How do satellites work?

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

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

This concept is about how to bring an object “toatmosphere and beyond ”- had to wait until Isaac Newton published his famous thought experiment with a cannonball in 1729. It looks something like this:

“Imagine you put a gun on topmountains and shot from it horizontally. The cannonball will travel parallel to the Earth’s surface for some time, but will eventually yield to gravity and fall to Earth. Now imagine that you continue to add gunpowder to the gun. With additional explosions, the core will travel farther and farther until it falls. Add the right amount of gunpowder and give the nucleus the correct acceleration, and it will constantly fly around the planet, always falling in the gravitational field, but never reaching the earth. ”

In October 1957, the Soviet Union finallyconfirmed Newton’s guess by launching Sputnik-1, the first artificial satellite in Earth’s orbit. This initiated a space race and numerous launches of objects that were intended to fly around the Earth and other planets of the solar system. Since the launch of Sputnik, some countries, most of the USA, Russia and China, have launched more than 3,000 satellites into space. Some of these human-made objects, such as the ISS, are large. Others fit perfectly in a small chest. Thanks to satellites, we receive weather forecasts, watch TV, surf the Internet and make phone calls. Even those satellites, whose work we do not feel and do not see, are perfectly in favor of the military.

Of course, the launch and operation of satellites ledto the problems. Today, given more than 1000 working satellites in Earth orbit, our nearest space region has become livelier than a large city at rush hour. Add to this non-working equipment, abandoned satellites, pieces of hardware and fragments from explosions or collisions that fill the sky with useful equipment. This orbital debris, which we wrote about in detail, has accumulated over the years and poses a serious threat to satellites currently circling around the Earth, as well as to future manned and unmanned launches.

In this article, we get into the gut of an ordinarysatellite and look into his eyes to see the views of our planet, which Socrates and Newton could not even dream of. But first, let's take a closer look at how, in fact, a satellite is different from other celestial objects.

Content

• 1 What is a satellite?
• 2 When were the satellites invented?
• 3 What is the difference between satellite and space debris?
• 4 What is inside an ordinary satellite?
• 5 How are satellites launched into orbit?
• 6 Orbital speed and altitude
• 7 Types of satellites
• 8 Famous Satellites
• 9 How much are the satellites?
• 10 The future of satellites

What is a satellite?

Satellite Is any object that moves along a curvearound 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 that a satellite follows is an orbit, sometimes taking the form of a circle.

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

Sometimes the satellite’s orbit looks like an ellipse,A flattened circle that runs around two points known as magic tricks. In this case, all the same laws of motion work, except that the planets are located in one of the tricks. As a result, the net force applied to the satellite does not pass evenly along its entire path, and the satellite’s speed 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 farther from the planet - at the point of apogee.

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

• Meteorological satellites help meteorologistsPredict the weather or see what is happening to her at the moment. The geostationary operational environmental satellite (GOES) provides a good example. These satellites typically include cameras that show the Earth’s weather.
• Communication satellites allow telephone callsRelay via satellite. The most important feature of a communication satellite is a transponder - a radio that receives a conversation at one frequency, and then amplifies it and transmits it back to Earth at a different frequency. A satellite usually contains hundreds or thousands of transponders. Communication satellites are usually geosynchronous (more on this later).
• Television satellites transmit television signals from one point to another (similar to communication satellites).
• Scientific satellites, like the Hubble Space Telescope, perform all kinds of scientific missions. They watch everything from sunspots to gamma rays.
• Navigation satellites help fly planes and sail ships. GPS NAVSTAR and GLONASS satellites are outstanding representatives.
• Rescue satellites respond to distress signals.
• Earth observation satellites note changes - from temperature to ice caps. The most famous are the Landsat series.

Military satellites are also in orbit, butmost of their work remains a mystery. They can relay encrypted messages, monitor nuclear weapons, enemy movements, warn about missile launches, listen to land radio, perform radar surveying and mapping.

When were the satellites invented?

