Apparatus and method for measuring relative pose of non-cooperative spacecraft based on polarimetric imaging

Abstract

The device and method for measuring relative position of non-cooperative spacecraft based on polarization imaging belong to the technical field of image processing. The device and method are characterized in that: a polarization imaging is performed on a non-cooperative spacecraft to be measured by an observation satellite carrying a polarization camera system for capturing and tracking, a plurality of polarization image sequences are obtained, and data processing is performed to calculate and obtain the attitude angle of the non-cooperative spacecraft. All the polarization images, the processed polarization degree images and the attitude angle of the non-cooperative spacecraft are sent to the ground to realize continuous tracking and imaging of the non-cooperative spacecraft. The device and method are helpful to improve the detection capability of the observation satellite on the non-cooperative spacecraft, provide accurate data for orbit determination of the non-cooperative spacecraft, and improve the accuracy of orbit determination and prediction. The device and method are helpful to enhance the monitoring capability on space targets, especially small targets and large elliptical targets.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of image processing, and particularly relates to a relative pose measurement device and method for a non-cooperative spacecraft based on polarization imaging. BACKGROUND

[0002] In recent years, it has become a consensus in the academic field that the polarization parameter of light waves has unique characteristic information different from light intensity, phase and spectrum, and more and more attention is paid to the research and use of the characteristics. In the field of imaging and detection, due to the sensitivity of the polarization degree of scattered polarization light to the scattering effect of the scattering medium and the material of the target, the information provided by the polarization state can effectively distinguish scattering bodies of different materials and different surface morphologies, and scattered polarization light imaging has the advantages of improving the contrast of the target and distinguishing the material compared with traditional light intensity imaging, and has great application potential in the field of target imaging, identification and clutter suppression.

[0003] In addition, with the increase in the number of artificial spacecraft, more and more attention has been paid to the research on space target identification technology, and the attitude of the non-cooperative spacecraft also needs to be measured. For example, in order to realize the tasks of repairing a faulty spacecraft and cleaning a failed spacecraft, it is required to have a certain operation and control ability for the space target. The non-cooperative spacecraft cannot transmit its position and attitude information through an inter-satellite link, nor is it equipped with auxiliary measurement marker targets. In order to realize the docking and capturing of the target spacecraft, the attitude thereof needs to be acquired. The measurement method for the non-cooperative spacecraft is mainly an optical measurement method, and polarization detection as a new type of optical measurement technology can more easily highlight the target when the radiation of the target is weak and the background radiation is strong, and is helpful to determine the surface information of the target, survey the surface contour information, obtain the characteristic information of the target, and has important application value in the field of space target monitoring. At present, there is no related report on the use of polarization detection to measure the attitude of the non-cooperative spacecraft.

[0004] Therefore, there is an urgent need in the prior art for a new technical solution to solve this problem. SUMMARY

[0005] The present application solves the technical problem that there is no related report on the use of polarization detection to measure the attitude of the non-cooperative spacecraft.

[0006] The device for measuring relative position and pose of non-cooperative spacecraft based on polarization imaging comprises two observation satellites located at different positions, and each of the observation satellites is provided with a space-based load; the space-based load comprises an optical observation platform, an operation control system and a general control system; the general control system is connected with the optical observation platform and the operation control system respectively, and is used for operation control of each part of the optical observation platform and the operation control system; the optical observation platform comprises a large-aperture observation system, a capture tracking polarization camera system, an image processing system and a storage system, and is used for image acquisition, image preprocessing and storage of the non-cooperative spacecraft, and sends information to a ground-based tracking system through a communication system of the operation control system;

[0007] The operation control system further comprises a time system and a servo control system, and is used for time unification, image information sending to the ground, miss distance measurement and control of a turntable provided on the capture tracking polarization camera system according to the miss distance;

[0008] The large-aperture observation system is connected with the capture tracking polarization camera system through optical transmission, and is electrically connected with the servo control system; the capture tracking polarization camera system is electrically connected with the image processing system; the image processing system is electrically connected with the storage system and the communication system respectively; the servo control system is electrically connected with the capture tracking polarization camera system; and the time system is used for unifying time references of the observation satellite and the ground-based tracking system.

