JPH10258799A - Sun synchronous orbit satellite system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cover the entire earth by a small number of satellites regarding a sun synchronous orbit satellite system having a plurality of satellites on a sun synchronous orbit and used for satellite communications. SOLUTION: A plurality of satellites 4a to 4d are disposed at specified peripheral direction intervals on an orbit 3 where a locus surface maintains a specified angle against a straight line 2 for connecting the earth 1 and the sun. For securing continuous communications in one point on the earth 1 directly below the orbit 3, it is necessary to arrange a sufficient number of satellites on the orbit 3. The specified peripheral direction intervals are decided according to this satellite number. Since the earth 1 is self-rotated in the direction of an arrow 5 and the orbit 3 is a sun synchronous locus, the one point does not always stay directly below the orbit 3, but communication services are provided for about two and half hours even at a satellite altitude of 1400k. If a time zone for receiving the services is matched with a time zone having dense communication traffic, satellite communications are provided over the world even if the number of satellites is small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a satellite-synchronous orbit satellite system, and more particularly to a solar-synchronous orbit satellite system in which a plurality of satellites are arranged in a solar-synchronous orbit and used for satellite communication.

In recent years, satellite communication systems using a number of orbiting satellites arranged in low orbit as relay devices have been developed. In such a communication system, the output of the ground station device can be small, and miniaturization of the ground station device can be expected. Therefore, there is a possibility that the ground station can be configured as a mobile radio device.

[0003]

2. Description of the Related Art In general, a low orbit is used at an altitude of about 700 to 1,400 km while avoiding a part affected by the atmosphere and avoiding a Van Allen band where space radiation is strong. The orbital cycle of the satellite in such a low orbit is about one and a half hours, and the visible time from one point on the ground is about ten and several minutes. Therefore, a large number of satellites orbiting the same orbit are required to ensure continuous communication.

[0004] On the other hand, even if many satellites orbit,
Since the service area on the ground that can be covered by this one orbit is a limited area in a circular shape along the orbit, a large number of orbits are required to cover everything on the earth.

Conventionally, a satellite arrangement has been proposed which can cover the whole world with equal communication quality as much as possible. According to this proposal, a very large number of satellites are required. For example, in the iridium system, a plurality of polar orbits are arranged at substantially equal intervals in the longitudinal direction, and satellites are arranged at substantially equal intervals on each orbit.

[0006]

However, since the cost of the satellite itself and the launch cost are extremely high, there is a strong demand to cover the entire earth with as few satellites as possible.

Further, since launching of satellites cannot be performed uniformly for all satellites due to cost and required time, it is important that satellites can be used effectively even in a transient state before all satellites have been launched. It has been demanded.
That is, there is a demand for so-called growth, which can provide the minimum service for the time being even with a small number of satellites and can enhance the service as the number of satellites increases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a sun-synchronous orbit satellite system capable of covering the entire earth with a small number of satellites.

Another object of the present invention is to provide a sun-synchronous orbit satellite system in which the satellites can be effectively used even in a transient state before all satellites have been launched.

[0010]

According to the present invention, in order to achieve the above object, as shown in FIG. 1, an orbital surface having a predetermined constant angle with respect to a straight line 2 connecting the earth 1 and the sun. A plurality of satellites 4a arranged at predetermined circumferential intervals on
-4d, a solar-synchronous orbit satellite system is provided.

In the configuration as described above, the orbit 3 is a sun-synchronous orbit in which the orbital plane always keeps a predetermined constant angle with respect to the straight line 2 connecting the earth 1 and the sun, and the north pole and the south pole of the earth 1 This is an orbit close to the polar orbit passing through.
A plurality of satellites 4a to 4d are arranged on this orbit 3 at predetermined circumferential intervals.

In order to ensure continuous communication at one point on the earth 1 directly below the orbit 3, a sufficient number of satellites must be arranged in the orbit 3. The predetermined circumferential interval is determined according to the number of satellites.

By the way, since the earth 1 is rotating in the direction of arrow 5 and the orbit 3 is a sun-synchronous orbit, the above-mentioned one point cannot always stay directly below the orbit 3, but the satellite altitude 1400
It is possible to receive a communication service for about 2.5 hours in the case of km.

