Observation satellite

Abstract

To enable observation of celestial objects while moving relative to them. [Solution] The observation satellite 200 moves eastward relative to the space object between 10:00 and 18:00 solar time in the target area, changing the direction of its observation device from the anti-Earth direction to the east within a range of 30 to 90 degrees to allow the observation device to observe the space object, and then allows the observation device to observe the space object above the far side of the Earth between 18:00 and 6:00 solar time.

Description

Technical Field

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

Background Art

[0002] As debris increases, the collision risk of space objects is increasing. If a space object flying in a geostationary orbit can be observed by a satellite flying near the geostationary orbit, such observation is effective for risk countermeasures such as collision avoidance. When observation is performed using an optical observation device, the optical observation device observes the sunlight reflected from the observation target. Therefore, the relative positional relationship among the sun, the observation satellite, and the observation target is one of the constraint conditions.

[0003] A satellite called a geostationary satellite orbits the earth in synchronization with the rotation of the earth. Therefore, when viewed from the earth's surface, the satellite appears to be stationary. Therefore, the relative positional relationship between the sun and the geostationary satellite is determined depending on time.

[0004] Patent Document 1 discloses a method for observing space debris in a space where sunlight is backlight.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] The method described in Patent Document 1 requires a laser transmitting device to irradiate space debris with laser light, in addition to the camera. Furthermore, an optical filter must be placed in front of the camera lens to block sunlight. Therefore, the method described in Patent Document 1 makes it difficult to miniaturize observation satellites. Furthermore, it is difficult to reduce the cost of observation satellites.

[0007] This disclosure aims to enable the observation of a cosmic object while moving relative to that object. [Means for solving the problem]

[0008] The observation satellite disclosed herein is An observation satellite that orbits the Earth, An observation device for observing space objects flying along geostationary orbit above the target area, A propulsion system for changing the flight speed of the observation satellite, Equipped with, The propulsion system reduces the flight speed, thereby lowering the orbital altitude of the observation satellite. As the orbital altitude of the observation satellite decreases, its orbital velocity increases, becoming faster than the Earth's rotation speed. The aforementioned observation satellite, Between 10:00 and 18:00 solar time in the aforementioned target area, while moving eastward relative to the space object, the direction of the observation device is changed to a range of 30 to 90 degrees eastward from the anti-Earth direction, and the observation device is made to observe the space object. The observation device is made to observe the space object in the sky above the far side of the Earth between 18:00 and 6:00 solar time. [Effects of the Invention]

[0009] According to this disclosure, it becomes possible to observe a cosmic object while moving relative to the object. [Brief explanation of the drawing]

[0010] [Figure 1] Figure showing the configuration of the observation system 100 in Embodiment 1. [Figure 2] Configuration diagram of the observation satellite 200 in Embodiment 1. [Figure 3] Figure showing Example 1(1) of the observation method in Embodiment 1. [Figure 4] Figure showing Example 1(2) of the observation method in Embodiment 1. [Figure 5] Figure showing Example 1(3) of the observation method in Embodiment 1. [Figure 6] Figure showing Example 1(4) of the observation method in Embodiment 1. [Figure 7] Figure showing Example 1(5) of the observation method in Embodiment 1. [Figure 8] Figure showing Example 2(1) of the observation method in Embodiment 1. [Figure 9] Figure showing Example 2(2) of the observation method in Embodiment 1. [Figure 10] Figure showing Example 2(3) of the observation method in Embodiment 1. [Figure 11] Figure showing Example 2(4) of the observation method in Embodiment 1. [Figure 12] Figure showing Example 2(5) of the observation method in Embodiment 1. [Figure 13] Figure showing the state of observation by the observation satellite 200 in Embodiment 2. [Figure 14] Table showing the profile of the parking orbit in Embodiment 2. [Figure 15] Table showing the relationship between the orbital inclination angle and the maximum distance to the geostationary orbit 103 in Embodiment 2. [Figure 16] Figure showing the state of observation by the observation satellite 200 in Embodiment 2. [Figure 17] Figure showing the state of observation by the observation satellite 200 in Embodiment 2. [Figure 18] Figure showing the state of observation by the observation satellite 200 in Embodiment 2. [Figure 19]A diagram showing the observations made by the observation satellite 200 in Embodiment 2. [Figure 20] A diagram showing the parking operation in Embodiment 2. [Figure 21] A diagram showing the spiral operation in Embodiment 2. [Figure 22] A diagram showing the observations made by the observation satellite 200 in Embodiment 3. [Figure 23] A table showing the spiral trajectory profile in Embodiment 3. [Figure 24] A table showing the spiral trajectory profile in Embodiment 3. [Figure 25] A table showing the spiral trajectory profile in Embodiment 3. [Figure 26] A table showing the relationship between the orbital inclination angle and the maximum distance to the geostationary orbit 103 in Embodiment 3. [Figure 27] A diagram showing the observation at perigee in Embodiment 3. [Figure 28] A diagram showing the observation at perigee in Embodiment 3. [Figure 29] A diagram showing the observation at the apogee in Embodiment 3. [Figure 30] A diagram showing the observations made by the observation satellite 200 in Embodiment 3. [Figure 31] A diagram showing the observations made by the observation satellite 200 in Embodiment 3. [Figure 32] A diagram showing the observations made by the observation satellite 200 in Embodiment 3. [Figure 33] A diagram showing the observations made by the observation satellite 200 in Embodiment 3. [Figure 34] A diagram showing the spiral operation in Embodiment 3. [Figure 35] A diagram showing the observations made by the observation satellite 200 in Embodiment 4. [Figure 36] A diagram showing the observations made by the observation satellite 200 in Embodiment 4. [Figure 37]A diagram showing the spiral operation in Embodiment 5. [Figure 38] A diagram showing the spiral operation in Embodiment 5. [Figure 39] Configuration diagram of the observation system 100 in Embodiment 7. [Figure 40] A diagram showing the unobservable situation in Embodiment 7. [Figure 41] A diagram showing the observable conditions in Embodiment 7. [Figure 42] A diagram showing the observations made by the observation satellite 200 in Embodiment 8. [Figure 43] A diagram showing the unobservable situation in Embodiment 8. [Figure 44] A diagram showing the observable situation in Embodiment 8. [Figure 45] A diagram showing the observations made by the observation satellite 200 in Embodiment 9. [Modes for carrying out the invention]

[0011] In the embodiments and drawings, the same or corresponding elements are denoted by the same reference numeral. The descriptions of elements denoted by the same reference numeral as the described elements are omitted or simplified as appropriate.

