Device for determining coordinates of low earth orbit object, method for determining coordinates, program, and recording medium

Abstract

This device for determining coordinates of a low Earth orbit object is provided with: a narrow-field optical telescope (10) comprising a narrow-field image-forming optical system (11) that has a narrow viewing angle and high resolution, a narrow-field light selecting means (12) for selecting, from light concentrated by the narrow-field image-forming optical system (11), light coming from a low Earth orbit object, and a narrow-field image sensor (13) for outputting, as narrow-field image data, the light selected by the narrow-field light selecting means (12); a wide-field optical telescope (20) comprising a wide-field image-forming optical system (21) that has a wider viewing angle and lower resolution than those of the narrow-field image-forming optical system (11) and that is oriented in the same direction as an orientation direction of the narrow-field image-forming optical system (11), a wide-field light selecting means (12) for selecting, from light concentrated by the wide-field image-forming optical system (21), light coming from a star, and a wide-field image sensor (23) for outputting, as wide-field image data, the light selected by the wide-field light selecting means (22); and a low Earth orbit object position coordinate computation device (50) for identifying celestial sphere coordinates of the low Earth orbit object by using detected position coordinates of the low Earth orbit object detected from the narrow-field image data from the narrow-field image sensor (13) and detected position coordinates of the star detected from the wide-field image data from the wide-field image sensor (23).

Description

Coordinate determination device, coordinate determination method, program, and recording medium for low-orbit object

[0001] The present disclosure relates to a coordinate determination device, a coordinate determination method, a program, and a recording medium for determining the coordinate position of a low-orbit object such as space debris.

[0002] Patent Document 1 discloses a method for detecting flying objects, such as space debris or meteors, by observation from the ground in order to avoid collisions between satellites or collisions with space debris in orbits near the Earth or in distant geostationary orbits.

[0003] The line image detection method disclosed in Patent Document 1 performs image data processing in all directions of the planar image, which consists of a division process that divides the image data of a planar image, which is a CCD image of the sky taken by a camera equipped with a CCD imaging element installed on a telescope, into multiple parallel columnar image data, and a representative value selection process that sets the median value obtained for each columnar image data as the representative value for that columnar image data.The method then performs analysis processing that consists of a significance value detection process that detects whether the representative value of each columnar image data is a significant value, and a line image position identification process that sets the column position of the columnar image data whose representative value indicates a significant value as the line image position.

[0004] Japanese Patent Application Laid-Open No. 2003-132357

[0005] The line image detection method disclosed in Patent Document 1 is configured as described above, and therefore has the problem of high costs for image processing, since it performs image processing by assuming the direction of movement of a flying object in a brute-force manner based on image data of a planar image, which is a CCD image of the sky taken by a camera.

[0006] The present disclosure has been made in consideration of the above points, and aims to provide a coordinate determination device for low-orbit objects, such as satellites, space debris, or meteors, that is, low-orbit objects, that can easily determine the position coordinates of such objects.

[0007] The coordinate determination device for a low-orbit object according to the present disclosure comprises: a narrow-field optical telescope having a narrow-field imaging optical system with a narrow field of view and high resolution, a narrow-field light selection means for selecting light from the low-orbit object from light collected by the narrow-field imaging optical system, and a narrow-field image sensor that outputs the light selected by the narrow-field light selection means as narrow-field image data; a wide-field optical telescope having a wide-field imaging optical system with a wider field of view than the narrow-field imaging optical system and low resolution, and oriented in the same direction as the narrow-field imaging optical system, a wide-field light selection means for selecting light from fixed stars from light collected by the wide-field imaging optical system, and a wide-field image sensor that outputs the light selected by the wide-field light selection means as wide-field image data; and a position coordinate calculation device for a low-orbit object that identifies the celestial coordinates of the low-orbit object using the detected position coordinates of the low-orbit object detected from the narrow-field image data from the narrow-field image sensor and the detected position coordinates of the fixed stars detected from the wide-field image data from the wide-field image sensor.

[0008] The present disclosure facilitates determining the position coordinates of low orbital objects.

[0009] FIG. 1 is a configuration diagram showing a coordinate determination device for a low orbital object according to embodiment 1. FIG. 2 is a flowchart showing a tracking control function in the coordinate determination device for a low orbital object according to embodiment 1. FIG. 3 is a flowchart showing a data acquisition control function in the coordinate determination device for a low orbital object according to embodiment 1. FIG. 4 is a flowchart showing a position coordinate calculation function in the coordinate determination device for a low orbital object according to embodiment 1. FIG. 5 is a configuration diagram showing a hardware configuration of a position coordinate calculation device in the coordinate determination device for a low orbital object according to embodiment 1. FIG. 6 is a configuration diagram showing a coordinate determination device for a low orbital object according to embodiment 2. FIG. 7 is a flowchart showing a position coordinate calculation function in the coordinate determination device for a low orbital object according to embodiment 2.

[0010] Embodiment 1. A coordinate determination device for a low-orbit object according to embodiment 1 will be described with reference to Figures 1 to 5. The coordinate determination device for a low-orbit object according to embodiment 1 is a position measurement device for a low-orbit object that tracks orbital objects such as satellites, space debris, or meteors in near-Earth orbits and distant geostationary orbits, i.e., low-orbit objects, with a highly sensitive primary telescope and identifies the position coordinates of the low-orbit object from the positions of fixed stars captured with a secondary telescope that has a wide field of view and is pointed in the same direction as the primary telescope.

[0011] The coordinate determination device for low-orbit objects according to the first embodiment uses a low-resolution secondary telescope in a low-orbit object tracking mode to detect low-orbit objects as dark line images, but by tracking low-orbit objects using a highly sensitive primary telescope, it is possible to detect low-orbit objects as bright point images. On the other hand, when tracking low-orbit objects, a star that serves as a reference for determining the position of the low-orbit object is observed simultaneously with the low-orbit object using a secondary telescope with a wide field of view, thereby introducing the bright star into the field of view.

[0012] The coordinate determination device for a low-orbit object according to the first embodiment comprises a narrow-field optical telescope 10, a wide-field optical telescope 20, an optical axis adjustment device 30, a drive device 40, a position coordinate calculation device 50, and a database 60. The narrow-field optical telescope 10 is a highly sensitive primary telescope for tracking low-orbit objects, and is a telescope with a narrow field of view and high resolution.

[0013] The narrow-field optical telescope 10 is a device designed to observe light reaching the telescope from low-orbit objects with a high signal-to-noise ratio. Light from low-orbit objects refers collectively to light that is sunlight reflected or scattered by the low-orbit object, light that is laser light emitted from the ground and reflected or scattered by the low-orbit object, or light emitted by the low-orbit object itself.

[0014] The narrow-field optical telescope 10 has a narrow-field imaging optical system 11, a narrow-field light selection means 12, and a narrow-field image sensor 13. The narrow-field imaging optical system 11 is an optical system with a narrow field of view and high resolution, and efficiently guides the received light.

[0015] The narrow-field imaging optical system 11 has a reflecting mirror and a lens, and functions to focus plane wave light incident on the aperture to a single point. The focusing position depends on the angle of incidence on the aperture, and the narrow-field imaging optical system 11 forms an image on a plane (focal plane) perpendicular to the optical axis direction, a focal length away from the narrow-field imaging optical system 11. The narrow-field imaging optical system 11 is intended to detect even dark objects in low orbit, i.e., weak light from objects in low orbit, with a high signal-to-noise ratio, and therefore has a large aperture that can focus more light.

[0016] The reflecting mirrors and lenses that make up the narrow-field imaging optical system 11, as well as the support materials that support the reflecting mirrors and lenses, are thermally deformed, so the light-focusing position of the narrow-field imaging optical system 11 also depends on temperature. Therefore, the narrow-field optical telescope 10 has a fine distance adjustment mechanism that finely adjusts the distance from the narrow-field imaging optical system 11 to the light-receiving surface of the narrow-field image sensor 13, which serves as the focal plane. The fine distance adjustment mechanism may be either an automatic or manual mechanism that finely adjusts the distance between the narrow-field imaging optical system 11 and the narrow-field image sensor 13.

[0017] The narrow-field light selecting means 12 is connected to the narrow-field imaging optical system 11, selects light collected by the narrow-field imaging optical system 11, and guides the selected light to the light receiving surface of the narrow-field image sensor 13. The light selected by the narrow-field light selecting means 12 is mainly light from low-orbit objects. The narrow-field light selecting means 12 has a plurality of optical filters and a filter wheel.

[0018] When the narrow-field light selection means 12 selects an optical filter from the filter wheel, the filter selection, the timing of starting exposure to light from the narrow-field imaging optical system 11 incident via the narrow-field light selection means 12, and the frame rate are input as control information from the control unit 52, and the narrow-field light selection means 12 is controlled by the control unit 52.

[0019] The control information input as control information from the control unit 52 to the narrow-field light selection means 12, indicating the filter selection, the timing of the start of exposure to light from the narrow-field imaging optical system 11, and the frame rate, is hereinafter referred to as narrow-field filter selection information. The information indicating the optical filter selection is information on which optical filter from the filter wheel to select. The information indicating the timing of the start of exposure to light from the narrow-field imaging optical system 11 corresponds to the timing when the narrow-field optical telescope 10 detects a low-orbit object in observation mode and starts tracking the detected low-orbit object.

[0020] The narrow-view light selection means 12 receives information indicating the timing of exposure start in the narrow-view filter selection information from the control unit 52, and selects an optical filter based on the information indicating the filter selection in the narrow-view filter selection information from the control unit 52. The narrow-view light selection means 12 also receives information indicating the frame rate in the narrow-view filter selection information from the control unit 52, and selects an optical filter based on the information indicating the filter selection in the narrow-view filter selection information from the control unit 52 in accordance with the frame rate.

[0021] Note that the information indicating the frame rate does not have to be included in the narrow-field filter selection information, but may be held by the control unit 52, and an optical filter may be selected in accordance with the frame rate upon receiving information indicating filter selection from the control unit 52. Also, even in the case where the optical filter selected based on the information indicating filter selection upon receiving information indicating the timing of exposure start is to remain the same throughout the tracking period of a targeted low-orbit object, the control information indicating the frame rate does not have to be included in the narrow-field filter selection information.

[0022] Optical filters are either wavelength filters or polarizing filters, or both. Wavelength filters include those that transmit only specific wavelengths, those that block only specific wavelengths, and those whose transmittance changes continuously with wavelength. When using wavelength filters, for example, wideband filters such as those used in the Sloan / SDSS system or Johnson system, or narrowband filters that transmit only the wavelength of laser light, are used.

[0023] Furthermore, when using a polarizing filter, a PL filter that transmits only linearly polarized light in a specific direction or a C-PL filter that transmits only circularly polarized light in a specific direction is used. In order to efficiently select light from a low-orbit object, wavelength filters and polarizing filters are prepared according to the wavelength and polarization component of the light from the low-orbit object.

