Spacecraft in all their diversity are both the pride and concern of humanity. Their creation was preceded by a centuries-old history of the development of science and technology. The space age, which allowed people to look at the world in which they live from the outside, has taken us to a new level of development. A rocket in space today is not a dream, but a matter of concern for highly qualified specialists who are faced with the task of improving existing technologies. What types of spacecraft are distinguished and how they differ from each other will be discussed in the article.
Definition
Spacecraft is a general name for any device designed to operate in space. There are several options for their classification. In the simplest case, spacecraft are divided into manned and automatic. The former, in turn, are divided into spaceships and stations. Different in their capabilities and purpose, they are similar in many respects in structure and equipment used.
Flight Features
After launch, any spacecraft goes through three main stages: insertion into orbit, flight itself and landing. The first stage involves the device developing the speed necessary to enter outer space. In order to get into orbit, its value must be 7.9 km/s. Complete overcoming of gravity involves the development of a second equal to 11.2 km/s. This is exactly how a rocket moves in space when its target is remote areas of the Universe.
After liberation from attraction, the second stage follows. During an orbital flight, the movement of spacecraft occurs by inertia, due to the acceleration given to them. Finally, the landing stage involves reducing the speed of the ship, satellite or station to almost zero.
"Filling"
Each spacecraft is equipped with equipment that matches the tasks it is designed to solve. However, the main discrepancy is related to the so-called target equipment, which is necessary precisely for obtaining data and various scientific research. Otherwise, the equipment of the spacecraft is similar. It includes the following systems:
- energy supply - most often solar or radioisotope batteries, chemical batteries, and nuclear reactors supply spacecraft with the necessary energy;
- communication - carried out using a radio wave signal; at a significant distance from the Earth, accurate pointing of the antenna becomes especially important;
- life support - the system is typical for manned spacecraft, thanks to it it becomes possible for people to stay on board;
- orientation - like any other ships, space ships are equipped with equipment to constantly determine their own position in space;
- movement - spacecraft engines allow changes in flight speed, as well as in its direction.
Classification
One of the main criteria for dividing spacecraft into types is the operating mode that determines their capabilities. Based on this feature, devices are distinguished:
- located in a geocentric orbit, or artificial earth satellites;
- those whose purpose is to study remote areas of space - automatic interplanetary stations;
- used to deliver people or necessary cargo into the orbit of our planet, they are called spaceships, can be automatic or manned;
- created for people to stay in space for a long period - this is;
- engaged in the delivery of people and cargo from orbit to the surface of the planet, they are called descent;
- those capable of exploring the planet, directly located on its surface, and moving around it are planetary rovers.
Let's take a closer look at some types.
AES (artificial earth satellites)
The first devices launched into space were artificial Earth satellites. Physics and its laws make launching any such device into orbit a difficult task. Any device must overcome the gravity of the planet and then not fall on it. To do this, the satellite needs to move at or slightly faster. Above our planet, a conditional lower limit of the possible location of an artificial satellite is identified (passes at an altitude of 300 km). A closer placement will lead to a fairly rapid deceleration of the device in atmospheric conditions.
Initially, only launch vehicles could deliver artificial Earth satellites into orbit. Physics, however, does not stand still, and today new methods are being developed. Thus, one of the methods often used recently is launching from another satellite. There are plans to use other options.
The orbits of spacecraft revolving around the Earth can lie at different altitudes. Naturally, the time required for one lap also depends on this. Satellites, whose orbital period is equal to a day, are placed on the so-called It is considered the most valuable, since the devices located on it appear motionless to an earthly observer, which means there is no need to create mechanisms for rotating antennas.
AMS (automatic interplanetary stations)
Scientists obtain a huge amount of information about various objects of the Solar System using spacecraft sent beyond the geocentric orbit. AMS objects are planets, asteroids, comets, and even galaxies accessible for observation. The tasks posed to such devices require enormous knowledge and effort from engineers and researchers. AWS missions represent the embodiment of technological progress and are at the same time its stimulus.
Manned spacecraft
Devices created to deliver people to their intended destination and return them back are in no way inferior in technological terms to the described types. The Vostok-1, on which Yuri Gagarin made his flight, belongs to this type.