[0012] Embodiment 1. The configuration for observing the space object 110 will be explained based on Figures 1 to 12.

[0013] ***Explanation of the structure*** Based on Figure 1, the configuration of the observation system 100 will be explained. Observation system 100 is a system for observing space object 110. "Observation" includes concepts such as "surveillance" or "photography."

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

[0015] The observation system 100 is equipped with an observation satellite 200. Observation satellite 200 is an artificial satellite that orbits the Earth at point 101. Observation satellite 200 will orbit Earth 101, flying in or near geostationary orbit 103. Observation satellite 200 will optically photograph space object 110 from an altitude different from the altitude at which space object 110 is located.

[0016] The altitude of geostationary orbit 103 is approximately 36,000 kilometers. A geostationary satellite is an artificial satellite that orbits the Earth in a geostationary orbit (103) in sync with the Earth's rotation (101). In other words, a geostationary satellite completes one orbit in geostationary orbit (103) per day. To put it another way, a geostationary satellite completes one orbit in geostationary orbit (103) every 24 hours. Space object 110, like a geostationary satellite, orbits geostationary orbit 103 once per day. Observation satellite 200 orbits geostationary orbit 103 or near geostationary orbit 103 once per day. The directions in which space object 110 and observation satellite 200 orbit are the same as the directions in which geostationary satellites orbit.

[0017] The light from Sun 102 is called sunlight. The side of Earth 101 that receives sunlight is called the near side of Earth 101. The side of Earth 101 that is not exposed to sunlight is called the far side of Earth 101. In Figure 1, the space object 110 and the observation satellite 200 are both orbiting the near side of Earth 101.

[0018] Based on Figure 2, the configuration of observation satellite 200 will be explained. The observation satellite 200 is equipped with an observation instrument 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] Observation device 201 is a device for observing space object 110. The observation instrument 201 optically photographs the space object 110 flying at an altitude different from the orbital altitude of the observation satellite 200. Specifically, the observation instrument 201 is a visible optical sensor. The observation device 201 generates observational data. Observational data is data obtained through observations performed by the observation device 201. For example, the observational data corresponds to data representing an image of the space object 110.

[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 predetermined procedures or various commands transmitted from ground equipment.

[0021] Communication device 203 is a device that communicates with ground facilities. The communication device 203 transmits observation data to ground equipment. The communication device 203 also receives various commands transmitted from 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. Specifically, the propulsion system 204 is an electric propulsion system. For example, the propulsion system 204 is 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. Alternatively, the attitude control device 205 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 instrument 201. The attitude control device 205 comprises attitude sensors, actuators, and a controller. The attitude sensors include gyroscopes, earth sensors, solar sensors, star trackers, thrusters, or magnetic sensors. The actuators include attitude control thrusters, momentum wheels, reaction wheels, or control moment gyros. The controller controls the actuators by executing a control program based on measurement data obtained from the attitude sensors or according to control commands from ground equipment.

[0024] The power supply unit 206 is equipped with solar cells, batteries, and a power control device, and supplies power to each device of the observation satellite 200.

[0025] Let me add some information about the satellite control device 202. The satellite control device 202 is equipped with a processing circuit. The processing circuit may be dedicated hardware or a processor that executes a program stored in memory. The processing circuit functions as an observation and control unit that controls the propulsion device 204. In a processing circuit, some functions may be implemented by dedicated hardware, while the remaining functions are implemented by software or firmware. In other words, a processing circuit can be implemented using hardware, software, firmware, or a combination thereof. Dedicated hardware includes, for example, single circuits, complex circuits, programmed processors, parallel programmed processors, ASICs, FPGAs, or combinations thereof. ASIC is an abbreviation for Application Specific Integrated Circuit. FPGA is an abbreviation for Field Programmable Gate Array.

[0026] I will provide additional information about the pointing function of observation satellite 200. Observation satellite 200 has a pointing function to orient its observation direction toward space object 110. For example, observation satellite 200 is equipped with reaction wheels. Reaction wheels are devices used to control the attitude of observation satellite 200. The attitude of observation satellite 200 is controlled by the reaction wheels, enabling body pointing. For example, the observation device 201 is equipped with 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 may be used in the pointing mechanism.

[0027] I will provide additional information about the observation functions of observation device 201. The observation device 201 has a variable resolution function and an autofocus function. The variable resolution function allows you to change the resolution during observation. The autofocus function is a feature that focuses on space object 110.

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

[0029] I will now explain the overview of the observation method. The propulsion system 204 changes the flight speed of the observation satellite 200 after it has begun orbiting either the near side or the far side of Earth 101. This causes the orbital altitude of the observation satellite 200 to change from the altitude of geostationary orbit 103. The propulsion system 204 changes the flight speed of the observation satellite 200 before it begins orbiting the other side of Earth 101, which is either the near side or the far side. This causes the observation satellite 200's orbital altitude to return to the altitude of geostationary orbit 103. The observation device 201 optically photographs the space object 110 flying at an altitude different from the orbital altitude of the observation satellite 200.

[0030] The observation method will be explained based on Figures 3 to 12. The four times "00:00", "06:00", "12:00", and "18:00" assigned to geostationary orbit 103 represent the time in a specific region of Earth 101 (for example, Japan). Observation satellite 200 orbits the near side of Earth 101 during daylight hours (06:00 to 18:00) in a specific region. In other words, observation satellite 200 begins orbiting the near side of Earth 101 around 6:00 and finishes orbiting the near side of Earth 101 around 18:00. Observation satellite 200 orbits the far side of Earth 101 during nighttime hours (18:00 to 06:00) in a specific region. In other words, observation satellite 200 begins orbiting the far side of Earth 101 around 18:00 and finishes orbiting the far side of Earth 101 around 6:00.

[0031] <Example 1> Example 1 will be described based on Figures 3 to 7. Example 1 is an example in which the observation satellite 200 orbits the near side of the Earth 101.

