A time control method for star sensor using domestic rolling exposure detector

Abstract

A method for controlling the time of a star sensor using a domestic rolling shutter exposure detector belongs to the technical field of star sensor control. To improve the accuracy of the star sensor, in the present invention, the exposure detector of the star sensor is selected as the domestic rolling shutter exposure detector GSENSE2020BSI; the design of the driving timing of the exposure detector and the time control method of the star sensor is implemented using an FPGA; the data update rate of the star sensor is set to 10 Hz, and the starting moment T0 of each frame is used as the starting point of the time slice of the exposure detector. The reset of 2048 rows of the exposure detector is sequentially performed within 68.8128 milliseconds; the exposure midpoint moment defined by the full-cycle exposure time is calculated; the rolling compensation of the star point coordinates is performed based on the exposure midpoint moment defined by the full-cycle exposure time. Under the uniform motion condition, the present invention can be improved by about 30%; under the uniformly accelerated variable motion condition, it is improved by about 77%; under the variably accelerated variable motion condition, it is improved by about 92%.

Description

Technical Field

[0001] The invention belongs to the technical field of star sensor control, and in particular relates to a star sensor time control method using a domestic rolling curtain exposure detector. Background Art

[0002] As one of the key components for spacecraft attitude determination, star sensors play a vital role in spacecraft autonomous navigation systems. Traditional star sensors usually use fixed exposure time or a single type of exposure detector for image acquisition, which has certain limitations when facing celestial bodies under different lighting conditions, such as overexposure or underexposure, resulting in low star point recognition rate and poor positioning accuracy.

[0003] In recent years, with the increasing complexity of spacecraft missions and the higher performance requirements for star sensors, it has become particularly important to develop star sensors that can adapt to a wider range of working environments. Among them, the selection and optimization of exposure detectors has become one of the key factors in improving the performance of star sensors. The rolling shutter exposure detector can achieve line-by-line or pixel-by-pixel exposure in a single exposure process, so that the exposure time can be dynamically adjusted according to the actual lighting conditions. In theory, it can better adapt to various lighting environments and improve the accuracy and stability of star point recognition.

[0004] The rolling shutter detector is an imaging device based on the rolling shutter principle. Compared with the global shutter, it acquires images by exposing them line by line, which has the advantages of low cost, low power consumption, and compact size, and is particularly suitable for space applications. However, this line-by-line exposure method also brings some inherent limitations, especially when dealing with fast-moving objects, it is easy to produce image distortion.

[0005] When existing star sensors use rolling shutter exposure detectors, due to the characteristics of line-by-line exposure, there is a slight time difference between the exposure moments of different lines, which may cause geometric distortion of the image and affect the accuracy of attitude measurement. In star sensors, in order to ensure the accuracy of attitude measurement, it is necessary to calculate an accurate timestamp for each image frame. However, the existing timestamp calculation method is not the optimal method. Summary of the invention

[0006] The problem to be solved by the present invention is to improve the accuracy of a star sensor, and a time control method for a star sensor using a domestic rolling shutter exposure detector is proposed.

[0007] To achieve the above object, the present invention is implemented through the following technical solutions:

[0008] A method for controlling the time of a star sensor using a domestic rolling shutter exposure detector comprises the following steps:

[0009] S1. The exposure detector of the star sensor is selected as the domestic rolling shutter exposure detector GSENSE2020BSI;

[0010] S2. Based on the GSENSE2020BSI selected in step S1, FPGA is used to implement the design of the exposure detector drive timing and the star sensor time control method; the exposure detector has a total of 2048 rows, and the drive time of each row is 33.6 microseconds, including row readout and row reset. The exposure time Exp_Time is set to an integer multiple of 33.6 microseconds, and the number of exposure rows is Line_Num; the time slide is set to control the detector exposure and data readout processing, and the time of the time slide is 68.8128 milliseconds;

[0011] S3. Set the star sensor data update rate to 10 Hz, and the start time of each frame to T 0 As the starting point of the exposure detector time slice, the 2048 rows of exposure detectors are reset sequentially within 68.8128 milliseconds;

[0012] Set to T 0 +Exp_Time is used as the starting point of the exposure detector data readout processing time slide, and the data of 2048 rows of the exposure detector are read out and processed in sequence within 68.8128 milliseconds;

[0013] S4. Calculate the exposure midpoint defined by the full cycle exposure time. First, define the full cycle exposure time T exp_all The expression is:

[0014] T exp_all =(Line_Num-1)×Line_Time+Exp_Time

[0015] Wherein, Line_Time is the time for processing a line, Line_Time = 33.6 μs;

[0016] Then the exposure midpoint time defined by the full cycle exposure time is taken as the exposure midpoint time T exp_mid , the calculation method is:

[0017]

[0018] Among them, T exp_start is the exposure starting time;

[0019] S5. Perform rolling shutter compensation of the star point coordinates based on the exposure midpoint time defined by the full cycle exposure time.

