Background
In the known inertial navigation equipment, the star sensor is used as a measuring instrument with the highest measuring precision, the measuring precision can reach a sub-second level or even higher, the measuring precision does not drift along with time, and stable three-axis attitude angle information output is provided for long-time high-precision flight of an aerospace craft, so that the star sensor is widely applied to the field of high-precision autonomous navigation.
The star sensor optical system is used as a core device of the star sensor and is a key component for realizing high-signal-to-noise ratio constant star spectral energy collection and high-precision star centroid position detection by the star sensor. The object detected by the star sensor optical system is a fixed star with weak energy and wide spectral distribution, and belongs to point target detection. In order to realize sub-pixel subdivision and improve the star position measurement precision, the star light energy needs to be dispersed to 2 x 2 pixels to 5 x 5 pixels for subsequent electronics to carry out subdivision processing so as to achieve the centroid measurement precision of the sub-pixels.
The main parameters of the star sensor optical system comprise focal length, field of view, relative aperture, imaging spectrum, single star measurement accuracy and the like. The focal length of the star sensor optical system is inversely proportional to the single star measurement precision, and the longer the focal length is, the higher the measurement precision is. The focal length of the optical system of the current mainstream star sensor is generally not more than 50mm, most of the focal length is concentrated in the range of 20 mm-30 mm, the detection view field is larger, the detection spectrum range is generally not more than 300nm, the measurement precision of a single star is not high, and the detection capability of the fixed star is limited. In order to pursue higher star detection accuracy, the adoption of a long-focus optical system is an effective means. With the development of the technologies in the fields of high-resolution earth stereo mapping cameras, space astronomical observation telescopes, space guidance weapon systems and the like, the requirements on the star sensor with the sub-second level or even higher precision are provided, and the key performances of high-precision earth positioning, long-time image-stabilized observation or autonomous navigation of flight attitude during long voyage and the like of an application system are met. The core technology is that a long-focus star sensor optical system is adopted to improve the single-pixel resolution, and then a subdivision algorithm is adopted to further improve the accuracy of the centroid resolution.
However, when the focal length of the optical system of the star sensor is close to or reaches the meter level, the pure transmission optical system is not only long in system size, but also difficult to correct the secondary spectral aberration under the broad spectrum, and cannot realize collection of the stellar optical signal of the broad spectrum, and the application requirements of the space platform cannot be met in terms of both the size and the performance; although the reflection type optical system can realize the folding of the optical path and obtain the compact layout design of the optical system, the aspheric surface is needed to be adopted in the aspect of correcting the aberration, the manufacturing and adjusting difficulty is high, and the cost is not reduced.
SUMMERY OF THE UTILITY MODEL
The utility model discloses the technical problem that the type will be solved is: the conventional star sensor optical system realizes high precision and long system size, and is difficult to correct secondary spectrum aberration under a wide spectrum.
The utility model provides a super wide spectral length long focus star sensor optical system improves spectral range and measurement accuracy, shortens optical system's length dimension simultaneously by a wide margin, effectively realizes lightly small-size.
The utility model provides a solution of its technical problem is:
an optical system of a super-wide-spectrum long-focus star sensor comprises a front lens group, a reflector group, a rear lens group and an image plane which are sequentially arranged from front to back along a light incidence direction, wherein the front lens group comprises a first lens and a second lens which are sequentially arranged from front to back, and the rear lens group comprises a third lens and a fourth lens which are sequentially arranged from front to back; the first lens is a biconvex positive focal power lens, the second lens is a meniscus negative focal power lens, the third lens is a biconcave negative focal power lens, the fourth lens is a meniscus positive focal power lens, and the third lens and the fourth lens form a double cemented lens; the secondary reflector and the main reflector are spherical;
the reflector group comprises a secondary reflector and a main reflector which are sequentially arranged from front to back, the secondary reflector is a convex reflector, the main reflector is a concave reflector, the reflecting surfaces of the secondary reflector and the main reflector are opposite, and a through hole is formed in the middle of the main reflector; an aperture diaphragm is arranged on the reflecting surface of the main reflecting mirror;
incident light sequentially passes through the first lens and the second lens and then is emitted to the main reflector, light beams are reflected by the main reflector and reach the secondary reflector, the secondary reflector reflects the light beams to form reflected light, and the reflected light sequentially passes through the third lens and the fourth lens after passing through the through hole of the main reflector.
The utility model has the advantages that: the optical system adopts a catadioptric optical system structure type, and the light path is folded by two reflectors, so that the length size of the long-focus star sensor optical system is greatly shortened, the light and the small are effectively realized, and the collection efficiency of the stellar optical signals is improved.
The first lens, the second lens, the third lens and the fourth lens are all spherical surface type.
