RU2791102C1 - Global satellite communications using medium circular orbits - Google Patents

Abstract

FIELD: satellite communication systems.

SUBSTANCE: invention relates to satellite communication systems. The effect is achieved by the fact that the global satellite communication system using medium circular orbits includes an orbital constellation of twelve artificial satellites 1 placed in two medium circular orbits 2, 3, six artificial satellites 1 in each orbit 2, 3, the first of two medium of circular orbits 2 has a polar inclination of 90°, and the second of two medium circular orbits 3 has an equatorial inclination of 0°, artificial satellites 1 are equipped with communication equipment with a network of ground stations located in the service area and providing communication through these artificial satellites 1 .

EFFECT: providing 100% coverage of the earth's surface for elevation angles of at least 15° and the maximum coverage ratio for latitudes in the range from 40° N.L. to 20° S.L., that is, in the regions of the Earth with the highest population density, which allows to increase the number of users served with the same quality of service.

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Description

The invention relates to satellite communications systems, and more specifically to a global satellite communications system using medium circular orbits and is intended to provide various types of communications to vast regions of the globe.

At present, the expansion of the telecommunications services market has led not only to a constant increase in the number of geostationary communication satellites, but also to the emergence of a significant number of projects for global and / or regional communication systems using artificial satellite (IS) systems in low and medium circular orbits. In the conditions of fierce competition, the feasibility and viability of such expensive projects largely depend on a reasonable combination of cost and quality indicators of communication systems.

Known combined satellite systems for regional communications (for example, for the Northern Hemisphere) using elliptical and circular orbits, including geostationary (US patent N 5931417, class 244/158R; system "Ellipso Borealis / Concordia" - see Proulx R.J., et al., "Automated Station-Keeping for Satellite Constellations", AAS/AIAA Astrodynamics Conference, Sun Valley, Aug. 1997). The use of such systems has certain advantages, which consist in expanding the boundaries of the service area, covering equatorial regions. However, these systems use a relatively large number of satellites (US patent N 5931417 - up to 24 satellites; system "Ellipso Borealis/Concordia" - 17 satellites).

From the existing prior art, various satellite communication systems are known, in which it is proposed to use a plurality of satellites in a non-geostationary orbit (see patents RU No. 2107990, 2496233, 2302695).

However, each of these systems has an IS orbital constellation, which is built on the basis of two orbits of different heights. This orbital construction leads to an increase in the cost of launching the IS into orbits, increases the signal transmission delay time and complicates the determination of the energy characteristics of user terminals due to the difference in the energy of radio links between user terminals and IS in different orbits.

There is a known class of kinematically correct satellite systems in circular orbits, first introduced by Mozhaev G.V. (Mozhaev G.V. The problem of a continuous survey of the Earth and kinematically correct satellite systems I, II. Space research, 1972, vol. 10, issue 6, pp. 833-840; 1973, vol. 11, issue 1, p. 59-69; Mozhaev G.V. Synthesis of orbital structures of satellite systems. - M: Mashinostroenie, 1989, 304 s; RF patent N 2065550, class 6 H04B 7/185), and independently of it J.G. J.G. Walker, Some circular orbit patterns providing continuous whole Earth coverage. Journal of the British Interplanetary Societ. Vol.24, 1971, pp. 369-384; J.G. Walker, Satellite constellations. Journal of the British Interplanetary Society. Vol.37 , 1984, pp.559-571). This type of constellation of satellites is envisaged, in particular, in the Globalstar project.

The use of circular orbits in relation to regional communications is not always justified, since they have the same coverage characteristics and, accordingly, communications in both hemispheres of the Earth, which is redundant for communication systems, for example, in the Northern Hemisphere and, therefore, unreasonably expensive.

