Positioning method

Abstract

To enable positioning measurement in an inertial coordinate system of a flying object by simultaneously receiving a positioning signal transmitted from a stationary satellite and a positioning signal transmitted from a quasi-zenith satellite from three or more units of the stationary satellites or the quasi-zenith satellites.SOLUTION: A flying object 500 flies in the outer space toward the moon or a planet from the earth, or in the vicinity of the moon or the planet. The flying object 500 includes a positioning signal receiving device 501. The flying object 500 simultaneously receives a positioning signal transmitted from a stationary satellite 200 which has known position coordinates in an earth-fixed coordinate system or inertial coordinate system and a positioning signal transmitted from a quasi-zenith satellite 300 which has known position coordinates in the earth-fixed coordinate system or inertial coordinate system, from three or more units of the stationary satellites 200 or the quasi-zenith satellites 300, and measures a position coordinate in the inertial coordinate system.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present disclosure relates to a positioning method, a lunar positioning system, and a positioning satellite.

Background Art

[0002] The advancement to planets such as the moon and Mars is accelerating. Therefore, it is necessary to prepare the means for measuring the position and the environment of flying objects going from the Earth to the moon or planets, flying objects traveling back and forth, and flying objects orbiting the moon or planets. On the Earth and in the atmosphere, it is possible to measure the position in the Earth-fixed coordinate system by a group of positioning satellites. Also, around the Earth, it is possible to measure the position in the Earth-fixed coordinate system by the positioning signals of the group of positioning satellites, similar to that on the Earth and in the atmosphere.

[0003] Patent Document 1 discloses a method of propelling a transport ship from a low Earth orbit or a geostationary orbit to a target orbit or a destination by electric propulsion.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The positioning signals transmitted by the positioning satellite are managed by the ITU in order to maintain a sound radio wave environment. Therefore, there are restrictions on the frequency and the transmission level, and there is a problem that when flying far from the Earth, it is buried in noise and positioning becomes impossible. ITU is an abbreviation for International Telecommunication Union.

[0006] This disclosure aims to enable position measurement of a flying object in an inertial coordinate system by simultaneously receiving positioning signals transmitted from geostationary satellites and positioning signals transmitted from quasi-zenith satellites from three or more geostationary or quasi-zenith satellites. [Means for solving the problem]

[0007] The positioning method described herein is a positioning method for measuring the position coordinates of a flying object flying in outer space or in the vicinity of the Moon or a planet, traveling from the Earth towards the Moon or a planet. The aforementioned flying body, Equipped with a positioning signal receiving device, The system simultaneously receives positioning signals from three or more geostationary or quasi-zenith satellites, which are equipped with positioning signal transmitting devices and whose position coordinates in the Earth-fixed coordinate system or inertial coordinate system are known, and positioning signals from quasi-zenith satellites, which are equipped with positioning signal transmitting devices and whose position coordinates in the Earth-fixed coordinate system or inertial coordinate system are known, to measure the position coordinates in the inertial coordinate system. [Effects of the Invention]

[0008] The positioning method described herein measures the position coordinates of a flying object flying in space from the Earth toward the Moon or a planet, or in the vicinity of the Moon or a planet. The flying object is equipped with a positioning signal receiving device and a positioning signal transmitting device, and simultaneously receives positioning signals from three or more geostationary satellites or quasi-zenith satellites whose position coordinates in the Earth-fixed coordinate system or inertial coordinate system are known, and positioning signals from quasi-zenith satellites equipped with a positioning signal transmitting device and whose position coordinates in the Earth-fixed coordinate system or inertial coordinate system are known, to measure its position coordinates in the inertial coordinate system. Coordinate transformation is possible between the Earth-fixed coordinate system and the inertial coordinate system, and the position coordinates of the geostationary satellite 200 or quasi-zenith satellite 300 whose position coordinates in the Earth-fixed coordinate system are known can be transformed into the inertial coordinate system. Therefore, the positioning method described herein has the effect of enabling position measurement of the flying object in the inertial coordinate system. [Brief explanation of the drawing]

