Reflecting telescope mounted on a small satellite and its manufacturing method

Abstract

The present invention provides a reflecting telescope to be mounted on a small satellite that is less susceptible to temperature changes in space and can perform as a specified reflecting telescope, and a method for manufacturing the same. [Solution] The problem is solved by a reflecting telescope 10 mounted on a small satellite, the reflecting telescope 10 being a Cassegrain type reflecting telescope in which a primary mirror section 11 and a secondary mirror section 12 are assembled and fixed within a housing 31, and the diameter of the reflective surface of the secondary mirror section 12 is smaller than the diameter of the primary mirror section 11, and the problem is solved by a reflecting telescope and its manufacturing method in which the housing 31, primary mirror section 11 and secondary mirror section 12 are formed from aluminum or an aluminum alloy.

Description

[Technical Field]

[0001] The present invention relates to a reflecting telescope to be mounted on a small satellite and a method for manufacturing the same. [Background technology]

[0002] In recent years, the increasing volume of content being transmitted has led to a growing demand for ultra-high speed and capacity wireless communication technologies. Conventional wireless communication technologies include RF (Radio Frequency) communication, which has a wide communication range. The spread angle of the Ka band of the DRTS (Data Relay Satellite System) is 0.24°, which means that, for example, a ground station 36,000 km away has a spread angle of 150 km. Thus, RF communication has the advantage of a wide communication range and the ability to communicate through obstructions such as clouds.

[0003] However, RF communications have limited available frequencies, making it difficult to further increase speed and capacity. Moreover, the signal spreads over a large distance on the ground, making it susceptible to eavesdropping and interference.

[0004] In this situation, optical communication in space is attracting attention as a technology that enables high-speed, large-capacity optical communication without being restricted by frequency resources. One example of a technology for optical communication in space is to install communication equipment on artificial satellites and send and receive optical signals between artificial satellites.

[0005] On the other hand, in recent years, it has become possible for private companies to operate rockets and artificial satellites, and the launch of small satellites with low mass (for example, less than 100 kg) that can be manufactured at low cost is increasing. Some of these small satellites are equipped with, for example, a telescope as a communication device. For example, Patent Document 1 describes technology related to a telescope mounted on a small satellite that can be used in outer space, and the telescope in question is a catadioptric optical telescope. However, in addition to this type of telescope, other telescopes that can be mounted on small satellites include, for example, a Cassegrain reflecting telescope, which has mirrors such as a primary mirror and a secondary mirror mounted on a housing and reflects and focuses light from outside using the mirrors. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2017-513074 Summary of the Invention [Problem to be solved by the invention]

[0007] Small satellites orbit the Earth along a predetermined orbit, but during their orbit, they are sometimes located on the front side of the Earth relative to the sun and sometimes on the back side. The temperature of the small satellite itself fluctuates greatly between daylight when sunlight hits the small satellite and shaded when it is in the Earth's shadow and not exposed to sunlight, and the temperature of the reflecting telescope mounted on the small satellite also fluctuates greatly (for example, a temperature fluctuation of 80 degrees). When exposed to such an environment, the casing and mirror of the reflecting telescope constantly contract and expand due to temperature changes, causing distortion and posing a problem of interfering with measurement and communication.

[0008] Therefore, the present invention aims to provide a reflecting telescope to be mounted on a small satellite that is less susceptible to temperature changes in outer space and can perform as a specified reflecting telescope, and a method for manufacturing the same. [Means for solving the problem]

[0009] The above-mentioned problems are solved by the following aspects. (First aspect) A reflecting telescope mounted on a small satellite, The reflecting telescope is a housing, and a primary mirror unit and a secondary mirror unit are assembled and fixed in the housing; the diameter of the reflecting surface of the secondary mirror is smaller than the diameter of the primary mirror, a Cassegrain reflecting telescope in which light from outside enters the housing, is reflected by the primary mirror and the secondary mirror in this order, and is then emitted to the outside of the housing; the housing, the primary mirror section, and the secondary mirror section are formed of aluminum or an aluminum alloy; A reflecting telescope mounted on a small satellite.

[0010] (Second aspect) A reflecting telescope mounted on a small satellite, The reflecting telescope is a housing; a photoelectric conversion element; and a primary mirror unit and a secondary mirror unit assembled and fixed in the housing; the diameter of the reflecting surface of the secondary mirror is smaller than the diameter of the primary mirror, a Cassegrain reflecting telescope for optical communications in which external light enters the housing, is reflected by the primary mirror and the secondary mirror in this order, and is then collected and received by the photoelectric conversion element; the housing, the primary mirror section, and the secondary mirror section are formed of aluminum or an aluminum alloy; A reflecting telescope mounted on a small satellite.

[0011] (Third aspect) A reflecting telescope mounted on a small satellite, The reflecting telescope is a housing; a photoelectric conversion element; and a primary mirror unit and a secondary mirror unit assembled and fixed in the housing; the diameter of the reflecting surface of the secondary mirror is smaller than the diameter of the primary mirror, a Cassegrain reflecting telescope for optical communications, wherein light emitted by the photoelectric conversion element is reflected by the secondary mirror and the primary mirror in this order, and then emitted to the outside; the housing, the primary mirror section, and the secondary mirror section are formed of aluminum or an aluminum alloy; A reflecting telescope mounted on a small satellite.

[0012] (Fourth aspect) A method for manufacturing a reflecting telescope mounted on a small satellite, comprising: The reflecting telescope is a housing, and a primary mirror unit and a secondary mirror unit are assembled and fixed in the housing; the diameter of the reflecting surface of the secondary mirror is smaller than the diameter of the primary mirror, a Cassegrain reflecting telescope in which light from outside enters the housing, is reflected by the primary mirror and the secondary mirror in this order, and is then collected; The housing, the primary mirror section, and the secondary mirror section are formed from aluminum or an aluminum alloy. A method for manufacturing a reflecting telescope to be mounted on a small satellite.

