Positioning method, lunar positioning system, and positioning satellite

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. For this reason, it is necessary to prepare the means and environment for position measurement 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, position measurement in the Earth-fixed coordinate system is possible by a group of positioning satellites. Also, around the Earth, position measurement in the Earth-fixed coordinate system is possible by the positioning signals of the group of positioning satellites, similar to on the Earth and in the atmosphere.

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

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 positioning satellites are managed by the ITU in order to maintain a healthy radio environment. Therefore, there are restrictions on the frequency and transmission level, and there is a problem that positioning becomes impossible because it is buried in noise when flying far from the Earth. ITU is an abbreviation for International Telecommunication Union.

[0006] In the present disclosure, the object is to simultaneously receive positioning signals transmitted from three or more geostationary satellites or quasi-zenith satellites, including positioning signals transmitted from geostationary satellites and positioning signals transmitted from quasi-zenith satellites, so as to enable position measurement of a flying object in an inertial coordinate system.

Means for Solving the Problems

[0007] The positioning method according to the present disclosure is a positioning method for measuring the position coordinates of a flying object flying in space from the Earth to 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, is equipped with a positioning signal transmitting device, and receives positioning signals transmitted from three or more geostationary satellites or quasi-zenith satellites simultaneously, including positioning signals transmitted from geostationary satellites with known position coordinates in the Earth-fixed coordinate system or inertial coordinate system and positioning signals transmitted from quasi-zenith satellites with known position coordinates in the Earth-fixed coordinate system or inertial coordinate system, and measures the position coordinates in the inertial coordinate system.

Advantages of the Invention

[0008] In the positioning method according to the present disclosure, the position coordinates of a flying object flying in space from the Earth to the Moon or a planet or in the vicinity of the Moon or a planet are measured. The flying object is equipped with a positioning signal receiving device and a positioning signal transmitting device, and receives positioning signals transmitted from three or more geostationary satellites or quasi-zenith satellites simultaneously, including positioning signals transmitted from geostationary satellites with known position coordinates in the Earth-fixed coordinate system or inertial coordinate system and positioning signals transmitted from quasi-zenith satellites with known position coordinates in the Earth-fixed coordinate system or inertial coordinate system, and measures the position coordinates in the inertial coordinate system. The Earth-fixed coordinate system and the inertial coordinate system can be coordinate-transformed, and the position coordinates of geostationary satellites 200 or quasi-zenith satellites 300 with known position coordinates in the Earth-fixed coordinate system can be transformed into the inertial coordinate system. Therefore, according to the positioning method according to the present disclosure, there is an effect of enabling position measurement of the flying object in the inertial coordinate system.

Brief Description of the Drawings

[0009]

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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 "up", "down", "left", "right", "front", "rear", "front side", and "back side" may be indicated. Those notations are only 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 the 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 transmitting device 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 measurement 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 1 of the positioning method> FIG. 3 is a diagram showing Example 1 of the positioning method according to the present embodiment. Example 1 of the positioning method is realized by the positioning system 800. In Example 1 of the positioning method, the positioning system 800 includes four ground stations 100 installed on the ground of the Earth 70.

[0016] The flying object 500 simultaneously receives the positioning signal 21 transmitted from the four ground stations 100 and measures its position coordinates in the Earth-fixed coordinate system. Specifically, the flying object 500 receives, by means of the positioning signal receiving device 501, the positioning signal 21 transmitted in a narrow beam having directivity from the positioning signal transmitting device 10 of the ground station 100 towards the flying object 500. The positioning signal receiving device 501 simultaneously receives the positioning signal 21 from the four ground stations 100. Then, the flying object 500 measures, by means of the measurement device 502, its position coordinates in the Earth-fixed coordinate system using the positioning signals 21 simultaneously received from the four ground stations 100.

[0017] In recent years, there has been a need to improve the means for measuring the positions and the environment of flying objects traveling from the Earth to the Moon or planets, round-trip flying objects, and flying objects orbiting the Moon or planets. The positioning signals transmitted by positioning satellites are managed by the ITU in order to maintain a healthy radio wave environment. Therefore, there are restrictions on the frequency and transmission level, and when flying far from the Earth, the signals may be buried in noise and positioning may become impossible.

[0018] In Example 1 of the positioning method shown in FIG. 3, the positioning signal 21 is transmitted in a narrow beam having directivity from the ground station 100 whose position coordinates in the Earth-fixed coordinate system are known, towards the flying object 500 flying far away. As a result, the positioning signal 21 can be transmitted with a significant signal strength, and it becomes possible to measure the position of the flying object 500 in the Earth-fixed coordinate system.