A global satellite communication system in medium circular orbits is known (patent RU No. 2695540), which we have chosen as a prototype and contains an orbital constellation of artificial satellites, a ground-based flight control center, regional stations for organizing communication and ensuring interfacing with external networks and ground-based consumer facilities. According to this invention, the orbital constellation contains twelve artificial satellites located in three medium circular orbits in three orbital planes, four artificial satellites in each plane, that is, in each orbit, while the orbital planes have equal inclination and are shifted by an angle of 120 ° one relative to another.

RU patent No. 2695540 states that the system provides reliable global coverage when using medium circular orbits with a height of 8070 km and an orbital inclination of 51.6°. Moreover, it is indicated that with these parameters of the orbital constellation, two-fold coverage of 99.53% of the territory of the Russian Federation is provided at an elevation angle of 10 ° (the angle between the direction to the IS and the horizon plane at the user's location) and three-fold coverage of 45.0% of the Earth's territory.

At the same time, there is no information in the said patent about at what minimum values of the elevation angle a continuous (100%) coverage of the earth's surface is provided, which is an important indicator of the effectiveness of a satellite communication system.

According to the recommendations of the International Telecommunication Union, the minimum acceptable elevation angle is an angle of at least 15 °, which is used by almost all designers of satellite constellations, based on acceptable radio noise levels.

The efficiency of a satellite communication system is determined by the possibility of global coverage with an elevation angle of at least 15°, as well as by the multiplicity of coverage of the earth's surface, proportional to the population.

For a well-known satellite system (prototype), which belongs to the class of kinematically symmetrical satellite systems in circular orbits with equal inclinations and equal heights, at each moment of time on the inspected sphere - the earth's surface for each circular orbit, it is possible to allocate a certain circular radio visibility band of a certain width, symmetrical relative to each plane of the orbit, for any point of which the elevation angle will be at least a given value. In this context, a circular radio visibility band is understood as a space, the boundaries of which are formed by connecting the intersection points of the radio visibility zones of each of the ISs of the considered orbital plane in the direction of the IS movement, and the width of such a radio visibility band changes in proportion to the value of the elevation angle. This issue will be considered in more detail below.

In the well-known satellite system (prototype) there are three circular bands of radio visibility, located relative to the equator at the same angles of 51.6°. The authors of the present invention for the known satellite communication system were calculated coverage ratio in the average circular orbit with a height of 8070 km and an orbital inclination of 51.6° for an elevation angle of 15°. These calculations showed that when the elevation angle is 15°, there is no 100% coverage of the earth's surface, which will be further presented in tables and diagrams.

In addition, the well-known satellite communication system is built without taking into account the distribution of population density over the Earth's surface. However, it is precisely for regions with the highest population density (population per 1 sq. km), lying in the latitude range from 40 ° north latitude (N) to the equator in the northern hemisphere and from the equator to 20 ° south latitude (S .l) in the southern hemisphere, the maximum coverage factor should be achieved (the number of simultaneously visible ISs with an elevation angle of at least 15°).

As mentioned above, in the well-known satellite communication system, in order to launch artificial satellites into three circular orbits, it is required to carry out three launches using three launch vehicles that put four IS into each orbit, which results in high energy consumption for using this system.

The invention is based on the task of developing an economical global satellite communication system using medium circular orbits, in which, by using a minimum number of artificial satellite orbits and such an arrangement of artificial satellites in these orbits, as well as choosing the parameters of medium circular orbits, global coverage of the earth's surface was provided with an angle places of at least 15° with a maximum coverage ratio in the Earth's zones with the highest population density while reducing energy costs for the use of the proposed system.

The problem is solved by the fact that in a global satellite communication system using medium circular orbits, including a network of ground points and an orbital constellation of twelve artificial satellites, evenly placed in the corresponding medium circular orbits and equipped with communication equipment with a network of ground points located in the service area and providing communication through these artificial satellites, according to the invention, artificial satellites are placed in two medium circular orbits, each of which has six artificial satellites in two orbital planes, and the first of these two medium circular orbits has a polar inclination, essentially equal to 90° , and the second of these two mean circular orbits has an equatorial inclination essentially equal to 0°.

