At what altitude do satellites fly, orbit calculation, speed and direction of movement. Geostationary orbit

Planet (dwarf planet)	Orbital speed, km/s
Mercury










Makemake

Spacecraft orbits around the Earth

Orbit	Distancebetween centers of mass	Height above the Earth's surface	Orbital speed	Orbital period	specific orbital energy(English)
Surface of the Earth, for comparison
Low reference orbit	6,600 - 8,400 km	200 - 2,000 km	Circular orbit: 6.9 - 7.8 km/s Elliptical orbit: 6.5 - 8.2 km/s	89 - 128 min
Highly elliptical orbit of the Molniya satellites	6,900 - 46,300 km	500 - 39,900 km	1.5 - 10.0 km/s	11 hours 58 minutes
Geostationary orbit				23 h 56 min
Moon orbit	363,000 - 406,000 km	357,000 - 399,000 km	0.97 - 1.08 km/s

Low reference orbit(NOO, low Earth orbit) is the orbit of a spacecraft near the Earth. It is right to call an orbit “reference” if it is expected to change - an increase in altitude or a change in inclination. If maneuvers are not provided or the spacecraft does not have its own propulsion system at all, it is preferable to use the name “low Earth orbit”. In general, a spacecraft is considered to be in a reference orbit if it is moving at escape velocity and is at an altitude where the corresponding density of the upper layers of the atmosphere, as a first approximation, allows for circular or elliptical motion. At the same time, a device can be in an orbit of this type for at least one orbit. Typical parameters of the reference orbit, using the Soyuz-TMA spacecraft as an example, are:

minimum altitude above sea level (superheigh) – 193 km,

maximum altitude above sea level (wapogee) – 220 km,

inclination – 51.6 degrees,

the circulation period is about 88.3 minutes.

When determining height NOO it is important to indicate from which model of the Earth it is measured. Russian ballistics traditionally indicate the height above the ellipsoid, and American ones - above the sphere; as a result, the difference can reach 20 km (approximately corresponds to the difference between the equatorial and polar radii of the Earth), and the positions of apogee and perigee can shift.

Since the daily rotation of the Earth is involved in launching the launch vehicle into orbit, the payload capacity depends on the inclination of the orbit to the equatorial plane. The best conditions are achieved if NOO has an inclination towards the equator, which coincides with the latitude of the launch site from which the launch was carried out. Other orbital inclinations lead to a decrease in the parameters of the launch vehicle in terms of its ability to launch cargo into orbit. However, it is not possible for all cosmodromes to launch in the most energetically favorable direction; for example, for Baikonur, with a latitude of about 46 degrees, it is impossible to launch at an inclination of less than 48.5 degrees due to restrictions on the location of the fall areas of separated rocket parts (exclusion zones). The most commonly used inclination for launches from Baikonur is 51.6 degrees, lower inclinations are rarely used.

Lifetime, or time spent by the spacecraft on NOO, depend on the ballistic parameters of the artificial celestial body and on the activity of the Sun during this period, which affects the height of the upper layers of the Earth’s atmosphere.

The lower the orbit, the greater the mass of cargo that the launch vehicle can launch into it, all other things being equal. Therefore, it is advantageous to make the reference orbit as low as possible. In practice, an orbital flight time (before entering the dense layers of the atmosphere) of less than one day can cause problems in case of failures on board the spacecraft, so such low orbits are practically not used. In addition, the minimum altitude of the reference orbit is affected by the value of the insertion error, since with an unfavorable combination of errors in measuring instruments, controls and external factors, the orbit may turn out to be too low and the spacecraft will return to the Earth’s atmosphere and burn up before it has time to maneuver. However, there are known cases of launching vehicles into orbits with an orbital period of less than 88 minutes and a perigee altitude of 121-150 km. For example, the automatic station Luna-7 was launched into a reference orbit with a perigee of 129 km.

The concept of “reference orbit” came into use with the start of launches of the four-stage 8K78 Molniya rocket, the fourth stage of which was launched in weightlessness after completing approximately 3/4 of a revolution around the Earth, as required for interplanetary and lunar spacecraft.

