An optical simulation analysis method for measuring the pointing change of a space camera

Abstract

This invention discloses an optical simulation analysis method for measuring pointing changes of a space camera, belonging to the field of optical remote sensing technology. The method first determines the central reference position in optical design simulation software and imports the space camera optical system model, camera imaging focal plane model, and optical path constraint structure model. A point light source is set at the center of the image plane, and through reverse ray tracing, optical transmission elements and emission components in the transmission path are set to obtain a preliminary model of the pointing change measurement path. Then, forward ray tracing is performed, and parameter settings are iteratively optimized to obtain a complete model of the pointing change measurement link. Based on the complete model, the measurement simulation and analysis of pointing changes of the space camera are realized.

Description

Technical Field

[0001] This invention relates to an optical simulation analysis method for measuring the pointing change of a space camera, belonging to the field of optical remote sensing technology. Background Technology

[0002] Satellite payload pointing variation refers to the change in the optical axis orientation of a payload system during on-orbit operation due to the influence of space forces and thermal environment. Space cameras are optical payloads on aerospace satellites, commonly used for Earth observation, while star sensors (or star cameras) are primarily used for real-time satellite attitude measurement. In recent years, the aerospace remote sensing field has been committed to developing high spatiotemporal resolution integrated remote sensing systems, and has promoted the rapid development and research of large-aperture, multi-channel optical systems. However, this has also brought significant challenges to the radiometric geometric accuracy of space remote sensing images. Changes in the pointing of space cameras and star cameras will affect the ground positioning accuracy of remote sensing images, hindering the application effectiveness of space remote sensing systems. Therefore, the design of camera pointing variation measurement is of great application value for aerospace optical remote sensing systems to acquire high-precision attitude information.

[0003] In 1998, the GLAS team published "Geoscience Laser Altimeter System GLAS Science Requirements Document" at NASA Goddard Space Flight Center, and Shuman CA et al. published "ICESat Antarctic elevation data: preliminary precision and accuracy assessment" in Geophysical Research Letters. These two articles introduced the design and concept of the pointing variation between the STAR TRACKER camera and the laser receiving system in the GLAS system's on-orbit measurement. The Advanced Terrain Laser Altimeter System (ATLAS) configured on the subsequent ICESat-2 also adopted a similar angle measurement technology. AWYu et al. published "Space Laser Transmitter Development for ICESat-2 Mission" at the 2010 SPIE conference. The aforementioned published documents briefly introduced the design of an angle measurement module suitable for improving the positioning accuracy of laser payloads, but did not further elaborate on the specific design and simulation demonstration of the module. In recent years, some research teams in domestic universities have also carried out research on the measurement method of small angles of some space-use payloads based on external mechanical references. Currently, the research and development of on-orbit optical axis pointing measurement technology for space cameras is progressing gradually. This requires the construction of design models and the implementation of simulation analysis. However, research on methods in this area is relatively lacking, and no publicly available research data has been found.

[0004] To overcome the limitations of integrated satellite design and thermal control capabilities, and to effectively monitor changes in the pointing of space cameras in orbit, the Beijing Institute of Space Electromechanical Engineering has proposed a measurement system in recent years. This system is based on the original optical system of the space camera. It uses a central reference and light guide components to transmit light and obtain the positional changes of the camera's pointing relative to the reference component. However, for complex types of space cameras such as large-aperture and multi-channel cameras, it faces many challenges, such as limited structural space, envelope design constraints, weight constraints, and long and complex optical paths, which pose challenges to the design and analysis of the measurement path. Summary of the Invention

[0005] The technical problem solved by this invention is to overcome the shortcomings of the prior art and propose a simulation analysis method for a space camera pointing change measurement system based on the full optical path. It comprehensively considers the path and spatial layout of the camera optical system and constructs an optical model of the measurement path by combining coordinate three-dimensional transformation, providing support and analytical reference for the design and optimization of the space camera pointing measurement system.

