Attitude calculation method and system for remote sensing satellite observing stars

Abstract

The application provides a remote sensing satellite observation star attitude calculation method and system, including the following steps: step S1: establishing a satellite observation star attitude reference, constraining a star sun array to face the sun, and ensuring satellite platform energy safety; step S2: performing star search on the satellite observation star attitude reference to obtain a target star; step S3: calculating a satellite load observation target star observation platform attitude; step S4: star sensor earth blocking analysis: ensuring star sensor calibration of the target star, avoiding earth blocking star sensors, and obtaining an avoidance angle; step S5: optimizing the observation platform attitude according to the avoidance angle, and outputting an optimal platform attitude. The application fully considers safety and engineering realizability, requires a small satellite platform maneuvering angle, and is suitable for various high-precision remote sensing satellites.

Description

Technical Field

[0001] This invention relates to remote sensing satellite calibration and positioning technology, specifically to a method and system for calculating the attitude of stars observed by remote sensing satellites. Background Technology

[0002] In recent years, with the continuous development of satellite remote sensing technology, the demand for calibration and positioning accuracy of remote sensing images has been increasing. Especially in the field of infrared radiometric calibration, traditional infrared remote sensing systems mainly achieve on-orbit radiometric calibration through on-board object-side and image-side blackbodies. However, with the increase in the aperture of infrared optical remote sensing instruments, placing a large-aperture blackbody in front of the optical path has become difficult to achieve in engineering. Stars, with their stable spatial position and relatively stable spectral characteristics, are important calibration sources for quantitative remote sensing satellites. With the improvement of instrument sensitivity, star-based calibration schemes have become one of the main radiometric calibration schemes for large optical cameras in recent years.

[0003] Based on literature review, a calibration method based on stellar observations was disclosed in the paper "Research on the Method for Determining Observed Stars for On-Ship Calibration" (Chinese Space Science and Technology, Vol. 37, No. 3, 2017). This method treats stars as point sources and models their irradiance. Based on this, a Taylor series expansion and an improved genetic algorithm are proposed to solve for the temperature of the stars. Then, the irradiance of stars in the WISE catalog is extrapolated, and the spectral distribution characteristics of stars at different accuracies are analyzed and summarized to determine the irradiance of the observed stars in the camera's detection band. This article focuses on the stellar-based radiometric calibration algorithm and does not cover how to maneuver and observe stars after the satellite enters orbit.

[0004] The paper "On-orbit Correction of Pointing Deviation of Geostationary Orbit Imager Based on Stellar Observations" (Acta Optica Sinica, Vol. 29, No. 9, 2009) discloses a geometric positioning method based on stellar observations. It establishes an on-orbit correction model for payload pointing deviation incorporating stellar information, proposes methods for selecting several key parameters in the model, and analyzes the impact of digital delay integration techniques and system point source spread functions on pointing deviation accuracy. This paper focuses on the stellar-based geometric positioning method and does not address how the satellite maneuvers to observe stars after entering orbit.

[0005] Patent document CN105387996A discloses a method for calibrating the optical axis consistency of a multi-optical-axis ground-based stellar observation system. It proposes a fast and high-precision parallelism calibration method for multi-optical-axis systems using a stellar tracking system. This method utilizes the slit field of view of an imaging spectrometer to scan stars and fit the received energy to determine the center, thus overcoming the difficulty of determining the field of view position in the spectral dimension. This patent focuses on a star-based geometric calibration method and does not address how to maneuver and observe stars after the satellite enters orbit.

[0006] Patent document CN107945229A discloses a method for extracting the centroid of stars for an array instrument on a geostationary Earth observation satellite. It utilizes image sequence fusion to fuse image sequences after removing fixed-pattern noise into a star trajectory image and determines the star trajectory region within this image. This patent focuses on the processing method after star observation but does not address how the satellite maneuvers to observe stars after entering orbit. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method and system for calculating the attitude of stars observed by remote sensing satellites. The proposed method for calculating the attitude of stars by remote sensing satellites fully considers safety and engineering feasibility, requires a small maneuvering angle for the satellite platform, and is applicable to various types of high-precision remote sensing satellites.