[0013] (Fifth aspect) A method for manufacturing a reflecting telescope mounted on a small satellite, comprising: The reflecting telescope is a housing; a photoelectric conversion element; and a primary mirror unit and a secondary mirror unit assembled and fixed in the housing; the diameter of the reflecting surface of the secondary mirror is smaller than the diameter of the primary mirror, a Cassegrain reflecting telescope for optical communications in which external light enters the housing, is reflected by the primary mirror and the secondary mirror in this order, and is then collected and received by the photoelectric conversion element; The housing, the primary mirror section, and the secondary mirror section are formed from aluminum or an aluminum alloy. A method for manufacturing a reflecting telescope to be mounted on a small satellite.

[0014] (Sixth aspect) A method for manufacturing a reflecting telescope mounted on a small satellite, comprising: The reflecting telescope is a housing; a photoelectric conversion element; and a primary mirror unit and a secondary mirror unit assembled and fixed in the housing; the diameter of the reflecting surface of the secondary mirror is smaller than the diameter of the primary mirror, a Cassegrain reflecting telescope for optical communications, wherein light emitted by the photoelectric conversion element is reflected by the secondary mirror and the primary mirror in this order, and then emitted to the outside; The housing, the primary mirror section, and the secondary mirror section are formed from aluminum or an aluminum alloy. A method for manufacturing a reflecting telescope to be mounted on a small satellite, comprising:

[0015] In the first to sixth aspects described above, the housing, primary mirror, and secondary mirror of the reflecting telescope are formed from aluminum or an aluminum alloy, i.e., a single type of material. Therefore, even if the temperature of the entire reflecting telescope changes (for example, the temperature fluctuates by 80 degrees), the primary mirror and secondary mirror are incorporated and fixed within the housing, so the housing, primary mirror, and secondary mirror expand or contract at the same expansion rate, maintaining a similar optical positional relationship between the primary mirror and secondary mirror, making it less likely for distortion to occur in the image. Additionally, aluminum or aluminum alloys are lightweight, which is an advantage when they are installed on small satellites. [Effects of the Invention]

[0016] According to the present invention, there is provided a reflecting telescope to be mounted on a small satellite that is less susceptible to temperature changes in outer space and can perform as a specified reflecting telescope, and a method for manufacturing the same. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is an explanatory diagram illustrating an example of a satellite network. [Figure 2] FIG. 1 is a perspective view illustrating an example of the appearance of a reflecting telescope. [Figure 3] This is a conceptual diagram of a cross section of the reflecting telescope in Figure 1 taken along the XX line. [Figure 4] FIG. 1 is a diagram showing the transmitted wavefront accuracy of a reflecting telescope measured by a laser interferometer. [Figure 5] FIG. 1 is a diagram showing the transmitted wavefront accuracy of a reflecting telescope measured by a laser interferometer. [Figure 6] FIG. 1 is a diagram showing the transmitted wavefront accuracy of a reflecting telescope measured by a laser interferometer. [Figure 7] FIG. 1 is a diagram showing an example of a method for collecting external light using a reflecting telescope and converting it into an electrical signal. [Figure 8] FIG. 10 is a diagram showing an example of a method for emitting light emitted by a photoelectric conversion element to the outside from a reflecting telescope. [Figure 9] 10 is a diagram showing an example of measuring the transmitted wavefront accuracy of a reflecting telescope using a laser interferometer. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The present embodiment is merely an example of the present invention. The scope of the present invention is not limited to the scope of the present embodiment.

[0019] The reflecting telescope of the present invention is intended to be used, for example, as part of Japan's information and communications technology strategy in the "Beyond 5G Promotion Plan," particularly as a reflecting telescope to be mounted on "non-geostationary satellites" and "geostationary satellites" in "satellite networks."

[0020] Explaining satellite constellation technology with reference to Figure 1, a satellite network 3 is formed using reflecting telescopes 2 mounted on multiple geostationary satellites 1, and if the laser beam from an OICET laser has a divergence angle of 0.003°, for example, at a ground station 4 located 36,000 km away, the divergence angle will be 180 m, but because it is optical communication, it allows for high-capacity communication, consumes little power, is less susceptible to eavesdropping and interference, and ensures high security. On the other hand, it has the disadvantage that it is significantly affected by cloudiness and atmospheric turbulence, and communication is difficult if there are obstructions.

[0021] However, although there are drawbacks, there are also advantages that outweigh these drawbacks, and if a satellite network is constructed using a large number (for example, in the thousands or tens of thousands) of non-geostationary satellites, the drawbacks can be eliminated.

[0022] Therefore, the first problem is to obtain a reflecting telescope that is less susceptible to temperature changes in space in order to configure the satellite network 3.

[0023] The second challenge is to manufacture a large number of reflecting telescopes cheaply and under conditions of sufficiently high productivity, and reflecting telescopes, in particular, must have a high degree of precision that can withstand optical communications. A satellite constellation refers to a group system of multiple artificial satellites based on a specific method. Each satellite is launched into a system-designed orbit and operates in coordination to achieve the system's objectives.

