RU2517979C1 - Optical solar sensor - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: sensor includes a wide-field input optical element, a coding mask, a light filter, a protective shield and a matrix photodetector. The input optical element is in form of a composite monoblock and has the shape of a quadrangular prism. The monoblock comprises a central prism in form of a quadrangular truncated regular pyramid, lateral faces of which have an absorbent coating and four identical lateral prisms in form of quadrangular irregular pyramids. One of the faces of each lateral prism has a mirror coating and that face is connected to the corresponding absorbent face of the central prism. The composite monoblock rests on the surface of the coding mask in which there is a central identification marker which is aligned with the axis of symmetry of the central prism and four identification markers which are symmetrically arranged around the central marker.

EFFECT: high accuracy of determining coordinates and providing uniformity of distribution of resolution of the sensor on the entire field of view.

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Description

The invention relates to static precision solar orientation devices (PIC), which are intended for use as part of orientation systems and autonomous navigation of spacecraft (SC).

The POS generates digital signals proportional to the deviation of the direction to the center of the Sun relative to the instrumental coordinate system and, paired with the instrument of orientation on the Earth, allows for triaxial stabilization of the spacecraft by roll, pitch and yaw. The widespread use of PIC in space technology is due to the fact that in near-Earth space solar radiation has a high intensity (133,000 lux) and a fairly small divergence of the radiation flux up to 32.5 minutes.

The prior art sensors of the position of the radiation source, made on a matrix photodetector (MFP), which are described in patent sources (US 4792245, IPC G01J 1/20, NPK 250/203, publ. 12/27/1988) / 1 /, (US 6853445, IPC G01J 1/20, NPK 35/121, publ. 02.08. 2005) / 2 /. Known devices provide control of the orientation of the spacecraft and contain a camera made with an input window in the form of slits or slits or with an input window in which a simple optical element is installed, an MFP, an electronic unit that generates a signal that represents the angle at which radiation falls on the sensor. Known sensors have a limited field of view, which is associated with the design of the input window and the optical properties of the MFP, which at large angles (more than 68 °) loses sensitivity. The use of MFPU in a static-type PIC in comparison with previous devices allows avoiding the complex design of the device (reducing weight, dimensions, power consumption), which is extremely important for onboard based devices on spacecraft.

Universal modern PIC should have a set of characteristics:

- hemispherical field of view;

- minimum dimensions, weight, power consumption;

- goniometric error of less than 1 arc minute over the entire field of view.

A typical precision POS contains a wide-field input optical element, a code mask on a glass plate, a photosensitive transducer with a protective glass, and interface electronics that converts current signals into digital signals arriving at the KA orientation control processor (US 6310336, NKI 250 / 203.4, publ. 30.10 .2001) / 3 /. The patent does not describe the design of the optical system of the sensor, but provides data on the accuracy of measuring the angular coordinates of the Sun, which it provides - 0.1 degrees, which is not enough for modern PIC.

The problem of obtaining a hemispherical field of view of 180 ° × 180 ° was solved in an optical solar sensor (US 5914483, IPC G01J 1/20, NPK 250 / 203.4, publ. 22. 06.1999) / 4 /, which contains a cylindrical lens with two input and output slots, protective lenses, photodetector line and information processing unit. A linear coordinate corresponding to a certain angle of incidence of the radiation is formed in the photodetector line when the spacecraft rotates, therefore, the known solar sensor cannot be used in stabilized spacecraft.

A known sensor of the angular coordinate of the Sun in the spacecraft coordinate system (RU 2244263 C1, IPC 7 G01C 21/24, G01J 1/20, publ. 10.011.2005) / 5 /, which contains an optical spectral filter, a slit mask, a multi-element photosensitive receiver, consisting from elementary photosensitive photodetectors located one after another on a second-order curve, which allows to exclude trigonometric calculations and expand the field of view. This sensor is not technologically advanced and has not found practical application.

The solar sensor (SU 1779932, 5 IPC G01C 21/24, publ. 07.12.92) / 6 / for expanding the field of view has a complex aperture made in the form of a spherical circle on which diffraction holes are located, connected to the photodetector by optical fibers. Due to the technological complexity of the implementation, the known sensor also did not find practical application.