[0008] A method for calculating the attitude of a star observed by a remote sensing satellite according to the present invention includes the following steps:

[0009] Step S1: Establish the attitude reference for satellite observation of stars, constrain the star solar array to face the sun, and ensure the energy security of the satellite platform;

[0010] Step S2: Perform a star search based on the attitude reference of the observed stars by the satellite to obtain the target star;

[0011] Step S3: Calculate the observation platform attitude of the target star as observed by the satellite payload;

[0012] Step S4: Star sensor occlusion analysis: Ensure the star sensor is calibrated to the target star, avoid the Earth occluding the star sensor, and obtain the avoidance angle;

[0013] Step S5: Optimize the attitude of the observation platform according to the avoidance angle and output the optimal platform attitude.

[0014] Preferably, the star search requires that the angle between the orientation of the solar array and the solar vector be less than a safety threshold to ensure that the solar array is always illuminated during the calibration process.

[0015] Preferably, the steps of the star search are as follows:

[0016] a) Calculate the vector pointing from the satellite to the Earth's center;

[0017] b) Search for valid stars that meet energy security requirements: Import the star database and obtain valid stars based on the criteria for determining valid stars that meet energy security requirements;

[0018] The criteria for determining a valid star that meets energy security requirements are as follows:

[0019]

[0020] in The energy security protection angle, θ, represents the threshold angle between the orientation of the solar array panels and the solar vector; star_cam This is the angle between the satellite payload's optical axis and the star's vector.

[0021] c) Based on the satellite's vector pointing towards the Earth's center, remove stars that are blocked by the Earth: determine the Earth-blocked stars for the valid stars, remove stars that are blocked by the Earth, and obtain the filtered stars.

[0022] The criteria for determining Earth's occlusion are as follows:

[0023]

[0024] In the above formula, The angle of occlusion for Earth, θ earth_cam This is the angle between the satellite payload's optical axis and the star's vector;

[0025] d) Determine the target star: Select the star with the smallest angle to the satellite payload vector from the screened stars as the target star for observation.

[0026] Preferably, the attitude of the observation platform is calculated by using the plane normal formed by the target star vector and the initial vector of the satellite payload as the rotation axis, and determining the attitude of the satellite payload to observe the target star by means of a dual-vector attitude determination method.

[0027] Preferably, the calculation steps of the two-vector attitude determination method are as follows:

[0028] a) Determine vector one as the target star vector;

[0029] b) Determine vector two as the normal vector of the plane formed by the target star and the initial optical axis of the satellite payload;

[0030] c) Dual-vector attitude determination calculation: Perform a difference multiplication operation on vector one and vector two, and obtain the attitude matrix of the target star observed by the satellite payload according to the coordinate transformation principle.

[0031] Preferably, the avoidance angle is determined by a method to avoid Earth's obstruction, which determines whether the satellite's star sensor is obstructed by Earth during star observation. If it is obstructed, the avoidance angle is calculated to ensure that the star sensor can be used during star observation and to guarantee the safety of the satellite platform.

[0032] Preferably, the method for avoiding Earth's shading includes:

[0033] a) Determining if the star sensor is blocked by the Earth: The criterion for determining if the star sensor is blocked by the Earth is that the angle between the star sensor's optical axis vector and the vector pointing from the satellite to the Earth is less than the Earth's protection angle. The expression is:

[0034]

[0035] In the above formula, Earth shielding protection angle for star sensors; θ earth_st The angle between the optical axis vector of the star sensor and the vector pointing from the satellite to Earth;

[0036] b) Calculation of the avoidance angle for the star sensor to avoid being blocked by the Earth: If the star sensor is detected to be blocked by the Earth, the avoidance angle is calculated to make the optical axis of the star sensor move away from the Earth.

[0037] This invention also provides a system for calculating the attitude of stars observed by remote sensing satellites, comprising:

[0038] Module M1: Establishes the attitude reference for satellite observation of stars, constrains the star solar array to face the sun, and ensures the energy security of the satellite platform;

[0039] Module M2: Performs star search based on the attitude reference of the observed stars by the satellite to acquire the target star;

[0040] Module M3: Calculates the attitude of the observation platform as observed by the satellite payload of the target star;

[0041] Module M4: Star Sensor Occlusion Analysis: Ensures the star sensor is calibrated to the target star, avoids Earth obscuring the star sensor, and obtains the avoidance angle;

[0042] Module M5: Optimizes the attitude of the observation platform based on the avoidance angle and outputs the optimal platform attitude.