[0024] The filter wheel is equipped with a plurality of optical filters, and a desired optical filter is selected from the plurality of optical filters installed manually or automatically in response to narrow-field filter selection information from the control unit 52. For example, the filter wheel receives the filter slot number on the filter wheel, which is filter selection information in the narrow-field filter selection information from the control unit 52, and rotates the filter wheel so that the designated filter slot is on the optical axis of the narrow-field imaging optical system 11. The optical filter selected by the filter wheel selects the desired light from the light collected by the narrow-field imaging optical system 11 and directs it to the light-receiving surface of the narrow-field image sensor 13.

[0025] The narrow-field image sensor 13 is connected to the narrow-field light selection means 12, and its light-receiving surface is placed on the focal plane where light is collected by the narrow-field imaging optical system 11. The narrow-field image sensor 13 converts the amount of light or light intensity incident on each of the many pixels spread two-dimensionally on the light-receiving surface into a digital value and outputs the digital value as narrow-field image data, which is two-dimensional image data.

[0026] When acquiring narrow-field image data, the narrow-field image sensor 13 receives sensor parameters such as the timing of exposure start for light from the narrow-field imaging optical system 11 incident via the narrow-field light selection means 12, exposure time, frame rate, gain, and pixels to be read as control information from the control unit 52, and is controlled by the control unit 52.

[0027] A long exposure time is set for the narrow-field image sensor 13 in order to detect weak light from low-orbit objects with a high signal-to-noise ratio. The control information input to the narrow-field image sensor 13 from the control unit 52 as control information indicates sensor parameters such as the timing of starting exposure to light from the narrow-field imaging optical system 11, the exposure time, frame rate, gain, and pixels to be read out, and is hereinafter referred to as narrow-field light control information.

[0028] The narrow-view image sensor 13 starts imaging in the tracking mode upon receiving information indicating the timing of exposure start in the narrow-view light control information from the control unit 52. The narrow-view image sensor 13 receives information indicating the frame rate in the narrow-view light control information from the control unit 52, and continuously performs imaging using the exposure time in the narrow-view light control information in accordance with the frame rate until the tracking mode ends.

[0029] In addition, the control information indicating the frame rate does not have to be included in the narrow-field light control information, and the control unit 52 may hold the frame rate and receive information from the control unit 52 to perform imaging according to the frame rate from the control unit 52, and perform imaging.

[0030] The narrow-field light control information and the narrow-field filter selection information are synchronized, and the narrow-field light selection means 12 and the narrow-field image sensor 13 are controlled in synchronization with the narrow-field filter selection information and the narrow-field light control information. By synchronizing the narrow-field light control information and the narrow-field filter selection information, it is also possible to change the filter to be used each time narrow-field image data is acquired in accordance with the frame rate in the narrow-field light control information from the control unit 52.

[0031] The narrow-field image sensor 13 may be a thermal sensor or a quantum sensor. When using a thermal sensor, a bolometer or thermopile sensor is used, which converts the light intensity incident on each element (corresponding to each pixel) into heat and then reads it out as a voltage value. When using a quantum sensor, a CCD sensor or CMOS sensor for visible light, or an nGaAs sensor, InSb sensor, or HgCdTe sensor for infrared light, is used, which converts photons into electrons by the internal photoelectric effect using semiconductor elements and reads them out.

[0032] The wide-field optical telescope 20 is a secondary telescope with a wide field of view that simultaneously observes with the narrow-field optical telescope 10 and introduces stars that serve as a reference for determining the position of low-orbit objects into its field of view, and has a wider field of view and lower resolution than the narrow-field optical telescope 10. The wide-field optical telescope 20 is a device designed to observe the light that reaches the telescope from many bright stars located around low-orbit objects.

[0033] The wide-field optical telescope 20 has a wide-field imaging optical system 21, a wide-field light selection means 22, and a wide-field image sensor 23. The wide-field imaging optical system 21 is connected to the narrow-field imaging optical system 11 by an optical axis adjustment device 30 so that the direction of the wide-field imaging optical system 21 and the narrow-field imaging optical system 11 are the same.

[0034] The wide-field imaging optical system 21 is mounted on the narrow-field imaging optical system 11 and fixed to the narrow-field imaging optical system 11 by a three-point holding mechanism at two locations in the optical axis adjustment device 30. The screws of the three-point holding mechanism in the optical axis adjustment device 30 are used as push-pull screws, and the deviation in the pointing direction of the wide-field imaging optical system 21 relative to the narrow-field imaging optical system 11 is adjusted in two axes by the screws of the three-point holding mechanism.

[0035] As a result, the pointing direction of the narrow field imaging optical system 11 and the pointing direction of the wide field imaging optical system 21 can be made to coincide with each other by the optical axis adjustment device 30. That is, the optical axis of the wide field imaging optical system 21 is made parallel to the optical axis of the narrow field imaging optical system 11 by the optical axis adjustment device 30. In short, the optical axis adjustment device 30 fixes the wide field imaging optical system 21 to the narrow field imaging optical system 11 so that the difference in pointing direction between the wide field imaging optical system 21 and the narrow field imaging optical system 11 can be adjusted along two axes.

[0036] The wide-field imaging optical system 21 is an optical system that has a wider field of view and lower resolution than the narrow-field imaging optical system 11, and is capable of collecting light from a wide field of view. Because the wide-field imaging optical system 21 is an optical system that can collect light from a wide field of view, even though it has low resolution, it is possible to detect as many bright stars located around a low-orbit object as possible within the field of view.

[0037] The wide-field imaging optical system 21 has a reflecting mirror and a lens, and functions to focus the plane wave light incident on the aperture to one point. The focusing position depends on the angle of incidence on the aperture, and the wide-field imaging optical system 21 forms an image on a plane (focal plane) perpendicular to the optical axis direction, which is a focal length away from the wide-field imaging optical system 21.

[0038] The reflecting mirrors and lenses that make up the wide-field imaging optical system 21, as well as the support materials that support the reflecting mirrors and lenses, are thermally deformed, so the light-focusing position of the wide-field imaging optical system 21 also depends on temperature. Therefore, the wide-field optical telescope 20 has a fine distance adjustment mechanism that finely adjusts the distance from the wide-field imaging optical system 21 to the light-receiving surface of the wide-field image sensor 23, which serves as the focal plane. The fine distance adjustment mechanism may be either an automatic or manual mechanism that finely adjusts the distance between the wide-field imaging optical system 21 and the wide-field image sensor 23.

[0039] The wide-field light selection means 22 is connected to the wide-field imaging optical system 21, selects the light collected by the wide-field imaging optical system 21, and directs the selected light to the light receiving surface of the wide-field imaging optical system 21. The light selected by the wide-field light selection means 22 is mainly light from stars located around the low-orbit object.

[0040] The wide-field light selecting means 22 has a plurality of optical filters and a filter wheel. When selecting an optical filter from the filter wheel, the wide-field light selecting means 22 receives control information from the control unit 52, including the filter selection, the timing to start exposure to light from the wide-field imaging optical system 21, and the frame rate, and is controlled by the control unit 52. The control information, which is input to the wide-field light selecting means 22 from the control unit 52 as control information and indicates the filter selection, the timing to start exposure to light from the wide-field imaging optical system 21, and the frame rate, is hereinafter referred to as wide-field filter selection information.

[0041] The information indicating the timing of exposure start for light from the wide-field imaging optical system 21 and the information indicating the frame rate in the wide-field filter selection information from the control unit 52 are the same as the information indicating the timing of exposure start for light from the narrow-field imaging optical system 11 and the information indicating the frame rate in the narrow-field filter selection information.

[0042] The wide-field light selection means 22 receives information indicating the exposure start timing in the wide-field filter selection information from the control unit 52, and selects an optical filter based on the information indicating the filter selection in the wide-field filter selection information from the control unit 52. The wide-field light selection means 22 also receives information indicating the frame rate in the wide-field filter selection information from the control unit 52, and selects an optical filter in accordance with the frame rate based on the information indicating the filter selection in the wide-field filter selection information from the control unit 52.

[0043] Note that the information indicating the frame rate does not have to be included in the wide-field filter selection information, and the control unit 52 may hold the frame rate and select an optical filter in accordance with the frame rate upon receiving information indicating filter selection from the control unit 52. Also, even in the case where an optical filter selected based on information indicating the timing of exposure start and information indicating filter selection is to be the same as the tracking period during the tracking period of a targeted low-orbit object, the control information indicating the frame rate does not have to be included in the wide-field filter selection information.

[0044] The optical filter is either a wavelength filter or a polarizing filter, or both, similar to the optical filter in the narrow-field light selection means 12. When a wavelength filter is used as the optical filter, for example, a wideband filter such as that used in the Sloan / SDSS system or the Johnson system, or a narrowband filter that transmits only the wavelength of laser light, is used. When a polarizing filter is used as the optical filter, a PL filter or a C-PL filter is used.

[0045] In order to efficiently select light from a star, wavelength filters and polarizing filters are prepared according to the wavelength and polarization components of the light from the star. A plurality of optical filters are installed on the filter wheel, and a desired optical filter is selected from the plurality of optical filters installed manually or automatically based on wide-field filter selection information from the control unit 52.

[0046] For example, the filter wheel receives the filter slot number on the filter wheel, which is filter selection information in the wide-field filter selection information from the control unit 52, and rotates it so that the designated filter slot is on the optical axis of the wide-field imaging optical system 21. The optical filter selected by the filter wheel selects the desired light from the light collected by the wide-field imaging optical system 21 and directs it to the light receiving surface of the wide-field image sensor 23.

[0047] The wide-field image sensor 23 is connected to the wide-field light selection means 22, and its light receiving surface is placed on the focal plane where light is collected by the wide-field imaging optical system 21. The wide-field image sensor 23 converts the amount of light or light intensity incident on each of the many pixels spread two-dimensionally on the light receiving surface into a digital value and outputs it as wide-field image data, which is two-dimensional image data.

[0048] When acquiring wide-field image data, the wide-field image sensor 23 receives sensor parameters such as the timing of exposure start for light from the wide-field imaging optical system 21 incident via the wide-field light selection means 22, exposure time, frame rate, gain, and pixels to be read as control information from the control unit 52, and is controlled by the control unit 52.

[0049] The control information input as control information from the control unit 52 to the wide-field image sensor 23 indicates sensor parameters such as the timing of starting exposure to light from the wide-field imaging optical system 21, exposure time, frame rate, gain, and pixels to be read out, and is hereinafter referred to as wide-field light control information.

[0050] The wide-field image sensor 23 starts imaging in the tracking mode upon receiving information indicating the exposure start timing in the wide-field light control information from the control unit 52. The wide-field image sensor 23 receives information indicating the frame rate in the wide-field light control information from the control unit 52, and continuously performs imaging using the exposure time in the wide-field light control information in accordance with the frame rate until the tracking mode ends.