The problems of implementing wide-angle lenses are reported in a review article (A.Ya. Gebgart. Design Features of Some Types of Extra-Wide-Angle Lenses. © 2010, OAO Geophysics-Cosmos, Moscow. Optical Journal, 77, 9, 2010, 05.05 .2010) / 7/111, which analyzes existing especially wide-angle lenses with an angular field of the order of 180 ° for static devices for orienting spacecraft on the Sun and the Earth and formulates lens requirements for such high-precision devices. Design features of these lenses are considered. The schemes of the developed four-lens lenses, which have almost the same sensor resolution over the entire field of view, are given and analyzed. The average angular pixel size of the Sun sensor using a wide-angle lens is about 11 angular minutes with a matrix format of 1024 × 1024 elements. With such an angular pixel size, it is very difficult to obtain an accuracy of determining the angular coordinates of less than 1 arc minute.

The closest analogue of the claimed invention for its intended purpose, the result achieved and the majority of coinciding essential features is the sensor of the angular position of the sun (RU 2308005 C1, 6 IPC G01C 21/24, G01J 1/20, date of publication. 10.10.2007) / 8 /, taken as prototype of the present invention. The sensor contains an optical system made in the form of a wide-angle lens, consisting of an input and output flat-convex lenses, between which there is a diaphragm (code mask), in the hole of which an optical element is located. The filter is located in front of the MFP, which is connected to the input of the information processing unit and calculates the angular coordinates. The optical element installed in the aperture opening and the ratio of refractive indices ensure the signal from the radiation source to the MFP within the hemisphere of the field of view without large losses of light flux due to the elimination of the effect of total internal reflection, and the use of a flat MFP makes the device cheap and technological.

However, the use of focusing optics elements in the form of an input and output plane-convex lenses in the design of a prototype sensor when a high-intensity solar radiation is incident on them, which is typical for near-Earth space, can lead to radiation focusing and failure of the MFP, which reduces the reliability of the sensor. Therefore, when designing a PIC, it is desirable to avoid the use of focusing optics.

The optical scheme of the sensor incorrectly shows the presence of refraction of the beam passing through the center of curvature of the output lens.

The disadvantages of the prototype sensor are not high enough accuracy in determining the angular coordinates of the Sun, which is due to:

- uneven distribution of the resolution of the sensor throughout the field of view 180 ° × 180 °;

- nonlinearity of the dependence of the displacement of the image of the code mask on the MFP on the angular coordinates of the Sun, which also leads to a decrease in the resolution of the sensor.

The optical system of the known sensor has an irreparable field curvature, which leads to a significant change in the size of the image of the diaphragm (code mask) from the center to the edge of the field of view.

The nonlinearity of the dependence of the displacement of the light radiation transmitted through the optical system on the angle of incidence is due to the fact that the light radiation passes through the diaphragm window in the center of curvature of the output lens, therefore, it is not refracted at the output of the lens and the amount of radiation displacement is determined by the formula: Δ = H · tgU ′ , where H is the distance from the center of curvature of the output lens to the plane of the sensitive areas of the MFP, U ′ is the angle of inclination of the radiation when exiting the output lens. In this case, the average angular pixel size with a matrix format of 1024 × 1024 elements is about 10 angular minutes, due to non-linearity at the edge of the field of view, the angular pixel size is 3-4 angular minutes, and in the center of the field of view 30-40 angular minutes.

The problem solved by the present invention is to increase the accuracy of determining the angular coordinates of the Sun in less than 1 arc minute over the entire field of view 190 ° × 190 ° by increasing the resolution of the sensor, as well as ensuring uniform distribution of resolution of the sensor throughout the field of view by eliminating non-linear dependence image mask code offsets on the MFP from the angle of incidence of light radiation.

These technical results are achieved by the fact that the optical solar sensor contains a sequentially wide-field input optical element made of radiation-resistant glass, a code mask, a light filter, a protective glass and an MFP, the output of which is connected to the information processing unit and calculates the angular coordinates.

According to the invention, the wide-field input optical element is made in the form of a composite monoblock and has the shape of a quadrangular prism, the side faces of which at a given angle β have a slope to the vertical axis of the composite monoblock, which contains a central prism connected by optical glue in the form of a quadrangular truncated regular pyramid, the apex of which facing down and has a predetermined angle α at its apex, the side faces of which have an absorbing coating, four identical identical prisms in the shape of a quadrilateral of irregular pyramids, one of the faces of each prism has a mirror coating and this face is connected to the corresponding absorbing face of the central prism, the composite monoblock rests on the surface of the code mask, in which the central identification marker is combined with the vertical axis of symmetry of the central prism, and four identification markers symmetrically located around the central identification marker for identifying light radiation from each of the side prisms, and a light filter contains two made of optical colored glass plate mounted on one another.