The utility model discloses optical system focal power distribution is reasonable, and the structure is well-balanced, and all lenses and speculum are the spherical surface type, and manufacturing and assembly tolerance are loose more, reduce the processing degree of difficulty and the dress and transfer the degree of difficulty, are favorable to improving long focus star sensor optical system's manufacturability and assembly yield.
As a further improvement of the above technical solution, the focal power of the first lens is
The focal power of the second lens is
The optical system has an optical power of
Then
And
satisfies the following conditions:
as a further improvement of the technical scheme, the combined focal power of the reflector group is
The optical system has an optical power of
Then
And
satisfies the following conditions:
as a further improvement of the technical scheme, the combined focal power of the rear lens group is
The optical system has an optical power of
Then
And
satisfies the following conditions:
as a further improvement of the above technical solution, the total length of the optical system is L, where L is a 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。
as a further improvement of the technical scheme, the curvature radius of the front surface of the first lens is 3488.5mm, the curvature radius of the rear surface of the first lens is-783.6 mm, the center thickness of the first lens is 11mm, and the light-passing portHas a diameter of
The curvature radius of the front surface of the second lens is-266.7 mm, the curvature radius of the rear surface of the second lens is-455.6 mm, the center thickness of the second lens is 7mm, and the aperture of the light-transmitting aperture is
The curvature radius of the secondary reflector is-141.6 mm; the curvature radius of the main reflector is-406.8 mm; the curvature radius of the front surface of the third lens is-77.8 mm, the curvature radius of the rear surface of the third lens is 37.8mm, and the center thickness of the third lens is 7 mm; the radius of curvature of the front surface of the fourth lens is 37.8mm, the radius of curvature of the rear surface of the fourth lens is 90.1mm, and the center thickness of the fourth lens is 5 mm.
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.
The optical system adopts a catadioptric optical system structure type, and the light path is folded by two reflectors, so that the design result that the length of the optical system is far smaller than the focal length can be obtained, the lightness and the miniaturization are effectively realized, the image quality close to the diffraction limit is realized, and the collection efficiency of the stellar optical signal is improved.
Embodiment 1, referring to fig. 1, an optical system of a super-wide-band long-focus star sensor includes a front lens group 100, a reflector group 200, a rear lens group 300, and an image plane 400, which are sequentially arranged from front to back along a light incidence direction, where the front lens group 100 includes a first lens 101 and a second lens 102, which are sequentially arranged from front to back, and the rear lens group 300 includes a third lens 301 and a fourth lens 302, which are sequentially arranged 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;
the reflector group 200 comprises a secondary reflector 201 and a main reflector 202 which are sequentially arranged from front to back, wherein the secondary reflector 201 is a convex reflector, the main reflector 202 is a concave reflector, the reflecting surfaces of the secondary reflector 201 and the main reflector 202 are opposite, and a through hole 203 is formed in the middle of the main reflector 202; an aperture diaphragm 204 is arranged on the reflecting surface of the main reflecting mirror 202;
incident light sequentially passes through the first lens 101 and the second lens 102 and then is emitted to the main reflector 202, light beams are reflected by the main reflector 202 and reach the secondary reflector 201, the secondary reflector 201 reflects the light beams to form reflected light, the reflected light passes through the through hole 203 of the main reflector 202 and then sequentially passes through the third lens 301 and the fourth lens 302, and finally an image is formed on the image surface 400.
The through hole 203 is for reflected light formed by the sub-mirror 201.
The combined 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-split lens.
The secondary reflector 201 and the primary reflector 202 are all spherical, and the first lens 101, the second lens 102, the third lens 301 and the fourth lens 302 are all spherical, so that the difficulty and the cost of processing and detection are reduced, and the manufacturing and the detection of all optical elements can be realized by adopting a conventional processing technology.
In operation, a starry optical signal first passes through the front lens group 100 with a combined focal power close to zero, the light propagation direction is substantially unchanged, then the optical signal is collected through the spherical secondary mirror 201 and the spherical primary mirror 202, and the mirror group 200 bears the primary focal power of the optical system. Since the sub mirror 201 and the main mirror 202 are both spherical, a large amount of aberrations such as spherical aberration, coma, and the like are generated, and these aberrations are mainly corrected by the front lens group 100. When the focal power of the current lens group 100 is close to zero, even if the same glass material is adopted, the generated axial chromatic aberration and vertical axis chromatic aberration are both very small, and the reflector group 200 does not generate chromatic aberration, thereby laying a foundation for the optical system to realize the collection of optical signals in an ultra-wide spectrum band. The residual spherical aberration, coma aberration and chromatic aberration are corrected by the small-aperture double cemented lens of the rear lens group.
