An optical system for ultra-wide spectrum and long focal length star sensor

Abstract

The invention discloses an ultra-wide spectrum band long focal length star sensor optical system, comprising a front lens group, a reflector group, a rear lens group and an image plane arranged in sequence from front to back along a light incident direction, wherein the front lens group comprises a first lens and a second lens arranged in sequence from front to back, and the rear lens group comprises a third lens and a fourth lens arranged in sequence from front to back; the reflector group comprises a secondary reflector and a primary reflector arranged in sequence from front to back, wherein the secondary reflector is a convex reflector and the primary reflector is a concave reflector; the optical system adopts a catadioptric optical system structure based on a spherical optical element, and by folding an optical path with two reflectors, a design result can be obtained in which the length of the optical system is much smaller than the focal length, thereby effectively realizing lightness and miniaturization and improving the efficiency of collecting star light signals.

Description

Technical Field

[0001] The present invention relates to the technical field of optical systems, and more particularly to an ultra-wide spectrum and long focal length star sensor optical system. Background Art

[0002] Among the known inertial navigation devices, star sensors are one of the most accurate measuring instruments, with a measurement accuracy of sub-second or even higher. The measurement accuracy does not drift over time, and provides stable three-axis attitude angle information output for long-term and high-precision flight of spacecraft. Therefore, they have been widely used in the field of high-precision autonomous navigation.

[0003] As the core device of the star sensor, the star sensor optical system is a key component for the star sensor to achieve high signal-to-noise ratio star spectrum energy collection and high-precision star center of mass position detection. The star sensor optical system detects stars with weak energy and wide spectral distribution, which belongs to point target detection. In order to achieve sub-pixel segmentation and improve the accuracy of star position measurement, it is necessary to disperse the starlight energy into 2×2 pixels to 5×5 pixels for subsequent electronic segmentation processing to achieve sub-pixel center of mass measurement accuracy.

[0004] The main parameters of the star sensor optical system include focal length, field of view, relative aperture, imaging spectrum, and single star measurement accuracy. The focal length of the star sensor optical system is inversely proportional to the single star measurement accuracy. The longer the focal length, the higher the measurement accuracy. The focal length of the current mainstream star sensor optical system generally does not exceed 50mm, and most of them are concentrated in the range of 20mm to 30mm. The detection field of view is relatively large, the detection spectrum range generally does not exceed 300nm, the single star measurement accuracy is not high, and the star detection capability is relatively limited. In order to pursue higher star detection accuracy, the use of long-focal-length optical systems is an effective means. With the development of technologies in the fields of high-resolution stereo mapping cameras, space astronomical observation telescopes, and space-guided weapon systems, there is a demand for sub-second or even higher-precision star sensors to meet the key performance requirements of high-precision ground positioning, long-term image stabilization observation, or autonomous navigation of long-duration flight attitudes in the application system. The core technology is to use a long-focal-length star sensor optical system to improve the resolution of a single pixel, and then use a subdivision algorithm to further improve the accuracy of the centroid resolution.

[0005] However, when the focal length of the star sensor optical system approaches or reaches the meter level, the pure transmission optical system not only has a long system size, but also has difficulty in correcting secondary spectral aberrations under a wide spectrum, and cannot realize the collection of wide-spectrum star light signals. It cannot meet the application requirements of the space platform in terms of size or performance. Although the reflective optical system can realize light path folding and obtain a compact optical system layout design, it needs to use aspherical surfaces to correct aberrations, which are difficult to manufacture and assemble, and are not conducive to reducing costs. Summary of the invention

[0006] The technical problem to be solved by the present invention is that the existing star sensor optical system has a long system size while achieving high precision, and it is difficult to correct the secondary spectral aberration under a wide spectrum.

[0007] The present invention provides an ultra-wide spectrum band long focal length star sensor optical system, which improves the spectral range and measurement accuracy, while greatly shortening the length of the optical system, effectively achieving lightness and compactness.