[0009] The capture tracking polarization camera system is provided with a multi-angle polarization imaging device, which is used for simultaneously taking pictures of multi-angle polarization components.

[0010] The method for measuring relative position and pose of non-cooperative spacecraft based on polarization imaging utilizes the device for measuring relative position and pose of non-cooperative spacecraft based on polarization imaging, and comprises the following steps, which are sequentially performed:

[0011] Step one: a monitoring area of a non-cooperative spacecraft to be measured is given by a ground-based tracking system, a tolerance range for observing the non-cooperative spacecraft is determined, then two observation satellites are respectively launched into designated areas, and it is ensured that the non-cooperative spacecraft to be measured appears in the field of view of each of the two observation satellites, and a world coordinate system, a camera coordinate system and a pixel coordinate system of a capture tracking polarization camera system on each of the two observation satellites are determined;

[0012] Step two: after the non-cooperative spacecraft is illuminated by sunlight, the non-cooperative spacecraft is detected by the large-aperture observation system, after the non-cooperative spacecraft enters the field of view of the large-aperture observation system, the capture tracking polarization camera system is started, the non-cooperative spacecraft is photographed by the capture tracking polarization camera system, and each frame of image is sent to the image processing system.

[0013] The image processing system calculates the lateral deviation and longitudinal deviation of the image of the tracked non-cooperative spacecraft from the cross center of the capture tracking polarized camera system, and further obtains a miss distance, and the servo control system adjusts the satellite attitude according to the real-time obtained miss distance, so that the non-cooperative spacecraft continues to be imaged in the capture tracking polarized camera system.

[0014] The servo control system adjusts the attitude of the capture tracking polarized camera system during the shooting time to ensure that the non-cooperative spacecraft has a large contrast with the imaging background until the non-cooperative spacecraft leaves the field of view of the tracking polarized camera system, and the tracking polarized camera system simultaneously takes multiple-angle polarized component photographs of the non-cooperative spacecraft by using a multi-angle polarized imaging device, obtains a plurality of polarized image sequences corresponding to the polarized component, and transmits the polarized image sequences to the image processing system for storage and processing.

[0015] Step three, the image processing system processes the plurality of polarized image sequences respectively, reduces the contrast between the non-cooperative spacecraft and the imaging background, detects the specified feature structure on the non-cooperative spacecraft, restores the polarized images by difference value respectively to obtain polarized sequence images corresponding to the angles, calculates and obtains Strokes polarized images based on the Strokes vector method, further calculates polarized degree images, and transmits all polarized images and corresponding polarized degree images during the shooting time to the database of the ground-based tracking system for storage.

[0016] Step four, the polarized degree images of the two observation satellites are located in the world coordinate system, and the image processing system calculates and obtains the pitch angle, yaw angle and roll angle of the non-cooperative spacecraft according to the camera coordinate system, pixel coordinate system and detected feature structure on the non-cooperative spacecraft of the two observation satellites, and transmits the obtained values to the ground-based tracking system through the communication system.

[0017] The two observation satellites are provided with a time system, which is used to unify the time reference of the observation satellite and the ground-based tracking system.

[0018] The multi-angle polarized components include polarized components of 0 degrees, 45 degrees, 90 degrees and 135 degrees.

[0019] Through the above design scheme, the present application can bring the following beneficial effects:

[0020] The present application performs polarized imaging on the non-cooperative spacecraft to be measured by the observation satellite carrying the capture tracking polarized camera system, obtains a plurality of polarized image sequences and performs data processing, so as to calculate and obtain the attitude angle of the non-cooperative spacecraft. All polarized images, processed polarized degree images and attitude angles of the non-cooperative spacecraft are sent to the ground to realize continuous tracking and imaging of the non-cooperative spacecraft.

[0021] This invention helps improve the ability of observation satellites to detect non-cooperative spacecraft, helps provide accurate data for orbit determination of non-cooperative spacecraft, and improves the accuracy of orbit determination and prediction.

