A method for suppressing reflected stray light of an optical sensor of a large satellite platform

Abstract

The application discloses a method for suppressing reflected stray light of an optical sensor of a large satellite platform, comprising an optical sensor, a monochromatic filter and a surface array photoelectric conversion chip capable of high-precision time measurement, and an optical system, a circuit system and software, wherein a stray light interference output failure processing module is added in the software, and the optical system comprises a light shield, an optical lens and an imaging assembly. The application adds the monochromatic filter under the condition of the existing optical sensor, adopts only one set of optical path, and performs intensity correlation between different image elements of the surface array detector. Therefore, the architecture of the existing optical sensor does not need to be redesigned, and only the reflection stray light suppression mode is started under the output failure conditions such as strong light interference and stray light interference of the optical sensor. In the mode, the monochromaticity of the input light signal is improved, the time measurement precision of the detector is improved, the stray light interference is suppressed, and finally the output is normal.

Description

Technical Field

[0001] This invention relates to the field of spacecraft development technology, and in particular to a method for suppressing stray light reflected from optical sensors on large satellite platforms. Background Technology

[0002] Current large satellite platforms are equipped with various large deployable payloads and high-power solar panels, relying on multiple optical sensors, such as star sensors, solar sensors, infrared Earth sensors, ultraviolet imaging sensors, X-ray pulsar detectors, and various optical cameras, for optical measurements. If stray light reflected from the payload or solar panels enters the field of view during optical signal measurement, abnormal output data will occur, or even photoelectric conversion failure due to strong light. For example, a star sensor on a mainstream satellite platform with a field of view of 26° experienced stray light interference during its on-orbit operation. Analysis revealed that sunlight reflected from the surface of satellite components such as solar panels entered the star sensor's field of view. The goal was to extend the star sensor's field of view to an unobstructed 36° range within the overall satellite layout. However, due to the presence of multiple extravehicular components, the layout was already constrained. Ultimately, an unobstructed field of view within this range was achieved, but it could not guarantee that no stray light signals (reflected light from deployed components) would enter the field of view. Therefore, optical sensors need to employ stray light suppression measures for the input light signal. There are three main traditional methods: (1) Light shield: Using a multi-layered nested light shield to restrict the path of the input signal light and prevent stray light from reaching the photoelectric conversion chip. (2) Filter: Using a filter to set the admission for light of only a certain wavelength, while filtering out light of other frequency bands. (3) Image processing algorithm: Using various classification algorithms in data processing to map and transform the mixed signal containing noise to other spaces, and then setting resolution rules to separate the signal and noise, thereby achieving the noise filtering effect.

[0003] Patent CN2011046094.5 proposes a star sensor shield design method with stray light suppression, achieving noise filtering based on the irradiance comparison between stars and stray light. Patent 201611061344.9 proposes a stray light suppression method for an imaging spectrometer, achieving stray light suppression through integrated filter spectral splitting and the use of color-separating elements for spectral band separation. Patent CN20181080273.9 proposes a lunar stray light suppression method applied to star sensors, dividing the star image acquired by the detector into four partitions, performing adaptive threshold calculation on the image, and re-extracting the image for star image recognition. Patent CN201810770994.3 invented a fast and robust image stray light suppression method and system. Patent CN201810226593.1 invented a micro / nano-scale star sensor optical system based on joint stray light elimination.

[0004] CN201910749353.4 proposes a method for suppressing stray light from external optical payloads based on ray tracing. Various stray light suppression optical methods have been proposed in papers such as "Analysis and Suppression of Stray Radiation in Composite Optical Systems" (Applied Optics, Vol. 40, No. 1), "Analysis and Suppression Structure Design of Stray Light from Transmitting Infrared Lenses" (Infrared Technology, Vol. 40, No. 11), and "Strait Light Suppression Method for Horseshoe-Shaped Cassegrain Reflective Optical Systems for Star Sensors" (Chinese Journal of Inertial Technology, Vol. 24, No. 2). However, even with these three methods used for optical sensor field-of-view design on large satellite platforms with multiple complex payloads or after solar panel deployment, overall satellite layout remains challenging. Summary of the Invention

[0005] The purpose of this invention is to provide a method for suppressing stray light reflected from optical sensors on large satellite platforms in order to solve the above-mentioned problems.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for suppressing stray light reflected from an optical sensor on a large satellite platform includes an optical sensor comprising an optical system, a circuit system, and software. The optical sensor also includes a monochromatic filter and a photoelectric conversion chip capable of high-precision time measurement. A stray light interference output fault handling module is added to the software.

