Monitoring system, artificial satellite, and ground facility

Abstract

To enable monitoring of a monitoring object from an artificial satellite.SOLUTION: A monitoring system 100 includes an artificial satellite 101 that revolves along an orbit an integer number of times per day. The orbit is a sun synchronous orbit, an inclined orbit, and a circular orbit. The artificial satellite 101 flies over a northernmost point of the orbit at a timing when a local time of a monitoring object is 12 o'clock. The artificial satellite 101 includes: a monitoring device 102 for monitoring the monitoring object; a pointing function for changing a monitoring direction of the monitoring device; and a monitoring control device 110 that directs the monitoring direction toward the monitoring object by controlling the pointing function.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a system for monitoring objects on the Earth or in space from space.

Background Art

[0002] A system for monitoring a target area on the Earth by an artificial satellite orbiting the Earth is known. Patent Document 1 discloses a system for observing an observation target area using a plurality of observation satellite groups orbiting the Earth. The construction cost of the system increases as the number of artificial satellites used increases.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present disclosure is to enable monitoring of a monitoring target from an artificial satellite.

Means for Solving the Problems

[0006] The monitoring system of the present disclosure includes an artificial satellite that orbits an integer number of times per day. The orbit is a sun-synchronous orbit, an inclined orbit, and a circular orbit, the artificial satellite flies over the northernmost point of the orbit at the timing when the local time of the object to be monitored reaches 12:00, the artificial satellite is provided with a monitoring device for monitoring the object to be monitored, a pointing function for changing the monitoring direction of the monitoring device, and a monitoring control device that directs the monitoring direction to the object to be monitored by controlling the pointing function.

Advantages of the Invention

[0007] According to the present disclosure, it becomes possible to monitor an object to be monitored from an artificial satellite.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

Figure 22

Figure 23

Figure 24

Figure 25

Figure 26

Mode for Carrying Out the Invention

[0009] In the embodiments and the drawings, the same elements or corresponding elements are denoted by the same reference numerals. The description of the elements denoted by the same reference numerals as those described will be omitted or simplified as appropriate.

[0010] Embodiment 1. The monitoring system 100 will be described based on FIGS. 1 to 5. The monitoring system 100 is a system for monitoring objects to be monitored, such as features on the earth's surface or objects in outer space, from space under observation conditions with a high degree of freedom in the monitoring time zone and preferable observation conditions.

[0011] In Embodiment 1, values such as time, altitude, distance, or number of orbits are approximate values.

[0012] ***Description of the configuration*** Based on FIG. 1, the configuration of the monitoring system 100 will be described. The monitoring system 100 is realized by the artificial satellite 101. The number of artificial satellites 101 may be plural. The artificial satellite 101 includes a monitoring device 102, a propulsion device 103, a communication device 104, an attitude control device 105, a power supply device 106, and the like. The monitoring device 102 is mounted on the artificial satellite 101 and monitors the object to be monitored. Specifically, the monitoring device 102 is a visible optical sensor or an infrared optical sensor. However, the monitoring device 102 may be a synthetic aperture radar (SAR) or other device. "Monitoring" may be read as "observation" or "imaging". The propulsion device 103 is mounted on the artificial satellite 101 and changes the speed of the artificial satellite 101. Specifically, the propulsion device 103 is an electric propulsion engine. For example, the propulsion device 103 is an ion engine or a Hall thruster. The communication device 104 is mounted on the artificial satellite 101 and communicates monitoring data and the like. The monitoring data is data obtained by the monitoring performed by the monitoring device 102. The monitoring data corresponds to an image in which the object to be monitored is reflected. The attitude control device 105 is mounted on the artificial satellite 101 and controls attitude elements such as the attitude of the artificial satellite 101, the angular velocity of the artificial satellite 101, and the line-of-sight direction of the monitoring device 102. The attitude control device 105 changes each attitude element in a desired direction. Or, the attitude control device 105 maintains each attitude element in a desired direction. The attitude control device 105 includes an attitude sensor, an actuator, and a controller. For example, the attitude sensors are a gyroscope, an earth sensor, a sun sensor, a star tracker, a thruster, a magnetic sensor, and the like. For example, the actuators are an attitude control thruster, a momentum wheel, a reaction wheel, a control moment gyro, and the like. For example, the controller controls the actuator by executing a control program based on the measurement data of the attitude sensor or a control command from the ground facility 140. The power supply device 106 includes a solar cell, a battery, a power control device, etc., and supplies power to each device mounted on the artificial satellite 101.

[0013] The artificial satellite 101 further includes a monitoring control device 110. The monitoring control device 110 is mounted on the artificial satellite 101. The monitoring control device 110 controls the propulsion device 103, the monitoring device 102, and the attitude control device 105 so that the monitoring device 102 can monitor the monitoring target under favorable monitoring conditions for as long a time as possible. For example, the monitoring control device 110 performs various controls by executing a control program based on a control command from the ground facility 140. For example, the monitoring control device 110 is a computer.

[0014] The monitoring control device 110 includes a processing circuit 111. The processing circuit 111 may be dedicated hardware or a processor that executes a program stored in a memory. The processing circuit 111 functions as a monitoring control unit that controls the propulsion device 103. In the processing circuit 111, some functions may be realized by dedicated hardware, and the remaining functions may be realized by software or firmware. That is, the processing circuit 111 can be realized by hardware, software, firmware, or a combination thereof. The dedicated hardware is, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC, an FPGA, or a combination thereof. ASIC is an abbreviation for Application Specific Integrated Circuit. FPGA is an abbreviation for Field Programmable Gate Array.

[0015] The pointing function of the artificial satellite 101 will be described. The artificial satellite 101 has a pointing function for directing the monitoring direction of the monitoring device 102 toward the monitoring target. The pointing function is a function for changing the monitoring direction. For example, the artificial satellite 101 includes a reaction wheel. The reaction wheel is a device for controlling the attitude of the artificial satellite 101. By controlling the attitude of the artificial satellite 101 with the reaction wheel, body pointing is realized. For example, the monitoring device 102 includes a pointing mechanism. The pointing mechanism is a mechanism for changing the direction to be monitored. For example, a driving mirror or the like is used for the pointing mechanism.

[0016] The monitoring function of the monitoring device 102 will be described. The monitoring device 102 has a variable resolution function and an autofocus function. The variable resolution function is a function for changing the resolution. The autofocus function is a function for focusing.

