A method for calculating a viewing direction applied to a space target space-based detection platform

Abstract

A kind of application in space target space-based detection platform's direction of view calculation method, it is related to space target's space-based detection technical field, solve the existing method based on star sensor determination space-based platform's attitude, there is star identification calculation long time, and waste space on star, there is certain energy consumption and increase launch cost etc. problem, the method of the present application is based on the principle of spherical astronomy according to the position and velocity vector under the inertial coordinate system of space-based platform, solve the static direction of view of platform under the celestial coordinate system;And according to the rotation of space-based platform, solve the additional rotation angle of platform external rotation, and determine the direction of view of space-based platform under the celestial coordinate system according to the obtained static direction of view.This method saves space on star, reduces overall power consumption, reduces calculation time and helps to control the launch cost of space-based platform.The results obtained by the method of the present application have reached the accuracy similar to that of star sensor.

Description

Technical Field

[0001] This invention relates to the field of space-based detection technology for space targets, and specifically to a line-of-sight calculation method applied to a space-based detection platform for space targets. Background Technology

[0002] Space-based detection of space targets currently refers primarily to optical detection, which involves mounting optical telescopes on a satellite platform to detect space targets. These optical telescopes mainly consist of an optical system, a detector, and a frame. As satellite technology matures, the development and launch costs of detection platforms are gradually decreasing. Compared to traditional ground-based observation, space-based observation of space targets can be conducted 24 / 7 without interruption, unaffected by weather conditions. Furthermore, due to weaker atmospheric disturbances and lower background light, space-based platforms offer superior observation conditions. In addition, space-based observation is less constrained by geographical location and offers greater mobility. Therefore, space-based detection of space targets has significant scientific and practical importance and is a hot research area in space situational awareness.

[0003] Stellar data within the line-of-sight region of a space-based telescope is essential for determining the location of space targets. Therefore, to locate a space target, the first step is to calculate the line-of-sight of the telescope. For ground-based telescopes, encoders can be used to determine the pointing area of ​​the sky. Attitude determination for space-based platforms is typically based on star sensors. However, star identification calculations by star sensors are time-consuming, waste onboard space, consume energy, and increase launch costs.

[0004] This invention integrates the spatial position, velocity, and attitude information of the detection platform, as well as the electronic control information of its onboard telescope, based on spherical astronomy, to quickly calculate the line of sight of the detection platform and thus locate the position of space targets in real time. Summary of the Invention

[0005] This invention addresses the problems of existing methods for determining the attitude of space-based platforms based on star sensors, which suffer from long star identification calculation times, wasted space, high energy consumption, and increased launch costs. It provides a line-of-sight calculation method applicable to space-based target detection platforms.

[0006] A line-of-sight calculation method applied to a space-based target detection platform, the method comprising the following steps:

[0007] Step 1: Based on the position and velocity vectors of the space-based platform in the inertial coordinate system, solve for the static line of sight of the platform in the celestial coordinate system based on the principles of spherical astronomy;

[0008] Step 2: Based on the rotation of the space-based platform, calculate the additional rotation angle of the platform's external rotation, and determine the viewing direction of the space-based platform in the celestial coordinate system based on the static viewing direction obtained in Step 1.

[0009] Furthermore, the controllable rotating telescope mounted on the space-based platform calculates the additional rotation angle based on the rotation matrix, and then calculates the line of sight of the space-based platform in the celestial coordinate system.

[0010] The beneficial effects of this invention are:

[0011] 1. The method described in this invention does not require a star sensor, saving on-board space, reducing overall power consumption, decreasing computation time, and helping to control the launch cost of the space-based platform. Based on data transmitted from the essential sensors of the space-based platform, the observation direction of its onboard telescope is calculated, and the results obtained by the method of this invention have achieved an accuracy approximately equivalent to that of a star sensor.

[0012] 2. The method described in this invention is entirely based on the principles of classical spherical astronomy, which is easy for practitioners in this field to understand and is also beneficial for further optimization and improvement of this invention.