[0008] Preferably, the optical system includes a light shield, an optical lens, and an imaging component. The light shield is directly mounted on the light signal inlet of the main structure of the optical sensor, and the imaging component consists of an array detector arranged on the focal plane of the optical system.

[0009] Preferably, the monochromatic filter is controlled by a motor and mounted on a light shield, and the monochromatic filter has a retractable structure.

[0010] Preferably, the monochromatic filter is controlled by a motor and mounted on a light shield, and the monochromatic filter has a rotatable structure.

[0011] Preferably, a method for suppressing stray light reflected from optical sensors of large satellite platforms includes the following steps:

[0012] S1.1 When the optical sensor determines that it is affected by stray light interference according to the fault diagnosis algorithm and the output is abnormal, the motor is started to drive the monochromatic filter to extend and retract, so that the monochromatic filter extends out of the light shield.

[0013] S1.2 The light signal entering the optical system is filtered by a monochromatic filter. The sensor array photoelectric conversion device receives the monochromatic weak light signal after being filtered by the filter, marks the arrival time of the photons with high precision, and searches for photon correlation pairs on adjacent pixels through software algorithms.

[0014] S1.3 When the number of associated photon pairs in pixel AB is much greater than the number of associated photon pairs in other pixels, i.e. when an association peak appears, the neighboring pixels are considered to be the true image of the stellar light signal. By taking a reasonable association peak threshold for the neighboring pixels on all the arrays, the stellar star map is obtained.

[0015] S1.4. Within a certain period of time, multiple adjacent pixels may have a correlation photon pair that is much larger than the average value. These pixels with abnormal correlation photons are considered to be images of stars. By pairing the star map composed of these image points with the angular position in the star catalog software, the attitude in the inertial frame can be obtained, thereby achieving the effect of suppressing stray light reflection.

[0016] Preferably, a method for suppressing stray light reflected from optical sensors of large satellite platforms includes the following steps:

[0017] S2.1 When the optical sensor determines that it is affected by stray light interference according to the fault diagnosis algorithm and the output is abnormal, the motor is started to drive the monochromatic filter to rotate and rotate the monochromatic filter out of the light shield.

[0018] S2.2 The light signal entering the optical system is filtered by a monochromatic filter. The sensor array photoelectric conversion device receives the monochromatic weak light signal after being filtered by the filter, marks the photon arrival time with high precision, and searches for photon correlation pairs on adjacent pixels through software algorithms.

[0019] S2.3 When the number of associated photon pairs in pixel AB is much greater than the number of associated photon pairs in other pixels, i.e. when an association peak appears, the neighboring pixels are considered to be the true image of the stellar light signal. By taking a reasonable association peak threshold for the neighboring pixels on all the arrays, the stellar star map is obtained.

[0020] S2.4. Within a certain period of time, multiple adjacent pixels in a 1024*1024 array may have a correlation photon pair that is much larger than the average value. These pixels with abnormal correlation photons are considered to be images of stars. By pairing the star map composed of these image points with the angular position in the star catalog software, the attitude in the inertial frame can be obtained, thereby achieving the effect of suppressing reflected stray light.

[0021] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0022] 1. This application adds a monochromatic filter to the existing optical sensor and uses only one optical path to perform intensity correlation between different pixels of the array detector. Therefore, it is not necessary to redesign the architecture of the existing optical sensor. It only activates the reflection stray light suppression mode for output failures of the optical sensor under strong light interference, stray light interference, etc. In this mode, the monochromaticity of the input light signal and the time measurement accuracy of the detector will be improved to suppress stray light interference and finally achieve normal output. The reflection stray light suppression method proposed in this application can reduce the difficulty of the overall satellite layout design and upgrade the hardware and software of the existing optical sensor. The main upgrades include: (1) adding a filter to achieve monochromaticity of light; (2) improving the time measurement accuracy of the detector chip to achieve high-precision time-matched intensity correlation; (3) adding a correlation algorithm software module for the output failure mode caused by stray light and strong light interference of the star sensor. Attached Figure Description

[0023] Figure 1 A basic schematic diagram of a general optical sensor provided according to an embodiment of the present invention is shown;

[0024] Figure 2 A schematic diagram of an installation method for adding a filter element to a general optical sensor, according to an embodiment of the present invention, is shown.