[0024] The reflecting telescope 10 mounted on the small satellite of this embodiment is a Cassegrain reflecting telescope in which a primary mirror section 11 and a secondary mirror section 12 are assembled and fixed into a housing 31, the diameter of the reflective surface of the secondary mirror section 12 is smaller than the diameter of the primary mirror section 11, and light L from outside enters the housing 31, is reflected by the primary mirror section 11 and the secondary mirror section 12 in that order, and is then focused, and is characterized in that the housing 31, primary mirror section 11, and secondary mirror section 12 are formed of aluminum or an aluminum alloy. As another embodiment of the reflecting telescope 10, there is provided a housing 31, a photoelectric conversion element 35, and a primary mirror 11 and a secondary mirror 12 assembled and fixed within the housing 31, with the diameter of the reflecting surface of the secondary mirror 12 being smaller than the diameter of the primary mirror. The telescope can be a Cassegrain reflecting telescope for optical communications in which light L from outside enters the housing 31, is reflected by the primary mirror 11 and then the secondary mirror 12, and is then collected and received by the photoelectric conversion element 35. Alternatively, the telescope can be a Cassegrain reflecting telescope for optical communications in which light emitted by the photoelectric conversion element 35 is reflected by the secondary mirror 12 and then the primary mirror 11, and is then emitted to the outside. Furthermore, the reflecting telescope 10 may be a Cassegrain reflecting telescope for optical communications in which light L from outside enters the housing 31, is reflected by the primary mirror section 11 and the secondary mirror section 12 in that order, is then collected, and is received by the photoelectric conversion element 35, and the light emitted by the photoelectric conversion element 35 is reflected by the secondary mirror section 12 and the primary mirror section 11 in that order, and is then emitted to the outside. The reflecting telescope 10 and its manufacturing method will now be described in detail.

[0025] The reflecting telescope 10 according to this embodiment is a Cassegrain reflecting telescope having a housing 31 and a primary mirror 11 and a secondary mirror 12 within the housing 31. The housing 31 has an entrance 32 into which light L emitted from a light-emitting object located outside the housing 31 enters, and an exit 33 from which light L reflected by the secondary mirror 12 exits the housing 31. Light L (particularly parallel light) from an external object enters the housing 31 through the entrance 32, is reflected by the primary mirror 11, which has a concave surface facing the object side, and is further reflected by the secondary mirror 12, which is located on the object side of the primary mirror 11 and returns the light reflected from the primary mirror 11 to the image plane side, where it is then focused. The focus (image point) of the focused light may be located, for example, closer to the image plane than the exit 33 of the housing 31 (i.e., outside the housing 31), or it may be located inside the housing 31. The housing 31 can include a cylindrical baffle 24 inside the housing 31. The baffle 24 can be provided, for example, at a position facing the secondary mirror 12, so that the axis of the baffle 24 is perpendicular to the center of the reflecting surface of the secondary mirror 12 (i.e., the surface that reflects light). In particular, the baffle 24 should be placed in an opening 13 of the primary mirror 11 (described below) so that its axis is perpendicular to the center of the reflecting surface of the secondary mirror 12. Note that it is desirable that the optical axis of light L from an external object that enters the reflecting telescope 10 be perpendicular to the primary mirror 11 and the secondary mirror 12.

[0026] The baffle 24 guides light scattered within the housing 31 that enters the baffle 24 to be emitted to the outside through the exit 33 of the housing 31, blocking light other than that entering the baffle 24. Light L reflected by the secondary mirror 12 forms an image after passing through the baffle 24 and the exit 33 of the housing 31. A camera 23 can be installed at the position where the light L forms an image, and the image of the light L can be captured by the camera 23. The camera 23 is not particularly limited, but a CCD camera, CMOS camera, or the like can be used. This embodiment of the reflecting telescope 10 can be mounted on an earth observation satellite and used for earth observation. Furthermore, when using the reflecting telescope 10 according to this embodiment for optical wireless communication, the camera 23 can be removed, the tip of an optical fiber can be installed at the position of the camera 23, and the light L can be introduced into the optical fiber, as shown in FIGS. 7 and 8 . The optical fiber used here has a core diameter of 9 to 50 μm, but is not particularly limited.

[0027] 7, light incident on the reflecting telescope 10 mounted on the small satellite may be reflected and collected by a mirror, passed through an optical fiber 34, and converted into an electrical signal by a photoelectric conversion element 35 for data processing. Alternatively, the light may be processed as data by detecting the light that has passed through the optical fiber 34 with a photon detector and processing the results as data.

[0028] On the other hand, it is also possible to convert an electrical signal into an optical signal and emit light from the small satellite toward another small satellite. For example, referring to Figure 8, light L converted from an electrical signal to an optical signal by photoelectric conversion element 35 can be emitted toward secondary mirror 12 via optical fiber 34 and emission section 33, reflected by secondary mirror 12 and primary mirror 11 in this order, and emitted outside of reflecting telescope 10 from incidence section 32. In this way, optical wireless communication can be performed by repeating the emission and incidence of light L between small satellites equipped with reflecting telescopes 10, and between a ground station and a small satellite.

[0029] The photoelectric conversion element 35 according to this embodiment may be, for example, at least one of a light-receiving element that converts an optical signal into an electrical signal and a light-emitting element that converts an electrical signal into an optical signal, or may include both a light-receiving element and a light-emitting element. Examples of light-receiving elements include an imaging element, a photodiode, a phototransistor, a photocell, a phototube, and a photomultiplier tube. Examples of light-emitting elements include a light-emitting diode and a semiconductor laser.

[0030] The reflecting telescope 10 according to this embodiment can be mounted on a small satellite and used, for example, for optical wireless communication. One or more, and preferably 4 to 6, units can be mounted on each small satellite. Furthermore, many small satellites can fly in low Earth orbit, with the distance between them being, for example, 400 to 4,000 km. Therefore, when the reflecting telescope 10 according to this embodiment is mounted on a small satellite, for example, light emitted from a certain small satellite A is received by a reflecting telescope 10 mounted on another small satellite B, which is 400 to 4,000 km away. After receiving the light by the reflecting telescope 10 of the other small satellite B, the other small satellite B further emits light to yet another small satellite C. In this way, optical wireless communication between small satellites is possible. Furthermore, optical wireless communication using the reflecting telescope 10 can be performed not only between small satellites, but also between a ground station and a small satellite by providing a reflecting telescope 10 in a ground station.