[0022] This invention helps to enhance the monitoring capabilities of space targets, especially small targets and large elliptical targets. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0024] Fig. 1 This is a block diagram of the relative attitude measurement device and method for non-cooperative spacecraft based on polarization imaging according to the present invention.

[0025] Fig. 2 This is a schematic diagram of the coordinate system and imaging of two observation satellites in the relative pose measurement device and method for non-cooperative spacecraft based on polarization imaging of the present invention;

[0026] Fig. 3 This is a schematic diagram illustrating the roll angle calculation principle in the relative attitude measurement device and method for non-cooperative spacecraft based on polarization imaging of the present invention.

[0027] In the figure, 1-Optical observation platform, 2-Operation control system, 3-Master control system, 11-Large aperture observation system, 12-Acquisition and tracking polarization camera system, 13-Image processing system, 14-Storage system, 21-Time system, 22-Communication system, 23-Servo control system. Detailed Implementation

[0028] like Figs. 1-3 As shown, the relative attitude measurement device for non-cooperative spacecraft based on polarization imaging includes two observation satellites located at different positions, each carrying a space-based payload. The space-based payload includes an optical observation platform 1, an operation control system 2, and a central control system 3. The central control system 3 is connected to both the optical observation platform 1 and the operation control system 2, and is used to control the operation of various parts of the optical observation platform 1 and the operation control system 2. The optical observation platform 1 includes a large-aperture observation system 11, a capture and tracking polarization camera system 12, an image processing system 13, and a storage system 14. The optical observation platform 1 is used to acquire, preprocess, and store images of the non-cooperative spacecraft, and transmit the information to the ground-based tracking system through the communication system 22 of the operation control system 2.

[0029] The operation control system 2 further comprises a time system 21 and a servo control system 23, and the operation control system 2 is used for completing time unification, sending image information to the ground, measuring the off-target amount, and controlling the working of the turntable arranged on the capture tracking polarization camera system 12 according to the off-target amount; and the photoelectric tracking device is also integrated on the capture tracking polarization camera system 12;

[0030] The large-aperture observation system 11 is connected with the capture tracking polarization camera system 12 through optical transmission, and the large-aperture observation system 11 is electrically connected with the servo control system 23; the capture tracking polarization camera system 12 is electrically connected with the image processing system 13, and the capture tracking polarization camera system 12 is arranged with a multi-angle polarization imaging device for simultaneously taking photos of multi-angle polarization components; the image processing system 13 is electrically connected with the storage system 14 and the communication system 22 respectively; the servo control system 23 is electrically connected with the capture tracking polarization camera system 12; and the time system 21 is used for ensuring that the time base of the receiving observation satellite and the ground-based tracking system can be unified.

[0031] When the device works, the total control system 3 makes the non-cooperative spacecraft appear in the field of view of the large-aperture observation system 11 through the servo control system 23, and makes the capture tracking polarization camera system 12 track and observe the non-cooperative spacecraft; after the non-cooperative spacecraft leaves the field of view 11 of the large-aperture observation system, the servo control system 23 adjusts the attitude of the observation satellite according to the detected real-time off-target amount, so that the non-cooperative spacecraft is re-imaged on the capture tracking polarization camera system 12 for observation.

[0032] The polarization image obtained by the capture tracking polarization camera system 12 is sent to the storage system 14 for initial recording, and the polarization image obtained by the capture tracking polarization camera system 12 is processed at the same time; then the processed data is sent to the ground-based tracking system through the communication system 22, and the attitude of the non-cooperative spacecraft to be measured is determined in real time.

[0033] The relative pose measurement method of the non-cooperative spacecraft based on polarization imaging utilizes the relative pose measurement device of the non-cooperative spacecraft based on polarization imaging, and comprises the following steps, which are sequentially performed:

[0034] Step one:

[0035] The known spacecraft near the non-cooperative spacecraft is given by the ground tracking system, the known spacecraft is used to confirm the orbit parameters, and then the tracking error range of the non-cooperative spacecraft is determined, the two observation satellites are launched and then reach the vicinity of the known spacecraft without colliding with the known spacecraft, the world coordinate system and the camera coordinate system of the capture tracking polarization camera system 12 on the two observation satellites are determined, the non-cooperative spacecraft to be measured is detected, and it is determined that it is in the field of view of the large-aperture observation system 11. As the observation satellite and the non-cooperative spacecraft to be measured move along the orbit respectively, it may not be measurable, so the capture tracking polarization camera system 12 is only turned on during the observable period to save energy.