Perhaps Newton in his fantasies startedsatellites, but before we actually accomplished this feat, a lot of time passed. One of the first visionaries was science fiction writer Arthur Clark. In 1945, Clark suggested that the satellite could be placed in orbit so 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, 1957of the year. Then the Soviet Union launched Sputnik-1, the first artificial satellite, into orbit of the Earth. The Sputnik was 58 centimeters in diameter, weighed 83 kilograms and was made in the shape of a ball. Although this was a remarkable achievement, the content of Sputnik was meager by today's standards:

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

On the outside of the "Sputnik" four pinantennas transmitted at a shortwave frequency above and below the current standard (27 MHz). Tracking stations on Earth caught the radio signal and confirmed that the tiny satellite survived the launch and successfully set off 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 upwith their adversaries in the Cold War, American scientists tried to launch a satellite into orbit with the planet Vanguard. Unfortunately, the rocket crashed and burned out at the take-off stage. Shortly afterwards, on January 31, 1958, the United States repeated the success of the USSR by adopting Werner von Braun’s plan, which was to launch the Explorer-1 satellite with the U.S. Redstone Explorer-1 carried tools for detecting cosmic rays and discovered during an experiment by James Van Allen from the University of Iowa that cosmic rays are much smaller than expected. This led to the discovery of two toroidal zones (ultimately named after Van Allen) filled with charged particles captured by the Earth's magnetic field.

Encouraged by these successes, some companiesbegan to develop and launch satellites in the 60s. One of them was Hughes Aircraft with star engineer Harold Rosen. Rosen led the team that embodied Clark’s idea - 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 signed a contract with Hughes to build a series of Syncom satellites (synchronous communications). In July 1963, Rosen and his colleagues saw how Syncom-2 took off into space and entered a rough geosynchronous orbit. President Kennedy used the new system to speak with the Prime Minister of Nigeria in Africa. Soon, Syncom-3 also took off, which in fact could broadcast a television signal.

The age of the satellites has begun.

What is the difference between satellite and space debris?

Technically, a satellite is any object thatrevolves around 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 still continue to find new moons.

Man-made objects, like Sputnik and Explorer,can also be classified as satellites, since they, like the moons, revolve around the planet. Unfortunately, human activity has led to a huge amount of garbage in the Earth’s orbit. All these pieces and debris behave like large rockets - they revolve around the planet at high speed in a circular or elliptical way. 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. Debris and other rubbish fall into the category of orbital debris.

Orbital debris comes from many sources:

• The rocket explosion that produces the most trash.
• The astronaut relaxed his hand - if the astronautrepairs something in space and misses a wrench, that one 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 can be disastrous. Large objects, like the ISS, are a big target for space debris.
• Discarded items. Parts of launch containers, caps of camera lenses and so on.

NASA has launched a special satellite calledLDEF for studying the long-term effects of a collision with space debris. Over six years, satellite instruments recorded about 20,000 collisions, some of which were caused by micrometeorites, and others by orbital debris. NASA scientists continue to analyze LDEF data. But in Japan they are already planning to deploy a giant network for catching space debris.

What's inside a regular satellite?

Satellites come in different shapes and sizes andperform many different functions, but all, in principle, are similar. They all have a metal or composite frame and a body, which English-speaking engineers call the bus, and the Russians - the space platform. The space platform brings everything together and provides enough measures for the tools to survive the launch.

All satellites have a power source (usuallysolar panels) and batteries. Arrays of solar panels allow you to charge batteries. Newer satellites include fuel cells. Satellite energy is very expensive and extremely limited. Nuclear batteries are commonly used to send space probes to other planets.

All satellites have an on-board computer forcontrol and monitoring of various systems. Everyone has a radio and antenna. At a minimum, most satellites have a radio transmitter and a radio receiver, so the crew of the ground crew can request information about the status of the satellite and observe it. Many satellites allow a lot of different things: from changing the orbit to reprogramming a computer system.

As expected, assemble all of these systemsputting it together is not an easy task. It takes years. It all starts with determining the purpose of the mission. Determining its parameters allows engineers to assemble the necessary tools and install them in the correct order. Once the specification is approved (and budget), satellite assembly begins. It takes place in a clean room, in a sterile environment, which allows you to maintain the desired temperature and humidity and protect the satellite during development and assembly.