Therefore, for about two and a half hours centering on the same local time on the earth 1, communication services can be received in any area on the earth 1. If this service is available at a time when communication traffic density is high, satellite communication is possible around the world even with a small number of satellites. Of course, if the number of orbits is increased, the width of the time zone in which the service can be received can be increased.

[0015] Communication traffic is not uniform throughout the 24 hours of the day, for example, generally during the day the traffic density is high and at night it is low. In the present invention, it is possible to set the trajectory according to the traffic density during the day, and therefore, compared to the case where the trajectory is uniformly arranged,
The required number of satellites can be reduced.

Further, even in a transient state in which the number of orbits of the complete system to be finally set does not reach the number of orbits, the existing satellite can be operated only by narrowing the time zone in which the service can be received. Therefore, the satellites can be effectively used even in a transient state before all the satellites have been launched, and a system with growth potential can be constructed.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. First, a principle configuration of an embodiment of the present invention will be described with reference to FIG. In the embodiment of the sun-synchronous orbit satellite system according to the present invention, the orbit plane is the earth 1
It comprises a plurality of satellites 4a to 4d arranged at a predetermined circumferential interval on an orbit 3 maintaining a predetermined fixed angle with respect to a straight line 2 connecting the sun and the sun.

In the configuration as described above, the orbit 3 is a sun-synchronous orbit in which the orbital surface always maintains a predetermined constant angle with respect to the straight line 2 connecting the earth 1 and the sun, and the north pole and the south pole of the earth 1 This is an orbit close to the polar orbit passing through.
A plurality of satellites 4a to 4d are arranged on this orbit 3 at predetermined circumferential intervals.

In order to ensure continuous communication at one point on the earth 1 directly below the orbit 3, a sufficient number of satellites must be arranged in the orbit 3. The predetermined circumferential interval is determined according to the number of satellites.

Incidentally, since the earth 1 rotates in the direction of arrow 5 and the orbit 3 is a sun-synchronous orbit, the above-mentioned one point cannot always stay directly below the orbit 3, but the satellite altitude 1400
It is possible to receive a communication service for about 2.5 hours in the case of km.

Therefore, for about two and a half hours around the same time in each local time on the earth 1, communication services can be received in any area on the earth 1. If this service is available at a time when communication traffic density is high, satellite communication is possible around the world even with a small number of satellites. Of course, if the number of orbits is increased, the width of the time zone in which the service can be received can be increased.

Communication traffic is not uniform throughout the 24 hours of the day, for example, generally during the day the traffic density is high and at night it is low. In the present invention, it is possible to set the trajectory according to the traffic density during the day, and therefore, compared to the case where the trajectory is uniformly arranged,
The required number of satellites can be reduced.

Further, even in a transient state in which the number of orbits of the complete system to be finally set does not reach the number of orbits, the existing satellite can be operated only by narrowing the time zone in which the service can be received. Therefore, the satellites can be effectively used even in a transient state before all the satellites have been launched, and a system with growth potential can be constructed.

Next, the sun-synchronous orbit will be described. The Earth is not a true sphere, but has a larger equatorial radius than a polar radius. The orbit of an artificial satellite orbiting the earth is affected by such a flat shape of the earth, and the orbital plane rotates with time. That is, the point at which the satellite passes the earth's equatorial plane moves eastward or westward over time. The rotation direction and the rotation speed vary depending on the orbit inclination angle. The orbit inclination angle is the angle that the satellite orbit plane indicates with respect to the equatorial plane.

The rotation of the orbit of the satellite is shifted eastward by three times a year.
If it can be set to rotate by 60 °, the orbital plane will always have a fixed angle with respect to the straight line connecting the earth and the sun. Such an orbit whose orbital plane always has a fixed angle with respect to a straight line connecting the earth and the sun is known as a sun-synchronous orbit. In other words, the local time at which the orbital surface of the sun-synchronous orbit passes one point on the earth is always constant. The local time is a time set in each region on the earth as midday of the sun at noon.