[0008] The solution of the present invention to solve its technical problem is:

[0009] An ultra-wide spectrum band long focal length star sensor optical system, comprising a front lens group, a reflector group, a rear lens group and an image plane arranged in sequence from front to back along a light incident direction, the front lens group comprises a first lens and a second lens arranged in sequence from front to back, the rear lens group comprises a third lens and a fourth lens arranged in sequence from front to back; the first lens is a biconvex positive power lens, the second lens is a meniscus negative power lens, the third lens is a biconcave negative power lens, the fourth lens is a meniscus positive power lens, the third lens and the fourth lens form a double cemented lens; the secondary reflector and the primary reflector are both spherical;

[0010] The reflector group comprises a secondary reflector and a main reflector which are arranged in sequence from front to back, the secondary reflector is a convex reflector, the main reflector is a concave reflector, the reflective surfaces of the secondary reflector and the main reflector are opposite, a through hole is opened in the middle of the main reflector; an aperture stop is arranged on the reflective surface of the main reflector;

[0011] The incident light passes through the first lens and the second lens in sequence and then is emitted to the primary reflector. The light beam is reflected by the primary reflector and reaches the secondary reflector. The secondary reflector reflects the light beam to form reflected light. The reflected light passes through the through hole of the primary reflector and then passes through the third lens and the fourth lens in sequence.

[0012] The beneficial effects of the present invention are as follows: the optical system adopts a catadioptric optical system structure, and folds the light path through two reflectors, thereby greatly shortening the length of the optical system of the long-focal-length star sensor, effectively realizing lightweight and miniaturization, and improving the efficiency of collecting star light signals.

[0013] The first lens, the second lens, the third lens and the fourth lens are all spherical.

[0014] The optical system of the present invention has reasonable focal power distribution and symmetrical structure. All lenses and reflectors are spherical. The processing, manufacturing and assembly tolerances are relatively loose, which reduces the difficulty of processing and assembly, and is conducive to improving the manufacturability and assembly yield of the long-focal-length star sensor optical system.

[0015] As a further improvement of the above technical solution, the optical power of the first lens is The optical power of the second lens is The optical power of the optical system is but and satisfy:

[0016]

[0017]

[0018] As a further improvement of the above technical solution, the combined optical power of the reflector group is The optical power of the optical system is but and satisfy:

[0019]

[0020] As a further improvement of the above technical solution, the combined focal length of the rear lens group is The optical power of the optical system is but and satisfy:

[0021]

[0022] As a further improvement of the above technical solution, the total length of the optical system is L, where L is the distance from the front surface of the first lens to the image plane, and the focal length of the optical system is f, then L and f satisfy:

[0023] L / f≤0.275.

[0024] As a further improvement of the above technical solution, the first lens has a front surface curvature radius of 3488.5 mm, a rear surface curvature radius of -783.6 mm, a center thickness of 11 mm, and a light aperture of The front surface curvature radius of the second lens is -266.7mm, the rear surface curvature radius is -455.6mm, the center thickness is 7mm, and the light aperture is The curvature radius of the secondary reflector is -141.6mm; the curvature radius of the primary reflector is -406.8mm; the front surface curvature radius of the third lens is -77.8mm, the rear surface curvature radius is 37.8mm, and the center thickness is 7mm; the front surface curvature radius of the fourth lens is 37.8mm, the rear surface curvature radius is 90.1mm, and the center thickness is 5mm.

[0025] As a further improvement of the above technical solution, the first lens and the second lens are made of crown glass, the third lens is made of crown glass, and the fourth lens is made of heavy lanthanum flint glass.

[0026] This optical system adopts a catadioptric optical system structure. By folding the light path through two reflectors, the optical system length can be designed to be much smaller than the focal length, effectively realizing lightweight and miniaturization, achieving image quality close to the diffraction limit, and improving the efficiency of star light signal collection. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly describes the drawings required for use in the description of the embodiments. Obviously, the drawings described are only part of the embodiments of the present invention, not all of the embodiments, and those skilled in the art can also obtain other design solutions and drawings based on these drawings without creative work.