[0032] In Figure 3, after the observation satellite 200 begins orbiting the near side of the Earth 101, the propulsion system 204 increases the flight speed of the observation satellite 200. Specifically, the satellite control device 202 determines whether or not the observation satellite 200 has begun orbiting the near side of the Earth 101. For example, the satellite control device 202 makes this determination by referring to the time. If the observation satellite 200 has begun orbiting the near side of the Earth 101, the satellite control device 202 instructs the propulsion device 204 to increase its speed. The propulsion device 204 then increases the flight speed of the observation satellite 200. As a result, the orbital altitude of observation satellite 200 will rise from the altitude of geostationary orbit 103.

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

[0034] Figure 5 shows how space object 110, which has caught up with observation satellite 200, is photographed by observation satellite 200. Figure 6 shows how space object 110, which overtook observation satellite 200, is photographed by observation satellite 200. While the observation satellite 200 is orbiting the near side of the Earth 101, the observation instrument 201 photographs the space object 110 flying at an altitude lower than the orbital altitude of the observation satellite 200. As a result, the observation instrument 201 photographs the space object 110 in direct sunlight. Specifically, while the observation satellite 200 is orbiting the near side of Earth 101, the observation instrument 201 takes pictures in the direction of Earth 101. As a result, the observation instrument 201 takes pictures of space object 110 that is flying in geostationary orbit 103 and overtaking the observation satellite 200.

[0035] In Figure 7, before the observation satellite 200 begins orbiting the far side of Earth 101, the propulsion system 204 reduces the flight speed of the observation satellite 200. Specifically, the satellite control device 202 determines whether or not the observation satellite 200 is about to begin orbiting the far side of Earth 101. For example, the satellite control device 202 makes this determination by referring to the time. Before the observation satellite 200 begins orbiting the far side of Earth 101, the satellite control device 202 instructs the propulsion device 204 to decelerate. The propulsion device 204 then reduces the flight speed of the observation satellite 200. As a result, the orbital altitude of observation satellite 200 will descend to the altitude of geostationary orbit 103.

[0036] <Example 2> Example 2 will be described based on Figures 8 to 12. Example 2 is an example in which observation satellite 200 orbits on the far side of Earth 101.

[0037] In Figure 8, after the observation satellite 200 begins orbiting the far side of Earth 101, the propulsion system 204 reduces the flight speed of the observation satellite 200. Specifically, the satellite control device 202 determines whether or not the observation satellite 200 has begun orbiting the far side of the Earth 101. For example, the satellite control device 202 makes this determination by referring to the time. If the observation satellite 200 has begun orbiting the far side of the Earth 101, the satellite control device 202 instructs the propulsion system 204 to decelerate. The propulsion system 204 then reduces the flight speed of the observation satellite 200. As a result, the orbital altitude of observation satellite 200 will decrease from the altitude of geostationary orbit 103.

[0038] In Figure 9, as the orbital altitude of observation satellite 200 decreases from the altitude of geostationary orbit 103, the ground velocity of observation satellite 200 increases. In other words, the ground velocity of observation satellite 200 will be faster than the ground velocity of space object 110.

[0039] Figure 10 shows how space object 110, which has been overtaken by observation satellite 200, is photographed by observation satellite 200. Figure 11 shows how space object 110, which has been overtaken by observation satellite 200, is photographed by observation satellite 200. While observation satellite 200 is orbiting on the far side of Earth 101, observation instrument 201 photographs space object 110 flying at an altitude higher than the orbital altitude of observation satellite 200. As a result, observation instrument 201 photographs space object 110 in direct sunlight. Specifically, while the observation satellite 200 is orbiting on the far side of Earth 101, the observation instrument 201 photographs the opposite side from Earth 101. As a result, the observation instrument 201 photographs the space object 110 as it is overtaken by the observation satellite 200 while flying in geostationary orbit 103.

[0040] In Figure 12, before the observation satellite 200 begins orbiting the near side of the Earth 101, the propulsion system 204 increases the flight speed of the observation satellite 200. Specifically, the satellite control device 202 determines whether or not the observation satellite 200 is about to begin orbiting the near side of Earth 101. For example, the satellite control device 202 makes this determination by referring to the time. Before the observation satellite 200 begins orbiting the near side of Earth 101, the satellite control device 202 instructs the propulsion device 204 to increase its speed. The propulsion device 204 then increases the flight speed of the observation satellite 200. This will raise the orbital altitude of observation satellite 200 to the altitude of geostationary orbit 103.

[0041] ***Effects of Embodiment 1*** Observation satellite 200 will fly in or near geostationary orbit 103. Observation satellite 200 will increase its speed and rise its orbital altitude after 6:00. Then, observation satellite 200 will photograph space object 110 as it flies through geostationary orbit 103 and overtakes observation satellite 200. Finally, observation satellite 200 will decelerate and descend its orbital altitude before 18:00. As observation satellite 200 increases its speed, its orbital altitude rises. As the orbital altitude of observation satellite 200 increases, its velocity relative to the ground decreases. Therefore, observation satellite 200 is overtaken by space object 110 flying in geostationary orbit 103. Observation satellite 200 flies at an orbital altitude higher than the altitude of geostationary orbit 103 between 6:00 and 18:00. Observation satellite 200 receives solar reflected light from space object 110 flying in geostationary orbit 103. This allows observation satellite 200 to observe space object 110 under favorable conditions.

[0042] Observation satellite 200 will decelerate after 18:00 and descend its orbital altitude. Then, observation satellite 200 will photograph space object 110 as it flies through geostationary orbit 103 and is overtaken by observation satellite 200. After that, observation satellite 200 will accelerate before 6:00 the following day and ascend its orbital altitude. As observation satellite 200 decelerates, its orbital altitude decreases. As the orbital altitude of observation satellite 200 decreases, its velocity over the ground increases. Therefore, observation satellite 200 overtakes space object 110 flying in geostationary orbit 103. Observation satellite 200 flies at an orbital altitude lower than the altitude of geostationary orbit 103 between 18:00 and 6:00 the following day. Observation satellite 200 receives reflected sunlight from space object 110 flying in geostationary orbit 103. This allows observation satellite 200 to observe space object 110 under favorable conditions.