[0017] Based on FIG. 1, the configuration of the ground facility 140 will be described. The ground equipment 140 includes a communication device 141 and a satellite control device 142, and controls the artificial satellite 101 by communicating with the artificial satellite 101. For example, the ground equipment 140 controls the monitoring and control device 110 of the artificial satellite 101. The satellite control device 142 is a computer that generates various commands for controlling the artificial satellite 101, and includes hardware such as a processing circuit and an input / output interface. The processing circuit generates various commands. An input device and an output device are connected to the input / output interface. The satellite control device 142 is connected to the communication device 141 via the input / output interface. The communication device 141 communicates with the artificial satellite 101. Specifically, the communication device 141 transmits various commands to the artificial satellite 101. In addition, the communication device 141 receives monitoring data transmitted from the artificial satellite 101. The satellite control device 142 processes the monitoring data.

[0018] ***Description of Operations*** Based on FIG. 2, the operations of the artificial satellite 101 and the monitoring and control device 110 will be described. The artificial satellite 101 orbits the Earth 120. The orbit in which the artificial satellite 101 orbits the Earth 120 is referred to as an orbital path 122. The orbital path 122 will be described later.

[0019] The case where an object existing in the target area 121 becomes a monitoring target will be described. The monitoring of the target area 121 corresponds to the monitoring of the monitoring target. However, the monitoring target may be an object existing in outer space. The monitoring and control device 110 adjusts the relative position of the artificial satellite 101 with respect to the target area 121 in the target time zone so that the time during which the artificial satellite 101 flies over the target area 121 is extended. The target area 121 is an area to be monitored. For example, the target area 121 is Japan. The target time zone is the time zone during which the target area 121 is monitored. For example, the target time zone is daytime.

[0020] Specifically, the monitoring and control device 110 controls the propulsion device 103 while the artificial satellite 101 orbits the Earth 120. For example, the monitoring and control device 110 instructs the propulsion device 103 to increase or decrease the thrust, and the propulsion device 103 increases or decreases the thrust according to the instruction. As a result, the artificial satellite 101 accelerates or decelerates. For example, the monitoring and control device 110 inputs a determined control signal to the propulsion device 103 etc. at a determined time zone by executing a monitoring and control program. Or, the monitoring and control device 110 receives control data from ground facilities via the communication device 104, and inputs a control signal to the propulsion device 103 etc. according to the control data from the ground facilities. For example, the monitoring and control device 110 controls the injection direction, injection amount, injection time, etc. of the propellant by the propulsion device 103.

[0021] Various parameters of the artificial satellite 101 are changed by the control of the monitoring and control device 110. For example, parameters such as the satellite altitude or the increase / decrease of the thrust are changed.

[0022] Based on FIG. 3, the relationship between the satellite speed and the satellite altitude will be described. The black circle marked in the Earth 120 represents the North Pole. When the flight speed of the artificial satellite 101 increases, the altitude of the artificial satellite 101 rises. And when the altitude of the artificial satellite 101 rises, the ground speed of the artificial satellite 101 decreases. When the flight speed of the artificial satellite 101 decreases, the altitude of the artificial satellite 101 descends. And when the altitude of the artificial satellite 101 descends, the ground speed of the artificial satellite 101 increases.

[0023] Based on FIG. 4, each of the orbiting orbit 122 and the monitoring will be described. Each time indicated on the Earth 120 is the Japan Standard Time (JST). The time indicated on the orbiting orbit 122 is the JST when the artificial satellite 101 passes through. The dotted arrow represents the flight range of the artificial satellite 101 in the time zone when Japan comes into view.

[0024] The circular orbit 122 is a circular orbit above the equator. For example, the artificial satellite 101 crosses directly under the sun at noon, and the artificial satellite 101 flies in the circular orbit 122. The altitude of the circular orbit 122 is 20,000 kilometers. The revolution period of the circular orbit 122 is half a day, that is, 12 hours. The artificial satellite 101 orbits the circular orbit 122 twice a day.

[0025] The monitoring device 102 continuously monitors Japan for 6 hours during the time from 9:00 to 15:00, that is, during the daytime. Based on the current state of the art, it is assumed that a telescope with a ground sampling distance (GSD) of about 5 meters from the geostationary orbit will be realized in the future. Furthermore, it is assumed that the resolution will be improved to about 3 meters by applying super-resolution technology when the same monitoring target is imaged multiple times. Then, when converted by the GSD improvement effect due to the difference in orbital altitude, the GSD will be 2.8 meters or more and 10 meters or less, and the resolution will be 1.7 meters or more.

[0026] Based on FIG. 5, the relationship between the satellite altitude and the time will be described. The shading represents the sunlight or shaded condition of the target area 121. The dashed line indicates the altitude of the artificial satellite 101 at each time.

[0027] The speed of the artificial satellite 101 is controlled by electric propulsion, and the revolution period is maintained by a combination of acceleration and deceleration, and the artificial satellite 101 orbits the circular orbit 122 twice a day. The average satellite altitude during the daytime is high, and after sunset, the artificial satellite 101 decelerates and the satellite altitude decreases. Before sunrise, the artificial satellite 101 accelerates, and the satellite altitude rises until sunrise. Since the ground speed decreases as the satellite altitude increases, the monitoring time during the daytime is extended.

[0028] ***Supplement to Embodiment 1*** Supplement to the monitoring control device 110. The "ground speed" is the orbital speed of the artificial satellite 101 relative to the rotation speed of the Earth 120. The monitoring and control device 110 controls the propulsion device 103 so that the artificial satellite 101 decelerates. The orbital altitude of the artificial satellite 101 decreases due to the deceleration of the artificial satellite 101. The ground speed of the artificial satellite 101 increases as the orbital altitude decreases. The artificial satellite 101 moves eastward relative to the monitoring target as the ground speed increases. After the artificial satellite 101 starts to move eastward relative to the monitoring target, the monitoring and control device 110 operates the monitoring device 102.

[0029] The monitoring and control device 110 controls the propulsion device 103 so that the artificial satellite 101 accelerates. The orbital altitude of the artificial satellite 101 increases due to the acceleration of the artificial satellite 101. The ground speed of the artificial satellite 101 decreases as the orbital altitude increases. The artificial satellite 101 moves westward relative to the monitoring target as the ground speed decreases. After the artificial satellite 101 starts to move westward relative to the monitoring target, the monitoring and control device 110 operates the monitoring device 102.

[0030] The monitoring and control device 110 adjusts the orbital period of the artificial satellite 101 by decelerating and accelerating the artificial satellite 101. The monitoring device 102 operates at any timing during the eastward movement of the artificial satellite 101 and at any timing during the westward movement of the artificial satellite 101. Then, the average orbital period of the artificial satellite 101 is adjusted.

[0031] The monitoring and control device 110 maintains the average relative position of the artificial satellite 101 with respect to the monitoring target by decelerating and accelerating the artificial satellite 101. The monitoring device 102 operates at any timing during the eastward movement of the artificial satellite 101 and at any timing during the westward movement of the artificial satellite 101. Then, the average relative position of the artificial satellite 101 with respect to the monitoring target is maintained.