[0009] [Figure 1] It is a diagram showing a configuration example of the positioning system 800 according to Embodiment 1. [Figure 2] A diagram showing a functional configuration example of the flying object according to Embodiment 1. [Figure 3] A diagram showing Example 1 of the positioning method according to Embodiment 1. [Figure 4] A diagram showing a configuration example of the satellite according to Embodiment 2. [Figure 5] A diagram showing Example 2 of the positioning method according to Embodiment 2. [Figure 6] A diagram showing a functional configuration example of the geostationary satellite according to Embodiment 2. [Figure 7] A diagram showing a functional configuration example of the quasi-zenith satellite according to Embodiment 2. [Figure 8] A diagram showing Example 3 of the positioning method according to Embodiment 2. [Figure 9] A diagram showing a functional configuration example of the flying object in Example 3 of the positioning method according to Embodiment 2. [Figure 10] A diagram showing Example 5 of the positioning method according to Embodiment 3. [Figure 11] A diagram showing a configuration example of the first flying object according to Embodiment 3. [Figure 12] A diagram showing Example 6 of the positioning method according to Embodiment 4. [[ID=3�]] [Figure 13] A diagram showing Example 7 of the positioning method according to Embodiment 4. [Figure 14] A diagram showing a configuration example of the lunar station according to Embodiment 4. [Figure 15] A diagram showing Example 8 of the positioning method according to Embodiment 4. [Figure 16] A diagram showing a configuration example of the lunar positioning system according to Embodiment 5. [Figure 17] A diagram showing a configuration example of the third flying object according to Embodiment 5. [Figure 18] A diagram showing a configuration example of the positioning satellite according to Embodiment 6. [Figure 19] A diagram showing an example of transmission of a positioning signal using the positioning satellite according to Embodiment 6.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals. In the description of the embodiments, the description of the same or corresponding parts will be omitted or simplified as appropriate. Also, in the following drawings, the size relationships of the respective components may be different from the actual ones. Further, in the description of the embodiments, directions or positions such as "above", "below", "left", "right", "front", "rear", "front side", and "back side" may be indicated. Those notations are only described as such for convenience of explanation, and do not limit the arrangement and orientation of components such as devices, instruments, or parts.

[0011] Embodiment 1. ***Description of Configuration*** FIG. 1 is a diagram showing a configuration example of a positioning system 800 according to the present embodiment. FIG. 2 is a diagram showing a functional configuration example of a flying object 500 according to the present embodiment.

[0012] In the present embodiment, a positioning method for measuring the position coordinates of a flying object 500 flying in the space from the earth to the moon or a planet, or in the vicinity of the moon or a planet will be described.

[0013] The ground station 100 is a station installed on the ground and having known position coordinates in the earth-fixed coordinate system. The ground station 100 includes a positioning signal transmitter 10 which is a positioning signal transmitter with a direction control function. The ground station 100 transmits a positioning signal 21 by the positioning signal transmitter 10 in a narrow beam having directivity toward the flying object 500 flying far away.

[0014] The flying object 500 flies in the space from the earth to the moon or a planet, or in the vicinity of the moon or a planet. The flying object 500 includes a positioning signal receiver 501. Further, the flying object 500 includes a measuring device 502. The positioning signal receiver 501 receives the positioning signal 21. The measuring device 502 measures the position coordinates of the flying object 500 based on the positioning signal 21 received by the positioning signal receiving device 501.

[0015] <Example of positioning method 1> Figure 3 shows an example 1 of the positioning method according to this embodiment. Example 1 of the positioning method is implemented by the positioning system 800. In example 1 of the positioning method, the positioning system 800 includes four ground stations 100 located on the Earth's surface.

[0016] The flying object 500 receives positioning signals 21 transmitted from ground stations 100 simultaneously from four ground stations 100 to measure its position coordinates in the Earth-fixed coordinate system. Specifically, the flying object 500 receives the positioning signal 21 transmitted from the positioning signal transmitter 10 of the ground station 100 to the flying object 500 in a directional narrow beam via the positioning signal receiver 501. The positioning signal receiver 501 simultaneously receives the positioning signal 21 from four ground stations 100. Then, the flying object 500 uses a measuring device 502 to measure its position coordinates in the Earth-fixed coordinate system using positioning signals 21 received simultaneously from four ground stations 100.

[0017] In recent years, there has been a need to improve the means and environment for determining the position of projectiles traveling from Earth to the Moon or other planets, projectiles making round trips to the Moon or other planets, and projectiles orbiting the Moon or other planets. Positioning signals transmitted by positioning satellites are managed by the ITU to maintain a healthy radio environment. Therefore, there are restrictions on frequency and transmission level, and when projectiles fly far from Earth, the signals may be buried in noise, making positioning impossible.

[0018] In Example 1 of the positioning method shown in Figure 3, a positioning signal 21 is transmitted from a ground station 100, whose position coordinates in the Earth-fixed coordinate system are known, to a flying object 500 flying at a distance using a directional narrow beam. This allows the positioning signal 21 to be transmitted with a significant signal strength, making it possible to measure the position of the flying object 500 in the Earth-fixed coordinate system.

[0019] In spatial triangulation, the position coordinates can be determined by measuring a fixed point from three points whose position coordinates are known. Positioning signal receiving devices that do not have high-precision clocks such as atomic clocks have uncertainty in the time it takes for the signal to arrive. Therefore, by simultaneously receiving positioning signals 21 from four ground stations 100, the position coordinates of the flying object 500 can be measured. Since positioning accuracy improves with a larger solid angle over which points with known coordinates are visible, positioning with ground stations 100 dispersed in the north-south and east-west directions contributes to improved accuracy.

[0020] Embodiment 2. This embodiment mainly describes the points that are added to or differ from Embodiment 1. Note that components similar to those in Embodiment 1 are denoted by the same reference numerals, and their descriptions may be omitted.