In a preferred embodiment, the optical solar sensor has the following differences:

- the angle α at the apex of the central prism is 66 °;

- the angle β of the inclination of the side faces of the composite monoblock to the vertical axis is 10 °;

- the code mask is made on a glass substrate, on the surface of which an opaque chromium layer is deposited by vacuum deposition, in which five transparent identification markers are made by photolithography;

- identification markers of the code mask are made in the form of quadrangular windows that differ in shape and size;

- the light filter selects the region of light radiation with an average wavelength λav = 650 nm;

- the upper plate of the filter is made of red optical glass;

- the bottom plate of the filter is made of blue-green optical glass;

- the mirror coating of the side prism is applied by vacuum deposition of aluminum and has a protective film of quartz;

- As an absorbent coating of the side faces of the central prism, black deep-mat enamel was used.

An optical solar sensor, in contrast to the prototype, allows to obtain not one but a composite field of view, which is formed by five prisms of a composite monoblock and for all field of view all the elements of the MFP are used, which allows to increase the resolution of the sensor in the entire field of view by more than 2.5 times compared to the prototype. The use of glass filters with a refractive index of about 1.5 provides a linear dependence of the magnitude of the displacement of the incident light radiation relative to the code mask in the range of angles of incidence of radiation up to 65 °.

The invention is illustrated by drawings, where:

Figure 1 shows a drawing of an optical solar sensor, cross section.

Figure 2 - optical solar sensor, section A-A.

Figure 3 - optical solar sensor, section bB.

4 is a code mask, section B-B.

Figure 5 - optical solar sensor, appearance, in a perspective view.

6 is a scan of a side prism.

7 is a field diagram of the optical solar sensor.

Fig - comparative graphs of the dependence of the magnitude of the image shift Δ / H, (in relative units) on the angle of incidence U (in angular degrees) of the incident light radiation, where H (in mm) is the distance between the code mask and the surface of the sensitive MFP units for the claimed invention (graph 1) and prototype (graph 2).

The optical solar sensor contains a wide-field input optical element made in the form of a composite monoblock and has the shape of a quadrangular prism (figure 5), the side faces of which at a given angle β have an inclination to the vertical axis of the composite monoblock (figure 2). The composite monoblock (Figs. 1-3) contains a central prism 1 interconnected by optical glue in the form of a quadrangular truncated regular pyramid, the apex of which is directed downward and has a given angle α at its apex, the side faces of which have an absorbing coating (not shown in the drawing) , four identical side prisms 2, 3, 4, 5 in the form of quadrangular irregular pyramids, one of the faces of each prism has a mirror coating (Fig.6) and this face is connected to the corresponding absorbing face of the central prism 1. Mirror cover One of the faces of each side prism 2, 3, 4, 5 is deposited by vacuum deposition of aluminum and has a protective quartz film. As an absorbing coating of the side faces of the central prism 1, black deep-mat enamel was used.

The composite candy bar rests on the surface of the code mask 6, which is mounted on a filter with an average wavelength λav = 650, which contains an upper plate 7 of red optical glass and a lower plate 8 of blue-green optical glass, which is installed on the protective glass 9 of the MFP 10, the output of which by terminals 11 is connected to an information processing unit and calculating angular coordinates (not shown in the drawing).

The code mask 6 is made on a glass substrate, on the surface of which an opaque chromium layer is deposited by vacuum deposition, in which five transparent identification markers 12, 13, 14, 15, 16 (Fig. 4) are made by photolithography, which differ in shape and size. The central identification marker 12 is aligned with the vertical axis of symmetry of the central prism 1 to identify the light radiation of the central prism 1, and four identification markers 13, 14, 15, 16 are symmetrically located around the central identification marker 12 to identify the light radiation from each of the side prisms 2, 3 , 4, 5, respectively.

In a preferred embodiment, the identification mask of the code mask is made in the form of rectangular windows that differ from each other in shape and size, while the clear boundaries of the rectangular windows make it easier to recognize them on the MFP. The location of the rectangular windows 13, 14, 15, 16 for the entrance of light radiation from the outputs of the side prisms 2, 3, 4, 5 is selected from the condition of their closest approximation to the axis of symmetry of the sensor, which is its sensitivity axis, taking into account the technological capabilities of this approximation.