[0032] The monitoring control device 110 adjusts the relative position of the artificial satellite 101 with respect to the object to be monitored by controlling the propulsion device 103. The time period (monitoring time period) during which the monitoring device 102 monitors the object to be monitored is changed by adjusting the relative position. The time (monitoring time) during which the artificial satellite 101 flies over the object to be monitored is extended by adjusting the relative position.

[0033] ***Effects of Embodiment 1*** Even on the premise that electric propulsion is not used, when the artificial satellite 101 flies in a phase where it crosses directly under the sun at noon, it is possible to monitor the target area 121 for 6 hours from 9:00 to 15:00, that is, during the daytime. Embodiment 1 enables further extension of the monitorable time. Also, since the altitude of the artificial satellite 101 relative to the ground is 0.6 times that of a geostationary satellite, the resolution of the monitoring device 102 is improved by 1.8 times compared to the resolution of the monitoring device of a geostationary satellite.

[0034] By controlling the pointing function of the artificial satellite 101, the line-of-sight vector, that is, the monitoring direction, can be changed. Therefore, it is possible to stare at the target area 121 or change the target area 121.

[0035] During the period from when the artificial satellite 101 rises from the horizon, passes through the sky, and sinks into the horizon as seen from the target area 121, the distance from the artificial satellite 101 to the target area 121 (distance to the ground) changes. When the artificial satellite 101 flies near the horizon, the distance to the ground is short and the perspective angle is shallow. When the artificial satellite 101 passes through the sky, the distance to the ground is long and the perspective angle is deep. By controlling the monitoring function of the monitoring device 102 according to the distance to the ground, monitoring can be performed under optimal monitoring conditions according to the distance to the ground.

[0036] ***Summary of Embodiment 1*** The monitoring control device 110 is mounted on the artificial satellite 101. The artificial satellite 101 includes a monitoring device 102 for monitoring the target area 121 and a propulsion device 103 for changing the speed of the artificial satellite 101. The monitoring control device 110 adjusts the relative position of the artificial satellite 101 with respect to the target area 121 in the target time period by controlling the propulsion device 103 while the artificial satellite 101 orbits the circular orbit 122. The monitoring time during which the artificial satellite 101 flies over the target area 121 is extended by the adjustment of the relative position.

[0037] The circular orbit 122 is a circular orbit at an altitude of 20,000 kilometers above the equator. The artificial satellite 101 orbits the circular orbit 122 twice a day.

[0038] The monitoring control device 110 increases the altitude of the artificial satellite 101 in the target time period by accelerating the artificial satellite 101 before the target time period. The monitoring time is extended by the decrease in the speed (ground speed) of the artificial satellite 101 with respect to the target area 121 as the altitude of the artificial satellite 101 increases.

[0039] The artificial satellite 101 has a pointing function. The monitoring control device 110 directs the monitoring direction of the monitoring device 102 towards the target area 121 by controlling the pointing function.

[0040] The monitoring device 102 has a variable resolution function. The monitoring control device 110 adjusts the resolution of the monitoring device 102 by controlling the monitoring device 102 according to the change in the distance from the artificial satellite 101 to the target area 121.

[0041] Embodiment 2. For the monitoring system 100, the main differences from Embodiment 1 will be described based on FIGS. 6 and 7.

[0042] In Embodiment 2, values such as time, altitude, distance, or number of orbits are approximate values.

[0043] ***Description of the Configuration*** The configuration of the monitoring system 100 is the same as the configuration in the first embodiment (see FIG. 1).

[0044] ***Description of the Operation*** The basic operations of the artificial satellite 101 and the monitoring and control device 110 are the same as the operations in the first embodiment (see FIGS. 2 and 3).

[0045] Based on FIG. 6, the circular orbit 122 and the monitoring will be described respectively. The viewing direction of FIG. 6 is the same as that of FIG. 4. The circular orbit 122 is a circular orbit above the equator. For example, the artificial satellite 101 is in a phase where it crosses directly under the sun at noon, and the artificial satellite 101 flies in the circular orbit 122. The altitude of the circular orbit 122 is 14,000 kilometers. The revolution period of the circular orbit 122 is 8 hours. The artificial satellite 101 orbits the circular orbit 122 three times a day.

[0046] The monitoring device 102 continuously monitors Japan for 4 hours from 10:00 to 14:00, that is, during the daytime. When converted by the GSD improvement effect due to the difference in orbital altitude, the GSD is 1.9 meters or more and 7 meters or less, and the resolution is 1.2 meters or more.

[0047] Based on FIG. 7, the relationship between the satellite altitude and the time will be described. The viewing direction of FIG. 7 is the same as that of FIG. 5. The speed of the artificial satellite 101 is controlled by electric propulsion, and the revolution period is maintained by a combination of acceleration and deceleration, and the artificial satellite 101 orbits the circular orbit 122 three times a day. The average satellite altitude is high during the daytime, and after sunset, the artificial satellite 101 decelerates and the satellite altitude decreases. Before sunrise, the artificial satellite 101 accelerates, and the satellite altitude rises until sunrise. Since the ground speed decreases as the satellite altitude increases, the monitoring time during the daytime is extended.

[0048] ***Effects of the Second Embodiment*** Even on the premise that electric propulsion is not used, when the artificial satellite 101 flies in a phase where it crosses directly under the sun at noon, it is possible to monitor the target area 121 for 4 hours from 10:00 to 14:00, that is, during the 4 hours of daytime. Embodiment 2 enables further extension of the monitorable time. Also, since the altitude of the artificial satellite 101 relative to the ground is 0.4 times that of a geostationary satellite, the resolution of the monitoring device 102 is improved by 2.6 times compared to that of the monitoring device of a geostationary satellite.

[0049] ***Features of Embodiment 2*** The circular orbit 122 is a circular orbit at an altitude of 14,000 kilometers above the equator. The artificial satellite 101 orbits the circular orbit 122 three times a day.

[0050] Embodiment 3. Regarding the monitoring system 100, the main differences from Embodiment 1 will be described based on FIGS. 8 and 9.

[0051] In Embodiment 3, values such as time, altitude, distance, or the number of orbits are approximate values.

[0052] ***Explanation of the Configuration*** The configuration of the monitoring system 100 is the same as the configuration in Embodiment 1 (see FIG. 1).

[0053] ***Explanation of the Operation*** The basic operations of the artificial satellite 101 and the monitoring control device 110 are the same as the operations in Embodiment 1 (see FIGS. 2 and 3).

[0054] Based on FIG. 8, the circular orbit 122 and the monitoring will be described respectively. The viewing method of FIG. 8 is the same as that of FIG. 4. The circular orbit 122 is a circular orbit above the equator. The artificial satellite 101 flies in the circular orbit 122 in a phase where it crosses directly under the sun at noon. The altitude of the circular orbit 122 is 10,000 kilometers. The revolution period of the circular orbit 122 is 6 hours. The artificial satellite 101 orbits the circular orbit 122 four times a day.