[0043] ***Supplement to Embodiment 1*** Observation satellite 200 may fly in orbits other than geostationary orbit 103, or in the vicinity thereof. Space object 110 may fly in an orbit other than geostationary orbit 103. Also, space object 110 may fly in an orbit other than geostationary orbit. The ascent and descent of the orbital altitude may be carried out with intervals of several days. The longer the number of observation days from high altitude or low altitude, the longer the relative distance traveled in the longitude direction can be. The greater the difference in altitude due to the rise and fall of orbital altitude, the longer the relative distance traveled in the longitude direction can be. By using powerful thrusters such as chemical propulsion systems to raise and lower orbital altitude, it is possible to create a large altitude difference in a short period of time.

[0044] Embodiment 2. The main differences between the observation satellite 200 and Embodiment 1 will be explained based on Figures 13 to 21.

[0045] ***Explanation of the structure*** The configuration of the observation satellite 200 is the same as the configuration in Embodiment 1. Observation satellite 200 is an artificial satellite that orbits the Earth at an altitude of 35,800 kilometers above the equator. In Embodiment 2, the altitude of 35,800 kilometers is an approximate altitude. The observation satellite 200 is equipped with an observation instrument 201 and a propulsion system 204. Observation device 201 is a device for optically photographing space object 110 flying along geostationary orbit 103. Space object 110 flies in or near geostationary orbit 103. The propulsion system 204 changes the flight speed of the observation satellite 200.

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

[0047] This section describes the inclined elliptical orbit of observation satellite 200. The major axis points towards the sun. In other words, the direction of the major axis is equal to the direction from Earth 101 to Sun 102. The apogee is on the side of the sun. In other words, the apogee is on the side where the sun (102) is located. The normal vector of the orbital plane is inclined around the geocentric direction. An inclined elliptical orbit is a sun-synchronous orbit, where the major axis and normal vector are synchronized with the Sun 102.

[0048] ***Detailed explanation*** Figure 13 shows observation satellite 200, flying in an inclined elliptical orbit, observing space object 110 from a high altitude while being overtaken by it. Observation satellite 200 will use an inclined elliptical orbit. The orbital period of observation satellite 200 will be the same as that of a geostationary satellite. In other words, observation satellite 200 will orbit approximately once a day, completing one revolution in 365 days. This allows the observation satellite 200 to maintain its relative position to the geostationary object 110 over the long term. Furthermore, at its perigee, the observation satellite 200 can observe the object 110 while flying at an altitude lower than that of geostationary orbit 103 (low altitude), moving relatively eastward relative to the object 110. At its apogee, the observation satellite 200 can observe the object 110 while flying at an altitude higher than that of geostationary orbit 103 (high altitude), moving relatively westward relative to the object 110.

[0049] In the orbit of observation satellite 200, the orientation of its long axis is always the same as the direction of the sun. This is achieved by the satellite control device 202 controlling the propulsion system 204 to change the flight speed. This enables daytime monitoring from high altitudes at the apogee. Daytime monitoring is performed on the near side (sunlit side) of Earth-101. In addition, nighttime monitoring from low altitudes is performed at the perigee. Nighttime monitoring is performed on the far side (opposite the sunlit side) of Earth-101.

[0050] If the observation satellite 200's orbit does not have an inclination angle, there is a risk that the observation satellite 200 will collide with the geostationary object 110 when its orbital altitude becomes equal to that of geostationary orbit 103 during its journey from apogee to perigee. Therefore, an inclination angle is applied to the orbit of observation satellite 200. This ensures that when observation satellite 200 passes near geostationary orbit 103, a distance is created between observation satellite 200 and geostationary orbit 103 in the north-south direction.

[0051] To maintain the above operational conditions, the orbital plane of observation satellite 200 is maintained with the normal vector of the orbital plane tilted around the geocentric direction, thereby synchronizing the orbit of observation satellite 200 with the sun. It should be noted that an orbit in which the orbital plane is maintained with the long axis constantly pointed towards the sun, and in which the normal vector of the orbital plane revolves in synchronization with the sun 102, cannot be achieved solely through natural phenomena. However, by operating the propulsion device 204, such an orbit becomes possible. Furthermore, synchronizing orbital planes with large inclination angles usually requires a large amount of propellant. However, for gentle inclination angles of 1 degree or less, the amount of propellant required is limited, making it easier to achieve.

[0052] Figure 14 shows the profile of the parking track. If the orbital period of observation satellite 200 is equivalent to that of geostationary orbit 103, observation satellite 200 will orbit space object 110 once per day while oscillating in the longitude direction relative to space object 110. Such an orbit of observation satellite 200 is called a "parking orbit". The radius of Earth orbit 101 is approximately 6,400 kilometers, and the altitude of geostationary orbit 103 is approximately 35,800 kilometers. Therefore, the radius of geostationary orbit 103 is approximately 42,200 kilometers. In an elliptical orbit with a major axis approximately the same as the diameter of geostationary orbit 103, if the eccentricity is 1.001, the altitude difference between the apogee and geostationary orbit 103, and the altitude difference between the perigee and geostationary orbit 103, will be approximately 50 kilometers. Furthermore, if the eccentricity is 1.01, the respective altitude differences will be approximately 400 kilometers. A small altitude difference allows for high-resolution observation of space object 110, while a large altitude difference allows for an increase in the relative velocity with space object 110 in the longitude direction.

[0053] Figure 15 shows the relationship between the orbital inclination and the maximum distance to geostationary orbit 103. If the orbital inclination of observation satellite 200 is 0.1 degrees, then in the north-south direction, observation satellite 200 will be approximately 70 kilometers away from geostationary orbit 103. If the orbital inclination of observation satellite 200 is 0.7 degrees, then in the north-south direction, observation satellite 200 will be approximately 500 kilometers away from geostationary orbit 103. The orbit of the observation satellite 200 should be set to an inclination angle suitable for avoiding collisions with space objects 110, depending on the distribution of space objects 110 around the geostationary orbit 103.

[0054] Figure 16 shows observation satellite 200 flying at a low altitude, overtaking space object 110 while monitoring it. Figure 17 shows the observation satellite 200 passing through the altitude of geostationary orbit 103. Due to the inclination of the observation satellite 200's orbit, as the observation satellite 200 passes through the altitude of geostationary orbit 103, it moves away from the space object 110 in the north-south direction. Therefore, there is no risk of the observation satellite 200 colliding with the space object 110. If the average altitude of observation satellite 200 is lower than that of geostationary orbit 103, the orbital period of observation satellite 200 will be shorter than that of geostationary orbit 103. As a result, observation satellite 200 will move eastward relative to space object 110 each day. The flight path of observation satellite 200 will be spiral-shaped.

