A method for tracking stellar targets on board a satellite

Abstract

The present invention relates to a method for tracking a star target on a satellite, comprising: calculating a coordinate transformation matrix between a J2000 coordinate system and a platform coordinate system using the attitude parameters of an onboard platform; calculating a coordinate transformation matrix from the platform coordinate system to a payload coordinate system; calculating a coordinate transformation matrix from the payload coordinate system to a lens coordinate system; calculating a turntable angle for star guidance and tracking; and performing image stabilization tracking on the star based on the calculated turntable angle for star guidance and tracking. The present invention can keep the star within the field of view of a telescope, thereby achieving the purpose of star image stabilization.

Description

Technical Field

[0001] The invention relates to a method for tracking a star target on a star. Background Art

[0002] With the continuous advancement and maturity of space technology, humanity has conducted over 200 deep space exploration missions, making it a key development direction in the aerospace field. Deep space exploration can help study the origin, evolution, and current status of the solar system and the universe, further understanding the formation and evolution of the Earth's environment, and understanding the relationship between space phenomena and Earth's natural systems. This has crucial scientific and economic significance for deep space exploration and development. We will develop onboard detection of space target payloads, verify key technologies such as space-based optical detection and real-time detection of in-orbit targets, and conduct verification tests on the detection capability and positioning accuracy of space-based systems to enhance my country's space-based space target detection capabilities.

[0003] To detect distant stars and the planets around them, onboard telescopes must be precisely pointed at a fixed area of ​​the sky, enabling long-exposure imaging to capture information about faint targets. However, in actual operation, long-exposure star observations are affected by the relative motion of the aircraft. Furthermore, the current method of using star sensors for attitude determination is computationally complex and difficult to implement in embedded software. Summary of the Invention

[0004] In view of this, it is necessary to provide a method for tracking stellar targets on board a satellite.

[0005] The present invention provides a method for tracking a star target on a satellite, comprising the following steps: a. calculating a coordinate system transformation matrix between a J2000 coordinate system and a platform coordinate system by using a platform attitude parameter of an onboard platform; b. calculating a coordinate system transformation matrix from the platform coordinate system to a payload coordinate system; c. calculating a coordinate system transformation matrix from the payload coordinate system to a lens coordinate system; d. calculating a turntable angle during star guidance and tracking; and e. performing image stabilization tracking on the star based on the calculated turntable angle during star guidance and tracking.

[0006] Specifically, the method further comprises the steps before step a:

[0007] The onboard platform receives the onboard star tracking command issued.

[0008] Specifically, the platform attitude parameters include: onboard time, inertial attitude quaternion, and inertial attitude motion angular velocity.

[0009] Specifically, the step a comprises the following steps:

[0010] Step S11, calculate t a0 The coordinate transformation matrix A(ta0 );

[0011] On board a0 At this moment, the corresponding platform inertial attitude quaternion is [q1,q2,q3,q4]. Therefore, from J2000 to t a0 The coordinate transformation matrix of the platform coordinate system at this moment is as follows:

[0012]

[0013] Step S12, calculating the coordinate transformation matrix B corresponding to the attitude angle increment from the J2000 coordinate system to the platform coordinate system during the time interval Δt;

[0014] On board a0 The inertial attitude motion angular velocity vector corresponding to the moment [ω x0 ,ω y0 ,ω z0 ], let Δt be the time from the start time to the calculation sampling time, and the rotation angular velocity β after Δt is as follows:

[0015]

[0016] Calculate the rotation direction unit vector r a :

[0017]

[0018] The steps to solve the coordinate transformation matrix B corresponding to the attitude angle increment are as follows:

[0019] ΔB=β×Δt

[0020]

[0021]

[0022] Step S13, calculate and obtain a0 to t a0 The coordinate transformation matrix M1 between the J2000 coordinate system and the platform coordinate system at time +Δt:

[0023] M1=A(t a0 )×B.