[0055] The monitoring device 102 continuously monitors Japan for 3 hours during the day, i.e., from 10:30 to 13:30. When converted by the GSD improvement effect due to the difference in orbital altitude, the GSD is 1.5 meters or more and 5 meters or less, and the resolution is 0.9 meters or more.

[0056] Based on FIG. 9, the relationship between the satellite altitude and time will be described. The viewing method of FIG. 9 is the same as that of FIG. 5. The speed of the artificial satellite 101 is controlled by electric propulsion, and the revolution period is maintained by a combination of acceleration and deceleration, and the artificial satellite 101 orbits four times a day. The average satellite altitude during the day is high. After sunset, the artificial satellite 101 decelerates and the satellite altitude decreases. Before sunrise, the artificial satellite 101 accelerates, and the satellite altitude rises until sunrise. Since the ground speed decreases as the satellite altitude increases, the monitoring time during the day is extended.

[0057] ***Effects of Embodiment 3*** Even on the premise that electric propulsion is not used, when the artificial satellite 101 flies in a phase where it crosses directly under the sun at noon, it is possible to monitor the target area 121 for 3 hours during the day, i.e., from 10:30 to 13:30. Embodiment 3 enables further extension of the monitorable time. Also, since the altitude of the artificial satellite 101 relative to the ground is 0.3 times that of a geostationary satellite, the resolution of the monitoring device 102 is improved by 3.6 times compared to that of the monitoring device of a geostationary satellite.

[0058] ***Features of Embodiment 3*** The circular orbit 122 is a circular orbit at an altitude of 10,000 kilometers above the equator. The artificial satellite 101 flies in a phase where it crosses directly under the sun at noon and orbits the circular orbit 122 four times a day.

[0059] Embodiment 4. For the monitoring system 100, the differences mainly from Embodiment 1 will be described with reference to FIGS. 10 and 11.

[0060] In Embodiment 4, values such as time, altitude, distance, or number of orbits are approximate values.

[0061] ***Description of the configuration*** The configuration of the monitoring system 100 is the same as the configuration in Embodiment 1 (see FIG. 1).

[0062] ***Description of the operation*** The basic operations of the artificial satellite 101 and the monitoring and control device 110 are the same as the operations in Embodiment 1 (see FIGS. 2 and 3).

[0063] Based on FIG. 10, the circular orbit 122 and the monitoring will be described respectively. The viewing method of FIG. 10 is the same as that of FIG. 4. The circular orbit 122 is a circular orbit above the equator. The artificial satellite 101 flies in the circular orbit 122 at a phase where it crosses directly behind the Earth 120 at noon. The altitude of the circular orbit 122 is 10,000 kilometers. The revolution period of the circular orbit 122 is 6 hours. That is, the artificial satellite 101 orbits the circular orbit 122 four times a day.

[0064] The monitoring device 102 continuously monitors Japan from 7:30 to 9:30 and from 14:30 to 16:30. That is, the monitoring device 102 performs two continuous monitoring sessions of 2 hours during the day. When converted by the GSD improvement effect due to the difference in orbital altitude, the GSD is 1.5 meters or more and 5 meters or less, and the resolution is 0.9 meters or more.

[0065] Based on FIG. 11, the relationship between the satellite altitude and time will be described. The viewing method of FIG. 11 is the same as that of FIG. 5. The speed of the artificial satellite 101 is controlled by electric propulsion, and the revolution period is maintained by a combination of acceleration and deceleration, and the artificial satellite 101 orbits four times a day. The average satellite altitude during the day is low, and the artificial satellite 101 accelerates after sunset to increase the satellite altitude. The artificial satellite 101 decelerates before sunrise, and the satellite altitude drops until sunrise. Since the ground speed increases as the satellite altitude decreases, monitoring is possible during two orbits during the day. The (total) monitoring time during the day is extended. Note that even when the sun 123 illuminates the target area 121, the artificial satellite 101 cannot monitor the target area 121 while it is located below the horizon. Therefore, the continuous monitoring time per time is shorter than the continuous monitoring time in Embodiment 3.

[0066] ***Effects of Embodiment 4*** Even on the premise that electric propulsion is not used, when the artificial satellite 101 flies in a phase where it crosses the exact opposite side of the Earth 120 at noon, two-time monitoring from 7:30 to 9:30 and from 14:30 to 16:30 is possible. Embodiment 4 enables two-time monitoring in two time zones close to noon. In addition, since the altitude of the artificial satellite 101 relative to the ground is 0.3 times the altitude of the geostationary satellite relative to the ground, the resolution of the monitoring device 102 is improved by 3.6 times compared to the resolution of the monitoring device of the geostationary satellite.

[0067] ***Features of Embodiment 4*** The orbiting orbit 122 is a circular orbit at an altitude of 10,000 kilometers above the equator. The artificial satellite 101 flies in a phase where it crosses the exact opposite side of the Earth 120 at noon and orbits the orbiting orbit 122 four times a day.

[0068] The monitoring control device 110 lowers the altitude of the artificial satellite 101 in the target time zone by decelerating the artificial satellite 101 before the target time zone. The number of orbits of the artificial satellite 101 in the target time zone becomes two or more as the ground speed of the artificial satellite 101 increases with the decrease in the altitude of the artificial satellite 101. The monitoring time is extended when the number of orbits of the artificial satellite in the target time period is two or more.

[0069] Embodiment 5. For the monitoring system 100, the main differences from Embodiment 1 will be described based on FIGS. 12 to 14.

[0070] In Embodiment 5, values such as time, altitude, distance, or the number of orbits are approximate values.

[0071] ***Description of the configuration*** The configuration of the monitoring system 100 is the same as the configuration in Embodiment 1 (see FIG. 1).

[0072] ***Description of the operation*** The basic operations of the artificial satellite 101 and the monitoring and control device 110 are the same as the operations in Embodiment 1 (see FIGS. 2 and 3).

[0073] The orbiting orbit 122 and the monitoring will be described respectively. The orbiting orbit 122 is a sun-synchronous inclined circular orbit. That is, the orbiting orbit 122 is a sun-synchronous orbit, an inclined orbit, and a circular orbit. The artificial satellite 101 is a satellite flying in a sun-synchronous orbit (sun-synchronous satellite). The orbital inclination angle of the orbiting orbit 122 is 30 degrees or more and 60 degrees or less. The orbiting orbit 122 is an orbit at LST 12:00. LST means local standard time. The artificial satellite 101 flies over the northernmost point of the orbiting orbit 122 at the timing when the local time of the target area 121 is 12 o'clock. The number of orbits of the artificial satellite 101 is an integer number per day. The monitoring and control device 110 controls the pointing function. Thereby, the condition that the target area 121 is visible for 10 minutes or more is satisfied.