[0025] Figure 3 A schematic diagram of intensity interference of a sensor array photoelectric conversion device provided according to an embodiment of the present invention is shown. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Please see Figure 1-3 The present invention provides a technical solution:

[0028] A method for suppressing stray light reflected from an optical sensor on a large satellite platform includes an optical sensor, which comprises an optical system, a circuit system, and software. It also includes a monochromatic filter and a photoelectric conversion chip with a high-precision time measurement capability. A stray light interference output fault handling module is added to the software. According to the principle of intensity interference, the higher the time measurement accuracy and the shorter the wavelength, the easier it is to meet the interference conditions, that is, the higher the accuracy of judging two photons arriving within a specific time period as a correlated photon pair.

[0029] The optical system includes a light shield, optical lenses, and imaging components. The light shield is directly mounted on the light signal inlet of the main structure of the optical sensor, preventing stray light from entering within a certain field of view, thus reducing system noise. The optical lenses primarily perform light signal transmission, filtering, focusing, and correction of various distortions and aberrations. The imaging components consist of an array detector arranged on the focal plane of the optical system, converting light signals into electrical signals. The circuit system includes a secondary power supply, signal processing circuits, and a CPU circuit, mainly amplifying, reading out, and performing related digital processing on the electrical signals received by the detectors, realizing the data expression, storage, and information conversion of the optical image. The software runs on the CPU of the circuit system and includes system software, application software, and star catalog software. The system software, as the basic software for CPU operation, enables various hardware interface calls, interrupts, and task management. The star catalog software is a pre-installed database of angular position information of stars and other reference targets, used for star map matching. The application software is the main embodiment of the information processing algorithms, realizing data retrieval from the star catalog software, pixel extraction, star map matching, and information conversion.

[0030] The monochrome filter is controlled by a motor and is mounted on a light shield. The monochrome filter has a retractable structure.

[0031] The monochrome filter is controlled by a motor and is mounted on a light shield. The monochrome filter has a rotatable structure.

[0032] A method for suppressing stray light reflected from optical sensors on large satellite platforms includes the following steps:

[0033] S1.1 When the optical sensor determines that it is affected by stray light interference according to the fault diagnosis algorithm and the output is abnormal, the motor is started to drive the monochromatic filter to extend and retract, so that the monochromatic filter extends out of the light shield.

[0034] S1.2 The light signal entering the optical system is filtered by a monochromatic filter. The sensor array photoelectric conversion device receives the monochromatic weak light signal after being filtered by the filter, marks the arrival time of the photons with high precision, and searches for photon correlation pairs on adjacent pixels through software algorithms.

[0035] S1.3 When the number of associated photon pairs in pixel AB is much greater than the number of associated photon pairs in other pixels, i.e. when an association peak appears, the neighboring pixels are considered to be the true image of the stellar light signal. By taking a reasonable association peak threshold for the neighboring pixels on all the arrays, the stellar star map is obtained.

[0036] S1.4. Within a certain period of time, multiple adjacent pixels may have a correlation photon pair that is much larger than the average value. These pixels with abnormal correlation photons are considered to be images of stars. By pairing the star map composed of these image points with the angular position in the star catalog software, the attitude in the inertial frame can be obtained, thereby achieving the effect of suppressing stray light reflection.

[0037] A method for suppressing stray light reflected from optical sensors on large satellite platforms includes the following steps:

[0038] S2.1 When the optical sensor determines that it is affected by stray light interference according to the fault diagnosis algorithm and the output is abnormal, the motor is started to drive the monochromatic filter to rotate and unscrew the monochromatic filter out of the light shield.

[0039] S2.2 The light signal entering the optical system is filtered by a monochromatic filter. The sensor array photoelectric conversion device receives the monochromatic weak light signal after being filtered by the filter, marks the photon arrival time with high precision, and searches for photon correlation pairs on adjacent pixels through software algorithms.

[0040] S2.3 When the number of associated photon pairs in pixel AB is much greater than the number of associated photon pairs in other pixels, i.e. when an association peak appears, the neighboring pixels are considered to be the true image of the stellar light signal. By taking a reasonable association peak threshold for the neighboring pixels on all the arrays, the stellar star map is obtained.

[0041] S2.4. Within a certain period of time, multiple adjacent pixels in a 1024*1024 array may have a correlation photon pair that is much larger than the average value. These pixels with abnormal correlation photons are considered to be images of stars. By pairing the star map composed of these image points with the angular position in the star catalog software, the attitude in the inertial frame can be obtained, thereby achieving the effect of suppressing reflected stray light.