[0006] The technical solution of this invention is:

[0007] An optical simulation analysis method for measuring pointing changes in a space camera includes:

[0008] In the optical design simulation software, a central reference position is set, and the optical system model of the space camera, the camera imaging focal plane model, and the optical path constraint structure model are imported to determine the relative positional relationship of each model.

[0009] A point light source is set at the center of the image plane, and an optical transmission element is set up by tracing the light rays in reverse. An emission light source is set up, and an emission assembly is designed and set up to obtain a preliminary model of the pointing change measurement path.

[0010] Based on the preliminary model of the pointing change measurement path, the point light source is hidden, the emission light source is activated, and forward ray tracing is performed to verify the feasibility and correctness of the pointing change measurement path. If the feasibility and correctness are satisfied, the complete model of the pointing change measurement path is obtained.

[0011] Based on the complete model of the pointing change measurement path, a simulation of the camera pointing change measurement path with a full optical path is performed to monitor the measurement of the pointing change of the space camera by the pointing change measurement path.

[0012] Preferably, a point light source is set at the center of the image plane, and an optical transmission element is set by reverse ray tracing, including:

[0013] A point light source is used as the input for reverse ray tracing. The main optical path of the space camera is reused to perform reverse ray tracing. The light travels through the entire optical path. The first optical transmission element is placed at a position without structural obstruction or constraint at the exit pupil of the autonomous optical path, and the spatial angle of the optical transmission element is set.

[0014] By means of light transmission, several optical transmission elements are successively set in the transmission path until they are associated with the central reference position.

[0015] Preferably, the spatial angle setting of the optical transmission element includes:

[0016] Export the model that has been set in the optical design simulation software, open the model in the structural design software, select a point as the basic position of the optical transmission element within the settable range of the optical transmission element along the direction of the last ray in the ray path, and measure the spatial coordinates of the point.

[0017] The angle between the direction of the last ray in the ray path and the three coordinate axes in the camera body coordinate system is measured, and the rotation angle of the optical transmission element is calculated to obtain the Euler angle of the optical transmission element, which is used as the spatial angle of the optical transmission element.

[0018] Preferably, the spatial angle of the optical transmission element is set in a way that minimizes error by not changing the direction of light or by propagating in completely opposite directions at 180°.

[0019] Preferably, the launch assembly is designed to include:

[0020] Based on the design requirements, determine the range of imaging spot size for the image plane;

[0021] The beam waist size theoretically emitted from the central reference position is calculated. Based on this size parameter, the focal lengths of the two lenses used for converging and collimating in the emitting assembly are designed so that the image waist of the first lens in the emitting assembly falls on the back focal plane of the second lens.

[0022] Preferably, the emitting light source is placed at the central reference position, and the emitting component is set up with the emitting light source and the emitting component having the same optical axis.

[0023] The method for configuring the transmission component is as follows:

[0024] Export the model that has been set in the optical design simulation software, open the model in the structural design software, select a point as the basic position of the emitting component along the direction of the last ray in the ray path, within the settable range of the emitting component, and measure the spatial coordinates of that point;

[0025] The angle between the direction of the last ray in the ray path and the three coordinate axes in the camera body coordinate system is measured, and the rotation angle of the pointing setting of the emitting component is calculated to obtain the Euler angle of the emitting component, which is used as the spatial angle of the emitting component.

[0026] Preferably, the feasibility and correctness of the pointing change measurement path are verified. If the feasibility and correctness are not met, the position and pointing parameters of the optical transmission element are iteratively adjusted so that the light reaches the center of the image plane, thus obtaining a complete model of the pointing change measurement path.

[0027] Preferably, based on the complete model of the pointing change measurement path, a simulation of the camera pointing measurement path with the entire optical path is performed, including:

[0028] According to the mission requirements, the beam divergence angle and power value of the emitted light source are set in the optical model of the direction change measurement path, and several analysis surfaces are set at different optical transmission element positions in the entire optical path.

