Communication satellite geostationary orbit altitude. Geostationary launch statistics

The geostationary orbit with zero inclination and an altitude of 35756 km remains to this day a strategically important orbit for artificial earth satellites. Satellites placed in this orbit revolve around the center of the Earth at the same angular velocity as the Earth's surface. Due to this, there is no need for satellite antennas to track geostationary satellites - a geostationary satellite for a specific location on the Earth's surface is always located at one point in the sky.

An example of a constellation of Russian geostationary communication satellites in 2005:

But checking the latest graph with Gunther's website shows that no more than 40 geostationary satellites were launched in 2017, even if that number includes satellite launches on GPO (geo-transfer orbit) and Lightning orbits (Cosmos-2518). In connection with this discrepancy, I tried to independently assess the dynamics of annual launches into geostationary orbit and the dynamics of changes in the total mass of launched geostationary satellites using the same site of Gunther.

Most geostationary satellites are launched on geotransfer orbits (GPO), and then, with the help of their own engines, the perihelion is raised and entered the geostationary orbit. This is due to the desire to minimize the clogging of the strategically important geostationary orbit (the upper stages of the LV on the GPO burn out much faster than on the GSO due to the low perihelion of the orbits). In this regard, the starting mass of geostationary satellites is most often indicated at the initial launch at the GPO. Therefore, I decided to calculate the mass of geostationary satellites on GPO, as well as to include in the calculation satellites that were originally intended to operate on GPO or other elliptical orbits located between low and geostationary orbits (mainly Lightning-type orbits). On the other hand, in some cases, satellites are directly injected into a geostationary orbit (for example, in the case of Soviet, Russian and American military satellites), in addition, for military satellites, the mass is often simply unknown (in this case, it is necessary to indicate the upper limit of the capabilities of the launch vehicle during launches on GPO). In this regard, the calculations are only preliminary. At the moment, 35 years out of 60 years of the space age have been processed, and the following situation takes place over the years:

1) In 2017, a new record (192 tons) was actually set in terms of the mass to be put into the GPO and Molniya orbits:

2) There is no particular growth in the number of spacecraft launched into these types of orbits (the black line is the trend line):

3) A similar situation is observed with the number of launches:

In general, there is a tendency for a stable increase in cargo traffic to highly elliptical high orbits. Average values ​​over decades:

By the average area of ​​space objects ( cumulative cross sectional area, measured in square meters) geostationary satellites are even more superior to low-orbit vehicles (even taking into account the upper stages - RB):

This is probably due to the large number of deployable structures in geostationary satellites (antennas, solar panels and thermoregulation batteries).

Over the years, the number of operating satellites in geostationary orbit has been steadily growing. In this decade alone, their number has grown from four to five hundred:

According to the database of active satellites, the relay satellite is currently the oldest operational satellite in the GSO. TDRS-3 launched in 1988. In total, 40 devices are currently operating at the GSO, whose age has exceeded 20 years:

The total number of geostationary satellites, taking into account the disposal orbits, already exceeds a thousand vehicles (with a minimum number of upper stages ( RB) rockets in these orbits):

Examples of geostationary satellite constellations:

The growing overcrowding of the geostationary orbit is leading to a continuing trend towards an increase in the weight of geostationary satellites. If the first GSO satellites weighed only 68 kg, then in 2017 China tried to start a 7.6 ton machine. It is obvious that the growing overcrowding of the geostationary orbit will lead in the future to the creation there of large geostationary platforms with reusable elements. Probably, such platforms will solve several tasks at once: communication and observation of the Earth's surface for meteorology, defense needs, and so on.

Geostationary communication satellite with a mass of 7.6 tons, created on the basis of a new Chinese platform DFH-5

We rarely think about how the movement in near-earth space is organized. For example, that from the Earth to the space station is just a stone's throw away than from Moscow to St. Petersburg, and the signal received by the satellite dish has traveled a longer distance than the average car travels in five years. In addition, each launch is preceded by a careful design of the orbit along which the vehicle will move in outer space. The orbits that we choose

When in 1961 the specialists of Korolev's OKB-1 began to create the first Soviet communications satellite "Molniya-1" for the television system "Orbit", they faced the problem of choosing a target orbit for their brainchild. The most effective, at first glance, seemed to be a geostationary orbit with an altitude of 36 thousand kilometers. The satellite located on it is in direct line of sight around the clock for about 1/3 of the Earth's surface. However, from such an orbit it is impossible to provide communication in high latitudes and television broadcasting in the regions of the Far North. In addition, the Soviet Union did not then have carriers for putting heavy satellites into geostationary orbit.

A way out was found by ballistics, who invented an orbit into which a communications satellite could be launched by a rocket already in development. It was a highly elongated orbit with a minimum altitude (perigee) of 500 kilometers and a maximum (apogee) of 40,000 kilometers. The orbital period was 12 hours, and in accordance with the laws of celestial mechanics, the satellite spent most of its time in the apogee region. The orbital inclination (63.4 °) was chosen so that during this period the satellite was visible from most of the territory of the USSR. Favorable conditions for communication lasted eight hours, after which the satellite went to the other side of the Earth, and on the next orbit passed the apogee over North America. Once again, it became available for retransmission of television only after 16 hours.