The most difficult task for the creators of a manned spacecraft is ensuring the safety of the crew during the return to Earth. Also an important part of such devices is the emergency rescue system, which may be necessary when the ship is launched into space using a launch vehicle.
Spacecraft, like all astronautics, are constantly being improved. Recently, the media have often seen reports about the activities of the Rosetta probe and the Philae lander. They embody all the latest achievements in the field of space shipbuilding, calculation of vehicle motion, and so on. The landing of the Philae probe on the comet is considered an event comparable to Gagarin's flight. The most interesting thing is that this is not the crown of humanity’s capabilities. New discoveries and achievements still await us in terms of both space exploration and the structure
From early childhood, when a person looks at the starry sky and the Moon, he wonders how space, stars, planets, the galaxy, and the universe work. We are attracted by everything unknown and incomprehensible. Soviet scientists managed to lift the curtain on the mystery of space under the leadership of the brilliant design engineer Sergei Pavlovich Korolev, under whose leadership they launched the first artificial Earth satellite (abbreviated as AES).
First start
It was the USSR that, on October 4, 1957, was the first to launch the simplest earth satellite, or PS-1, into outer space on an R-7 launch vehicle from the Baikonur Cosmodrome. The creative team of the satellite’s creators was headed by Sergei Korolev.
Sergei Korolev and Yuri Gagarin
The technical characteristics of the first artificial earth satellite are quite primitive compared to satellites that are launched in our time.
PS-1 was a ball with a diameter of approximately 58 cm, to which four antennas 2.4 and 2.9 meters long were attached; they were needed to receive radio reception. The mass of PS-1 was 83.6 kg. Inside the satellite there were pressure and temperature sensors, fans turned on by relays, which began to work if the temperature rose above +30C, switching the device that transmitted the signal from the satellite to Earth.
PS-1 separated from the launch vehicle 295 seconds after launch, and already 315 seconds after launch, it sent the first radio signal to the ground that any radio amateur could receive; these were signals repeated for about 2 minutes: “Beep, Beep.” These signals shocked the whole world, the era of cosmonautics and the arms race between the USSR and the USA began.
PS-1 stayed in the elliptical orbit of the Earth for 92 days and completed 1440 revolutions around the planet; it continued to transmit a radio signal for 20 days. After which the rotation speed of PS-1 began to decrease, and on January 4, 1957, it burned up in the dense layers of the atmosphere due to high friction.
Space technology
Nowadays, approximately 13 thousand artificial Earth satellites already roam the expanses of the universe, most of them belong to the USA, Russia, and China. The technology for launching satellites is to give it as high a speed as possible when launching. Once in the elliptical orbit of the earth, the satellite will be able to rotate and transmit signals for a long time due to the acquired speed, without turning on the engines.
For the modern world, artificial satellites are an integral part of our world; communication satellites, navigation satellites, meteorological satellites, reconnaissance satellites, biosatellites and many other artificial satellites help us in everyday life.
We forecast the weather, plot new routes, use cellular communications, satellite television, wireless Internet, draw maps and register land plots linked to a satellite, and all this thanks to artificial earth satellites.
Space exploration
There are many interesting facts about artificial satellites of the Earth, but unmanned spacecraft are also exploring other planets. So, in addition to the satellites that make our daily lives easier, humanity does not stand still and currently there are artificial satellites of the Moon, Mars, the Sun, and Venus.
The artificial satellite of the Moon was first launched by scientists of the USSR; this satellite transmitted photographs of the surface of the moon, with the help of which scientists were convinced of its specific shape, learned its structure and the characteristics of gravity.
Artificial satellite of Mars: at the same time, three satellites began to study this planet, two Soviet and one American.
All these satellites had different tasks, some photographed the surface of the planet, others studied the temperature, relief, streamlining of the planet, the presence of water, but it is worth noting that the first artificial satellite that made a soft landing on the surface of this planet was the Soviet satellite Mars-3.