[0024] Specifically, the step b specifically includes:

[0025] The coordinate system transformation matrix M2 from the platform coordinate system to the payload coordinate system is obtained by ground processing of the calibrated image data. The steps of calibrating M2 include:

[0026] Step S21: The payload coordinate system is parallel to the lens coordinate system after the pitch and azimuth motions. Therefore, when the turntable is at zero position, the lens coordinate system and the payload coordinate system are considered to coincide. When the turntable is at zero position, an image of a known star is taken and the star coordinates in the J2000 coordinate system are obtained by searching the star catalog. The coordinates of the star in the lens coordinate system are obtained by downloading the image, and the coordinate transformation matrix M from the J2000 to the lens coordinate system is calculated. z .

[0027] Step S22: Calculate the coordinate transformation matrix M from the J2000 coordinate system to the platform coordinate system at the exposure time of the payload based on the posture broadcast data when the image is taken. At .

[0028] Step S23, calculate M2.

[0029] M2=M z M At .

[0030] Specifically, the step c includes:

[0031] Assume that the initial turntable angle is [E0, A0], and the coordinate transformation matrix M from the load coordinate system to the lens coordinate system is g0 for:

[0032]

[0033] After a period of time i, the turntable angle is [E t ,A t ], the coordinate transformation matrix M from the load coordinate system to the lens coordinate system gt for:

[0034]

[0035] Among them, g t It is the theoretical image rotation angular velocity, which is transmitted to the ground as auxiliary information for ground processing.

[0036] Specifically, the step d includes:

[0037] Step S41: Set the exposure start time t a0 , the turntable angle is [E0, A0], and the transformation matrix from the J2000 coordinate system to the lens coordinate system is:

[0038] M P0 =M g0 M2A(t a0 )

[0039] In the above formula, M g0 The parameters are the turntable angle [E0, A0], A(t a0 ) is ta0 Transformation matrix from the J2000 coordinate system to the platform coordinate system at time instant.

[0040] Step S42, calculate t a0 At time +Δt, the transformation matrix from the J2000 coordinate system to the lens coordinate system is:

[0041] M P =M gt M2M1

[0042] In the above formula, M gt The parameter is the turntable angle [E t ,A t ], M1 is t a0 +Δt time J2000 coordinate system to platform coordinate transformation matrix.

[0043] set up

[0044]

[0045] Available

[0046]

[0047] This application can keep stars within the telescope's field of view, achieving stellar image stabilization. When guiding and tracking stars, it is necessary to use the attitude information broadcast by the platform to predict the orientation of the payload in inertial space during the exposure time and calculate the turntable's two-axis angle data to ensure that the angular coordinates of a certain direction in inertial space in the optical lens remain stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a flow chart of the on-planet star target tracking method of the present invention. DETAILED DESCRIPTION

[0049] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] See Figure 1 FIG. 1 is a flowchart of a preferred embodiment of the on-board star target tracking method of the present invention.

[0051] Step S1: Calculate the coordinate transformation matrix between the J2000 coordinate system and the platform coordinate system using the platform attitude parameters of the onboard platform. Specifically:

[0052] The onboard platform can obtain the transformation matrix of the platform coordinate system in the J2000 coordinate system through the platform attitude parameters, which include: onboard time, inertial attitude quaternion, and inertial attitude motion angular velocity. The calculation method of the coordinate transformation matrix from the J2000 coordinate system to the platform coordinate system is as follows:

[0053] Step S11, calculate t a0 The coordinate transformation matrix A(t a0 ).

[0054] On board a0 At this moment, the corresponding platform inertial attitude quaternion is [q1,q2,q3,q4]. Therefore, from J2000 to t a0 The coordinate transformation matrix of the platform coordinate system at this moment is as follows:

[0055]

[0056] Step S12: Calculate the coordinate transformation matrix B corresponding to the attitude angle increment from the J2000 coordinate system to the platform coordinate system during the time interval Δt.

