellites. GPS in our cars and smartphones allows us to get to the right place. 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 the orbit. Let's get to know them.

1. Landsat satellites have been photographing the Earth since the early 1970s, and in terms of observations of the Earth's surface, they are champions. Landsat-1, known at the 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 took 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 flew two Earth-observing sensors, Operational Land Imager and Thermal Infrared Sensor, collecting multispectral images of coastal regions, polar ice, islands and continents.
2. Geostationary Operational Environmental Satellites (GOES) circle the Earth in geostationary orbit, each responsible for a fixed part of the globe. This allows satellites to closely monitor the atmosphere and detect changes in weather patterns that can lead to tornadoes, hurricanes, floods and lightning storms. Satellites are also used to estimate the amount of precipitation and snow accumulation, measure the degree 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 GOES West and GOES East satellites are monitoring the weather at the same time.
3. Jason-1 and Jason-2 have played a key role in the long-term analysis of the Earth's oceans. NASA launched Jason-1 in December 2001 to replace the NASA/CNES Topex/Poseidon satellite that had been orbiting Earth since 1992. For nearly thirteen years, Jason-1 has 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 precision instruments to measure the distance from the satellite to the ocean surface with an accuracy of a few centimeters. These data, in addition to being valuable to oceanographers, provide an extensive look at the behavior of the world's climate patterns.

How much do satellites cost?

After Sputnik and Explorer, satellites have gotten bigger and more complex. Take, for example, TerreStar-1, a commercial satellite that was supposed to provide mobile data transmission in North America for smartphones and similar devices. Launched in 2009, TerreStar-1 weighed 6910 kilograms. And when fully deployed, it revealed an 18-meter antenna and massive solar arrays with a wingspan of 32 meters.

Building such a complex machine requires a lot of resources, so historically only government departments and corporations with deep pockets could get into 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. The spy satellite will cost $100 million more. Add to this the cost of maintaining and repairing satellites. Companies must pay for satellite bandwidth in the same way that phone owners pay for cellular communications. It sometimes costs more than 1.5 million dollars a year.

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

Despite the costs and risks involved in building, launching and operating satellites, some companies have managed to build entire businesses around it. For example, Boeing. In 2012, the company delivered about 10 satellites into space 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 US, for example, has spent almost $200 billion since the start of the military satellite program and now, despite all this, has a fleet of aging satellites waiting to be replaced. Many experts fear that the construction and deployment of large satellites simply cannot exist on taxpayer money. The solution that could turn everything upside down remains private companies like SpaceX and others that clearly won't be caught in bureaucratic stagnation like NASA, NRO and NOAA.

Another solution is to reduce the size and complexity of the satellites. Scientists at Caltech and Stanford University have been working since 1999 on a new type of CubeSat satellite, 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 workload. By standardizing designs 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 and three CubeSats based on commercial smartphones. The goal was to put the microsatellites into orbit for a short time and take some pictures with the phones. The agency now plans to deploy an extensive network of such satellites.

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

As you know, geostationary satellites hang motionless above the earth over the same point. Why don't they fall? Is there no gravity at that height?

Answer

A geostationary artificial Earth satellite is a device that moves around the planet in an easterly direction (in the same direction as the Earth itself rotates), along a circular equatorial orbit with a period of revolution equal to the period of the Earth's own rotation.

Thus, if we look from the Earth at a geostationary satellite, we will see it hanging motionless in the same place. Because of this immobility and the high altitude of about 36,000 km, from which almost half of the Earth's surface is visible, relay satellites for television, radio and communications are placed into geostationary orbit.

From the fact that a geostationary satellite constantly hangs over the same point on the Earth's surface, some people make the wrong conclusion that the force of attraction to the Earth does not act on the geostationary satellite, that the force of gravity disappears at a certain distance from the Earth, i.e. they refute the very Newton. Of course it is not. The very launch of satellites into geostationary orbit is calculated precisely according to Newton's law of universal gravitation.

Geostationary satellites, like all other satellites, actually fall to the Earth, but do not reach its surface. They are affected by the force of attraction to the Earth (gravitational force), directed towards its center, and in the opposite direction, the satellite is affected by the centrifugal force repelling from the Earth (inertia force), which balance each other - the satellite does not fly away from the Earth and does not fall on it exactly just like a bucket spinning on a rope remains in its orbit.

If the satellite did not move at all, then it would fall to the Earth under the influence of attraction to it, but satellites move, including geostationary ones (geostationary ones - with an angular velocity equal to the angular velocity of the Earth's rotation, i.e. one revolution per day, and for satellites of lower orbits, the angular velocity is greater, i.e., they have time to make several revolutions around the Earth in a day). The linear velocity reported to the satellite parallel to the Earth's surface during direct launch into orbit is relatively large (in low Earth orbit - 8 kilometers per second, in geostationary orbit - 3 kilometers per second). If there were no Earth, then the satellite would fly in a straight line at such a speed, but the presence of the Earth makes the satellite fall on it under the influence of gravity, bending the trajectory towards the Earth, but the surface of the Earth is not flat, it is curved. As far as the satellite approaches the surface of the Earth, so much the surface of the Earth goes from under the satellite and, thus, the satellite is constantly at the same height, moving along a closed trajectory. The satellite is falling all the time, but it can never fall.

So, all artificial satellites of the Earth fall to the Earth, but - along a closed trajectory. Satellites are in a state of weightlessness, like all falling bodies (if the elevator in a skyscraper breaks down and starts to fall freely, then the people inside will also be in a state of weightlessness). The astronauts inside the ISS are in weightlessness not because the force of attraction to the Earth does not act in orbit (it is almost the same there as on the surface of the Earth), but because the ISS falls freely to the Earth - along a closed circular trajectory.