[0029] By changing the pointing parameters of the optical system of the space camera under test, the imaging spot of the image plane of the measurement path is simulated under the change of pointing. The changes in the pointing of the optical system and the corresponding changes in the centroid of the image spot are analyzed and compared with the simulation results and theoretical calculations, so as to realize the simulation of the camera pointing measurement path of the entire optical path.

[0030] Preferably, after setting several analysis surfaces at different optical transmission element positions in the entire optical path, the spot condition of the simulated beam on the analysis surface, including size, energy distribution and spot centroid position, is ensured to ensure the image quality of the imaging spot image pointing to the measurement path.

[0031] Preferably, both the point light source and the emitted light source have a two-dimensional beam divergence angle, and the central ray points within the camera's field of view envelope.

[0032] The advantages of this invention compared to the prior art are:

[0033] (1) This invention provides an optical modeling design and analysis method using the full optical path for the research and development of pointing change measurement of space optical cameras, and provides quantitative data support for improving the accuracy of attitude angle.

[0034] (2) This invention proposes for the first time the design modeling process and simulation method of the space camera pointing change measurement path, which can be applied to the demonstration and design of the pointing on-orbit measurement scheme of various types of space optical remote sensing systems such as single-channel small aperture, large aperture, and multi-channel.

[0035] (3) The three-dimensional spatial angle transformation calculation method used in this invention is easy to implement in software and can be easily implemented using Matlab or VC programming. Attached Figure Description

[0036] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0037] Figure 1 This is a flowchart of the simulation analysis method for the space camera pointing change measurement system according to an embodiment of the present invention;

[0038] Figure 2 This is a schematic diagram showing the rotation angle relationship of the spatial optical conduction component layout in an embodiment of the present invention. Detailed Implementation

[0039] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0040] To address the pointing changes of space cameras caused by internal and external factors, and considering the development needs of large-aperture, multi-channel space cameras, this invention proposes a simulation analysis method for measuring pointing changes in the entire optical link of large-aperture, multi-channel space cameras. This method overcomes the challenges of complex, large-scale optical systems with strong spatial limitations, numerous constraints, long light paths, and difficulties in conducting full-link design analysis. It comprehensively considers the complexity of the camera's optical system path and its structural spatial layout, and constructs an optical model of the measurement path using a three-dimensional coordinate transformation algorithm. Simulation iteratively revises the relevant design parameters of the measurement path, providing data support and analytical references for the design and optimization of space camera pointing measurement systems.

[0041] like Figure 1 As shown, this method specifically includes:

[0042] Step S1: Based on the overall design of the space camera system and the pointing measurement system scheme, determine the position of the central reference in the camera system according to the central reference position set in the scheme. Create a new model in the optical design simulation software and import the existing space remote sensing camera optical system model, remote sensing camera imaging focal plane model, central reference model, and optical path constraint structure models such as frame envelope, substrate and support components that have important constraints on the optical path. According to the design scheme, set the coordinate position of each sub-model in the camera body coordinate system in the new model to ensure the accurate relative positional relationship between them.

[0043] Step S2: Based on the receiving focal plane position determined by the pointing monitoring system scheme and the field of view of a certain channel optical system of the space camera to be designed, a point light source, generally a laser light source, is set at the center of the image plane as the input for modeling in reverse ray tracing. This light source has a two-dimensional beam divergence angle and the central ray points within the camera's field of view envelope.

[0044] Step S3: Using reverse ray tracing, the main optical system of the remote sensing camera is reused, and the light travels through the entire optical path. Optical transmission elements are set up.

[0045] A point light source is used as the input light source for reverse analysis. The main optical path of the camera optical system is reused to perform reverse ray tracing. The light travels through the entire optical system path and the first optical transmission element is placed at a position without structural obstruction or constraint at the exit pupil of the main optical path of a certain channel of the camera optical system. The angle between the direction of the last light ray in the light path and the three coordinate axes in the camera coordinate system is measured. The Euler angle of the optical transmission element is calculated to obtain the Euler angle of the optical transmission element, which is used as the spatial angle of the optical transmission element.