Artificial satellites are usually producedto order. Some companies have developed modular satellites, that is, designs, the assembly of which allows the installation of additional elements according to the specification. For example, the Boeing 601 satellites had two basic modules - a chassis for transporting the engine subsystem, electronics and batteries; and a set of cell shelves for equipment storage. This modularity allows engineers to assemble satellites not from scratch, but from the workpiece.

How are satellites launched into orbit?

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

On most satellite launches, rocket launchesgoing straight up, this allows you to quickly pass it through a thick layer of the atmosphere and minimize fuel consumption. After the rocket takes off, the rocket control mechanism uses an inertial guidance system to calculate the necessary adjustments to the rocket nozzle to provide the desired tilt.

After the rocket goes sparseair, at a height of about 193 kilometers, the navigation system produces small rackets, which is enough to flip the rocket to a horizontal position. After that, a satellite is released. Small rockets are launched again and provide a difference in the distance between the rocket and the satellite.

Orbital speed and altitude

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

The satellite's orbital speed depends on itsheights 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 the orbit at an altitude of 35,786 kilometers, the satellite must circulate at a speed of 11,300 kilometers per hour. This orbital speed allows the satellite to make one flyby in 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 surface of the Earth. This position is called geostationary. The geostationary orbit is ideal for meteorological and communications satellites.

In general, the higher the orbit, the longer the satellitecan stay on 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.

Types of satellites

On earth, all the satellites look like - shinyboxes or cylinders decorated with wings from solar panels. But in space, these clumsy machines behave very differently depending on the flight path, altitude and orientation. As a result, the classification of satellites is turning into a complicated matter. One approach is to determine the orbit of an apparatus relative to a planet (usually Earth). Recall that there are two main orbits: circular and elliptical. Some satellites start in an ellipse, and then enter a circular orbit. Others move along an elliptical path known as the Lightning orbit. These objects, as a rule, circle from north to south through the poles of the Earth and complete a complete flyby in 12 hours.

Polar orbiting satellites also pass throughpoles 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 beneath a satellite in polar orbit. Since polar orbits provide excellent planet coverage, they are used for mapping and photography. Forecasters also rely on a global network of polar satellites that fly around 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 (DOE) - DOE Satellitesoccupy an area of ​​space from 180 to 2000 kilometers above the Earth. Satellites that move close to the Earth’s surface are ideal for observing, for military purposes, and for collecting weather information.
• Middle Earth Orbit (COO) - these satellites fly from 2,000 to 36,000 km above the Earth. GPS navigation satellites work well at this altitude. Approximate orbital speed - 13 900 km / h.
• Geostationary (geosynchronous) orbit -geostationary satellites move around the earth at an altitude exceeding 36,000 km and at the same rotation speed as the planet. Therefore, the satellites in this orbit are always positioned to the same place on Earth. Many geostationary satellites fly around the equator, which has created many “traffic jams” in this region of space. Several hundred television, communication and weather satellites use geostationary orbit.

And finally, you can think about satellites in thatsense where they are "looking." Most of the objects sent into space over the past few decades, look at the Earth. These satellites have cameras and equipment that can see our world at different wavelengths of light, which allows you to enjoy the breathtaking sight in the ultraviolet and infrared colors of our planet. Fewer satellites turn their eyes to a space where they observe stars, planets and galaxies, and also scan objects like asteroids and comets that can collide with the Earth.

Famous satellites

Until recently, satellites remainedexotic and top-secret devices that were used mainly for military purposes for navigation and espionage. Now they have become an integral part of our daily lives. Thanks to them, we will find out the weather forecast (although weather forecasters oh how often wrong). We watch TV and work with the Internet also thanks to satellites. GPS in our cars and smartphones allows you 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.