Low Earth orbit can be used not only as a reference orbit, but also as a working one. In general, orbits with an apogee altitude of up to 2000 km are considered low. A special type of low Earth orbit is the sun-synchronous orbit. Earth remote sensing satellites are launched into such orbits.

The ISS is located in low Earth orbit. Since the end of the Apollo program in 1972, all manned space flights have taken place in low Earth orbit. Due to intensive use in low orbits, a large amount of space debris circulates, which leads to complications in the operation of the ISS.

The time a satellite spends in LEO depends on many factors, especially the influence of the Moon and the altitude above the dense layers of the atmosphere. For example, the orbit of the Explorer-6 satellite (USA) changed every 3 months from 250 to 160 km, which led to the satellite’s service life of 2 years instead of the planned 20, also the first Earth satellite lasted 3 months (perigee 215 km, apogee 939 km ). Increased solar activity can lead to a sharp increase in the density of the upper atmosphere - as a result, the satellite is slowed down more, and the altitude of its orbit decreases faster. The shape of the satellite also plays a significant role, namely the area of its midsection (cross section); For satellites specifically designed to operate in low orbits, a swept-back, aerodynamically streamlined body shape is often chosen.

Sun-synchronous orbit(sometimes called heliosynchronous) - a geocentric orbit with such parameters that an object located on it passes over any point on the earth's surface at approximately the same local solar time. Thus, the angle of illumination of the earth's surface will be approximately the same on all satellite passes. Such constant lighting conditions are very suitable for satellites that receive images of the earth's surface (including remote sensing satellites, weather satellites). However, there are annual variations in solar time caused by the ellipticity of the Earth's orbit.

For example, the LandSat-7 satellite, located in a sun-synchronous orbit, can cross the equator fifteen times a day, each time at 10:00 local time.

To achieve these characteristics, orbital parameters are chosen so that the orbit precesses eastward by 360 degrees per year (approximately 1 degree per day), compensating for the rotation of the Earth around the Sun. Precession occurs due to the interaction of the satellite with the Earth, which is nonspherical due to polar compression. The rate of precession depends on the inclination of the orbit. The required precession speed can be achieved only for a certain range of orbit altitudes (as a rule, values of 600-800 km are chosen, with periods of 96-100 minutes), the required inclination for the mentioned altitude range is about 98°. Orbits with higher altitudes require very high inclination values, which is why the polar regions no longer fall within the satellite's visiting area.

This type of orbit can have various variations. For example, sun-synchronous orbits with high eccentricity are possible. In this case, the solar transit time will be recorded for only one point in the orbit (usually perigee).

The orbital period is selected in accordance with the required period of repeated passes over the same surface point. Although a satellite in a circular sun-synchronous orbit crosses the equator at the same local time, it does so at different points on the equator (at different longitudes) due to the Earth rotating some angle between satellite passes. Let's assume the orbital period is 96 minutes. This value completely divides solar day 7 into fifteen. Thus, in one day the satellite will pass over fifteen different points of the equator on the day side of the orbit (and another fifteen on the night side) and return to the first point. By selecting more complex (non-integer) relations, the number of visited points can be increased by increasing the period of visiting the same point.

A special case of a sun-synchronous orbit is an orbit in which a visit to the equator occurs at noon/midnight, as well as an orbit lying in the terminator plane 8, that is, in the sunset and sunrise band. The latter option does not make sense for satellites carrying out optical photography, but is good for radar satellites, since it ensures that there are no orbital sections where the satellite falls into the Earth's shadow. Thus, in such an orbit, the satellite’s solar panels are constantly illuminated by the Sun.

Geocentric orbit– the trajectory of a celestial body along an elliptical path around the Earth.

One of the two foci of the ellipse along which the celestial body moves coincides with the Earth. In order for a spacecraft to be in this orbit, it must be given a speed that is less than the second escape velocity, but not less than the first escape velocity.