[0036] Step two:

[0037] The non-cooperative spacecraft to be measured is illuminated, the large-aperture observation system 11 detects the non-cooperative spacecraft, the capture tracking polarization camera system 12 is turned on after the non-cooperative spacecraft enters the field of view of the large-aperture observation system 11, the capture tracking polarization camera system 12 takes multiple images of the non-cooperative spacecraft, and the servo control system 23 adjusts the attitude of the capture tracking polarization camera system 12 during the imaging time to ensure that the non-cooperative spacecraft has a large contrast with the imaging background until the non-cooperative spacecraft leaves the field of view of the capture tracking polarization camera system 12. The capture tracking polarization camera system 12 obtains multiple sets of polarization image sequences and transmits them to the image processing system 13 for recording and processing. All polarization images and data processed by the image processing system 13 are stored in the storage system 14.

[0038] According to the calculation of the lateral deviation and longitudinal deviation of the image of the tracked non-cooperative spacecraft deviating from the cross center of the tracking polarization camera system 12 by the image processing system 13, the miss distance is obtained, the servo control system 23 controls the capture tracking polarization camera system 12 to adjust the pointing direction, so that the capture tracking polarization camera system 12 turns to the moving direction of the non-cooperative spacecraft, so that the non-cooperative spacecraft can continue to be imaged in the capture tracking polarization camera system 12.

[0039] When performing data processing on the polarization image, focal length error correction is required. The focal length of the device optical system is f. During the miss distance synthesis process, the angle dimension corresponding to a single pixel of the CCD detector is usually used instead of the focal length, and L X 、L Y are the dimensions of the azimuth angle and the elevation angle respectively. Then the measured length form miss distance can be converted into angle form miss distance. The image processing system 13 records the azimuth angle, elevation angle and polarization image of the non-cooperative spacecraft at each sampling time when the large-aperture optical detection system 11 tracks the non-cooperative spacecraft. The deviation of the polarization image of the non-cooperative spacecraft from the crosshair center (i.e. the projection of the collimation axis) is the miss distance ΔA, ΔE,

[0040]

[0041]

[0042] where (x, y) is the pixel number of the non-cooperative spacecraft deviating from the crosshair of the center of the field of view of the capture tracking polarization camera system, E is the elevation angle of the non-cooperative spacecraft relative to the optical observation platform; ΔA, ΔE are the miss distance values of the non-cooperative spacecraft, wherein ΔA is the difference between the azimuth angle of the actual position and the measured position of the non-cooperative spacecraft, and ΔE is the difference between the elevation angle of the actual position and the measured position of the non-cooperative spacecraft.

[0043] The calculation of the miss distance takes the observation satellite II of the two observation satellites as an example: during the same frame time period of the encounter of the observation satellite II and the non-cooperative spacecraft, the miss distance of the non-cooperative spacecraft in the field of view, i.e. the offset of the image center of the non-cooperative spacecraft relative to the center point of the optical axis on the target surface of the detector in the x and y directions, is fitted by a second-order polynomial.

[0044] Let t i be the time of the non-cooperative spacecraft, and x(t i ), y(t i ) be the miss distances of the non-cooperative spacecraft in the X and Y directions at time t i . i i Assuming that the exposure delay of the CCD camera in the capture tracking polarization camera system 12 of the observation satellite II is τ, the correction steps of the exposure delay are as follows:

[0045] The miss distances x(t i ), y(t i ) at time t i (i = 1,..., N) are fitted by a second-order polynomial respectively:

[0046]

[0047]

[0048] The second-order polynomial fitting coefficients a x , b x , c x , a y , b y , c y are obtained.