[0013] 3. The pointing calculation method for the space-based controllable altazimuth telescope provided by the method of the present invention can be used to calculate the line of sight of the most conceivable space-based platform, which has a certain degree of technical foresight. Attached Figure Description

[0014] Figure 1 A schematic diagram of the carrier coordinate system and its observation line of sight of the observation platform;

[0015] Figure 2 A schematic diagram of the orbital normal vector and northward tangent vector of the observation platform;

[0016] Figure 3 This is a schematic diagram of the carrier coordinate system of the observation platform and the positive direction of motion of the telescope it carries. Detailed Implementation

[0017] Combination Figures 1 to 3 This embodiment describes a line-of-sight calculation method applied to a space-based target detection platform. The method is implemented through the following steps:

[0018] Step 1: Based on the position and velocity vectors of the space-based observation platform in its inertial coordinate system, and combining this with the principles of spherical astronomy, determine the static orientation of the space-based platform in the celestial coordinate system; the specific process is as follows:

[0019] Step 1-1: According to convention, the coordinate system of the Earth-space-based observation platform adopts a front-right-bottom system (i.e., the X-axis points to the platform's heading, the Y-axis points to the right of the platform, and the Z-axis points to the direction of the platform relative to the Earth's center; XYZ conforms to the right-hand rule). The right direction pointed to by the Y-axis is the opposite direction of its orbital normal. Figure 1 As shown.

[0020] Steps 1-2, as follows Figure 2 As shown, the origin of the standard inertial coordinate system is defined as the geocenter, the Earth's equatorial plane is used as the reference plane, the Earth's axis is used as the reference axis, and the vernal equinox is defined as the starting point on the reference plane. The direction vector of the space-based observation platform in the standard inertial coordinate system is... It can be represented by position coordinates (x0, y0, z0), and its velocity vector It can be represented as

[0021] Steps 1-3: Based on the fundamental principles of spherical astronomy, the basic formula for converting horizontal coordinates (A, h) to hourly angular coordinates (t, δ) is as follows:

[0022]

[0023] In the formula, A is the turning azimuth angle of the space-based observation platform, which follows the definition of the horizontal coordinate system, i.e., the turning from north to east is positive; h is the turning altitude angle of the space-based observation platform, which follows the definition that the direction of the tangent of the Earth where the space-based observation platform is located is positive in the opposite direction to the Z-axis of the carrier coordinate system; t is the pointing hour angle, i.e., the right ascension α of the platform. PF The difference between the static viewpoint α of the platform and the static viewpoint α, i.e., t = α PF -α; δ represents the static line-of-sight declination of the space-based observation platform; δ PF Let (A, h) be the declination of the space-based observation platform. Therefore, the static line of sight of the space-based observation platform can be obtained through the horizontal coordinates (A, h).

[0024] Steps 1-4: As can be seen from the carrier coordinate system defined in Step 1-1, the turning altitude angle h of the space-based observation platform in the static line of sight is 0.

[0025] Steps 1-5: For the azimuth angle A of the space-based observation platform, it can be determined by the northward tangent vector of the celestial sphere where the space-based observation platform is located. With the platform orbital normal vector Solve for the angle between the two points.

[0026] We can assume that there exists a point P(0,0,c) on the Earth's axis (i.e., the z-axis in the standard inertial coordinate system), and the vector from the platform to this point is... When the approximate orbital plane of the platform is a great circle of the celestial sphere, the direction vector of the platform is... and Vertical, that is Seeking Due to the northward tangent vector Strict north orientation is required, ensuring the z-axis component is positive. Specifically, this is necessary when z0 > 0 in the platform's position coordinates. When z0 = 0, When z0 < 0

[0027] Steps 1-6: For the platform orbit normal vector Its direction satisfies the right-handed reference frame.

[0028] Steps 1-7: Based on steps 1-5, the platform's turning azimuth angle A is obtained using intermediate parameters. Note the symbols: when This indicates that the platform is flying north. The direction is westward, A = 2π - A′; when This indicates that the platform is flying south. The direction is eastward, A = A′; when v z0 =0, A=0 or π (depending on) and (directional relationship).

[0029] Steps 1-8: Note that for the calculation results, the platform's static line of sight α needs to be modulo 0 to 2π, and the platform's static line of sight declination δ needs to be modulo 0 to 2π. Modulo is used to satisfy the traditional definition.

[0030] Step 2: Based on the spin of the space-based observation platform, calculate the additional rotation angle of the external rotation, and combine this with Step 1 to determine the line of sight of the space-based platform in the celestial coordinate system. The specific process is as follows:

[0031] Step 2-1: Due to the microgravity environment in space, the platform flutter caused by various disturbance sources (such as high-speed rotation of the flywheel, stepping motion of the drive mechanism, etc.) on the space-based observation platform results in a large steady-state error and platform spin. For the platform spin, the sensors on the platform (such as gyroscopes, accelerometers, magnetometers, etc.) can directly obtain its spin based on the Euler angle of the axis of motion (internal rotation). Since the angle transformation sequence from the carrier coordinate system (front-right-down) to the reference coordinate system (east-north-sky) is usually ZXY, that is, rotating around the carrier coordinate system by yaw, roll, and pitch respectively, where yaw corresponds to the additional azimuth angle ΔA and roll corresponds to the additional altitude angle Δh.