[0074] Based on FIG. 12, a specific example of the circular orbit 122 will be described. The viewing direction of FIG. 12 is the same as that of FIG. 4. However, each time shown in FIG. 12 is the local standard time (LST) of the target area 121. The orbital altitude is 5,144 kilometers. The orbital inclination angle is 141.6 degrees. The revolution period is 3.4 hours. The artificial satellite 101 orbits the circular orbit 122 seven times a day. The monitoring range is from 38 degrees north latitude to 38 degrees south latitude. The monitoring device 102 continuously monitors the target area 121 for 0.75 hours from 7:45 to 8:30, 1.5 hours from 11:15 to 12:45, and 0.75 hours from 15:30 to 16:15. That is, the monitoring device 102 performs continuous monitoring for about 10 minutes or more three times during the day and monitors the target area 121 for about 3 hours during the day. However, when the target area 121 is Japan, the artificial satellite 101 in the orbital plane does not always fly over Japan by chance. Therefore, the time zone in which Japan can be monitored may deviate from the above time.

[0075] When the phase position of the artificial satellite 101 in the orbital plane is far from the target area 121, even if the sunlight conditions in the orbital plane are maintained, the monitoring conditions for the target area 121 are poor. Therefore, in order to enable monitoring of the target area 121 under suitable conditions, the monitoring control device 110 controls the thrust of the propulsion device 103 to bring the phase position of the artificial satellite 101 closer to the target area 121. Then, the monitoring control device 110 controls the thrust of the propulsion device 103 in the direction opposite to the controlled thrust direction. As a result, since the average orbital conditions are maintained, the sun-synchronous conditions are maintained. And continuous monitoring becomes possible.

[0076] Supplement to the circular orbit 122. Since the number of orbits of the artificial satellite 101 depends on the satellite altitude, once the number of orbits is determined, the satellite altitude is uniquely determined. For example, when the number of orbits of the artificial satellite 101 is seven orbits per day, the satellite altitude is 5,144 kilometers. The solar synchronous condition is caused by the uneven distribution of gravity associated with the oblate shape of the Earth 120 and is uniquely determined based on the correlation between the satellite altitude and the orbital inclination angle. When the satellite altitude is 5144 kilometers, the orbit with an orbital inclination angle of 141.6 degrees becomes a sun-synchronous orbit. When the orbital inclination angle is 141.6 degrees, the orbital plane is inclined 38.4 degrees (= 180 - 141.6) from the equator. Therefore, the artificial satellite 101 flies in the latitude range from +38 degrees to -38 degrees with respect to the Earth 120. The monitoring and control device 110 controls the monitoring direction in the latitude direction. As a result, it becomes possible for the monitoring device 102 to monitor the Earth 120 within the latitude range from +60 degrees to -60 degrees. If the circular orbit 122 has a solar incidence angle of LST 12:00, the Northern Hemisphere is always in sunlight on the orbital plane of the circular orbit 122. And the artificial satellite 101 will fly over the area at 38 degrees north latitude at the northernmost point of the circular orbit 122.

[0077] Based on FIG. 13, supplements regarding monitoring will be provided. If the target area 121 of the Earth 120 is in a sunlight state, the latitude of the northernmost point on the circular orbit 122 is near the latitude of the target area 121, and the artificial satellite 101 passes over the target area 121, monitoring can be performed under favorable conditions.

[0078] The circular orbit 122 may be an elliptical orbit with an eccentricity instead of a circular orbit. Even if the circular orbit 122 is an elliptical orbit, it is possible to realize the artificial satellite 101 that satisfies the solar synchronous condition.

[0079] ***Effects of Embodiment 5*** In a sun-synchronous orbit, the incident angle of sunlight with respect to the orbital plane is maintained substantially constant regardless of the passage of time and seasons. For example, for the purpose of monitoring near latitude 40 degrees, if the orbital plane is set so that the artificial satellite 101 flies directly above the target area 121 at 12:00, it is possible to maintain an orbit in which the artificial satellite 101 stays near 40 degrees north latitude during sunlight hours. Since the altitude of the artificial satellite 101 relative to the Earth is 0.14 times that of a geostationary satellite, the resolution of the monitoring device 102 is improved by a factor of 7 compared to that of the monitoring device of a geostationary satellite. Since the monitoring device of a geostationary satellite performs oblique monitoring of the vicinity of 40°N latitude, its resolution decreases. However, since the monitoring device 102 can perform nadir viewing of the vicinity of 40°N latitude, its resolution does not decrease.

[0080] ***Description of Embodiment*** Based on FIG. 14, an example of the circular orbit 122 will be described. The altitude of the circular orbit 122 is 4,163 kilometers. The orbital inclination angle of the circular orbit 122 is 125 degrees. The artificial satellite 101 orbits the circular orbit 122 eight times a day. Thereby, an orbital plane is realized in which the artificial satellite 101 flies in the range from +55°N latitude to -55°N latitude. And it becomes possible to continuously monitor the target area 121 for 0.75 hours from 8:15 to 9:00, 1.5 hours from 11:15 to 12:45, and 0.75 hours from 15:00 to 15:45. That is, it becomes possible to perform continuous monitoring for about 10 minutes or more three times during the day, and to perform monitoring for about 3 hours in total.

[0081] Even if the number of orbits per day is not an integer, the circular orbit 122, which is a sun-synchronous orbit, is realized by the following combinations. Assume that the circular orbit 122 is a circular orbit. (1) The orbital altitude is 4,000 kilometers. The orbital inclination angle is 123 degrees. The artificial satellite 101 flies in the range from +57° latitude to -57° latitude. The artificial satellite 101 orbits the circular orbit 122 eight times a day. The artificial satellite 101 orbits the circular orbit 122 once in 3 hours. (2) The orbital altitude is 4,500 kilometers. The orbital inclination angle is 130 degrees. The artificial satellite 101 flies in the range from +50° latitude to -50° latitude. The artificial satellite 101 orbits the circular orbit 122 seven to eight times a day. The artificial satellite 101 orbits the circular orbit 122 once in 3 to 4 hours. (3) The orbital altitude is 5,000 kilometers. The orbital inclination angle is 139 degrees. The artificial satellite 101 flies in the range from latitude +41 degrees to latitude -41 degrees. The artificial satellite 101 orbits the circular orbit 122 7 to 8 times a day. The artificial satellite 101 orbits the circular orbit 122 once in 3 to 4 hours. (4) The orbital altitude is 5,500 kilometers. The orbital inclination angle is 151 degrees. The artificial satellite 101 flies in the range from latitude +29 degrees to latitude -29 degrees. The artificial satellite 101 orbits the circular orbit 122 7 times a day. The artificial satellite 101 orbits the circular orbit 122 once in 4 hours. (1) to (4) The orbital plane of the circular orbit 122 is the orbital plane at LST 12:00, and the northernmost end is at noon. However, since the artificial satellite 101 does not necessarily fly at the northernmost end at 12:00, the times when the artificial satellite 101 passes through the northernmost end of the orbital plane will be around each other.