[0020] Furthermore, the specific implementation method of step S5 includes the following steps:

[0021] S5.1. Calculate the moving speed of the star point in the image coordinate system. The calculation expression is:

[0022]

[0023] Among them, v px is the x-axis moving speed of the star point in the image coordinate system, v py is the y-axis moving speed of the star point in the image coordinate system, (ω x ,ω y ,ω z ) is the three-axis angular velocity of the star sensor measurement system; f is the focal length of the star sensor; dp is the exposure detector pixel size;

[0024] S5.2. Calculate the exposure row number where the centroid of the star point is located. The calculation expression is:

[0025] Line_ID = floor(y)

[0026] Among them, floor is the round-down function, and Line_ID is the line number;

[0027] S5.3. Calculate the roller blind compensation amount. The calculation expression is:

[0028] dx=T line ·Line_ID·v px

[0029] dy=T line ·Line_ID·v py

[0030] Among them, T line is the exposure delay, dx is the rolling shutter compensation in the x direction, and dy is the rolling shutter compensation in the y direction;

[0031] S5.4. Calculate the rolling shutter compensation of the star point coordinates. The calculation formula is:

[0032] x rec =x-dx

[0033] y rec =y-dy

[0034] Among them, (x, y) is the coordinate of the star point before rolling shutter compensation, (x rec ,y rec ) is the star point coordinate after rolling shutter compensation.

[0035] Furthermore, the exposure time can be adjusted in a range of 1 line to 595 lines.

[0036] Furthermore, the star sensor uses the midpoint of exposure as the timestamp of the output posture of the frame. For GSENSE2020BSI, the calculation method is:

[0037]

[0038] Beneficial effects of the present invention:

[0039] The present invention discloses a star sensor time control method using a domestic rolling shutter exposure detector, which discloses for the first time a star sensor time control method using a domestic rolling shutter exposure detector GSENSE2020BSI. Compared with the commonly used method of taking the midpoint of the exposure time of the first row of the detector as the exposure midpoint, the exposure midpoint is calculated using the full cycle exposure time, and after the star point coordinates are compensated based on the time control method, the calculated star sensor attitude error (3σ, i.e., three times the standard deviation) can be improved by about 30% under uniform speed conditions; by about 77% under uniformly accelerated variable speed conditions; and by about 92% under variable acceleration variable speed conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the detector exposure method;

[0041] Figure 2 Schematic diagram of a time control method using the midpoint of the exposure time of the first row as a timestamp;

[0042] Figure 3 Schematic diagram of a time control method using the midpoint of the full cycle exposure time as a timestamp;

[0043] Figure 4 The total error curve under uniform speed condition when the midpoint of the exposure time of the first row of the detector is taken as the midpoint of exposure;

[0044] Figure 5 The total error curve at the midpoint of exposure is calculated using the full cycle exposure time under uniform speed conditions;

[0045] Figure 6 Under the condition of uniform acceleration and variable speed, the total error curve when the midpoint of the exposure time of the first row of the detector is taken as the midpoint of the exposure;

[0046] Figure 7 Under the condition of uniform acceleration and variable speed, the total error curve at the midpoint of exposure is calculated using the full cycle exposure time;

[0047] Figure 8 The total error curve under variable acceleration condition when the midpoint of the exposure time of the first row of the detector is taken as the midpoint of exposure;

[0048] Fig. 9 The total error curve at the midpoint of exposure is calculated using the full cycle exposure time under variable acceleration conditions. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the specific embodiments described are only part of the embodiments of the present invention, rather than all of the specific embodiments. The components of the specific embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations, and the present invention can also have other embodiments.