[0051] In addition, the control information indicating the frame rate does not have to be included in the wide-field light control information, but may be held by the control unit 52, and imaging may be performed by receiving information from the control unit 52 to perform imaging according to the frame rate from the control unit 52.

[0052] The wide-field light control information and the wide-field filter selection information are synchronized, and the wide-field light selection means 22 and the wide-field image sensor 23 are controlled in synchronization with the wide-field filter selection information and the wide-field light control information. By synchronizing the wide-field light control information and the wide-field filter selection information, it is also possible to change the filter to be used each time wide-field image data is acquired in accordance with the frame rate in the wide-field light control information from the control unit 52. Furthermore, the wide-field light control information and the wide-field filter selection information are synchronized with the narrow-field light control information and the narrow-field filter selection information.

[0053] The wide-field image sensor 23 uses a thermal sensor or a quantum sensor, similar to the narrow-field image sensor 13. When a thermal sensor is used as the wide-field image sensor 23, a sensor such as a bolometer or a thermopile is used. When a quantum sensor is used as the wide-field image sensor 23, a sensor that converts photons into electrons by the internal photoelectric effect using a semiconductor element, such as a CCD sensor or CMOS sensor for the visible light band, or an InGaAs sensor, InSb sensor, or HgCdTe sensor for the infrared band, is used.

[0054] The narrow-field imaging optical system 11 is mounted on the drive device 40. The narrow-field light selecting means 12 is connected to the narrow-field imaging optical system 11, and the narrow-field image sensor 13 is connected to the narrow-field light selecting means 12, so that the narrow-field light selecting means 12 and the narrow-field image sensor 13 are also mounted on the drive device 40. In short, the narrow-field optical telescope 10 is mounted on the drive device 40.

[0055] The wide-field imaging optical system 21 is mounted and fixed on the narrow-field imaging optical system 11, and is consequently mounted on the driving device 40. The wide-field light selecting means 22 is connected to the wide-field imaging optical system 21, and the wide-field image sensor 23 is connected to the wide-field light selecting means 22, and therefore the wide-field light selecting means 22 and the wide-field image sensor 23 are also consequently mounted on the driving device 40. In short, the wide-field optical telescope 20 is mounted on the driving device 40 and driven integrally with the narrow-field optical telescope 10.

[0056] The drive unit 40 automatically drives the mounted narrow-field optical telescope 10 so as to change the pointing direction of the narrow-field imaging optical system 11 along two axes, in accordance with input values ​​indicating the biaxial drive amounts from the control unit 52. By automatically driving the narrow-field optical telescope 10 along two axes, the drive unit 40 can cause the pointing direction of the narrow-field imaging optical system 11 in the narrow-field optical telescope 10 to track a low-orbit object. The drive unit 40 is, for example, a German-style equatorial mount, a fork-type equatorial mount, or an altazimuth-altitude mount having two rotation axes.

[0057] The position coordinate calculation device 50 for a low-orbit object has a position coordinate calculation function for obtaining the celestial coordinates of the low-orbit object, a data acquisition control function for controlling the acquisition of image data from the narrow-field optical telescope 10 and the wide-field optical telescope 20, and a tracking control function for controlling the drive of the drive device 40 to track the low-orbit object. The position coordinate calculation device 50 includes a tracking orbit determination unit 51, a control unit 52, an image recording unit 53, a preprocessing unit 54, a stationary object detection unit 55, a moving object detection unit 56, a star coordinate comparison unit 57, and a position coordinate determination unit 58 for the low-orbit object.

[0058] The position coordinate calculation function of the position coordinate calculation device 50 is a function that receives as input narrow-field image data from the narrow-field image sensor 13 in the narrow-field optical telescope 10 and wide-field image data from the wide-field image sensor 23 in the wide-field optical telescope 20, obtains the detected position coordinates of stars detected from the wide-field image data from the wide-field image sensor 23, obtains the detected position coordinates of low-orbit objects detected from the narrow-field image data from the narrow-field image sensor 13, and determines the celestial coordinates of the low-orbit objects using the obtained detected position coordinates of the stars.

[0059] The position coordinate calculation function in position coordinate calculation device 50 is achieved by image recording unit 53, preprocessing unit 54, stationary object detection unit 55, moving object detection unit 56, star coordinate comparison unit 57, and low-orbit object position coordinate determination unit 58. Image recording unit 53 receives narrow-field image data from narrow-field image sensor 13 and wide-field image data from wide-field image sensor 23, and stores narrow-field image data in which narrow-field light control information from control unit 52 is linked to the narrow-field image data, and wide-field image data in which wide-field light control information from control unit 52 is linked to the wide-field image data.

[0060] The narrow-field image data and the wide-field image data do not have to be linked with the light control information. Furthermore, the narrow-field image data from the narrow-field image sensor 13 and the wide-field image data from the wide-field image sensor 23 may be directly input to the preprocessing unit 54 without storing the data in the image recording unit 53.

[0061] The preprocessing unit 54 acquires the narrow-field image data stored in the image recording unit 53 and performs preprocessing, which involves subtracting dark current from the narrow-field image data and correcting sensitivity variations in the narrow-field image data. The preprocessing for dark current subtraction in the preprocessing unit 54 involves subtracting dark current image data stored in a database from the narrow-field image data.

[0062] In addition, the preprocessing for correcting sensitivity unevenness in the preprocessing unit 54 is a process performed using flat image data stored in a database from narrow-field image data, and is a process in which the narrow-field image data obtained by subtracting dark current image data from the narrow-field image data is divided by the flat image data.

[0063] The dark current image data is image data measured in advance without irradiating the narrow-field image sensor 13 with light, under the same operating temperature and exposure time as those used to obtain the narrow-field image data. The flat image data is image data measured in advance under conditions where light intensity is uniformly irradiated onto the light receiving surface of the narrow-field image sensor 13. The dark current image data and flat image data are stored in the database 60.

[0064] Furthermore, the preprocessing unit 54 may acquire the wide-field image data stored in the image recording unit 53 and perform preprocessing on the wide-field image data, such as subtracting dark current and correcting sensitivity variations in the narrow-field image data, in the same manner as the preprocessing on the narrow-field image data. In this case, too, the wide-field image sensor 23 is not irradiated with light, and dark current image data measured in advance under the same conditions as the wide-field image sensor 23 when obtaining the wide-field image data, such as the operating temperature and exposure time, is stored in the database 60.

[0065] Flat image data measured in advance under conditions where light intensity is uniformly irradiated onto the light receiving surface of the wide-field image sensor 23 is stored in a database 60. A preprocessing unit 54 obtains wide-field image data by performing preprocessing on the dark current image data and the flat image data stored in the database 60.

[0066] The stationary object detection unit 55 detects a point image from the narrow-field image data that has been preprocessed by the preprocessing unit 54, and sets the center coordinates of the detected point image as the detected position coordinates of the low-orbit object. The detected position coordinates of the low-orbit object are expressed as a coordinate group of multiple pixels, with each pixel in the narrow-field image sensor 13 regarded as one position coordinate.

[0067] The algorithm for detecting point images in the stationary object detection unit 55 extracts connected pixels with values ​​that are sufficiently large compared to the variation in values ​​in the surrounding sky region, and among the extracted connected pixels, the central coordinates of point images with a half-width of 3 to 10 arc seconds, including 5 arc seconds, which is a typical image blur size due to atmospheric turbulence, and with a ratio of the major axis to the minor axis of the connected pixel of 1.5 or less, are determined to be the detected position coordinates of the low-orbit object.

[0068] The narrow-field image data obtained by the narrow-field image sensor 13 is narrow-field image data obtained as a result of performing an exposure of about 1 second in tracking mode to detect dark low-orbit objects. Therefore, assuming that the typical speed of a low-orbit object is 30 arc minutes per second, even if a line image of a star appears in the narrow-field image data, the line image of the star will appear as a line image having a length of 30 arc minutes, and therefore the stationary object detection unit 55 will not detect the line image of the star from the narrow-field image data.

[0069] In the tracking mode, an example has been shown in which the exposure time for narrow-field image sensor 13 is about 1 second, but the exposure time may be as short as 0.01 second. If the exposure time is 0.01 second, even if a line image of a fixed star appears in the narrow-field image data, the line image of the fixed star will appear as a line image with a length of 18 arc seconds, which is sufficiently longer than the 5 arc seconds of image spread caused by typical atmospheric turbulence, and stationary object detection unit 55, which detects point images with a half-width of 3 to 10 arc seconds, will not detect the line image of the fixed star from the narrow-field image data.

[0070] Therefore, the stationary object detection unit 55, which detects point images with a half-width of 3 to 10 arc seconds and a ratio of the major axis to the minor axis of the connected pixels of 1.5 or less, can accurately detect point images of low-orbit objects from narrow-field image data.

[0071] The moving object detection unit 56 detects a line image from the wide-field image data from the wide-field image sensor 23, and sets the central coordinates of the detected line image as the detected position coordinates of the star. The detected position coordinates of the star are expressed as a coordinate group made up of multiple pixels, with each pixel in the wide-field image sensor 23 being regarded as one position coordinate. Note that the wide-field image data used by the moving object detection unit 56 to detect the detected position coordinates of the star may be wide-field image data from the wide-field image sensor 23 that has been preprocessed by the preprocessing unit 54.

[0072] The algorithm for detecting line images in the moving object detection unit 56 is similar to the detection of point images in the stationary object detection unit 55, in that it extracts connected pixels having values ​​that are sufficiently large compared to the variation in values ​​in the surrounding sky region, and among the extracted connected pixels, the central coordinates of a line image whose major axis has a half-width of 10 arc seconds or more, which is larger than the 5 arc seconds that is the typical size of image blur due to atmospheric turbulence, and whose ratio of the major axis to the minor axis of the connected pixel is 2 or more, are taken as the detected position coordinates of the star.

[0073] The wide-field image data obtained by the wide-field image sensor 23 is wide-field image data obtained as a result of an exposure time of 0.01 seconds in tracking mode. If we assume that the typical speed of a low-orbit object is 30 arc minutes / second, the line image of a star will appear as a line image of 18 arc seconds in size. Therefore, the moving object detection unit 56, which detects line images with a half-width of 10 arc seconds or more, can detect the line image of a star from the wide-field image data, and will not detect a point image of a low-orbit object.

[0074] Therefore, the moving object detection unit 56, which detects line images with a half-width of 10 arc seconds or more and a ratio of major axis to minor axis of 2 or more, can detect line images of fixed stars from wide-field image data with high accuracy. Note that in tracking mode, even if the exposure time of the wide-field image sensor 23 is set to 0.01 seconds or more, the line images of fixed stars obtained from the wide-field image data will only become longer, and the signal-to-noise ratio per pixel will not improve.

[0075] Therefore, it is preferable to set the exposure time of the wide-field image sensor 23 short and the exposure time of the narrow-field image sensor 13 longer than the exposure time of the wide-field image sensor 23. Furthermore, the threshold value for the ratio of the major axis to the minor axis of the line image to be detected by the moving object detection unit 56 may be set taking into consideration the speed of the low-orbit object and the length of the line image, which depends on the exposure time of the wide-field image sensor 23.