[0046] The spatial angle of the optical transmission element is set in a way that minimizes error by not changing the direction of light or by propagating in completely opposite directions at 180°.

[0047] By using light transmission and spatial angle calculation methods, several optical transmission elements are gradually set up in the transmission path. In order to reduce transmission errors, the number of optical elements is minimized, based on the principle of not affecting the design constraints of key structures and interference from the main light beam, until they are associated with the central reference position determined by the system scheme.

[0048] The spatial parameters of the optical transmission elements in the measurement path are mainly the coordinates in the camera coordinate system and the three-dimensional Euler angles, as follows:

[0049] a) Determine the possible installation range of optical transmission components by considering structural constraints, ease of later structural design, and conflicts with the main ray;

[0050] b) Export the current model (including rays) and open it in structural design software (such as ProE). In the ray path, select a point along the direction of the last ray and the range defined above as the basic position of this optical transmission element, and measure the spatial coordinates (x, y, z) of this point in the camera coordinate system.

[0051] c) Similarly, in the structural design software, measure the angle between the direction of the final ray in the ray path and the three coordinate axes in the camera coordinate system, such as... Figure 2 As shown, the rotation angle of the optical transmission element's orientation is calculated using three-dimensional spatial geometric relationships:

[0052] In parallel beam propagation, take the reverse unit vector of the incident ray that reaches the next optical component in the ray propagation path. This vector is the normal vector of the next optical component, and also the vector after the optical transmission element or sub-model needs to be rotated by an angle in the system.

[0053] By accurately measuring the position coordinates of the optical component's normal vector in the camera coordinate system and the angles between it and the three coordinate axes (X, Y, Z) of the coordinate system in the structural software, let the angles be a, b, and c respectively, and then obtaining the vector through geometric calculations. The projections of the three coordinate axes OXY, OZY, and OZX make angles η with the corresponding coordinate axes X, Y, and Z, respectively. X η Y η Z :

[0054]

[0055]

[0056]

[0057] Therefore, the required Euler angle for rotation of the optical transmission element with its normal vector along the Z-axis of the camera coordinate system is (90° - η). Y ,1 / sina,Ф) T For optical transmission elements that are centrally symmetrical (such as lenses with circular cross-sections), Ф = 0°; if they are asymmetrical in the horizontal and vertical directions, then according to the actual light propagation design requirements, the criterion is that the horizontal and vertical axes of the optical element cross-section after rotation around the XY axis are 0° or 90° apart from the horizontal and vertical axes of the previous optical element cross-section, and the included angle is measured to obtain Ф.

[0058] Step S4: Based on the design specifications and requirements, determine the range of the imaging spot size pointing to the image plane of the measurement system. According to the principle of optical focusing imaging, calculate the theoretical beam waist size emitted from the central reference point. Design the transmitting component based on this size parameter. The transmitting component should have the function of converging and collimating the Gaussian beam. The method for setting up the transmitting component is as follows:

[0059] First, based on the overall design requirements and the size constraints of the image sensor, the range of the measurement spot size of the image plane is determined;

[0060] The beam waist size theoretically emitted from the central reference position is calculated. Based on this size parameter, the focal lengths of the two lenses used for converging and collimating in the emitting assembly are designed so that the square waist of the image of the first lens in the emitting assembly falls on the back focal plane of the second lens.

[0061] Assuming λ is the wavelength of the beam, the relationship between the beam waist ω0 and the divergence angle θ0 of the Gaussian beam from the source (i.e., the object side) is as follows:

[0062] tan(θ0)=λ / πω0

[0063] The emitting assembly contains two converging lenses, one with a short focal length and the other with a long focal length, for beam convergence and collimation. The focal lengths F1 and F2 of the two lenses are set such that the beam divergence angle of the collimated beam after passing through the emitting assembly from the Gaussian beam emitted by the emitting source is very small, generally not greater than 0.5 mrad. The system achieves good collimation when the image-square waist of the first lens falls exactly on the back focal plane of the second lens. The beam divergence angle θ” is:

[0064]

[0065] The emission light source is placed at the central reference position, and the range of positions where the emission component can be set is determined based on the collinearity of the optical axis of the emission light source and the emission component.

