Artificial object identification method and observation satellite

Abstract

To identify an artificial object among space objects flying in or near a geosynchronous orbit.SOLUTION: An artificial object identification device 123 receives imaging data at each time point from an observation satellite 200 which performs forward-looking imaging while relatively moving eastward with respect to a space object on a geosynchronous orbit by flying at an altitude lower than the altitude of the geosynchronous orbit, specifies the space object that was not imaged before 12 o'clock but was imaged after 12 o'clock on the basis of the imaging data at each time point, and identifies the specified space object as an artificial object.SELECTED DRAWING: Figure 39

Description

[Technical field]

[0001] The present invention relates to a technique for observing space objects such as space debris. [Background technology]

[0002] As debris increases, the risk of collisions with space objects increases. If space objects flying in geostationary orbit can be observed by satellites flying close to the geostationary orbit, such observations will be effective in risk management such as collision avoidance. When observations are conducted using optical observation equipment, the optical observation equipment observes the sunlight reflected from the observation target, so the relative positions of the sun, observation satellite, and observation target are one of the constraints.

[0003] A satellite called a geostationary satellite orbits the Earth in sync with the Earth's rotation, so when viewed from the Earth's surface, the satellite appears to be stationary. Therefore, the relative positions of the sun and the geostationary satellite depend on time.

[0004] Patent Document 1 discloses a method for observing space debris in a space where sunlight is backlit. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2011-218834 A [Patent Document 2] U.S. Patent No. 5,927,652 [Patent Document 3] US Patent Application Publication No. 2011 / 0226907 Summary of the Invention [Problem to be solved by the invention]

[0006] The method of Patent Document 1 requires a laser transmitter for irradiating the space debris with a laser beam in addition to a camera. Furthermore, an optical filter for blocking sunlight must be placed in front of the camera lens. Therefore, it is difficult to miniaturize the observation satellite using the method of Patent Document 1. It is also difficult to reduce the cost of the observation satellite.

[0007] The present disclosure aims to make it possible to identify artificial objects among space objects flying in or near geostationary orbit. [Means for solving the problem]

[0008] The artificial object identification method of the present disclosure includes: An artificial object identification device receives photographing data at each time from an observation satellite that performs forward-looking photographing while moving eastward relative to space objects in geostationary orbit by flying at an altitude lower than that of a geostationary orbit, and identifies space objects that were photographed after 12 o'clock but not before 12 o'clock based on the photographing data at each time, and identifies the identified space objects as artificial objects. Effect of the Invention

[0009] According to the present disclosure, it becomes possible to identify artificial objects among space objects flying in or near geostationary orbit. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 shows a configuration of an observation system 100 according to the first embodiment. [Diagram 2] FIG. 2 is a configuration diagram of an observation satellite 200 according to the first embodiment. [Diagram 3] FIG. 2 is a diagram showing Example 1(1) of the observation method according to the first embodiment. [Figure 4] FIG. 13 is a diagram showing Example 1(2) of the observation method according to the first embodiment. [Diagram 5] FIG. 11 is a diagram showing Example 1(3) of the observation method according to the first embodiment. [Figure 6]FIG. 13 is a diagram showing Example 1(4) of the observation method according to the first embodiment. [Figure 7] FIG. 13 is a diagram showing Example 1(5) of the observation method according to the first embodiment. [Figure 8] FIG. 11 is a diagram showing Example 2(1) of the observation method according to the first embodiment. [Figure 9] FIG. 13 is a diagram showing Example 2(2) of the observation method according to the first embodiment. [Figure 10] FIG. 11 is a diagram showing Example 2(3) of the observation method according to the first embodiment. [Figure 11] FIG. 13 is a diagram showing Example 2(4) of the observation method according to the first embodiment. [Figure 12] FIG. 13 is a diagram showing Example 2(5) of the observation method according to the first embodiment. [Figure 13] FIG. 11 is a diagram showing an observation state by an observation satellite 200 in the second embodiment. [Figure 14] 11 is a table showing a profile of a parking trajectory in the second embodiment. [Figure 15] 11 is a table showing the relationship between the orbital inclination angle and the maximum distance to the geostationary orbit 103 in the second embodiment. [Figure 16] FIG. 11 is a diagram showing an observation state by an observation satellite 200 in the second embodiment. [Figure 17] FIG. 11 is a diagram showing an observation state by an observation satellite 200 in the second embodiment. [Figure 18] FIG. 11 is a diagram showing an observation state by an observation satellite 200 in the second embodiment. [Figure 19] FIG. 11 is a diagram showing an observation state by an observation satellite 200 in the second embodiment. [Figure 20] FIG. 11 is a diagram showing a parking operation in the second embodiment. [Figure 21] FIG. 11 is a diagram showing a spiral operation in the second embodiment. [Figure 22] FIG. 11 is a diagram showing an observation state by an observation satellite 200 in the third embodiment. [Figure 23] 13 is a table showing a profile of a spiral trajectory in the third embodiment. [Figure 24]13 is a table showing a profile of a spiral trajectory in the third embodiment. [Diagram 25] 13 is a table showing a profile of a spiral trajectory in the third embodiment. [Figure 26] 11 is a table showing the relationship between the orbital inclination angle and the maximum distance to the geostationary orbit 103 in the third embodiment. [Figure 27] FIG. 11 is a diagram showing an observation state at perigee in the third embodiment. [Figure 28] FIG. 11 is a diagram showing an observation state at perigee in the third embodiment. [Figure 29] FIG. 11 is a diagram showing an observation state at apogee in the third embodiment. [Diagram 30] FIG. 11 is a diagram showing an observation state by an observation satellite 200 in the third embodiment. [Diagram 31] FIG. 11 is a diagram showing an observation state by an observation satellite 200 in the third embodiment. [Diagram 32] FIG. 11 is a diagram showing an observation state by an observation satellite 200 in the third embodiment. [Diagram 33] FIG. 11 is a diagram showing an observation state by an observation satellite 200 in the third embodiment. [Diagram 34] FIG. 13 is a diagram showing a spiral operation in the third embodiment. [Diagram 35] FIG. 13 is a diagram showing an observation state by an observation satellite 200 in the fourth embodiment. [Diagram 36] FIG. 13 is a diagram showing an observation state by an observation satellite 200 in the fourth embodiment. [Figure 37] FIG. 13 is a diagram showing a spiral operation in the fifth embodiment. [Figure 38] FIG. 13 is a diagram showing a spiral operation in the fifth embodiment. [Figure 39] FIG. 23 is a configuration diagram of an observation system 100 according to a seventh embodiment. [Diagram 40] FIG. 23 is a diagram showing an unobservable situation in the seventh embodiment. [Diagram 41] FIG. 23 is a diagram showing an observable situation in the seventh embodiment. [Diagram 42] FIG. 23 is a diagram showing the state of observation by an observation satellite 200 in the eighth embodiment. [Diagram 43] FIG. 23 is a diagram showing an unobservable situation in the eighth embodiment. [Diagram 44] FIG. 23 is a diagram showing an observable situation in the eighth embodiment. [Diagram 45] FIG. 23 is a diagram showing the state of observation by an observation satellite 200 in the ninth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] In the embodiments and drawings, the same or corresponding elements are denoted by the same reference numerals. Descriptions of elements denoted by the same reference numerals as those of elements already described will be omitted or simplified as appropriate.