The communication satellite "Molniya-1" was successfully put into this orbit on the third attempt on April 23, 1965, and the very next day the first in the Soviet Union session of space communication between Moscow and Vladivostok took place. For round-the-clock television broadcasting, it was necessary to keep three Molniya satellites in space at the same time, and to build complex antennas on Earth. Large parabolic "mirrors" tracked the satellite's intricate trajectory in the sky: it quickly ascended in the west, ascended to the zenith, crossed over it, then began to move in the opposite direction, turned around again and, accelerating, descended to the eastern horizon. Another complicating factor was the significant changes in speed when moving in an elongated orbit, as a result of which, due to the Doppler effect, the frequency of the signal received on Earth constantly changed.

The trajectory chosen for the first Soviet communications satellite was later named the Molniya orbit. Its development with the advent of more powerful rockets was the Tundra high-elliptical orbit with a perigee of 500 kilometers, an apogee of 71,000 and an orbital period of 24 hours. Orbits with such a period are called geosynchronous, since, moving along them, the spacecraft always climbs over the same region of the Earth. The efficiency of using satellites in the Tundra orbit is significantly increased, since they can serve the selected area for more than 12 hours on each orbit, and two devices are enough to organize round-the-clock communication. However, ground-based equipment remains complex as geosynchronous satellites are constantly changing their position in the sky, and they have to be monitored.

Hanging in the sky

Receiving equipment is drastically simplified if the satellite remains stationary relative to the Earth. Of the entire set of geosynchronous orbits, this is achieved only on one circular one, located strictly above the equator (inclination 0 °). This orbit is called geostationary, because in it the satellite seems to hover over a selected point on the equator at an altitude of 35,786 kilometers.

The Americans were the first to launch a geostationary satellite, but they did not succeed right away. The first two attempts in 1963 ended in failure, and only on September 10, 1964 the Sinkom-3 satellite entered the GSO. It is interesting that he launched into space on August 19, and for almost a month, with the help of his own engine, sneaked up to the point of standing chosen for him. The first domestic geostationary satellite "Raduga-1" was launched only on December 22, 1975. Since then, the GSO has been constantly replenished, and today there are more than 400 satellites on it and another 600 vehicles are moving near it.

Strictly speaking, due to various perturbations and inference errors, the geostationary satellite does not "hang" completely motionless over the equator, but makes an oscillatory motion relative to its standing point. When projected onto the earth's surface, its trajectory resembles a small figure eight. In addition, due to gravitational perturbations, the vehicle can "drift" along its orbit. In order to stay in the chosen position and not leave the alignment of the ground antennas, the device must regularly adjust its orbit. For this, there is a supply of fuel on board. The service life of a geostationary satellite sometimes depends on it.

Simple geometric constructions show that at latitudes above 81 °, geostationary satellites are below the horizon, which means that communication with their help in the polar regions is impossible. In practice, mobile communication via geostationary satellite is limited to latitude 65-70 °, and fixed - 70-75 °. Communication via GSO has one more serious drawback. On the way to the satellite and back, the radio signal travels more than 70 thousand kilometers, spending a quarter of a second on it. Taking into account the time for signal processing and transmission over land lines, the delay can significantly exceed half a second. As a result, Internet services via satellite respond slowly, and telephone communication becomes uncomfortable, since even modern means of "echo cancellation" do not always cope with long delays. To get rid of these disadvantages, it is necessary to reduce the height of the satellites.

Orbital elements

The word "orbit" in Latin means "track" or "path". The near-earth orbit is characterized by a number of parameters: the lowest and highest altitude (perigee and apogee, which also determine the orbital period), inclination (the angle between the orbital plane and the plane of the earth's equator), the longitude of the ascending node, which sets “in which direction” (around which line in equatorial plane) the orbit is tilted, and the perigee argument specifying how the elliptical orbit is rotated in its own plane. Gravitational disturbances from other planets, the pressure of solar radiation, the non-spherical shape of the Earth, its magnetic field and atmosphere lead to the fact that the orbits of satellites can change noticeably over time. Therefore, during the operation of the satellite, trajectory measurements are regularly carried out, and, if necessary, its orbit is corrected.

Constellation Iridium

In relatively low orbits, commercial and government communications satellite systems are being formed. Technically, these trajectories cannot be called convenient for communication, since satellites on them are visible most of the time low above the horizon, which negatively affects the quality of reception, and with mountainous terrain can make it impossible. Therefore, the lower the orbit, the more satellites there should be in the system. While three satellites are sufficient for the global communications system in the GSO, then in medium-altitude orbits (5000-15,000 kilometers), 8 to 12 spacecraft are required. And for heights of 500-2000 kilometers, more than fifty satellites are needed.

And yet, by the end of the 1980s, the prerequisites for the implementation of low-orbit communication systems were formed. First, the satellites were getting closer and closer to the GSO. "Parking spaces" in this orbit are subject to international registration, and nearby satellites should not operate on the same radio frequencies, so as not to interfere with each other. Secondly, progress in the field of radio electronics has made it possible to create inexpensive (and most importantly, light) satellites with fairly broad capabilities. A rocket capable of launching only one large communications satellite into the GSO could throw a whole "bundle" of such devices into low orbit. Third, the end of the cold war and the disarmament process released hundreds of intercontinental ballistic missiles that could be used at bargain prices to launch small satellites. And finally, it was during these years that the demand for mobile communications began to grow rapidly, which is characterized by the use of low-power omnidirectional antennas that “do not finish off” the GSO. All these factors made the launch of even a very large number of inexpensive LEO satellites more profitable than creating a constellation of several heavy geostationary vehicles.

