RU2442109C1 - Celestial angle measurement device - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: device comprises a light input unit which lets the light enter the stellar lens, and the stellar lens itself. A matrix light receiver is located in the focal plane of the lens. The receiver is connected to the computer unit. The stellar lens forms the first bitmap image from the astronomical light source on the matrix light receiver. The light input unit and the stellar lens form the second bitmap image from the said astronomic source o the matrix light receiver.

EFFECT: device reliability increase while design complexity remains the same; the device still cannot decalibrate; mass and size reduction.

6 cl, 3 dwg

Description

In stellar instruments (hereinafter - ZP), the orientations of spacecraft have found widespread use of channels of a geometric standard (hereinafter - CGE). Using this channel, the instrumentation coordinate system of the RF is materialized, and the property of non-upsetability is attached to its optical system [1, 2]. Relative to this coordinate system of the RFP, the angular coordinates of the sighted stars are measured.

Known CGEs have an intra-instrument illuminator, with the help of which the illumination of the collimator diaphragm of the specified channel is carried out. The presence of such a lighter reduces the reliability of the RF, since with a long period of its operation there is always a certain probability of failure of the luminous source of radiation.

A CGE, which has an intra-instrument radiation source, can be called active, without such a source - passive.

The main idea of the inventive angle measuring star device is to create a passive CGE, which is implemented as follows:

1. As a source of radiation of the CGE, the astronomical radiation source sighted by the GP is used (hereinafter - AII).

2. The ZP lens and the matrix of pixels of the matrix radiation receiver, for example, a charge-coupled device (hereinafter - CCD) located in the focal plane of the lens, in the aggregate form a known retroreflector.

The aim of the invention is to increase the reliability of the RF without complicating its design, while maintaining its non-upsetability and reducing the overall mass characteristics of the device.

The goal is achieved in that the stellar angle measuring device comprises a geometric reference channel made in the form of a radiation source, a collimator unit and a radiation input device into the stellar channel lens, a stellar channel lens, in the focal plane of which a photodetector is installed, and a computing unit, while the stellar lens channel implements the formation of the first point image from an astronomical radiation source on a photodetector, as a radiation source and a block of the channel standard limator of the geometric standard uses the specified astronomical radiation source having angular sizes less than the angular field of the lens and located inside the angular field of the lens, while the input device of radiation into the lens of the stellar channel and the star channel lens generate a second point image from the specified astronomical radiation source on the photodetector .

In addition, it is preferable that the device for introducing radiation into the lens of the stellar channel be a transparent plane-parallel plate on which a beam splitting coating or a reflective coating can be applied to form a second point image from an astronomical radiation source on a photodetector.

It is also preferred that the charge-coupled array type radiation detector (CCD receiver) is used as the photodetector.

It is also preferred that a lens hood be installed in front of the radiation input device into the star channel lens.

Also, the device for introducing radiation into the lens of the stellar channel can be a protective glass of the device.

The proposed device is illustrated by the following figures:

figure 1 - the optical system of the device with a channel of a geometric standard containing a radiation source, a collimator unit and a radiation input device (analogue);

figure 2 - the optical system of the device without a geometric reference channel with a diagram of the path of rays in the lens of the device;

figure 3-optical system of the proposed device (with a channel of a geometric standard) with a diagram of the path of rays in the lens of the device.

Figure 1 shows the optical diagram of a stellar instrument (analogue) with a channel of a geometric standard [1, 2] containing a radiation source, a collimator unit and a radiation input device. The device consists of a lens 1, which is a complex multi-lens design, in the focal plane of which, for example, a matrix of pixels 2 of a charge-coupled device (CCD) 3 is located. Hereinafter, for clarity, illustrate the passage of rays through a lens, which is shown as its input and output refracting surface, it presents its combined main plane NN '. A device is located in front of the lens for introducing radiation into the lens of the stellar channel (mirror-prism system - a monoblock of prisms) 6. One prism is a BkR-180 ° (corner reflector), and the other complements the mirror-prism system to a plane-parallel plate. A beam splitter 9 can be located inside the device 6. A block collimator 8 is installed in front of the input face of the BkR-180 ° prism 8. Parallel beam beams come out of the collimator block. Structurally, this collimator is rigidly connected to the instrument seat. The image of its point aperture, illuminated by the radiation source 7, focuses on the matrix 2. The image of the point target (star) also focuses on the matrix 2. Optical elements 7, 8, 6 form the channel of the geometric standard.