[0012] Embodiment 1 The configuration for observing a space object 110 will be described with reference to FIGS.

[0013] ***Configuration Description*** The configuration of an observation system 100 will be described with reference to FIG. The observation system 100 is a system for observing a space object 110 . "Observation" includes concepts such as "monitoring" or "filming."

[0014] A space object 110 is an object that exists in space. A specific example of a space object 110 is space debris. A space object 110 orbits the Earth 101 in a geostationary orbit 103 .

[0015] The observation system 100 includes an observation satellite 200 . The observation satellite 200 is an artificial satellite that orbits the Earth 101 . The observation satellite 200 orbits the Earth 101 in a geostationary orbit 103 or near the geostationary orbit 103 . The observation satellite 200 optically photographs the space object 110 from an altitude different from the altitude at which the space object 110 is located.

[0016] The altitude of geostationary orbit 103 is approximately 36,000 kilometers. Artificial satellites called geostationary satellites orbit in a geostationary orbit 103 in sync with the rotation of the Earth 101. That is, a geostationary satellite orbits the geostationary orbit 103 once per day. In other words, a geostationary satellite orbits the geostationary orbit 103 once every 24 hours. Space object 110, like a geostationary satellite, orbits geostationary orbit 103 once per day. The observation satellite 200 orbits the geostationary orbit 103 or in the vicinity of the geostationary orbit 103 once a day. The directions in which the space object 110 and the observation satellite 200 orbit are the same as the direction in which a geostationary satellite orbits.

[0017] Light from the sun 102 is called sunlight. The side of the Earth 101 that receives sunlight is referred to as the near side of the Earth 101 . The side of the Earth 101 that is not exposed to sunlight is referred to as the backside of the Earth 101. In FIG. 1, a space object 110 and an observation satellite 200 each orbit around the near side of the Earth 101 .

[0018] The configuration of the observation satellite 200 will be described with reference to FIG. The observation satellite 200 comprises an observation device 201 , a satellite control device 202 , a communication device 203 , a propulsion device 204 , an attitude control device 205 , and a power supply device 206 .

[0019] The observation device 201 is a device for observing the space object 110 . The observation device 201 optically captures images of the space object 110 flying at an altitude different from the orbital altitude of the observation satellite 200. Specifically, the observation device 201 is a visible optical sensor. The observation device 201 generates observation data. The observation data is data obtained by observation performed by the observation device 201. For example, the observation data corresponds to data representing an image in which the space object 110 is captured.

[0020] The satellite control device 202 is a computer that controls the observation satellite 200 . The satellite control device 202 controls the observation device 201, the propulsion device 204, and the attitude control device 205 according to a predetermined procedure or in accordance with various commands transmitted from ground facilities.

[0021] The communication device 203 is a device that communicates with ground facilities. The communication device 203 transmits observation data to the ground equipment and receives various commands transmitted from the ground equipment.

[0022] The propulsion device 204 is a device that provides thrust to the observation satellite 200 and changes the speed of the observation satellite 200 . In particular, the propulsion device 204 is an electric propulsion device, for example, an ion engine or a Hall thruster.

[0023] The attitude control device 205 is a device for controlling the attitude elements of the observation satellite 200 . The attitude control device 205 changes the attitude elements of the observation satellite 200 in a desired direction, or maintains the attitude elements of the observation satellite 200 in a desired direction. Specifically, the attitude elements of the observation satellite 200 are the attitude of the observation satellite 200, the angular velocity of the observation satellite 200, and the line of sight of the observation device 201. The attitude control device 205 includes an attitude sensor, an actuator, and a controller. The attitude sensor is a gyroscope, an earth sensor, a sun sensor, a star tracker, a thruster, a magnetic sensor, or the like. The actuator is an attitude control thruster, a momentum wheel, a reaction wheel, a control moment gyro, or the like. The controller controls the actuator by executing a control program based on the measurement data obtained by the attitude sensor or according to a control command from the ground equipment.

[0024] The power supply unit 206 includes a solar cell, a battery, a power control device, and the like, and supplies power to each device of the observation satellite 200 .

[0025] The satellite control device 202 will now be described in more detail. The satellite controller 202 includes processing circuitry. The processing circuit may be a dedicated hardware or a processor that executes a program stored in a memory. The processing circuit functions as an observation control unit that controls the propulsion device 204. In the processing circuit, some functions may be realized by dedicated hardware and the remaining functions may be realized by software or firmware, i.e., the processing circuit may be realized by hardware, software, firmware, or a combination thereof. The dedicated hardware may be, for example, a single circuit, multiple circuits, a programmed processor, parallel programmed processors, an ASIC, an FPGA, or a combination of these. ASIC is an abbreviation for Application Specific Integrated Circuit. FPGA is an abbreviation for Field Programmable Gate Array.

[0026] The pointing function of the observation satellite 200 will now be explained in more detail. The observation satellite 200 has a pointing function for directing the observation direction toward the space object 110 . For example, the observation satellite 200 is equipped with a reaction wheel. The reaction wheel is a device for controlling the attitude of the observation satellite 200. The reaction wheel controls the attitude of the observation satellite 200, thereby achieving body pointing. For example, the observation device 201 includes a pointing mechanism. The pointing mechanism is a mechanism for changing the line of sight of the observation device 201. For example, a drive mirror or the like is used for the pointing mechanism.

[0027] The observation function of the observation device 201 will now be described. The observation device 201 has a variable resolution function and an autofocus function. The variable resolution function is a function that changes the resolution during observation. The autofocus function is a function for focusing on the space object 110 .

[0028] ***Explanation of Operation*** The operation of the observation system 100, and in particular the operation of the observation satellites 200, corresponds to an observation method.

[0029] An overview of the observation method will be given. The propulsion device 204 changes the flight speed of the observation satellite 200 after the observation satellite 200 starts to orbit either the near side of the Earth 101 or the far side of the Earth 101. This causes the orbital altitude of the observation satellite 200 to change from the altitude of the geostationary orbit 103. The propulsion device 204 changes the flight speed of the observation satellite 200 before the observation satellite 200 starts to orbit the other of the near side of the Earth 101 and the far side of the Earth 101. This causes the orbital altitude of the observation satellite 200 to return to the altitude of the geostationary orbit 103. The observation device 201 optically photographs a space object 110 flying at an altitude different from the orbital altitude of the observation satellite 200 .

[0030] The observation method will be described with reference to FIGS. The four times "00:00", "06:00", "12:00" and "18:00" assigned to the geostationary orbit 103 indicate the time in a specific region of the Earth 101 (for example, Japan). The observation satellite 200 orbits the near side of the Earth 101 during the daytime hours (06:00 to 18:00) in a specific region. In other words, the observation satellite 200 starts orbiting the near side of the Earth 101 at around 6:00 and finishes orbiting the near side of the Earth 101 at around 18:00. The observation satellite 200 orbits the far side of the Earth 101 during the nighttime hours (18:00 to 06:00) in a specific region. In other words, the observation satellite 200 starts orbiting the far side of the Earth 101 at around 18:00 and finishes orbiting the far side of the Earth 101 at around 6:00.