Orbcomm (USA) and Gonets (Russia) were among the first LEO communication systems. They did not provide voice transmission, but were intended to send text messages and collect information from various sensors, such as meteorological ones. Today, Orbcomm includes 29 satellites weighing 42 kilograms in orbits with an altitude of 775 kilometers. The Gonets system originally contained only 6 satellites, which could delay the delivery of messages by several hours. Now the third generation of satellites is being replaced in it, the number of working devices has reached nine, but in the future it should be brought to 45 - nine each in five almost polar orbits (inclination 82.5 °) at an altitude of 1500 kilometers.

Polar orbits are called orbits that pass over the North and South poles of the Earth, that is, they are located perpendicular to the equator. Any part of the earth's surface periodically falls into the field of view of a satellite in a polar orbit. If you use several of these orbits, rotated at an angle to each other, and for each at equal intervals to launch several satellites, you can continuously survey the entire surface of the Earth. This is how the Iridium satellite telephony network works. It uses polar orbits with an inclination of 86.4 ° and an altitude of 780 kilometers. Initially, they housed 77 satellites, hence the name of the system: iridium - the 77th element of Mendeleev's Periodic Table. However, nine months after launch, in November 1998, Iridium went bankrupt. The call cost, which reached seven dollars a minute, proved too high for consumers, in part because the Iridium system provided truly global connectivity, pole-to-pole. Launched a little later, the GlobalStar system, for the sake of economy, uses instead of polar orbits with an inclination of 52 °, which limits communication to the 70th parallel (approximately at the latitude of Yamal). But 48 satellites are enough for operation (plus four spare), and the cost of communication in the same 1999 was no more than two dollars per minute.

Iridium satellites were already preparing to deorbit and burn in the dense layers of the atmosphere when the entire system was bought by the US Department of Defense. To this day, Iridium remains the only satellite communications system that provides continuous telephone communications across the globe. For example, since 2006, through it, a permanent Internet connection has been provided for the Amundsen-Scott polar station at the South Pole. The connection speed is 28.8 kilobits per second, like on an old telephone modem.

Use of near-earth space

In a first approximation, the orbits of satellites are divided into low (up to 2000 kilometers from the Earth), medium (below the geostationary orbit) and high. Manned flights are made no higher than 600 kilometers, since spaceships should not enter the radiation belts surrounding our planet. Energetic protons of the inner radiation belt pose a danger to the life of astronauts. The maximum radiation intensity is reached at an altitude of about 3000 kilometers, which all spacecraft avoid. An external electronic belt is not that dangerous. Its maximum lies somewhere between the zones of navigation and geostationary satellites. Satellites operating in highly elongated elliptical orbits usually rise even higher. Such are, for example, the Chandra X-ray observatory (USA), which, in order to avoid interference, observes far from the radiation belts, and the future Russian Radioastron observatory, the data of which are more accurate the greater the distance from those working with it in a pair of terrestrial radio telescopes. The highest near-earth orbits, which can equally be considered circumsolar, lie at an altitude of 1.5 million kilometers near the so-called Lagrange points.

Together with the sun

Close to polar ones is another important class of orbits, called solar-synchronous (SSO), which always have a constant orientation relative to the Sun. At first glance, it seems that this contradicts the laws of celestial mechanics, according to which the orbital plane remains constant, which means that during the movement of the Earth around the Sun, it must turn to it from one side or the other. But if we take into account that the Earth has a flattened shape, it turns out that the orbital plane is experiencing precession, that is, it turns slightly from turn to turn. By choosing the correct height and inclination, it is possible to achieve that the rotation of the orbital plane exactly corresponds to the arc traversed by the Earth around the Sun. For example, for an orbital altitude of 200 kilometers, the inclination should be slightly more than 96 ° degrees, and for 1000 kilometers - already more than 99 ° (numbers over 90 ° correspond to orbital motion against the daily rotation of the Earth).

The value of the SSO lies in the fact that, moving along it, the satellite flies over terrestrial objects always at the same time of day, which is important for conducting space imagery. In addition, due to the proximity of the MTR to polar orbits, it is possible to monitor the entire earth's surface from them, which is important for meteorological, cartographic and reconnaissance satellites, which are collectively called Earth remote sensing satellites (ERS). A certain choice of SSO parameters allows the satellite never to go into the shadow of the Earth, always staying in the sun near the border of day and night. At the same time, the satellite does not experience temperature drops, and solar panels continuously provide it with energy. Such orbits are convenient for radar mapping of the earth's surface.

Civilian remote sensing satellites, which are required to distinguish between objects of the order of a meter, usually operate at altitudes of 500-600 kilometers. For military reconnaissance satellites with a survey resolution of 10-30 centimeters, such heights are too high. Therefore, their orbits are often chosen so that the perigee lies above the survey point. If there is more than one "object of attention", the scout has to change the shape of the orbit with the help of the engine, sometimes making "dives" to the upper layers of the atmosphere, dropping to heights of about 150 kilometers. The need to "get close" to the Earth as close as possible has a significant drawback - the resistance of the atmosphere dramatically reduces the duration of the satellite's stay in space. You gape a little - and the atmosphere will drag the satellite into its abyss, where it will inevitably burn out. Because of this, on board LEO "spies" have to keep large reserves of fuel to correct the orbit and periodic rise in altitude. For example, out of 18 tons of the launch mass of the American photo reconnaissance KH-11, fuel accounts for about 40%. Thus, the chosen orbit can directly affect the design, and sometimes the appearance of the vehicle.