[0055] Figure 18 shows observation satellite 200 flying at high altitude and monitoring space object 110 while being overtaken by it. Figure 19 shows the observation satellite 200 passing through the altitude of geostationary orbit 103. Due to the inclination of the observation satellite 200's orbit, as the observation satellite 200 passes through the altitude of geostationary orbit 103, it moves away from the space object 110 in the north-south direction. Therefore, there is no risk of the observation satellite 200 colliding with the space object 110. If the average altitude of observation satellite 200 is higher than that of geostationary orbit 103, the orbital period of observation satellite 200 will be longer than that of geostationary orbit 103. As a result, observation satellite 200 will move westward relative to space object 110 each day. The flight path of observation satellite 200 will be spiral-shaped. By using the propulsion system 204, the orbit of the observation satellite 200 can be maintained with its major axis pointing towards the sun 102. As a result, the observation satellite 200 will be at its apogee around 12:00 each day, making it possible to monitor the space object 110 from a high altitude during daylight hours.

[0056] By employing an eccentric elliptical orbit in the observation system 100, and by keeping the direction of the major axis of the elliptical orbit always the same as the direction of the sun, it is possible to achieve both sunlit monitoring from high altitudes and nighttime monitoring from low altitudes. By setting the orbit of observation satellite 200 to an inclined orbit, when the orbital radius becomes equivalent to that of geostationary orbit 103 (when flying near the perpendicular axis of the major axis), the orbit of observation satellite 200 moves out of the plane of geostationary orbit 103. Furthermore, by setting the orbit of observation satellite 200 to an elliptical orbit, when observation satellite 200 passes within the orbital plane of geostationary orbit 103 (when flying near the major axis and when flying near the minor axis), the orbital altitude of observation satellite 200 is different from that of geostationary orbit 103, thus eliminating the risk of observation satellite 200 colliding with the satellites of geostationary orbit 103.

[0057] Figure 20 shows the parking operation using an inclined elliptical orbit. When the orbital period of observation satellite 200 is the same as that of geostationary orbit, observation satellite 200 orbits in the equatorial plane in the direction perpendicular to the geocenter, as shown in Figure 20, within one day. If the major axis of the elliptical orbit of observation satellite 200 is made approximately the same as the diameter of geostationary orbit 103, the orbital period of observation satellite 200 will be the same as that of geostationary orbit 103. As a result, observation satellite 200 will orbit approximately once a day. Therefore, observation satellite 200 will maintain approximately the same longitude as space object 110 and orbit space object 110 once a day relative to its direction of flight.

[0058] Figure 21 shows the spiral operation of an inclined elliptical orbit. When the orbital period of observation satellite 200 is longer than the orbital period of geostationary orbit, observation satellite 200 will orbit in the equatorial plane in the direction perpendicular to the geocenter as shown in Figure 21 within one day. If the major axis of the elliptical orbit of observation satellite 200 is longer than the diameter of geostationary orbit 103, then the orbital period of observation satellite 200 will be longer than the orbital period of geostationary orbit 103. As a result, observation satellite 200 will move westward relative to space object 110. In other words, observation satellite 200 will move in a spiral pattern. However, at the perigee side, observation satellite 200 will move eastward relative to space object 110. If the major axis of the elliptical orbit of observation satellite 200 is shorter than the diameter of geostationary orbit 103, then the orbital period of observation satellite 200 will be shorter than the orbital period of geostationary orbit 103. As a result, observation satellite 200 will move eastward relative to space object 110. In other words, observation satellite 200 will move in a spiral pattern. However, at the apogee, observation satellite 200 will move westward relative to space object 110.

[0059] Embodiment 3. The differences between observation satellite 200 and Embodiment 1 or Embodiment 2 will be explained primarily based on Figures 22 to 34.

[0060] ***Explanation of the structure*** The configuration of the observation satellite 200 is the same as the configuration in Embodiment 1. Observation satellite 200 is an artificial satellite that orbits the Earth 101 at an altitude of 35,800 kilometers above the equator. In Embodiment 3, the altitude of 35,800 kilometers is an approximate altitude. The observation satellite 200 is equipped with an observation instrument 201 and a propulsion system 204. Observation device 201 is a device for optically photographing space object 110 flying along geostationary orbit 103. Space object 110 flies in or near geostationary orbit 103. The propulsion system 204 changes the flight speed of the observation satellite 200.

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

[0062] This section describes the inclined elliptical orbit of observation satellite 200. The major axis points towards the sun when viewed from the North Pole. In other words, the direction of the major axis is equal to the direction from Earth 101 to Sun 102 when viewed from the North Pole. Perigee is on the side of the sun. In other words, perigee is on the side where Sun 102 is located. The normal vector of the orbital plane is inclined around the minor axis of the ellipse. An inclined elliptical orbit is a sun-synchronous orbit, where the major axis and normal vector are synchronized with the Sun 102.

[0063] ***Explanation of Effects*** Figure 22 shows the observation satellite 200 observing space object 110 while being overtaken by space object 110. If the average altitude of observation satellite 200 is high, and observation satellite 200 observes space object 110 while moving westward relative to space object 110, then observation satellite 200 can observe space object 110 without backlighting, both during daytime flight from 6:00 to 18:00 and during nighttime flight from 18:00 to 6:00. Observation satellite 200 can observe all faces of space object 110 except the face opposite to the side facing Earth 101. In other words, observation satellite 200 can observe the face of space object 110 facing Earth 101, as well as the sides of space object 110. In the longitude zone where observation satellite 200 crosses the congested region of the geostationary orbit, the orbital altitude of observation satellite 200 differs from the altitude of geostationary orbit 103. This allows for the avoidance of collisions between observation satellite 200 and space objects in the congested region. In the orbit of observation satellite 200, it oscillates in a north-south direction relative to space object 110. To prevent a collision between observation satellite 200 and space object 110, the orbital altitude of observation satellite 200 when it passes through the geostationary orbit plane is higher than the altitude of geostationary orbit 103.