[0031] <Example 1> A first embodiment will be described with reference to FIGS. In the first embodiment, an observation satellite 200 orbits the near side of the Earth 101 .

[0032] In FIG. 3, after the observation satellite 200 starts orbiting the near side of the Earth 101, the propulsion device 204 increases the flight speed of the observation satellite 200. Specifically, the satellite control device 202 determines whether the observation satellite 200 has started to orbit the near side of the Earth 101. For example, the satellite control device 202 makes this determination by referring to the time. When the observation satellite 200 has started to orbit the near side of the Earth 101, the satellite control device 202 instructs the propulsion device 204 to increase speed. Then, the propulsion device 204 increases the flight speed of the observation satellite 200. As a result, the orbital altitude of the observation satellite 200 increases from the altitude of the geostationary orbit 103 .

[0033] In FIG. 4, as the orbital altitude of the observation satellite 200 rises from the altitude of the geostationary orbit 103, the ground speed of the observation satellite 200 decreases. In other words, the ground speed of the observation satellite 200 is slower than the ground speed of the space object 110 .

[0034] FIG. 5 shows the state in which the space object 110 that has caught up with the observation satellite 200 is photographed by the observation satellite 200. FIG. 6 shows a state in which a space object 110 that has overtaken an observation satellite 200 is photographed by the observation satellite 200. While the observation satellite 200 orbits the near side of the Earth 101, the observation device 201 photographs the space object 110 flying at an altitude lower than the orbital altitude of the observation satellite 200. In this way, the observation device 201 photographs the space object 110 with direct sunlight. Specifically, while the observation satellite 200 orbits the near side of the Earth 101, the observation device 201 photographs the direction toward the Earth 101. In this way, the observation device 201 photographs the space object 110 that passes the observation satellite 200 while flying in the geostationary orbit 103.

[0035] In FIG. 7, before the observation satellite 200 starts to orbit behind the Earth 101, the propulsion device 204 reduces the flight speed of the observation satellite 200. Specifically, the satellite control device 202 determines whether the observation satellite 200 will start orbiting on the far side of the Earth 101. For example, the satellite control device 202 makes this determination by referring to the time. Before the observation satellite 200 starts orbiting on the far side of the Earth 101, the satellite control device 202 instructs the propulsion device 204 to decelerate. Then, the propulsion device 204 reduces the flight speed of the observation satellite 200. As a result, the orbital altitude of the observation satellite 200 descends to the altitude of the geostationary orbit 103 .

[0036] <Example 2> A second embodiment will be described with reference to FIGS. In the second embodiment, an observation satellite 200 orbits on the other side of the Earth 101 .

[0037] In FIG. 8, after the observation satellite 200 starts orbiting the other side of the Earth 101, the propulsion device 204 slows down the flight speed of the observation satellite 200. Specifically, the satellite control device 202 determines whether the observation satellite 200 has started to orbit behind the Earth 101. For example, the satellite control device 202 makes this determination by referring to the time. When the observation satellite 200 has started to orbit behind the Earth 101, the satellite control device 202 instructs the propulsion device 204 to decelerate. Then, the propulsion device 204 reduces the flight speed of the observation satellite 200. As a result, the orbital altitude of the observation satellite 200 descends from the altitude of the geostationary orbit 103 .

[0038] In FIG. 9, as the orbital altitude of the observation satellite 200 descends from the altitude of the geostationary orbit 103, the ground speed of the observation satellite 200 increases. In other words, the ground speed of the observation satellite 200 becomes faster than the ground speed of the space object 110 .

[0039] FIG. 10 shows how a space object 110 that has been caught up with an observation satellite 200 is photographed by the observation satellite 200. FIG. 11 shows how a space object 110 that has been overtaken by an observation satellite 200 is photographed by the observation satellite 200. While the observation satellite 200 orbits on the far side of the Earth 101, the observation device 201 photographs the space object 110 flying at an altitude higher than the orbital altitude of the observation satellite 200. In this way, the observation device 201 photographs the space object 110 with direct sunlight. Specifically, while the observation satellite 200 orbits the far side of the Earth 101, the observation device 201 photographs the opposite side of the Earth 101. In this way, the observation device 201 photographs the space object 110 that is overtaken by the observation satellite 200 while flying in the geostationary orbit 103.

[0040] In FIG. 12, before the observation satellite 200 starts to orbit around the near side of the Earth 101, the propulsion device 204 increases the flight speed of the observation satellite 200. Specifically, the satellite control device 202 determines whether the observation satellite 200 will start orbiting the near side of the Earth 101. For example, the satellite control device 202 makes this determination by referring to the time. Before the observation satellite 200 starts orbiting the near side of the Earth 101, the satellite control device 202 instructs the propulsion device 204 to increase speed. Then, the propulsion device 204 increases the flight speed of the observation satellite 200. As a result, the orbital altitude of the observation satellite 200 increases to the altitude of the geostationary orbit 103 .

[0041] ***Advantages of the First Embodiment*** The observation satellite 200 flies in or near the geostationary orbit 103 . After 6:00, the observation satellite 200 accelerates and increases its orbital altitude. Then, the observation satellite 200 photographs the space object 110 flying in the geostationary orbit 103 and overtaking the observation satellite 200. Also, before 18:00, the observation satellite 200 decelerates and decreases its orbital altitude. When the observation satellite 200 accelerates, the orbital altitude of the observation satellite 200 increases. When the orbital altitude of the observation satellite 200 increases, the ground speed of the observation satellite 200 decreases. Therefore, the observation satellite 200 is overtaken by the space object 110 flying in the geostationary orbit 103. The observation satellite 200 flies at an orbital altitude higher than the altitude of the geostationary orbit 103 between 6:00 and 18:00. The observation satellite 200 receives sunlight reflected from the space object 110 flying in the geostationary orbit 103. This allows the observation satellite 200 to observe the space object 110 under optimal conditions.

[0042] After 18:00, the observation satellite 200 decelerates and lowers its orbital altitude. Then, the observation satellite 200 photographs the space object 110 that flies in the geostationary orbit 103 and is overtaken by the observation satellite 200. Then, before 6:00 the next day, the observation satellite 200 increases its speed and raises its orbital altitude. When the observation satellite 200 decelerates, the orbital altitude of the observation satellite 200 descends. When the orbital altitude of the observation satellite 200 decreases, the ground speed of the observation satellite 200 increases. Therefore, the observation satellite 200 overtakes the space object 110 flying in the geostationary orbit 103. The observation satellite 200 flies at an orbital altitude lower than the altitude of the geostationary orbit 103 after 6:00 p.m. and before 6:00 a.m. the next day. The observation satellite 200 receives sunlight reflected from the space object 110 flying in the geostationary orbit 103. This allows the observation satellite 200 to observe the space object 110 under optimal conditions.