This dependence was especially clearly manifested in the design of the European scientific apparatus GOCE, recently launched from the Russian Plesetsk cosmodrome. It has an unusual swept shape, unlike the angular contours of most modern satellites, and even evokes associations with a high-speed aircraft. The fact is that for a satellite studying the Earth's gravitational field, a low MTR with a height of 240-250 kilometers was chosen. It is optimal from the point of view of measurement accuracy, but in order to withstand the braking effect of the atmosphere, the satellite was shaped with a minimum cross section. In addition, ion electric rocket engines are installed in the aft part of the device for trajectory correction.

Clark's Orbit

Probably the first to talk about the possibility of geostationary satellites were Konstantin Eduardovich Tsiolkovsky and Herman Potochnik, a cosmonautics theorist from Slovenia, better known as Herman Noordung. However, the idea of ​​using them for communication became widespread at the suggestion of the famous British scientist and science fiction writer Arthur Clarke. In 1945, he published a popular science article in Wireless World describing communications satellites in the geostationary orbit (GEO), now often referred to as the "Clarke Orbit."

Global view

But not all remote sensing satellites require high resolution. What is the use of being able to detect an object 30 centimeters in size, if the task of the apparatus is to track regional or global movements of air masses and thermal regimes of large regions. For its implementation, the breadth of coverage is much more important. For global meteorological monitoring, satellites are usually placed in GSO or high MTR, and for regional monitoring, in a relatively low orbit (500-1000 kilometers) with an inclination that allows regular surveying of the selected area. For example, a promising Russian satellite

Meteor-M should monitor the hydrometeorological situation on a global scale with a MTR 830 kilometers high. And for the device "Electro-L" the GSO was chosen, since its main purpose will be to survey the entire disk of the Earth in the visible and infrared ranges. In addition, GSO in this case is optimal for obtaining information about global atmospheric processes occurring in the equatorial zone.

Precisely because a significant part of the earth's surface can be surveyed from the GSO, it is "populated" not only by communication devices and meteorological satellites, but also by missile attack warning systems. Their main task is to detect the launches of ballistic missiles, for which the equipment includes an infrared telescope capable of detecting the torch of a running engine. The shortcomings of the GSO in this case do not play a role - after all, the satellite does not need to transmit information to the North or South Pole, but a third of the earth's surface is in full view.

The choice of orbit parameters for the satellites of the global navigation systems GPS and GLONASS turned out to be very difficult. Although the idea itself (using the signal delay to measure the distance to satellites with well-known coordinates) was obvious, its implementation took decades. In the USSR, research in this direction began as early as 1958. Five years later, work began on the first satellite navigation system "Tsikada", which was commissioned only 16 years later. Its four navigation satellites were operating in low circular orbits with an altitude of 1000 kilometers and an inclination of 83 °. Their orbital planes were evenly distributed along the equator. Approximately once every one and a half to two hours, a consumer could enter into radio contact with one of the Tsikada satellites and, after 5-6 minutes of communication, determine his latitude and longitude. Of course, the military customers of satellite navigation did not like this mode of operation. They needed at an arbitrary moment and at any point on the Earth to determine three spatial coordinates, a velocity vector and exact time. To do this, it is necessary to simultaneously receive signals from at least four satellites. In low orbits, this would require placing hundreds of spacecraft, which would be not only insanely expensive, but also simply impracticable. The fact is that the service life of Soviet satellites did not exceed one or two years (and more often several months), and it would turn out that the entire rocket and space industry would work exclusively on the manufacture and launch of navigation satellites. In addition, LEO satellites experience significant disturbances due to the influence of the earth's atmosphere, which affects the accuracy of the coordinates determined from them.

Studies have shown that the necessary parameters of the navigation system are provided when satellites are placed on circular trajectories with a height of 19,000-20,000 kilometers (an altitude of 19,100 kilometers was selected for GLONASS) with an inclination of about 64 °. The influence of the atmosphere here is already insignificant, and gravitational perturbations from the Moon and the Sun do not yet lead to rapid changes in the orbit.

Companion graveyard

In the past 20 years, more and more countries have acquired their own telecommunications, meteorological and military satellites in geostationary orbit. As a result, the GSO became cramped. The average distance between satellites is about 500 kilometers, and in some parts of it, heavy vehicles "hang" just a few tens of kilometers from each other. This can interfere with communications and even lead to collisions. It is too expensive to return satellites from high orbit to Earth. Therefore, in order to clear the GSO, it was decided that after the completion of active operation, they should be transferred to the "disposal orbit" located 200-300 kilometers higher on the remains of fuel. This "satellite graveyard" is still much freer than the working orbit.

Theoretically, at such an altitude, 18 satellites in three orbital planes are enough for at least four vehicles to be seen simultaneously from any point on Earth. But in fact, in order to improve the accuracy of determining the location of the spacecraft themselves, the GLONASS constellation will have to be expanded to 24 operating satellites, and taking into account the reserve, it is necessary to have 27-30 satellites in the system. Other navigation systems, such as GPS (USA), Galileo (Europe) and Beidou (China), are based on approximately the same principles. Their satellite constellations are located in circular orbits with an altitude of 20,000-23,500 kilometers with an inclination of 55-56 °.