The first artificial satellite near the Sun appeared when there was absolutely no intention of launching it there. A NASA satellite that was supposed to explore the lunar surface flew past the orbit of the moon and stopped in the orbit of the sun. Russia also has its own artificial satellite of the sun, which studies salt activity and transmits geomagnetic flares and fluctuations.
Exploration of Phobos, the moon of Mars
Artificial satellites of Venus. The Soviet Union was the first to send artificial satellites in 1975, with the help of which they obtained high-quality images of the surface of this planet.
October 4, 1957 is a memorable date for all humanity; on this day the Russian Federation celebrates the Day of the Russian Space Forces, and the whole world celebrates the launch of the first earth satellite.
In astronomy and space flight dynamics, the concepts of three cosmic velocities are used. First cosmic speed (circular velocity) is the lowest initial speed that must be imparted to a body in order for it to become an artificial satellite of the planet; for the surfaces of the Earth, Mars and the Moon, the first escape velocities correspond to approximately 7.9 km/s, 3.6 km/s and 1.7 km/s.
Second escape velocity(parabolic speed) is the minimum initial speed that must be imparted to a body so that it, having started moving at the surface of the planet, overcomes its gravity; for the Earth, Mars and the Moon, the second escape velocities are respectively approximately 11.2 km/s, 5 km/s and 2.4 km/s.
Third cosmic speed is called the lowest initial speed, possessing which a body overcomes the gravity of the Earth, the Sun and leaves the Solar system; equal to approximately 16.7 km/s.
Artificial satellites, essentially, are all flying spacecraft launched into orbit around the Earth, including spacecraft and orbital stations with crews. However, it is customary to classify artificial satellites as mainly automatic satellites that are not intended to be operated by a human cosmonaut. This is due to the fact that manned spacecraft differ significantly in their design features from automatic satellites. Thus, spaceships must have life support systems, special compartments - descent vehicles in which astronauts return to Earth. For automatic satellites, this kind of equipment is not necessary or completely unnecessary.
The dimensions, weight, and equipment of satellites depend on the tasks that the satellites solve. The world's first Soviet satellite had a mass of 83.6 kg, the body was in the form of a ball with a diameter of 0.58 m. The mass of the smallest satellite was 700 g.
AES are launched into orbit using stepped launch vehicles, which lift them to a certain height above the Earth's surface and accelerate them to a speed equal to or exceeding (but not more than 1.4 times) the first cosmic speed. AES launches using their own launch vehicles are carried out by Russia, the USA, France, Japan, China and the UK. A number of satellites are launched into orbit as part of international cooperation. Such are, for example, the Intercosmos satellites.
Movement of artificial satellites The Earth is not described by Kepler's laws, which is due to two reasons:
1) The Earth is not exactly a sphere with a uniform density distribution over its volume. Therefore, its gravitational field is not equivalent to the gravitational field of a point mass located at the geometric center of the Earth; 2) The Earth's atmosphere has a braking effect on the movement of artificial satellites, as a result of which their orbit changes its shape and size and, as a result, the satellites fall to the Earth.
Based on the deviation of the satellites’ motion from the Keplerian one, one can draw a conclusion about the shape of the Earth, the distribution of density over its volume, and the structure of the Earth’s atmosphere. Therefore, it was the study of the movement of artificial satellites that made it possible to obtain the most complete data on these issues.
If the Earth were a homogeneous ball and there was no atmosphere, then the satellite would move in orbit, the plane maintaining a constant orientation in space relative to the system of fixed stars. The orbital elements in this case are determined by Kepler's laws. Since the Earth rotates, with each subsequent revolution the satellite moves over different points on the earth's surface. Knowing the satellite's path for one revolution, it is not difficult to predict its position at all subsequent times. To do this, it is necessary to take into account that the Earth rotates from west to east at an angular speed of approximately 15 degrees per hour. Therefore, on the next revolution, the satellite crosses the same latitude to the west by as many degrees as the Earth turns to the east during the period of rotation of the satellite.