When the satellite orbit is a circular orbit, the rotation speed V of the orbit surface is represented by the following equation (1).

[0027]

[Number 1] _{V = -9.97 × (a e /} a) 3.5 × cos i ··· (1) The unit of the rotation speed V is in degrees (°) / day, the east direction +, the west direction -. a _e is the equatorial radius of the earth (6,3
78 km), a is the satellite orbit radius, and i is the orbit inclination angle.

The rotation speed V is defined as the speed at which the earth rotates around the sun (360 ° / 365.25 days = 0.9856 ° /
The following relational expression (2) can be obtained by using the satellite orbit radius a and the orbit inclination angle i as variables.

[0029]

0.9856 = -9.97 × (6378 / a) ^3.5 × cos i (2) Altitude of about 700 to 1,400k while avoiding the part affected by the atmosphere and avoiding the Van Allen zone where cosmic radiation is strong
The orbit inclination angle i when the satellite orbit is provided at m is ± 98 to ± 102 ° based on the above equation (2).

Therefore, altitudes of about 700 to 1,400 k
The m sun-synchronous orbit will be close to the polar orbit passing through the North and South Pole. In FIG. 1, when the orbital plane 3 close to the polar orbital plane is made parallel to the straight line 2 connecting the earth 1 and the sun, the sun is directly south (northern hemisphere) or true north (southern hemisphere) in various parts of the world. At noon and half a day later,
It is possible to secure a satellite elevation angle exceeding a certain value continuously. this,
This will be described with reference to FIG.

FIG. 2 is a diagram showing satellite elevation angle characteristics when 12 satellites are arranged at 30 ° intervals in a satellite orbit at an altitude of 1,400 km. The satellite elevation angle is the angle from the horizon to the satellite when viewing the satellite on the ground. This satellite elevation angle is a measure for obtaining good communication quality. FIG. 2 shows an example in which the orbit inclination angle is −101 °, the ground station is on the equator, and the orbit time of the satellite is 114 minutes.

Each of the curves G1 to G17 in the figure shows the elevation angle characteristic of one satellite, and the curve G13 is the elevation angle characteristic shown again after the satellite corresponding to the curve G1 has made one round of the earth. Similarly, the curves G2 and G14, the curves G3 and G15, the curves G4 and G16, and the curves G5 and G17
Are elevation characteristics of the same satellite. Since an elevation angle of about 10 ° or more is necessary to obtain normal communication quality, it can be seen from FIG. 2 that the communication service can be provided during the daytime and the night and about 2.5 hours.

Such a service available area shifts to the west along with the rotation of the earth, but in the shifted area, the service is always provided at the same local time because the local time of the area is applied. Will be. In other words, for example, when a communication service of about two and a half hours is set around noon, twelve satellites arranged in one sun-synchronous orbit will provide about two and a half hours around noon in any region of the world. Can be implemented.

Further, by preparing another sun-synchronous orbit at intervals of, for example, about 30 ° in the longitude direction and performing similar satellite constellation, communication service is provided for about four and a half hours during the day and at night. It can be implemented.

Therefore, it is possible to start the service with a small number of orbits at first, perform the service by sequentially increasing the number of orbits, grow over time, and complete the entire system without interruption of the communication service throughout 24 hours a day. it can.

In a completed system in which almost the same communication conditions are established at any time in the world, a plurality of orbital planes are arranged at equal orbital plane intervals (intervals in the longitudinal direction), and a satellite is placed on each orbit at equal intervals. Placed at intervals. In addition, satellite positions are arranged in zigzag (staggered) on adjacent orbits, so that each region on the earth is covered under equal conditions as much as possible. However, in two orbits in which the directions of movement of the satellites are opposite in adjacent orbits, the communication conditions inevitably deteriorate in each region on the earth covered by the two orbits. A little narrower interval.

FIG. 3 is a diagram showing an example of the arrangement of a plurality of track surfaces in a completed system in which growth has been completed and communication service has been cut off. In FIG. 3, five track surfaces F1 to F5
Are sequentially provided at the track surface interval θ1. The arrows in the figure indicate the direction of movement of the satellite. Here, the orbital plane F1 and the orbital plane F5 adjacent to each other have opposite movement directions of the satellite.
Therefore, the track surface interval θ2 between the track surface F1 and the track surface F5 is set to a value smaller than the track surface interval θ1.