[0021] This embodiment describes a positioning method for measuring the position coordinates of a flying object 500 flying in outer space from the Earth toward the Moon or a planet, or in the vicinity of the Moon or a planet. In Embodiment 1, the position coordinates of the flying object 500 were measured by simultaneously receiving positioning signals 21 from four ground stations 100. In this embodiment, a method for measuring the position coordinates of a flying object 500 by receiving positioning signals 21 from various satellites 30 will be described.

[0022] First, an example of the configuration of the satellite 30 according to this embodiment will be described using Figure 4. Satellite 30 comprises a satellite control device 31, a satellite communication device 32, a propulsion device 33, an attitude control device 34, and a power supply device 35. While it also includes other components for various functions, Figure 4 will focus on explaining the satellite control device 31, satellite communication device 32, propulsion device 33, attitude control device 34, and power supply device 35.

[0023] The satellite control device 31 is a computer that controls the propulsion system 33 and the attitude control device 34, and is equipped with processing circuits. Specifically, the satellite control device 31 controls the propulsion system 33 and the attitude control device 34 according to various commands transmitted from ground equipment. The satellite communication device 32 is a device that communicates with ground facilities. Specifically, the satellite communication device 32 transmits various data related to its own satellite to ground facilities. In addition, the satellite communication device 32 receives various commands transmitted from ground facilities. The propulsion device 33 is a device that provides thrust to the satellite 30 and changes the speed of the satellite 30. Specifically, the propulsion device 33 is an electric propulsion system. Specifically, the propulsion device 33 is an ion engine or a Hall thruster. The attitude control device 34 is a device for controlling attitude elements such as the attitude of the satellite 30, its angular velocity, and its line of sight. The attitude control device 34 changes each attitude element in a desired direction, or maintains each attitude element in a desired direction. The attitude control device 34 comprises attitude sensors, actuators, and a controller. The attitude sensors include devices such as gyroscopes, Earth sensors, solar sensors, star trackers, thrusters, and magnetic sensors. The actuators include devices such as attitude control thrusters, momentum wheels, reaction wheels, and control moment gyros. The controller controls the actuators according to the measurement data from the attitude sensors or various commands from ground equipment. The power supply unit 35 is equipped with devices such as solar cells, batteries, and a power control device, and supplies power to each device mounted on the satellite 30.

[0024] The processing circuits provided in the satellite control device 31 will now be described. The processing circuit may be dedicated hardware, or it may be a processor that executes a program stored in memory. 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. The dedicated hardware specifically includes 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.

[0025] <Example of positioning method 2> Figure 5 shows an example 2 of the positioning method according to this embodiment. Figure 6 is a diagram showing an example of the functional configuration of the geostationary satellite 200 according to this embodiment. Figure 7 shows an example of the functional configuration of the Quasi-Zenith Satellite 300 according to this embodiment. In example 2 of the positioning method, the positioning system 800 is equipped with geostationary satellites 200 or quasi-zenith satellites 300.

[0026] In addition to the configuration shown in Figure 4, the geostationary satellite 200 also has the function of a positioning signal transmitter 10. The geostationary satellite 200 has known positional coordinates in the Earth-fixed coordinate system. In addition to the configuration shown in Figure 4, Quasi-Zenith Satellite System 300 also has the function of a positioning signal transmitter 10. The position coordinates of Quasi-Zenith Satellite-300 in the Earth-fixed coordinate system are known.

[0027] In example 2 of the positioning method, the flying object 500 simultaneously receives positioning signals 21 transmitted from the geostationary satellite 200 and positioning signals 21 transmitted from the quasi-zenith satellite 300 from four geostationary satellites 200 or quasi-zenith satellites 300 to measure its position coordinates in the Earth-fixed coordinate system. The positioning signal transmitter 10 provided by the geostationary satellite 200 or the quasi-zenith satellite 300 may be a positioning signal transmitter with a direction control function, or it may not be a positioning signal transmitter with a direction control function. Furthermore, in example 2 of the positioning method, the following effects are obtained even if the positioning signal transmitting device 10 is not a positioning signal transmitting device with a directional control function.

[0028] In Embodiment 1, the positioning method involved transmitting a positioning signal 21 from a ground station 100. However, the positioning signal 21 transmitted from the ground station 100 suffers from a large positioning error due to the delay effect when passing through the ionosphere. In contrast, using a positioning signal 21 transmitted from a satellite has the advantage of high positioning accuracy because the positioning signal 21 can be transmitted and received without passing through the ionosphere.

[0029] Geostationary satellite 200 orbits approximately 36,000 km above the equator in sync with the Earth's rotation, making it appear stationary above the Earth's surface. When geostationary satellite 200 is orbited at an orbital inclination of about 45° and orbited in sync with the Earth's rotation, it appears to move north-south from the Earth's surface, and more precisely, combined with lateral movement, it appears to trace a figure-eight pattern each day. This is a quasi-zenith orbit, and quasi-zenith satellite 300 is used as a positioning satellite in the quasi-zenith positioning satellite system.