[0064] Figures 23, 24, and 25 show the spiral trajectory profile during westward movement. The radius of Earth orbit 101 is approximately 6,400 kilometers, and the altitude of geostationary orbit 103 is approximately 35,800 kilometers. Therefore, the radius of geostationary orbit 103 is approximately 42,200 kilometers. In an elliptical orbit having a major axis approximately the same as that of geostationary orbit 103, if the eccentricity is 1.001, the altitude difference between the perigee and geostationary orbit 103 is approximately 50 kilometers. Furthermore, if the eccentricity is 1.01, the altitude difference between the perigee and geostationary orbit 103 is approximately 400 kilometers. A small altitude difference allows for high-resolution observation of space object 110, while a large altitude difference allows for an increase in the relative velocity with space object 110 in the longitude direction.

[0065] ***Detailed explanation*** Figure 26 shows the relationship between the orbital inclination and the maximum distance to geostationary orbit 103. If the orbital inclination of observation satellite 200 is 0.1 degrees, then in the north-south direction, observation satellite 200 will be approximately 70 kilometers away from geostationary orbit 103. If the orbital inclination of observation satellite 200 is 0.7 degrees, then in the north-south direction, observation satellite 200 will be approximately 500 kilometers away from geostationary orbit 103. A shorter distance between observation satellite 200 and geostationary orbit satellite 103 allows for high-resolution observations.

[0066] Figure 27 shows the observations at perigee when the altitude of perigee is equivalent to the altitude of geostationary orbit 103. If the altitude of the perigee is approximately 35,800 kilometers, which is equivalent to the altitude of geostationary orbit 103, then at the perigee, observation satellite 200 will observe space object 110 from the south or north. The observation will not be backlit, and it will be possible to observe the solar reflection from space object 110.

[0067] Figure 28 shows the observations at perigee when the altitude of perigee is lower than the altitude of geostationary orbit 103. If the altitude of the perigee is lower than the altitude of the geostationary orbit 103, at the perigee, the observation satellite 200 will observe the space object 110 from the south or north with a line-of-sight vector tilted toward the sun. The observation will not be backlit, and it will be possible to observe the solar reflected light from the space object 110.

[0068] Figure 29 shows the observation at the apogee. At its apogee, observation satellite 200 will observe space object 110 from the south or north with a line-of-sight vector tilted towards the sun. The observation will not be backlit, and it will be possible to observe the solar reflection from space object 110.

[0069] Figures 30 to 33 show the observation satellite 200 observing space object 110 while being overtaken by it.

[0070] Figure 34 shows the spiral operation using an inclined elliptical orbit. Viewed from a direction perpendicular to the geocenter within the equatorial plane, observation satellite 200 orbits in the manner shown in Figure 34 over the course of a day.

[0071] Embodiment 4. The differences between the observation satellite 200 and embodiments 1 to 3 will be explained primarily based on Figures 35 and 36.

[0072] ***Explanation of the structure*** The configuration of the observation satellite 200 is the same as the configuration in Embodiment 1. Observation satellite 200 is an artificial satellite that orbits the Earth 101 at an altitude of 35,800 kilometers above the equator. In Embodiment 3, the altitude of 35,800 kilometers is an approximate altitude. The observation satellite 200 is equipped with an observation instrument 201 and a propulsion system 204. Observation device 201 is a device for optically photographing space object 110 flying along geostationary orbit 103. Space object 110 flies in or near geostationary orbit 103. The propulsion system 204 changes the flight speed of the observation satellite 200.

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

[0074] This section describes the inclined elliptical orbit of observation satellite 200. The major axis points towards the sun when viewed from the North Pole. In other words, the direction of the major axis is equal to the direction from Earth 101 to Sun 102 when viewed from the North Pole. The apogee is on the side of the sun. In other words, the apogee is on the side where the sun (102) is located. The normal vector of the orbital plane is inclined around the minor axis of the ellipse. An inclined elliptical orbit is a sun-synchronous orbit, where the major axis and normal vector are synchronized with the Sun 102.

[0075] ***Explanation of Effects*** Figures 35 and 36 show the observation satellite 200 observing the space object 110 while being overtaken by the space object 110. Observation satellite 200 can observe the side of space object 110 and the Earth-facing plane of space object 110 at close range around midnight. Except for a short period when space object 110 is in the shadow of Earth 101, observation satellite 200 can observe space object 110 under daylight conditions. By setting a higher average altitude for observation satellite 200, the speed at which it moves westward relative to space object 110 per orbit can be increased. As a result, a predetermined longitude range can be covered in a shorter period of time. When observing space object 110 at close range near its perigee, the relative velocity of observation satellite 200 to space object 110 is slow. Therefore, space object 110 can be observed in detail. If the orbital altitude of observation satellite 200 at perigee is equal to the altitude of geostationary orbit 103, observation satellite 200 will fly at a speed approximately equal to the velocity of space object 110 in the longitude direction. If the orbital altitude of observation satellite 200 at perigee is lower than the altitude of geostationary orbit 103, observation satellite 200 will temporarily fly while moving eastward relative to space object 110.

[0076] Embodiment 5. The differences between the observation satellite 200 and embodiments 3 and 4 will be explained primarily based on Figures 37 and 38.

[0077] ***Example 1*** Figure 37 shows the spiral operation of the inclined elliptical orbit during the summer. Viewed from a direction perpendicular to the geocenter within the equatorial plane, observation satellite 200 orbits in the manner shown in Figure 37 over the course of a day. In the inclined elliptical orbit of geostationary orbit 103, the normal vector to the orbital plane is inclined around the minor axis of the inclined ellipse. The perigee of the inclined ellipse is located to the north.

[0078] ***Example 2*** Figure 38 shows the spiral operation of the inclined elliptical orbit during winter. Viewed from a direction perpendicular to the geocenter within the equatorial plane, observation satellite 200 orbits in the manner shown in Figure 38 over the course of a day. In the inclined elliptical orbit of geostationary orbit 103, the normal vector to the orbital plane is inclined around the minor axis of the inclined ellipse. The perigee of the inclined ellipse is located to the south.

[0079] ***Effects of the Example*** Because the Earth's rotational axis is tilted, the angle of incidence of sunlight on the geostationary orbit plane varies by +23.6 degrees or -23.6 degrees between summer and winter. Therefore, to avoid backlighting and to ensure that the reflection of 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, observational data with superior image quality can be obtained. During daytime observations in summer from 6:00 to 18:00, and during nighttime observations in winter from 18:00 to 6:00, the inclined elliptical orbit of geostationary orbit 103 tilts so that its perigee is located north of geostationary orbit 103. Also, during nighttime observations in summer and daytime observations in winter, the inclined elliptical orbit of geostationary orbit 103 tilts so that its perigee is located south of geostationary orbit 103. These conditions are advantageous for observation.