High elliptical orbit (HEO) is a type of elliptical orbit in which the altitude at apogee is many times greater than the altitude at perigee.

According to Kepler's laws, satellites using high elliptical orbits move at very high speeds at perigee and then slow down greatly at apogee. When a spacecraft is close to its apogee, a ground observer has the impression that the satellite hardly moves for several hours, that is, its orbit becomes quasi-geostationary. Within 3.5 hours, the signal from it can be received on an antenna with a diameter of 0.6 m without using a rotating device. On the other hand, the quasi-geostationary point can be located above any point on the globe, and not just above the equator, as with geostationary satellites. This property is used in northern and southern latitudes, very far from the equator (above 76 - 78° N/S), where the elevation angle of geostationary satellites can be very low, or even negative. In these areas, reception from a geostationary satellite is very difficult or completely impossible, and satellites in highly elliptical orbits are the only way to provide service. The elevation angles of highly elliptical satellites exceed 40° at the edges of the service area and reach 90° at its center.

VEO orbits can have any inclination, but often have an inclination close to zeroing out the disturbance caused by the irregular shape of the Earth, similar to an oblate ellipsoid. Using this inclination stabilizes the orbit.

For elliptical orbits, a perigee argument between 180° and 360° means that the apogee is over the Northern Hemisphere. If the perigee argument is between 0° and 180°, the apogee is over the Southern Hemisphere. The apogee of an orbit with a perigee argument of 0° or 180° will be located exactly above the equator, which from a practical point of view does not make sense, since in this case it is cheaper and easier to use a spacecraft in geostationary orbit (you will only need one satellite instead of three).

VEO satellites have the following advantages:

ability to serve a very large area. For example, such a system can serve the entire territory of Russia;

possibility of servicing high latitudes. The elevation angle in these zones for HEO systems is much greater than for geostationary satellites;

widespread use of various frequency ranges in VEO without registration (unlike the geostationary orbit, where there is practically no free space or free frequencies left);

cheaper launch into orbit (about 1.8 times).

At the same time, systems in highly elliptical orbits currently have more disadvantages than advantages. Disadvantages include:

the need to have at least three satellites in orbit (instead of one geostationary one) to create a quasi-geostationary system. In case of providing round-the-clock continuous broadcasting, the number of satellites increases to seven;

The receiving antenna must have a tracking function (swivel drive). Therefore, the initial cost of such an antenna and the cost of its maintenance will be higher than that of a simple fixed antenna;

in high latitudes the population density is much lower than in middle areas, so the issue of the payback of such a system is very doubtful;

the apogee of VEO satellites is higher than that of GSO, so the transmitter power should be higher, up to 400-500 watts. This makes satellites more expensive;

The orbit of HEO satellites usually crosses radiation belts, which greatly reduces the service life of the spacecraft. In order to get rid of this problem, it is necessary to have an orbit with an apogee of about 50 thousand km and a perigee of about 20 thousand km;

since spacecraft move in orbit, the Doppler effect creates additional difficulties for receivers on Earth;

Due to the long signal propagation time, difficulties arise when using real-time applications (for example, telephony).

Geotransfer orbit(GPO) – an orbit that is a transition between a low reference orbit (LEO) (altitude of about 200 km) and a geostationary orbit (GSO) (35,786 km). Unlike LEO and GEO, which are circular to a first approximation, a transfer orbit is a highly elongated elliptical trajectory of the spacecraft, the perigee of which lies at the distance of LEO from the Earth, and the apogee at the distance of GEO (Homan-Vetchinkin orbit).

The completion of the KANaGSO withdrawal occurs when it reaches apogee while moving in a geotransfer orbit. At this moment, the upper stage imparts an accelerating impulse to the device, which turns its elliptical motion into a circular one, with a period of revolution around the Earth equal to a day.