[0019] In spatial triangulation, if a point to be fixed is measured from three points with known position coordinates, the position coordinates are determined. In a positioning signal receiving device that does not have a high-precision clock such as an atomic clock, there is uncertainty in the signal arrival time. Therefore, by receiving the positioning signal 21 from four ground stations 100 simultaneously, the position coordinates of the flying object 500 can be measured. Since the positioning accuracy improves as the solid angle covering the points with known position coordinates becomes larger, the ground stations 100 contribute to improving the accuracy when performing positioning in a state dispersed in the north-south direction and the east-west direction.

[0020] Embodiment 2. In this embodiment, mainly, the points added to or different from Embodiment 1 will be described. Note that the same components as those in Embodiment 1 may be denoted by the same reference numerals, and the description thereof may be omitted.

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

[0022] First, with reference to FIG. 4, a configuration example of the satellite 30 according to this embodiment will be described. The satellite 30 includes 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. In addition, it includes components for realizing various functions. However, in FIG. 4, the satellite control device 31, the satellite communication device 32, the propulsion device 33, the attitude control device 34, and the power supply device 35 will be described.

[0023] The satellite control device 31 is a computer that controls the propulsion device 33 and the attitude control device 34, and includes a processing circuit. Specifically, the satellite control device 31 controls the propulsion device 33 and the attitude control device 34 according to various commands transmitted from the ground facilities. The satellite communication device 32 is a device that communicates with the ground facilities. Specifically, the satellite communication device 32 transmits various data related to the satellite to the ground facilities. Also, the satellite communication device 32 receives various commands transmitted from the ground facilities. The propulsion device 33 is a device that applies a propulsion force to the satellite 30 and changes the speed of the satellite 30. Specifically, the propulsion device 33 is an electric propulsion engine. 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, the angular velocity of the satellite 30, and the line of sight direction. The attitude control device 34 changes each attitude element in a desired direction. Or, the attitude control device 34 maintains each attitude element in a desired direction. The attitude control device 34 includes an attitude sensor, an actuator, and a controller. The attitude sensor is a device such as a gyroscope, an earth sensor, a sun sensor, a star tracker, a thruster, and a magnetic sensor. The actuator is a device such as an attitude control thruster, a momentum wheel, a reaction wheel, and a control moment gyro. The controller controls the actuator according to the measurement data of the attitude sensor or various commands from the ground facilities. The power supply device 35 includes devices such as a solar cell, a battery, and a power control device, and supplies power to each device mounted on the satellite 30.

[0024] The processing circuit provided in the satellite control device 31 will be described. The processing circuit may be dedicated hardware or a processor that executes a program stored in a memory. In the processing circuit, some functions may be realized by dedicated hardware, and the remaining functions may be realized by software or firmware. That is, the processing circuit can be realized by hardware, software, firmware, or a combination thereof. Specifically, the dedicated hardware is a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC, an FPGA, or a combination thereof. ASIC is an abbreviation for Application Specific Integrated Circuit. FPGA is an abbreviation for Field Programmable Gate Array.

[0025] <Example 2 of the positioning method> FIG. 5 is a diagram showing Example 2 of the positioning method according to the present embodiment. FIG. 6 is a diagram showing an example of the functional configuration of the geostationary satellite 200 according to the present embodiment. FIG. 7 is a diagram showing an example of the functional configuration of the quasi-zenith satellite 300 according to the present embodiment. In Example 2 of the positioning method, the positioning system 800 includes the geostationary satellite 200 to the quasi-zenith satellite 300.

[0026] In addition to the configuration of FIG. 4, the geostationary satellite 200 has the function of the positioning signal transmitter 10. The geostationary satellite 200 has known position coordinates in the Earth-fixed coordinate system. In addition to the configuration of FIG. 4, the quasi-zenith satellite 300 has the function of the positioning signal transmitter 10. The quasi-zenith satellite 300 has known position coordinates in the Earth-fixed coordinate system.

[0027] In Example 2 of the positioning method, the flying object 500 simultaneously receives the positioning signal 21 transmitted from the geostationary satellite 200 and the positioning signal 21 transmitted from the quasi-zenith satellite 300 from four geostationary satellites 200 to quasi-zenith satellites 300, and measures the position coordinates in the Earth-fixed coordinate system. The positioning signal transmission device 10 provided in the geostationary satellite 200 or the quasi-zenith satellite 300 may or may not be a positioning signal transmission device with a pointing direction control function. In addition, in Example 2 of the positioning method, even when the positioning signal transmission device 10 is not a positioning signal transmission device with a pointing direction control function, there are the following effects.

[0028] In Embodiment 1, it was a positioning method of transmitting the positioning signal 21 from the ground station 100. The positioning signal 21 transmitted from the ground station 100 has a problem that the positioning error is large due to the delay effect when passing through the ionosphere. On the other hand, according to the positioning signal 21 transmitted from the satellite, since the positioning signal 21 can be transmitted and received without passing through the ionosphere, there is an effect that the positioning accuracy is high.