[0042] The process by which this invention achieves the suppression of stray light reflected from optical sensors (taking a star sensor as an example) is as follows:

[0043] Step 1: Design the optical system and circuit system according to the existing star sensor development process. A monochromatic filter is set on the aperture stop of the light shield. In addition, the array photoelectric conversion chip is replaced with a time measurement accuracy of more than 1μs (currently, the APD array chip can achieve a time measurement accuracy of more than ns).

[0044] Step 2: Set stray light and strong light interference diagnostic conditions in the existing star sensor application software. Scenario 1: When the star sensor is working in capture mode, if the noise of the obtained star points is greater than the general background level, first increase the background threshold to obtain a star image. If the background threshold exceeds the set threshold and a matching star image cannot be obtained after a certain time (e.g., 120s), switch to the reflection stray light suppression module. Scenario 2: When the star sensor is working normally in window tracking mode, once the software detects multiple noise points suddenly appearing in the star image, it exits from normal mode back to capture mode. The output displays interference from reflected light from the sun, moon, or earth. If attitude data still cannot be obtained in capture mode, the same as in Scenario 1 applies, switching to the reflection stray light suppression module.

[0045] Step 3: Add a stray light suppression module to the existing star sensor application software. When the star sensor determines that it is being interfered with by stray light according to the stray light and strong light interference diagnosis algorithm in Step 2 and the output is abnormal, the software activates the stray light suppression module and sends a command to control the motor to drag the monochromatic filter to extend (or rotate), so that the monochromatic filter extends (or rotates out) from the light shield. At this time, the light signal entering the optical system is filtered by the monochromatic filter, and the sensor's area array photoelectric conversion device receives the monochromatic weak light signal after being filtered by the filter.

[0046] Step 4: Since the stellar light signal is filtered by a monochromatic filter, the light signal is attenuated into an extremely weak single-photon signal. The software sets the mode of the array photoelectric converter device to work in single-photon detection mode (extremely low dark current, contrast reduced to the lowest level, and the row and column frame scanning mode when reading out the signal is converted to pulse readout mode). Once the signal processing circuit obtains the photon pulse signal from the photoelectric conversion chip, it marks the photon arrival time with high precision, and finally forms a photon arrival time sequence of 1024*1024 pixels.

[0047] Step 5: Perform correlation operations on the photon arrival time series. For example... Figure 3 As shown, when the arrival time of the photon pulse received by pixels A and B is less than a threshold (e.g., 1 μs), it is considered that there is a correlated photon pair between pixels A and B. The time difference between the photon arrival pulses of the 8 pixels near pixel i with photon arrival pulses and the photon arrival pulse of pixel i is calculated to determine whether they are correlated photon pairs.

[0048] Step 6: When a certain pixel and its neighboring pixels show significantly more photon correlation pairs than other pixels, that is, when the array pixel has a correlation peak at this point, it is considered that the pixel and its neighboring pixels are the true image of the stellar light signal. By taking a reasonable correlation peak threshold for all neighboring pixels on the array, the stellar star map is obtained.

[0049] Step 7: Within a certain period of time (e.g., 300s), there may be multiple adjacent pixels in the 1024*1024 array with a number of correlated photon pairs that are much greater than the average value. If these pixels with an unusually large number of correlated photon pairs are considered to be images of stars.

[0050] Step 8: Using a star map recognition algorithm, the star map composed of these image points is paired with the angular positions in the star catalog software. Finally, the attitude orientation of the star sensor system in the inertial frame can be obtained, thereby achieving normal star sensor output.

[0051] Step 9: After the star sensor has been operating in the reflection stray light suppression module for a certain period of time (e.g., 600 seconds), attempt to return to the capture mode. If a star map can be captured in capture mode, switch to the window tracking mode under normal conditions. If a star map still cannot be captured in capture mode, switch back to the reflection stray light suppression module. To prevent software nested loops, the number of attempts to return to capture mode can be set, such as three. If the third attempt fails, a manual command is required to re-enter capture mode.

[0052] When the star sensor receives a space light signal, it is equipped with a light shield and a stray light processing algorithm to take into account general stray light interference. The star sensor CPU performs star map matching on the received light signal according to the image processing algorithm and outputs the attitude of the star sensor system relative to the inertial frame. Once stray sunlight reflected from other components on the surface of a star, such as solar panels or antennas, enters the star sensor's field of view, causing the star map to fail to match, the star sensor exits the window tracking mode and enters the capture mode. At this time, the star sensor determines that it is being interfered with by stray light according to the fault handling algorithm and activates the reflection stray light suppression module of the optical sensor based on intensity correlation proposed in this invention. Similar to a camera shutter, the optical system of the star sensor is equipped with a filter that allows light signals with a wavelength of 512nm (±0.1nm) to pass through. When the filter is opened, the photosensitive array chip receives the signal and searches for pixels with strong light intensity signals. It performs intensity correlation on two strong signal pixels that are close in position. If there is a correlation peak, the pixel pair is considered a valid pixel; if there is no correlation peak, it is judged as an invalid pixel. Finally, the valid pixel array is output for star map matching and identification again, and the attitude in the relative inertial frame is output according to the star table, thereby achieving the effect of reflection stray light suppression.