[0043] Preferably, the star search of module M2 requires that the angle between the orientation of the solar array and the solar vector be less than a safety threshold to ensure that the solar array is always illuminated during the calibration process.

[0044] Preferably, the method for calculating the attitude of the observation platform of module M3 is as follows: using the plane normal formed by the target star vector and the initial vector of the satellite payload as the rotation axis, the attitude of the satellite payload observing the target star is determined by a dual-vector attitude determination method. The calculation steps of the dual-vector attitude determination method are as follows:

[0045] a) Determine vector one as the target star vector;

[0046] b) Determine vector two as the normal vector of the plane formed by the target star and the initial optical axis of the satellite payload;

[0047] c) Dual-vector attitude determination calculation: Perform a difference multiplication operation on vector one and vector two, and obtain the attitude matrix of the target star observed by the satellite payload according to the coordinate transformation principle.

[0048] Preferably, module M4 uses an Earth-avoidance design method to determine whether the satellite's star sensor is obstructed by the Earth during star observation. If it is obstructed, an avoidance angle calculation is performed to ensure that the star sensor can be used during star observation and to guarantee the safety of the satellite platform.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] 1. This invention focuses on how to acquire the target star after the satellite enters orbit and input the attitude of the star observed by the satellite.

[0051] 2. This invention fully considers safety and engineering feasibility, requires a small maneuvering angle of the satellite platform, and is suitable for various high-precision remote sensing satellites. Attached Figure Description

[0052] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0053] Figure 1 This is a flowchart of the method for calculating the attitude of stars observed by remote sensing satellites according to the present invention;

[0054] Figure 2 Spatial geometric relationship diagram of stars observed by satellite Detailed Implementation

[0055] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0056] Stars, with their stable spatial positions and relatively stable spectral characteristics, are important calibration sources for quantitative remote sensing satellites and are widely used for geometric and radiometric calibration of remote sensing instruments. This invention proposes a method for calculating the attitude of stars observed by remote sensing satellites. This method can search for the optimal stellar observation target and output the observation attitude of the satellite platform, while ensuring satellite energy security.

[0057] This invention provides a method for calculating the attitude of stars observed by remote sensing satellites, comprising the following steps:

[0058] Step S1: Establish the attitude reference for satellite observation of stars, constrain the star solar array to face the sun, and ensure the energy security of the satellite platform;

[0059] Step S2: Perform a star search based on the attitude reference of the observed stars by the satellite to obtain the target star;

[0060] The star search requires constraining the angle between the orientation of the solar array and the solar vector to be less than a safety threshold, ensuring that the solar array is always illuminated during the calibration process. The specific implementation steps are as follows:

[0061] a) Calculate the vector pointing from the satellite to the Earth's center;

[0062] The vector pointing from the satellite to the Earth's center is calculated based on the satellite's orbital position; assuming the three-dimensional projection of the satellite's real-time orbital position in the inertial reference frame is [s] x s y s z Then, the projection expression of the vector pointing from the satellite to the Earth's center in the inertial reference frame can be written as:

[0063]

[0064] Where S x This represents the projection of the satellite's position vector onto the x-axis coordinate system of the inertial reference frame; S y S represents the projection of the satellite's position vector onto the y-axis coordinate system of the inertial reference frame; z R represents the projection of the satellite's position vector onto the z-axis coordinate system of the inertial reference frame. i s_e This is the projection of the vector pointing from the satellite to the Earth's center onto the inertial reference frame.

[0065] b) Search for valid stars that meet energy security requirements: Import the star database and obtain valid stars based on the criteria for determining valid stars that meet energy security requirements;

[0066] The criteria for determining a valid star that meets energy security requirements are as follows: in The energy security protection angle, θ, represents the threshold angle between the orientation of the solar array panels and the solar vector; star_cam This is the angle between the satellite payload's optical axis and the star's vector.

[0067] Specifically, in this embodiment, the satellite payload can be a satellite camera; it includes the three-dimensional projection R of each star vector in the inertial reference frame. i star Based on the attitude reference definition for stellar observation, the projection R of the satellite camera's optical axis in the inertial coordinate system can be obtained. i cam Criteria for determining effective stars that meet energy security requirements:

[0068]

[0069] In the above formula, θ is the energy security protection angle, representing the threshold angle between the orientation of the solar array panels and the solar vector. star_cam Let be the angle between the satellite camera's optical axis and the star's vector, calculated as follows:

[0070]

[0071] Where R i s_e The projection of the satellite's vector pointing towards the Earth's center into the inertial reference frame; the three-dimensional projection R of each star's vector into the inertial reference frame. i star The projection R of the satellite payload camera's optical axis in the inertial coordinate system i cam .