[0043] ***Addition to the first embodiment*** The observation satellite 200 may fly in an orbit other than the geostationary orbit 103 or in its vicinity. The space object 110 may fly in an orbit other than the geostationary orbit 103. Also, the space object 110 may fly in an orbit other than a circular orbit. The orbital altitude may be increased and decreased over a period of multiple days. The longer the number of days of observations from a higher altitude or from a lower altitude, the longer the relative longitudinal movement distance can be. The greater the difference in altitude due to the ascent and descent of the orbital altitude, the longer the relative movement distance in the longitude direction can be. Raising and lowering the orbital altitude using high thrust means such as chemical propulsion can provide large altitude differences in a short period of time.

[0044] Embodiment 2 The observation satellite 200 will be described with reference to Figs. 13 to 21, focusing mainly on the points that differ from the first embodiment.

[0045] ***Configuration Description*** The configuration of the observation satellite 200 is the same as that in the first embodiment. The observation satellite 200 is an artificial satellite that orbits the Earth 101 at an altitude of 35,800 kilometers above the equator. In the second embodiment, the altitude of 35,800 kilometers is an approximate altitude. The observation satellite 200 includes an observation device 201 and a propulsion device 204 . The observation device 201 is a device for optically photographing a space object 110 flying along a geostationary orbit 103. The space object 110 flies in or near the geostationary orbit 103. The propulsion device 204 changes the flight speed of the observation satellite 200 .

[0046] ***Explanation of Operation*** The observation satellite 200 flies in an inclined elliptical orbit using a propulsion system 204 . The inclined elliptical orbit of the observation satellite 200 has an inclination angle relative to an orbit at an altitude of 35,800 km above the equator.

[0047] The inclined elliptical orbit of the observation satellite 200 will now be described. The major axis is oriented toward the sun. In other words, the direction of the major axis is equal to the direction from the Earth 101 to the Sun 102. The apogee is on the sun side, i.e., the side where the sun 102 is located. The normal vector of the orbital plane tilts about the center of the earth. The inclined elliptical orbit is a sun-synchronous orbit, and the major axis and normal vector revolve synchronously with the sun 102.

[0048] ***Detailed Description*** FIG. 13 shows how an observation satellite 200 flying in an inclined elliptical orbit observes a space object 110 from a high altitude while being overtaken by the space object 110. The observation satellite 200 is adapted to have an inclined elliptical orbit. The orbital period of the observation satellite 200 is set to be equal to that of a geostationary satellite. In other words, the observation satellite 200 makes about one revolution per day, and completes one revolution in 365 days. As a result, the observation satellite 200 maintains its relative position with the space object 110 on the geostationary orbit for a long period of time. Then, on the perigee side, the observation satellite 200 can observe the space object 110 while flying at an altitude (low altitude) lower than the altitude of the geostationary orbit 103 and moving eastward relative to the space object 110. Also, on the apogee side, the observation satellite 200 can observe the space object 110 while flying at an altitude (high altitude) higher than the altitude of the geostationary orbit 103 and moving westward relative to the space object 110.

[0049] In the orbit of the observation satellite 200, the direction of the major axis is always the same as the direction of the sun. This is achieved by the satellite control device 202 controlling the propulsion device 204 to change the flight speed. This allows daytime surveillance from a high altitude at apogee. Daytime surveillance is surveillance of the near side (sunlit side) of the Earth 101. Also, nighttime surveillance is allowed from a low altitude at perigee. Nighttime surveillance is surveillance of the far side (opposite the sunlit side) of the Earth 101.

[0050] If the orbit of the observation satellite 200 does not have an inclination angle, there is a risk that the observation satellite 200 will collide with a space object 110 in geostationary orbit when the orbital altitude of the observation satellite 200 becomes equal to the orbital altitude of the geostationary orbit 103 while the observation satellite 200 is traveling from apogee to perigee. Therefore, an inclination angle is added to the orbit of the observation satellite 200. As a result, when the observation satellite 200 passes near the geostationary orbit 103, the distance between the observation satellite 200 and the geostationary orbit 103 in the north-south direction increases.

[0051] In order to maintain the above operating conditions, the orbital plane of the observation satellite 200 is maintained with the normal vector of the orbital plane of the observation satellite 200 tilted about the earth's center, and the orbit of the observation satellite 200 is synchronized with the sun. It is not possible to realize an orbit by natural phenomena alone, in which the orbital plane is maintained with the major axis always pointing toward the sun and the normal vector of the orbital plane revolves synchronously with the sun 102. However, by operating the propulsion device 204, such an orbit can be realized. In addition, a large amount of propellant is usually required to keep an orbit with a large inclination angle in synchronism with the sun, but a gentle inclination angle of less than 1 degree requires only a limited amount of propellant and is easy to achieve.

[0052] FIG. 14 shows the profile of the parking trajectory. When the orbital period of the observation satellite 200 is equal to the orbital period of the geostationary orbit 103, the observation satellite 200 orbits the space object 110 once per day while swinging in the longitude direction relative to the space object 110. Such an orbit of the observation satellite 200 is called a "parking orbit." The radius of the Earth 101 is approximately 6,400 kilometers, and the altitude of the geostationary orbit 103 is approximately 35,800 kilometers. Therefore, the radius of the geostationary orbit 103 is approximately 42,200 kilometers. In an elliptical orbit having a major axis approximately equal to the diameter of geostationary orbit 103, when the eccentricity is 1.001, the difference in altitude between the apogee and geostationary orbit 103 and the difference in altitude between the perigee and geostationary orbit 103 are approximately 50 kilometers. When the eccentricity is 1.01, the difference in altitude between each is approximately 400 kilometers. If the difference in altitude is small, the space object 110 can be observed with high resolution, and if the difference in altitude is large, the relative speed with respect to the space object 110 in the longitude direction can be increased.

[0053] FIG. 15 shows the relationship between the orbital inclination angle and the maximum distance to the geostationary orbit 103. When the orbital inclination angle of the observation satellite 200 is 0.1 degrees, the observation satellite 200 is approximately 70 kilometers away from the geostationary orbit 103 in the north-south direction. When the orbital inclination angle of the observation satellite 200 is 0.7 degrees, the observation satellite 200 is about 500 kilometers away from the geostationary orbit 103 in the north-south direction. The orbit of the observation satellite 200 may be set at an inclination angle suitable for avoiding collision with the space object 110 depending on the distribution of the space object 110 around the geostationary orbit 103 .

[0054] FIG. 16 shows an observation satellite 200 monitoring a space object 110 while flying at a low altitude and overtaking the space object 110. 17 shows the observation satellite 200 passing at the altitude of the geostationary orbit 103. Since the orbit of the observation satellite 200 has an inclination angle, the observation satellite 200 moves away from the space object 110 in the north-south direction when the observation satellite 200 passes at the altitude of the geostationary orbit 103. Therefore, there is no risk of the observation satellite 200 colliding with the space object 110. If the average altitude of the observation satellite 200 is lower than that of the geostationary orbit 103, the orbital period of the observation satellite 200 becomes shorter than that of the geostationary orbit 103. Then, the observation satellite 200 moves eastward relative to the space object 110 every day. The flight state of the observation satellite 200 becomes spiral.