Landsat satellites take pictures of the earth from the beginning1970s, and in terms of observations of the Earth’s surface, they are champions. Landsat-1, known at one time as ERTS (Earth Resources Technology Satellite) was launched on July 23, 1972. He carried two main tools: a camera and a multispectral scanner, created by the Hughes Aircraft Company and capable of recording data in green, red and two infrared spectra. The satellite made such gorgeous images and was considered so successful that a whole series followed. NASA launched the last Landsat-8 in February 2013. Two sensors monitoring the Earth flew on this device, Operational Land Imager and Thermal Infrared Sensor, collecting multispectral images of coastal regions, polar ice, islands and continents.

Geostationary operational environmentalsatellites (GOES) circling above the Earth in a geostationary orbit, each responsible for a fixed part of the globe. This allows satellites to closely monitor the atmosphere and detect changes in weather conditions that can lead to tornadoes, hurricanes, floods and thunderstorms. Satellites are also used to estimate the amount of precipitation and accumulation of snow, measure the extent of snow cover and track the movements of sea and lake ice. Since 1974, 15 GOES satellites have been put into orbit, but only two GOES “West” and GOES “East” satellites are monitoring the weather.

Jason-1 and Jason-2 played a key role inlong-term analysis of the Earth's oceans. NASA launched Jason-1 in December 2001 to replace the NASA / CNES Topex / Poseidon satellite, which has been working on Earth since 1992. For nearly thirteen years, Jason-1 has been measuring sea level, wind speed, and wave height of more than 95% of the ice-free earth's oceans. NASA officially retired Jason-1 on July 3, 2013. In 2008, Jason-2 entered orbit. He carried high-precision instruments to measure the distance from a satellite to the surface of the ocean with an accuracy of several centimeters. These data, in addition to value for oceanologists, provide an extensive look at the behavior of global climate patterns.

How much are the satellites?

After Satellite and Explorer, satellites becamebigger and harder. Take TerreStar-1, for example, a commercial satellite that was supposed to provide mobile data transmission in North America for smartphones and similar devices. Launched in 2009, the TerreStar-1 weighed 6910 kilograms. And being fully deployed, he revealed an 18-meter antenna and massive solar panels with a wingspan of 32 meters.

Building such a complex machine requires massresources, so historically only government departments and corporations with deep pockets could enter the satellite business. Most of the cost of the satellite lies in the equipment - transponders, computers and cameras. An ordinary meteorological satellite costs about $ 290 million. 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. Sometimes it costs more than $ 1.5 million a year.

Another important factor is the launch cost. The launch of 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 could launch a low-orbit 18,000-kilogram satellite for $ 165 million.

Despite the costs and risks associated withBy building, launching and operating satellites, some companies have managed to build a whole business on this. For example, Boeing. In 2012, the company delivered about 10 satellites into space and received orders for more than seven years, which brought it almost $ 32 billion in revenue.

The future of satellites

Almost fifty years after launchSputnik, satellites, like budgets, are growing and gaining ground. The United States, for example, has spent nearly $ 200 billion since the start of the military satellite program, and now, despite all this, it has a fleet of aging vehicles waiting to be replaced. Many experts fear that the construction and deployment of large satellites simply cannot exist with taxpayer money. Private companies like SpaceX, Virgin Galactic, and others that are clearly not in the bureaucratic stagnation of NASA, NRO, and NOAA are left with a solution that can turn everything upside down.

Another solution is to reduce size and complexity.satellites. Since 1999, scientists from Caltech and Stanford University have been working on a new type of CubeSat satellite, which is based on building blocks with a facet of 10 centimeters. Each cube contains prefabricated components and can combine with other cubes to increase efficiency and reduce load. By standardizing the design and reducing the cost of creating each satellite from scratch, one CubeSat can cost as little as $ 100,000.

In April 2013, NASA decided to test thisa simple principle and launched three CubeSat-based commercial smartphones. The goal was to bring microsatellites into orbit for a short time and take a few shots on phones. Now the agency plans to deploy an extensive network of such satellites.

Being big or small, companions of the futureshould be able to communicate effectively with ground stations. Historically, NASA has relied on radio frequency communications, but RF has reached its limit as demand for greater power has arisen. To overcome this obstacle, 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.