Geostationary orbit(GSO) is a circular orbit located above the Earth’s equator (0° latitude), while in which an artificial satellite orbits the planet with an angular velocity equal to the angular velocity of the Earth’s rotation around its axis. In a horizontal coordinate system, the direction to the satellite does not change either in azimuth or height above the horizon; the satellite “hangs” motionless in the sky. Geostationary orbit is a type of geosynchronous orbit and is used to place artificial satellites (communications, television broadcasting, etc.).

The satellite should orbit in the direction of Earth's rotation, at an altitude of 35,786 km above sea level. It is this height that provides the satellite with a period of revolution equal to the period of rotation of the Earth relative to the stars (Stellar day: 23 hours 56 minutes 4.091 seconds).

The advantages of the geostationary orbit became widely known after the publication of Arthur C. Clarke's popular science article in Wireless World magazine in 1945, so in the West geostationary and geosynchronous orbits are sometimes called " Clarke orbits" A " Clark's belt" refers to the region of outer space at a distance of 36,000 km above sea level in the plane of the earth's equator, where the orbital parameters are close to geostationary. The first satellite successfully launched into GEO was Syncom-3, launched by NASA in August 1964.

A satellite located in geostationary orbit is stationary relative to the Earth's surface, therefore its location in orbit is called its stationary point. As a result, a satellite-oriented and fixed directional antenna can maintain constant communication with this satellite for a long time.

Geostationary orbit can only be accurately achieved on a circle located directly above the equator, with an altitude very close to 35,786 km.

After completing active operation on the remaining fuel, the satellite must be transferred to a disposal orbit located 200-300 km above GEO.

Standing point

where is the mass of the satellite, is the mass of the Earth in kilograms, is the gravitational constant, and is the distance in meters from the satellite to the center of the Earth or, in this case, the radius of the orbit.

The magnitude of the centrifugal force is equal to:

where is the centripetal acceleration that occurs during circular motion in orbit.

As you can see, the mass of the satellite is present as a factor in the expressions for the centrifugal force and for the gravitational force, that is, the altitude of the orbit does not depend on the mass of the satellite, which is true for any orbits and is a consequence of the equality of gravitational and inertial mass. Consequently, the geostationary orbit is determined only by the altitude at which the centrifugal force will be equal in magnitude and opposite in direction to the gravitational force created by the Earth's gravity at a given altitude.

Centripetal acceleration is equal to:

where is the angular speed of rotation of the satellite, in radians per second.

Let's make one important clarification. In fact, centripetal acceleration has a physical meaning only in an inertial frame of reference, while centrifugal force is a so-called imaginary force and occurs exclusively in frames of reference (coordinates) that are associated with rotating bodies. Centripetal force (in this case, the force of gravity) causes centripetal acceleration. In absolute value, the centripetal acceleration in the inertial reference frame is equal to the centrifugal acceleration in the reference frame associated in our case with the satellite. Therefore, further, taking into account the remark made, we can use the term “centripetal acceleration” together with the term “centrifugal force”.

Equating the expressions for gravitational and centrifugal forces with the substitution of centripetal acceleration, we obtain:

Reducing , translating to the left and to the right, we get:

This expression can be written differently, replacing it with the geocentric gravitational constant:

Angular velocity is calculated by dividing the angle traveled per revolution (radians) by the orbital period (the time it takes to complete one revolution in the orbit: one sidereal day, or 86,164 seconds). We get:

rad/s

The resulting orbital radius is 42,164 km. Subtracting the equatorial radius of the Earth, 6,378 km, we get an altitude of 35,786 km.

You can do the calculations in another way. The altitude of the geostationary orbit is the distance from the center of the Earth where the angular velocity of the satellite, coinciding with the angular velocity of the Earth's rotation, generates an orbital (linear) velocity equal to the first escape velocity (to ensure a circular orbit) at a given altitude.

The linear speed of a satellite moving with angular velocity at a distance from the center of rotation is equal to

The first escape velocity at a distance from an object of mass is equal to

Equating the right-hand sides of the equations to each other, we arrive at the previously obtained expression radius GSO:

Orbital speed

The speed of movement in geostationary orbit is calculated by multiplying the angular speed by the radius of the orbit:

km/s

This is approximately 2.5 times less than the first escape velocity of 8 km/s in low-Earth orbit (with a radius of 6400 km). Since the square of the speed for a circular orbit is inversely proportional to its radius,

then the decrease in speed relative to the first cosmic speed is achieved by increasing the orbital radius by more than 6 times.