The optical system adopts a catadioptric optical system structure type, and the light path is folded by two reflectors, so that the length size of the long-focus star sensor optical system is greatly shortened, the lightness and the miniaturization are effectively realized, the image quality close to the diffraction limit is realized, and the collection efficiency of the stellar optical signals is improved.
Further as a 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:
L/f≤0.275。
the optical system adopts the reflector group 200 to realize light path folding, and the size of the optical system is shortened.
The reflecting surface of the secondary mirror 201 is a surface that reflects an incident light beam, and the reflecting surface of the primary mirror 202 is also a surface that reflects an incident light beam.
The optical system adopts a catadioptric optical system structure type, avoids the problem that the pure transmission type optical system is difficult to correct wide spectrum chromatic aberration, particularly secondary spectrum under the condition of long focal length design, and can obtain very compact structure layout. The light path is folded by the two reflectors, so that the design result that the length of the optical system is far shorter than the focal length can be obtained, and the long-focal-length optical system can be applied to a space flight platform with severe requirements on importance and size.
Further preferably, the
first lens 101 has an optical power of
The focal power of the
second lens 102 is
The optical system has an optical power of
Then
And
satisfies the following conditions:
further preferably, the combined focal power of the
reflector set 200 is
The optical system has an optical power of
Then
And
satisfies the following conditions:
further preferably, the combined power of the
rear lens group 300 is
The optical system has an optical power of
Then
And
satisfies the following conditions:
in a further preferred embodiment, the
first lens 101 has a front surface curvature radius of 3488.5mm, a rear surface curvature radius of-783.6 mm, a center thickness of 11mm, and a clear aperture of
The radius of curvature of the front surface of the
second lens 102 is-266.7 mm, the radius of curvature of the rear surface is-455.6 mm, the center thickness is 7mm, and the aperture of the light transmission aperture is
The curvature radius of the
secondary reflector 201 is-141.6 mm; the radius of curvature of the
primary mirror 202 is-406.8 mm; the radius of curvature of the front surface of the
third lens 301 is-77.8 mm, the radius of curvature of the rear surface of the third lens is 37.8mm, and the center thickness of the third lens is 7 mm; the
fourth lens 302 has a front surface curvature radius of 37.8mm, a rear surface curvature radius of 90.1mm, and a center thickness of 5 mm.
In a 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.
In this embodiment, the first lens 101 and the second lens 102 are made of the same crown glass.
The distance between the rear surface of the first lens 101 and the front surface of the second lens 102 is 8mm, the distance between the rear surface of the second lens 102 and the front surface of the main reflector 202 is 157.2mm, the distance between the front surface of the main reflector 202 and the rear surface of the secondary reflector 201 is 152.2mm, the distance between the rear surface of the secondary reflector 201 and the front surface of the third lens 301 is 160.8mm, and the distance between the rear surface of the fourth lens 302 and the image plane 400 is 14.1 mm.
The technical indexes of the optical system of the ultra-wide spectrum long-focus star sensor in the embodiment are as follows:
focal length: 795 mm;
relative pore diameter: f/6.8;
visual field: 1.5 degrees;
spectral range: 450 nm-1100 nm;
relative distortion: less than or equal to 0.001 percent;
total optical length: less than or equal to 213.3 mm.
The optical system achieves a single pixel resolution accuracy of 1.38 "when matched to a cmos detector having a pixel size of 5.5 μm.
Referring to fig. 2, fig. 2 represents the optical transfer function curve distribution of the whole optical system in the example of the present invention, the average optical transfer function value of the optical system reaches above 0.45 at 50lp/mm, which is close to the diffraction limit image quality, and the imaging quality is excellent.
Referring to fig. 3, fig. 3 depicts an energy concentration profile of an optical system in an example of the invention, except for the edge field of view
The energy concentration ratio in the range reaches more than 80%, and the stellar optical signals are well gathered.
Referring to fig. 4, fig. 4 represents the relative distortion design result of the optical system in the example of the present invention, the distortion is not more than 0.001%, and is close to zero, thereby avoiding the measurement error of the star position caused by the distortion.
The utility model discloses optical system designs compactly, realizes the high folding of light path under the long focus, avoids big colour difference optical element's use, realizes the design of low colour difference and second grade spectrum, obtains the spectrum detection of super wide spectral length. Simultaneously the utility model discloses optical system adopts global face optical element, reduces processing and manufacturing cost by a wide margin, realizes being close to diffraction limit's image matter, improves the stellar light signal collection efficiency.
While the preferred embodiments of the present invention have been described in detail, it will be understood by those skilled in the art that the invention is not limited to the details of the embodiments shown, but is capable of various modifications and substitutions without departing from the spirit of the invention.