[0082] ***Features of Embodiment 5*** The monitoring system 100 includes an artificial satellite 101 that orbits the circular orbit 122 an integer number of times a day. The circular orbit 122 is a sun-synchronous orbit, an inclined orbit, and a circular orbit. The artificial satellite 101 flies over the northernmost point of the circular orbit 122 at the timing when the local time of the target area 121 is 12:00.

[0083] Embodiment 6. Regarding the monitoring system 100, the main differences from Embodiment 1 will be described.

[0084] In Embodiment 6, values such as time, altitude, distance, or number of orbits are approximate values.

[0085] ***Description of the Configuration*** The configuration of the monitoring system 100 is the same as the configuration in Embodiment 1 (see Fig. 1).

[0086] ***Description of the Operation*** The basic operations of the artificial satellite 101 and the monitoring and control device 110 are the same as those in the first embodiment (see FIGS. 2 and 3).

[0087] The orbiting orbit 122 will be described. The orbiting orbit 122 is a sun-synchronous inclined elliptical orbit. That is, the orbiting orbit 122 is a sun-synchronous orbit and an inclined orbit. Furthermore, the orbiting orbit 122 is an elliptical orbit with a high eccentricity. The orbital altitude is 5100 kilometers. The orbital semi-major axis is 11478 kilometers. The eccentricity is 0.418. The orbital inclination angle is 121.88 degrees. The apogee altitude is 9898 kilometers. The perigee altitude is 302 kilometers.

[0088] The orbiting orbit 122 is an orbit at LST 12:00. The artificial satellite 101 flies through the perigee of the orbiting orbit 122 at the timing when the local time of the target area 121 becomes 12:00. The perigee of the orbiting orbit 122 is the northernmost point of the orbiting orbit 122.

[0089] ***Effects of the Sixth Embodiment*** By flying the artificial satellite 101 in the orbiting orbit 122, the condition that the target area 121 is visible for 10 minutes or more is satisfied.

[0090] ***Features of the Sixth Embodiment*** The orbiting orbit 122 is a sun-synchronous orbit, an inclined orbit, and an elliptical orbit. The artificial satellite 101 flies through the perigee of the orbiting orbit 122 at the timing when the local time of the target area 121 becomes 12:00.

[0091] Seventh Embodiment. The satellite constellation 130 will be mainly described based on FIGS. 15 to 20, focusing on the differences from the first embodiment.

[0092] In Embodiment 7, values such as time, altitude, distance, or number of orbits are approximate values.

[0093] ***Description of Configuration*** The configuration of the monitoring system 100 is the same as the configuration in Embodiment 1 (see FIG. 1).

[0094] Based on FIGS. 15 to 19, the configuration of the satellite constellation 130 will be described. FIG. 15 shows the satellite constellation 130 as viewed from the normal direction of the orbital plane. FIG. 16 shows the satellite constellation 130 as viewed from the orbital plane. For example, FIG. 16 shows the satellite constellation 130 as viewed from above the equator. FIGS. 17, 18, and 19 show the state in which the major axes of the elliptical orbits of the respective artificial satellites (101A to 101C) rotate around the Earth 120 in the orbital plane. Each artificial satellite (101A to 101C) is the same type of artificial satellite as the artificial satellite 101.

[0095] Each artificial satellite (101A to 101C) orbits a sun-synchronous inclined elliptical orbit. Monitoring of the Northern Hemisphere during the day is maintained by three artificial satellites (101A to 101C).

[0096] The orbits of the respective artificial satellites (101A to 101C) are non-frozen orbits. That is, the orbits of the respective artificial satellites (101A to 101C) are not frozen orbits, and the major axis rotates around the Earth 120 over time.

[0097] The three artificial satellites (101A to 101C) alternately monitor the target area 121 of the Earth 120 from the perigee, apogee, or midpoint. The midpoint is a point located between the perigee and the apogee. At the perigee, monitoring can be performed with high resolution although for a short time. At the apogee, monitoring can be performed for a long time although with low resolution.

[0098] The major axis of each of the three orbits is inclined, being shifted by 120 degrees from one another in the circumferential direction, i.e., the latitude direction, centered on the Earth 120. That is, the three major axes of the orbits are arranged at equal intervals in the latitude direction. The major axis of each orbit rotates with respect to the sun 123, but the relative relationship of the three orbits is maintained.

[0099] In the three orbits, the relative relationship between the normal direction and the solar incident angle is maintained.

[0100] At 12:00 noon, the phase of each artificial satellite (101A to 101C) has no correlation with the latitude of the target area 121 of the Earth 120.

[0101] One of the three artificial satellites (101A to 101C) can monitor the target area 121 of the Earth 120. And the three artificial satellites can continuously monitor the target area 121.

[0102] When each artificial satellite (101A to 101C) passes over the target area 121 of the Earth 120 on the apogee side, each artificial satellite can monitor the target area 121 of the Earth 120 for a long time, although with low resolution. When each artificial satellite passes over the target area 121 of the Earth 120 on the perigee side, each artificial satellite can monitor the target area 121 of the Earth 120 with high resolution for a short time.

[0103] Specific examples of the orbits of each artificial satellite (101A to 101C) are as follows. The altitude of the circular orbit that is the basis of the elliptical orbit is 5,100 kilometers. The eccentricity of the elliptical orbit is 0.418. The orbital inclination angle is 122 degrees. The apogee altitude is 9,898 kilometers. The perigee altitude is 302 kilometers.

[0104] Based on FIG. 20, the relationship between altitude and latitude of the orbit of each artificial satellite (101A to 101C) will be described. The dotted line represents the orbit of the artificial satellite 101A. The dashed-dotted line represents the orbit of the artificial satellite 101B. The dashed line represents the orbit of the artificial satellite 101C.

[0105] "Ha" is the perigee altitude, and "Hc" is the constant perigee utilization altitude. The constant perigee utilization altitude is an altitude at which at least one of the three artificial satellites (101A to 101C) can monitor the target area 121 from the perigee side. "Hb" is the apogee altitude, and "Hd" is the constant apogee utilization altitude. The constant apogee utilization altitude is an altitude at which at least one of the three artificial satellites (101A to 101C) can monitor the target area 121 from the apogee side. Each utilization altitude (Hd, Hc) corresponds to the altitude of the intersection of the two orbits in the graph of FIG. 20.