[0032] Step 2-2: Based on the rotation angle relationship between internal and external rotation, the ZXY rotation based on the motion axis is equivalent to the YXZ rotation based on the fixed axis. The platform rotation can be decoupled into first rotating Roll around the X axis, and then rotating in the direction of the Z axis to the Y axis. That is, the negative increment of the platform turning height angle: Δh = -Roll.

[0033] Steps 2-3: The platform's rotation along the Z-axis (Yaw) can be decoupled into a rotation along the Y-axis in the positive direction of the X-axis. Thus, when the platform flies north, this direction corresponds to turning from north to east; when the platform flies south, this direction corresponds to turning from south to west. Both are positive increments of the platform's turning azimuth angle: ΔA = Yaw.

[0034] That is, the final platform turning azimuth angle is A = A + ΔA, and the platform turning altitude angle is h = h + Δh.

[0035] In this embodiment, the spin of the space-based observation platform also involves the electric control of the onboard telescope. The method described in this embodiment is used for the electric steering control of the telescope. For the controllable rotating telescope mounted on the space-based observation platform, the overall additional rotation angles (yaw′, pitch′, and roll′) are solved according to the rotation matrix, and the line of sight of the space-based observation platform in the celestial coordinate system is calculated. The specific process is as follows:

[0036] Step 3-1: Calculate the telescope's electronic steering to correspond to the rotation angle of the space-based observation platform. For example... Figure 3 As shown, when the telescope is in the zero position during installation, it should point in the opposite direction to the Y-axis of the space-based observation platform's coordinate system. Typically, this electronically controlled steering A... tp h tp The direction follows the definition of exorotation: h tp The positive direction is from Y to Z; A tp The positive direction is from X to Y.

[0037] Step 3-2: The overall rotation matrix of the platform and the mounted telescope is calculated as follows:

[0038] M = M PF ×M tp (2)

[0039] Among them, M PF The rotation matrix for the platform's rotation is:

[0040]

[0041] M tp The rotation matrix of the mounted tracking telescope is:

[0042]

[0043] Among them, A tp h tp This is for the electronically controlled steering of the telescope.

[0044] Step 3-3: Calculate the overall additional rotation angles yaw′, pitch′, and roll′ (Euler angles) using the rotation matrix. This can be solved using formula (5) as follows:

[0045]

[0046]

[0047] In the formula, asin is the inverse trigonometric function of sine, and atan2 is the inverse trigonometric function of tangent. Note the range of each angle: yaw′∈[0,360°), pitch′ and roll′∈[-90°, 90°].

[0048] Additional azimuth angle ΔA′=yaw′, additional elevation angle Δh′=-roll′.

[0049] The final platform turning azimuth angle is A = A + ΔA′, and the platform turning altitude angle is h = h + Δh′.

[0050] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0051] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A line-of-sight calculation method applied to a space-based target detection platform, characterized by: This method is implemented by the following steps: Step 1: Based on the position and velocity vectors of the space-based observation platform in the inertial coordinate system, and in conjunction with the principles of spherical astronomy, solve for the static line of sight of the space-based observation platform in the celestial coordinate system; Step 2: Based on the spin of the space-based observation platform, calculate the additional rotation angle of the external rotation, and based on the static line of sight obtained in Step 1, finally determine the line of sight of the space-based platform in the celestial coordinate system; the specific process is as follows: Step 21: Obtain the Euler angles of the space-based observation platform's spin based on the motion axis through the sensors mounted on the space-based observation platform. Set the angle transformation order from the carrier coordinate system to the reference coordinate system as ZXY. Then, the yaw angle, roll angle, and pitch angle of rotation around the carrier coordinate system are respectively called Yaw, Roll, and Pitch. The yaw angle Yaw corresponds to the additional azimuth angle ΔA, and the roll angle Roll corresponds to the additional altitude angle Δh. Step 22: Based on the rotation angle relationship between internal and external rotation, the rotation of the space-based observation platform is decoupled into first rotating around the X-axis (Roll), and then rotating around the Z-axis and Y-axis. That is, the negative increment of the turning elevation angle of the space-based observation platform is Δh = -Roll. Step 23: The rotation of the space-based observation platform along the Z-axis, Yaw, is decoupled to the rotation of the Y-axis in the positive direction of the X-axis. Then, the positive increment of the turning azimuth angle of the space-based observation platform, ΔA, is equal to Yaw. Step 24: Based on the negative increment Δh of the elevation angle obtained in Step 22, the positive increment ΔA of the azimuth angle obtained in Step 23, and the static line of sight obtained in Step 1, the line of sight of the space-based observation platform in the celestial coordinate system is finally obtained.