[0072] c) Based on the satellite's vector pointing towards the Earth's center, remove stars that are blocked by the Earth: determine the Earth-blocked stars for the valid stars, remove stars that are blocked by the Earth, and obtain the filtered stars.

[0073] The criteria for determining Earth's occlusion are as follows:

[0074]

[0075] In the above formula, The angle of occlusion for Earth, θ earth_cam This is the angle between the satellite payload's optical axis and the star's vector;

[0076] θ earth_cam The calculation formula is as follows:

[0077]

[0078] d) Determine the target star: Select the star with the smallest angle to the satellite payload vector from the screened stars as the target star for observation.

[0079] Step S3: Calculate the attitude of the observation platform when the satellite payload observes the target star; The method for calculating the attitude of the observation platform is as follows: Using the plane normal formed by the target star vector and the initial vector of the satellite payload as the rotation axis, the attitude of the satellite payload observing the target star is determined by the dual-vector attitude determination method, which can ensure that the satellite maneuver angle is minimized.

[0080] Specifically, the calculation steps of the two-vector attitude determination method are as follows:

[0081] a) Determine vector one as the target star vector;

[0082] The calculation steps for Vector 1 are as follows: To ensure the satellite payload can observe the star, the camera's optical axis must be parallel to the star's vector in the new attitude. To facilitate the description of coordinate transformation, we define the camera's optical axis as parallel to the +Z axis of the satellite's body coordinate system. The projection expression of the camera's optical axis in the inertial coordinate system is then:

[0083] R z_i =R istar

[0084] In the above formula, R i star This is the projection of the target star in the inertial coordinate system.

[0085] The projection expression of the camera optical axis in the body coordinate system:

[0086]

[0087] b) Determine vector two as the normal vector of the plane formed by the target star and the initial optical axis of the satellite payload;

[0088] The calculation steps for Vector 2 are as follows: The projection expression of the normal vector of the plane formed by the target star and the camera's initial optical axis in the inertial coordinate system is as follows:

[0089] R y_i =R i star ×R i cam

[0090] In the above formula, R i star R is the projection of the target star in the inertial coordinate system. i cam The initial projection of the satellite camera's optical axis in the inertial coordinate system.

[0091] The projection expression of the normal vector in the body coordinate system is as follows:

[0092] R y_b =C i_b0 ·R y_i

[0093] In the above formula, C i_b0 This is the rotation matrix of the inertial reference frame relative to the star observation attitude reference coordinate system, which can be calculated according to the definition of the star observation attitude reference.

[0094] c) Two-vector attitude determination calculation: Perform a difference multiplication operation on vector one and vector two, and according to the coordinate transformation principle,

[0095] Obtain the attitude matrix of the target star observed by the satellite payload;

[0096] Specific calculation steps: Perform a difference multiplication operation on vector one and vector two to obtain the third vector expression:

[0097]

[0098] In the above formula, R x_i R is the projection of the difference vector in the inertial coordinate system. x_bThis is the projection of the difference vector onto the body coordinate system.

[0099] Based on the principle of coordinate transformation, the attitude matrix C of the satellite body coordinate system relative to the coordinate system during the payload's sidereal observation can be obtained. i_b1 The expression is:

[0100] C i_b1 =[R x_b R y_b R z_b ]·[R x_i R y_i R z_i ] T

[0101] In the above formula, [·] T This represents the matrix transpose operation.

[0102] Step S4: Star sensor occlusion analysis: Ensure the star sensor is calibrated to the target star, avoid the star sensor being occluded by the Earth, and obtain the avoidance angle; when the satellite payload camera is observing stars, in order to avoid the star sensor being occluded by the Earth, it is necessary to optimize the observation attitude of the target star to ensure that the star sensor is in a usable state.

[0103] The avoidance angle is determined by a method to avoid Earth's obstruction, which determines whether the satellite's star sensor is obstructed by Earth during star observation. If it is obstructed, the avoidance angle is calculated to ensure that the star sensor can be used during star observation and to guarantee the safety of the satellite platform.