[0049] The miss distance fitting value at time t i -τ output by the second-order polynomial is taken as the miss distance value at time t i :

[0050] x'(t i ) = a x (t i -τ) 2 +b x(t i -τ)+c x (5)

[0051] y′(t i ) = a y (t i -τ) 2 +b y (t i -τ)+c x (6)

[0052] Using x′(t) i ) and y′(t i Angle synthesis is performed according to the following formula to complete the exposure delay correction of the CCD camera.

[0053]

[0054]

[0055] The miss distances ΔA and ΔE, combined with the corresponding measurements recorded by image processing system 13, yield a directional ray for the non-cooperative spacecraft. The calculation formula is as follows:

[0056] A = A e +ΔA (9)

[0057] E = E e +ΔE (10)

[0058] A is the azimuth angle of the non-cooperative spacecraft relative to the optical observation platform, and E is the elevation angle of the non-cooperative spacecraft relative to the optical observation platform; A e It is the azimuth angle and E output by the image processing system 13. e It is the pitch angle output by the image processing system 13;

[0059] Similarly, observation satellite I also obtained the corresponding miss distance value;

[0060] Step 3:

[0061] The image processing system 13 performs preprocessing, polarization sequence image acquisition, and polarization feature image extraction based on the polarization image sequence captured by the acquisition and tracking polarization camera system 12. This reduces the imaging background signal noise in the spectral range of the non-cooperative spacecraft, detects feature structures such as cuboids and triangles on the non-cooperative spacecraft for subsequent attitude determination, and transmits all polarization images and corresponding polarization degree images back to the database of the ground-based tracking system through the communication system 22.

[0062] The specific processing method is as follows:

[0063] Strokes vector method uses a column matrix to describe the polarization state of light, and uses I, Q, U, V four letters to replace S0, S1, S2, S3 in the formula respectively:

[0064]

[0065] In the formula, S0 represents the total intensity of light wave, S1 reflects the intensity difference between horizontal polarization light and vertical polarization light, S2 reflects the intensity difference of linear polarization component light in ± 45° direction, and S3 reflects the intensity difference between left circular polarization light and right circular polarization component light, wherein S0>0, and S1, S2, S3 are determined according to the size of polarization component in different directions. For completely polarized light, S0 2 =S1 2 +S2 2 +S3 2 ;

[0066] Among them, I, Q, U, V can be represented by the components of electric field vector in xy coordinate plane:

[0067]

[0068]

[0069] U=S2=2E 0x E 0y cosφ (14)

[0070] V=S3=2E 0x E 0y sinφ (15)

[0071] In the formula, E 0x , E 0y is the amplitude of electric field vector in xy coordinate plane, and φ is the phase of electric field vector in xy coordinate plane;

[0072] Each Strokes parameter can also be expressed by light intensity as follows:

[0073]

[0074] Among them, I 0° , I 45° , I 90° , I 135° respectively represent the polarization component light intensity value of 0°, 45°, 90°, 135°, I R represents the right circular polarization component light intensity value, and I L represents the left circular polarization component light intensity value.

[0075] The formula for calculating the degree of polarization (DOP) of the non-cooperative spacecraft is shown below. Since the circular polarization component of the non-cooperative spacecraft in most natural environments can be ignored within a certain detection range, V can be taken as 0 in most cases.

[0076]

[0077] The formula for calculating the angle of polarization (AOP) of the non-cooperative spacecraft is as follows:

[0078]

[0079] The capture and tracking polarization camera system 12 uses a multi-angle polarization imaging device to simultaneously take pictures of the 0°, 45°, 90°, and 135° polarization components of the non-cooperative spacecraft, and real-time polarization information is extracted. The image processing system 13 calculates the strokes polarization components S0, S1, and S2 of the non-cooperative spacecraft, and further calculates the degree of polarization image from these three polarization components. This process is performed for each frame during the imaging of the non-cooperative spacecraft, and a series of polarization degree images within the shooting time are obtained.

[0080] Step four, the image processing system 13 processes the polarization degree image of the non-cooperative spacecraft and stores it in the storage system 14. The pitch angle, yaw angle, and roll angle of the non-cooperative spacecraft are calculated, and the processed information is transmitted back to the ground tracking system through the communication system 22.