[0053] This application adds a monochromatic filter to the existing optical sensor and uses only one optical path to perform intensity correlation between different pixels of the area array detector. Therefore, it does not require a redesign of the existing optical sensor architecture. It only activates a reflection stray light suppression mode in the event of output failures such as strong light interference or stray light interference. In this mode, the monochromaticity of the input light signal and the time measurement accuracy of the detector are improved to suppress stray light interference, ultimately achieving normal output.

[0054] The above description of the embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for suppressing stray light reflected from optical sensors of large satellite platforms, characterized in that, Includes the following steps: S1.1 When the optical sensor determines that it is affected by stray light interference according to the fault diagnosis algorithm and the output is abnormal, the motor is started to drive the monochromatic filter to extend and retract, so that the monochromatic filter extends out of the light shield. S1.2 The light signal entering the optical system is filtered by a monochromatic filter. The sensor array photoelectric conversion device receives the monochromatic weak light signal after being filtered by the filter, marks the arrival time of the photons with high precision, and searches for photon correlation pairs on adjacent pixels through software algorithms. S1.3 When the number of associated photon pairs in pixel AB is much greater than the number of associated photon pairs in other pixels, i.e. when an association peak appears, the neighboring pixels are considered to be the true image of the stellar light signal. By taking a reasonable association peak threshold for the neighboring pixels on all the arrays, the stellar star map is obtained. S1.4 If, within a certain period of time, multiple adjacent pixels in a 1024*1024 array have a correlation photon pair greater than the average value, then these pixels with abnormal correlation photons are considered to be images of stars. By pairing the star map composed of these image points with the angular positions in the star catalog software, the attitude in the inertial frame is obtained, thereby achieving the effect of suppressing reflected stray light. S2.1 When the optical sensor determines that it is affected by stray light interference according to the fault diagnosis algorithm and the output is abnormal, the motor is started to drive the monochromatic filter to rotate and rotate the monochromatic filter out of the light shield. S2.2 The light signal entering the optical system is filtered by a monochromatic filter. The sensor array photoelectric conversion device receives the monochromatic weak light signal after being filtered by the filter, marks the photon arrival time with high precision, and searches for photon correlation pairs on adjacent pixels through software algorithms. S2.3 When the number of associated photon pairs in pixel AB is much greater than the number of associated photon pairs in other pixels, i.e. when an association peak appears, the neighboring pixels are considered to be the true image of the stellar light signal. By taking a reasonable association peak threshold for the neighboring pixels on all the arrays, the stellar star map is obtained. S2.4 If, within a certain period of time, multiple adjacent pixels in a 1024*1024 array have a correlation photon pair greater than the average value, then these pixels with abnormal correlation photons are considered to be images of stars. By pairing the star map composed of these image points with the angular positions in the star catalog software, the attitude in the inertial frame is obtained, thereby achieving the effect of suppressing stray light reflection.

2. The method for suppressing stray light reflection from optical sensors of large satellite platforms according to claim 1, characterized in that, It includes an optical sensor, which comprises an optical system, a circuit system, and software. It also includes a monochromatic filter and a planar photoelectric conversion chip capable of high-precision time measurement. The software includes a stray light interference output fault handling module.

3. The method for suppressing stray light reflection from optical sensors of large satellite platforms according to claim 1, characterized in that, The optical system includes a light shield, an optical lens, and an imaging component. The light shield is directly mounted on the light signal inlet of the main structure of the optical sensor, and the imaging component consists of an array detector arranged on the focal plane of the optical system.

4. The method for suppressing stray light reflection from optical sensors of large satellite platforms according to claim 2, characterized in that, The monochrome filter is controlled by a motor and is mounted on a light shield. The monochrome filter has a retractable structure.

5. The method for suppressing stray light reflection from optical sensors of a large satellite platform according to claim 2, characterized in that, The monochromatic filter is controlled by a motor and is mounted on a light shield. The monochromatic filter has a rotatable structure.

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