[0104] Specifically, design methods to avoid Earth's shading include:

[0105] a) Determining if the star sensor is blocked by the Earth: The criterion for determining if the star sensor is blocked by the Earth is that the angle between the star sensor's optical axis vector and the vector pointing from the satellite to the Earth is less than the Earth's protection angle. The expression is:

[0106]

[0107] In the above formula, Earth shielding protection angle for star sensors; θ earth_st The angle between the optical axis vector of the star sensor and the vector pointing from the satellite to Earth;

[0108] Specifically, first, the projection R of the star sensor's optical axis vector in the inertial reference frame is calculated when the camera observes the star. st_i The calculation expression is as follows:

[0109] R st_i =[C i_b1 T·R st_b

[0110] In the above formula, Ci_b1 R is the attitude matrix of the satellite's local coordinate system relative to the orbital time of the payload observation. st_b The projection of the star sensor's optical axis vector onto the body coordinate system can be determined based on the star sensor's layout on the satellite.

[0111] The criterion for determining whether a star sensor is blocked by the Earth is whether the angle between the star sensor's optical axis pointing vector and the satellite's vector pointing towards the Earth is less than the Earth's protection angle. If it is less, it is considered blocked; the expression is:

[0112]

[0113] In the above formula, The Earth shielding angle for the star sensor can be determined based on a combination of the satellite's orbital altitude and the star sensor's performance. θ earth_st Let be the angle between the optical axis vector of the star sensor and the vector pointing from the satellite to Earth, calculated as follows:

[0114]

[0115] In the above formula, R i s_e R is the projection of the vector pointing from the satellite to the Earth's center into the inertial reference frame. st_i This is the projection of the star sensor's optical axis pointing vector onto the inertial reference frame.

[0116] b) Calculation of the avoidance angle for the star sensor to avoid being blocked by the Earth: If the star sensor is detected to be blocked by the Earth, the avoidance angle is calculated to make the optical axis of the star sensor move away from the Earth.

[0117] Specifically, if the star sensor is detected to be blocked by the Earth, that is, the angle between the star sensor's optical axis vector and the vector pointing from the satellite to the Earth is less than the Earth's protection angle, then an anti-blocking design is required.

[0118] Step S5: Optimize the attitude of the observation platform according to the avoidance angle and output the optimal platform attitude.

[0119] Specifically, to ensure the camera can observe the star, the satellite can be rotated around the Z-axis of its own coordinate system (defining the camera's optical axis as pointing towards the body coordinate system + Z-axis). This ensures the camera's optical axis points towards the star while simultaneously moving the star sensor's optical axis away from Earth. Therefore, the final optimal platform attitude expression is:

[0120]

[0121] Where C i_b1 is the attitude matrix of the satellite's own system relative coordinate system when the satellite payload observes sidereal time; rollz is the rotation angle of the star sensor to avoid the Earth, which can be calculated based on the optical axis pointing vector of the star sensor and the Earth blocking protection angle of the star sensor.

[0122] Based on the attitude calculation method for stars observed by remote sensing satellites described above, this invention also provides an attitude calculation system for stars observed by remote sensing satellites, comprising:

[0123] Module M1: Establishes the attitude reference for satellite observation of stars, constrains the star solar array to face the sun, and ensures the energy security of the satellite platform;

[0124] Module M2: Performs star search based on the attitude reference of the observed stars by the satellite to obtain the target star; the star search of Module M2 must constrain the angle between the orientation of the solar array and the solar vector to be less than a safety threshold to ensure that the solar array is always illuminated during the calibration process.

[0125] Module M3: Calculates the attitude of the observation platform when the satellite payload observes the target star; The method for calculating the attitude of the observation platform in Module M3 is as follows: The attitude of the satellite payload observing the target star is determined by using the plane normal formed by the target star vector and the initial vector of the satellite payload as the rotation axis and the dual-vector attitude determination method.

[0126] Module M4: Star Sensor Earth Obstruction Analysis: Ensures the star sensor is calibrated to the target star, avoids Earth obstruction of the star sensor, and obtains avoidance angles; Module M4 uses an Earth obstruction avoidance design method to determine whether the satellite's star sensor is obstructed by Earth during star observation. If obstructed, it calculates avoidance angles to ensure that the star sensor can be used during star observation and to guarantee the safety of the satellite platform.