[0029] The geostationary satellite 200 is a satellite that orbits at about 36,000 km above the equator in synchronization with the rotation of the Earth 70, and thus appears to be stationary in the sky as viewed from the Earth's surface. If an orbital inclination angle of about 45° is given to the orbital plane of the geostationary satellite 200 and it is orbited in synchronization with the rotation of the Earth, it appears to move north and south as viewed from the Earth's surface, and strictly speaking, it appears to draw an eight-shaped figure in a day in combination with the left and right movements. This is the quasi-zenith orbit, and the quasi-zenith satellite 300 is utilized as a positioning satellite in the quasi-zenith positioning satellite system.

[0030] In addition to the ground station 100 and the geostationary satellite 200, if the position measurement of the flying object 500 is performed including the positioning signal 21 from the quasi-zenith satellite 300 whose position coordinates in the Earth-fixed coordinate system are known, since the solid angle further expands, there is an effect that the measurement accuracy of a distant flying object is improved. Since the larger the solid angle for looking over a point with known position coordinates, the higher the positioning accuracy, receiving the positioning signal 21 from two geostationary satellites 200 separated in the east-west direction and two quasi-zenith satellites 300 separated in the east-west direction contributes to the improvement of the positioning accuracy.

[0031] In addition, since the Earth rotates, it is impossible to continuously transmit a positioning signal to a flying object flying around the moon at a specific ground station. For this reason, there has been a problem that a large number of ground stations are required. In contrast, although there are some geometric constraints where the stationary satellite 200 and the quasi-zenith satellite 300 are in the shadow of part of the Earth, compared to ground stations, there is an effect that a single satellite can continuously transmit the positioning signal 21 to the flying object 500 for a longer time. For this reason, there is an effect that the total number of required satellites can be smaller compared to the total number of ground stations required when transmitting the positioning signal 21 only from ground stations.

[0032] In addition, when the positioning signal transmission device 10 is a positioning signal transmission device with a pointing direction control function, there are further effects as follows. When the flying position of the flying object 500 is at a long distance, there is a problem that the positioning signal transmitted from a normal positioning signal transmitter is buried in noise and cannot be measured. Therefore, the positioning signal 21 is transmitted from the stationary satellite 200 or the quasi-zenith satellite 300 whose position coordinates in the Earth-fixed coordinate system are known, in a narrow beam having directivity toward the flying object 500 flying far away. Thereby, the positioning signal can be transmitted with a significant signal intensity, and the position measurement of the flying object 500 in the Earth-fixed coordinate system becomes possible.

[0033] <Example 3 of the positioning method> FIG. 8 is a diagram showing Example 3 of the positioning method according to the present embodiment. FIG. 9 is a diagram showing an example of the functional configuration of the flying object 500 in Example 3 of the positioning method according to the present embodiment.

[0034] In Example 3 of the positioning method, the flying object 500 includes a high-precision clock 503 in addition to the positioning signal receiving device 501 and the measuring device 502. A specific example of the high-precision clock 503 is a high-precision clock such as an atomic clock or an optical lattice clock.

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

[0036] The positioning signal transmission device 10 provided in the geostationary satellite 200 or the quasi-zenith satellite 300 may or may not be a positioning signal transmission device with a pointing 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 the position coordinates only by receiving the positioning signals 21 from three locations with known position coordinates. If the geostationary satellite 200 or the quasi-zenith satellite 300 is equipped with a positioning signal transmission device with a pointing direction control function, it is the same as Example 2 of the positioning method that even a more distant flying object can be position-measured.

[0038] <Example 4 of the positioning method> In Example 4 of the positioning method, the flying object 500 includes 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 transmission device 10, and the position coordinates in the Earth-fixed coordinate system or the inertial coordinate system are known. The quasi-zenith satellite 300 is equipped with a positioning signal transmission device 10, and the position coordinates in the Earth-fixed coordinate system or the inertial coordinate system are known.

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

[0040] The Earth-fixed coordinate system and the inertial coordinate system can be transformed. Therefore, the position coordinates of the geostationary satellite 200 or the quasi-zenith satellite 300 with known position coordinates in the Earth-fixed coordinate system can be transformed into the inertial coordinate system. For the flying object 500 equipped with the high-precision clock 503, the flying object 500 can receive the positioning signals 21 from three geostationary satellites 200 or quasi-zenith satellites 300 to measure the position coordinates. On the other hand, for the flying object 500 not equipped with the high-precision clock 503, the flying object 500 can receive the positioning signals 21 from four geostationary satellites 200 or quasi-zenith satellites 300 to measure the position coordinates.