[0080] Embodiment 6. Examples of the observation satellite 200, from Embodiment 2 to Embodiment 5, will be described below.

[0081] ***Example A*** In the inclined elliptical orbit of observation satellite 200, the eccentricity is between 1.001 and 1.01.

[0082] ***Example B*** In the inclined elliptical orbit of observation satellite 200, the inclination angle is 1 degree or less.

[0083] ***Example C*** The observation instrument 201 photographs the space object 110 flying at an altitude lower than the apogee altitude of its inclined elliptical orbit while the observation satellite 200 is orbiting the near side of the Earth 101. As a result, the observation instrument 201 photographs the space object 110 in direct sunlight.

[0084] ***Example D*** Observation device 201 photographs space object 110 flying at an altitude higher than the perigee altitude of its inclined elliptical orbit while observation satellite 200 is orbiting on the far side of Earth 101. As a result, observation device 201 photographs space object 110 in direct sunlight.

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

[0086] ***Example F*** Observation device 201 photographs the direction toward Earth while observation satellite 200 is orbiting the near side of Earth 101. As a result, observation device 201 photographs space object 110 that is flying in geostationary orbit 103 and overtaking observation satellite 200.

[0087] ***Example G*** Observation device 201 photographs the direction opposite to the Earth while observation satellite 200 is orbiting on the far side of Earth 101. As a result, observation device 201 photographs space object 110 as it is overtaken by observation satellite 200 while flying in geostationary orbit 103.

[0088] ***Example H*** The observation instrument 201 photographs the Earth-facing side or the side of the space object 110 from either the south side or the north side of the space object 110 while the observation satellite 200 is orbiting the near side of the Earth 101.

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

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

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

[0092] Embodiment 7. The observation system 100 will be described, primarily based on the differences between it and embodiments 1 to 6, using Figures 39 to 41.

[0093] ***Explanation of the structure*** Based on Figure 39, the configuration of the observation system 100 will be explained. The observation system 100 is equipped with ground facilities 120. Ground equipment 120 is equipment for communicating with and controlling the observation satellite 200, and is installed on the ground. The ground equipment 120 includes communication equipment 121, a satellite management device 122, an artificial object identification device 123, and a space object management device 124. Communication equipment 121 is for communicating with observation satellite 200. Specifically, communication equipment 121 receives observation data and telemetry from observation satellite 200. Communication equipment 121 also transmits control commands and space object information to 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 observational data from the observation satellite 200. The space object management device 124 manages information about the space object 110 (space object information). For example, the space object management device 124 manages the position information of the space object 110 at each time point and the orbital information of the space object 110. Each of the satellite management device 122, the artificial object identification device 123, and the space object management device 124 is equipped with a processing circuit. These processing circuits are similar to those of the satellite control device 202.

[0094] ***Explanation of operation*** Observation satellite 200 will fly at a low altitude, moving eastward relative to space object 110, while taking forward-looking images. Observation satellite 200 will then transmit the image data (observation data) at each time point. The artificial object identification device 123 receives image data at each time point via the communication equipment 121. Based on the image data at each time point, the artificial object identification device 123 identifies the observed artificial object. Specifically, the artificial object identification device 123 identifies space objects 110 that were not photographed before 12:00 but were photographed after 12:00, and identifies the identified space objects 110 as artificial objects.

[0095] Observation satellite 200 moves westward relative to space object 110 by flying at a high altitude, taking rear-view images. Observation satellite 200 then transmits the image data at each time point. The artificial object identification device 123 receives image data at each time point via the communication equipment 121. Based on the image data at each time point, the artificial object identification device 123 identifies the observed artificial object. Specifically, the artificial object identification device 123 identifies space objects 110 that were not photographed before 12:00 but were photographed after 12:00, and identifies the identified space objects 110 as artificial objects.

[0096] Figure 40 shows a situation where artificial object 111 cannot be observed because it is located in the shade before 12:00. Figure 41 shows the conditions under which artificial object 111 can be observed because it is positioned in the sunlight after 12:00. Space objects 110 orbiting geostationary orbit 103 include both natural and artificial objects. Natural objects have random shapes, making them less likely to reflect sunlight. Artificial objects have highly regular shapes, such as cubes. Therefore, by observing the sunlight (reflected light) reflected from space object 110 and examining the characteristics of the observed reflected light, artificial objects can be identified.

[0097] Embodiment 8. The main differences between observation satellite 200 and embodiments 1 to 7 will be explained based on Figures 42 to 44.

[0098] ***Explanation of the structure*** The configuration of the observation satellite 200 is the same as the configuration in Embodiment 1. Observation satellite 200 is an artificial satellite that orbits the Earth at point 101. The observation satellite 200 is equipped with an observation instrument 201 and a propulsion system 204. Observation device 201 is a device for observing space object 110 flying along geostationary orbit 103 above the target area. Space object 110 flies in or near geostationary orbit 103. The propulsion system 204 changes the flight speed of the observation satellite 200.

[0099] ***Explanation of operation*** The propulsion system 204 lowers the orbital altitude of the observation satellite 200 by reducing its flight speed. The orbital velocity of observation satellite 200 increases as its orbital altitude decreases. Eventually, the orbital velocity of observation satellite 200 becomes faster than the rotation speed of Earth 101. Observation satellite 200 moves eastward relative to space object 110 between 10:00 and 18:00 solar time (LST) in the target region. During this time, observation satellite 200 changes the direction of observation instrument 201 from the anti-Earth direction to an eastward direction of 30 to 90 degrees, allowing observation instrument 201 to observe space object 110. Observation satellite 200 will have its observation instrument 201 observe space object 110 in the atmosphere above the far side of Earth 101 between 18:00 and 6:00 solar time in the target region. LST is an abbreviation for Local Sun Time.