[0055] FIG. 18 shows an observation satellite 200 flying at a high altitude and monitoring a space object 110 while being overtaken by the space object 110. 19 shows the observation satellite 200 passing at the altitude of the geostationary orbit 103. Since the orbit of the observation satellite 200 has an inclination angle, the observation satellite 200 moves away from the space object 110 in the north-south direction when the observation satellite 200 passes at the altitude of the geostationary orbit 103. Therefore, there is no risk of the observation satellite 200 colliding with the space object 110. If the average altitude of the observation satellite 200 is higher than that of the geostationary orbit 103, the orbital period of the observation satellite 200 will be longer than the orbital period of the geostationary orbit 103. Then, the observation satellite 200 moves westward relative to the space object 110 every day. The flight state of the observation satellite 200 becomes spiral. By using the propulsion device 204, the orbit of the observation satellite 200 can be maintained with the major axis pointing toward the sun 102. This causes the position of the observation satellite 200 to reach the apogee around 12 o'clock every day, making it possible to monitor the space object 110 from a high altitude during daylight hours.

[0056] By adopting an eccentric elliptical orbit for the observation system 100 and always aligning the direction of the major axis of the elliptical orbit with the solar direction, it is possible to achieve both daytime monitoring from high altitudes and nighttime monitoring from low altitudes. By making the orbit of the observation satellite 200 an inclined orbit, when the orbital radius becomes equal to that of the geostationary orbit 103 (when flying near the major axis perpendicular axis), the orbit of the observation satellite 200 moves away from the geostationary orbit 103 in an out-of-plane direction. Furthermore, by making the orbit of the observation satellite 200 an elliptical orbit, when the observation satellite 200 passes through the orbital plane of the geostationary orbit 103 (when flying near the major axis and when flying near the minor axis), the orbital altitude of the observation satellite 200 is different from that of the geostationary orbit 103, so there is no risk of the observation satellite 200 colliding with the group of satellites in the geostationary orbit 103.

[0057] Fig. 20 shows the parking operation by the inclined elliptical orbit. When the orbital period of the observation satellite 200 is the same as that of the geostationary orbit, the observation satellite 200 orbits as shown in Fig. 20 in one day when viewed from the direction perpendicular to the center of the earth in the equatorial plane. If the major axis of the elliptical orbit of the observation satellite 200 is made approximately the same as the diameter of the geostationary orbit 103, the orbital period of the observation satellite 200 will be the same as the orbital period of the geostationary orbit 103. The observation satellite 200 then makes one orbit approximately per day. Therefore, the observation satellite 200 maintains approximately the same longitude as the space object 110 and makes one orbit around the space object 110 in the flight direction per day.

[0058] Fig. 21 shows a spiral operation in an inclined elliptical orbit. When the orbital period of the observation satellite 200 is longer than that of a geostationary orbit, the observation satellite 200 orbits in one day as shown in Fig. 21 when viewed from a direction perpendicular to the center of the earth on the equatorial plane. If the major axis of the elliptical orbit of the observation satellite 200 is longer than the diameter of the geostationary orbit 103, the orbital period of the observation satellite 200 will be longer than the orbital period of the geostationary orbit 103. Then, the observation satellite 200 moves westward relative to the space object 110. In other words, the observation satellite 200 moves in a spiral shape. However, on the perigee side, the observation satellite 200 moves eastward relative to the space object 110. If the major axis of the elliptical orbit of the observation satellite 200 is shorter than the diameter of the geostationary orbit 103, the orbital period of the observation satellite 200 will be shorter than the orbital period of the geostationary orbit 103. Then, the observation satellite 200 moves eastward relative to the space object 110. In other words, the observation satellite 200 moves in a spiral shape. However, on the apogee side, the observation satellite 200 moves westward relative to the space object 110.

[0059] Embodiment 3 The observation satellite 200 will be described with reference to Figs. 22 to 34, focusing mainly on the points that differ from the first or second embodiment.

[0060] ***Configuration Description*** The configuration of the observation satellite 200 is the same as that in the first embodiment. The observation satellite 200 is an artificial satellite that orbits the Earth 101 at an altitude of 35,800 kilometers above the equator. In the third embodiment, the altitude of 35,800 kilometers is an approximate altitude. The observation satellite 200 includes an observation device 201 and a propulsion device 204 . The observation device 201 is a device for optically photographing a space object 110 flying along a geostationary orbit 103. The space object 110 flies in or near the geostationary orbit 103. The propulsion device 204 changes the flight speed of the observation satellite 200 .

[0061] ***Explanation of Operation*** The observation satellite 200 flies in an inclined elliptical orbit using a propulsion system 204 . The inclined elliptical orbit of the observation satellite 200 has an inclination angle relative to an orbit at an altitude of 35,800 km above the equator.

[0062] The inclined elliptical orbit of the observation satellite 200 will now be described. The major axis is oriented toward the sun when viewed from the North Pole. In other words, the direction of the major axis is the same as the direction from the Earth 101 to the Sun 102 when viewed from the North Pole. The perigee is on the sun side, i.e., the side where the sun 102 is located. The normal vector to the orbital plane is tilted about the minor axis of the ellipse. The inclined elliptical orbit is a sun-synchronous orbit, and the major axis and normal vector revolve synchronously with the sun 102.

[0063] ***Effect Description*** FIG. 22 shows an observation satellite 200 observing a space object 110 while being overtaken by the space object 110. When the observation satellite 200 has a high average altitude and observes the space object 110 while moving westward relative to the space object 110, the observation satellite 200 can observe the space object 110 without being backlit, both during daytime flights from 6:00 to 18:00 and during nighttime flights from 18:00 to 6:00. The observation satellite 200 can observe faces of the space object 110 other than the face opposite to the face pointing toward the Earth 101. In other words, the observation satellite 200 can observe the face of the space object 110 pointing toward the Earth 101, as well as the side of the space object 110. In the longitude band where the observation satellite 200 crosses the congested region of the geostationary orbital plane, the orbital altitude of the observation satellite 200 is different from the altitude of the geostationary orbit 103. This makes it possible to avoid collisions between the observation satellite 200 and space objects in the congested region. In its orbit, the observation satellite 200 oscillates in a north-south direction relative to the space object 110. In order to prevent a collision between the observation satellite 200 and the space object 110, the orbital altitude of the observation satellite 200 when it passes through the geostationary orbit plane is higher than the altitude of the geostationary orbit 103.

[0064] Figures 23, 24 and 25 show the profile of the spiral orbit during westward movement. The radius of the Earth 101 is approximately 6,400 kilometers, and the altitude of the geostationary orbit 103 is approximately 35,800 kilometers. Therefore, the radius of the geostationary orbit 103 is approximately 42,200 kilometers. In an elliptical orbit having a major axis almost equal to that of geostationary orbit 103, when the eccentricity is 1.001, the difference in altitude between the perigee and geostationary orbit 103 is about 50 kilometers. When the eccentricity is 1.01, the difference in altitude between the perigee and geostationary orbit 103 is about 400 kilometers. If the difference in altitude is small, the space object 110 can be observed with high resolution, and if the difference in altitude is large, the relative speed with respect to the space object 110 in the longitude direction can be increased.