[0031] By mounting the reflecting telescope 10 of this embodiment on a small satellite, the advantages of optical wireless communication, such as ultra-high speed communication and large capacity communication, can be realized, and power consumption can be relatively reduced, enabling highly secure communication. Note that the light L incident on the reflecting telescope 10 of this embodiment is not particularly limited, but may be, for example, visible light or near-infrared light, and specifically, light with a wavelength of 400 to 2500 nm is preferred.

[0032] The three-dimensional size of the housing 31 of the reflecting telescope 10 according to this embodiment is, for example, 50 cm or less in length, width, and depth. In particular, the three-dimensional size may be, for example, an approximately cube or rectangular parallelepiped with length, width, and depth of about 10 to 20 cm. The diameter of the reflecting surface of the primary mirror 11 fixed within the housing 31 is 80 to 200 mm, and the diameter of the reflecting surface of the secondary mirror 12 is 20 to 70 mm, with the diameter of the reflecting surface of the secondary mirror 12 being smaller than the diameter of the reflecting surface of the primary mirror 11. The primary mirror 11 has an opening 13 (aperture) in the center, allowing light L reflected by the secondary mirror 12 to pass through the opening 13.

[0033] The reflecting telescope 10 according to this embodiment is mounted on a small satellite. Examples of small satellites that can be mounted on this telescope include small satellites weighing 100 kg or more but less than 500 kg, and micro satellites weighing 20 kg or more but less than 100 kg. It can also be used as a satellite or Earth observation satellite that flies in a low orbital region at an altitude of 2000 km or less. Meanwhile, the lower limit of the orbital region in which a small satellite that can be mounted with the reflecting telescope 10 according to this embodiment flies is, for example, an altitude of 350 km.

[0034] Although not particularly limited, the reflecting telescope 10 according to this embodiment may have the housing 31, primary mirror section 11, and secondary mirror section 12 made of aluminum or an aluminum alloy.

[0035] Forming the housing 31, primary mirror 11, and secondary mirror 12 from aluminum or an aluminum alloy offers the following advantages: A small satellite orbits the Earth along a predetermined orbit. During the orbit, the Earth, the small satellite, and the sun are aligned in this order, so that the small satellite is sometimes positioned in the sunlit area, and sometimes positioned in the shaded area. Therefore, when the small satellite is positioned in the sunlit area, it receives heat from the sun and its temperature rises. On the other hand, when the small satellite is positioned in the shaded area, its temperature drops. Similarly, the temperature of the reflecting telescope mounted on the small satellite rises or falls, and therefore, naturally, the temperatures of the housing, primary mirror, and secondary mirror that make up the reflecting telescope also rise or fall. Aluminum, aluminum alloys, glass, ceramics, and other materials each have different thermal expansion coefficients, and therefore the degree of expansion per unit temperature change varies. For example, if the housing is made of an aluminum alloy and the primary and secondary mirror sections are made of glass or ceramics, even if the housing expands or contracts due to temperature changes, the primary and secondary mirror sections will not expand or contract at the same rate, which will result in a misalignment of the optical positional relationship between the primary and secondary mirror sections in the housing from the start, distorting the image and potentially interfering with optical wireless communication.

[0036] In addition, there has been a conventional manufacturing method in which the reflective surface of the mirror material, such as the primary mirror or secondary mirror, is subjected to a rough cutting process, followed by electroless nickel plating (NiP), and then a cutting process to obtain the mirror. Mirrors manufactured by this method have excellent reflective surface precision, but if the mirror material and the metal used for plating are different, distortion may occur due to temperature changes, making them unsuitable for use in reflecting telescopes, which are constantly exposed to temperature changes.

[0037] On the other hand, in a reflecting telescope in which the housing, primary mirror, and secondary mirror are made of the same material, the housing, primary mirror, and secondary mirror expand or contract at the same expansion rate (i.e., similar expansion or contraction), so even if they expand or contract, the optical positional relationship between the primary mirror and secondary mirror is maintained similarly, making it less likely that distortion will occur in the image.

[0038] The aluminum alloy that can be used as the material for the housing 31, primary mirror 11, and secondary mirror 12 according to this embodiment is not particularly limited, but is preferably, for example, an Al-Mg-Si (6000)-based aluminum alloy, which is aluminum to which magnesium and silicon are added. Specific examples include A6061, A6063, and RSA6061 manufactured by a rapid solidification method. Other examples include A1070, RSA0303, RSA905, and AA6061 manufactured by a rapid solidification method. These aluminum alloys are commercially available, and A6061 and aluminum manufactured by a rapid solidification method (especially RSA6061) are particularly preferred because they have high strength, excellent corrosion resistance, and excellent workability, and their performance can be improved by heat treatment.

[0039] Furthermore, the aluminum alloy according to this embodiment is preferably a solid obtained by a rapid solidification method, since relatively large crystallized particles are not formed in the solid, resulting in excellent amorphous properties, fewer corrosion pits, and the ability to be processed into a highly accurate reflective surface. The rapid solidification method is a method for producing a solid, for example, by the following procedure. First, molten metal is sprayed onto the surface of a rotating cooling drum. The molten metal rapidly solidifies upon contact with the cooling drum. The cooling rate of the molten metal can be changed by adjusting the surface temperature of the cooling drum, and can be cooled to, for example, 104 to 106 Kelvin / second. The solidified metal is then crushed into powder, and the crushed metal powder is agglomerated and pressurized to form a metal ingot. The metal ingot is then extruded to form a solid. Examples of rapid solidification methods include planar flow casting, twin-roll melt spinning, and automatic injection melt spinning.