[0127] Module M5: Optimizes the attitude of the observation platform based on the avoidance angle and outputs the optimal platform attitude.

[0128] The working principle of this invention is as follows:

[0129] 1. Establish attitude references for satellite observation of stars.

[0130] When defining the initial attitude reference for observing a star, it is necessary to ensure that the satellite's solar array normals are aligned with the Sun to guarantee energy security. (See Appendix) Figure 2 The constraints on the satellite's rotation around the solar panel normal can be determined based on the satellite's own characteristics. For example, for traditional Earth remote sensing satellites, the constraint can be to minimize the angle between the camera's optical axis and the star-ground vector to determine the satellite's initial stellar observation attitude. Simultaneously, the timing of stellar observations must avoid stellar obstruction.

[0131] 2. Perform star searches based on the attitude reference of stars observed by satellites.

[0132] Star search requires two conditions to be met: First, the angle between the solar array's solar panels and the solar vector must be less than a safe threshold while the satellite is maneuvering to observe stars, ensuring the solar array remains illuminated throughout the calibration process; second, the stars observed by the satellite must not be obscured by Earth. Based on these two constraints, the steps for star search are as follows:

[0133] a) Calculate the vector pointing from the satellite to the Earth's center.

[0134] The vector pointing from the satellite to the Earth's center can be calculated based on the satellite's orbital position. Let the three-dimensional projection of the satellite's real-time orbital position in the inertial reference frame be [s]. x s y s z Then, the projection expression of the vector pointing from the satellite to the Earth's center in the inertial reference frame can be written as:

[0135]

[0136] Where R i s_e This is the projection of the vector pointing from the satellite to the Earth's center onto the inertial reference frame.

[0137] b) Search for effective stars that meet energy security requirements

[0138] Import a stellar database containing the three-dimensional projection R of each stellar vector in the inertial reference frame. i star Based on the attitude reference definition for stellar observation, the projection R of the satellite camera's optical axis in the inertial coordinate system can be obtained. i cam The criteria for determining a valid star that meets energy security requirements are as follows:

[0139]

[0140] In the above formula, θ is the energy security protection angle, representing the threshold angle between the orientation of the solar array panels and the solar vector. star_cam Let be the angle between the satellite camera's optical axis and the star's vector, calculated as follows:

[0141]

[0142] c) Eliminate stars that are obscured by Earth.

[0143] After screening based on energy security constraints, the remaining stars obscured by Earth were removed. The criteria for removing stars were as follows:

[0144]

[0145] In the above formula, The angle of obstruction for Earth is generally determined based on the satellite's orbital altitude. θ earth_cam Let be the angle between the satellite camera's optical axis and the star's vector, calculated as follows:

[0146]

[0147] d) Identify the target star

[0148] Among the selected stars, the one with the smallest angle to the camera vector is chosen as the star to be observed.

[0149] 3. Calculate the attitude of the observed star using the payload.

[0150] The attitude of the observed star was calculated using a two-vector attitude determination method.

[0151] a) Vector Calculation Steps

[0152] The first vector is the observed star vector. To ensure the camera can observe the star, the camera's optical axis must be parallel to the star vector in the new attitude. For ease of describing the coordinate transformation, we define the camera's optical axis as parallel to the +Z axis of the satellite's body coordinate system. Therefore, the projection expression of the camera's optical axis in the inertial coordinate system is:

[0153] R z_i =R i star

[0154] In the above formula, R i star This is the projection of the target star in the inertial coordinate system.

[0155] The projection expression of the camera optical axis in the body coordinate system:

[0156]

[0157] b) Steps for calculating vector two

[0158] The second vector can be the normal to the plane formed by the target star and the camera's initial optical axis. The projection expression of the normal vector of the plane formed by the target star and the camera's initial optical axis in the inertial coordinate system is as follows:

[0159] R y_i =R i star ×R i cam

[0160] In the above formula, R i star R is the projection of the target star in the inertial coordinate system. i cam The initial projection of the satellite camera's optical axis in the inertial coordinate system.

[0161] The projection expression of the normal vector in the body coordinate system is as follows:

[0162] R y_b =C i_b0 ·R y_i

[0163] In the above formula, C i_b0 This is the rotation matrix of the inertial reference frame relative to the star observation attitude reference coordinate system, which can be calculated according to the definition of the star observation attitude reference.