[0041] For a flying object aimed at lunar exploration or planetary exploration, it is more reasonable to measure the position in the inertial coordinate system than in the Earth-fixed coordinate system that rotates synchronously with the rotation of the Earth. Therefore, according to Example 4 of the positioning method, there is an effect that it is excellent in convenience as a positioning method for a flying object for lunar and planetary exploration purposes.

[0042] Embodiment 3. In this embodiment, mainly, the points added to or different from Embodiments 1 and 2 will be described. Note that the same components as those in Embodiments 1 and 2 may be denoted by the same reference numerals, and the description thereof may be omitted.

[0043] In this embodiment, a positioning method for measuring the position coordinates of the second flying object 520 equipped with the positioning signal receiving device 501 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.

[0044] <Example 5 of the positioning method> FIG. 10 is a diagram showing Example 5 of the positioning method according to this embodiment. FIG. 11 is a diagram showing a configuration example of the first flying object 510 according to this embodiment. In Example 5 of the positioning method, the positioning system 800 is composed of the first flying object 510, the geostationary satellite 200, and the 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 flying object 520 is a flying object equipped with a positioning signal receiving device 501. The second flying object 520 also includes a measuring device 502. The geostationary satellite 200 is equipped with a positioning signal transmitting device 10, and its position coordinates in the earth-fixed coordinate system or the inertial coordinate system are known. The quasi-zenith satellite 300 is equipped with a positioning signal transmitting device 10, and its position coordinates in the earth-fixed coordinate system or the inertial coordinate system are known.

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

[0047] Since the first flying object 510 is equipped with a high-precision clock 503, it can measure the position coordinates by receiving the positioning signal 21 from three geostationary satellites 200 or quasi-zenith satellites 300, and can transmit the positioning signal 21 as a flying object with known position coordinates. The second flying object 520 without a high-precision clock can measure the position coordinates including the time uncertainty by receiving the positioning signal 21 from four locations with known position coordinates simultaneously. Therefore, the second flying object 520 without a high-precision clock can measure the position coordinates by receiving the positioning signal 21 from the first flying object 510 and three geostationary satellites 200 or quasi-zenith satellites 300. Note that the geostationary satellites 200 or quasi-zenith satellites 300 from which the first flying object 510 receives the positioning signal 21 may be different satellites from the geostationary satellites 200 or quasi-zenith satellites 300 from which the second flying object 520 receives the positioning signal 21.

[0048] Embodiment 4. In this embodiment, mainly, points added to or different from Embodiments 1 to 3 will be described. Note that the same components as those in Embodiments 1 to 3 may be denoted by the same reference numerals, and the description thereof may be omitted.

[0049] In this embodiment, a positioning method for measuring the position coordinates of a second flying object 500 equipped with a positioning signal receiving device 501 while flying in outer space from the Earth toward the Moon or a planet or in the vicinity of the Moon or a planet will be described.

[0050] <Example 6 of positioning method> FIG. 12 is a diagram showing Example 6 of the positioning method according to this embodiment. In Example 6 of the positioning method, the positioning system 800 is composed of a first flying object 510, a geostationary satellite 200, and a quasi-zenith satellite 300. The first flying object 510 orbits the Moon 71. The first flying object 510 is equipped with a positioning signal transmitting device 10 and orbits the Moon 71, and the position coordinates in the Moon-fixed coordinate system or the inertial coordinate system are known. The geostationary satellite 200 is equipped with a positioning signal transmitting device 10, and the position coordinates in the inertial coordinate system are known. The quasi-zenith satellite 300 is equipped with a positioning signal transmitting device 10, and the position coordinates in the inertial coordinate system are known. The second flying object 520 simultaneously receives a positioning signal 21 from the first flying object 510 and three geostationary satellites 200 or quasi-zenith satellites 300, and measures the position coordinates in the inertial coordinate system.

[0051] As the Moon-fixed coordinate system, a lunar coordinate system is known in which a small bowl-shaped crater called "Mesting A" is used as a reference position, and the position coordinates on the lunar surface are defined by two values corresponding to the longitude and latitude of the Earth. It is possible to define a Moon-fixed coordinate system as a three-dimensional coordinate system with the center of gravity of the Moon as the origin and adding altitude to the longitude and latitude. The lunar orbital plane (the plane of revolution around the Earth) is inclined at 5.15° with respect to the ecliptic, and the lunar axis of rotation is inclined at 6.69° from the perpendicular to the ecliptic. In the Earth where the axis of rotation is inclined at 23.4° from the perpendicular to the ecliptic, similar to the ability to perform coordinate transformation between the Earth-fixed coordinate system and the inertial coordinate system, it is possible to perform coordinate transformation between the moon-fixed coordinate system and the inertial coordinate system.