[0028] Figure 1 Schematic diagram of the composition structure of the optical system of this embodiment;

[0029] Figure 2 is the optical transfer function curve of the optical system of this embodiment;

[0030] Figure 3 is the energy concentration curve of the optical system of this embodiment;

[0031] Figure 4 It is the distortion design curve of the optical system of this embodiment. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the concept, specific structure and technical effects of the present invention in combination with the embodiments and drawings, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by technicians in this field without creative work are all within the scope of protection of the present invention. In addition, all the connection relationships mentioned in the text do not refer to the direct connection of components, but refer to the fact that a better connection structure can be formed by adding or reducing connecting accessories according to the specific implementation situation. The various technical features in the invention can be combined interchangeably without conflicting with each other.

[0033] Example 1, reference Figure 1, an ultra-wide spectrum long focal length star sensor optical system, comprising a front lens group 100, a reflector group 200, a rear lens group 300 and an image plane 400 arranged in sequence from front to back along the light incident direction, the front lens group 100 comprises a first lens 101 and a second lens 102 arranged in sequence from front to back, the rear lens group 300 comprises a third lens 301 and a fourth lens 302 arranged in sequence from front to back; the first lens 101 is a biconvex positive power lens, the second lens 102 is a meniscus negative power lens, the third lens 301 is a biconcave negative power lens, the fourth lens 302 is a meniscus positive power lens, and the third lens 301 and the fourth lens 302 form a double cemented lens;

[0034] The reflector assembly 200 includes a secondary reflector 201 and a primary reflector 202 which are arranged in sequence from front to back. The secondary reflector 201 is a convex reflector, and the primary reflector 202 is a concave reflector. The reflective surfaces of the secondary reflector 201 and the primary reflector 202 are opposite to each other. A through hole 203 is opened in the middle of the primary reflector 202. An aperture stop 204 is arranged on the reflective surface of the primary reflector 202.

[0035] The incident light passes through the first lens 101 and the second lens 102 in sequence and then is emitted to the primary reflector 202. The light beam is reflected by the primary reflector 202 and reaches the secondary reflector 201. The secondary reflector 201 reflects the light beam to form reflected light. The reflected light passes through the through hole 203 of the primary reflector 202 and then passes through the third lens 301 and the fourth lens 302 in sequence, and finally forms an image on the image plane 400.

[0036] The through hole 203 is used for reflecting light formed by the secondary reflector 201 to pass through.

[0037] The combined optical power of the front lens group 100 is close to zero, and the first lens 101 and the second lens 102 in the front lens group 100 form a double separated lens.

[0038] The secondary reflector 201 and the primary reflector 202 are both spherical, and the first lens 101, the second lens 102, the third lens 301 and the fourth lens 302 are all spherical, which reduces the difficulty and cost of processing and testing, and all optical components can be manufactured and tested using conventional processing technology.

[0039] When working, the starlight signal first passes through the front lens group 100 with a combined focal power close to zero, and the light propagation direction remains basically unchanged. Then, the light signal is gathered through the spherical secondary reflector 201 and the main reflector 202. The reflector group 200 bears the main focal power of the optical system. Since the secondary reflector 201 and the main reflector 202 are both spherical, a large number of aberrations such as spherical aberration and coma are generated, and these aberrations are mainly corrected by the front lens group 100. When the focal power of the front lens group 100 is close to zero, even if the same glass material is used, the axial chromatic aberration and vertical chromatic aberration generated are very small, and the reflector group 200 does not produce chromatic aberration, which lays the foundation for the optical system to realize the collection of ultra-wide spectrum light signals. The residual spherical aberration, coma and chromatic aberration are corrected by the small-diameter double cemented lens of the rear lens group.

[0040] This optical system adopts a catadioptric optical system structure. It folds the light path through two reflectors, greatly shortening the length of the optical system of the long-focal-length star sensor, effectively realizing lightweight and miniaturization, achieving image quality close to the diffraction limit, and improving the efficiency of collecting star light signals.