[0164] c) Two-vector attitude determination

[0165] Performing the difference product operation on the two vectors above, we obtain the third vector expression:

[0166]

[0167] In the above formula, R x_i R is the projection of the difference vector in the inertial coordinate system. x_b This is the projection of the difference vector onto the body coordinate system.

[0168] Based on the principle of coordinate transformation, the attitude matrix C of the satellite's local system relative coordinate system during the sidereal time of payload observation can be obtained. i_b1 The expression is:

[0169] C i_b1 =[R x_b R y_b R z_b ]·[R x_i R y_i R z_i ] T

[0170] In the above formula, [·] T This represents the matrix transpose operation.

[0171] 4. Star sensor design to avoid Earth's obstruction

[0172] When the camera is observing stars, the star sensor needs to be optimized for observation to ensure it is usable, in order to prevent the star sensor from being blocked by the Earth. The main processing steps are as follows:

[0173] a) Determine if the star sensor is blocked by the Earth.

[0174] First, calculate the projection R of the star sensor's optical axis vector in the inertial reference frame when the camera observes the star. st_i The calculation expression is as follows:

[0175] R st_i =[C i_b1 ]T ·R st_b

[0176] In the above formula, C i_b1 R is the attitude matrix of the satellite's local coordinate system relative to the orbital time of the payload observation. st_b The projection of the star sensor's optical axis onto the body coordinate system can be determined based on the star sensor's layout on the satellite.

[0177] The criterion for determining whether a star sensor is blocked by the Earth is whether the angle between the star sensor's optical axis vector and the vector pointing from the satellite to the Earth is less than the Earth's protection angle. The expression is:

[0178]

[0179] In the above formula, The Earth shielding angle for the star sensor can be determined based on a combination of the satellite's orbital altitude and the star sensor's performance. θ earth_st Let be the angle between the optical axis vector of the star sensor and the vector pointing from the satellite to Earth, calculated as follows:

[0180]

[0181] In the above formula, R i s_e R is the projection of the vector pointing from the satellite to the Earth's center into the inertial reference frame. st_i This is the projection of the star sensor's optical axis vector onto the inertial reference frame.

[0182] b) Star sensor design to avoid Earth's obstruction

[0183] If the star sensor is detected to be obstructed by Earth, an obstruction avoidance design is required. To ensure the camera can observe the star, the satellite can be rotated around its own coordinate system (Z-axis) to move the star sensor's optical axis away from Earth. Therefore, the final expression for the observed star's attitude is:

[0184]

[0185] Where C i_b1 is the attitude matrix of the satellite's relative coordinate system during sidereal time observations; rollz is the rotation angle by which the star sensor avoids Earth.

[0186] 5. Output the final observed star attitude.

[0187] Based on the above analysis, after designing to avoid Earth's eclipse, the final observed star attitude matrix C is obtained. i_b2 By maneuvering the satellite to this attitude, it is possible to calibrate the camera using stars while ensuring the satellite's energy security.

[0188] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0189] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for calculating the attitude of stars observed by a remote sensing satellite, characterized in that, Includes the following steps: Step S1: Establish the attitude reference for satellite observation of stars, constrain the star solar array to face the sun, and ensure the energy security of the satellite platform; Step S2: Perform a star search based on the attitude reference of the observed stars by the satellite to obtain the target star; Step S3: Calculate the observation platform attitude of the target star as observed by the satellite payload; Step S4: Star sensor occlusion analysis: Ensure the star sensor is calibrated to the target star, avoid the Earth occluding the star sensor, and obtain the avoidance angle; Step S5: Optimize the attitude of the observation platform based on the avoidance angle, and output the optimal platform attitude; The star search includes: a) Calculate the vector pointing from the satellite to the Earth's center; b) Search for valid stars that meet energy security requirements: Import the star database and obtain valid stars based on the criteria for determining valid stars that meet energy security requirements; c) Based on the satellite's vector pointing towards the Earth's center, remove stars that are blocked by the Earth: determine the Earth-blocked stars for the valid stars, remove stars that are blocked by the Earth, and obtain the filtered stars. d) Identify the target star: Select the star with the smallest angle to the satellite payload vector from the screened stars as the target star for observation; The method for calculating the attitude of the observation platform is as follows: the attitude of the satellite payload to observe the target star is determined by using the plane normal formed by the target star vector and the initial vector of the satellite payload as the rotation axis and the dual-vector attitude determination method. The calculation steps of the two-vector attitude determination method are as follows: a) Determine vector one as the target star vector; b) Determine vector two as the normal vector of the plane formed by the target star and the initial optical axis of the satellite payload; c) Dual-vector attitude determination calculation: Perform a difference multiplication operation on vector one and vector two, and obtain the attitude matrix of the target star observed by the satellite payload according to the coordinate transformation principle.