[0106] The length of time that each artificial satellite (101A to 101C) stays over the target area 121 is referred to as the stay time of the artificial satellite. On the apogee side, the stay time of each artificial satellite is long, and the field of view range of each artificial satellite is wide. The utilization altitude Hb and the viewing angle of the monitoring device 102 are each determined so that the target area 121 is within the field of view range when each artificial satellite (101A to 101C) is flying at an altitude higher than the utilization altitude Hd. Thereby, constant monitoring of the target area 121 becomes possible. On the perigee side, the stay time of each artificial satellite (101A to 101C) is short, so the monitoring on the perigee side does not have constancy. However, no matter what latitude the target area 121 is at, at least one of the artificial satellites can monitor the target area 121 from an altitude lower than the utilization altitude Hc.

[0107] The resolution of the monitoring device 102 is determined so that a desired resolution is achieved at the utilization altitude Hc. Thereby, it becomes possible to monitor the target area 121 with high resolution.

[0108] ***Effects of Embodiment 7*** Since the three artificial satellites (101A to 101C) stay near the apogee alternately for a long time, continuous monitoring is possible. High-resolution observation is possible by the artificial satellite passing near the perigee among the three artificial satellites.

[0109] ***Features of Embodiment 7*** The satellite constellation 130 includes three artificial satellites (101A to 101C). The orbit 122 of each artificial satellite is a sun-synchronous orbit, an inclined orbit, and an elliptical orbit. The three orbits 122 of the three artificial satellites are arranged such that the major axes of the orbits are shifted by 120 degrees each in the latitude direction and inclined.

[0110] Embodiment 8. Regarding the monitoring system 100, the differences mainly from Embodiment 1 will be described based on FIG. 21.

[0111] In Embodiment 8, values such as time, altitude, distance, or number of orbits are approximate values.

[0112] ***Description of Configuration*** The configuration of the monitoring system 100 is the same as the configuration in Embodiment 1 (see FIG. 1).

[0113] ***Description of Operation*** The respective basic operations of the artificial satellite 101 and the monitoring and control device 110 are the same as the operations in Embodiment 1 (see FIGS. 2 and 3).

[0114] Based on FIG. 21, a specific example of the orbit 122 will be described. The solid curve shown on the map represents the orbit 122. The orbit 122 is an inclined elliptical orbit. The perigee altitude is 7000 kilometers. The apogee altitude is 34000 kilometers. The orbit inclination angle is in the range of 20 degrees to 60 degrees. The revolution period is 12 hours. The artificial satellite 101 orbits the circular orbit 122 twice a day. In the monitoring of apogee utilization, the monitoring device 102 can monitor Japan for 6 hours from 9:00 to 15:00. The GSD is 5 meters or more and 17 meters or less.

[0115] ***Effects of Embodiment 8*** It is possible to continuously monitor the sky above the target area 121 for 6 hours during the day. It is possible to directly view the target area 121 from the apogee at an altitude of 34,000 kilometers. On the way from the horizon to the apogee and on the way from the apogee to the horizon, as the artificial satellite 101 moves away from the apogee, the ground distance becomes smaller, enabling high-resolution monitoring. It is possible to continuously monitor the target area 121 with only one artificial satellite 101 for 6 hours from 9:00 am to 3:00 pm, which is frequently used in monitoring by a visible telescope.

[0116] An orbital inclination angle of about 35 to 40 degrees is suitable for monitoring Japan, China, the Korean Peninsula, etc. On the other hand, an orbital inclination angle of about 50 degrees is suitable for monitoring major European countries, and an orbital inclination angle of about 60 degrees is suitable for monitoring northern Europe. Also, an orbital inclination angle of about 20 to 30 degrees is suitable for monitoring northern Africa, the Middle East, India, etc.

[0117] ***Features of Embodiment 8*** The monitoring control device 110 is mounted on the artificial satellite 101 orbiting the circular orbit 122. The circular orbit 122 is an elliptical orbit and an inclined orbit. The monitoring control device 110 controls the propulsion device 103 while the artificial satellite 101 orbits the circular orbit 122, causing the artificial satellite 101 to fly over the sky of the target area 121 at the apogee of the circular orbit 122.

[0118] The perigee altitude of the circular orbit 122 is 7,000 kilometers. The apogee altitude of the circular orbit 122 is 34,000 kilometers. The artificial satellite 101 orbits the circular orbit 122 twice a day.

[0119] Embodiment 9. For the monitoring system 100, the differences mainly from Embodiment 1 will be described based on FIG. 22.

[0120] In Embodiment 9, values such as time, altitude, distance, or number of orbits are approximate values.

[0121] ***Description of the configuration*** The configuration of the monitoring system 100 is the same as the configuration in Embodiment 1 (see FIG. 1).

[0122] ***Description of the operation*** The respective basic operations of the artificial satellite 101 and the monitoring and control device 110 are the same as the operations in Embodiment 1 (see FIGS. 2 and 3).

[0123] Based on FIG. 22, a specific example of the circular orbit 122 will be described. The solid curve shown on the map represents the circular orbit 122. The circular orbit 122 is an inclined elliptical orbit. The perigee altitude is 4,000 kilometers. The apogee altitude is 25,000 kilometers. The orbit inclination angle ranges from 20 degrees to 60 degrees. The revolution period is 8 hours. The artificial satellite 101 orbits the circular orbit 122 three times a day. In the monitoring of apogee utilization, the monitoring device 102 can monitor Japan for 4 hours from 10:00 to 14:00. The GSD is 3.4 meters or more and 12 meters or less.

[0124] ***Effects of Embodiment 9*** It is possible to continuously monitor the sky over the target area 121 for 4 hours during the day. It is possible to directly view the target area 121 from an apogee at an altitude of 25,000 kilometers. On the way from the horizon to the apogee and on the way from the apogee to the horizon, as the artificial satellite 101 moves farther from the apogee, the ground distance becomes smaller, enabling high-resolution monitoring. It is possible to continuously monitor the target area 121 with two artificial satellites 101 for 6 hours from 9:00 am to 3:00 pm, which is frequently used for monitoring with a visible telescope.

[0125] ***Features of Embodiment 9*** The perigee altitude of the circular orbit 122 is 4,000 kilometers. The apogee altitude of the circular orbit 122 is 25,000 kilometers. The artificial satellite 101 orbits the circular orbit 122 three times a day.

[0126] Embodiment 10. Regarding the monitoring system 100, the differences mainly from Embodiment 1 will be described based on FIG. 23.

[0127] In Embodiment 10, values such as time, altitude, distance, or number of orbits are approximate values.

[0128] ***Description of the Configuration*** The configuration of the monitoring system 100 is the same as the configuration in Embodiment 1 (see FIG. 1).

[0129] ***Description of the Operation*** The basic operations of the artificial satellite 101 and the monitoring control device 110 are the same as the operations in Embodiment 1 (see FIGS. 2 and 3).