Orbit length

Geostationary orbit length: . With an orbital radius of 42,164 km, we obtain an orbital length of 264,924 km.

The length of the orbit is extremely important for calculating the “standing points” of the satellites.

Keeping a satellite in orbital position in geostationary orbit

A satellite orbiting in geostationary orbit is under the influence of a number of forces (disturbances) that change the parameters of this orbit. In particular, such disturbances include gravitational lunar-solar disturbances, the influence of the inhomogeneity of the Earth’s gravitational field, the ellipticity of the equator, etc. Orbital degradation is expressed in two main phenomena:

1) The satellite moves along the orbit from its original orbital position towards one of the four points of stable equilibrium, the so-called. “potential geostationary orbit holes” (their longitudes are 75.3°E, 104.7°W, 165.3°E, and 14.7°W) above the Earth’s equator;

2) The inclination of the orbit to the equator increases (from the initial 0) at a rate of about 0.85 degrees per year and reaches a maximum value of 15 degrees in 26.5 years.

To compensate for these disturbances and keep the satellite at the designated stationary point, the satellite is equipped with a propulsion system (chemical or electric rocket). By periodically turning on the low-thrust engines (correction “north-south” to compensate for the increase in orbital inclination and “west-east” to compensate for drift along the orbit), the satellite is kept at the designated stationary point. Such inclusions are made several times every few (10-15) days. It is significant that the north-south correction requires a significantly larger increase in the characteristic velocity (about 45-50 m/s per year) than for the longitudinal correction (about 2 m/s per year). To ensure correction of the satellite's orbit throughout its entire service life (12-15 years for modern television satellites), a significant supply of fuel on board is required (hundreds of kilograms, in the case of using a chemical engine). The satellite's chemical rocket engine has a displacement fuel supply (charge gas-helium) and runs on long-lasting high-boiling components (usually unsymmetrical dimethylhydrazine and dinitrogen tetroxide). A number of satellites are equipped with plasma engines. Their thrust is significantly less than chemical ones, but their greater efficiency allows (due to long-term operation, measured in tens of minutes for a single maneuver) to radically reduce the required mass of fuel on board. The choice of the type of propulsion system is determined by the specific technical features of the device.

The same propulsion system is used, if necessary, to maneuver the satellite into another orbital position. In some cases - usually at the end of the satellite's life, to reduce fuel consumption, the north-south orbit correction is stopped, and the remaining fuel is used only for the west-east correction.

Fuel reserve is the main limiting factor in the service life of a satellite in geostationary orbit.

Disadvantages of geostationary orbit

Signal delay

Communications via geostationary satellites are characterized by large delays in signal propagation. With an orbital altitude of 35,786 km and a speed of light of about 300,000 km/s, the Earth-to-satellite beam travel requires about 0.12 s. Beam path “Earth (transmitter) → satellite → Earth (receiver)” ≈0.24 s. The ping (response) will be half a second (more precisely 0.48 s). Taking into account the signal delay in satellite equipment and equipment of ground services, the total signal delay on the route “Earth → satellite → Earth” can reach 2-4 seconds. This delay makes it impossible to use satellite communications using GSO in various real-time services (for example, in online games).

Invisibility of GSO from high latitudes

Since the geostationary orbit is not visible from high latitudes (from approximately 81° to the poles), and at latitudes above 75° it is observed very low above the horizon (in real conditions, satellites are simply hidden by protruding objects and terrain) and only a small part of the orbit is visible ( see table), then communication and television broadcasting using GSO is impossible in the high-latitude regions of the Far North (Arctic) and Antarctica. For example, American polar explorers at the Amundsen-Scott station use a fiber-optic cable 1,670 kilometers long to communicate with the outside world (telephony, Internet) to a location located at 75° S. the French Concordia station, from which several American geostationary satellites are already visible.