[0057] On board a0 The inertial attitude motion angular velocity vector [ω x0 ,ω y0 ,ω z0 ]. Let Δt be the duration from the start time to the calculation sampling time, and the rotation angular velocity β after Δt is as follows:

[0058]

[0059] Calculate the rotation direction unit vector r a :

[0060]

[0061] The steps to solve the coordinate transformation matrix B corresponding to the attitude angle increment are as follows:

[0062] ΔB=β×Δt

[0063]

[0064]

[0065] Step S13, calculate and obtain a0 to t a0 The coordinate transformation matrix M1 between the J2000 coordinate system and the platform coordinate system at time +Δt:

[0066] M1=A(t a0 )×B.

[0067] Step S2: Calculate and obtain the coordinate system transformation matrix from the platform coordinate system to the load coordinate system.

[0068] Specifically:

[0069] Systematic errors caused by factors such as payload installation, cabin docking, and differences in coordinate axis orientation result in a coordinate transformation matrix between the platform coordinate system and the payload coordinate system, represented as M2. M2 is obtained by ground-processing the calibrated image data and annotated. After calibration, M2 serves as a constant matrix.

[0070] The steps to calibrate M2 include:

[0071] Step S21: The payload coordinate system is parallel to the lens coordinate system after the pitch and azimuth motions. Therefore, when the turntable is at zero position, the lens coordinate system and the payload coordinate system are considered to coincide. When the turntable is at zero position, an image of a known star is taken and the star coordinates in the J2000 coordinate system are obtained by searching the star catalog. The coordinates of the star in the lens coordinate system are obtained by downloading the image, and the coordinate transformation matrix M from the J2000 to the lens coordinate system is calculated. z .

[0072] Step S22: Calculate the coordinate transformation matrix M from the J2000 coordinate system to the platform coordinate system at the exposure time of the payload based on the posture broadcast data when the image is taken. At .

[0073] Step S23, calculate M2.

[0074] M2=M z M At .

[0075] Step S3: Calculate and obtain the coordinate system transformation matrix from the load coordinate system to the lens coordinate system.

[0076] Specifically:

[0077] The load coordinate system and the lens coordinate system are rotated in azimuth and pitch directions by a two-dimensional turntable so that the coordinate axes are parallel to each other. Assume that the turntable angle at the initial moment is [E0, A0], and the coordinate transformation matrix M from the load coordinate system to the lens coordinate system is g0 for:

[0078]

[0079] After a period of time i, the turntable angle is [E t ,A t ], the coordinate transformation matrix M from the load coordinate system to the lens coordinate system gt for:

[0080]

[0081] Among them, g t It is the theoretical image rotation angular velocity, which is transmitted to the ground as auxiliary information for ground processing.

[0082] Step S4, calculate the turntable angle for star guidance and tracking. Specifically:

[0083] Step S41, set the exposure start time t a0 , the turntable angle is [E0, A0], and the transformation matrix from the J2000 coordinate system to the lens coordinate system is:

[0084] M P0 =M g0 M2A(t a0 )

[0085] In the above formula, M g0 The parameters are the turntable angle [E0, A0], A(t a0 ) is t a0 Transformation matrix from the J2000 coordinate system to the platform coordinate system at time instant.

[0086] Step S42, calculate t a0 At time +Δt, the transformation matrix from the J2000 coordinate system to the lens coordinate system is:

[0087] M P =M gt M2M1

[0088] In the above formula, M gt The parameter is the turntable angle [E t ,A t ], M1 is t a0 +Δt time J2000 coordinate system to platform coordinate transformation matrix.

[0089] set up

[0090]

[0091] Available

[0092] A t =arcsin(q 31 )

[0093]

[0094]

[0095] Step S5: performing image stabilization tracking on the star according to the calculated turntable angle during star guidance tracking.

[0096] This application uses an open-loop guidance and tracking algorithm to achieve stellar targeting. Based on the attitude data provided by the platform, the platform's attitude is predicted over a period of time. A dual-axis stabilization design, in both azimuth and elevation, is employed. By adjusting the turntable's azimuth and elevation axes, the telescope's optical axis is fixed and the field of view is stabilized.