[0076] The star coordinate comparison unit 57 compares the detected position coordinates of stars obtained by the moving object detection unit 56 with the celestial coordinate data of known stars stored in the database 60, and obtains a correspondence relationship between the celestial coordinate data of the stars and the detected position coordinates of the stars. The correspondence relationship between the coordinates of the stars indicates a correspondence relationship between coordinates that associate the position coordinates of pixels in the wide-field image sensor 23 with celestial coordinates in a celestial coordinate system. The celestial coordinate data of known stars is data listed in a star catalog such as the UCAC4 catalog, and is expressed in the equatorial coordinate system (right ascension and declination) or the galactic coordinate system (longitude and latitude).

[0077] The correspondence between the celestial coordinate data of a star and the detected position coordinates of the star is obtained, for example, as follows: The celestial coordinate data of a star is expressed mainly using angles such as right ascension and declination or azimuth and altitude. On the other hand, the detected position coordinates of a star are expressed by the pixel positions in the wide-field image sensor 23, where each pixel is regarded as a single position coordinate, that is, by coordinates on a two-dimensional plane of x and y coordinates.

[0078] Therefore, the correspondence between the coordinates represented on a two-dimensional plane of the wide-field image data in the wide-field image sensor 23 and the celestial coordinate data of the fixed stars is obtained in advance, for example, as a correspondence table. The star coordinate comparison unit 57 compares the detected position coordinates of the fixed stars obtained by the moving object detection unit 56 with the celestial coordinate data of the fixed stars using the correspondence table, thereby determining the direction on the celestial sphere to which the position coordinates of the pixels in which the fixed stars are reflected correspond. As a result, it is determined which direction on the celestial sphere each pixel of the wide-field image data corresponds.

[0079] The low-orbit object position coordinate determiner 58 identifies the celestial coordinates of the low-orbit object based on the detected position coordinates of the low-orbit object by the stationary object detector 55 and the comparison result of the star coordinate comparator 57, i.e., the correspondence relationship between the celestial coordinate data of the stars and the detected position coordinates of the stars. The position coordinate determiner 58 uses the detected position coordinates of the low-orbit object by the stationary object detector 55, the correspondence relationship between the celestial coordinate data of the stars and the detected position coordinates of the stars, and the correspondence relationship between image data coordinates stored in the database 60, between pixel position coordinates of the narrow-field image data in the narrow-field image sensor 13 and pixel position coordinates of the wide-field image data in the wide-field image sensor 23, to determine the celestial coordinates of the low-orbit object based on the correspondence relationship between the star coordinates and the correspondence relationship between the image data coordinates of the optical system.

[0080] The correspondence relationship between the image data coordinates of the optical systems is based on data obtained by measuring the position coordinates of pixels relative to narrow-field image data in the narrow-field image sensor 13 and the position coordinates of pixels relative to wide-field image data in the wide-field image sensor 23 when the optical axis of the wide-field imaging optical system 21 is adjusted by the optical axis adjustment device 30 and fixed to the narrow-field imaging optical system 11. The data on the correspondence relationship between the image data coordinates of the optical systems is stored in the database 60.

[0081] The correspondence relationship between the measured image data coordinates of the optical system corresponds to the correspondence relationship between the coordinates of the narrow field-of-view image data from the narrow field-of-view image sensor 13 and the wide field-of-view image data from the wide field-of-view image sensor 23. The correspondence relationship between the image data coordinates of the optical system is, for example, the correspondence relationship between the coordinates of the narrow field-of-view image data in the narrow field-of-view image sensor 13 and the wide field-of-view image data in the wide field-of-view image sensor 23 in a narrow field-of-view optical telescope with a field of view of 0.5 deg x 0.5 deg and a wide field-of-view optical telescope with a field of view of about 8 deg x 8 deg, with the target low orbital object as the center of the field of view.

[0082] The identification of the celestial coordinates of the low-orbit object by the low-orbit object position coordinate determiner 58, that is, the specific determination of the celestial coordinates of the low-orbit object, is performed, for example, as follows: The correspondence between the coordinates of the narrow-field image data and the celestial coordinate data is determined based on the correspondence between the image data coordinates of the optical system, that is, the correspondence between the coordinates of the narrow-field image data and the wide-field image data, and the correspondence between the coordinates of the wide-field image data and the celestial coordinate data of the fixed stars.

[0083] Next, the celestial coordinates of the low orbit object are determined by comparing the position coordinates of the low orbit object detected by the stationary object detection unit 55 with the celestial coordinate data using the correspondence between the coordinates of the narrow-field image data and the celestial coordinate data.

[0084] The data acquisition control function in the position coordinate calculation device 50 is a control function that controls the wide-field light selection means 22 and narrow-field image sensor 13 in the narrow-field optical telescope 10 and the wide-field light selection means 22 and wide-field image sensor 23 in the wide-field optical telescope 20, and obtains narrow-field image data from the narrow-field image sensor 13 that is easy to obtain point images of low-orbit objects, and wide-field image data from the wide-field image sensor 23 that is easy to obtain line images of stars.

[0085] The data acquisition control function in the position coordinate calculation device 50 is achieved by the control unit 52. The control unit 52 provides narrow-field filter selection information to the narrow-field light selection means 12, causing the narrow-field light selection means 12 to select an appropriate filter at the timing of starting exposure to light from the narrow-field imaging optical system 11. The control unit 52 provides narrow-field light control information to the narrow-field image sensor 13, causing the narrow-field image sensor 13 to output narrow-field image data that enables low-orbit objects to be detected as bright point images at the timing, frame rate, and exposure time of starting exposure to light from the narrow-field imaging optical system 11.

[0086] The control unit 52 provides wide-field filter selection information to the wide-field light selection means 22, causing the wide-field light selection means 22 to select an appropriate filter at the timing of starting exposure to light from the wide-field imaging optical system 21. The control unit 52 provides wide-field light control information to the wide-field image sensor 23, causing the wide-field image sensor 23 to output wide-field image data capable of detecting the positions of fixed stars in a wide field of view at the timing, frame rate, and exposure time of starting exposure to light from the wide-field imaging optical system 21. The control unit 52 controls the narrow-field image sensor 13, the wide-field light selection means 22, and the wide-field image sensor 23 in synchronization with each other.

[0087] The tracking control function in the position coordinate calculation device 50 estimates the predicted trajectory of the low-orbit object based on information about the target low-orbit object, calculates a two-axis drive amount based on the estimated predicted trajectory and the current pointing direction of the narrow-field imaging optical system 11 from the drive device 40, provides the calculated two-axis drive amount to the drive device 40, and controls the drive device 40 using the two-axis drive amount to align the pointing direction of the narrow-field imaging optical system 11 with the predicted trajectory of the low-orbit object.

[0088] The tracking control function in the position coordinate calculation device 50 is achieved by a control unit 52 and a tracking trajectory determination unit 51. The tracking trajectory determination unit 51 estimates predicted trajectory coordinates of the low orbit object in time series based on information about the target low orbit object.

[0089] The information on the target low-orbit object is, in observation mode, coordinate position information of the observation position in the coordinate system of the narrow-field image data of the low-orbit object observed from the narrow-field image data by the narrow-field optical telescope 10. The time-series predicted trajectory coordinates of the low-orbit object are information converted into celestial coordinates centered on the coordinate position information of the observation position in the coordinate system.

[0090] The observation location refers to the latitude, longitude, and altitude of the location where the observer makes the observation, while the predicted orbit coordinates in the information about the target LEO are the coordinates converted into celestial coordinates where the LEO's passage is observed, based on the latitude, longitude, and altitude of the location where the LEO is expected to actually pass.

[0091] When information about a target low-orbit object is expressed as two-line elements (TLEs) including information about Keplerian orbital elements in a geocentric coordinate system, the tracking orbit determination unit 51 calculates the predicted orbit of the observed low-orbit object based on the two-line orbital elements. The tracking orbit determination unit 51 converts the obtained predicted orbit coordinates into celestial coordinates centered on the coordinate position information of the observation position of the observed low-orbit object, and estimates the predicted orbit coordinates of the observed low-orbit object over time.

[0092] The predicted trajectory coordinates in time series are, for example, １ From time t Ｎ The coordinates are estimated N times in a time series up to time t. N is a natural number equal to or greater than 2. １ is the time t when a point image of a low-orbit object is observed from the narrow-field image data of the narrow-field optical telescope 10 in the observation mode. ０ is the time one frame forward from time t Ｎ is the time immediately before the predicted orbit coordinates determined by the tracking orbit determination unit 51 exceed the range in which the narrow-field optical telescope 10 can observe low-orbit objects.

[0093] Time t ｎ The intervals (n = 1 to N) are intervals that conform to the frame rate. The calculation algorithm used by the tracking orbit determination unit 51 is SGP4 (Simplified General Perturbations Satellite Orbit Model 4). Note that although the coordinates estimated in time series in the predicted orbit coordinates are intervals that conform to the frame rate, they may also be an integer fraction of the intervals that conform to the frame rate.

[0094] The control unit 52 calculates the biaxial drive amount for each time when the predicted trajectory coordinates are estimated based on the predicted trajectory coordinates from the tracking trajectory determination unit 51 and the pointing direction of the narrow-field imaging optical system 11 from the drive unit 40, and provides the drive control signal indicating the calculated biaxial drive amount to the drive unit 40. ｎ The biaxial drive amount at each time t ｎThis is a two-axis drive amount calculated based on the separation information obtained by the difference between the position coordinates of the low-orbit object predicted in the predicted trajectory coordinates from the tracking trajectory determination unit 51 and the position coordinates in the pointing direction of the narrow-field imaging optical system 11 from the drive device 40.

[0095] The control unit 52 provides the drive control signal indicating the biaxial drive amount to the drive device 40, thereby controlling the direction of the narrow-field imaging optical system 11 so that the drive device 40 tracks the target low-orbit object. ｎ In the case where the drive of the drive device 40 controlled by the drive control signal causes the point image of the low orbit object to deviate from the narrow field image data from the narrow field image sensor 13, an offset is provided to the position coordinates of the low orbit object predicted in the predicted trajectory coordinates from the tracking trajectory determination unit 51, the separation information is changed by the offset amount, and the two-axis drive amount is changed so that the low orbit object comes within the light receiving surface of the narrow field image sensor 13.

[0096] The drive unit 40 drives the two-axis drive amount, which is a drive control signal from the control unit 52, as the drive angle amount of the two drive axes. １ From time t Ｎ By continuously manipulating the drive angle amounts of the two drive axes up to this point, the narrow-field imaging optical system 11 tracks the target low-orbit object. Finally, when the predicted trajectory coordinates from the tracking trajectory determination unit 51 exceed the observable range of the narrow-field imaging optical system 11, the tracking of the target low-orbit object by the narrow-field imaging optical system 11 driven by the drive device 40 ends.