The design of the protractor is made so that all the optical elements of the system and their rigid connections are stable, i.e. they always retain their geometric similarity. However, in the process of operation, their operational spatial linear and angular microdisplacements are possible.

The purpose of the goniometer is to determine the angular coordinates of the target (star). In front of the lens 1 in its angular field (2ΔW) is an infinitely distant point target (for example, a star). Physically, the coordinates of the target are determined relative to the origin of the reference point on the matrix 2, formed by the point image of the diaphragm of the collimator unit. The line passing through the center of the point image and the main points of the lens 1 is the target line of the RF. This line in the space of objects in the RF in this device is perpendicular to its seat and is one of the axes of its instrument coordinate system, relative to which the angular coordinates of the sighted stars are measured.

First, we will evaluate the micro displacements of the radiation input device 6 of the mirror-prism system. It is known that in the parallel path of the rays, linear displacements of the prism-mirror system do not affect their angular position. The angular rotations of this mirror-prism system do not affect the angular position of the rays passing through it either. Prism BkR-180 ° as a retroreflector, only rotates the beam of rays incident on it by 180 °. The plane-parallel plate in front of the lens 1 also does not change the angular position of the rays from the star.

Thus, two beams of rays (from the star and from the channel of the geometric standard) enter the input of the lens 1.

Now we will evaluate the effect of microdisplacements of elements 1, 2. Since, after the mirror-prism system, the ray path from the target (star) and the collimator block is joint, due to this, any microdisplacements of the lenses of the lens 1 and matrix 2 lead to simultaneous and identical displacement of the target images ( stars) and the diaphragm of the collimator block in matrix 2. Recall that the actual measurement of the target coordinates in this device is relative to the point image of the diaphragm of the collimator block. Therefore, microdisplacement of elements 1, 2, leading to the joint movement of images of the target (star) and the diaphragm of the collimator unit, does not affect the measurement accuracy.

Figure 2 presents the optical system of the device without a geometric reference channel with a beam pattern in the lens of the device. The device consists of a lens 1 with an aperture diaphragm (entrance pupil) 5, in the focal plane of which there is a sensitive area 2 of the radiation receiver 3 connected to the computing unit 4. As a rule, sensitive areas of the radiation receivers have a mirroring property. Therefore, a lens with the indicated sensitive area can be considered as a retroreflector, which has the following well-known property - to reflect the rays entering it back [1]. The parallel beam of rays entering the lens 1 will focus on the mirror 2, will be reflected from it and exit the lens 1 in the form of a parallel beam of rays. This beam of rays emerging from the reflector (lens 1) is always strictly parallel to the incoming beam of rays and directed in the opposite direction.

Figure 2 shows a special case when the entrance pupil 5 of the lens 1 is located in its front focal plane. This is the so-called telecentric ray path. Figure 2 shows the passage of only the extreme rays of the beam passing through the edge of the pupil 5. In this Fig. it is seen that the input and output rays are parallel. The indicated property of the retroreflector is practically preserved [2] and with some violation of its geometric pattern, which may occur during its operation under the influence of temperature changes, vibrations, etc. With this violation, micro-tilts and micro-movements of its individual elements (objective lens 1 and mirror 2) can take place.