[0040] For example, if the manufacturing method for the reflecting telescope 10 according to this embodiment includes a solidification step in which molten light metal is solidified by a rapid solidification process to obtain a solid material, and the solid material is used as the raw material for the primary mirror 11 and / or the secondary mirror 12, the polishing step described below can produce a secondary mirror 12 with superior shape precision compared to manufacturing a secondary mirror using an aluminum alloy that has not undergone the solidification step. In particular, if the size of the individual crystals forming the solid material is 1 μm or less, etch pits are less likely to form, and the primary mirror 11 and / or the secondary mirror 12 with superior shape precision can be obtained, which is preferable. In particular, since the reflecting telescope 10 according to this embodiment requires precise processing of the raw material for the secondary mirror, it is preferable to include a solidification step in which molten aluminum alloy is solidified by a rapid solidification process to obtain a solid material, and the solid material is used as the raw material for at least the secondary mirror 12. Note that etch pits are holes formed in the surface of a solid material when relatively large crystals forming the surface of the solid material are removed during polishing.

[0041] On the other hand, the reflecting telescope 10 according to this embodiment may have two mirrors that reflect light L, the primary mirror 11 and the secondary mirror 12, or may have three or more mirrors added. However, if the reflecting telescope 10 is made up of the primary mirror 11 and the secondary mirror 12, it is possible to manufacture a reflecting telescope 10 that has high performance while relatively shortening the manufacturing time.

[0042] The reflecting surfaces of the primary mirror section 11 and the secondary mirror section 12 according to this embodiment may be spherical mirrors or aspherical mirrors such as parabolic or hyperbolic mirrors.

[0043] The manufacture of mirrors such as the primary mirror 11 and secondary mirror 12 according to this embodiment can be carried out using, for example, glass, ceramics, or light metal as the raw material for the mirror, and can include a rough cutting process for roughly cutting the raw material, a cutting process for cutting the target reflection surface of the roughly cut mirror, and a polishing process for polishing the cut target reflection surface. However, some raw materials can be obtained commercially that can be subjected to the cutting process without the rough cutting process.

[0044] Of the primary mirror 11 and secondary mirror 12, we will first explain the processing steps for manufacturing the primary mirror 11. The primary mirror 11 provided in the reflecting telescope 10 has a shape accuracy (RMS) of preferably 100 nm RMS or less, more preferably 50 nm RMS or less, of the reflective surface (i.e., the surface that reflects light), and the reflective surface is processed to fall within this shape accuracy range. The processing steps performed on the reflective surface of the primary mirror 11 consist of a rough cutting process and a cutting process.

[0045] (Rough cutting process of the primary mirror) The primary mirror rough cutting process, which is performed on the reflection target surface of the material of the primary mirror section 11, is a process of roughly removing the portion that should be removed from the material of the primary mirror section 11. The rough cutting process is preferably performed, for example, by removing 80% to 95% by volume of the portion that should be removed, as this can be done relatively easily and in a short time.

[0046] (Primary mirror cutting process) The primary mirror cutting process, which is performed on the material of the primary mirror section 11, is a process in which a cutting tool is used to cut the reflective surface of the primary mirror section 11. This process is not particularly limited as long as it can be performed with a predetermined precision, but diamond turning, in which the primary mirror section 11 is rotated and processing is performed using a diamond tool and ultra-precision processing equipment, is desirable.

[0047] In the cutting process, the time required for the manufacturing process of the primary reflecting surface varies depending on the material of the raw material of the primary mirror section 11, the diameter of the reflecting surface, etc. To manufacture a primary mirror section 11 with a reflecting surface diameter of 80 to 200 mm, it takes 40 to 80 hours if the raw material of the primary mirror section 11 is glass or ceramic, and it takes 8 to 16 hours if the raw material of the primary mirror section 11 is aluminum or an aluminum alloy. Using aluminum or an aluminum alloy instead of glass or ceramic as the material is easier to cut and reduces the time required to process it to the specified shape precision, which is preferable.

[0048] Conventionally, a polishing process was performed on the primary reflecting surface of the primary mirror portion formed by a cutting process. The polishing process performed on the first reflecting surface of the primary mirror portion 11 takes approximately 25 hours, which is the reason why the manufacturing of conventional reflecting telescopes takes a long time. On the other hand, the primary mirror portion 11 according to this embodiment is manufactured without the time-consuming polishing process, thereby significantly shortening the manufacturing time of the reflecting telescope 10.

[0049] Next, the processing steps for manufacturing the secondary mirror 12 will be described. The reflecting telescope 10 according to this embodiment is a reflecting telescope 10 that is formed by combining the primary mirror 11 and the secondary mirror 12, and preferably has a transmitted wavefront accuracy of 60 nm RMS or less. The transmitted wavefront accuracy is determined by the relationship between the shape of the reflecting surface of the primary mirror 11 and the shape of the reflecting surface of the secondary mirror 12. The higher the precision with which the RMS of the primary mirror 11 and the RMS of the secondary mirror 12 are machined, the higher the transmitted wavefront accuracy tends to be. Therefore, conventionally, a manufacturing method has been used in which the primary mirror 11 and the secondary mirror 12 are machined separately to high precision.

[0050] On the other hand, in the reflecting telescope 10 according to this embodiment, the primary mirror 11 and the secondary mirror 12 can be manufactured by, for example, cutting the target reflection surface of the raw material of the primary mirror 11, measuring the transmitted wavefront accuracy of the reflecting telescope 10 using a laser interferometer, and polishing only the secondary mirror 12 using magnetic fluid polishing to obtain a secondary reflecting surface so that the measured transmitted wavefront accuracy is equal to or less than a predetermined transmitted wavefront accuracy. Here, the predetermined transmitted wavefront accuracy is, for example, 60 nm RMS or less. Because the diameter of the reflecting surface of the secondary mirror 12 is smaller than that of the primary mirror 11, the time required for the cutting and polishing processes is significantly shorter for the secondary mirror 12 than for the primary mirror 11. Therefore, since the target reflection surface of the primary mirror 11 is left as it is after the cutting process and no polishing process is performed, a high-precision reflecting telescope can be manufactured in a short time.