In a specific example of an optical solar sensor, the angle α at the apex of the central prism 1 is 66 °; and the angle β of inclination of the side faces of the composite monoblock to the vertical axis is 10 °. To calculate the values of the angles α and β based on the given geometry of the path of the rays for the field of view of the sensor 190 ° × 190 ° of this type of square matrix and image on the matrix of a rectangular window, a specially developed program “Mathematical modeling of signal processing algorithms for a static solar orientation device” was used .

The optical solar sensor operates as follows. Each element of the composite monoblock forms its part of the field of view and each of the field of view enters the entire surface of the photosensitive areas of the MFP 10, which leads to a decrease in the pixel division price of the matrix and an increase in the resolution of the sensor by 2.5 times in comparison with the known sensors. As shown in the diagram of the sensor’s total field of view (Fig. 7), the field 17 is formed by the central prism 1 and is 100 °, the fields of view 18, 19, 20, 21 formed by each side prism 2, 3, 4, 5, respectively, are 50 ° × 100 °. The fields of view of the central and lateral zones slightly overlap with each other, which ensures continuity of orientation when moving from one zone to another. The angle α at the apex of the central prism 11 is 66 °, which provides a central field of view 17. The angle β of inclination of the outer faces of the side prisms 2, 3, 4, 5 to the vertical axis of the central truncated regular pyramid 1 is 10 °, which provides side fields of view 18, 19, 20, 21. The formation of the central zone 17 of the field of view is ensured by the passage of solar radiation through the central prism 1 and identification marker 12, filters 7 and 8, a protective glass 9 and hit of the transmitted radiation on the surface of sensitive areas of the MFP 10. The linear coordinates of the image of the marker 12 are uniquely associated with the angular coordinates of the center of the Sun relative to the coordinate system of the solar sensor. Using the linear coordinates of the marker position, the block for processing and calculating the angular coordinates performs calculations and provides the values of the angular coordinates of the Sun in digital form.

Light radiation, incident on one of the side faces of a composite monoblock, is refracted and reflected from the mirror inner face, passes through the identification marker 13, 14, 15, 16 (figure 4) of the code mask 6 corresponding to each side prism 2, 3, 4, 5 and passes through the glass plates 7 and 8 of the light filter, which attenuates the radiation of the Sun and selects a working spectral region with a wavelength λav = 650 nm, which allows the MFP 10 to work in its dynamic range. The absorbent coating on the side surface of the central prism 1 eliminates sun glare. The placement of glass filters 8, 9 with a glass refractive index of about 1.5 after the code mask 6 eliminates the inherent prototype tangential dependence of the displacement of the image of the code mask on the angle of incidence of light radiation U.

Fig. 8 shows comparative graphs of the dependence of the image displacement Δ / H (in relative units) on the incidence angle U (in angular degrees) of incident light radiation, where H (in mm) is the distance between the code mask and the surface of the sensitive areas of the matrix obtained by calculation for the claimed invention (graph 1) and prototype (graph 2). Graph 1 was obtained when registering light radiation transmitted through a medium with a refractive index of the order of 1.5 (glass) of thickness H, in mm. Under these conditions, the amount of displacement of the image of the code mask is determined by the formula:

$$\Delta =H\cdot \sin U/\sqrt{U^2-{\sin }^2}U$$

where U is the angle of incidence of light radiation on the code mask, in degrees.

Figure 2 is obtained in the presence of a gap of P, in mm, between the code mask and the surface of the sensitive areas of the MFP. The amount of displacement of the image of the code mask from the angle of incidence of light radiation is determined by the formula: Δ = P · tgU, where U is the angle of incidence of light radiation on the code mask, in degrees.

As follows from the graphs (Fig. 8), the non-linearity of the dependence of the displacement of the image of the code mask on the angle of incidence of light radiation for the invention (graph 1) is not more than 0.5%, and at the same time, for the prototype, the greatest non-linearity of this dependence in the presence of a gap is more than 20% for the angle of incidence U = 30 °. Therefore, reducing the non-linearity of the dependence of the displacement of the image of the code mask on the angle of incidence of light radiation compared with the prototype allows to obtain a uniform distribution of the resolution of the MFP over the entire surface of the photosensitive sites.

The composite field of view of the sensor is formed by five prisms and for each field of view the entire surface of the photosensitive areas of the matrix is used, which leads to an increase in resolution by more than 2.5 times compared to known sensors, due to the fact that the angular size of the pixel is reduced to 4 angular minutes for a matrix format of 1024 × 1024 elements over the entire field of view 190 ° × 190 °.