[0100] Figure 42 shows observation satellite 200 flying at a low altitude, overtaking space object 110 while observing it. If observation satellite 200 flies at a low altitude and pointed in the anti-Earth direction, it will be backlit around 12 o'clock, making observation impossible. However, if the direction of sight is changed to within a range of 30 to 90 degrees east of the anti-Earth direction, the time period of backlighting will be from 6 o'clock to 10 o'clock, and after that time, it will be able to monitor space object 110 while viewing it diagonally to the right (towards the sun) as it flies. Observation satellite 200 will observe space object 110 in direct sunlight, facing away from Earth, from 6 PM on the day of observation until 6 AM the following day. Space object 110 will be flying in front of observation satellite 200 during the time prior to this observation period. Therefore, by observing space object 110 in forward sight between 10 AM and 6 PM on the day of observation, it is possible to determine the error in the orbital information of space object 110 in advance. In forward-looking observation, the distance to space object 110 is large, resulting in a wider field of view. Therefore, even if there are errors in the orbital information of space object 110, the risk of space object 110 deviating from the field of view is small. The operation to change attitude towards the opposite direction after looking forward until 6 PM on the same day can be performed in a short time using the high-torque attitude control device 205.

[0101] ***Examples*** Observation satellite 200 moves eastward relative to space object 110 at a low altitude, and between 13:00 and 18:00 solar time, observation instrument 201 observes space object 110 in a forward view.

[0102] Figure 43 shows a situation where artificial object 111 cannot be observed because it is located in the shade before 12:00. Figure 44 shows the conditions under which artificial object 111 can be observed after 13:00 because it is positioned in the sunlight. When observing an artificial object 111 that is roughly rectangular in shape and flies near geostationary orbit 103 towards Earth 101, there is a risk that even if observation is made with a wide-angle camera before noon, only the shaded side of the artificial object 111 will be visible, making it impossible to observe the artificial object 111. If observations are made after 13:00, the western side of artificial object 111 will be illuminated by sunlight, making it possible to observe artificial object 111.

[0103] Embodiment 9. The main differences between observation satellite 200 and embodiments 1 to 8 will be explained based on Figure 45.

[0104] ***Explanation of the structure*** The configuration of the observation satellite 200 is the same as the configuration in Embodiment 1. Observation satellite 200 is an artificial satellite that orbits the Earth at point 101. The observation satellite 200 is equipped with an observation instrument 201 and a propulsion system 204. Observation device 201 is a device for observing space object 110 flying along geostationary orbit 103 above the target area. Space object 110 flies in or near geostationary orbit 103. The propulsion system 204 changes the flight speed of the observation satellite 200.

[0105] ***Explanation of operation*** The propulsion system 204 increases the orbital altitude of the observation satellite 200 by increasing its flight speed. The orbital velocity of observation satellite 200 decreases as its orbital altitude increases. Eventually, the orbital velocity of observation satellite 200 becomes slower than the rotation speed of Earth 101. Observation satellite 200 moves westward relative to space object 110 between 10pm and 6am solar time (LST) in the target region. During this time, observation satellite 200 changes the direction of observation instrument 201 to a range of 30 to 90 degrees westward from the Earth direction, allowing observation instrument 201 to observe space object 110. Observation satellite 200 will have its observation instrument 201 observe space object 110 in the sky above the near side of Earth 101 between 6:00 and 18:00 solar time in the target region.

[0106] Figure 45 shows observation satellite 200 flying at high altitude and observing space object 110 while being overtaken by it. When observation satellite 200 flies at a high altitude with its orientation directed towards Earth, it will be backlit around 10 PM, making observation impossible. However, if the orientation is changed to within a range of 30 to 90 degrees west of Earth, the time period with backlighting will be from 6 PM to 10 PM, and after that time, it will be able to monitor space object 110 while viewing it diagonally to the left (towards the sun) backward. Observation satellite 200 will observe space object 110 in direct sunlight, facing Earth, from 6:00 AM to 6:00 PM on the day of observation. Space object 110 will be flying behind observation satellite 200 during the time prior to that observation period. Therefore, by observing space object 110 in a rear view between 10:00 PM the previous day and 6:00 AM on the day of observation, it will be possible to determine the error in the orbital information of space object 110 in advance. In the rear view, the distance to space object 110 is greater, resulting in a wider field of view. Therefore, even if there are errors in the orbital information of space object 110, the risk of space object 110 deviating from the field of view is small. The operation to change attitude towards the Earth after looking backward until 6:00 AM on the day can be performed in a short time using the high-torque attitude control device 205.

[0107] ***Supplementary Information on the Embodiment*** Each embodiment is an example of a preferred form and is not intended to limit the technical scope of the present invention. Each embodiment may be carried out 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 system, 205 Attitude control system, 206 Power supply unit.

Claims

1. An observation satellite that orbits the Earth, An observation device for observing space objects flying along geostationary orbit above the target area, A propulsion system for changing the flight speed of the observation satellite, Equipped with, The propulsion system reduces the flight speed, thereby lowering the orbital altitude of the observation satellite. As the orbital altitude of the observation satellite decreases, its orbital velocity increases, becoming faster than the Earth's rotation speed. The aforementioned observation satellite, Between 10:00 and 18:00 solar time in the aforementioned target area, while moving eastward relative to the space object, the direction of the observation device is changed to a range of 30 to 90 degrees eastward from the anti-Earth direction, and the observation device is made to observe the space object. The observation device is made to observe the space object in the sky above the far side of the Earth between 18:00 and 6:00 solar time. Observation satellite.

2. The observation satellite moves eastward relative to the space object at an altitude lower than that of geostationary orbit, and the observation device observes the space object in a forward view between 13:00 and 18:00 solar time. The observation satellite according to claim 1.

3. An observation satellite that orbits the Earth, An observation device for observing space objects flying along geostationary orbit above the target area, A propulsion system for changing the flight speed of the observation satellite, Equipped with, The propulsion system increases the orbital altitude of the observation satellite by increasing its flight speed. As the orbital altitude of the observation satellite increases, its orbital velocity decreases, becoming slower than the Earth's rotation speed. The aforementioned observation satellite, Between 22:00 and 6:00 solar time in the aforementioned target area, while moving westward relative to the space object, the direction of the observation device is changed to a range of 30 to 90 degrees westward from the Earth direction, and the observation device is made to observe the space object. The observation device is to observe the space object in the upper atmosphere above the Earth's near side between 6:00 and 18:00 solar time. Observation satellite.

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