[0081] For each frame of polarization degree image obtained by the camera, it can be understood that the load I on satellite I is imaged on the non-cooperative spacecraft in the world coordinate system, and the central axis vector of the non-cooperative spacecraft is obtained. The central axis vector and the load I form a plane Γ1, and the load II on satellite II also forms a plane Γ2 with the central axis vector of the non-cooperative spacecraft. The equation of the straight line obtained by the intersection of the two straight lines in the world coordinate system determines the pitch angle and yaw angle of the non-cooperative spacecraft in the air.

[0082] From the imaging principle, the plane Γ1 can be obtained by the capture and tracking polarization camera system 12 of the observation satellite I, which contains the axis AB on the non-cooperative spacecraft, the line segment A1B1 obtained by imaging AB by the capture and tracking polarization camera system 12 of the observation satellite I, and the origin O c1 .

[0083] (1) The world coordinate system O w x w y w z w , used to represent the positions of the capture and tracking polarization camera system 12 and the non-cooperative spacecraft to be measured in the environment; the origin is O w , Y w points to the zenith perpendicular to the horizontal plane, and Z wConnect the origins of the two camera coordinate systems at point O. c1 O c2 At the same time, perpendicular to Y w Z w X w With Y w Z w Form a right-handed coordinate system.

[0084] (2) Camera coordinate system O c x c y c z c The camera coordinate system is fixed on the camera of the capture-tracking polarization camera system 12, with its origin at the camera's optical center and the distance from the optical center to the image plane being the camera's focal length. The origins of the two camera coordinate systems are set to O1 and O2 respectively. c1 O c2 The distance between these two points is 2L, O c1 O c2 O w Form a straight line, O w It is the midpoint of this straight line.

[0085] At a certain imaging time t, for the acquisition and tracking polarization camera system 12 of observation satellite I, the image A1B1 formed on the image plane of the central axis AB of the non-cooperative spacecraft, and the coordinate system origin O of the camera of observation satellite II. c1 Line O connecting to endpoint A of the non-cooperative spacecraft c1 The line vector connecting A1 in its camera coordinate system The following expressions are respectively

[0086]

[0087]

[0088] in Points A, B, and O in the camera coordinate system are respectively The coordinates below are f1, where f1 is the focal length of the acquisition and tracking polarization camera system 12 of the observation satellite I.

[0089] A1B1 and O c1 A1 forms plane Γ1, and its normal vector τ′1 and the corresponding vector τ1 transformed into the world coordinate system are expressed as follows:

[0090] τ′1=A1B1×O c1 A1 (21)

[0091]

[0092]

[0093]

[0094]

[0095] Among them, M x1 With M y1 M m1 M represents the coordinate transformation matrices for rotations about the x and y axes, respectively. m1 Let M be the coordinate transformation matrix for translation. A1 and E1 are the azimuth and elevation angles measured by the acquisition and tracking polarization camera system 12 of observation satellite I, respectively, and 2L is the distance between observation satellite I and observation satellite II. The same calculation method is used for the acquisition and tracking polarization camera system 12 of observation satellite II, but in calculating M... m1 When L becomes -L. Using the same calculation method, the vector τ2 in the world coordinate system can be obtained, and then the vector expression of the central axis AB of the non-cooperative spacecraft in the world coordinate system can be calculated:

[0096] AB=τ1×τ2=(l,m,n) (26)

[0097] Among them, l, m, n are components of the vector obtained by the above formulas (21) to (26);

[0098] The calculated yaw angle Φ and pitch angle Ψ at time t are as follows:

[0099]

[0100]

[0101] Point A on the surface of the non-cooperative spacecraft is in the camera coordinate system of the acquisition and tracking polarization camera system 12 of observation satellite I. The lower coordinate is This point is transformed to the world coordinate system O. w x w y w z w The coordinates below are

[0102] A w1 =M m1 M x1 M y1 A c1 (29)

[0103] M x1 With M y1 M m1 They are respectively around The coordinate transformation matrix M for rotation along the x and y axes. m1 The coordinate transformation matrix is ​​the translation matrix, and the specific expressions are shown in (23) to (25).