[0051] The processing steps performed on the reflection surface of the secondary mirror section 12 consist of, for example, a rough cutting step, a cutting step, and a polishing step, but the secondary mirror section 12 may be manufactured by performing only the cutting step and the polishing step depending on the quality of the raw materials for the secondary mirror section 12 prepared.

[0052] (Secondary mirror rough cutting process) The secondary mirror rough cutting process, which is performed on the reflection target surface of the secondary mirror portion 12, is a process of roughly removing the portion that should be removed from the reflection target surface of the secondary mirror portion 12. The rough cutting process is preferably performed, for example, to remove 80% to 95% by volume of the portion that should be removed, as this can be done relatively easily and in a short time.

[0053] (Secondary mirror cutting process) The secondary mirror cutting process, which is performed on the raw material to obtain the secondary mirror section 12, can be performed in the same manner as the cutting process for the primary mirror section 11, and is a process in which the reflective surface of the secondary mirror section 12 is cut using a cutting tool to obtain the primary reflective surface.

[0054] The cutting process takes 1 to 3 hours when manufacturing a secondary mirror section 12 with a reflective surface diameter of 20 to 70 mm, if the secondary mirror section 12 is made of glass, ceramics, aluminum, or aluminum alloy.

[0055] (Secondary mirror polishing process) The raw material for the secondary mirror 12 that has been cut is then subjected to the polishing process. Before the polishing process, the secondary mirror 12 may be combined with the primary mirror 11 and the transmitted wavefront accuracy (RMS and PV) may be measured using a laser interferometer, and the extent of polishing that should be performed may be determined from the measurement results.

[0056] The polishing process for the secondary mirror 12 is a process in which the primary reflecting surface of the secondary mirror 12 formed in the cutting process is polished to obtain a secondary reflecting surface. The polishing process is preferably performed by magnetic fluid polishing in order to process the reflecting surface with high precision. The polishing process takes 1 to 3 hours if the secondary mirror 12 is made of glass, ceramics, aluminum, or an aluminum alloy.

[0057] The polishing process according to this embodiment is specifically magnetorheological finishing. This polishing is performed using a fluid containing a magnetic material and an abrasive. For example, the magnetic material components contained in the magnetorheological fluid flowing around the apex of a rotating wheel are biased away from the mirror material toward the rotating wheel due to the action of a magnetic field, and the abrasive material oozes out. When the mirror material is brought into contact with this fluid, the abrasive material flows between the mirror material and the magnetic material components, exerting a shear force on the polished surface of the mirror material, thereby polishing it.

[0058] After polishing the primary reflecting surface of the secondary mirror 12 to obtain the secondary reflecting surface, the primary mirror 11 and secondary mirror 12 are combined to form a reflecting telescope, which is then subjected to a measurement process. In the measurement process, the transmitted wavefront accuracy (RMS and PV) of the reflecting telescope 10 can be measured using, for example, a laser interferometer. The process of measuring the transmitted wavefront accuracy of the reflecting telescope 10 takes 2 to 4 hours.

[0059] In addition to RMS, PV can also be measured during the measurement process. RMS and PV can be measured using a Fizeau interferometer in accordance with JIS B 0091:2010. RMS (root mean square) represents the deviation between the wavefront of actual light reflected from a mirror and the ideal wavefront. It is calculated by finding the distance from all points on the wavefront of the actual light to the ideal wavefront and taking the root mean square of this value. On the other hand, PV (peak to valley) represents the difference in height between the maximum (peak) and minimum (valley) values ​​of the error relative to the ideal shape.

[0060] The transmitted wavefront accuracy of the reflecting telescope according to this embodiment can be measured using a laser interferometer for a reflecting telescope equipped with a primary mirror and a secondary mirror. The transmitted wavefront accuracy of the reflecting telescope is not particularly limited, but can be measured, for example, as follows. Referring to FIG. 9 , a reflecting telescope is formed by fixing a primary mirror 53 and a secondary mirror 52 in predetermined positions. Parallel light L1 of wavelength λ emitted from light source 49 is reflected by mirror 50, a portion of which passes through reference plate 51 and travels toward primary mirror 53, is reflected by primary mirror 53, and travels toward secondary mirror 52 (L2), and is reflected by secondary mirror 52 and travels toward reflecting mirror 54, which is installed further back than image position I (L3). The collimated light reflected by reflecting mirror 54 travels back along its optical path toward secondary mirror 52 (L4), reflects off secondary mirror 52, travels toward primary mirror 53 (L5), reflects off primary mirror 53, passes through reference plate 51 (L6), and is detected by detector 55. The remaining portion of the collimated light (L12) emitted from light source 50 is reflected off reference plate 51 and travels directly toward detector 55 (L12) without traveling toward primary mirror 53, where it is detected by detector 55. Detector 55 detects and calculates the phase difference between the light that has traveled through L1, L2, L3, L4, L5, and L6 in that order and the light that has traveled through L1 and L12 in that order, thereby determining the transmitted wavefront accuracy. While FIG. 9 only partially illustrates the collimated light for illustrative purposes, in actual measurements, light source 49 emits collimated light so that the entire reflecting surface of primary mirror 53 is illuminated by the collimated light.

[0061] The transmitted wavefront accuracy (RMS and PV) obtained in the measurement process is checked, and if the transmitted wavefront accuracy (RMS) reaches the target accuracy (for example, 60 nm RMS or less), the processing process for the reflection target surfaces of the primary mirror 11 and secondary mirror 12 is completed, and the primary mirror 11 and secondary mirror 12 having the specified surface accuracy are obtained. On the other hand, if the transmitted wavefront accuracy (RMS) does not reach the target accuracy, the secondary mirror 12 is polished again. Then, after the polishing process is completed again, the transmitted wavefront accuracy (RMS) is checked.