[0041] As a further preferred embodiment, the total length of the optical system is L, where L is the distance from the front surface of the first lens 101 to the image plane 400, and the focal length of the optical system is f, then L and f satisfy:

[0042] L / f≤0.275.

[0043] The optical system adopts the reflector group 200 to realize the folding of the light path and shorten the size of the optical system.

[0044] The reflection surface of the secondary reflection mirror 201 is a surface for reflecting the incident light beam, and the reflection surface of the primary reflection mirror 202 is also a surface for reflecting the incident light beam.

[0045] This optical system adopts a catadioptric optical system structure, which avoids the difficulty of using a pure transmission optical system to correct wide spectrum chromatic aberration, especially the secondary spectrum, in a long focal length design, and can obtain a very compact structural layout. By folding the light path with two reflectors, the design result of the optical system length being much smaller than the focal length can be obtained, which makes it possible to apply the long focal length optical system to space flight platforms with strict requirements on importance and size.

[0046] As a further preferred embodiment, the optical power of the first lens 101 is The optical power of the second lens 102 is The optical power of the optical system is but and satisfy:

[0047]

[0048]

[0049] As a further preferred embodiment, the combined optical power of the reflector assembly 200 is The optical power of the optical system is but and satisfy:

[0050]

[0051] As a further preferred embodiment, the combined optical power of the rear lens group 300 is The optical power of the optical system is but and satisfy;

[0052]

[0053] As a further preferred embodiment, the first lens 101 has a front surface curvature radius of 3488.5 mm, a rear surface curvature radius of -783.6 mm, a center thickness of 11 mm, and a light aperture of The second lens 102 has a front surface curvature radius of -266.7 mm, a rear surface curvature radius of -455.6 mm, a center thickness of 7 mm, and a light aperture of The curvature radius of the secondary reflector 201 is -141.6 mm; the curvature radius of the primary reflector 202 is -406.8 mm; the front surface curvature radius of the third lens 301 is -77.8 mm, the rear surface curvature radius is 37.8 mm, and the center thickness is 7 mm; the front surface curvature radius of the fourth lens 302 is 37.8 mm, the rear surface curvature radius is 90.1 mm, and the center thickness is 5 mm.

[0054] As a further preferred embodiment, the first lens 101 and the second lens 102 are made of crown glass, the third lens 301 is made of crown glass, and the fourth lens 302 is made of heavy lanthanum flint glass.

[0055] In this embodiment, the first lens 101 and the second lens 102 are made of the same crown glass.

[0056] The distance between the rear surface of the first lens 101 and the front surface of the second lens 102 is 8 mm, the distance between the rear surface of the second lens 102 and the front surface of the primary reflector 202 is 157.2 mm, the distance between the front surface of the primary reflector 202 and the rear surface of the secondary reflector 201 is 152.2 mm, the distance between the rear surface of the secondary reflector 201 and the front surface of the third lens 301 is 160.8 mm, and the distance between the rear surface of the fourth lens 302 and the image plane 400 is 14.1 mm.

[0057] The technical indicators achieved by the ultra-wide spectrum long focal length star sensor optical system in this embodiment are:

[0058] Focal length: 795mm;

[0059] Relative aperture: F / 6.8;

[0060] Field of view: 1.5°;

[0061] Spectral range: 450nm~1100nm;

[0062] Relative distortion: ≤0.001%;

[0063] Total optical length: ≤213.3mm.

[0064] When the optical system is matched with a CMOS detector with a pixel size of 5.5μm, the single pixel resolution accuracy reaches 1.38″.

[0065] refer to Figure 2 , Figure 2 The optical transfer function curve distribution of the entire optical system in the example of the present invention is characterized. The average optical transfer function value of the optical system reaches above 0.45 at 50lp / mm, which is close to the diffraction limited image quality and has excellent imaging quality.

[0066] refer to Figure 3 , Figure 3 The energy concentration curve distribution of the optical system in the embodiment of the present invention is characterized. Except for the edge field of view, The energy concentration within the range reaches more than 80%, and the stellar light signals are well concentrated.