[0065] ***Detailed Description*** FIG. 26 shows the relationship between the orbital inclination angle and the maximum distance to the geostationary orbit 103. When the orbital inclination angle of the observation satellite 200 is 0.1 degrees, the observation satellite 200 is approximately 70 kilometers away from the geostationary orbit 103 in the north-south direction. If the orbital inclination angle of the observation satellite 200 is 0.7 degrees, the observation satellite 200 is approximately 500 kilometers away from the geostationary orbit 103 in the north-south direction. If the distance between the observation satellite 200 and the geostationary orbit 103 is short, high-resolution observations can be made.

[0066] FIG. 27 shows the state of observation at perigee when the altitude of the perigee is equal to the altitude of the geostationary orbit 103. When the altitude of the perigee is about 35,800 km, which is the same as the altitude of the geostationary orbit 103, the observation satellite 200 will observe the space object 110 from the south or north at the perigee. The observation will not be backlit, and it will be possible to observe the solar reflected light of the space object 110.

[0067] FIG. 28 shows the state of observation at perigee when the altitude of the perigee is lower than the altitude of the geostationary orbit 103. When the altitude of the perigee is lower than the altitude of the geostationary orbit 103, the observation satellite 200 at the perigee observes the space object 110 from the south or north with a line of sight vector inclined toward the sun. The observation is not backlit, and it is possible to observe the solar reflected light of the space object 110.

[0068] Figure 29 shows the observation at apogee. At the apogee, the observation satellite 200 observes the space object 110 from the south or north with a line of sight vector tilted toward the sun. The observation is not backlit, and it is possible to observe the solar reflected light of the space object 110.

[0069] 30 to 33 show how an observation satellite 200 observes a space object 110 while being overtaken by the space object 110. FIG.

[0070] Fig. 34 shows a spiral operation in an inclined elliptical orbit. When viewed from a direction perpendicular to the center of the earth on the equatorial plane, the observation satellite 200 orbits as shown in Fig. 34 in one day.

[0071] Embodiment 4 The observation satellite 200 will be described with reference to Figs. 35 and 36, focusing mainly on the points that differ from the first to third embodiments.

[0072] ***Configuration Description*** The configuration of the observation satellite 200 is the same as that in the first embodiment. The observation satellite 200 is an artificial satellite that orbits the Earth 101 at an altitude of 35,800 kilometers above the equator. In the third embodiment, the altitude of 35,800 kilometers is an approximate altitude. The observation satellite 200 includes an observation device 201 and a propulsion device 204 . The observation device 201 is a device for optically photographing a space object 110 flying along a geostationary orbit 103. The space object 110 flies in or near the geostationary orbit 103. The propulsion device 204 changes the flight speed of the observation satellite 200 .

[0073] ***Explanation of Operation*** The observation satellite 200 flies in an inclined elliptical orbit using a propulsion system 204 . The inclined elliptical orbit of the observation satellite 200 has an inclination angle relative to an orbit at an altitude of 35,800 km above the equator.

[0074] The inclined elliptical orbit of the observation satellite 200 will now be described. The major axis is oriented toward the sun when viewed from the North Pole. In other words, the direction of the major axis is the same as the direction from the Earth 101 to the Sun 102 when viewed from the North Pole. The apogee is on the sun side, i.e., the side where the sun 102 is located. The normal vector to the orbital plane is tilted about the minor axis of the ellipse. The inclined elliptical orbit is a sun-synchronous orbit, and the major axis and normal vector revolve synchronously with the sun 102.

[0075] ***Effect Description*** 35 and 36 show how an observation satellite 200 observes a space object 110 while being overtaken by the space object 110. FIG. The observation satellite 200 can observe the side of the space object 110 and the Earth-pointing surface of the space object 110 at close range around midnight. Except for a short period of time during which the space object 110 is in the shadow of the Earth 101, the observation satellite 200 can observe the space object 110 under daylight conditions. By setting the average altitude of the observation satellite 200 high, the speed at which the observation satellite 200 moves westward relative to the space object 110 per orbit can be increased, so that a given longitude range can be covered in a short period of time. When observing the space object 110 at a close distance on the perigee side, the relative speed of the observation satellite 200 to the space object 110 is slow. Therefore, the space object 110 can be observed at a leisurely pace. If the orbital altitude of the observation satellite 200 at perigee is equal to the altitude of the geostationary orbit 103, the observation satellite 200 flies in the longitude direction at a speed approximately equal to that of the space object 110. If the orbital altitude of the observation satellite 200 at perigee is lower than the altitude of the geostationary orbit 103, the observation satellite 200 flies while temporarily moving eastward relative to the space object 110.

[0076] Embodiment 5. The observation satellite 200 will be described with reference to Figs. 37 and 38, focusing mainly on the points that differ from the third and fourth embodiments.

[0077] ***Example 1*** Fig. 37 shows a state of spiral operation in an inclined elliptical orbit in summer. When viewed from a direction perpendicular to the center of the earth on the equatorial plane, the observation satellite 200 orbits as shown in Fig. 37 in one day. In the inclined elliptical orbit of the geostationary orbit 103, the normal vector of the orbital plane is inclined about the minor axis of the inclined elliptical orbit. The perigee of the inclined elliptical orbit is located on the north side.

[0078] ***Example 2*** Fig. 38 shows a state of spiral operation in an inclined elliptical orbit in winter. When viewed from a direction perpendicular to the center of the earth on the equatorial plane, the observation satellite 200 orbits as shown in Fig. 38 in one day. In the inclined elliptical orbit of the geostationary orbit 103, the normal vector of the orbital plane is inclined about the minor axis of the inclined elliptical orbit. The perigee of the inclined elliptical orbit is located on the south side.

[0079] ***Effects of the Example*** Because the rotation axis of the Earth 101 is tilted, the angle of incidence of sunlight on the geostationary orbit plane varies by plus or minus 23.6 degrees between summer and winter. Therefore, in order to avoid backlighting and to ensure that the reflected sunlight is suitable for observation, it is reasonable to adopt orbital conditions that allow observation of the space object 110 from the side where the Sun 102 is located. By adopting such orbital conditions, observation data with excellent image quality can be obtained. During daytime observations from 6:00 to 18:00 in the summer, and during nighttime observations from 18:00 to 6:00 in the winter, the inclined elliptical orbit of the geostationary orbit 103 is inclined so that the perigee is located on the north side of the geostationary orbit 103. Also, during nighttime observations in the summer and daytime observations in the winter, the inclined elliptical orbit of the geostationary orbit 103 is inclined so that the perigee is located on the south side of the geostationary orbit 103. These are advantageous for observations.

[0080] Embodiment 6 The observation satellite 200 will be described in terms of examples of a second to a fifth embodiment.

[0081] ***Example A*** In the inclined elliptical orbit of the observation satellite 200, the eccentricity is equal to or greater than 1.001 and equal to or less than 1.01.

[0082] ***Example B*** The observation satellite 200 is in an inclined elliptical orbit with an inclination angle of 1 degree or less.

[0083] ***Example C*** The observation device 201 photographs the space object 110 flying at an altitude lower than the apogee altitude of the inclined elliptical orbit while the observation satellite 200 is orbiting the near side of the Earth 101. In this way, the observation device 201 photographs the space object 110 in front light.