Pilot tracks

The orbits of the manned vehicles are specially selected. Thus, during the construction of the International Space Station (ISS), the convenience of launching new modules and spacecraft to it, the safety of the crew, and fuel consumption for maintaining altitude were taken into account. As a result, the station was launched into an orbit with an altitude of about 400 kilometers. This is slightly below the border of the Earth's radiation belt, in which charged particles of the solar wind accumulate under the influence of the magnetic field of our planet. A prolonged stay inside the radiation belt would expose the crew to dangerous radiation or would require powerful means of radiation protection of the orbital station. It is also impossible to lower the orbit significantly lower, otherwise, due to significant aerodynamic drag, the station will be decelerated and a lot of fuel will be required to maintain its height. The inclination of the orbital plane (51.6 °) is determined by the conditions of launches from Baikonur, the northernmost cosmodrome from which manned flights are carried out.

Similar considerations dictated the choice of the orbit for the Hubble Space Telescope, since from the very beginning it was assumed that astronauts would periodically visit it. Therefore, the orbital inclination of 28.5 ° was chosen according to the latitude of the American Canaveral cosmodrome. As a result, the orbits of the ISS and the telescope are located at a significant angle to each other, and the space shuttle cannot visit them in one flight, because changing the orbital plane is one of the most "expensive" maneuvers, the shuttle simply does not have enough fuel for it. Because of this, the work of the space telescope almost ended prematurely. After the disaster of the space shuttle Columbia in 2003, it was decided that astronauts should be able to take refuge on the ISS if serious damage to the spacecraft was discovered in flight. The flight to the Hubble telescope ruled out such a possibility and was almost canceled. In the end, it was still approved, and after a major modernization in 2009, the Hubble, which was on the verge of failure, will be able to work for another five years, until it is replaced by a new telescope named after James Webb. True, it will no longer be launched into near-earth orbit, but much further - to the Lagrange point at an altitude of 1.5 million kilometers, where the orbital period is exactly one year, and the telescope will constantly hide from the Sun behind the Earth. There are no manned flights there yet.

We have described a number of different orbits, but their diversity is by no means limited to this. For any type of orbit, there are variations designed to enhance their positive and weaken the negative properties. For example, some satellites move close to a geostationary orbit with an inclination of up to 10 °. This allows them to periodically "look" into high latitudes, but the terrestrial antennas need to be able to tilt up and down to track satellite vibrations. Various transition paths connecting the two orbits play an important role. With the proliferation of low-thrust ion thrusters in near-Earth space, complex spiral paths began to be used. The choice of the trajectory of the spacecraft is carried out by ballistics. There is even the term "ballistic design", meaning the joint development of the optimal flight path of the vehicle, its appearance and basic design parameters. In other words, the orbit is developed together with the satellite and the rocket that will launch it.

2007 year

Main idea

This site is dedicated to surveillance issues artificial earth satellites(Further Satellites ). Since the beginning of the space era (October 4, 1957, the first satellite, Sputnik-1, was launched), mankind has created a huge number of satellites that circle the Earth in all kinds of orbits. Today the number of such man-made objects exceeds tens of thousands. Basically it is "space debris" - satellites fragments, spent rocket stages, etc. Only a small part of them are operating satellites.
Among them are research and meteorological satellites, communications and telecommunications satellites, and military satellites. The space around the Earth is "populated" by them from heights of 200-300 km and up to 40,000 km. Only some of them are accessible for observation using inexpensive optics (binoculars, telescopes, amateur telescopes).

When creating this site, the authors set themselves the goal of collecting together information on the methods of observation and shooting of satellites, to show how to calculate the conditions for their flight over a certain terrain, to describe the practical aspects of the issue of observation and shooting. The site contains mainly the author's material obtained in the course of observations by the participants of the "Cosmonautics" section of the "hν" astronomical club at the Minsk Planetarium (Minsk, Belarus).

And yet, answering the main question - "Why?", The following must be said. Among all kinds of hobbies that a person is fond of, there is astronomy and astronautics. Thousands of astronomy lovers observe planets, nebulae, galaxies, variable stars, meteors and other astronomical objects, photograph them, hold their conferences and "master classes". What for? It's just a hobby, one of many. A way to get away from everyday problems. Even when amateurs do work of scientific importance, they remain amateurs who do it for their own pleasure. Astronomy and cosmonautics are very "technological" hobbies, where you can apply your knowledge of optics, electronics, physics, and other natural sciences. Or you may not use it - and just enjoy the pleasure of contemplation. With satellites, things are similar. It is especially interesting to keep track of those satellites, information about which is not disseminated in open sources - these are military intelligence satellites of different countries. In any case, the observation of satellites is a hunt. Often we can indicate in advance where and when the satellite will appear, but not always. And how he will "behave" is even more difficult to predict.

The described methods were created on the basis of observations and research, in which members of the hν astronomy club of the Minsk Planetarium (Belarus) took part:

• Bozbei Maxim.
• Dremin Gennady.
• Kenko Zoya.
• Mechinsky Vitaly.

Members of the "hν" club of astronomy lovers also helped a lot. Lebedeva Tatiana, Povalishev Vladimir and Alexey Tkachenko... Special thanks Alexander Lapshin(Russia), profi-s (Ukraine), Daniil Shestakov (Russia) and Anatoly Grigoriev (Russia) for their help in creating clause II §1 "AES Photometry", Chapter 2 and Chapter 5, and Elena (Tau, Russia) also for consulting and writing several calculation programs. The authors also thank Mikhail Abgaryan (Belarus), Yuri Goryachko (Belarus), Anatoly Grigorieva (Russia), Leonida Elenina (Russia), Viktor Zhuk (Belarus), Igor Molotov (Russia), Konstantin Morozov (Belarus), Sergey Plaks (Ukraine), Ivan Prokopyuk (Belarus) for the provided illustrations for some sections of the site.