[0030] By including positioning signals 21 from a quasi-zenith satellite 300 whose position coordinates in the Earth-fixed coordinate system are known, in addition to ground stations 100 and geostationary satellites 200, the solid angle is further expanded, resulting in improved measurement accuracy for distant objects. Since positioning accuracy improves with a larger solid angle over which points with known coordinates are visible, receiving positioning signals 21 from two geostationary satellites 200 located in the east-west direction and two quasi-zenith satellites 300 located in the east-west direction contributes to improving positioning accuracy.

[0031] Furthermore, because the Earth rotates, it is impossible for a single ground station to continuously transmit positioning signals to a projectile orbiting the Moon. This presented a challenge in that many ground stations would be required. In contrast, geostationary satellites 200 and quasi-zenith satellites 300, although subject to geometric constraints due to partial occlusion by the Earth, have the advantage of allowing a single satellite to continuously transmit positioning signals 21 to the projectile 500 for a longer period compared to ground stations. Therefore, the total number of satellites required is less compared to the total number of ground stations required when transmitting positioning signals 21 from ground stations alone.

[0032] Furthermore, if the positioning signal transmitter 10 is a positioning signal transmitter with a direction control function, the following additional effects are obtained. When the flight position of the projectile 500 becomes far away, there is a problem in that the positioning signal transmitted from a normal positioning signal transmitter becomes buried in noise and cannot be measured. Therefore, a positioning signal 21 is transmitted from a geostationary satellite 200 or quasi-zenith satellite 300, whose position coordinates in the Earth-fixed coordinate system are known, towards a flying object 500 in the distance using a directional narrow beam. This allows the positioning signal to be transmitted with a significant signal strength, making it possible to measure the position of the flying object 500 in the Earth-fixed coordinate system.

[0033] <Example of positioning method 3> Figure 8 shows an example 3 of the positioning method according to this embodiment. Figure 9 shows an example of the functional configuration of the flying object 500 in Example 3 of the positioning method according to this embodiment.

[0034] In example 3 of the positioning method, the flying object 500 is equipped with a positioning signal receiving device 501 and a measuring device 502, as well as a high-precision clock 503. Specific examples of high-precision clocks 503 include atomic clocks and optical lattice clocks.

[0035] The flying object 500 simultaneously receives positioning signals 21 transmitted from the geostationary satellite 200 and positioning signals 21 transmitted from the quasi-zenith satellite 300 from three geostationary satellites 200 or quasi-zenith satellites 300 to measure its position coordinates in the Earth-fixed coordinate system.

[0036] The positioning signal transmitter 10 provided by the geostationary satellite 200 or the quasi-zenith satellite 300 may be a positioning signal transmitter with a direction control function, or it may not be a positioning signal transmitter with a direction control function.

[0037] If the flying object 500 is equipped with a high-precision clock 503, such as an atomic clock or an optical lattice clock, the flying object 500 can measure its position coordinates simply by receiving positioning signals 21 from three locations whose position coordinates are known. Furthermore, if the geostationary satellite 200 or the quasi-zenith satellite 300 is equipped with a positioning signal transmitter with a direction control function, it becomes possible to measure the position of even more distant flying objects, as in Example 2 of the positioning method.

[0038] <Example of positioning method 4> In example 4 of the positioning method, the flying object 500 is equipped with a positioning signal receiving device 501 and a measuring device 502. The flying object 500 may or may not be equipped with a high-precision clock 503. The geostationary satellite 200 is equipped with a positioning signal transmitting device 10 and its position coordinates in a fixed Earth coordinate system or inertial coordinate system are known. The quasi-zenith satellite 300 is equipped with a positioning signal transmitting device 10, and its position coordinates in an Earth-fixed coordinate system or an inertial coordinate system are known.

[0039] The flying object 500 simultaneously receives positioning signals 21 transmitted from geostationary satellites 200 and positioning signals 21 transmitted from quasi-zenith satellites 300 from three or more geostationary satellites 200 or quasi-zenith satellites 300 to measure its position coordinates in an inertial coordinate system.

[0040] Coordinate transformations are possible between the Earth-fixed coordinate system and the inertial coordinate system. Therefore, the position coordinates of geostationary satellite 200 or quasi-zenith satellite 300, whose position coordinates are known in the Earth-fixed coordinate system, can be transformed into the inertial coordinate system. If the flying object 500 is equipped with a high-precision clock 503, the flying object 500 can receive positioning signals 21 from three geostationary satellites 200 or quasi-zenith satellites 300 to measure its position coordinates. On the other hand, if the flying object 500 is not equipped with a high-precision clock 503, the flying object 500 can measure its position coordinates by receiving positioning signals 21 from four geostationary satellites 200 or quasi-zenith satellites 300.

[0041] For spacecraft intended for lunar or planetary exploration, it is more rational to measure their position using an inertial coordinate system than using an Earth-fixed coordinate system that rotates in sync with the Earth's rotation. Therefore, according to Example 4 of the positioning method, there is an advantage in terms of convenience as a positioning method for spacecraft intended for lunar and planetary exploration.