[0052] There is a concept of LOP-G (hereinafter referred to as the Gateway) as a future base for lunar exploration. The Gateway is being considered to operate in a very elongated elliptical orbit called NRHO at the Lagrange point where the gravitational potentials of the Earth and the moon become equilibrium points. NRHO is an extremely elongated elliptical orbit that orbits the moon north-south with an altitude ranging from 4500 km to 75000 km. LOP-G is an abbreviation for Lunar Orbital Platform-Gateway. NRHO is an abbreviation for Near Rectilinear Halo Orbit.

[0053] Assume that the Gateway is equipped with a high-precision clock and a positioning signal transmitter, and the position coordinates in the moon-fixed coordinate system or the inertial coordinate system are known. At this time, for a second flying object flying between the Earth and the moon, called cislunar space, if the position coordinates of the Gateway are known and measurements can be made including the positioning signal from the Gateway, the solid angle becomes larger and the positioning accuracy is improved.

[0054] The position measurement of the Gateway may be carried out by any one of Example 2 to Example 5 of the positioning method, or may be analytically derived using distance measurement or angle measurement from the ground separately, and orbital information of the lunar orbit. By performing positioning including the first flying object 510 orbiting the moon, there is an effect that the distance measurement accuracy of the second flying object 520 flying between the Earth and the moon from the Earth is improved. Also, when the Gateway flies in NRHO, it moves southward to about 75000 km from the ecliptic plane, so positioning with a large solid angle is possible as seen from the second flying object 520, and there is an effect that the positioning accuracy is improved.

[0055] <Example 7 of the positioning method> FIG. 13 is a diagram showing Example 7 of the positioning method according to the present embodiment. FIG. 14 is a diagram showing a configuration example of the lunar station 550 according to the present embodiment. In Example 7 of the positioning method, the positioning system 800 is composed of the lunar station 550, the geostationary satellite 200, and the quasi-zenith satellite 300. The lunar station 550 is installed on the lunar surface and includes a high-precision clock 503 and a positioning signal transmitter 10. The geostationary satellite 200 includes a positioning signal transmitter 10, and its position coordinates in the inertial coordinate system are known. The quasi-zenith satellite 300 includes a positioning signal transmitter 10, and its position coordinates in the inertial coordinate system are known.

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

[0057] The lunar station 550 includes a high-precision clock 503 and a positioning signal transmitter 10, and is deployed on the lunar surface. The lunar station 550 has the effect that it can be permanently utilized as a position coordinate reference in the lunar coordinate system including maintenance or replacement of devices, compared with a flying object with a limited operation life.

[0058] <Example 8 of the positioning method> FIG. 15 is a diagram showing Example 8 of the positioning method according to the present embodiment. In Example 8 of the positioning method, the positioning system 800 is composed of the lunar station 550, the first flying object 510, the geostationary satellite 200, and the quasi-zenith satellite 300.

[0059] The lunar station 550 is installed on the lunar surface and includes a high-precision clock 503 and a positioning signal transmitter 10. The position coordinates of the lunar station 550 in the lunar-fixed coordinate system or the inertial coordinate system are known. The first flying object 510 orbits the moon. The first flying object 510 is equipped with a positioning signal transmitting device 10 and orbits the moon, and the position coordinates in the moon-fixed coordinate system or the inertial coordinate system are known. The geostationary satellite 200 is equipped with a positioning signal transmitting device 10, and the position coordinates in the inertial coordinate system are known. The quasi-zenith satellite 300 is equipped with a positioning signal transmitting device 10, and the position coordinates in the inertial coordinate system are known. The second flying object 520 simultaneously receives the positioning signal 21 from the lunar surface station 550, the first flying object 510, and two geostationary satellites 200 or quasi-zenith satellites 300, and measures the position coordinates in the 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, there is an effect that the flight position measurement accuracy of the second flying object 520 flying between the earth and the moon can be improved. In addition, there is an effect that it becomes possible to measure the position coordinates of the second flying object 520 such as a planetary exploration satellite flying farther from the earth than the moon.

[0061] Embodiment 5. In this embodiment, mainly, the points added to or different from Embodiments 1 to 4 will be described. Note that the same components as those in Embodiments 1 to 4 may be denoted by the same reference numerals, and the description thereof may be omitted.

[0062] In this embodiment, a lunar positioning system 801 that can measure the position coordinates in the moon-fixed coordinate system of a moving object on the lunar surface or a second flying object flying near the moon will be described.