[0104] Straight line O c1 A w1 The equation in the world coordinate system is

[0105]

[0106] The camera coordinate system O c2 x c2 y c2 z c2 The coordinates are The equation of straight line O c2 A w2 is calculated in the same way, and the origin of the camera coordinate system of the observation satellite II is O c1 :

[0107]

[0108] In formula (30) and (31), X, Y, and Z represent independent variables in the equation of a straight line.

[0109] Since A w1 , A w2 are the central projection points of point A in the two capture tracking polarization camera systems 12, straight lines O c1 A w1 , O c2 A w2 intersect at point A, and the coordinates of point A can be obtained from the above formulas.

[0110] Since it is assumed that the motion of the axis of the non-cooperative spacecraft is in the same plane, the coordinates of the end points A and B of the axis of the non-cooperative spacecraft at any time t are obtained as Let the starting time of a frame of a picture taken by the camera of the capture tracking polarization camera system 12 be t1, and the ending time be t2. It is assumed that the axis of the non-cooperative spacecraft moves in the same plane within this frame of picture, and that the axis AB of the non-cooperative spacecraft at time t1 is imaged as A1B1 on the image plane of the capture tracking polarization camera system 12 of the observation satellite I, and that the axis AB of the non-cooperative spacecraft at time t2 is imaged as A2B2 on the image plane of the capture tracking polarization camera system 12 of the observation satellite I.

[0111] The coordinates of the end points A and B of the non-cooperative spacecraft in the world coordinate system are where any time t includes time t1 and time t2, a plane Γ0 is drawn through A1B1 at time t1, and a straight line A2B2 is drawn through A2B2 at time t2, and the axis vectors of the non-cooperative spacecraft at times t1 and t2 are Then, the plane Γ0 can be represented by the following formula,

[0112]

[0113] x, y, z represent independent variables in the plane equation respectively;

[0114] The normal vector n0 of Γ0 is (A, B, C) from the above formula;

[0115] Passing through the point N on the non-cooperative spacecraft, a straight line MN is perpendicular to the central axis, intersecting the central axis at point M, and the angle between MN and the plane is is perpendicular to Γ0:

[0116]

[0117]

[0118] The normal vector of is The normal vector of is Passing through the point N on the non-cooperative spacecraft, a straight line MN is perpendicular to the central axis, intersecting the central axis at point M, and the angle between MN and the plane is Then we have:

[0119]

[0120]

[0121] Therefore, the size of the roll angle is

[0122]

[0123] The same processing is done for other frames, and the roll angle of the non-cooperative spacecraft at each sampling time point within the shooting time period can be obtained.

[0124] The attitude of the non-cooperative spacecraft within the shooting time period can be determined as above, and then the processed information is transmitted back to the ground-based tracking system by the communication system 22.​​

Claims

1. A device for measuring the relative pose of a non-cooperative space vehicle based on polarimetric imaging, characterized in that it comprises: The application relates to a space-based observation system, which comprises two observation satellites located at different positions, and the two observation satellites are both provided with space-based loads; the space-based loads comprise an optical observation platform (1), an operation control system (2) and a general control system (3); the general control system (3) is connected with the optical observation platform (1) and the operation control system (2) respectively, and is used for the operation control of each part of the optical observation platform (1) and the operation control system (2); the optical observation platform (1) comprises a large-aperture observation system (11), a capture tracking polarization camera system (12), an image processing system (13) and a storage system (14), and the optical observation platform (1) is used for the collection, image pre-processing and storage of non-cooperative spacecraft images, and the information is sent to a ground-based tracking system through a communication system (22) of the operation control system (2); The operation control system (2) further comprises a time system (21) and a servo control system (23), and the operation control system (2) is used for completing time unification, sending image information to the ground, measuring the off-target amount and controlling the working of a turntable arranged on the capture tracking polarization camera system (12) according to the off-target amount; photoelectric tracking equipment is further integrated and arranged on the capture tracking polarization camera system (12); The large-aperture observation system (11) is connected with the capture tracking polarization camera system (12) through light transmission, and the large-aperture observation system (11) is electrically connected with the servo control system (23); the capture tracking polarization camera system (12) is electrically connected with the image processing system (13); the image processing system (13) is electrically connected with the storage system (14) and the communication system (22) respectively; the servo control system (23) is electrically connected with the capture tracking polarization camera system (12); and the time system (21) is used for unifying the time reference of the observation satellite and the ground-based tracking system.