[0042] Embodiment 3. This embodiment mainly describes the points that are added to or differ from Embodiments 1 and 2. Note that components similar to those in Embodiments 1 and 2 are denoted by the same reference numerals, and their descriptions may be omitted.

[0043] This embodiment describes a positioning method for measuring the position coordinates of a second flying object 520 equipped with a positioning signal receiving device 501, which flies in outer space or in the vicinity of the Moon or a planet, from the Earth towards the Moon or a planet.

[0044] <Example of positioning method 5> Figure 10 shows an example 5 of the positioning method according to this embodiment. Figure 11 shows an example of the configuration of the first projectile 510 according to this embodiment. In example 5 of the positioning method, the positioning system 800 consists of a first flying object 510, a geostationary satellite 200, and a quasi-zenith satellite 300.

[0045] The first flying object 510 is a flying object equipped with a high-precision clock 503, a positioning signal receiving device 501, and a positioning signal transmitting device 10. The first flying object 510 also includes a measuring device 502. The second projectile 520 is a projectile equipped with a positioning signal receiving device 501. The second projectile 520 is also equipped with a measuring device 502. The geostationary satellite 200 is equipped with a positioning signal transmitting device 10, and its position coordinates in a fixed Earth coordinate system or an inertial coordinate system are known. The Quasi-Zenith Satellite 300 is equipped with a positioning signal transmitting device 10, and its position coordinates in an Earth-fixed coordinate system or an inertial coordinate system are known.

[0046] The first flying object 510 simultaneously receives positioning signals 21 from three or more geostationary satellites 200 or quasi-zenith satellites, measures its position coordinates in an Earth-fixed coordinate system or an inertial coordinate system, and transmits the positioning signals 21 as a flying object with known position coordinates. The second flying object 520 simultaneously receives positioning signals 21 from the first flying object 510 and three geostationary satellites 200 or quasi-zenith satellites 300 to measure its position coordinates in an Earth-fixed coordinate system or an inertial coordinate system.

[0047] Since the first flying object 510 is equipped with a high-precision clock 503, it can measure its position coordinates by receiving positioning signals 21 from three geostationary satellites 200 or quasi-zenith satellites 300, and can transmit the positioning signals 21 as a flying object with known position coordinates. The second flying object 520, which is not equipped with a high-precision clock, can measure its position coordinates, including the uncertainty of the time, if it simultaneously receives positioning signals 21 from four locations whose position coordinates are known. Therefore, the second flying object 520, which is not equipped with a high-precision clock, can measure its position coordinates if it receives positioning signals 21 from the first flying object 510 and three geostationary satellites 200 or quasi-zenith satellites 300. Furthermore, the geostationary satellite 200 or quasi-zenith satellite 300 from which the first flying object 510 receives the positioning signal 21 may be a different satellite from the geostationary satellite 200 or quasi-zenith satellite 300 from which the second flying object 520 receives the positioning signal 21.

[0048] Embodiment 4. This embodiment mainly describes the points that are added to or different from Embodiments 1 to 3. Note that components similar to those in Embodiments 1 to 3 are denoted by the same reference numerals, and their descriptions may be omitted.

[0049] This embodiment describes a positioning method for measuring the position coordinates of a second flying object 500 equipped with a positioning signal receiving device 501, which flies in outer space or in the vicinity of the Moon or a planet, from the Earth toward the Moon or a planet.

[0050] <Example of positioning method 6> Figure 12 shows an example 6 of the positioning method according to this embodiment. In example 6 of the positioning method, the positioning system 800 consists of a first flying object 510, a geostationary satellite 200, and a quasi-zenith satellite 300. The first flying object 510 orbits Moon 71. The first flying object 510 is equipped with a positioning signal transmitter 10 and orbits Moon 71, and its position coordinates in the lunar fixed coordinate system or inertial coordinate system are known. The geostationary satellite 200 is equipped with a positioning signal transmitting device 10, and its position coordinates in the inertial coordinate system are known. Quasi-Zenith Satellite 300 is equipped with a positioning signal transmitter 10, and its position coordinates in the inertial coordinate system are known. The second flying object 520 simultaneously receives positioning signals 21 from the first flying object 510 and three geostationary satellites 200 or quasi-zenith satellites 300 to measure its position coordinates in an inertial coordinate system.

[0051] As a fixed lunar coordinate system, the lunar coordinate system is known, which uses a small bowl-shaped crater called "Mesting A" as its reference point and defines the position coordinates on the lunar surface using two values ​​equivalent to Earth's longitude and latitude. It is possible to define a fixed lunar coordinate system as a three-dimensional coordinate system with the center of mass of the moon as the origin, and adding altitude to longitude and latitude. The Moon's orbital plane (the plane of revolution relative to the Earth) is tilted 5.15° with respect to the ecliptic, and the Moon's rotational axis is tilted 6.69° from the perpendicular to the ecliptic. Just as coordinate transformations between the Earth's fixed coordinate system and the inertial coordinate system are possible on Earth, where the rotational axis is tilted 23.4° from the perpendicular to the ecliptic, coordinate transformations between the Moon's fixed coordinate system and the inertial coordinate system are also possible.