Table of the observed sector of the geostationary orbit depending on the latitude of the place
All data is given in degrees and their fractions.

Latitude terrain	Visible orbital sector
Latitude terrain	Theoretical sector	Real (including relief) sector
90	--	--
82	--	--
81	29,7	--
80	58,9	--
79	75,2	--
78	86,7	26,2
75	108,5	77
60	144,8	132,2
50	152,8	143,3
40	157,2	149,3
20	161,5	155,1
0	162,6	156,6

From the table above it can be seen, for example, that if at the latitude of St. Petersburg (~ 60°) the visible sector of the orbit (and, accordingly, the number of received satellites) is equal to 84% of the maximum possible (at the equator), then at the latitude of Taimyr ( ~75°) the visible sector is 49%, and at the latitude of Spitsbergen and Cape Chelyuskin (~78°) it is only 16% of that observed at the equator. This sector of the orbit in the Siberian region contains 1-2 satellites (not always of the required country).

Solar interference

One of the most unpleasant disadvantages of the geostationary orbit is the reduction and complete absence of the signal in a situation where the sun and the transmitter satellite are in line with the receiving antenna (the “sun behind the satellite” position). This phenomenon is also inherent in other orbits, but it is in geostationary orbits, when the satellite is “stationary” in the sky, that it manifests itself especially clearly. In the mid-latitudes of the northern hemisphere, solar interference occurs during the periods from February 22 to March 11 and from October 3 to 21, with a maximum duration of up to ten minutes. In clear weather, the sun's rays focused by the light coating of the antenna can damage (melt) the receiving and transmitting equipment of the satellite antenna.

Notes

Noordung Hermann The Problem With Space Travel. - DIANE Publishing, 1995. - P. 72. - ISBN 978-0788118494
Extra-Terrestrial Relays - Can Rocket Stations Give Worldwide Radio Coverage? (English) (pdf). Arthur C. Clark (October 1945). Archived
The requirement that satellites remain stationary relative to the Earth in their orbital positions in geostationary orbit, as well as a large number of satellites in this orbit at different points, leads to an interesting effect when observing and photographing stars with a telescope using guiding - maintaining the orientation of the telescope at a given point in the starry sky to compensate for the daily rotation of the Earth (a task inverse to geostationary radio communications). If you observe the starry sky with such a telescope near the celestial equator, where the geostationary orbit passes, then under certain conditions you can see how satellites pass one after another against the backdrop of fixed stars within a narrow corridor, like cars on a busy highway. This is especially noticeable in photographs of stars with long exposures, see, for example: Babak A. Tafreshi. GeoStationary HighWay. (English) . The World At Night (TWAN). Archived from the original on August 23, 2011. Retrieved February 25, 2010. Source: Babak Tafreshi (Night World). Geostationary highway. (Russian) . Astronet.ru. Archived from the original on August 23, 2011. Retrieved February 25, 2010.
for orbits of satellites whose mass is negligible compared to the mass of the astronomical object attracting it
Orbits of artificial Earth satellites. Putting satellites into orbit
The Teledesic Network: Using Low-Earth-Orbit Satellites to Provide Broadband, Wireless, Real-Time Internet Access Worldwide
Magazine "Around the World". No. 9 September 2009. The orbits that we choose
Mosaic. Part II
the satellite exceeds the horizon by 3°
Attention! The period of active solar interference is coming!
Solar interference

Links

Orbits

Types

Basic

Box orbit Capture orbit Elliptical orbit /

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

Types of orbits

At what altitude do satellites fly? There are 3 types of near-Earth orbits: high, medium and low. At the highest level, farthest from the surface, as a rule, many weather and some communications satellites are located. 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 of their movement depends on the altitude at which satellites fly. As you approach the Earth, gravity becomes stronger and the movement accelerates. For example, NASA's Aqua satellite takes about 99 minutes to orbit our planet at an altitude of about 705 km, while a meteorological device 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 satellite's altitude also changes its orbital speed. There is a paradox here. If a satellite operator wants to increase its speed, he can't just fire up the engines to speed it up. This will increase the orbit (and altitude), resulting in a decrease in speed. Instead, the engines should be fired in the opposite direction of the satellite's motion, an action that would slow down a moving vehicle on Earth. This action will move it lower, allowing for increased speed.