It is advisable that artificial satellites be placed on each of the two medium circular orbits at an equal distance from one another with a phase shift of 60°.

It is desirable that artificial satellites be placed in adjacent medium circular orbits with a minimum phase shift of 30°.

It is possible for at least one additional artificial satellite to be placed in each of the two medium circular orbits.

The technical result of the present invention is the creation of an economical global satellite communication system that provides 100% coverage of the earth's surface for elevation angles of at least 15°, and the maximum coverage ratio (the number of simultaneously visible IPs with an elevation angle of at least 15°) for latitudes in the range of 40° With. sh. up to 20° S, that is, in the areas of the Earth with the highest population density, which allows you to increase the number of users served with the same quality of service compared to known technical solutions.

The claimed characteristics of the patented communication system are achieved through the use of a minimum number of medium circular orbits, only two orbits, and their mutual arrangement with the same total number of ICs as in the known system. Mathematical calculations show that 100% coverage of the earth's surface with the location of the IS in two circular planes - polar and equatorial for an elevation angle of at least 15° is achieved with the number of IS in each of the orbital planes equal to six.

In the event that a larger number of ISs are evenly placed on two circular orbits, for example, seven or more, then in order to achieve 100% global coverage, the elevation angle will increase, which makes it possible to reduce the radio noise level, but at the same time increases the cost of the system as a whole.

In the patented system, to launch artificial satellites into the declared medium circular orbits, two launches are required using two launch vehicles, which significantly reduces the energy costs for using the proposed system, that is, the energy costs for launching the IS and for the system as a whole.

In the future, the invention is explained by a description of specific examples of execution, drawings and diagrams, in which:

fig. 1 depicts an orbital constellation of artificial satellites in medium circular orbits in two orbital planes with polar and equatorial orbital inclinations, made according to the invention;

fig. 2 shows the construction of a circular visibility band for a polar inclination orbital plane of a medium circular orbit, an embodiment according to the invention;

fig. 3 shows the construction of a circular visibility band for an orbital plane with an equatorial inclination of a medium circular orbit, an embodiment according to the invention;

fig. 4 depicts a graphic diagram of the radio visibility intervals of all artificial satellites for a satellite communication system known from the prototype;

fig. 5 is a graphical diagram of the radio visibility intervals of all artificial satellites for a patent-pending satellite communication system made according to the invention;

fig. 6 depicts a fragment of a graphic diagram of the intervals of radio visibility of all artificial satellites for the patent-pending satellite communication system shown in figure 5, enlarged scale.

The inventive global satellite communications system using medium circular orbits contains a network of ground stations (not shown in the drawing) and an orbital constellation of twelve artificial satellites 1 (figure 1), evenly spaced in two medium circular orbits 2, 3, six artificial satellites 1 in each orbit 2, 3. Artificial satellites 1 are equipped with communication equipment (not shown in the drawing) with a network of ground stations located in the service area and providing communication through these artificial satellites 1.

Of particular importance is the choice of position in space of circular orbits 2,3, on which artificial satellites 1 are launched. When constructing the proposed satellite communication system, the authors proceeded from the fact that continuous global coverage of the earth's surface should be achieved in 100% of the time and with an elevation angle of at least 15 °.

The patented satellite communication system contains two circular orbits 2, 3 with a height of 8070 km, each of which contains six artificial satellites 1 in two orbital planes, the first of these two medium circular orbits 2 having a polar inclination essentially equal to 90°, and the second of said two mean circular orbits 3 has an equatorial inclination substantially equal to 0°. On each of these orbits 2, 3 are six IP 1, located at an equal distance from one another with a phase shift (angular distance), essentially equal to 60°. The magnitude of the phase shift between IS 1 in different circular orbits 2, 3 is half the phase shift between IS 1 in the same orbital plane and for the patented system is essentially 30°.