[0084] ***Example D*** The observation device 201 photographs the space object 110 flying at an altitude higher than the perigee altitude of the inclined elliptical orbit while the observation satellite 200 is orbiting on the far side of the Earth 101. In this way, the observation device 201 photographs the space object 110 in front light.

[0085] ***Example E*** When the observation satellite 200 passes the perigee of the inclined elliptical orbit or when the observation satellite 200 passes the apogee of the inclined elliptical orbit, the observation device 201 directs a line of sight vector in a direction outside the orbital plane of the geostationary orbit 103 to photograph the space object 110. In this way, the observation device 201 photographs the space object 110 in a situation that is not backlit.

[0086] ***Example F*** The observation device 201 photographs the direction toward the Earth while the observation satellite 200 is orbiting the near side of the Earth 101. In this way, the observation device 201 photographs the space object 110 that passes the observation satellite 200 while flying in the geostationary orbit 103.

[0087] ***Example G*** The observation device 201 photographs the direction opposite to the Earth while the observation satellite 200 orbits the other side of the Earth 101. In this way, the observation device 201 photographs the space object 110 that is overtaken by the observation satellite 200 while flying in the geostationary orbit 103.

[0088] ***Example H*** While the observation satellite 200 orbits the near side of the Earth 101, the observation device 201 photographs the Earth-pointing surface of the space object 110 or the side of the space object 110 from the south side of the space object 110 or the north side of the space object 110.

[0089] ***Example I*** The orbital period of the observation satellite 200 in the inclined elliptical orbit is equal to the orbital period of the geostationary orbit 103 .

[0090] ***Example J*** The orbital period of the observation satellite 200 in the inclined elliptical orbit is longer than the orbital period of the geostationary orbit 103. Therefore, the observation satellite 200 moves westward relative to the space object 110.

[0091] ***Example K*** The orbital period of the observation satellite 200 in the inclined elliptical orbit is shorter than the orbital period of the geostationary orbit 103. Therefore, the observation satellite 200 moves eastward relative to the space object 110.

[0092] Embodiment 7 The observation system 100 will be described with reference to Figs. 39 to 41, mainly focusing on the points that differ from the first to sixth embodiments.

[0093] ***Configuration Description*** The configuration of the observation system 100 will be described with reference to FIG. The observation system 100 includes a ground facility 120 . The ground facility 120 is a facility installed on the ground for communicating with the observation satellite 200 and controlling the observation satellite 200 . The ground equipment 120 includes a communication equipment 121, a satellite management device 122, an artificial object identification device 123, and a space object management device 124. The communication facility 121 is a facility for communicating with the observation satellite 200. Specifically, the communication facility 121 receives observation data, telemetry, and the like from the observation satellite 200. In addition, the communication facility 121 transmits control commands, space object information, and the like to the observation satellite 200. The satellite management device 122 generates commands (control commands) for controlling the observation satellite 200 . The artificial object identification device 123 identifies the observed space object 110 based on the observation data from the observation satellite 200. The space object management device 124 manages information (space object information) of the space object 110. For example, the space object management device 124 manages the position information of the space object 110 at each time, the orbit information of the space object 110, and the like. Each of the satellite manager 122, the artificial object identifier 123, and the space object manager 124 includes processing circuitry similar to the processing circuitry of the satellite controller 202.

[0094] ***Explanation of Operation*** The observation satellite 200 performs forward-looking photography while flying at a low altitude and moving eastward relative to the space object 110. The observation satellite 200 then transmits the photography data (observation data) at each time. The artificial object identification device 123 receives the photographed data at each time via the communication equipment 121. Then, the artificial object identification device 123 identifies the observed artificial object based on the photographed data at each time. Specifically, the artificial object identification device 123 identifies the space object 110 that was photographed after 12 o'clock but not before 12 o'clock, and identifies the identified space object 110 as an artificial object.

[0095] The observation satellite 200 flies at a high altitude and performs rear-view photography while moving westward relative to the space object 110. The observation satellite 200 then transmits the photography data at each time. The artificial object identification device 123 receives the photographed data at each time via the communication equipment 121. Then, the artificial object identification device 123 identifies the observed artificial object based on the photographed data at each time. Specifically, the artificial object identification device 123 identifies the space object 110 that was photographed after 12 o'clock but not before 12 o'clock, and identifies the identified space object 110 as an artificial object.

[0096] FIG. 40 shows a situation in which the artificial object 111 cannot be observed before 12 o'clock because the artificial object 111 is located in the shade. FIG. 41 shows a situation in which the artificial object 111 is in sunlight after 12 o'clock and therefore can be observed. Space objects 110 flying around geostationary orbit 103 include natural objects and man-made objects. Natural objects have random shapes and therefore do not reflect sunlight well. Artificial objects have highly regular shapes, such as a cube shape. Therefore, artificial objects can be identified by observing the sunlight (reflected light) reflected by the space object 110 and examining the characteristics of the observed reflected light.

[0097] Embodiment 8 The observation satellite 200 will be described with reference to Figs. 42 to 44, focusing mainly on the points that differ from the first to seventh embodiments.

[0098] ***Configuration Description*** The configuration of the observation satellite 200 is the same as that in the first embodiment. The observation satellite 200 is an artificial satellite that orbits the Earth 101 . The observation satellite 200 includes an observation device 201 and a propulsion device 204 . The observation device 201 is a device for observing a space object 110 flying above a target area along a geostationary orbit 103. The space object 110 flies in or near the geostationary orbit 103. The propulsion device 204 changes the flight speed of the observation satellite 200 .

[0099] ***Explanation of Operation*** The propulsion device 204 lowers the orbital altitude of the observation satellite 200 by slowing down the flight speed. The orbital speed of the observation satellite 200 increases as the orbital altitude of the observation satellite 200 decreases. The orbital speed of the observation satellite 200 becomes faster than the rotation speed of the Earth 101. The observation satellite 200 moves eastward relative to the space object 110 between 10:00 and 18:00 solar time (LST) in the target region. During this time, the observation satellite 200 changes the pointing direction of the observation device 201 within a range of 30 degrees to 90 degrees eastward from the anti-earth direction to allow the observation device 201 to observe the space object 110. The observation satellite 200 has an observation device 201 observe a space object 110 in the sky on the far side of the Earth 101 between 6:00 p.m. and 6:00 a.m. solar time in a target area. LST is an abbreviation for Local Sun Time.

[0100] FIG. 42 shows an observation satellite 200 flying at a low altitude and observing a space object 110 while overtaking the space object 110. When the observation satellite 200 flies at a low altitude pointing in a direction opposite to the Earth, it becomes backlit around 12 o'clock and becomes impossible to observe. However, if the direction of orientation is changed to within a range of 30 degrees to 90 degrees eastward from the direction opposite to the Earth, the time period when it becomes backlit is from 6:00 to 10:00, and after that time period, it is possible to monitor the space object 110 while looking forward diagonally to the right (toward the sun) in the direction of flight. The observation satellite 200 observes the space object 110 in a forward-looking manner between 6:00 p.m. on the same day and 6:00 a.m. the next day, pointing in a direction opposite to the Earth and in front of the sun. The space object 110 flies ahead of the observation satellite 200 during the time period prior to that. Therefore, if the space object 110 is observed in advance in a forward-looking manner between 10:00 p.m. on the same day and 6:00 p.m. on the same day, the error in the orbit information of the space object 110 can be known in advance. In the forward view, the distance to the space object 110 is far, so the observation field of view is wide. Therefore, even if there is an error in the orbit information of the space object 110, there is little risk that the space object 110 will deviate from the observation field of view. The operation of changing the attitude to a direction opposite to the Earth after looking forward until 6 p.m. on the day can be performed in a short time by using the high-torque attitude control device 205.