[0063] FIG. 16 is a diagram showing a configuration example of the lunar positioning system 801 according to this embodiment. FIG. 17 is a diagram showing a configuration example of the third flying object 530 according to this embodiment. The lunar surface station 550 is installed on the lunar surface, equipped with a high-precision clock 503 and a positioning signal transmitting device 10, and the position coordinates in the moon-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 the position coordinates in the moon-fixed coordinate system are known. The lunar positioning system 801 is composed of either or both of the lunar surface station 550 and the third flying object 530, and the total number of the lunar surface station 550 and the third flying object 530 is 4 or more. In addition, although FIG. 16 shows an example in which the third flying objects fly on the same orbital plane, it goes without saying that the third flying objects may fly on different orbital planes.

[0064] According to the lunar positioning system 801, in a moving object such as a rover that is equipped with a positioning signal receiving device and operates on the lunar surface, or in the second flying object 520 that flies near the moon, it is possible to measure the position coordinates in the moon-fixed coordinate system. Regarding a moving object on the lunar surface or the second flying object 520 that flies near the moon, if a positioning signal is received from four or more lunar surface stations 550 or lunar orbiting satellites (the third flying object 530) whose moon-fixed coordinate systems are known, it is possible to measure the position coordinates in the moon-fixed coordinate system in the same manner as the positioning satellite system on the earth. When the progress of human lunar exploration advances, securing a positioning base on the lunar surface and forming a positioning system for the moon-fixed coordinate system has the effect of enhancing the convenience of the operation control of lunar orbiting satellites.

[0065] According to Example 2 to Example 8 of the positioning method, it is possible to install lunar surface stations or lunar orbiting satellites whose inertial coordinate systems are known. Since coordinate conversion between the inertial coordinate system and the moon-fixed coordinate system is possible, it is possible to install lunar surface stations or lunar orbiting satellites whose position coordinates in the moon-fixed coordinate system are known.

[0066] Furthermore, including various measurement means associated with activities on the lunar surface, it is possible to increase the number of lunar surface stations or lunar orbiting satellites whose position coordinates in the moon-fixed coordinate system are known. Thereby, it is possible to construct a lunar positioning system in which a moving object on the lunar surface or the second flying object that flies near the moon can receive positioning signals from four or more lunar surface stations or lunar orbiting satellites at the same time. According to the lunar positioning system, there is an effect that the position coordinates of a moving body on the lunar surface or a second flying body flying near the moon in the lunar fixed coordinate system can be measured.

[0067] Embodiment 6. In this embodiment, mainly, the points added to or different from Embodiments 1 to 5 will be described. Note that the same components as those in Embodiments 1 to 5 may be denoted by the same reference numerals, and the description thereof may be omitted.

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

[0069] FIG. 18 is a diagram showing a configuration example of the positioning satellite 400 according to this embodiment. FIG. 19 is a diagram showing a transmission example of the positioning signal 21 using the positioning satellite 400 according to this embodiment.

[0070] The positioning satellite 400 flies in a geostationary orbit or a quasi-zenith orbit. In the positioning satellite 400, the X-axis of the satellite coordinate system is the eastward traveling direction, the Y-axis is the south direction, and the Z-axis is the earth direction. The positioning satellite 400 has a one-wing configuration of the solar cell paddle 401 on the north side (-Y). Further, the positioning satellite 400 is equipped with the positioning signal transmission device 10 on the south side (+Y). The positioning satellite 400 secures a positioning signal transmission field of view including Azimuth ±170 deg 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 deg or more (north side) and Elevation 36 deg or more (south side) with respect to the XZ plane.

[0071] Since the normal vector of the orbital plane of NRHO faces the earth direction, it is possible to communicate with the gateway without being in the shadow of the moon. On the other hand, in the case of a geostationary satellite of the earth, the positioning signal transmission is interrupted in the seasons and time zones when the positioning satellite is in the shadow of the earth with respect to the moon. Since the Earth's axis of rotation is inclined at approximately 23.4 degrees with respect to inertial space, there is a variation in the direction of orientation of ±23.4 degrees between the winter solstice and the summer solstice. The radius of the geostationary orbit is about 7 times that of the Earth's radius, which is about 6,400 km. Due to the inclination of the Earth's axis, there may be situations where the Earth's shadow does not occur depending on the season.

[0072] Therefore, in order to minimize the interruption of positioning signal transmission while the positioning satellite orbits once above the Earth's equator, a positioning signal transmission device that rotates the field of view around the north-south axis of the satellite is adopted. In order to eliminate field-of-view interference on the satellite, the positioning signal transmission device is mounted on the south side of the satellite where a wide field of view can be secured on the apogee side of the NRHO. By changing the two-axis pointing direction of Azimuth and Elevation, the positioning signal transmission field of view with the gateway is secured. As the driving range of the positioning signal transmission device, for a positioning signal transmission device that cannot rotate continuously by 360 degrees or more, the Earth direction is set as the dead zone, and as the Azimuth rotation range when mounted on the south side, it includes ±170 deg with respect to the anti-Earth direction. There are positioning signal transmission devices with ±175 deg, and the wider the field of view, the shorter the interruption period of positioning signal transmission can be.