The manufacturing technology of the optical solar sensor is represented by the following operations. Surfaces of specified shapes and sizes are formed from optical radiation-resistant glass of the K208 brand, they are ground and polished to a cleanliness class in which the width of the scratches should not exceed 0.004 mm. On the surface of the workpieces specified by the configuration design of the composite monoblock, apply a mirror or absorbent coating. The resulting finished elements are assembled into a composite monoblock by gluing side prisms 2, 3, 4, 5 with absorbing faces of the central prism 1 and the other two faces between each other with optical adhesive of the OK-72 _FT15 state standard specification 1488-70 type. The base of the manufactured composite monoblock is combined and glued under an instrumental microscope with a code mask 6 and glued glass plates 7, 8 of the filter. The assembly made is fixed in the housing or glued to the protective glass 9 of the MFPU 10, the conclusions of which 11 are sealed in a printed circuit board. An optical solar sensor is placed in the housing and mounted on a seat outside the spacecraft.

Stage of readiness of the sensor for industrial use: preliminary documentation is developed and a prototype is made.

Estimated specifications for the optical solar sensor:

Field of view - 190 ° × 190 °;

Accuracy - not worse than 45 arc seconds across the entire field of view;

Dimensions - about 120 × 130 × 70 mm;

Weight - no more than 0.8 kg.

Information sources

1. US 4792245, IPC G01J 1/20, NPK 250/203, publ. 12/27/1988.

2. US 6853445, IPC G01J 1/20, NPK 35/121, publ. 08/02. 2005.

3. US 6310336, NKI 250 / 203.4, date publ. 10/30/2001.

4. US 5914483, IPC G01J 1/20, NPK 250 / 203.4, publ. 22.06.1999.

5. RU2244263 C1, IPC7 G01C 21/24, G01J 1/20, publ. 01/10/2001.

6. SU 1779932, 5 IPC G01C 21/24, publ. 12/07/92.

7. A.Ya. Gebgart. Design features of some types of extra wide angle lenses. © 2010 NPP Geofizika-Cosmos, Moscow, Optical Journal, 77, 9, 2010. 05.05.2010.

8. RU 2308005 C1, 6 IPC G01C 21/24, G01J 1/20, date publ. 10/10/2007. - prototype.

Claims (10)

1. An optical solar sensor comprising sequentially arranged wide-field input optical element made of radiation-resistant glass, a code mask, a light filter, a protective screen and a photodetector array (MFP), the output of which is connected to the information processing and calculation of the angular coordinates unit, characterized in that the wide-field input optical element is made in the form of a composite monoblock and has the shape of a quadrangular prism, the side faces of which at a given angle β have a slope to the vertical of the axis of the composite monoblock, which contains a central prism interconnected by optical glue in the form of a quadrangular truncated regular pyramid, the vertex of which is directed downward and has a given angle α at its top, the side faces of which have an absorbing coating, four identical side prisms in the shape of quadrangular irregular pyramids , one of the faces of each prism has a mirror coating and this face is connected to the corresponding absorbing face of the central prism, the composite monoblock rests on the surface l code mask, in which a central identification marker is made, combined with the vertical axis of symmetry of the central prism, and four identification markers, symmetrically located around the central identification marker for identifying light radiation from each of the side prisms, and the filter contains two plates made of optical colored glass plates installed one on top of the other. 2. The optical solar sensor according to claim 1, characterized in that the angle α at the apex of the central prism is 66 °. 3. The optical solar sensor according to claim 1, characterized in that the angle β of inclination of the side faces of the composite monoblock to the vertical axis is 10 °. 4. The optical solar sensor according to claim 1, characterized in that the code mask is made on a glass substrate, on the surface of which an opaque chromium layer is deposited by vacuum deposition, in which five transparent identification markers are made by photolithography. 5. The optical solar sensor according to claim 1 or 4, characterized in that the identification markers of the code mask are made in the form of quadrangular windows that differ in shape and size from one another. 6. The optical solar sensor according to claim 1, characterized in that the light filter emits a region of light radiation with an average wavelength λav = 650 nm. 7. The optical solar sensor according to claim 1, characterized in that the upper plate of the filter is made of red optical glass. 8. The optical solar sensor according to claim 1, characterized in that the lower plate of the filter is made of blue-green optical glass. 9. The optical solar sensor according to claim 1, characterized in that the mirror coating of the side prism is applied by vacuum deposition of aluminum and has a protective film of quartz. 10. The optical solar sensor according to claim 1, characterized in that black deep-mat enamel is used as an absorbent coating of the side faces of the central prism.

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