[0050] Therefore, the following detailed description of the specific embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents the selected specific embodiments of the present invention. Based on the specific embodiments of the present invention, all other specific embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0051] In order to further understand the content, features and effects of the present invention, the following specific implementation methods are given as examples, and the attached Figure 1 -Attached Fig. 9 The detailed instructions are as follows: Specific implementation method one:

[0053] A method for controlling the time of a star sensor using a domestic rolling shutter exposure detector comprises the following steps:

[0054] S1. The exposure detector of the star sensor is selected as the domestic rolling shutter exposure detector GSENSE2020BSI;

[0055] S2. Based on the GSENSE2020BSI selected in step S1, FPGA is used to implement the design of the exposure detector drive timing and the star sensor time control method; the exposure detector has a total of 2048 rows, and the drive time of each row is 33.6 microseconds, including row readout and row reset. The exposure time Exp_Time is set to an integer multiple of 33.6 microseconds, and the number of exposure rows is Line_Num; the time slide is set to control the detector exposure and data readout processing, and the time of the time slide is 68.8128 milliseconds;

[0056] Further, such as Figure 2 As shown, the red ones are time slices and the blue ones are time slides;

[0057] S3. Set the star sensor data update rate to 10 Hz, and the start time of each frame to T 0 As the starting point of the exposure detector time slice, the 2048 rows of exposure detectors are reset sequentially within 68.8128 milliseconds;

[0058] Set to T 0 +Exp_Time is used as the starting point of the exposure detector data readout processing time slide, and the data of 2048 rows of the exposure detector are read out and processed in sequence within 68.8128 milliseconds;

[0059] S4. Calculate the exposure midpoint defined by the full cycle exposure time. First, define the full cycle exposure time T exp_all The expression is:

[0060] T exp_all =(Line_Num-1)×Line_Time+Exp_Time

[0061] Wherein, Line_Time is the time for processing a line, Line_Time = 33.6 μs;

[0062] Then the exposure midpoint time defined by the full cycle exposure time is taken as the exposure midpoint time T exp_mid , the calculation method is:

[0063]

[0064] Among them, T exp_start is the exposure starting time;

[0065] S5. Perform rolling shutter compensation of the star point coordinates based on the exposure midpoint time defined by the full cycle exposure time.

[0066] Furthermore, the specific implementation method of step S5 includes the following steps:

[0067] S5.1. Calculate the moving speed of the star point in the image coordinate system. The calculation expression is:

[0068]

[0069] Among them, v px is the x-axis moving speed of the star point in the image coordinate system, v py is the y-axis moving speed of the star point in the image coordinate system, (ω x ,ω y ,ω z ) is the three-axis angular velocity of the star sensor measurement system; f is the focal length of the star sensor; dp is the exposure detector pixel size;

[0070] S5.2. Calculate the exposure row number where the centroid of the star point is located. The calculation expression is:

[0071] Line_ID = floor(y)

[0072] Among them, floor is the round-down function, and Line_ID is the line number;

[0073] S5.3. Calculate the roller blind compensation amount. The calculation expression is:

[0074] dx=T line ·Line_ID·v px

[0075] dy=T line ·Line_ID·v py

[0076] Among them, T line is the exposure delay, dx is the rolling shutter compensation in the x direction, and dy is the rolling shutter compensation in the y direction;

[0077] S5.4. Calculate the rolling shutter compensation of the star point coordinates. The calculation formula is:

[0078] x rec =x-dx

[0079] y rec =y-dy

[0080] Among them, (x, y) is the coordinate of the star point before rolling shutter compensation, (x rec ,y rec ) is the star point coordinate after rolling shutter compensation.

[0081] Furthermore, the exposure time can be adjusted in a range of 1 line to 595 lines.

[0082] Furthermore, the star sensor uses the midpoint of exposure as the timestamp of the output posture of the frame. For GSENSE2020BSI, the calculation method is:

[0083]

[0084] The present embodiment describes a method for controlling the time of a star sensor using a domestic rolling shutter exposure detector, such as Figure 1 As shown, RdA is the readout of row A, and RB is the reset of row B. Therefore, the exposure time is from the reset of row B to the readout of row B.

[0085] like Figure 2 As shown, the midpoint of the exposure time of the first row is used as the timestamp of the star sensor, and the detector exposure and data readout processing are controlled using a time slide with a fixed length of 68.8128 milliseconds.

[0086] like Figure 3As shown, the midpoint of the full cycle exposure time (the total time from the start of the detector exposure start row to the end of the exposure end row) is used as the timestamp of the star sensor, and the detector exposure and data readout processing are controlled with a time slide of 68.8128 milliseconds as a fixed length.