[0073] Also, while the gateway is in the Earth's shadow, the Azimuth pointing angle is set to the easternmost end, and after emerging from the shadow, a communication link is formed. Since the Azimuth pointing angle rotates to the westernmost end while the positioning satellite orbits the Earth approximately once, the operation of setting the Azimuth pointing angle to the easternmost end again after entering the shadow is repeated.

[0074] The distance between the Earth and the Moon is about 385,000 km, the apogee altitude of the NRHO is about 75,000 km, and the perigee altitude is about 4,000 km. Therefore, the angle looking at the perigee above the North Pole of the NRHO from the positioning satellite is 1 degree or less in the Elevation north latitude direction with respect to the XZ plane of the satellite coordinate system, where the X-axis of the satellite coordinate system is the eastward traveling direction, the Y-axis is the south direction, and the Z-axis is the Earth direction. The angle looking at the apogee above the South Pole is 12 degrees or less in the Elevation south latitude direction with respect to the Z-axis (Earth direction) of the satellite.

[0075] Considering the variation of the inclination of the Earth's axis by approximately 23.4 degrees, it has a function of changing the pointing direction by 25 degrees or more in the north latitude direction of Elevation and 36 degrees or more in the south latitude direction of Elevation. As a result, communication is always possible in the flight path from the apogee to the perigee of the gateway. Manned activities are also planned for the gateway, and in events such as extravehicular activities involving human life, there is an effect that communication can be maintained with ground facilities without interruption for a long time. Needless to say, when the perigee of NRHO is set on the south pole side of the moon, the positioning satellites should also be arranged with the north and south reversed. Also, even if the orbit of the gateway changes during operation, it is possible to operate by rotating the positioning satellite 180 degrees around the Z axis to reverse the north and south, and the same effect as above can be obtained.

[0076] According to the positioning satellite 400 according to the present embodiment, in Examples 2 to 8 of the positioning method, there is an effect that a geostationary satellite or a quasi-zenith satellite equipped with a positioning signal transmission device with a pointing direction control function can be realized while compensating for the change in the attitude of the geostationary satellite or the quasi-zenith satellite accompanying the rotation of the Earth.

[0077] In the above-described Embodiments 1 to 6, each system, each satellite, each station, and each device include a computer, and a computer is used to realize the functions described in Embodiments 1 to 6. The computer includes a processor or an electronic circuit, and also includes other hardware such as a memory, an auxiliary storage device, an input interface, an output interface, and a communication device. The processor or the electronic circuit is connected to other hardware via signal lines and controls these other hardware.

[0078] In the above-described Embodiments 1 to 6, the configurations of each system, each satellite, each station, and each device do not necessarily have to be the same as those in the above-described embodiments. The configurations of each system, each satellite, each station, and each device may be any configuration as long as they can realize the functions described in Embodiments 1 to 6 above. Also, among Embodiments 1 to 6, a plurality of parts or examples may be combined and implemented. Alternatively, one part or example among these embodiments may be implemented. Additionally, these embodiments may be combined and implemented in any way, either as a whole or partially. That is, in Embodiments 1 to 6, free combinations of each embodiment, deformations of any constituent elements of each embodiment, or omissions of any constituent elements in each embodiment are possible.

[0079] Note that the above-described embodiments are essentially preferred examples and are not intended to limit the scope of the present disclosure, the scope of the applications of the present disclosure, or the scope of the uses of the present disclosure. The above-described embodiments can be variously modified as necessary.

Description of Reference Numerals

[0080] 10 Positioning signal transmission device, 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 cell paddle, 500 Flying object, 510 First flying object, 520 Second flying object, 530 Third flying object, 550 Lunar station, 501 Positioning signal receiving device, 502 Measuring device, 503 High-precision clock, 800, 801 Positioning system.

Claims

1. A positioning method for measuring the position coordinates of a flying object flying in space from the earth to the moon or a planet or in the vicinity of the moon or a planet, comprising: The flying object is equipped with a positioning signal receiving device, is equipped with a positioning signal transmitting device, and receives positioning signals transmitted from a geostationary satellite whose position coordinates in the earth-fixed coordinate system or the inertial coordinate system are known, and a positioning signal transmitting device, and receives positioning signals transmitted from a quasi-zenith satellite whose position coordinates in the earth-fixed coordinate system or the inertial coordinate system are known, and measures the position coordinates in the inertial coordinate system by receiving signals from three or more geostationary satellites or quasi-zenith satellites simultaneously.