[0052] There is a concept for LOP-G (hereinafter referred to as Gateway) as a base for future lunar and planetary exploration. Gateway is being considered to operate in an extremely elongated elliptical orbit called NRHO at the Lagrange point where the gravitational potentials of the Earth and the Moon are in equilibrium. NRHO is an extremely elongated elliptical orbit that circles the Moon from north to south, at an altitude of 4,500 km to 75,000 km. LOP-G is an abbreviation for Lunar Orbital Platform-Gateway. NRHO is an abbreviation for Near Rectilinear Halo Orbit.

[0053] Assume the gateway is equipped with a high-precision clock and a positioning signal transmitter, and that its position coordinates in the lunar fixed coordinate system or inertial coordinate system are known. In this case, for a second flying object flying between the Earth and the Moon in a space called cislunar space, if the position coordinates of the gateway are known and measurements can be taken including the positioning signal from the gateway, the solid angle will increase, resulting in improved positioning accuracy.

[0054] The gateway's position may be determined using any of the positioning methods from Example 2 to Example 5, or it may be analytically derived using distance measurement or angle measurement from the ground, and orbital information from the lunar orbit. By positioning the first projectile 510 orbiting the Moon, the accuracy of measuring the distance from Earth to the second projectile 520 flying between Earth and the Moon is improved. Furthermore, when the Gateway flies along the NRHO, it moves approximately 75,000 km south of the ecliptic plane, which allows for positioning with a larger solid angle from the perspective of the second projectile 520, resulting in improved positioning accuracy.

[0055] <Example of positioning method 7> Figure 13 shows an example 7 of the positioning method according to this embodiment. Figure 14 shows an example configuration of the lunar station 550 according to this embodiment. In example 7 of the positioning method, the positioning system 800 consists of a lunar station 550, a geostationary satellite 200, and a quasi-zenith satellite 300. Lunar station 550 is installed on the lunar surface and is equipped with a high-precision clock 503 and a positioning signal transmitting device 10. The geostationary satellite 200 is equipped with a positioning signal transmitting device 10, and its position coordinates in the inertial coordinate system are known. Quasi-Zenith Satellite 300 is equipped with a positioning signal transmitter 10, and its position coordinates in the inertial coordinate system are known.

[0056] The second flying object 520 simultaneously receives positioning signals 21 from the lunar station 550 and three geostationary satellites 200 or quasi-zenith satellites 300 to measure its position coordinates in an inertial coordinate system.

[0057] Lunar Station 550 is equipped with a high-precision clock 503 and a positioning signal transmitter 10, and is installed on the lunar surface. Compared to spacecraft with limited operational lifespans, Lunar Station 550 has the advantage of being able to be used permanently as a positional reference for the lunar coordinate system, including maintenance or replacement of equipment.

[0058] <Example of positioning method 8> Figure 15 shows an example 8 of the positioning method according to this embodiment. In example 8 of the positioning method, the positioning system 800 consists of a lunar station 550, a first flying object 510, a geostationary satellite 200, and a quasi-zenith satellite 300.

[0059] Lunar station 550 is installed on the lunar surface and is equipped with a high-precision clock 503 and a positioning signal transmitter 10. The position coordinates of lunar station 550 are known in either the lunar fixed coordinate system or the inertial coordinate system. The first flying object 510 orbits the Moon. The first flying object 510 is equipped with a positioning signal transmitter 10 and orbits the Moon, and its position coordinates in the Lunar fixed coordinate system or inertial coordinate system are known. The geostationary satellite 200 is equipped with a positioning signal transmitting device 10, and its position coordinates in the inertial coordinate system are known. Quasi-Zenith Satellite 300 is equipped with a positioning signal transmitter 10, and its position coordinates in the inertial coordinate system are known. The second flying object 520 simultaneously receives positioning signals 21 from the lunar station 550, the first flying object 510, and two geostationary satellites 200 or quasi-zenith satellites 300 to measure its position coordinates in an inertial coordinate system.

[0060] By measuring the position coordinates of the second flying object 520, including the lunar surface station 550 and the first flying object 510 orbiting the moon, it is possible to improve the accuracy of measuring the flight position of the second flying object 520 as it flies between the Earth and the Moon. Furthermore, it has the effect of enabling the measurement of the position coordinates of a second type of flying object, such as a planetary exploration satellite, that flies farther than the Moon from Earth's perspective.

[0061] Embodiment 5. This embodiment mainly describes the points that are added to or differ from Embodiments 1 to 4. Note that components similar to those in Embodiments 1 to 4 are denoted by the same reference numerals, and their descriptions may be omitted.

[0062] This embodiment describes a lunar positioning system 801 that can measure the position coordinates of a moving object on the lunar surface or a second flying object flying near the Moon in a fixed lunar coordinate system.