Figure 3 shows the proposed optical system RFP with passive CGE. The ZP lens is indicated by pos. 1, and pos. 2 is a CCD pixel matrix that is aligned with the rear focal plane of lens 1. Lens 1 and matrix 2 form a retroreflector. Passive CGE is an ordinary plane-parallel plate 6 (protective glass) installed parallel to the landing plane of the RF and in the entrance pupil 5 of lens 1. The normal to plate 6 is parallel to the optical axis of the lens. Under operating conditions of the RF, the indicated parallelism of the plate and the seat of the RF is ensured by constructive measures. From a comparison of FIG. 2 and FIG. 3, it follows that FIG. 3 differs from FIG. 2 only in the presence of a plate 6. Such a plate in modern RFPs made of radiation-resistant glass often acts as an element of protection for RF optics from the radiation effects of outer space in flight spacecraft.

Most CCD pixel matrices have the mirroring property, which, as shown by the practice of creating a CW, leads to the appearance of point flares on the matrix. Their appearance is clearly shown in figure 3. A beam of parallel rays from the sighted star, passing sequentially elements of the system 6, 5, 1, will focus in a point image on the matrix 2 (in the form of the desired image of the star). Then, the rays reflected from the matrix, passing successively the elements of the system 1, 5, 6, 5, 1, are again focused into a point image on the matrix 2 in the form of a point glare, in which the illumination is less than in the image of a star. In all known RFPs, unlike the proposed one, the fight against this flare is carried out. There are several ways to deal with this flare. By applying a high-quality antireflection coating to the plate 6, tilting the plate 6 relative to the optical axis of the lens 1, or using the method of amplitude selection of point images. In the latter case, the image of the star is detected by the RF, provided that the electric signal from the radiation receiver from the point image exceeds a certain predetermined threshold.

The work of passive CGE is as follows. AII (for example, a star or a planet whose angular dimensions are smaller than the angular field of the lens) is located in the angular field of the device. The optical system ZP builds its image (first image) on a matrix of pixels 2.

In this case, as described above, a flare will appear on the pixel array 2 (second image). By virtue of the law of reflection, a point lying in the middle of a line segment connecting the first and second image always indicates the angular position of the normal to the plate 6. We denote this point by the letter C. Figure 3 shows the case of nominal geometry when the point C coincides with the focus of the lens F '. The line passing through point C and the main points of the lens 1 is the target line of the RF. This line in the space of objects ZP is always perpendicular to its seat and is one of the axes of its instrument coordinate system, relative to which the angular coordinates of the sighted stars are measured. In this case, the possible operational micro-violations of the geometric system relative to the plate 6 practically do not lead to a change in the angular position of the target line of the RF in its space of objects.

The work of RFP with passive CGE is as follows.

AII is selected in the corner field of the RFP.

- Search and detection of a point image of AII on the CCD pixel matrix (first image) is performed.

- The coordinates of the first AII image are measured and stored in the memory of the RF processor.

- Search and detection of the second point image of the AII on the CCD pixel matrix is performed.

- The coordinates of the second AII image are measured and stored in the memory of the RF processor. It should be noted that the processing of the first and second point images is performed by the RF almost in real time.

- Based on the two coordinates found, the coordinates of point C are calculated (as the coordinates of the middle of the segment connecting the first and second point image). These coordinates of point C are recorded in the memory of the processor ZP.

- In the future, the coordinates of the sighted stars are determined relative to point C as the beginning of the instrument coordinate system.

The above procedure for determining the coordinates of point C is the process of calibrating the ZP according to AII.

The originality of this proposal lies in the fact that harm turns into benefit, harmful glare becomes a useful and necessary image.

This originality leads to a number of features of the construction of such RFPs.

1. The fact is that the illumination E 'of the second image of the AII will be K times different from the illumination of its first image E.

K = t ² rr _m ,

where t is the transmission coefficient of the lens;

p is the reflection coefficient of a plane-parallel plate;

p _m is the reflection coefficient of the CCD matrix.