2. The polarization imaging based non-cooperative space vehicle relative pose measurement apparatus of claim 1, wherein: A multi-angle polarization imaging device is arranged on the capture tracking polarization camera system (12) and is used for simultaneously taking pictures of multi-angle polarization components.

3. A method for measuring relative pose of a non-cooperative spacecraft based on polarimetric imaging, using the polarimetric imaging device for measuring relative pose of a non-cooperative spacecraft according to claim 1, characterized in that: The application further discloses a space-based observation method, which comprises the following steps in sequence: Step one: a monitoring area of a non-cooperative spacecraft to be measured is given by a ground-based tracking system, a tolerance range for observing the non-cooperative spacecraft is determined, then two observation satellites are respectively launched into the respective designated areas, it is ensured that the non-cooperative spacecraft to be measured appears in the visual field of the two observation satellites, and the world coordinate system, the camera coordinate system and the pixel coordinate system of the capture tracking polarization camera system (12) on the two observation satellites are respectively determined; Step two: after the non-cooperative spacecraft is illuminated by sunlight, the large-aperture observation system (11) detects the non-cooperative spacecraft, after the non-cooperative spacecraft enters the visual field of the large-aperture observation system (11), the capture tracking polarization camera system (12) is started, the capture tracking polarization camera system (12) takes pictures of the non-cooperative spacecraft and sends each frame of image to the image processing system (13); ​ ​ The image processing system (13) calculates the lateral deviation and longitudinal deviation of the tracked non-cooperative spacecraft image from the cross center of the capture tracking polarization camera system (12), and further obtains the miss distance, and the servo control system (23) adjusts the satellite attitude according to the real-time obtained miss distance, so that the non-cooperative spacecraft continues to be imaged in the capture tracking polarization camera system (12); During the shooting time, the servo control system (23) adjusts the attitude of the capture tracking polarization camera system (12) to ensure that the non-cooperative spacecraft has a large contrast with the imaging background until the non-cooperative spacecraft leaves the field of view of the tracking polarization camera system (12), and the tracking polarization camera system (12) simultaneously takes multi-angle polarization component photographs of the non-cooperative spacecraft using a multi-angle polarization imaging device, obtains a plurality of groups of polarization image sequences corresponding to the multi-angle polarization component, and transmits them to the image processing system (13) for storage and processing; Step three, the image processing system (13) processes a plurality of groups of polarization image sequences respectively, reduces the contrast between the non-cooperative spacecraft and the imaging background, detects the specified feature structure on the non-cooperative spacecraft, restores the polarization image by difference value respectively to obtain the polarization sequence image corresponding to the angle, and further calculates the Strokes polarization image based on the Strokes vector method, and further calculates the polarization degree image, and transmits all polarization images and corresponding polarization degree images during the shooting time to the database of the ground-based tracking system for storage; Step four, the polarization degree images of the two observation satellites are located in the world coordinate system, and the image processing system (13) calculates and obtains the pitch angle, yaw angle and roll angle of the non-cooperative spacecraft according to the camera coordinate system, pixel coordinate system and detected feature structure on the non-cooperative spacecraft, and transmits the obtained values to the ground-based tracking system through the communication system (22).

4. The polarimetric imaging based non-cooperative spacecraft relative pose measurement method according to claim 3, characterized in that: The two observation satellites are provided with a time system (21), which is used to unify the time reference of the observation satellite and the ground-based tracking system.

5. The polarization imaging based non-cooperative spacecraft relative pose measurement method according to claim 3, characterized in that: The multi-angle polarization component includes 0 degree, 45 degree, 90 degree and 135 degree polarization components.

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