[0067] refer to Figure 4 , Figure 4 The relative distortion design result of the optical system in the example of the present invention is characterized, and the distortion does not exceed 0.001%, which is close to zero, thereby avoiding the measurement error of the star position caused by the distortion.

[0068] The optical system of the present invention is compactly designed, and the optical path is highly folded under long focal length, avoiding the use of optical elements with large chromatic aberration, realizing the design of low chromatic aberration and secondary spectrum, and obtaining spectrum detection of ultra-wide spectrum. At the same time, the optical system of the present invention adopts full-spherical optical elements, which greatly reduces the processing and manufacturing costs, achieves image quality close to the diffraction limit, and improves the collection efficiency of star light signals.

[0069] The preferred embodiments of the present invention are specifically described above, but the invention is not limited to the embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. An ultra-wide spectrum long focal length star sensor optical system, characterized in that: it comprises a front lens group, a reflector group, a rear lens group and an image plane arranged in sequence from front to back along the light incident direction, the front lens group comprises a first lens and a second lens arranged in sequence from front to back, the rear lens group comprises a third lens and a fourth lens arranged in sequence from front to back; the first lens is a biconvex positive power lens, the second lens is a meniscus negative power lens, the third lens is a biconcave negative power lens, the fourth lens is a meniscus positive power lens, and the third lens and the fourth lens form a double cemented lens; The reflector group comprises a secondary reflector and a primary reflector which are arranged in sequence from front to back, the secondary reflector is a convex reflector, the primary reflector is a concave reflector, the reflective surfaces of the secondary reflector and the primary reflector are opposite, a through hole is opened in the middle of the primary reflector; an aperture stop is arranged on the reflective surface of the primary reflector; the secondary reflector and the primary reflector are both spherical; The incident light passes through the first lens and the second lens in sequence and then is emitted to the primary reflector. The light beam is reflected by the primary reflector and reaches the secondary reflector. The secondary reflector reflects the light beam to form reflected light. The reflected light passes through the through hole of the primary reflector and then passes through the third lens and the fourth lens in sequence. The focal power of the first lens is φA1, the focal power of the second lens is φA2, and the focal power of the optical system is φ, then φA1, φA2 and φ satisfy: 0.45≤φA1 / φ≤0.65; -0.65≤φA2 / φ≤-0.45; The combined focal power of the reflector group is φB, and the focal power of the optical system is φ, then φB and φ satisfy: 1.1≤φB / φ≤1.

25.

2. The ultra-wide spectrum long focal length star sensor optical system according to claim 1, characterized in that: The combined focal power of the rear lens group is φC, and the focal power of the optical system is φ, then φC and φ satisfy: -11.5≤φC / φ≤-10.

5.

3. The ultra-wide spectrum long focal length star sensor optical system according to claim 1, characterized in that: The total length of the optical system is L, where L is the distance from the front surface of the first lens to the image plane, and the focal length of the optical system is f, then L and f satisfy: L / f≤0.

275.

4. The ultra-wide spectrum long focal length star sensor optical system according to claim 1, characterized in that: The front surface curvature radius of the first lens is 3488.5mm, the rear surface curvature radius is -783.6mm, the center thickness is 11mm, and the light-clearing aperture is φ120.5mm; the front surface curvature radius of the second lens is -266.7mm, the rear surface curvature radius is -455.6mm, the center thickness is 7mm, and the light-clearing aperture is φ120.9mm; the curvature radius of the secondary reflector is -141.6mm; the curvature radius of the main reflector is -406.8mm; the front surface curvature radius of the third lens is -77.8mm, the rear surface curvature radius is 37.8mm, and the center thickness is 7mm; the front surface curvature radius of the fourth lens is 37.8mm, the rear surface curvature radius is 90.1mm, and the center thickness is 5mm.

5. The ultra-wide spectrum long focal length star sensor optical system according to claim 1, characterized in that: The first lens and the second lens are made of crown glass, the third lens is made of crown glass, and the fourth lens is made of heavy lanthanum flint glass.

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