[0097] Although the present invention has been described with reference to the current preferred embodiments, those skilled in the art should understand that the above-mentioned preferred embodiments are only used to illustrate the present invention and are not used to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for tracking a star target on a satellite, characterized in that: The method comprises the following steps: a. Calculate the coordinate transformation matrix between the J2000 coordinate system and the platform coordinate system using the platform attitude parameters of the onboard platform; b. Calculate the coordinate transformation matrix from the platform coordinate system to the load coordinate system; c. Calculate the coordinate transformation matrix from the load coordinate system to the lens coordinate system; d. Calculate the turntable angle for star guidance and tracking; e. Perform image stabilization tracking of stars based on the calculated turntable angle for star guidance tracking; The platform attitude parameters include: onboard time, inertial attitude quaternion, inertial attitude motion angular velocity; The step a specifically comprises the following steps: Step S11, calculate t a0 The coordinate transformation matrix A(t a0 ); On board a0 At this moment, the corresponding platform inertial attitude quaternion is [q1,q2,q3,q4]. Therefore, from J2000 to t a0 The coordinate transformation matrix of the platform coordinate system at this moment is as follows: Step S12, calculating the coordinate transformation matrix B corresponding to the attitude angle increment from the J2000 coordinate system to the platform coordinate system during the time interval Δt; On board a0 The inertial attitude motion angular velocity vector corresponding to the moment [ω x0 ,ω y0 ,ω z0 ], let Δt be the time from the start time to the calculation sampling time, and the rotation angular velocity β after Δt is as follows: Calculate the rotation direction unit vector r a : The steps to solve the coordinate transformation matrix B corresponding to the attitude angle increment are as follows: ΔB=β×Δt Step S13, calculate and obtain a0 to t a0 The coordinate transformation matrix M1 between the J2000 coordinate system and the platform coordinate system at time +Δt: M1=A(t a0 )×B; Described step c comprises: Assume that the initial turntable angle is [E0, A0], and the coordinate transformation matrix M from the load coordinate system to the lens coordinate system is g0 for: After a period of time i, the turntable angle is [E t ,A t ], the coordinate transformation matrix M from the load coordinate system to the lens coordinate system gt for: Among them, g t The theoretical image rotation angular velocity is transmitted to the ground as auxiliary information for ground processing; The step d comprises: Step S41: Set the exposure start time t a0 , the turntable angle is [E0, A0], and the transformation matrix from the J2000 coordinate system to the lens coordinate system is: M P0 =M g0 M2A(t a0 ) In the above formula, M g0 The parameters are the turntable angle [E0, A0], A(t a0 ) is t a0 Transformation matrix from the J2000 coordinate system to the platform coordinate system at time; Step S42, calculate t a0 At time +Δt, the transformation matrix from the J2000 coordinate system to the lens coordinate system is: M P =M gt M2M1 In the above formula, M gt The parameter is the turntable angle [E t ,A t ], M1 is t a0 +Δt time J2000 coordinate system to platform coordinate transformation matrix; set up Wherein, M2 is the coordinate system transformation matrix from the platform coordinate system to the payload coordinate system obtained by ground processing of the calibration image data; Available A t =arcsin(q 31 ) 2. The method according to claim 1, wherein The method further comprises the steps before step a: The onboard platform receives the onboard star tracking command issued.

3. The method according to claim 1, wherein The step b specifically includes: The coordinate system transformation matrix M2 from the platform coordinate system to the payload coordinate system is obtained by ground processing of the calibrated image data. The steps of calibrating M2 include: Step S21: The payload coordinate system is parallel to the lens coordinate system after the pitch and azimuth motions. Therefore, when the turntable is placed at zero position, the lens coordinate system and the payload coordinate system are considered to coincide. When the turntable is placed at zero position, an image of a known star is taken, and the star coordinates in the J2000 coordinate system are obtained by searching the star catalog. The coordinates of the star in the lens coordinate system are obtained by downloading the image, and the coordinate transformation matrix M from the J2000 to the lens coordinate system is calculated. z ; Step S22: Calculate the coordinate transformation matrix M from the J2000 coordinate system to the platform coordinate system at the exposure time of the payload based on the posture broadcast data when the image is taken. At ; Step S23, calculating M2; M2=M z M At 。

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