Some of the materials were received during the execution of the order of the Unitary Enterprise "Geographic Information Systems" of the National Academy of Sciences of Belarus. The submission of materials is carried out on a non-commercial basis in order to popularize the Belarusian space program among children and youth.

Vitaly Mechinsky, Curator of the "Cosmonautics" section of the "hν" astroclub.

Site news:

• 09/01/2013: Subparagraph 2 has been significantly updated "AES photometry per flight" p. II §1 - ​​added information on two methods of photometry of satellite tracks (method of photometric profile of a track and method of isophotic photometry).
• 09/01/2013: Sub-clause II §1 has been updated - added information on working with the Highecl program for calculating probable flares from the GSS.
• 01/30/2013: Updated "Chapter 3"- added information on working with the program "MagVision" for calculating the incidence of penetration from illumination from the Sun and Moon.
• 01/22/2013: Chapter 2 has been updated. Added animation of the movement of satellites across the sky in one minute.
• 01/19/2013: Updated subparagraph "Visual observations of satellites" p.1 "Determination of satellite orbits" §1 of Chapter 5. Added information about heating devices for electronics and optics to protect against dew, frost and excessive cooling.
• 01/19/2013: Added in "Chapter 3" information about the drop in penetration during exposure from the moon and twilight.
• 01/09/2013: Added subparagraph "Flares from the lidar satellite" CALIPSO " of the sub-item "Photographing flares", clause II "AES photometry" §1 of Chapter 5. Information on the features of observation of flares from the laser lidar of the "CALIPSO" satellite and the preparation process for them is described.
• 11/05/2012: The introductory part of §2 of Chapter 5 has been updated. Added information about the required minimum equipment for radio surveillance of satellites, and also shows a diagram of the LED indicator of the signal level, which is used to set the level of the input audio signal that is safe for the recorder.
• 11/04/2012: Subparagraph updated "Visual observations of satellites" p.1 "Determination of satellite orbits" §1 of Chapter 5. Added information about the star atlas of Brno, as well as about the red film on the LCD screens of electronic devices used in observations.
• 04/14/2012: The sub-item of the sub-item "Photo / video filming of satellites" has been updated, item 1 "Determination of AES orbits" §1 of Chapter 5. Added information about working with the "SatIR" program for identifying satellites in photographs with a wide field of view, as well as determining coordinates ends of satellite tracks on them.
• 04/13/2012: Subparagraph updated "AES astrometry in the obtained images: photo and video" sub-item "Photo / video filming of satellites" item 1 "Determination of satellites orbits" §1 of Chapter 5. Added information about working with the program "AstroTortilla" to determine the coordinates of the center of the field of view of images of the starry sky.
• 03/20/2012: Subclause 2 "Classification of AES orbits by the semiaxis major" §1 of Chapter 2 has been updated. Added information about the magnitude of the GSS drift and orbital disturbances.
• 03/02/2012: Added subparagraph "Observing and filming missile launches at a distance" sub-item "Photo / video filming of satellites" p. I "Determination of the orbits of satellites" §1 of Chapter 5. Information on the features of observation of the flight of launch vehicles at the stage of launching is described.
• "Converting astrometry to IOD format" sub-item "Photo / video filming of satellites" item I "Determination of satellites orbits" §1 of Chapter 5. Added description of work with the program "ObsEntry for Window" for converting astrometry of satellites into IOD-format - an analogue of the program "OBSENTRY", but for OS Windows.
• 02/25/2012: Subparagraph updated "Sun-synchronous orbits" p.1 "Classification of satellite orbits by inclination" §1 of Chapter 2. Added information on calculating the value of inclination i ss of the solar-synchronous orbit of the satellite, depending on the eccentricity and semi-major axis of the orbit.
• 09/21/2011: Sub-clause 2 "AES photometry for a flight" was updated. Clause II "AES photometry" §1 of Chapter 5. Added information about the synodic effect, which distorts the determination of the satellite rotation period.
• 09/14/2011: Subparagraph updated "Calculation of the orbital (Keplerian) elements of the satellite orbit based on astrometric data. One flyby" sub-item "Photo / video shooting of satellites", item I "Determination of satellites orbits" §1 of Chapter 5. Added information about the "SatID" program for identifying a satellite (using received TLEs) among satellites from a third-party TLE database, and also describes the method of identifying a satellite in the Heavensat program based on the flight seen near the reference star.
• 09/12/2011: The sub-item "Calculation of the orbital (Keplerian) elements of the satellite's orbit based on astrometric data has been updated. Several flights of the" sub-item "Photo / video shooting of the satellite" item I "Determination of the satellite's orbits" §1 of Chapter 5. Added information about the TLE recalculation program -elements for the desired date.
• 09/12/2011: Added subparagraph "Satellite entry into the Earth's atmosphere" of the sub-item "Photo / video filming of satellites", item I "Determination of the orbits of satellites" §1 of Chapter 5. Information on working with the "SatEvo" program for predicting the date of entry of satellites into the dense layers of the Earth's atmosphere is described.
• "Flares from geostationary satellites" subparagraph "Photographing flares", clause II "AES photometry" §1 of Chapter 5. Added information on the period of visibility of GSS flares.
• 09/08/2011: Subparagraph updated "Change in the brightness of the satellite during the flight" Subclause 2 "AES photometry over a span" Clause II "AES photometry" §1 of Chapter 5. Added information on the form of the phase function for several examples of reflecting surfaces.
• subparagraph 1 "Observation of satellites flares", item II "Photometry of satellites" §1 of Chapter 5. Added information about the irregularity of the time scale along the image of the satellites track on the photodetector matrix.
• 09/07/2011: Subparagraph updated "AES photometry per flight" p. II "AES photometry" §1 of Chapter 5. Added an example of a complex light curve of the "NanoSail-D" satellite (SCN: 37361) and modeling of its rotation.
• "Flares from LEO satellites" Subparagraph 1 "Observation of AES flares", Section II "AES Photometry" §1 of Chapter 5. Added a photograph and a photometric profile of a flare from LEO AES "METEOR 1-29".
• 09/06/2011: Updated subparagraph "Geostationary and geosynchronous satellite orbits"§1 of Chapter 2. Added information on the classification of geostationary satellites, information on the shape of the GSS trajectories.
• 09/06/2011: Updated subparagraph "AES flight survey: survey equipment. Optical elements" sub-item "Photo / video filming of satellites" p. I "Determination of satellites orbits" §1 of Chapter 5. Added links to reviews of domestic lenses as applied to satellites imaging.
• 09/06/2011: Updated subparagraph "Phase angle" p. II "AES photometry" §1 of Chapter 5. Added animation of the satellite phase change depending on the phase angle.
• 13.07.2011: Completed filling in all chapters and sections of the site.
• 07/09/2011: The writing of the introduction to clause II is completed "AES photometry"§1 of Chapter 5.
• 07/05/2011: Completed the writing of the introduction to §2 "Radio surveillance satellites" Chapters 5.
• 07/04/2011: Subparagraph updated "Processing observations" p. I "Reception of satellite telemetry" §2 of Chapter 5.
• 07/04/2011: Finished writing p. II "Obtaining images of cloudiness"§2 Chapter 5.
• 07/02/2011: Finished writing p. I "Reception of satellite telemetry"§2 Chapter 5.
• 07/01/2011: Completed the writing of the subparagraph "Photo / video filming of satellites" Clause I §1 of Chapter 5.
• 06/25/2011: Finished writing Applications.
• 06/25/2011: The writing of the introduction to Chapter 5 is finished: "What and how to observe?"
• 06/25/2011: The writing of the introduction to §1 is finished "Optical observations" Chapters 5.
• 06/25/2011: The writing of the introduction to clause I is finished "Determination of satellite orbits"§1 of Chapter 5.
• 06/25/2011: Chapter 4 is finished writing: "About the time".
• 01/25/2011: Chapter 2 is finished writing: "What kind of orbits and satellites are there?".
• 01/07/2011: Chapter 3 is finished writing: "Preparing for Observations".
• 01/07/2011: The writing of Chapter 1 is finished: "How are the satellites moving?"