FIG. 4 is a diagram showing the orbital plane interval, the satellite interval, and the satellite elevation angle from the ground when the number of orbital planes and the number of satellites in one orbit are variously set. In the figure, column C1 indicates the number of orbital planes and the number of satellites in one orbit, column C2 indicates the total number of satellites, and column C3 indicates the orbit when the satellites are moving in the same direction on adjacent orbital planes. Indicates the spacing between the faces,
Column C4 shows the interval between the orbital planes when the satellite is moving in the opposite direction on the adjacent orbital plane, column C5 shows the satellite interval on the orbit, and column C6 shows the distance from the area located on the equator. , And column C7 indicates the lowest satellite elevation angle from an area (eg, Japan) located at latitude 35 °.

In the satellite arrangement shown in FIG. 4, the satellite altitude is set to 1400 km. Further, as described above, since the orbit set here is not a perfect polar orbit, it is inevitable that a time zone in which the satellite arrangement is sparse in a high latitude area occurs. Therefore, the orbit inclination angle is set to a predetermined negative value (-101.4 °) so that this time zone is early in the morning in the Northern Hemisphere. In this case, the satellite travels from north to south during the day and from south to north at night.

As a region where the satellite elevation angle characteristics are deteriorated, the vicinity of the equator where the interval between the orbital planes is widened is conceivable. In addition, it is necessary to consider a high latitude region in the above-mentioned time zone. In the present embodiment, the satellite arrangement is determined so that the worst satellite elevation angle near the equator and the worst satellite elevation angle in the region of latitude 50 ° are equal.

By the way, in order to arrange a plurality of track surfaces in the completed system in which the growth has been completed and the communication service has been disconnected, there is also a method as follows in addition to the arrangement method illustrated in FIG. That is, the demand for satellite utilization has a substantially constant pattern throughout the day. In the case of sun-synchronous orbit, the same orbital plane is directly above every day at almost the same local time in any region of the world. Therefore, by setting the arrangement density of the orbital plane and the arrangement density of the satellites according to the traffic demand, an efficient whole system with a small number of satellites can be constructed. The arrangement density of the orbital plane can be adjusted by the longitudinal interval of the orbital plane, and the arrangement density of the satellites can be adjusted by the satellite interval on each orbit. This will be described with reference to FIG.

FIG. 5 is a diagram showing the arrangement of a plurality of track surfaces in which the arrangement density is set according to the traffic demand. In other words, a high-density type track surface (for example, F11 to F13) is prepared for daytime use with high traffic demand, and a good communication service is secured. Then, a low-orientation type orbital surface (for example, F14 to F17) is prepared for early morning and evening when traffic demand is low, and the total number of satellites in the entire system is reduced.

More specifically, based on the orbit arrangement and the satellite arrangement shown in FIG. 4, for the daytime with high traffic demand, the orbit plane is determined by the arrangement density of, for example, "9 orbits / 14 satellites" type. Three (F11 to F13) are prepared. As a result, a satellite elevation angle of 30 ° or more can be secured for 4 to 5 hours, and a communication service with good communication quality can be provided. And for early morning and evening when traffic demand is low,
For example, four orbital planes (F14 to F17) are prepared according to an arrangement density of "5 orbital planes / 8 satellites" type. As a result, a satellite elevation angle of approximately 10 ° or more can be ensured, and the total number of satellites in the entire system can be increased from 126 (see the “number of orbital planes 9 / number of satellites 14” type in FIG. 4) to 74 (= 14 × 3 + 8 ×
4) can be reduced. In addition, satellite elevation angle 10 °
In the vicinity, there is a decrease in communication quality, such as a slight increase in the chance of communication interruption due to rainfall.However, since traffic demand is low, there is not much problem even if there is an increase in data retransmission due to a decrease in communication quality. Not be. In the figure, the space between the orbital plane F16 and the orbital plane F17 is narrowed because the directions of movement of the satellites are opposite. Also, the raceway surface F11
Between the bearing surface F17 and the bearing surface F13 and the bearing surface F1
Since the number of satellites arranged in both orbits differs from each other between four and four (14 and eight), the satellite arrangement between the two orbits does not become zigzag (staggered). Therefore, the space between the two orbital planes is reduced.