[0066] Export the model that has been set in the optical design simulation software, open the model in the structural design software, select a point as the placement position of the emission component within the settable range of the emission component along the direction of the last ray in the ray path, and measure the spatial coordinates of the point.

[0067] The angle between the direction of the last ray in the ray path and the three coordinate axes in the camera body coordinate system is measured, and the Euler angle of the emitting component is calculated to obtain the Euler angle of the emitting component, which is used as the spatial angle of the emitting component.

[0068] Step S5: Based on the direction in which the ray from the reverse tracing finally reaches the reference point, set the central axis direction of the light source and the emitting component at the central reference. The emitting light source is a certain distance away from the emitting component and is collinear with the optical axis of the component. Calculate the spatial position and pointing parameters according to the operations in steps a), b), and c) of S3. Then, set the emitting component and the emitting light source by rotating Euler angles to complete the preliminary optical modeling of the pointing measurement path.

[0069] Step S6: In the measurement path established above, hide the beam divergence point light source of the previously set space camera imaging focal plane, activate the emission light source at the reference position as input, perform forward ray tracing, verify the feasibility and correctness of the preliminary model of the pointing measurement path, and iteratively optimize the model settings by appropriately adjusting the position and pointing parameters of the optical transmission elements in the path until the transmission beam finally reaches the center pixel area of ​​the measurement image plane, and complete the optical model of the pointing measurement path.

[0070] Step S7: Based on the constructed measurement path model and according to the task requirements, perform optical simulation of the pointing change measurement of the large-aperture camera's full optical link, and analyze the transmission of the camera's pointing change by the position of each link in the measurement link.

[0071] In the model, the beam divergence angle and power value of the emitted light source are set, and analysis planes are set at different optical transmission elements in the entire optical path. The beam spot situation on the analysis plane is simulated, including size, energy distribution and spot centroid position, to ensure the image quality of the beam spot image pointing to the measurement path.

[0072] By changing the pointing parameters (including focal length, rotation around the axis, etc.) of the optical system of the space optical camera under test, the imaging spot of the image plane in the pointing measurement path is simulated. The changes in the pointing of the optical system and the corresponding changes in the centroid of the image spot are analyzed. The simulation results are compared with the theoretical calculations to realize the simulation of the pointing measurement link of the entire optical path of the space camera.

[0073] The real-time on-orbit pointing monitoring of space optical remote sensing satellites is also linked to space cameras and star sensors (or star cameras). The same approach and mechanism can be used to design the measurement of optical axis pointing changes of star sensors (or star cameras), and their modeling and simulation methods can also be referenced from each other.