[0087] like Figure 4 As shown, under uniform speed conditions, the total error when the midpoint of the exposure time of the first row of the detector is taken as the midpoint of exposure is x / y / z (3sigma): 0.0252", 0.0242", 0.2197";

[0088] like Figure 5 As shown in the figure, under uniform speed conditions, the total error when calculating the exposure midpoint using the full cycle exposure time is x / y / z (3sigma): 0.0176”, 0.0143”, 0.2219”; Figure 4 The method is improved by about 30%;

[0089] like Figure 6 As shown, under the condition of uniform acceleration and variable speed, the total error when the midpoint of the exposure time of the first row of the detector is taken as the midpoint of exposure is x / y / z (3sigma): 32.3965", 61.695", 202.4948";

[0090] like Figure 7 As shown in the figure, under the condition of uniform acceleration and variable speed, the total error when calculating the exposure midpoint using the full cycle exposure time is x / y / z (3sigma): 7.3229", 7.214", 202.4892"; Figure 6 The method improved by about 77%;

[0091] like Figure 8 As shown, under variable acceleration conditions, the total error when the midpoint of the exposure time of the first row of the detector is taken as the exposure midpoint is x / y / z (3sigma): 1.5379", 1.5362", 5.1424";

[0092] like Fig. 9 As shown in the figure, under variable acceleration conditions, the total error when calculating the exposure midpoint using the full cycle exposure time is x / y / z (3sigma): 0.1206”, 0.1156”, 5.0625”; Figure 8 The method improved by about 92%.

[0093] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0094] Although the present application has been described above with reference to specific embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, the various features in the specific embodiments disclosed in the present application may be used in combination with each other in any manner, and the fact that these combinations are not exhaustively described in this specification is only for the sake of omitting space and saving resources. Therefore, the present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for controlling the time of a star sensor using a domestic rolling shutter exposure detector, characterized in that: The steps include: S1. The exposure detector of the star sensor is selected as the domestic rolling shutter exposure detector GSENSE2020BSI; S2. Based on the GSENSE2020BSI selected in step S1, FPGA is used to implement the design of the exposure detector drive timing and the star sensor time control method; the exposure detector has a total of 2048 rows, and the drive time of each row is 33.6 microseconds, including row readout and row reset. The exposure time Exp_Time is set to an integer multiple of 33.6 microseconds, and the number of exposure rows is Line_Num; the time slide is set to control the detector exposure and data readout processing, and the time of the time slide is 68.8128 milliseconds; S3. Set the star sensor data update rate to 10 Hz, take the start time T0 of each frame as the starting point of the exposure detector time slice, and reset the exposure detector 2048 rows in sequence within 68.8128 milliseconds; Set T0+Exp_Time as the starting point of the exposure detector data readout processing time slide, and read out and process the data of 2048 rows of the exposure detector in sequence within 68.8128 milliseconds; S4. Calculate the exposure midpoint defined by the full cycle exposure time. First, define the full cycle exposure time T exp_all The expression is: T exp_all =(Line_Num-1)×Line_Time+Exp_Time Wherein, Line_Time is the time for processing a line, Line_Time = 33.6 μs; Then the exposure midpoint time defined by the full cycle exposure time is taken as the exposure midpoint time T exp_mid , the calculation method is: Among them, T exp_start is the exposure starting time; S5. Perform rolling shutter compensation of the star point coordinates based on the exposure midpoint time defined by the full cycle exposure time.

2. The method for controlling the time of a star sensor using a domestic rolling shutter exposure detector according to claim 1, characterized in that: The specific implementation method of step S5 includes the following steps: S5.

1. Calculate the moving speed of the star point in the image coordinate system. The calculation expression is: Among them, v px is the x-axis moving speed of the star point in the image coordinate system, v py is the y-axis moving speed of the star point in the image coordinate system, (ω x ,ω y ,ω z ) is the three-axis angular velocity of the star sensor measurement system; f is the focal length of the star sensor; dp is the exposure detector pixel size; S5.

2. Calculate the exposure row number where the centroid of the star point is located. The calculation expression is: Line_ID = floor(y) Among them, floor is the round-down function, and Line_ID is the line number; S5.

3. Calculate the roller blind compensation amount. The calculation expression is: dx=T line ·Line_ID·v px dy=T line ·Line_ID·v py Among them, T line is the exposure delay, dx is the rolling shutter compensation in the x direction, and dy is the rolling shutter compensation in the y direction; S5.

4. Calculate the rolling shutter compensation of the star point coordinates. The calculation formula is: x rec =x-dx the rec =y-to Among them, (x, y) is the coordinate of the star point before rolling shutter compensation, (x rec ,y rec ) is the star point coordinate after rolling shutter compensation.

3. The method for controlling the time of a star sensor using a domestic rolling shutter exposure detector according to claim 2, characterized in that: The exposure time can be adjusted from 1 line to 595 lines.

4. The method for controlling the time of a star sensor using a domestic rolling shutter exposure detector according to claim 3, characterized in that: The star sensor uses the midpoint of exposure as the timestamp of the output posture of the frame. For GSENSE2020BSI, the calculation method is:

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