[0097] Next, the operation of the coordinate determination device for a low-orbit object according to the first embodiment will be described with reference to Figures 2 to 4. As shown in Figure 2, as a preliminary preparation, in step ST01, the optical axis of the narrow-field imaging optical system 11 and the optical axis of the wide-field imaging optical system 21 are adjusted by the optical axis adjustment device 30, and the optical axis of the narrow-field imaging optical system 11 and the optical axis of the wide-field imaging optical system 21 are made parallel by the optical axis adjustment device 30, and the wide-field optical telescope 20 is fixed to the narrow-field optical telescope 10. After adjusting the optical axis of the wide-field optical telescope 20 and fixing the wide-field optical telescope 20 to the narrow-field optical telescope 10, the fields of view of the narrow-field optical telescope 10 and the wide-field optical telescope 20 are measured, and the correspondence between the fields of view of the optical systems obtained by this is stored in database 60.

[0098] In step ST02, when the narrow-field optical telescope 10 detects a low-orbit object in observation mode, the tracking orbit determination unit 51 estimates the time-series predicted orbit coordinates of the target low-orbit object. After steps ST01 and ST02 are completed, the position coordinate calculation device 50 performs the tracking control function, data acquisition control function, and position coordinate calculation function.

[0099] The tracking control function starts a loop at time t １ In step ST11, the control unit 52 starts calculating the biaxial drive amount for the drive device 40 at time t １ The tracking orbit determination unit 51 calculates the difference between the time series predicted orbit coordinates of the target low orbit object estimated by the tracking orbit determination unit 51 at time t and the coordinates of the current pointing direction from the drive unit 40. １ The biaxial drive amount for the drive device 40 is calculated.

[0100] In step ST12, the drive device 40 is driven in response to an input value indicating the biaxial drive amount, which is a drive control signal from the control unit 52, and the mounted narrow-field optical telescope 10 automatically tracks the target low-orbit object by changing the pointing direction of the narrow-field imaging optical system 11 along two axes. １ When the driving of the driving device 40 at time t １Since the time when the predicted orbit coordinates from the tracking orbit determination unit 51 have not exceeded the observable range of the narrow-field imaging optical system 11 is not yet reached, the process returns to the loop start, and the drive control of the drive unit 40 in steps ST11 and ST12 is continued until time t ｎ is the time t immediately before the predicted orbit coordinates from the tracking orbit determination unit 51 exceed the observable range of the narrow-field imaging optical system 11. Ｎ This is repeated until

[0101] Time t Ｎ When the drive control of the drive device 40 in steps ST11 and ST12 is completed, the tracking control function in the position coordinate calculation device 50 is terminated at the loop end. When the tracking control function is started at the loop start, the data acquisition control function in the position coordinate calculation device 50 is started.

[0102] As shown in FIG. 3, the time t ０ Then, the narrow-field optical telescope 10 and the wide-field optical telescope 20 start photographing in tracking mode. When the tracking control function starts and photographing is started by the data acquisition control function, in step ST21, the control unit 52 sets narrow-field filter selection information for the narrow-field light selection means 12, narrow-field light control information for the narrow-field image sensor 13, wide-field filter selection information for the wide-field light selection means 22, and wide-field light control information for the wide-field image sensor 23.

[0103] The control unit 52 determines the time t immediately before imaging when a point image of a low-orbit object is observed from the narrow-field-of-view image data by the narrow-field-of-view optical telescope 10 in the observation mode. ０ In the narrow-field imaging optical system 11, information indicating the selection of a filter in the narrow-field filter selection information is provided to the narrow-field light selection means 12. The narrow-field light selection means 12 selects an optical filter based on the information indicating the selection of a filter, and positions the selected optical filter on the optical axis of the narrow-field imaging optical system 11.

[0104] Similarly, the control unit 52 ０In the step S100, information indicating the selection of a filter in the wide-field filter selection information is given to the wide-field light selection means 22. The wide-field light selection means 22 selects an optical filter based on the information indicating the selection of a filter, and positions the selected optical filter on the optical axis of the wide-field imaging optical system 21.

[0105] The control unit 52 ０ At time t ０ In the image sensor 23, information indicating sensor parameters in the wide-field light control information is provided to the wide-field image sensor 23. The wide-field image sensor 23 sets gain, pixels to be read out, and the like based on the information indicating the sensor parameters.

[0106] When the setting is completed, in step ST22, the narrow-field image sensor 13 captures an image using the exposure time set in accordance with the narrow-field light control information from the control unit 52. The process returns to step ST21 in accordance with the frame rate indicated by the narrow-field light control information, and steps ST21 and ST22 are repeated until the time t immediately before the predicted trajectory coordinates from the tracking trajectory determination unit 51 exceed the observable range of the narrow-field imaging optical system 11. Ｎ The narrow-field image sensor 13 outputs N narrow-field image data.

[0107] In step ST22, the wide-field image sensor 23 captures an image using the exposure time set in accordance with the wide-field light control information from the control unit 52. The process returns to step ST21 in accordance with the frame rate indicated by the wide-field light control information, and steps ST21 and ST22 are repeated until time t Ｎ The wide-field image sensor 23 outputs N wide-field image data.

[0108] During the period when a target low-orbit object is being tracked, narrow-field image data is output from the narrow-field image sensor 13 and wide-field image data is output from the wide-field image sensor 23, and when the tracking period ends, the narrow-field optical telescope 10 and the wide-field optical telescope 20 finish taking images in the tracking mode.

[0109] 4, when the narrow-field image data from the narrow-field image sensor 13 and the wide-field image data from the wide-field image sensor 23 are output, the position coordinate calculation function of the position coordinate calculation device 50 starts. In step ST31, when the narrow-field image data from the narrow-field image sensor 13 and the wide-field image data from the wide-field image sensor 23 are input to the position coordinate calculation device 50, they are stored in the image recording unit 53 as narrow-field image data in which the narrow-field light control information is linked to the narrow-field image data, and as wide-field image data in which the wide-field light control information is linked to the wide-field image data.

[0110] The narrow-field image data and the wide-field image data, each consisting of N consecutively captured images, are input to the position coordinate calculation device 50 at time t ｎ may be input to the position coordinate calculation device 50 at each time t ０ From time t Ｎ The N image data up to may be input all at once to the position coordinate calculation device 50. In short, it is sufficient that all of the narrow-field image data and wide-field image data captured during the period in which the target low-orbit object is being tracked are stored in the image recording unit 53.

[0111] In step ST32, preprocessing unit 54 acquires the narrow-field image data stored in image recording unit 53 and performs preprocessing on the narrow-field image data, such as subtracting dark current from the dark current image data and correcting sensitivity variations in the narrow-field image data based on the flat image data. Similarly, preprocessing unit 54 performs preprocessing on the wide-field image data stored in image recording unit 53, such as subtracting dark current from the dark current image data and correcting sensitivity variations in the narrow-field image data based on the flat image data.

[0112] Step ST32 is a preprocessing step in which the preprocessing unit 54 subtracts dark current from the narrow-field image data and the wide-field image data and corrects for uneven sensitivity. After the preprocessing step ST32 is completed, the preprocessed narrow-field image data is processed in step ST33, and the preprocessed wide-field image data is processed in step ST34.

[0113] In step ST33, stationary object detection unit 55 detects a point image from the narrow-field-of-view image data that has been preprocessed by preprocessing unit 54, and stationary object detection unit 55 sets the center coordinates of the detected point image in the narrow-field-of-view image data as the detected position coordinates of the low-orbit object. In step ST34, moving object detection unit 56 detects a line image from the wide-field-of-view image data that has been preprocessed by preprocessing unit 54, and moving object detection unit 56 sets the center coordinates of the detected line image in the wide-field-of-view image data as the detected position coordinates of the star.

[0114] In step ST35, the star coordinate comparison unit 57 compares the detected position coordinates of the star obtained by the moving object detection unit 56 with the celestial coordinate data of known stars stored in the database 60, and obtains a correspondence relationship between the celestial coordinate data of the star and the coordinates of the detected position coordinates of the star.

[0115] In step ST36, the celestial coordinates of the target low-orbit object are obtained from the detected position coordinates of the target low-orbit object based on the correspondence between the detected position coordinates of the low-orbit object obtained by the stationary object detection unit 55, the coordinates of the stars obtained by the star coordinate comparison unit 57, and the correspondence between the image data coordinates of the optical systems in the narrow-field imaging optical system 11 and the wide-field imaging optical system 21 stored in database 60.

[0116] That is, step ST36 determines the correspondence between the coordinates of the narrow-field image data and the celestial coordinate data based on the correspondence between the image data coordinates of the optical system and the correspondence between the coordinates of the fixed stars. Next, step ST36 determines the celestial coordinates for the detected position coordinates of the low-orbit object using the correspondence between the coordinates of the narrow-field image data and the celestial coordinate data. Step ST36 is a step in which position coordinate determiner 58 identifies the celestial coordinates of the low-orbit object from the detected position coordinates of the low-orbit object based on the correspondence between the coordinates of the fixed stars.

[0117] Having obtained the celestial coordinates of the low-orbit object, the position coordinate calculation function of the position coordinate calculation device 50 is completed. The celestial coordinates of the low-orbit object obtained by the position coordinate determination unit 58 are output to a display means (not shown).

[0118] The position coordinate calculation device 50 is realized by a computer hardware configuration, and as shown in FIG. 5, includes a CPU (Central Processing Unit) 50A, a large-capacity semiconductor memory (RAM: Random Access Memory) 50B, a storage device (ROM: Read only memory) 50C such as a hard disk device or a non-volatile storage device such as an SSD device, an input interface unit 50D, an output interface unit 50E, and a signal path (bus) 50F.

[0119] The CPU 50A controls and manages the RAM 50B, the ROM 50C, the input interface unit 50D, and the output interface unit 50E. The CPU 50A loads programs stored in the ROM 50C into the RAM 50B, and the CPU 1A executes various processes based on the programs loaded into the RAM 50B.

[0120] The tracking orbit determination unit 51, the control unit 52, the preprocessing unit 54, the stationary object detection unit 55, the moving object detection unit 56, the star coordinate comparison unit 57, and the position coordinate determination unit 58 are each configured by a CPU 50A, a RAM 50B, and a ROM 50C. The image recording unit 53 is configured by the RAM 50B. The database 60 may also be configured by the RAM 50B and the ROM 50C.

[0121] The coordinate determination program stored in ROM 50C and executed by CPU 50A to determine the position coordinates of a target low-orbit object includes the following steps: detecting a point image from narrow-field image data from narrow-field optical telescope 10, which has narrow-field imaging optical system 11 with a narrow field of view and high resolution, and setting the point image as the detected position coordinate of the low-orbit object; detecting a line image from wide-field image data from wide-field optical telescope 20, which has wide-field imaging optical system 21 with a wider field of view than narrow-field imaging optical system 11, lower resolution, and pointed in the same direction as narrow-field imaging optical system 11, and setting the line image as the detected position coordinate of a star; obtaining a correspondence between the celestial coordinate data of the star and the detected position coordinate of the star; and identifying the celestial coordinate of the low-orbit object from the detected position coordinate of the low-orbit object based on the correspondence between the celestial coordinates of the star.