[0130] Based on FIG. 23, a specific example of the circular orbit 122 will be described. The solid curve shown on the map represents the circular orbit 122. The circular orbit 122 is an inclined elliptical orbit. The perigee altitude is 1,700 kilometers. The apogee altitude is 17,000 kilometers. The orbital inclination angle ranges from 20 degrees to 60 degrees. The revolution period is 6 hours. The artificial satellite 101 orbits the circular orbit 122 four times a day. In the monitoring of apogee utilization, the monitoring device 102 can monitor Japan for 2 hours from 11:00 to 13:00. The GSD is 2.6 meters or more and 9 meters or less.

[0131] ***Effects of Embodiment 10*** It is possible to continuously monitor the sky above the target area 121 for 2 hours during the day. It is possible to view the target area 121 directly below from the apogee at an altitude of 17,000 kilometers. On the way from the horizon to the apogee and on the way from the apogee to the horizon, as the artificial satellite 101 moves away from the apogee, the ground distance decreases, enabling high-resolution monitoring. It is possible to continuously monitor the target area 121 with three artificial satellites 101 for 6 hours from 9:00 am to 3:00 pm, which is frequently used in monitoring with a visible telescope.

[0132] ***Features of Embodiment 10*** The perigee altitude of the circular orbit 122 is 1,700 kilometers. The apogee altitude of the circular orbit 122 is 17,000 kilometers. The artificial satellite 101 orbits the circular orbit 122 four times a day.

[0133] Embodiment 11. Regarding the monitoring system 100, the main differences from Embodiment 1 will be described based on FIGS. 24 to 26.

[0134] In Embodiment 11, values such as time, altitude, distance, or number of orbits are approximate values.

[0135] ***Description of the Configuration*** The configuration of the monitoring system 100 is the same as the configuration in Embodiment 1 (see FIG. 1).

[0136] ***Description of Operations*** The basic operations of the artificial satellite 101 and the monitoring and control device 110 are the same as those in the first embodiment (see FIGS. 2 and 3).

[0137] Based on FIG. 24, a specific example of the circular orbit 122 will be described. The solid curve shown on the map represents the circular orbit 122. The circular orbit 122 is an inclined elliptical orbit. The perigee altitude is 2,000 kilometers. The apogee altitude is 19,000 kilometers. The revolution period is 6 hours. The artificial satellite 101 orbits the circular orbit 122 four times a day. In the monitoring of perigee utilization, the monitoring device 102 can monitor Japan for one hour from 11:30 to 12:30. The GSD is 0.3 meter or more and 1.1 meter or less. The resolution is 0.2 meter or more.

[0138] Based on FIG. 25, a specific example of the circular orbit 122 will be described. The solid curve shown on the map represents the circular orbit 122. The circular orbit 122 is an inclined elliptical orbit. The perigee altitude is 4,000 kilometers. The apogee altitude is 25,000 kilometers. The revolution period is 8 hours. The artificial satellite 101 orbits the circular orbit 122 three times a day. In the monitoring of perigee utilization, the monitoring device 102 can monitor Japan for one hour from 11:30 to 12:30. The GSD is 0.6 meter or more and 2.1 meters or less. The resolution is 0.6 meter or more and 2.1 meters or less.

[0139] Based on FIG. 26, a specific example of the circular orbit 122 will be described. The solid curve shown on the map represents the circular orbit 122. The circular orbit 122 is an inclined elliptical orbit. The perigee altitude is 7,000 kilometers. The apogee altitude is 34,000 kilometers. The revolution period is 12 hours. The artificial satellite 101 orbits the circular orbit 122 twice a day. In the monitoring of perigee utilization, the monitoring device 102 can monitor Japan for 2 hours from 11:00 to 13:00. The GSD is 1 meter or more and 4 meters or less. The resolution is 0.6 meter or more.

[0140] ***Effects of Embodiment 11*** By the monitoring device 102 monitoring the target area 121 at the perigee, monitoring with significantly higher resolution than stationary observation becomes possible. The artificial satellite 101 flies across the sky of Asia including Japan and China. And during the day, the artificial satellite 101 has the opportunity to visit the Asian sky two or more times.

[0141] ***Features of Embodiment 11*** The monitoring control device 110 is mounted on the artificial satellite 101 orbiting the circular orbit 122. The circular orbit 122 is an elliptical orbit and an inclined orbit. The monitoring control device 110 controls the propulsion device 103 while the artificial satellite 101 orbits the circular orbit 122, causing the artificial satellite 101 to fly over the target area 121 at the perigee of the circular orbit 122.

[0142] ***Supplementary Explanation of Embodiment*** Each embodiment is an example of a preferred form and is not intended to limit the technical scope of the present disclosure. Each embodiment may be implemented partially or in combination with other forms.

Explanation of Reference Numerals

[0143] 100 Monitoring system, 101 Artificial satellite, 102 Monitoring device, 103 Propulsion device, 104 Communication device, 105 Attitude control device, 106 Power supply device, 110 Monitoring and control device, 111 Processing circuit, 120 Earth, 121 Target area, 122 Orbit, 123 Sun, 130 Satellite constellation, 140 Ground equipment, 141 Communication device, 142 Satellite control device.

Claims

1. Equipped with an artificial satellite that orbits an integral number of times per day, the orbit is a sun-synchronous orbit, an inclined orbit, and a circular orbit; The artificial satellite flies at the northernmost point of the orbit at a timing when the local time of the monitored object is 12:00, The artificial satellite, A monitoring device for monitoring the monitoring target; a pointing function for changing the monitoring direction of the monitoring device; a monitoring control device that controls the pointing function to direct the monitoring direction toward the monitoring target. Surveillance system.

2. Equipped with orbiting satellites, the orbit is a sun-synchronous orbit, an inclined orbit, and an elliptical orbit; The satellite flies through the perigee of the orbit at a timing when the local time of the monitored object is 12:00, The artificial satellite, A monitoring device for monitoring the monitoring target; a pointing function for changing the monitoring direction of the monitoring device; a monitoring control device that controls the pointing function to direct the monitoring direction toward the monitoring target. Surveillance system.

3. Equipped with three artificial satellites, The orbit of each artificial satellite is a sun-synchronous orbit, an inclined orbit, and an elliptical orbit; The three orbits of the three artificial satellites are arranged such that the major axes of the orbits are inclined at an angle of 120 degrees in the latitudinal direction, Each satellite, A monitoring device for monitoring a monitoring target; a pointing function for changing the monitoring direction of the monitoring device; a monitoring control device that controls the pointing function to direct the monitoring direction toward the monitoring target. Surveillance system.

4. A satellite constituting the monitoring system according to any one of claims 1 to 3.

5. A ground facility that controls the monitoring system according to any one of claims 1 to 3.

Images