Just as theater seats provide different perspectives on a show, different satellite orbits provide perspective, each with a different purpose. Some seem to hang over a point on the surface, they provide a constant view of one side of the Earth, while others circle around our planet, sweeping over many places in a day.

Orbit types

At what altitude do the satellites fly? There are 3 types of near-earth orbits: high, medium and low. On the high, most distant from the surface, as a rule, there are many weather and some communications satellites. Satellites rotating in medium-earth orbit include navigation and special ones designed to monitor a specific region. Most scientific spacecraft, including NASA's Earth Observing System fleet, are in low orbit.

The speed at which the satellites fly depends on the speed of their movement. As you get closer to the Earth, gravity becomes stronger and the movement accelerates. 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 located 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 revolution in 28 days.

Aerodynamic paradox

Changing the altitude of a satellite also changes its orbital speed. There is a paradox here. If the satellite operator wants to increase its speed, he cannot simply start the thrusters to accelerate. This will increase the orbit (and altitude), resulting in a decrease in speed. Instead, the engines should be started in the opposite direction to the direction of the satellite's movement, that is, to perform an action that on Earth would slow down a moving vehicle. Doing so will move it lower, which will increase the speed.

Orbit characteristics

In addition to altitude, the satellite's path 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 a circular one. The eccentric orbit is elliptical. The distance from the spacecraft to the Earth depends on its position.

Inclination is the angle of the orbit in relation to the equator. A satellite that orbits directly over the equator has zero tilt. If the spacecraft passes over the north and south poles (geographic, not magnetic), its tilt is 90 °.

Together - height, eccentricity, and inclination - determine the satellite's motion and how the Earth will look from its perspective.

High near-earth

When the satellite reaches exactly 42164 km from the center of the Earth (about 36 thousand km from the surface), it enters the zone where its orbit corresponds to the rotation of our planet. Since the spacecraft moves at the same speed as the Earth, i.e., its orbital period is 24 hours, it seems that it remains in place above a single longitude, although it can drift from north to south. This special high orbit is called geosynchronous.

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

The Molniya orbit (inclination 63.4 °) is used for observation at high latitudes. Geostationary satellites are anchored to the equator, so they are not suitable for distant northern or southern regions. This orbit is quite eccentric: the spacecraft moves in an elongated ellipse with the Earth located close to one edge. Since the satellite is accelerated by 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 edge farthest 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. It is used for communication in the far north or south.