Due to the resistance of the earth's atmosphere, satellites cannot move for a long time at altitudes below 160 km. The minimum period of revolution at such an altitude in a circular orbit is approximately 88 minutes, that is, approximately 1.5 hours. During this time, the Earth rotates by 22.5 degrees. At a latitude of 50 degrees, this angle corresponds to a distance of 1400 km. Therefore, we can say that a satellite with an orbital period of 1.5 hours at a latitude of 50 degrees will be observed with each subsequent revolution of approximately 1400 km. further west than the previous one.
However, such a calculation provides sufficient prediction accuracy for only a few satellite revolutions. If we are talking about a significant period of time, then we must take into account the difference between a sidereal day and 24 hours. Since the Earth makes one revolution around the Sun in 365 days, in one day the Earth around the Sun describes an angle of approximately 1 degree in the same direction in which it rotates around its axis. Therefore, in 24 hours the Earth rotates relative to the fixed stars not by 360 degrees, but by 361 and, therefore, makes one revolution not in 24 hours, but in 23 hours 56 minutes. Therefore, the satellite’s latitude path shifts westward not by 15 degrees per hour, but by 15.041 degrees.
The circular orbit of a satellite in the equatorial plane, moving along which it is always above the same point of the equator, is called geostationary. Almost half of the earth's surface can be connected to a satellite in synchronous orbit by linearly propagating high-frequency signals or light signals. Therefore, satellites in synchronous orbits are of great importance for the communication system.
AES can be classified according to various criteria. The basic principle of classification is based on the launch goals and tasks solved with the help of satellites. In addition, satellites differ in the orbits into which they are launched, the types of some on-board equipment, etc.
According to the goals and objectives, satellites are divided into two large groups – scientific research And applied. Scientific research satellites are designed to obtain new scientific information about the Earth and near-Earth space, to conduct astronomical research in the field of biology and medicine and other fields of science.
Applied satellites are designed to solve practical human needs, obtain information in the interests of the national economy, conduct technical experiments, as well as test and test new equipment.
Scientific research Satellites solve a wide variety of problems in the study of the Earth, the Earth's atmosphere and near-Earth space, and celestial bodies. With the help of these satellites, important and major discoveries were made, the Earth's radiation belts, the Earth's magnetosphere, and the solar wind were discovered. Interesting research is being carried out with the help of specialized biological satellites: the influence of outer space on the development and condition of animals, higher plants, microorganisms, and cells is being studied.
Are becoming increasingly important astronomical AES. The equipment installed on these satellites is located outside the dense layers of the earth's atmosphere and makes it possible to study radiation from celestial objects in the ultraviolet, x-ray, infrared and gamma spectral ranges.
Satellitescommunications serve to transmit television programs, messages on the Internet, provide radio - telephone, cellular, telegraph and other types of communications between ground points located at large distances from each other.
Meteorological Satellites regularly transmit images of the Earth's cloud, snow and ice covers to ground stations; information about the temperature of the earth's surface and various layers of the atmosphere. This data is used to clarify the weather forecast and provide timely warnings about impending hurricanes, storms, and typhoons.
Gained great importance specialized satellites for studying natural resources Earth. The equipment of such satellites transmits information important for various sectors of the national economy. It can be used to predict agricultural yields, identify areas promising for the search for minerals, to identify forest areas infested with pests, and to control environmental pollution.
Navigational AES quickly and accurately determine the coordinates of any ground object and provide invaluable assistance in orientation on land, on water and in the air.
Military satellites can be used for space reconnaissance, to guide missiles, or serve as weapons themselves.
Manned ships - satellites and manned orbital stations are the most complex and advanced satellites. They are, as a rule, designed to solve a wide range of problems, primarily for conducting complex scientific research, testing space technology, studying the Earth's natural resources, etc. The first launch of a manned satellite was carried out on April 12, 1961 on the Soviet spacecraft - satellite " Vostok", pilot-cosmonaut Yu.A. Gagarin flew around the Earth in an orbit with an apogee altitude of 327 km. On February 20, 1962, the first American spacecraft entered orbit with astronaut J. Genn on board.
On October 4, 1957, the world's first artificial Earth satellite was launched into low-Earth orbit. Thus began the space age in human history. Since then, artificial satellites have been regularly helping to study the cosmic bodies of our galaxy.