[0062] The polishing and measuring steps for the secondary mirror 12 can be repeated until the transmitted wavefront accuracy (RMS) reaches a target accuracy.

[0063] Specific examples of manufacturing the reflecting telescope 10 according to this embodiment are as follows: The reflecting surfaces of the primary mirror 11 and the secondary mirror 12 are obtained by diamond turning. Alternatively, the reflecting surfaces of the primary mirror 11 and the secondary mirror 12 are obtained by diamond turning, and the secondary mirror 12 is further polished by magnetorheological polishing to obtain a secondary reflecting surface. Alternatively, the reflecting surfaces of the primary mirror 11 and the secondary mirror 12 are obtained by diamond turning, and the primary mirror 11 is left as it was by diamond turning. The transmitted wavefront accuracy of the reflecting telescope 10 is measured with a laser interferometer, and only the secondary mirror 12 is polished by magnetorheological polishing to obtain a secondary reflecting surface so that the measured transmitted wavefront accuracy is equal to or less than a predetermined transmitted wavefront accuracy. These reflecting telescope 10 primary and secondary mirrors 11 and 12 are formed. [Example]

[0064] The raw materials for the primary and secondary mirrors of a reflecting telescope were prepared and machined to produce the primary and secondary mirrors. The transmitted wavefront accuracy (nmRMS) of the reflecting telescope was measured. The raw material for the primary and secondary mirrors was RSA6061, a rapidly solidified aluminum alloy manufactured by RSP technologies. The primary and secondary mirrors were fabricated using diamond turning (DT) machining, while the secondary mirror's secondary reflecting surface was fabricated using magnetorheological polishing (MRF). The diamond turning (DT) machining was performed using the Nanoform 700ultra manufactured by AMETEC, and the magnetorheological polishing (MRF) machining was performed using the Q-flex300 manufactured by QED technologies. The primary mirror was made of aluminum (A6061), and the secondary mirror was made of aluminum (RSA6061). Table 1 shows the processing steps for the mirrors (primary and secondary mirrors), their shape accuracy after the processing steps, the transmitted wavefront accuracy of the reflecting telescope combining the primary and secondary mirrors, and the time required for processing (processing time). The shape accuracy of the primary and secondary mirrors and the transmitted wavefront accuracy of the reflecting telescope were measured using a laser interferometer (AMETEC's "Verifire" product) with a He-Ne laser at a measurement wavelength of 632.8 nm. The specific measurement procedure was to measure the transmitted wavefront accuracy of the reflecting telescope with the laser interferometer, and if the measurement result exceeded 60 RMS, this result was entered into the laser interferometer's calculation software as an error due to the secondary mirror alone. The secondary mirror was then subjected to the magnetic polishing process again, and the secondary mirror and the primary mirror were combined to form a reflecting telescope. The transmitted wavefront accuracy was then measured with the laser interferometer, and this procedure was repeated until it was 60 RMS or less.

[0065] [Table 1]

[0066] As a result of diamond turning on the reflective surface of the primary mirror, the shape accuracy of the primary mirror (after DT) was 357nmPV and 57nmRMS. Next, as a result of diamond turning on the reflective surface of the secondary mirror, the shape accuracy of the secondary mirror (after DT) was 177nmPV and 32nmRMS. The processing times for diamond turning on the reflective surface of the primary mirror and the reflective surface of the secondary mirror were 2 hours and 1 hour, respectively.

[0067] Here, the transmitted wavefront accuracy of the reflecting telescope was measured using a Fizeau interferometer, and the results are shown in Figure 4. The transmitted wavefront accuracy was 836 nmPV and 95 nmRMS. In Figure 4, there are concave and convex portions 41 and 42, which are significantly distorted compared to the ideal wavefront.

[0068] The secondary mirror (after DT) was subjected to the first and second magnetic fluid polishing processes, resulting in the secondary mirror after the second MRF process. The secondary mirror after the second MRF process had a transmitted wavefront accuracy of 378nmPV and 76nmRMS. Furthermore, when the primary mirror after DT processing and the secondary mirror after the second MRF process were combined to form a reflecting telescope, the transmitted wavefront accuracy was 255nmPV and 38nmRMS. The processing time for the magnetic fluid polishing process performed on the secondary mirror was 1 to 1.5 hours per process for both the first and second processes.

[0069] Focusing on the secondary mirror, the shape accuracy of the secondary mirror after DT processing was 32 nm RMS, while that of the secondary mirror after the second MRF processing was 76 nm RMS. The shape accuracy of the secondary mirror alone was higher immediately after the second MRF processing than immediately after DT processing. However, the transmitted wavefront accuracy of the reflecting telescope was 95 nm RMS when the secondary mirror after DT processing was used as the secondary mirror, and 38 nm RMS when the secondary mirror after the second MRF processing was used. It can be seen that the transmitted wavefront accuracy was lower after the secondary mirror was MRF processed. Figure 5 shows the wavefront shape of the reflecting telescope after the second magnetic fluid polishing processing of the secondary mirror. In Figure 5, there is a convex portion 42, which is significantly distorted relative to the ideal wavefront.

[0070] Figure 6 shows the wavefront shape of the reflecting telescope after the second magnetic fluid polishing process was performed on the secondary mirror. No characteristic concave or convex portions are visible, and the distortion seen in Figures 4 and 5 has been eliminated.