[0063] Figure 16 shows an example of the configuration of the lunar positioning system 801 according to this embodiment. Figure 17 shows an example of the configuration of the third projectile 530 according to this embodiment. Lunar station 550 is installed on the lunar surface and is equipped with a high-precision clock 503 and a positioning signal transmitter 10, and its position coordinates in the lunar fixed coordinate system are known. The third flying object 530 orbits the Moon. The third flying object 530 is equipped with a high-precision clock 503 and a positioning signal transmitter 10, and orbits the Moon, and its position coordinates in the lunar fixed coordinate system are known. The lunar positioning system 801 consists of either or both of the lunar station 550 and the third flying object 530, and the total number of lunar stations 550 and third flying objects 530 is four or more. Although Figure 16 shows an example where the third projectile flies along the same orbital plane, it goes without saying that the third projectile may also fly along a different orbital plane.

[0064] According to the lunar positioning system 801, a mobile object such as a rover operating on the lunar surface equipped with a positioning signal receiving device, or a second flying object 520 flying near the moon, can measure its position coordinates in the lunar fixed coordinate system. If a moving object on the lunar surface or a second flying object 520 flying near the moon receives positioning signals from four or more lunar stations 550 or lunar orbiting satellites (third flying object 530) with known lunar fixed coordinate systems, it becomes possible to measure its position coordinates in the lunar fixed coordinate system, similar to positioning satellite systems on Earth. If humanity's exploration of the lunar surface progresses, securing positioning bases on the lunar surface and establishing a positioning system for a fixed lunar coordinate system would have the effect of improving the convenience of operating and controlling lunar orbiting satellites.

[0065] According to positioning method examples 2 through 8, it is possible to establish lunar stations or lunar orbiting satellites with known inertial coordinate systems. Since coordinate transformation between the inertial coordinate system and the lunar fixed coordinate system is possible, it is possible to establish lunar stations or lunar orbiting satellites with known position coordinates in the lunar fixed coordinate system.

[0066] Furthermore, by including various measurement methods associated with lunar surface activities, it becomes possible to increase the number of lunar stations or lunar orbiting satellites whose position coordinates in the lunar fixed coordinate system are known. This makes it possible to construct a lunar positioning system in which a moving object on the lunar surface or a second flying object flying near the moon can simultaneously receive positioning signals from four or more lunar stations or lunar orbiting satellites. According to the lunar positioning system, this has the effect of making it possible to measure the position coordinates in the lunar fixed coordinate system of a moving object on the lunar surface or a second flying object flying near the moon.

[0067] Embodiment 6. This embodiment mainly describes the points that are added to or different from Embodiments 1 to 5. Note that components similar to those in Embodiments 1 to 5 are denoted by the same reference numerals, and their descriptions may be omitted.

[0068] In this embodiment, the configuration of the positioning satellite 400, such as the geostationary satellite 200 or quasi-zenith satellite 300 used in positioning method examples 2 to 8, will be described.

[0069] Figure 18 shows an example of the configuration of the positioning satellite 400 according to this embodiment. Figure 19 shows an example of transmitting a positioning signal 21 using a positioning satellite 400 according to this embodiment.

[0070] Positioning satellite 400 will orbit in either a geostationary or quasi-zenith orbit. For the positioning satellite 400, the X-axis of the satellite coordinate system is the direction of eastward travel, the Y-axis is the direction southward, and the Z-axis is the direction towards the Earth. Positioning satellite 400 has a single solar panel 401 facing north (-Y). Positioning satellite 400 is also equipped with a positioning signal transmitter 10 on its south face (+Y). Positioning satellite 400 ensures a positioning signal transmission field of view encompassing Azimuth ± 170 degrees from the anti-Earth direction (-Z axis) around the north-south axis (Y axis), and a positioning signal transmission field of view of Elevation -25 degrees or more (north side) and Elevation 36 degrees or more (south side) for the XZ plane.

[0071] Because the NRHO's orbital plane normal vector points towards Earth, it can communicate with the gateway without being obscured by the Moon. On the other hand, with geostationary satellites, the transmission of positioning signals is interrupted during seasons and times when the Earth's shadow is cast on the Moon. Because the Earth's axis is tilted at approximately 23.4 degrees relative to inertial space, there is a variation of ±23.4 degrees in its direction of orientation between the winter and summer solstices. While the Earth's radius is approximately 6,400 km, the geostationary orbit radius is approximately 42,000 km, about seven times larger. Due to the tilt of the Earth's axis, there may be times in certain seasons when the Earth's shadow does not occur.

[0072] Therefore, in order to minimize the interruption of positioning signal transmission while the positioning satellite orbits the Earth's equator, a positioning signal transmitter that rotates its field of view around the satellite's north-south axis is employed. To eliminate field of view interference on the satellite, the positioning signal transmitter is mounted on the south face of the satellite, which can secure a wide field of view on the apogee side of the NRHO, and the field of view for positioning signal transmission with the gateway is secured by changing the two-axis pointing direction of Azimuth and Elevation. For positioning signal transmitters that cannot rotate continuously more than 360 degrees within their operating range, the Earth-facing direction is designated as the dead zone, and the Azimuth rotation range when mounted on the south side includes ±170 degrees relative to the anti-Earth direction. Positioning signal transmitters with a range of ±175 degrees do exist, and the wider the field of view, the shorter the interruption period of positioning signal transmission can be.