For example, at t = 0.85, p = 0.08, p _m = 0.5-K = 0.0289. For example, with the illumination E of the first image, E = 1 lux, E '= 0.0289 lux. Therefore, to align the exposures of the first and second AII images on the CCD pixel matrix, it is necessary to have different accumulation times when processing these two images. Exposition is a product of illumination against time. Illuminations created by different navigation stars at the input of the optical system of the RF have a large scatter (up to 100 ... 200 times). If a planet is chosen as the AI, then it is necessary to reduce the accumulation time from the first image. If a relatively faint star is chosen as the AII, then it is necessary to increase the accumulation time from the second image. In the above example, with equal exposures, the accumulation time between the first and second image will differ by 34.6 times. The condition for equal exposure is rather arbitrary. In practice, the accumulation time between the first and second image may differ by a smaller amount.

2. For the nominal geometry of the considered RFP, the position on the pixel matrix of the second image is known. In this case, the second image will be located symmetrically to the first image relative to the point of intersection of the optical axis of the lens 1 and the matrix 2 (relative to the back focus of the lens 1-F '). Therefore, in the case of broken geometry of the device, the zone in which the second image is located is significantly smaller than the size of the linear field of the RF (the size of the CCD pixel matrix), and the position of this zone on the matrix is approximately known by virtue of the foregoing. All this leads to the fact that the search time for the second point image will be significantly reduced, which is a positive point in the work of the RF. The specified search zone is commensurate with the magnitude of the violation of the geometric pattern of the RF and its dimensions will be units of angular minutes. The center of the search zone of the second image should be located symmetrically with respect to point C, the coordinates of which were determined in the previous calibration session by the AII.

3. The location of the entrance pupil of the lens in its front focal plane (telecentric ray path) when combining plane-parallel plate 6 with it is the most optimal. In this case, there is no vignetting of the rays of the second image of the AII. For other variants of the location of the pupil 5 and plate 6, some vignetting of the second image will take place.

4. Stars in the visible range of the spectrum differ in spectrum. The emission spectrum of most navigational stars is more intense in the red part of the spectrum compared to its blue part. The number of “red” stars is significantly greater than the “blue” stars, which can be neglected (not used) to solve the problems of spacecraft orientation. Therefore, it is possible to optimize the calibration procedure for RFP according to AII by using the spectral selection method.

Consider here the selection at a qualitative level. A spectral beam splitter is applied to plate 6. In the red part of the visible spectrum, it has high transmittance and low reflection coefficient. In the blue part of the spectrum, on the contrary, it has a high reflection coefficient and a relatively low transmittance. Only the blue stars are selected for the AF calibration mode according to AII. Then, in this case, provided that the exposures in the first and second images are equal, the accumulation time in these images will differ relatively little.

LITERATURE

1. Fedoseev V.I., Kolosov M.P. Optoelectronic devices for orienting and navigating spacecraft - M.: Logos, 2007, 248 p.

2. Kolosov M.P. Optics of adaptive goniometers - M: LLC "SCAN-1", 1997, 212 p.

Claims (6)

1. An angle measuring device comprising a radiation input device into the lens of a stellar channel, a stellar channel lens, in the focal plane of which a matrix radiation detector is connected to the computing unit, while the stellar channel lens generates a first point image from an astronomical radiation source on the matrix radiation detector and the input device of radiation into the lens of the stellar channel and the lens of the stellar channel carry out the formation of the second point image e. from the specified astronomical radiation source at the matrix radiation receiver. 2. The angle measuring instrument according to claim 1, characterized in that the radiation input device into the stellar channel lens is a transparent plane-parallel plate. 3. The angle measuring device according to claim 2, characterized in that a plane-parallel reflective coating is applied to the plane-parallel plate to increase the illumination in the second point image from an astronomical radiation source on a photodetector. 4. The angle measuring device according to claim 1, characterized in that a matrix radiation detector is used, such as a charge-coupled device. 5. The angle measuring device according to claim 1, characterized in that a hood is installed in front of the radiation input device into the star channel lens. 6. The angle measuring device according to claim 5, characterized in that the radiation input device into the star channel lens is a protective glass of the device.

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