[0122] The coordinate determination device for a low-orbit object according to the first embodiment includes a narrow-field optical telescope 10 having a narrow-field imaging optical system 11 with a narrow field of view and high resolution, and a wide-field optical telescope 20 having a wide-field imaging optical system 21 with a wider field of view than the narrow-field imaging optical system 11, lower resolution, and pointed in the same direction as the narrow-field imaging optical system 11. The device also includes a low-orbit object position coordinate calculation device 50 that acquires detected position coordinates of low-orbit objects from narrow-field image data from a narrow-field image sensor 13 in the narrow-field optical telescope 10, acquires detected position coordinates of fixed stars from wide-field image data from a wide-field image sensor 23 in the wide-field optical telescope 20, and identifies the celestial coordinates of the low-orbit object using the detected position coordinates of the fixed stars. This makes it possible to easily determine the position coordinates of a target low-orbit object, and to easily obtain the celestial coordinates of the low-orbit object with high accuracy.

[0123] Embodiment 2. A coordinate determination device for a low-orbit object according to embodiment 2 will be described with reference to Figures 6 and 7. The coordinate determination device for a low-orbit object according to embodiment 1 identifies the celestial coordinates of the target low-orbit object using one narrow-field-of-view image data output from the narrow-field-of-view optical telescope 10. In contrast, the coordinate determination device for a low-orbit object according to embodiment 2 is the same as the first embodiment except that it identifies the celestial coordinates of the target low-orbit object using two narrow-field-of-view image data output from the narrow-field-of-view optical telescope 10. Therefore, the following description will focus on the differences from the coordinate determination device for a low-orbit object according to embodiment 1. In Figure 6, the same reference numerals as those in Figure 1 indicate the same or equivalent parts.

[0124] The coordinate determination device for a low-orbit object according to the second embodiment comprises a narrow-field optical telescope 10, a wide-field optical telescope 20, an optical axis adjustment device 30, a drive device 40, a position coordinate calculation device 50, and a database 60. The narrow-field optical telescope 10 has a narrow-field imaging optical system 11, a narrow-field light selection means 12, a first narrow-field image sensor 13, and a second narrow-field image sensor 14. The narrow-field light selection means 12 selects light from the low-orbit object from the light collected by the narrow-field light selection means 12 using an optical filter, and splits the light selected by the optical filter into two beams having different wavelength information or polarization information.

[0125] One of the two beams of light branched from the narrow-view light selection means 12 is guided along a first optical path to the light-receiving surface of the first narrow-view image sensor 13. The other of the two beams of light branched from the narrow-view light selection means 12 is guided along a second optical path different from the first optical path to the light-receiving surface of the second narrow-view image sensor 14.

[0126] A dichroic mirror is used as the narrow-view light selection means 12 when splitting into two light beams having different wavelength information. A dichroic mirror has the function of transmitting light in a specific wavelength band and reflecting light in other wavelength bands, so it can split into transmitted light and reflected light having different wavelength information.

[0127] The narrow-view light selection means 12 uses a polarizing beam splitter when splitting into two beams having different polarization information. A polarizing beam splitter transmits P-polarized light and reflects S-polarized light, that is, it has the function of separating light into P-polarized light and S-polarized light, so it can split light into P-polarized light and S-polarized light having different polarization information. The selection of optical filters in the narrow-view light selection means 12 is the same as that in the narrow-view light selection means 12 in embodiment 1.

[0128] The first narrow-field image sensor 13 has a light-receiving surface located on a focal plane where one of the two beams of light is focused. The first narrow-field image sensor 13 converts the amount or intensity of incident light into a digital value for each of the many pixels spread two-dimensionally on the light-receiving surface, and outputs the digital value as first narrow-field image data, which is two-dimensional image data.

[0129] The second narrow-field image sensor 14 has a light-receiving surface located on a focal plane where the other of the two beams of light is focused. The second narrow-field image sensor 14 converts the amount or intensity of incident light into a digital value for each of the many pixels spread two-dimensionally on the light-receiving surface, and outputs the digital value as second narrow-field image data, which is two-dimensional image data.

[0130] The first narrow-field image sensor 13 and the second narrow-field image sensor 14 correspond to the narrow-field image sensor 13 in embodiment 1, and just as the narrow-field image sensor 13 in embodiment 1 is controlled by the control unit 52, the first narrow-field image sensor 13 and the second narrow-field image sensor 14 are each controlled by the control unit 52, and output the branched light selected by the narrow-field light selection means 12 as first narrow-field image data and second narrow-field image data, respectively, in tracking mode.

[0131] The first narrow-field image sensor 13 and the second narrow-field image sensor 14 are controlled by the same narrow-field light control information from the control unit 52. Therefore, the first narrow-field image data and the second narrow-field image data are synchronized and acquired simultaneously at the same timing. The first narrow-field image sensor 13 and the second narrow-field image sensor 14 each use a sensor similar to the narrow-field image sensor 13 in the first embodiment.

[0132] The wide-field optical telescope 20, the optical axis adjusting device 30, and the driving device 40 are the same as the wide-field optical telescope 20, the optical axis adjusting device 30, and the driving device 40 in the first embodiment, respectively, and therefore description thereof will be omitted.

[0133] The position coordinate calculation device 50 for a low-orbit object has a position coordinate calculation function for obtaining the celestial coordinates of the low-orbit object, a data acquisition control function for controlling the acquisition of image data from the narrow-field optical telescope 10 and the wide-field optical telescope 20, and a tracking control function for controlling the drive of the drive device 40 to track the low-orbit object. The position coordinate calculation device 50 includes a tracking orbit determination unit 51, a control unit 52, an image recording unit 53, a preprocessing unit 54, a division processing unit 541, a stationary object detection unit 551, a moving object detection unit 561, a star coordinate comparison unit 57, and a position coordinate determination unit 58 for the low-orbit object.

[0134] The data acquisition control function and tracking control function in the position coordinate calculation device 50 are the same as the data acquisition control function and tracking control function in the position coordinate calculation device 50 in embodiment 1, and therefore will not be described here. The position coordinate calculation function in the position coordinate calculation device 50 is achieved by the image recording unit 53, the preprocessing unit 54, the division processing unit 541, the stationary object detection unit 551, the moving object detection unit 561, the star coordinate comparison unit 57, and the low orbit object position coordinate determination unit 58.

[0135] The image recording unit 53 receives the first narrow-field image data from the first narrow-field image sensor 13, the second narrow-field image data from the second narrow-field image sensor 14, and the wide-field image data from the wide-field image sensor 23, and stores first narrow-field image data and second narrow-field image data in which the first narrow-field image data and the second narrow-field image data are linked to the first narrow-field light control information and the second narrow-field light control information by the control unit 52, respectively, and wide-field image data in which the wide-field image data is linked to the wide-field light control information by the control unit 52.

[0136] The preprocessing unit 54 acquires the first narrow-field image data and the second narrow-field image data stored in the image recording unit 53, and performs preprocessing on the first narrow-field image data and the second narrow-field image data, respectively, by subtracting dark current and correcting sensitivity variations in the narrow-field image data. The preprocessing on the first narrow-field image data and the second narrow-field image data is the same as the preprocessing on the narrow-field image data in the first embodiment.

[0137] In addition, the pre-processing unit 54 may acquire the wide-field image data stored in the image recording unit 53 and perform pre-processing on the wide-field image data, such as subtracting dark current and correcting sensitivity variations in the narrow-field image data, in a manner similar to the pre-processing performed on the first narrow-field image data and the second narrow-field image data.

[0138] The division processing unit 541 acquires the first narrow-field image data and the second narrow-field image data that have been preprocessed by the preprocessing unit 54, divides the first narrow-field image data by the second narrow-field image data, and obtains the image data resulting from the division as narrow-field image data for point image detection. The first narrow-field image data and the second narrow-field image data are narrow-field image data acquired at the same time by the first narrow-field image sensor 13 and the second narrow-field image sensor 14.

[0139] If the target low-orbit object has wavelength or polarization characteristics different from those of the surrounding sky, spatial sky fluctuations are removed from the narrow-field image data for point image detection obtained by division processing unit 541 from the first narrow-field image data from first narrow-field image sensor 13 and the second narrow-field image data from second narrow-field image sensor 14, which are obtained by light branched with wavelength or polarization characteristics by narrow-field light selection means 12. As a result, the narrow-field image data for point image detection has a high signal-to-noise ratio.

[0140] In particular, when observing laser light emitted from the ground and reflected by a low-orbit object, the narrow-field light selection means 12 is configured to transmit only the laser wavelength and reflect only wavelengths surrounding it. Narrow-field image data for point image detection is obtained by a division processing unit 541 from first narrow-field image data from a first narrow-field image sensor 13 using light of the transmitted laser wavelength and second narrow-field image data from a second narrow-field image sensor 14 using light of wavelengths surrounding the laser wavelength that are reflected.

[0141] The narrow-field-of-view image data for point image detection obtained by the division processing unit 541 has a value different from that of the surrounding sky area in the region of the low-orbit object where laser reflection occurs, and the bandwidth is significantly narrowed, so that it is not affected by most of the reflected solar radiation. As a result, it is possible to detect the target low-orbit object from the narrow-field-of-view image data for point image detection with a high signal-to-noise ratio.

[0142] Stationary object detection unit 551 detects point images from the narrow-field-of-view image data for point image detection obtained by division processing unit 541, and sets the center coordinates of the detected point images as the detected position coordinates of the low-orbit object. Detection of point images from narrow-field-of-view image data for point image detection by stationary object detection unit 551 is performed in the same manner as detection of point images from narrow-field-of-view image data by stationary object detection unit 55 in Embodiment 1.

[0143] In the first embodiment, an example was described in which the exposure time for exposure according to the frame rate is about 0.01 seconds and the moving speed of the target low-orbit object is about 30 arc minutes / second. However, if the narrow-field optical telescope 10 takes an image using an exposure time shorter than 0.01 seconds, or if the moving speed of the target low-orbit object is significantly slower than 30 arc minutes / second, when detecting a point image from the narrow-field image data for point image detection, under the conditions described in the first embodiment, it may be impossible to distinguish whether the point image is a point image caused by a low-orbit object or a line image caused by a star.

[0144] In this case, the following condition is further added to detect point images from narrow-field-of-view image data for point image detection. That is, point images with the same position coordinates among N pieces of narrow-field-of-view image data for point image detection obtained from N pieces of first narrow-field-of-view image data and N pieces of second narrow-field-of-view image data continuously captured during the tracking period are detected as point images caused by a low-orbit object. On the other hand, point images whose position coordinates move among N pieces of narrow-field-of-view image data for point image detection are regarded as line images in the N pieces of narrow-field-of-view image data for point image detection, and are not considered to be point images caused by a low-orbit object.