Low Earth

Most scientific satellites, many meteorological and space stations are in almost 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 remaining close to the equator.

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

As the satellite moves, the Earth rotates beneath it. By the time the spacecraft enters the illuminated area, it is above the area adjacent to the zone 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 one point, polar-orbiting satellites have the ability to stay at the same time. Their orbit is sun-synchronous - when the 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 after 99 minutes over Ecuador or Colombia also takes place at 10:30 local time.

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

The satellite's path 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 unacceptable. Since atmospheric drag and the gravitational pull of the Sun and Moon alter the craft's orbit, it needs to be adjusted regularly.

In orbit: launch

Launching a satellite requires energy, the amount of which depends on the location of the launch site, the altitude and slope of its future trajectory. It takes more energy to get to a distant orbit. Satellites with a significant tilt (for example, polar ones) are more energy intensive than those that circle above the equator. Launching into orbit with low inclination is assisted by the rotation of the Earth. moves at an angle of 51.6397 °. This is necessary to make it easier for space shuttles and Russian rockets to reach it. ISS altitude - 337-430 km. Polar satellites, on the other hand, do not receive assistance from the Earth's impulse, so they need more energy to climb the same distance.

Adjustment

After launching a satellite, efforts must be made to keep it in a specific 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), alters the inclination of the orbit. Throughout its lifetime, the GOES satellites have been corrected three or four times. NASA LEOs must adjust their tilt annually.

In addition, Earth's satellites are affected by the atmosphere. The uppermost layers, although thin enough, offer strong enough resistance to pull them closer to Earth. The action of gravity causes the satellites to accelerate. 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 hot air balloon expands and rises when it heats up, the atmosphere rises and expands when the sun gives it extra energy. The thinner layers of the atmosphere rise, and denser ones take their place. Therefore, satellites in Earth's orbit must change their position about four times a year to compensate for atmospheric drag. When solar activity is at its maximum, the position of the apparatus has to be corrected every 2-3 weeks.

Space debris

The third reason forcing the change in orbit is space debris. One of the communication satellites Iridium collided with a non-functioning Russian spacecraft. They shattered, forming a debris cloud of over 2,500 pieces. Each element was 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, since space debris has already had to change orbits several times due to space debris.

Engineers track the position of space debris and satellites that could obstruct movement and carefully plan evasive maneuvers as needed. The same team plans and performs maneuvers to adjust the tilt and altitude of the satellite.

"The satellite was launched into geostationary orbit" ... how many times have we heard this phrase in the news on television! What should be understood by this - where is it located, more precisely - where does such a satellite rotate?

To begin with, the satellite, whatever it may be, must keep in touch with the Earth (otherwise there is no need to launch it). But the satellite moves relative to the Earth, revolving around it, and the antenna, which must be tuned to it, is stationary relative to the Earth ... how to resolve this contradiction? It's very simple: the satellite must become stationary relative to the point where the antenna is located ... how is this possible?

When we say that a certain object remains motionless relative to another object that is moving at this time, in reality we mean that the mentioned objects move with the same speed relative to some third object. Here you are motionless relative to the car, but if you consider separately your movement and the movement of the car relative to the road, it turns out that you are moving at the same speed. It doesn't matter if you are in a car or not: if you were flying over it through the air at the same speed as a car (let's imagine for a moment such a fantastic situation), you would also be motionless relative to the car.

Thus, in order for a satellite to be stationary relative to an antenna on Earth, it must rotate around our planet at the same speed with which it rotates around its axis. This is exactly what happens in geostationary orbit! Its position in orbit is called a "standing point", because from the point of view of an observer on Earth, such a satellite does not "fly", but "hangs" motionless in the sky.

In geostationary orbit, the satellite, on the one hand, does not approach the Earth, on the other, it does not move away from it. For this to be possible, the centrifugal force, "carrying" the satellite away from the Earth, must balance the force of gravity, "pulling" it to the planet. This becomes possible when the satellite rotates in an orbit along the equator, and the orbit height above the Earth's surface is 35,786 kilometers.

However, keeping a satellite in geostationary orbit is not so easy: it is not only the Earth's gravity that affects it - the gravity of the Moon and the Sun will not go anywhere either, the Earth's gravitational field is not completely uniform, and our equator is not perfectly round. Because of all these circumstances, the so-called. “Potential geostationary orbit holes” are points above the equator at 75.3 and 165.3 degrees East and 14.7 and 104.7 degrees West, at which the satellite is displaced from its original orbit. In general, the orbit deviates by 0.85 degrees per year and after 26 and a half years it is already tilted 15 degrees relative to the equatorial plane! To overcome such disturbances, the satellite is equipped with a propulsion system, for which hundreds of kilograms of fuel have to be loaded - and it is its reserve that limits the satellite's service life (for example, modern television satellites operate from 12 to 15 years).

For all its advantages, the geostationary orbit is not always applicable: it is connected with the equator, therefore, the further from the equator, the more difficult it is to “get” such a satellite - for example, it is no longer possible to provide communication in the Far North with the help of such a satellite. In addition, the signal can weaken and even disappear when the sun, satellite and antenna are in the same line. This phenomenon (the so-called solar interference) occurs in the northern hemisphere (more precisely, in its middle latitudes) February 22-March 11 and October 3 - 21 for periods of up to 10 minutes. So the geostationary orbit is not always applicable - there are satellites that are launched into other orbits.