[0101] ***Example*** The observation satellite 200 moves eastward relative to the space object 110 at a low altitude, and has the observation device 201 observe the space object 110 in a forward-looking manner between 13:00 and 18:00 solar time.

[0102] FIG. 43 shows a situation in which the artificial object 111 cannot be observed before 12 o'clock because the artificial object 111 is located in the shade. FIG. 44 shows a situation in which the artificial object 111 is in sunlight after 13:00 and therefore can be observed. When observing the artificial object 111, which is roughly rectangular and flies near the geostationary orbit 103 toward the Earth 101, there is a risk that even if one observes it with a wide-angle camera before 12 o'clock, only the shaded side of the artificial object 111 will be visible, and the artificial object 111 will not be observed. If observation is made after 13:00, the western surface of the artificial object 111 will be exposed to sunlight, and therefore the artificial object 111 can be observed.

[0103] Embodiment 9 The observation satellite 200 will be described with reference to FIG. 45, focusing mainly on the points that differ from the first to eighth embodiments.

[0104] ***Configuration Description*** The configuration of the observation satellite 200 is the same as that in the first embodiment. The observation satellite 200 is an artificial satellite that orbits the Earth 101 . The observation satellite 200 includes an observation device 201 and a propulsion device 204 . The observation device 201 is a device for observing a space object 110 flying above a target area along a geostationary orbit 103. The space object 110 flies in or near the geostationary orbit 103. The propulsion device 204 changes the flight speed of the observation satellite 200 .

[0105] ***Explanation of Operation*** The propulsion device 204 increases the orbital altitude of the observation satellite 200 by increasing the flight speed. The orbital speed of the observation satellite 200 decreases as the orbital altitude of the observation satellite 200 increases. The orbital speed of the observation satellite 200 becomes slower than the rotation speed of the Earth 101. The observation satellite 200 moves westward relative to the space object 110 between 10 p.m. and 6 a.m. solar time (LST) in the target region. During this time, the observation satellite 200 changes the pointing direction of the observation device 201 within a range of 30 degrees to 90 degrees westward from the direction of the Earth, causing the observation device 201 to observe the space object 110. The observation satellite 200 has an observation device 201 observe a space object 110 in the sky above the near side of the Earth 101 between 6:00 and 18:00 solar time in the target area.

[0106] FIG. 45 shows an observation satellite 200 flying at a high altitude and observing a space object 110 while being overtaken by the space object 110. When the observation satellite 200 flies at a high altitude pointing toward the Earth, it becomes backlit around 10 p.m., making observation impossible. However, if the direction of orientation is changed to within a range of 30 degrees to 90 degrees west of the Earth, the time period when it becomes backlit is from 6 p.m. to 10 p.m., and after that time period, it is possible to monitor the space object 110 while looking backwards diagonally left (toward the sun) in the direction of flight. The observation satellite 200 observes the space object 110 in front light, pointing toward the Earth, between 6:00 and 18:00 on the same day. The space object 110 flies behind the observation satellite 200 during the time period prior to this. Therefore, if the space object 110 is observed in advance in a backward-looking manner between 22:00 on the previous day and 6:00 on the same day, the error in the orbit information of the space object 110 can be known in advance. In the backward view, the distance to the space object 110 is far, so the observation field of view is wide. Therefore, even if there is an error in the orbit information of the space object 110, there is a small risk that the space object 110 will deviate from the observation field of view. The operation of changing the attitude to face the Earth after looking backward until 6:00 on the day can be performed in a short time by using the high-torque attitude control device 205.

[0107] ***Supplementary explanation of implementation form*** Each embodiment is an example of a preferred embodiment, and is not intended to limit the technical scope of the present invention. Each embodiment may be implemented in part or in combination with other embodiments. [Explanation of symbols]

[0108] 100 Observation system, 101 Earth, 102 Sun, 103 Geostationary orbit, 110 Space object, 111 Artificial object, 120 Ground equipment, 121 Communication equipment, 122 Satellite management equipment, 123 Artificial object identification equipment, 124 Space object management equipment, 200 Observation satellite, 201 Observation equipment, 202 Satellite control equipment, 203 Communication equipment, 204 Propulsion equipment, 205 Attitude control equipment, 206 Power supply equipment.

Claims

1. An artificial object identification method in which an artificial object identification device receives photographing data at each time from an observation satellite that takes forward-looking photographs while moving eastward relative to a space object in a geostationary orbit by flying at an altitude lower than the altitude of a geostationary orbit, identifies space objects that were photographed after 12:00 but not before 12:00 based on the photographing data at each time, and identifies the identified space objects as artificial objects.

2. An artificial object identification method in which an artificial object identification device receives photographing data at each time from an observation satellite that takes rear-view photographs while moving westward relative to space objects in geostationary orbit by flying at an altitude higher than the altitude of a geostationary orbit, identifies space objects that were photographed after 12:00 but not before 12:00 based on the photographing data at each time, and identifies the identified space objects as artificial objects.

3. An observation satellite orbiting the Earth, an observation device for observing a space object flying along a geostationary orbit above a target area; a propulsion device for varying the flight speed of the observation satellite; Equipped with the propulsion device reduces the flight speed to lower the orbital altitude of the observation satellite; the orbital speed of the observation satellite increases as the orbital altitude of the observation satellite decreases, thereby becoming faster than the rotation speed of the Earth; The observation satellite, While moving eastward relative to the space object between 10:00 and 18:00 solar time in the target area, the pointing direction of the observation device is changed within a range of 30 degrees to 90 degrees eastward from the anti-earth direction to allow the observation device to observe the space object; The observation device is caused to observe the space object in the sky on the other side of the Earth between 18:00 and 6:00 solar time. Observation satellite.

4. The observation satellite moves eastward relative to the space object at an altitude lower than that of a geostationary orbit, and causes the observation device to observe the space object in a forward-looking manner between 13:00 and 18:00 solar time. The observation satellite according to claim 3.

5. An observation satellite orbiting the Earth, an observation device for observing a space object flying along a geostationary orbit above a target area; a propulsion device for varying the flight speed of the observation satellite; Equipped with the propulsion device increases the orbital altitude of the observation satellite by increasing the flight speed; the orbital speed of the observation satellite decreases as the orbital altitude of the observation satellite increases, thereby becoming slower than the rotation speed of the Earth; The observation satellite, While moving westward relative to the space object between 10 p.m. and 6 a.m. solar time in the target area, the observation device is caused to observe the space object by changing the direction of orientation of the observation device within a range of 30 degrees to 90 degrees westward from the direction of the Earth; The observation device is caused to observe the space object in the sky above the near side of the Earth between 6:00 and 18:00 solar time. Observation satellite.

Images