[0071] The measurement time using the laser interferometer was two hours per measurement to measure the transmitted wavefront accuracy when using a reflecting telescope. [Industrial Applicability]

[0072] The reflecting telescope 10 manufactured by the manufacturing method of the reflecting telescope 10 according to the present invention can be used in outer space, and is suitable for applications such as communications, observation, and positioning, particularly for earth observation, optical communications, and optical wireless communications. [Explanation of symbols]

[0073] 10 reflecting telescope 11 Primary mirror 12 Secondary mirror section 13 Opening 21 Lead screw 22 Sensor support 23 CCD sensors 24 baffle 31 Case 32 Incidence part 33 Exit section 34 Optical Fiber 35 Photoelectric conversion element 41 Recess 42 Convex part 49 Light source 50 Mirror 51 Reference plate 52 Secondary mirror section 53 Primary mirror 54 Reflector 55 detector L light

Claims

1. A reflecting telescope mounted on a small satellite, The reflecting telescope is a housing, and a primary mirror unit and a secondary mirror unit are assembled and fixed in the housing; the diameter of the reflecting surface of the secondary mirror is smaller than the diameter of the primary mirror, a Cassegrain reflecting telescope in which light from outside enters the housing, is reflected by the primary mirror and the secondary mirror in this order, and is then collected; the housing, the primary mirror section, and the secondary mirror section are formed of aluminum or an aluminum alloy; A reflecting telescope mounted on a small satellite.

2. A reflecting telescope mounted on a small satellite, The reflecting telescope is a housing; a photoelectric conversion element; and a primary mirror unit and a secondary mirror unit assembled and fixed in the housing; the diameter of the reflecting surface of the secondary mirror is smaller than the diameter of the primary mirror, a Cassegrain reflecting telescope for optical communications in which external light enters the housing, is reflected by the primary mirror and the secondary mirror in this order, and is then collected and received by the photoelectric conversion element; the housing, the primary mirror section, and the secondary mirror section are formed of aluminum or an aluminum alloy; A reflecting telescope mounted on a small satellite.

3. A reflecting telescope mounted on a small satellite, The reflecting telescope is a housing; a photoelectric conversion element; and a primary mirror unit and a secondary mirror unit assembled and fixed in the housing; the diameter of the reflecting surface of the secondary mirror is smaller than the diameter of the primary mirror, a Cassegrain reflecting telescope for optical communications, wherein light emitted by the photoelectric conversion element is reflected by the secondary mirror and the primary mirror in this order, and then emitted to the outside; the housing, the primary mirror section, and the secondary mirror section are formed of aluminum or an aluminum alloy; A reflecting telescope mounted on a small satellite.

4. 4. The reflecting telescope mounted on a small satellite according to claim 1, wherein the three-dimensional size of the housing of the reflecting telescope is 50 cm or less in length, width, and depth.

5. 4. The reflecting telescope mounted on a small satellite according to claim 1, wherein the transmitted wavefront accuracy of the reflecting telescope is less than 60 nm RMS.

6. 4. The reflecting telescope to be mounted on a small satellite according to claim 1, wherein the aluminum alloy is an Al-Mg-Si (6000) based aluminum alloy in which magnesium and silicon are added to aluminum.

7. 7. The reflecting telescope to be mounted on a small satellite according to claim 6, which is obtained by rapidly solidifying a molten liquid of an aluminum alloy.

8. A method for manufacturing a reflecting telescope mounted on a small satellite, comprising: The reflecting telescope is a housing, and a primary mirror unit and a secondary mirror unit are assembled and fixed in the housing; the diameter of the reflecting surface of the secondary mirror is smaller than the diameter of the primary mirror, a Cassegrain reflecting telescope in which light from outside enters the housing, is reflected by the primary mirror and the secondary mirror in this order, and is then collected; The housing, the primary mirror section, and the secondary mirror section are formed from aluminum or an aluminum alloy. A method for manufacturing a reflecting telescope to be mounted on a small satellite.

9. A method for manufacturing a reflecting telescope mounted on a small satellite, comprising: The reflecting telescope is a housing; a photoelectric conversion element; and a primary mirror unit and a secondary mirror unit assembled and fixed in the housing; the diameter of the reflecting surface of the secondary mirror is smaller than the diameter of the primary mirror, a Cassegrain reflecting telescope for optical communications in which external light enters the housing, is reflected by the primary mirror and the secondary mirror in this order, and is then collected and received by the photoelectric conversion element; The housing, the primary mirror section, and the secondary mirror section are formed from aluminum or an aluminum alloy. A method for manufacturing a reflecting telescope to be mounted on a small satellite.

10. A method for manufacturing a reflecting telescope mounted on a small satellite, comprising: The reflecting telescope is a housing; a photoelectric conversion element; and a primary mirror unit and a secondary mirror unit assembled and fixed in the housing; the diameter of the reflecting surface of the secondary mirror is smaller than the diameter of the primary mirror, a Cassegrain reflecting telescope for optical communications, wherein light emitted by the photoelectric conversion element is reflected by the secondary mirror and the primary mirror in this order, and then emitted to the outside; The housing, the primary mirror section, and the secondary mirror section are formed from aluminum or an aluminum alloy. A method for manufacturing a reflecting telescope to be mounted on a small satellite.

11. The manufacturing method of a reflecting telescope to be mounted on a small satellite according to any one of claims 8 to 10, wherein the reflective surfaces of the material of the primary mirror section and the secondary mirror section are obtained by diamond turning.

12. The secondary mirror is made by diamond turning the reflective surface of the material to obtain the primary reflecting surface. The method for manufacturing a reflecting telescope to be mounted on a small satellite according to claim 11, further comprising polishing the reflecting telescope by magnetic fluid polishing to obtain a secondary reflecting surface.

13. The primary mirror has a reflective surface made of diamond-turned material. The transmitted wavefront accuracy of the reflecting telescope is measured by a laser interferometer, and the measured transmitted wavefront accuracy is adjusted to be equal to or less than a predetermined transmitted wavefront accuracy. The method for manufacturing a reflecting telescope to be mounted on a small satellite according to claim 11, wherein only the secondary mirror portion is polished by magnetic fluid polishing to obtain a secondary reflecting surface.

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