2. The method for calculating the attitude of stars observed by remote sensing satellites according to claim 1, characterized in that, The star search requires that the angle between the orientation of the solar array and the solar vector be less than a safety threshold to ensure that the solar array is always illuminated during the calibration process.

3. The method for calculating the attitude of stars observed by remote sensing satellites according to claim 1, characterized in that, The criteria for determining a valid star that meets energy security requirements are as follows: ， in The energy security protection angle is the threshold angle between the orientation of the solar array panels and the solar vector. This is the angle between the satellite payload's optical axis and the star's vector; The criteria for determining Earth's occlusion are as follows: In the above formula, To shield the Earth's angle, This is the angle between the satellite payload's optical axis and the star's vector.

4. The method for calculating the attitude of stars observed by remote sensing satellites according to claim 1, characterized in that, The avoidance angle is determined by the design method of avoiding Earth's obstruction to determine whether the satellite's star sensor is obstructed by Earth when observing stars; If obstructed, an avoidance angle calculation is performed to ensure that the star sensor can be used when the satellite is observing stars, thus guaranteeing the safety of the satellite platform.

5. The method for calculating the attitude of stars observed by remote sensing satellites according to claim 4, characterized in that, The method for avoiding Earth's shielding includes: a) Determining if the star sensor is blocked by the Earth: The criterion for determining if the star sensor is blocked by the Earth is that the angle between the star sensor's optical axis vector and the vector pointing from the satellite to the Earth is less than the Earth's protection angle. The expression is: In the above formula, Earth shielding protection angle for star sensors; The angle between the optical axis vector of the star sensor and the vector pointing from the satellite to Earth; b) Calculation of the avoidance angle for the star sensor to avoid being blocked by the Earth: If the star sensor is detected to be blocked by the Earth, the avoidance angle is calculated to make the optical axis of the star sensor move away from the Earth.

6. A system for calculating the attitude of stars observed by a remote sensing satellite, characterized in that, include: Module M1: Establishes the attitude reference for satellite observation of stars, constrains the star solar array to face the sun, and ensures the energy security of the satellite platform; Module M2: Performs star search based on the attitude reference of the observed stars by the satellite to acquire the target star; Module M3: Calculates the attitude of the observation platform as observed by the satellite payload of the target star; Module M4: Star Sensor Occlusion Analysis: Ensures the star sensor is calibrated to the target star, avoids Earth obscuring the star sensor, and obtains the avoidance angle; Module M5: Optimizes the attitude of the observation platform based on the avoidance angle and outputs the optimal platform attitude; The star search includes: a) Calculate the vector pointing from the satellite to the Earth's center; b) Search for valid stars that meet energy security requirements: Import the star database and obtain valid stars based on the criteria for determining valid stars that meet energy security requirements; c) Based on the satellite's vector pointing towards the Earth's center, remove stars that are blocked by the Earth: determine the Earth-blocked stars for the valid stars, remove stars that are blocked by the Earth, and obtain the filtered stars. d) Identify the target star: Select the star with the smallest angle to the satellite payload vector from the screened stars as the target star for observation; The method for calculating the attitude of the observation platform is as follows: the attitude of the satellite payload to observe the target star is determined by using the plane normal formed by the target star vector and the initial vector of the satellite payload as the rotation axis and the dual-vector attitude determination method. The calculation steps of the two-vector attitude determination method are as follows: a) Determine vector one as the target star vector; b) Determine vector two as the normal vector of the plane formed by the target star and the initial optical axis of the satellite payload; c) Dual-vector attitude determination calculation: Perform a difference multiplication operation on vector one and vector two, and obtain the attitude matrix of the target star observed by the satellite payload according to the coordinate transformation principle.

7. The attitude calculation system for remote sensing satellite observation of stars according to claim 6, characterized in that, The star search of module M2 must constrain the angle between the orientation of the solar array and the solar vector to be less than a safety threshold to ensure that the solar array is always illuminated during the calibration process.

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