As noted earlier, at each moment of time on the examined sphere - the earth's surface, it is possible to select a certain circular band of radio visibility of a certain width, symmetrical with respect to each plane of the orbit, for any point of which the elevation angle will be at least a given value.

As an example, figure 2 shows a circular band 4 radio visibility, formed by six artificial satellites 1 in a circular orbit 2 with a polar inclination of 90°. The circular band 4 of radio visibility has a variable width and is formed by the superposition of circles, in the center of each of which is the projection of each of the IS 1. By connecting the intersection points of the radio visibility zones of each of the IS 1 of the considered orbital plane in the direction of movement of the IS 1, a band 4 of radio visibility is formed, the width of which is proportional to elevation angle value.

As can be seen from figure 2, the circular band 4 radio visibility, formed by IP 1 in a circular orbit 2 with a polar inclination of 90°, covers all regions of the earth's surface with the exception of the equatorial regions.

Figure 3 shows a circular band 5 radio visibility, formed by six IP 1, located in a circular orbit 3 with an equatorial inclination of 0°, which covers all regions of the earth's surface except for the northern and southern polar regions.

Both visibility bands 4, 5 correspond to an elevation angle of 15° and an altitude of circular orbits 2, 3 of 8070 km. Combining (overlaying) bands 4, 5 radio visibility provides 100% coverage of the earth's surface.

As mentioned above, the patented communication system is built taking into account the distribution of population density over the Earth's surface. At the same time, the developers were guided by data published on the NASA socio-economic research website (Documentation "Administrative Unit Center Points with Population Estimates, v4.11: Gridded Population of the World (GPW), v4 SEDAC (columbia.edu)", indicating significant uneven distribution of population density over the Earth's surface According to these data, the highest population density is in the latitude range from 40° N to 20° S.

When developing a patented communication system, the geocentric reference system was adopted as the basis for comparing orbital constellations, for which calculation formulas are known that allow determining its location (coordinates) in space depending on the time of day by the parameters of the orbit of an artificial satellite. Knowing the coordinates of the artificial satellite 1 for a given user location, it is possible to determine the time intervals during which the artificial satellite 1 will be observed with an elevation angle of at least 15°.

To identify the advantages of the patented communication system, the authors of the present invention carried out calculations of the radio visibility zones of each of the artificial satellites 1 for the claimed communication system and each of the artificial satellites for the known communication system (prototype) when the user's technical means are located at a point with coordinates 40° N. latitude. , 90°E with an elevation angle of at least 15°.

As an example, figure 4 shows a graphic diagram of the radio visibility intervals of all artificial satellites for a known satellite communication system on a conditional 48-hour interval for randomly selected dates April 8 and 9. The diagram corresponds to a minimum elevation angle of 15° and the location of user facilities at a point with coordinates 40° N, 90° E. (the IS number consists of the number of the orbital plane and the number of the IS in the plane).

From figure 4 it follows that at the time intervals 02:00-03:00 on April 8 and 9, there is no radio visibility of all artificial satellites for user facilities located at a point with coordinates 40°N, 90°E. with an elevation angle of 15°. This significantly limits the use of the known satellite communication system, since it does not provide round-the-clock continuous coverage of the earth's surface.

When shifting the technical means of the user in latitude 40 ° N.S. the lack of radio visibility remains, only the boundaries of the time interval are shifted.

Figure 5 presents a graphic diagram of the intervals of radio visibility of all artificial satellites 1 for the patent-pending communication system on a conditional 48-hour interval. The diagram corresponds to a minimum elevation angle of 15° and the location of the user's technical means at a point with coordinates of 40° N. latitude, 90° E

Figure 6 shows a fragment of the diagram shown in figure 5, on an enlarged scale.

The diagrams shown in Fig.5, 6 show that artificial satellites 1 (A21-A26) in a circular orbit 3 with an equatorial inclination of 0° completely provide continuous coverage of the earth's surface with an elevation angle of 15° for a latitude of 40 N, and artificial satellites 1 (A11-A16) in a circular orbit 2 with a polar inclination of 90° increase the coverage factor.