[0073] Furthermore, while the gateway is in the Earth's shadow, the Azimuth aiming angle is set to the easternmost point. After the shadow is lifted, a communication link is formed, and as the positioning satellite orbits the Earth approximately once, the Azimuth aiming angle rotates to the westernmost point. This process is then repeated, setting the Azimuth aiming angle to the easternmost point again after the gateway enters the shadow.

[0074] The distance between the Earth and the Moon is approximately 385,000 km, the apogee altitude of the NRHO is approximately 75,000 km, and the perigee altitude is approximately 4,000 km. Therefore, the angle at which a positioning satellite can observe the perigee above the North Pole of the NRHO is less than 1 degree in the north latitude direction relative to the satellite's XZ plane, with the X-axis representing the eastward direction of travel, the Y-axis representing the southward direction, and the Z-axis representing the Earth's direction. The angle at which a satellite can observe the apogee above the South Pole is less than 12 degrees in the south latitude direction relative to the satellite's Z-axis (Earth's direction).

[0075] Taking into account the Earth's axial tilt variation of approximately 23.4 degrees, the system is equipped with a directional adjustment function that allows for elevation changes of 25 degrees or more in the north latitude direction and 36 degrees or more in the south latitude direction. This ensures that communication is always possible along the flight path from the apogee to the perigee of the gateway. The Gateway is also planned for manned operations, and will have the effect of being able to communicate with ground facilities for extended periods without interruption during events such as extravehicular activities that involve human lives. Furthermore, if the perigee of the NRHO is set on the lunar south pole side, it goes without saying that the positioning satellites will also be configured with their north and south orientations reversed. Furthermore, even if the gateway's orbit changes during operation, it is possible to rotate the positioning satellite 180 degrees around the Z-axis to reverse the north-south orientation, thereby achieving the same effect as described above.

[0076] According to the positioning satellite 400 of this embodiment, in Examples 2 to 8 of the positioning method, it is possible to realize a geostationary satellite or quasi-zenith satellite equipped with a positioning signal transmitting device with a directional control function while compensating for the change in attitude of the geostationary satellite or quasi-zenith satellite due to the rotation of the Earth.

[0077] Each system, satellite, station, and device described in Embodiments 1 to 6 above is equipped with a computer, and the computer is used to realize the functions described in Embodiments 1 to 6. A computer comprises a processor or electronic circuitry, as well as other hardware such as memory, auxiliary storage devices, input interfaces, output interfaces, and communication devices. The processor or electronic circuitry is connected to and controls the other hardware via signal lines.

[0078] In embodiments 1 to 6 described above, the configuration of each system, satellite, station, and device does not have to be as described in the embodiments above. The configuration of each system, satellite, station, and device can be any configuration as long as it can realize the functions described in embodiments 1 to 6 described above. Furthermore, multiple parts or embodiments from Embodiments 1 to 6 may be implemented in combination. Alternatively, only one part or embodiment from these embodiments may be implemented. In addition, these embodiments may be combined in any way, either as a whole or in part. In other words, in embodiments 1 to 6, it is possible to freely combine each embodiment, modify any component of each embodiment, or omit any component in each embodiment.

[0079] The embodiments described above are essentially preferred examples and are not intended to limit the scope of the Disclosure, the scope of the Applications of the Disclosure, or the scope of Uses of the Disclosure. The embodiments described above can be modified in various ways as needed. [Explanation of symbols]

[0080] 10 Positioning signal transmitter, 21 Positioning signal, 30 Satellite, 31 Satellite control device, 32 Satellite communication device, 33 Propulsion device, 34 Attitude control device, 35 Power supply device, 70 Earth, 71 Moon, 100 Ground station, 200 Geostationary satellite, 300 Quasi-zenith satellite, 400 Positioning satellite, 401 Solar panel, 500 Flying object, 510 First flying object, 520 Second flying object, 530 Third flying object, 550 Lunar station, 501 Positioning signal receiver, 502 Measuring device, 503 High-precision clock, 800, 801 Positioning system.

Claims

[Claim 1] A positioning method for measuring the positional coordinates of a flying object traveling from Earth to the Moon or a planet in outer space or in the vicinity of the Moon or a planet, The aforementioned flying body, Equipped with a positioning signal receiving device, A positioning method that measures the position coordinates in an inertial coordinate system by simultaneously receiving positioning signals transmitted from three or more geostationary or quasi-zenith satellites, which are equipped with a positioning signal transmitting device and whose position coordinates in a fixed Earth coordinate system or inertial coordinate system are known, and positioning signals transmitted from three or more geostationary or quasi-zenith satellites, which are equipped with a positioning signal transmitting device and whose position coordinates in a fixed Earth coordinate system or inertial coordinate system are known.

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