Artificial Earth satellites (AES)
In 1957, the USSR was the first to launch a satellite into low-Earth orbit. The United States was the second to do this, a year later. Later, many countries launched their satellites into Earth orbit - however, satellites purchased from the USSR, USA or China were often used for this. Nowadays satellites are launched even by radio amateurs. However, many satellites have important tasks: astronomical satellites explore the galaxy and space objects, biosatellites help conduct scientific experiments on living organisms in space, meteorological satellites help predict the weather and observe the Earth's climate, and the tasks of navigation and communication satellites are clear from their names. Satellites can be in orbit from several hours to several years: for example, manned spacecraft can become a short-term artificial satellite, and a space station can become a long-term spacecraft in Earth orbit. In total, more than 5,800 satellites have been launched since 1957, 3,100 of them are still in space, but of these three thousand, only about one thousand are operational.
Artificial lunar satellites (ALS)
At one time, ISLs were very helpful in studying the Moon: when entering its orbit, satellites photographed the lunar surface in high resolution and sent pictures to Earth. In addition, by changing the trajectory of the satellites, it was possible to draw conclusions about the gravitational field of the Moon, the features of its shape and internal structure. Here the Soviet Union was again ahead of everyone: in 1966, the Soviet automatic station Luna-10 was the first to enter lunar orbit. And over the next three years, 5 more Soviet satellites of the Luna series and 5 American satellites of the Lunar Orbiter series were launched.
Artificial satellites of the Sun
It is curious that until the 1970s, artificial satellites appeared near the Sun... by mistake. The first such satellite was Luna 1, which missed the Moon and entered the orbit of the Sun. And this despite the fact that switching to a heliocentric orbit is not so simple: the device must reach the second cosmic speed without exceeding the third. And when approaching planets, the device can slow down and become a satellite of the planet, or speed up and completely leave the solar system. But NASA satellites orbiting the Sun near the Earth’s orbit began to take detailed measurements of the solar wind parameters. The Japanese satellite observed the Sun in X-rays for about ten years - until 2001. Russia launched a solar satellite in 2009: Coronas-Photon will study the most dynamic solar processes and monitor solar activity around the clock to predict geomagnetic disturbances.
Artificial satellites of Mars (ISM)
The first artificial satellites of Mars were... three ISMs at once. Two space probes were launched by the USSR (“Mars-2” and “Mars-3”) and another by the USA (“Mariner-9”). But the point is not that the launch was a “race” and there was such an overlap: each of these satellites had its own task. All three ISMs were launched into significantly different elliptical orbits and performed different scientific research, complementing each other. Mariner 9 produced a map of the surface of Mars for mapping, and Soviet satellites studied the characteristics of the planet: the flow of solar wind around Mars, the ionosphere and atmosphere, topography, temperature distribution, the amount of water vapor in the atmosphere and other data. In addition, Mars 3 was the first in the world to make a soft landing on the surface of Mars.
Artificial Satellites of Venus (ASV)
The first WIS were again Soviet spacecraft. Venera 9 and Venera 10 entered orbit in 1975. Having reached the planet. They were divided into satellites and devices lowered to the planet. Thanks to WIS radar, scientists were able to obtain radio images with a high degree of detail, and the devices that softly descended to the surface of Venus took the world's first photographs of the surface of another planet... The third satellite was the American Pioneer Venera 1 - it was launched three years later.
On the outside of Sputnik, four whip antennas transmitted at 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 in the Earth's magnetic field.
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 the new system to talk to 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 resulted in a huge amount of debris in Earth's orbit. 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 generally consider satellites to be those objects that perform a 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 different functions, but they are all fundamentally 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 an on-board computer to control and monitor 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 the 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 additional elements to be installed according to specifications. 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 a 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 adorned 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. GPS navigation satellites work well at this altitude. 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 daily 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 monitor the atmosphere and detect changes in weather conditions that can lead to tornadoes, hurricanes, floods 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 service. This sometimes costs more than $1.5 million a year.
Another 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 US, for example, has spent almost $200 billion since the start of its military satellite program and now, despite all this, has a fleet of aging satellites 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, 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.