[0145] In other words, whether or not a point image is caused by a low-orbit object is identified based on whether the point image is a stationary point image whose position coordinates remain unchanged or a moving point image whose position coordinates change among the N pieces of narrow-field-of-view image data for point image detection. Therefore, the stationary object detection unit 551 does not detect point images (line images) caused by fixed stars from the N pieces of narrow-field-of-view image data for point image detection.

[0146] The moving object detection unit 561 detects a line image from the wide-field image data from the wide-field image sensor 23, and sets the center coordinates of the detected line image as the detected position coordinates of the star. The detection of a line image from the wide-field image data by the moving object detection unit 561 is performed in the same manner as the detection of a line image from the wide-field image data by the moving object detection unit 56 in the first embodiment.

[0147] However, when the wide-field optical telescope 20 takes an image with an exposure time shorter than 0.01 seconds, or when the target low-orbit object moves at a speed significantly slower than 30 arc minutes per second, it may not be possible to distinguish the line images of stars from the wide-field image data under the conditions described in embodiment 1.

[0148] In this case, the following condition is further added to detect line images from the wide-field image data: That is, among N wide-field image data pieces captured continuously during the tracking period, point images whose position coordinates move are regarded as line images in the N wide-field image data pieces and are detected as line images caused by fixed stars. On the other hand, among N wide-field image data pieces, point images whose position coordinates are the same are regarded as point images in the N wide-field image data pieces and are not considered as line images caused by fixed stars.

[0149] In other words, whether or not a line image is caused by a star is determined based on whether the point image is moving with its position coordinates changing or whether the point image is stationary with its position coordinates remaining unchanged among the N pieces of wide-field-of-view image data. Therefore, the moving object detection unit 561 will not detect point images caused by low-orbit objects from the N pieces of wide-field-of-view image data.

[0150] The star coordinate comparison unit 57 functions and operates in the same way as the star coordinate comparison unit 57 in embodiment 1, and compares the detected position coordinates of stars obtained by the moving object detection unit 561 with the celestial coordinate data of known stars stored in the database 60, and obtains the correspondence between the celestial coordinate data of the stars and the coordinates of the detected position coordinates of the stars.

[0151] That is, the correspondence between the coordinates represented on a two-dimensional plane of the wide-field image data in the wide-field image sensor 23 and the celestial coordinate data of the fixed stars is obtained in advance, for example, as a correspondence table. The star coordinate comparison unit 57 compares the detected position coordinates of the fixed stars obtained by the moving object detection unit 56 with the celestial coordinate data of the fixed stars using the correspondence table, thereby determining the direction on the celestial sphere to which the position coordinates of the pixels in which the fixed stars are reflected correspond. As a result, it is determined which direction on the celestial sphere each pixel of the wide-field image data corresponds.

[0152] Low-orbit object position coordinate determiner 58 functions and operates in the same way as position coordinate determiner 58 in embodiment 1, and identifies the celestial coordinates of the low-orbit object based on the position coordinates detected by stationary object detector 551 and the comparison results of star coordinate comparator 57, that is, the correspondence between the celestial coordinate data of the stars and the coordinates of the stars of the detected position coordinates of the stars.

[0153] That is, the correspondence between the coordinates of the narrow-field image data and the celestial coordinate data is determined based on the correspondence between the image data coordinates of the optical system, i.e., the correspondence between the coordinates of the narrow-field image data and the wide-field image data, and the correspondence between the coordinates of the wide-field image data and the celestial coordinate data of the fixed stars. Next, the celestial coordinates of the low-orbit object are determined by comparing the position coordinates of the low-orbit object detected by the stationary object detection unit 55 with the celestial coordinate data using the correspondence between the coordinates of the narrow-field image data and the celestial coordinate data.

[0154] Next, the operation of the low-orbit object coordinate determination device according to the second embodiment will be described with reference to Figure 6. Steps ST01 and ST02 as advance preparations, steps ST11 and ST12 as tracking control functions, and steps ST21 and ST22 as data acquisition control functions are the same as steps ST01 and ST02, ST11 and ST12, and ST21 and ST22 in the first embodiment, and therefore will not be described again. Note that the narrow-field image sensor 13 in steps ST21 and ST22 should be read as the first narrow-field image sensor 13 and the second narrow-field image sensor 14.

[0155] 7 illustrates the operation of the position coordinate calculation function in the position coordinate calculation device 50. In step ST31A, the first narrow-field image data from the first narrow-field image sensor 13, the second narrow-field image data from the second narrow-field image sensor 14, and the wide-field image data from the wide-field image sensor 23 are input to the position coordinate calculation device 50. The first narrow-field image data and the second narrow-field image data are linked to the narrow-field light control information as first narrow-field image data and second narrow-field image data, and the wide-field image data is linked to the wide-field image data as wide-field light control information as wide-field image data. Step ST31A corresponds to step ST31 in the first embodiment.

[0156] In step ST32A, preprocessing unit 54 acquires the first narrow-field image data and the second narrow-field image data stored in image recording unit 53, and performs preprocessing on each of the first narrow-field image data and the second narrow-field image data, including subtracting dark current based on the dark current image data and correcting sensitivity variations in the narrow-field image data based on the flat image data. Similarly, preprocessing unit 54 performs preprocessing on the wide-field image data stored in image recording unit 53, including subtracting dark current based on the dark current image data and correcting sensitivity variations in the narrow-field image data based on the flat image data. Step ST32A corresponds to step ST32 in embodiment 1.

[0157] In step ST32B, the division processing unit 541 simultaneously acquires the first narrow-field image data and the second narrow-field image data that have been preprocessed by the preprocessing unit 54, that is, acquires the first narrow-field image data and the second narrow-field image data in a synchronized state, performs division between the first narrow-field image data and the second narrow-field image data, and obtains the image data resulting from the division as narrow-field image data for point image detection.

[0158] In step ST33A, stationary object detection unit 551 detects a point image (still point image) from the narrow-field-of-view image data for point image detection obtained by division processing unit 541, and stationary object detection unit 551 sets the center coordinates of the detected point image in the narrow-field-of-view image data for point image detection as the detected position coordinates of the low-orbit object. Step ST33A corresponds to step ST33 in embodiment 1.

[0159] In step ST34A, the moving object detection unit 561 detects a line image (moving point image) from the wide-field image data that has been preprocessed by the preprocessing unit 54, and the moving object detection unit 561 sets the central coordinates of the detected line image in the wide-field image data as the detected position coordinates of the star. Step ST34A corresponds to step ST34 in embodiment 1.

[0160] In step ST35A, the star coordinate comparison unit 57 compares the detected position coordinates of the star obtained by the moving object detection unit 561 with the celestial coordinate data of known stars stored in the database 60, and obtains a correspondence relationship between the celestial coordinate data of the star and the coordinates of the detected position coordinates of the star. Step ST35A corresponds to step ST35 in the first embodiment.

[0161] In step ST36A, the celestial coordinates of the target low-orbit object are obtained from the detected position coordinates of the target low-orbit object based on the correspondence between the detected position coordinates of the low-orbit object obtained by the stationary object detection unit 551, the coordinates of the stars obtained by the star coordinate comparison unit 57, and the correspondence between the image data coordinates of the optical systems in the narrow-field imaging optical system 11 and the wide-field imaging optical system 21 stored in database 60. Step ST36A corresponds to step ST36 in embodiment 1.

[0162] The position coordinate calculation device 50 is realized by the hardware configuration of a computer shown in Fig. 5, similar to the position coordinate calculation device 50 in embodiment 1. The tracking trajectory determination unit 51, control unit 52, preprocessing unit 54, division processing unit 541, stationary object detection unit 551, moving object detection unit 561, star coordinate comparison unit 57, and position coordinate determination unit 58 are each configured by a CPU 50A, RAM 50B, and ROM 50C. The image recording unit 53 is configured by RAM 50B.

[0163] The coordinate determination program stored in the ROM 50C and executed by the CPU 50A to determine the position coordinates of a target low-orbit object includes a procedure for dividing first narrow-field image data from a narrow-field optical telescope 10 having a narrow-field imaging optical system 11 with a narrow viewing angle and high resolution by second narrow-field image data having a wavelength or polarization different from that of the first narrow-field image data, and obtaining the narrow-field image data resulting from the division as narrow-field image data for point image detection; and a procedure for detecting a point image from the narrow-field image data for point image detection and calculating the coordinates of the detected point image as the low-orbit object. The system includes a procedure for determining the detected position coordinates of the object, a procedure for detecting a line image from wide-field image data from a wide-field optical telescope (20) having a wide-field imaging optical system (21) that has a wider field of view than the narrow-field imaging optical system (11), lower resolution, and is pointed in the same direction as the narrow-field imaging optical system (11), and determining the detected position coordinates of the star, a procedure for obtaining a correspondence between the celestial coordinate data of the star and the coordinates on the star of the detected position coordinates of the star, and a procedure for identifying the celestial coordinates of the low orbit object from the detected position coordinates of the low orbit object based on the correspondence between the coordinates on the star.

[0164] The coordinate determination device for a low-orbit object according to the second embodiment comprises a narrow-field optical telescope 10 having a narrow-field imaging optical system 11 with a narrow field of view and high resolution, and a wide-field optical telescope 20 having a wide-field imaging optical system 21 with a wider field of view than the narrow-field imaging optical system 11, lower resolution, and oriented in the same direction as the narrow-field imaging optical system 11, and determines the coordinates of the low-orbit object according to the result of dividing first narrow-field image data from a first narrow-field image sensor 13 in the narrow-field optical telescope 10 by second narrow-field image data from a second narrow-field image sensor 14, the second narrow-field image data having a wavelength or polarization different from that of the first narrow-field image data. The system is equipped with a position coordinate calculation device (50) for a low-orbit object that acquires the detected position coordinates of a low-orbit object detected from narrow-field-of-view image data for point image detection, acquires the detected position coordinates of a star detected from wide-field-of-view image data from wide-field-of-view image sensor (23) in wide-field-of-view optical telescope (20), and identifies the celestial coordinates of the low-orbit object using the acquired detected position coordinates of the star.Since the narrow-field-of-view image data for point image detection has a high signal-to-noise ratio, the position coordinates of the target low-orbit object can be easily determined, and the celestial coordinates of the low-orbit object can be easily obtained with high accuracy.

[0165] It should be noted that the embodiments may be freely combined, or any of the components in each embodiment may be modified, or any of the components in each embodiment may be omitted.

[0166] The coordinate determination device for a low-orbit object according to the present disclosure is suitable for a low-orbit object position measurement device that determines the orbit of a low-orbit object such as a satellite, space debris, or meteor in advance by observation from the ground.