The calculation results showed that, unlike the known communication system, the patented satellite system provides 100% coverage of the earth's surface, regardless of the latitude of the location of the user's technical facilities for elevation angles of at least 15°. The data for the northern and southern hemispheres are symmetrical. The results obtained for the coverage of the earth's surface for known and patented satellite communication systems are shown in Table 1.

When building real satellite constellations, their cost is determined, among other things, by the number of launch vehicles needed to launch artificial satellites. At the same time, for each specific launch, the required initial inclination of the orbit to which the artificial satellites are launched is initially set. It is known that changing the inclination of the orbit is an extremely energy-consuming maneuver. So, for satellites in low orbit (having an orbital speed of about 8 km/s), changing the inclination of the orbit to the equator by 45° will require approximately the same energy (increment of the characteristic velocity) as for launching satellites into orbit, that is, about 8 km/s. With. Therefore, in order to reduce the cost of launching artificial satellites, it is desirable to use the minimum number of orbits that will provide 100% coverage of the earth's surface.

In the patented communication system, only two circular orbits 2, 3 are used, each of which has six artificial satellites 1, that is, the proposed system is as simple and economical as possible.

In addition, the construction of the proposed system using medium circular orbits 2, 3 allows you to operate low-cost small-sized spacecraft, which generally allows you to create an economical satellite communications system, including by simplifying the launch of artificial satellites 1 into each orbit through group launches. A low orbital altitude of 8070 km improves the energy of radio links compared to ISs located in geostationary orbit, since at such an orbital altitude, losses due to the propagation of electromagnetic waves in free space are significantly reduced compared to spacecraft in geostationary orbit.

As mentioned above, the highest population density (persons per sq. km) falls on the earth's surface in the latitude range from 40 ° N.L. up to 20°S Therefore, it is for such latitudes that the maximum multiplicity of coverage is required (the number of simultaneously visible artificial satellites with an elevation angle of at least 15°), which is achieved in the patented communication system.

Table 2 presents the comparative characteristics of the coverage ratio of the earth's surface for known and patented satellite systems.

As can be seen from the above data, in the claimed system, the coverage ratio for latitudes with a maximum population density lying in the range from 40 ° N.L. up to 20° S, higher than known from the prototype satellite system. Table 2 compares coverage ratios in the range from 40°N. to 0° (from 40° S to 0°) are highlighted for clarity. Increased in comparison with the known from the prototype communication system multiplicity of coverage allows you to increase the number of users served with equal quality of service.

The present invention provides for the placement of more artificial satellites in two circular orbits, for example seven or more. To achieve 100% global coverage, the elevation angle will increase, which will reduce the radio noise level, but at the same time increase the cost of the system as a whole.

Thus, the use of the proposed invention ensures the creation of an economical satellite communication system that provides 100% coverage of the earth's surface for elevation angles of at least 15° and a maximum coverage ratio for latitudes in the range from 40° N. latitude. up to 20° S

Claims (4)

1. Global satellite communication system using medium circular orbits, including a network of ground stations and an orbital constellation of twelve artificial satellites located in the corresponding medium circular orbits and equipped with communication equipment with a network of ground stations located in the service area and providing communication through the indicated artificial satellites , characterized in that the artificial satellites are placed in two medium circular orbits, each of which has six artificial satellites in two orbital planes, the first of the two medium circular orbits having a polar inclination equal to 90°, and the second of the two medium circular orbits have an equatorial inclination of 0°. 2. The global satellite communication system according to claim 1, characterized in that the artificial satellites are placed on each of the two medium circular orbits at an equal distance from one another with a phase shift of 60°. 3. The global satellite communications system according to claim 2, characterized in that the artificial satellites are placed in adjacent medium circular orbits with a minimum phase shift of 30°. 4. The global satellite communications system according to claim 1, characterized in that at least one additional artificial satellite is placed on each of the two medium circular orbits.

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