2. A positioning method for a positioning system for measuring the position coordinates of a second flying object flying in space from the earth to the moon or a planet or in the vicinity of the moon or a planet and equipped with a positioning signal receiving device, comprising: The positioning system comprises a first flying object equipped with a high-precision clock, a positioning signal receiving device, and a positioning signal transmitting device, a geostationary satellite equipped with a positioning signal transmitting device and having known position coordinates in the earth-fixed coordinate system or the inertial coordinate system, and a quasi-zenith satellite equipped with a positioning signal transmitting device and having known position coordinates in the earth-fixed coordinate system or the inertial coordinate system constituted thereby, The first flying object receives positioning signals from three or more geostationary satellites or quasi-zenith satellites simultaneously, measures the position coordinates in the earth-fixed coordinate system or the inertial coordinate system, and transmits positioning signals as a flying object with known position coordinates, The second flying object simultaneously receives positioning signals from the first flying object and three geostationary satellites or quasi-zenith satellites, and measures the position coordinates in the earth-fixed coordinate system or the inertial coordinate system.

3. A positioning method for a positioning system for measuring the position coordinates of a second flying object flying in space from the earth to the moon or a planet or in the vicinity of the moon or a planet and equipped with a positioning signal receiving device, comprising: The positioning system comprises a first flying object equipped with a positioning signal transmitting device and orbiting the moon and having known position coordinates in the moon-fixed coordinate system or the inertial coordinate system, a geostationary satellite equipped with a positioning signal transmitting device and having known position coordinates in the inertial coordinate system, and a quasi-zenith satellite equipped with a positioning signal transmitting device and having known position coordinates in the inertial coordinate system constituted thereby, The second flying object simultaneously receives positioning signals from the first flying object and three geostationary satellites or quasi-zenith satellites, and measures the position coordinates in the inertial coordinate system.

4. A positioning method for a positioning system that measures the position coordinates of a second flying object equipped with a positioning signal receiving device while flying in space from the Earth towards the Moon or a planet or in the vicinity of the Moon or a planet, wherein the positioning system includes a lunar station installed on the lunar surface, equipped with a high-precision clock and a positioning signal transmitting device, and having known position coordinates in a lunar-fixed coordinate system or an inertial coordinate system, a geostationary satellite equipped with a positioning signal transmitting device and having known position coordinates in an inertial coordinate system, and a quasi-zenith satellite equipped with a positioning signal transmitting device and having known position coordinates in an inertial coordinate system and is composed of wherein the second flying object simultaneously receives positioning signals from the lunar station and three geostationary satellites or quasi-zenith satellites to measure position coordinates in an inertial coordinate system. **Claim 5** A positioning method for a positioning system that measures the position coordinates of a second flying object equipped with a positioning signal receiving device while flying in space from the Earth towards the Moon or a planet or in the vicinity of the Moon or a planet, wherein the positioning system includes a lunar station installed on the lunar surface, equipped with a high-precision clock and a positioning signal transmitting device, and having known position coordinates in a lunar-fixed coordinate system or an inertial coordinate system, a first flying object equipped with a positioning signal transmitting device, orbiting the Moon, and having known position coordinates in a lunar-fixed coordinate system or an inertial coordinate system, a geostationary satellite equipped with a positioning signal transmitting device and having known position coordinates in an inertial coordinate system, and a quasi-zenith satellite equipped with a positioning signal transmitting device and having known position coordinates in an inertial coordinate system and is composed of wherein the second flying object simultaneously receives positioning signals from the lunar station, the first flying object, and two geostationary satellites or quasi-zenith satellites to measure position coordinates in an inertial coordinate system. **Claim 6** Composed of either or both of a lunar station installed on the lunar surface, equipped with a high-precision clock and a positioning signal transmitting device, and having known position coordinates in a lunar-fixed coordinate system, and a third flying object equipped with a high-precision clock and a positioning signal transmitting device, orbiting the Moon, and having known position coordinates in a lunar-fixed coordinate system and having a total number of the lunar station and the third flying object of 4 or more. A lunar positioning system. **Claim 7** Flying in a geostationary orbit or a quasi-zenith orbit, with the X-axis of the satellite coordinate system as the eastward traveling direction, the Y-axis as the south direction, and the Z-axis as the Earth direction, having a solar panel paddle configuration with one wing on the north side (-Y), and mounting a positioning signal transmitting device on the south side (+Y). A positioning satellite that secures a positioning signal transmission field including Azimuth ±170 deg from the anti-earth direction (-Z axis) around the north-south axis (Y axis), and a positioning signal transmission field of Elevation -25 deg or more (north side) and Elevation 36 deg or more (south side) with respect to the XZ plane.

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