Orbit characteristics

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

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

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

High near-Earth

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

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

The Molniya orbit (inclination 63.4°) is used for observation at high latitudes. Geostationary satellites are tied to the equator, so they are not suitable for far northern or southern regions. This orbit is quite eccentric: the spacecraft moves in an elongated ellipse with the Earth located close to one edge. Because the satellite is accelerated by gravity, it moves very quickly when it is close to our planet. As it moves away, its speed slows down, so it spends more time at the top of its orbit at the edge farthest from 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 near-Earth

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

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

As the satellite moves, the Earth rotates underneath it. By the time the vehicle moves to the illuminated area, it is over the area adjacent to the zone of its last orbit. In a 24-hour period, the 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 located above the equator, which allows them to remain above one point, polar orbiting satellites have the ability to remain at the same time. Their orbit is sun-synchronous - when the spacecraft crosses the equator, local solar time is always the same. For example, the Terra satellite always crosses it over Brazil at 10:30 am. The next crossing 99 minutes later over Ecuador or Colombia also occurs at 10:30 local time.

A sun-synchronous orbit is essential for science because it allows the angle of incidence of sunlight on the Earth's surface to be maintained, although it will vary depending on the season. This consistency means scientists can compare images of our planet from the same season over several years without worrying about too big jumps in light, which could create the illusion of change. Without a sun-synchronous orbit, it would be difficult to track them over time and collect the information needed to study climate change.

The satellite's path here is very limited. If it is at an altitude of 100 km, the orbit should have an inclination of 96°. Any deviation will be unacceptable. Because atmospheric resistance and the gravitational force of the Sun and Moon change the spacecraft's orbit, it must be adjusted regularly.

Injection into orbit: launch

Launching a satellite requires energy, the amount of which depends on the location of the launch site, the height and inclination of the future trajectory of its movement. Getting to a distant orbit requires more energy. Satellites with a significant inclination (for example, polar ones) are more energy-intensive than those circling the equator. Insertion into a low-inclination orbit is aided 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. The height of the ISS is 337-430 km. Polar satellites, on the other hand, do not receive any assistance from the Earth's momentum, so they require more energy to rise the same distance.

Adjustment

Once a satellite is launched, efforts must be made to keep it in a certain orbit. Because the Earth is not a perfect sphere, its gravity is stronger in some places. This irregularity, along with the gravitational pull of the Sun, Moon and Jupiter (the solar system's most massive planet), changes the inclination of the orbit. Throughout their lifetime, the GOES satellites have been adjusted three or four times. NASA's low-orbiting vehicles must adjust their inclination annually.

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

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

Space debris

The third reason forcing a change in orbit is space debris. One of Iridium's communications satellites collided with a non-functioning Russian spacecraft. They crashed, creating a cloud of debris consisting of more than 2,500 pieces. Each element was added to the database, which today includes over 18,000 objects of man-made origin.

NASA carefully monitors everything that may be in the path of satellites, since orbits have already had to be changed several times due to space debris.

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

orbital speed- orbitinis greitis statusas T sritis Standartizacija ir metrologija apibrėžtis Greitis, kuriuo kūnas arba dalelė juda tam tikra orbita. atitikmenys: engl. orbital velocity vok. orbitale Geschwindigkeit, f rus. orbital speed, f pranc.… … Penkiakalbis aiškinamasis metrologijos terminų žodynas

orbital speed- orbitinis greitis statusas T sritis fizika atitikmenys: engl. orbital velocity vok. orbitale Geschwindigkeit, f rus. orbital speed, f pranc. vitesse orbitale, f … Fizikos terminų žodynas

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