[0074] The embodiments described above are merely preferred embodiments of the present invention. Ordinary variations and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of optical simulation analysis for measuring a pointing change of a space camera, characterized in that, The application relates to a pointing change measurement path simulation method for a space camera. The method comprises the following steps: In optical design simulation software, a central reference position is set, a space camera optical system model, a camera imaging focal plane model and a light path constraint structure model are imported, and the relative position relationship of the models is determined; A point light source is set at the center of an image plane, and an optical transmission element is set through reverse ray tracing; An emission light source is set, an emission assembly is designed and set, and a preliminary model of the pointing change measurement path is obtained; Based on the preliminary model of the pointing change measurement path, the point light source is hidden, the emission light source is activated, forward ray tracing is performed, and the feasibility and correctness of the pointing change measurement path are verified; if the feasibility and correctness are met, a complete model of the pointing change measurement path is obtained; 2. The method of claim 1, wherein, Based on the complete model of the pointing change measurement path, simulation of the camera pointing change measurement path of the whole optical path is performed, and the measurement of the pointing change measurement path on the pointing change of the space camera is monitored. A point light source is set at the center of an image plane, and an optical transmission element is set through reverse ray tracing, which comprises the following steps: The point light source is used as the input of reverse ray tracing, the main light path of the space camera is multiplexed, reverse ray tracing is performed, and the light ray selects a position without structure shielding and constraint from the exit pupil of the main light path to place the first optical transmission element, and the spatial angle of the optical transmission element is set; 3. The method of claim 2, wherein the method further comprises: Through light transmission, a plurality of optical transmission elements are sequentially set in the transmission path until the central reference position is associated. The spatial angle of the optical transmission element is set, which comprises the following steps: The current model set in the optical design simulation software is exported, the model is opened in the structure design software, a point is selected as the basic position of the optical transmission element in the settable range of the optical transmission element along the last light ray direction in the light path, and the spatial coordinates of the point are measured; 4. The method of claim 2, wherein the method further comprises: The angle between the last light ray direction in the light path and the three coordinate axes in the camera body coordinate system is measured, the rotation angle calculation of the pointing setting of the optical transmission element is performed, the Euler angle of the optical transmission element is obtained, and the spatial angle of the optical transmission element is set.

5. The method of claim 1, wherein, The spatial angle of the optical transmission element is set in the mode of minimum error without changing the light direction or 180 degrees completely opposite direction propagation. The emission assembly is designed, which comprises the following steps: Based on the design requirements, the imaging spot size range of the image plane is determined; 6. The method of claim 1, wherein: The waist size of the light beam emitted by the central reference position in theory is calculated, the focal length of the two lenses for convergence and collimation in the emission assembly is designed according to the size parameter, and the first lens image waist spot in the emission assembly falls on the back focal plane of the second lens. The emission light source is placed at the central reference position, and the emission assembly is set, the emission light source and the emission assembly are collinear along the optical axis; The method for setting the emission assembly is as follows: The current model set in the optical design simulation software is exported, the model is opened in the structure design software, a point is selected as the basic position of the emission assembly in the settable range of the emission assembly along the last light ray direction in the light path, and the spatial coordinates of the point are measured; The angle between the last light direction in the light path and the three coordinate axes in the camera body coordinate system is measured, the rotation angle of the pointing setting of the emission assembly is calculated, and the Euler angle of the emission assembly is obtained as the spatial angle of the emission assembly.

7. The method of claim 1, wherein: The feasibility and correctness of the on-off of the pointing change measurement path are verified, and if the feasibility and correctness are not met, the position and pointing parameters of the optical transmission element are iteratively adjusted to make the light reach the center of the image plane, i.e., to obtain the complete model of the pointing change measurement path.

8. The method of claim 1, wherein: Based on the complete model of the pointing change measurement path, the simulation of the camera pointing measurement path of the full optical path is carried out, including: According to the task requirements, the beam divergence angle and power value of the emission light source are set in the optical model of the pointing change measurement path, and a plurality of analysis planes are set at different positions of the optical transmission element in the full optical path; The pointing parameters of the optical system of the space camera to be measured are changed, the imaging spot situation of the image plane of the pointing change measurement path is simulated, the pointing change of the optical system and the change of the corresponding image plane spot centroid are analyzed, and the simulation results are compared with the theoretical calculation to realize the simulation of the camera pointing measurement path of the full optical path.

9. The method of claim 8, wherein the method further comprises: After setting a plurality of analysis planes at different positions of the optical transmission element in the full optical path, the spot situation of the light beam on the analysis plane is simulated, including the size, energy distribution and spot centroid position, to ensure the image quality of the imaging spot image of the pointing measurement path.

10. The method of claim 1, wherein: The point light source and the emission light source both have two-dimensional beam divergence angles, and the central light direction is within the envelope of the camera field of view angle.

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