[0167] 10 Narrow field optical telescope, 11 Narrow field imaging optical system, 12 Narrow field light selection means, 13 Narrow field image sensor, 20 Wide field optical telescope, 21 Wide field imaging optical system, 22 Wide field light selection means, 23 Wide field image sensor, 30 Optical axis adjustment device, 40 Drive device, 50 Position coordinate calculation device, 51 Tracking orbit determination unit, 52 Control unit, 53 Image recording unit, 54 Preprocessing unit, 541 Division processing unit, 55, 551 Stationary object detection unit, 56, 561 Moving object detection unit, 57 Star coordinate comparison unit, 58 Position coordinate determination unit.

Claims

1. A coordinate determination device for a low-orbit object comprising: a narrow-field optical telescope having a narrow-field imaging optical system with a narrow field of view and high resolution, a narrow-field light selection means for selecting light from low-orbit objects from light collected by the narrow-field imaging optical system, and a narrow-field image sensor that outputs the light selected by the narrow-field light selection means as narrow-field image data; a wide-field optical telescope having a wide-field imaging optical system with a wider field of view than the narrow-field imaging optical system and low resolution, and pointed in the same direction as the narrow-field imaging optical system, a wide-field light selection means for selecting light from fixed stars from light collected by the wide-field imaging optical system, and a wide-field image sensor that outputs the light selected by the wide-field light selection means as wide-field image data; and a low-orbit object position coordinate calculation device that identifies the celestial coordinates of the low-orbit object using the detected position coordinates of the low-orbit object detected from the narrow-field image data from the narrow-field image sensor and the detected position coordinates of the fixed stars detected from the wide-field image data from the wide-field image sensor.

2. The coordinate determination device for a low-orbit object as described in claim 1, further comprising an optical axis adjustment device that fixes the wide-field imaging optical system to the narrow-field imaging optical system so that the difference in pointing direction between the wide-field imaging optical system and the narrow-field imaging optical system can be adjusted on two axes.

3. A coordinate determination device for a low orbit object as described in claim 1 or claim 2, further comprising a drive device mounted with said narrow field imaging optical system and adapted to change the pointing direction of said narrow field imaging optical system along two axes.

4. The position coordinate calculation device is a coordinate determination device for a low orbit object described in any one of claims 1 to 3, which has a tracking trajectory determination unit that estimates the time-series predicted trajectory coordinates of the low orbit object based on information about the target low orbit object, and a control unit that provides a drive control signal that controls the drive of the drive device based on the predicted trajectory coordinates estimated by the tracking trajectory determination unit and the pointing direction of the narrow-field imaging optical system from the drive device.

5. A coordinate determination device for a low orbit object described in any one of claims 1 to 4, wherein the position coordinate calculation device provides the narrow-field light selection means with narrow-field filter selection information including the timing of exposure start for light from the narrow-field imaging optical system and filter selection information, provides the narrow-field image sensor with narrow-field light control information including the timing of exposure start for light from the narrow-field imaging optical system and exposure time, provides the wide-field light selection means with wide-field filter selection information including the timing of exposure start for light from the wide-field imaging optical system and filter selection, and provides the wide-field image sensor with wide-field light control information including the timing of exposure start for light from the wide-field imaging optical system and exposure time, and has a control unit in which the narrow-field filter selection information, narrow-field light control information, wide-field filter selection information, and wide-field light control information are synchronized information.

6. The position coordinate calculation device comprises a stationary object detection unit, a moving object detection unit, a star coordinate comparison unit, and a low orbit object position coordinate determination unit, wherein the detection of the detected position coordinate of the low orbit object is carried out by the stationary object detection unit detecting a point image from the narrow field of view image data and detecting the center coordinate of the detected point image as the detected position coordinate of the low orbit object, the detection of the detected position coordinate of the star is carried out by the moving object detection unit detecting a line image from the wide field of view image data and detecting the center coordinate of the detected line image as the detected position coordinate of the star, and the identification of the celestial coordinate of the low orbit object is carried out by the star coordinate comparison unit comparing the detected position coordinate of the star by the moving object detection unit with the position coordinate of a known star, and the low orbit object position coordinate determination unit identifying the detected position coordinate of the low orbit object by the stationary object detection unit based on the comparison result of the star coordinate comparison unit. A coordinate determination device for a low orbit object according to any one of claims 1 to 5.

7. The coordinate determination device for low orbit objects described in claim 6, wherein the narrow-field image data from which point images are detected by the stationary object detection unit is narrow-field image data output from the narrow-field image sensor that has been preprocessed using dark current image data and flat image data.

8. A coordinate determination device for low orbit objects as described in claim 6 or claim 7, wherein the point image detected by the stationary object detection unit is a point image of connected pixels obtained from the narrow field of view image data, having a half-width of 3 to 10 arc seconds, and with a ratio of the major axis to the minor axis of the connected pixel of 1.5 or less.

9. A coordinate determination device for low orbit objects as described in claim 8, wherein the line image detected by the moving object detection unit is a line image of connected pixels obtained from the wide-field image data, having a half-width of 10 arc seconds or more and with a ratio of the major axis to the minor axis of the connected pixels of 2 or more.

10. A coordinate determination device for a low orbit object described in any one of claims 1 to 9, wherein the narrow-field light selection means splits the selected light into two light beams having different wavelengths or polarizations, the narrow-field image sensor has a first narrow-field image sensor that outputs one of the light beams split from the narrow-field light selection means as first narrow-field image data, and a second narrow-field image sensor that outputs the other light beam split from the narrow-field light selection means as second narrow-field image data, and the detected position coordinates of the low orbit object obtained by the position coordinate calculation device are detected position coordinates detected from narrow-field image data that are the result of dividing the first narrow-field image data from the first narrow-field image sensor and the second field of view image data from the second narrow-field image sensor.

11. The narrow-field light selection means splits the selected light into two beams of light having different wavelengths or polarizations, the narrow-field image sensor has a first narrow-field image sensor that outputs one beam of light split from the narrow-field light selection means as first narrow-field image data, and a second narrow-field image sensor that outputs the other beam of light split from the narrow-field light selection means as second narrow-field image data, the position coordinate calculation device has a division processing unit, a stationary object detection unit, a moving object detection unit, a star coordinate comparison unit, and a unit for determining the position coordinates of a low-orbit object, the division processing unit divides the first narrow-field image data and the second narrow-field image data, and obtains the narrow-field image data, which is the result of the division, as narrow-field image data for point image detection, the detection of the detected position coordinates of a low-orbit object is performed by the stationary object detection unit detecting a point image from the narrow-field image data for point image detection, and detecting the center coordinates of the detected point image as the detected position coordinates of the low-orbit object, 6. The coordinate determination device for a low orbit object according to any one of claims 1 to 5, wherein the detection of the detected position coordinates of the star is carried out by the moving object detection unit detecting a line image from the wide-field image data and detecting the center coordinates of the detected line image as the detected position coordinates of the star; and the identification of the celestial coordinates of the low orbit object is carried out by the star coordinate comparison unit comparing the detected position coordinates of the star by the moving object detection unit with position coordinates of known stars, and the low orbit object position coordinate determination unit identifying the detected position coordinates of the low orbit object by the stationary object detection unit based on the comparison result of the star coordinate comparison unit.

12. The coordinate determination device for a low orbit object described in claim 11, wherein the first narrow field of view image data and the second narrow field of view image data each consist of a plurality of narrow field of view image data taken consecutively at the same time, the narrow field of view image data for point image detection consists of a plurality of narrow field of view image data that are the result of dividing the first narrow field of view image data and the second narrow field of view image data acquired simultaneously, the stationary object detection unit detects point images with the same position coordinates among the plurality of narrow field of view image data in the narrow field of view image data for point image detection as point images caused by a low orbit object, the wide field of view image data consists of a plurality of wide field of view image data taken consecutively, and the moving object detection unit regards point images with moving position coordinates in the plurality of wide field of view image data in the wide field of view image data as line images in the wide field of view image data and detects them as line images caused by fixed stars.

13. A method for determining the position coordinates of a target low-orbit object using narrow-field image data from a narrow-field optical telescope having a narrow-field imaging optical system with a narrow field of view and high resolution, and wide-field image data from a wide-field optical telescope having a wide-field imaging optical system with a wider field of view than the narrow-field imaging optical system, lower resolution, and pointed in the same direction as the narrow-field imaging optical system, comprising the steps of: a stationary object detection unit detecting a point image from the narrow-field image data and setting the coordinates of the detected point image as the detected position coordinates of the low-orbit object; a moving object detection unit detecting a line image from the wide-field image data and setting the coordinates of the detected line image as the detected position coordinates of a fixed star; a star coordinate comparison unit obtaining a correspondence between the celestial coordinate data of the fixed star and the detected position coordinates of the fixed star; and a position coordinate determination unit identifying the celestial coordinates of the low-orbit object from the detected position coordinates of the low-orbit object based on the correspondence between the coordinates of the fixed star.

14. A method for determining the coordinates of a low orbit object as described in claim 13, wherein the narrow-field image data from the narrow-field optical telescope is first narrow-field image data and second narrow-field image data split into two beams of light having different wavelengths or polarizations, and further comprising a step in which a division processing unit divides the first narrow-field image data and the second narrow-field image data together to obtain the narrow-field image data resulting from the division as narrow-field image data for point image detection, and wherein the detection of point images from the narrow-field image data is performed by the stationary object detection unit detecting point images from the narrow-field image data for point image detection.

15. A coordinate determination program for determining the position coordinates of a target low-orbit object using narrow-field image data from a narrow-field optical telescope having a narrow-field imaging optical system with a narrow field of view and high resolution, and wide-field image data from a wide-field optical telescope having a wide-field imaging optical system with a wider field of view than the narrow-field imaging optical system, lower resolution, and pointed in the same direction as the narrow-field imaging optical system, the program causing a computer to execute the following steps: detect a point image from the narrow-field image data and use it as the detected position coordinate of the low-orbit object; detect a line image from the wide-field image data and use it as the detected position coordinate of a star; obtain a correspondence relationship between the celestial coordinate data of the star and the detected position coordinate of the star; and identify the celestial coordinate of the low-orbit object from the detected position coordinate of the low-orbit object based on the correspondence relationship between the coordinates of the star.

16. A recording medium storing a program for determining the position coordinates of a target low-orbit object using narrow-field image data from a narrow-field optical telescope having a narrow-field imaging optical system with a narrow field of view and high resolution, and wide-field image data from a wide-field optical telescope having a wide-field imaging optical system with a wider field of view than the narrow-field imaging optical system, lower resolution, and pointed in the same direction as the narrow-field imaging optical system, the recording medium storing the program causing a computer to execute the following steps: detect a point image from the narrow-field image data and use it as the detected position coordinates of the low-orbit object; detect a line image from the wide-field image data and use it as the detected position coordinates of a star; obtain a correspondence relationship between the celestial coordinate data of the star and the detected position coordinates of the star; and identify the celestial coordinates of the low-orbit object from the detected position coordinates of the low-orbit object based on the correspondence relationship between the coordinates of the star.

Images