In the above-described embodiment, satellites are used for communication. However, the present invention is not limited to satellites used for communication, but may be applied to earth observation satellites, meteorological satellites, geodetic satellites, and broadcasts. It is also applicable to satellites such as satellites and navigation satellites.

[0045]

As described above, according to the present invention, a plurality of satellites are arranged at predetermined circumferential intervals on a sun-synchronous orbit. Communication traffic is not uniform during the 24 hours a day, for example, generally during the day there is high traffic density,
Low at night. If the orbit is set according to the traffic density during the day, the number of required satellites can be reduced as compared with the case where the orbit is uniformly arranged. That is, in the communication service, it is possible to cover the entire earth with a small number of satellites.

Further, such orbits are sequentially provided, and the operation of the existing satellite is started. Even in the transient state where the number of orbits of the complete system to be finally set is not reached,
Existing satellites are operable only by the narrow range of service hours. Therefore, the satellites can be effectively used even in a transient state before all the satellites have been launched, and a system with growth potential can be constructed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a diagram showing satellite elevation angle characteristics when 12 satellites are arranged at 30 ° intervals in a satellite orbit at an altitude of 1,400 km.

FIG. 3 is a diagram illustrating an example of an arrangement of a plurality of track surfaces in a completed system in which growth has been completed and communication service has been disconnected;

FIG. 4 is a diagram illustrating orbital plane intervals, satellite intervals, and satellite elevation angles from the ground when the number of orbital planes and the number of satellites in one orbit are set variously.

FIG. 5 is a diagram showing an arrangement of a plurality of track surfaces whose arrangement densities are set according to traffic demand.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Earth 2 Straight line connecting the earth and the sun 3 Orbit 4a-4d Satellite 5 Arrow (rotation direction)

Claims (5)

[Claims] 1. A sun-synchronous orbit satellite system using a sun-synchronous orbit, wherein an orbital surface is disposed at a predetermined circumferential interval on an orbit that maintains a predetermined constant angle with respect to a straight line connecting the earth and the sun. A sun-synchronous orbit satellite system having a plurality of satellites. 2. A sun-synchronous orbit satellite system using a sun-synchronous orbit, wherein each orbit plane has a predetermined orbit on a plurality of orbits which maintain different angles with respect to a straight line connecting the earth and the sun. A sun-synchronous orbit satellite system comprising a plurality of satellites each arranged at directional intervals. 3. A sun-synchronous orbit satellite system using a sun-synchronous orbit, wherein the orbital plane is placed on a first orbit that maintains a first fixed angle with respect to a straight line connecting the earth and the sun, and has a predetermined circumferential direction. A first plurality of satellites arranged at intervals, and after the first plurality of satellites are arranged and operated on the first orbit, the orbital plane is relative to a straight line connecting the earth and the sun. And a second plurality of satellites arranged at the predetermined circumferential interval on a second orbit holding a second fixed angle different from the first fixed angle. Sun-synchronous orbit satellite system. 4. In a sun-synchronous orbit satellite system using a sun-synchronous orbit, each orbital plane keeps a different angle with respect to a straight line connecting the earth and the sun, and each orbital plane has a first angle with each other.
A plurality of satellites respectively arranged at a first circumferential interval on a first plurality of orbits maintaining the angle of And a second circumferential direction different from the first circumferential interval is set on a second plurality of tracks in which each track surface holds a second angle different from the first angle. A solar-synchronous orbit satellite system, comprising: a plurality of satellites respectively arranged at intervals. 5. The first angle, the second angle, the first circumferential interval, and the second circumferential interval are set according to a time pattern in a day of the degree of satellite use demand. The satellite-synchronous orbit satellite system according to claim 4, wherein