2. The line-of-sight calculation method for a space-based target detection platform according to claim 1, characterized in that: The method also includes step three, which involves mounting a controllable rotating telescope on the space-based observation platform; solving for the overall additional rotation angle based on the rotation matrix of the telescope; and obtaining the line of sight of the space-based observation platform in the celestial coordinate system.

3. The line-of-sight calculation method for a space-based target detection platform according to claim 2, characterized in that: The specific process of step three is as follows: Step 31: Calculate the spin of the space-based observation platform and the overall rotation matrix M of the onboard telescope; M=M PF ×M tp In the formula, M PF Let be the rotation matrix of the space-based observation platform's spin, i.e.: M tp The rotation matrix of the mounted telescope is: In the formula, A tp h tp For the electronically controlled steering of the telescope; Step 32: Solve for the overall additional rotation angles yaw′, pitch′, and roll′ based on the rotation matrix obtained in Step 31. The results are expressed as follows: In the formula, asin is the inverse trigonometric function of sine, atan2 is the inverse trigonometric function of tangent, and M... 11 M 21 M 31 M 32 M 33 All are elements in M; Obtain the additional azimuth angle ΔA′=yaw′ and the additional elevation angle Δh′=-roll′.

4. The line-of-sight calculation method for a space-based target detection platform according to claim 3, characterized in that: The range of each angle in the overall additional rotation angle is defined as follows: yaw′∈[0,360°), pitch′ and roll′∈[-90°,90°].

5. The line-of-sight calculation method for a space-based target detection platform according to claim 1, characterized in that: The specific process of step one is as follows: Step 11: Set the carrier coordinate system XYZ for the Earth-orbiting space-based observation platform; the X-axis points to the platform's heading, the Y-axis points to the right of the platform, and the Z-axis points to the direction of the platform relative to the Earth's center; the right direction pointed to by the Y-axis is the opposite direction of its orbital normal. Steps 1 and 2: Define the origin of the standard inertial coordinate system as the geocenter, the Earth's equatorial plane as the reference plane, the Earth's axis as the reference axis, and the vernal equinox as the starting point on the reference plane. The direction vector of the space-based observation platform in the standard inertial coordinate system... Represented by position coordinates (x0, y0, z0), its velocity vector Represented as Step 13: According to the principles of spherical astronomy, the basic formula for converting horizontal coordinates (A,h) to hourly angular coordinates (t,δ) is as follows: In the formula, A is the azimuth angle of the space-based observation platform, h is the altitude angle of the space-based observation platform, and t is the pointing hour angle, i.e., the right ascension α of the space-based observation platform. PF The difference between the static line of sight α and that of the space-based observation platform; δ is the declination of the static line of sight of the space-based observation platform; δ PF The declination of the space-based observation platform is given, and the static line of sight of the platform is obtained through the horizontal coordinates (A,h). Step 14: According to the carrier coordinate system defined in Step 11, the turning elevation angle h of the space-based observation platform in the static line of sight is 0; the turning azimuth angle A of the space-based observation platform is the northward tangent vector through the celestial sphere where the space-based observation platform is located. With the platform orbital normal vector Solve for the angle between the two points.

6. The line-of-sight calculation method for a space-based target detection platform according to claim 5, characterized in that: The platform's static line of sight α is modulo 0 to 2π, and the platform's static line of sight declination δ is modulo 0 to 2π. Take the mold.

7. The line-of-sight calculation method for a space-based target detection platform according to claim 5, characterized in that: The process of solving for the turning azimuth angle A of the space-based observation platform is as follows: Assuming there exists a point P(0,0,c) on the z-axis in the standard inertial coordinate system, the vector pointing from the space-based observation platform to this point is... When the orbital plane of an approximate space-based observation platform is a great circle of the celestial sphere, the direction vector of the space-based observation platform. and Vertical, that is get When z0>0 in the position coordinates of the celestial observation platform, When z0 = 0, When z0 < 0 The orbital normal vector of the space-based observation platform when This indicates that the space-based observation platform is flying north. The direction is westward, A = 2π - A′; when This indicates that the space-based observation platform is flying south. The direction is east, A = A′; when A = 0 or π.

8. The line-of-sight calculation method for a space-based target detection platform according to claim 7, characterized in that: intermediate quantity

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