A method for lunar calibration suitable for single-axis control

Abstract

The application discloses a method for lunar calibration suitable for single-axis control, which comprises the following steps: firstly, selecting a time window for lunar calibration; then, describing a lunar vector in an orbit system within the time window to obtain a description result; taking a moment when the description result is maximum in the -Z direction as a calibration window to solve a central roll angle; and finally, controlling a roll angle change of the probe according to the solved central roll angle.

Description

Technical Field

[0001] This invention relates to the field of aerospace technology, and in particular to a lunar calibration method suitable for single-axis control. Background Technology

[0002] With the continuous development of space remote sensing technology and the increasing demands for quantitative applications of remote sensing products, the importance and necessity of high-precision calibration of space remote sensors are becoming increasingly prominent. The reliability, depth, and breadth of remote sensing data largely depend on the accuracy of remote sensor calibration. Although calibration is performed on the ground before satellite launch, the impact and vibration on the instruments during launch, as well as changes in the on-orbit working environment, can cause the satellite's calibration parameters to deviate from the pre-launch laboratory calibration results. To monitor changes in the calibration parameters of on-orbit detectors, on-orbit calibration of remote sensing satellites is essential.

[0003] In-orbit celestial body calibration methods have gradually become the mainstream in-orbit calibration methods due to their low susceptibility to environmental factors and high calibration frequency. Among celestial body calibration methods, the Moon has significant advantages such as a large field of view, stable spectral characteristics, no influence from the Earth's atmosphere, a wide spectral coverage, and light intensity within the detector's dynamic range. Therefore, using the Moon as an ideal calibration source for in-orbit lunar calibration is an important means to improve radiometric calibration efficiency and monitor the stability of detector imaging.

[0004] There are many methods for lunar calibration, most of which involve attitude maneuvers via three-axis pointing. For example, patent CN202010543415 proposes a method for evaluating lunar calibration parameters for a large remote sensing satellite's multi-angle camera, overcoming the problem that large remote sensing satellites cannot perform multi-angle lunar calibration within a single orbit. Patent CN201610262304 uses measurable orbital elements and ephemeris data from the satellite for analysis and calculation, and then uses the results as input parameters for satellite attitude maneuvers to perform attitude maneuvers for lunar calibration. CN 201610262686 and patent CN 202110219884 propose two different methods for the time planning problem of lunar calibration. The former uses satellite software tools and lunar ephemeris data for calculation, while the latter uses satellite software tools to analyze the angle between the field of view vector and the lunar vector to solve for the timing of lunar calibration. However, none of the above patents consider lunar calibration methods for constrained spacecraft. Summary of the Invention

[0005] To address some or all of the problems in existing technologies and to achieve lunar calibration of spacecraft under constrained conditions, this invention provides a lunar calibration method suitable for single-axis control, comprising:

[0006] Select the time window for monthly calibration and perform monthly calibration;

[0007] The lunar vector is described in the orbital system, and the description result is obtained;

[0008] Using the description result at its maximum in the -Z direction as the calibration window, the center roll angle is calculated; and

[0009] The roll angle of the detector is controlled according to the center roll angle.

[0010] Furthermore, the lunar calibration method also includes:

[0011] If the size of the detector is larger than a preset value, the real-time roll angle of the detector is calculated based on the center roll angle, and the spacecraft is controlled to rotate based on the real-time roll angle.

[0012] Furthermore, selecting the time window includes:

[0013] The estimation is based on the lunar date, including: using the time difference from the 15th of the lunar month as the timing, and selecting the time window when the lunar vector is in a specified position.

[0014] Furthermore, the selection of the time window includes: selecting a time when the Sun-Earth-Moon intersection angle is >150° as the timing, and selecting the time window when the Moon vector is in a specified position.

[0015] Furthermore, the Sun-Earth-Moon intersection angle is calculated by consulting the solar and lunar ephemeris, including:

[0016] Determine the calculation time, look up the corresponding solar ephemeris, and convert the right ascension and declination in the ephemeris into the first angle and the second angle;

[0017] Based on the first angle and the second angle, the direction vector from Earth to Sun in the J2000 system at the calculation time is determined;

[0018] Look up the corresponding lunar ephemeris and convert the right ascension and declination in the ephemeris into third and fourth angles;

[0019] Based on the third and fourth angles, determine the direction vector from Earth to Moon in the J2000 system at the calculation time; and

[0020] Find the angle between the direction vector of Earth pointing towards the Sun and the direction vector of Earth pointing towards the Moon.

[0021] Furthermore, calculating the center roll angle includes:

[0022] The direction vector pointing to the moon in the J2000 system is obtained from the lunar ephemeris.

[0023] Transform the direction vector into the orbital frame to obtain the angle between the lunar direction vector and the orbital frame's Z-axis; and

[0024] The center rolling angle is determined based on the included angle.

[0025] Furthermore, calculating the real-time roll angle includes:

[0026] The real-time roll angle is determined based on the angles between each point on the probe's centerline and the probe's center, as well as the angle between the lunar direction vector and the orbital system's Z-axis.

[0027] Furthermore, the spacecraft's orbit is located within a shadowed region where the angle between the Sun, Earth, and Moon is greater than 150°, and the spacecraft's orbital beta angle is [in the case of low Earth orbit]. , Within the range, To shield the Earth from view.

[0028] This invention provides a lunar calibration method applicable to single-axis control, which can complete the lunar calibration orientation of the spacecraft payload through single-axis adjustment control, thereby realizing on-orbit lunar calibration of spacecraft with limited conditions. It provides a feasible method for spacecraft with degraded functions and limited angles, and at the same time provides a new lunar calibration approach for normal spacecraft. Attached Figure Description

[0029] To further illustrate the above and other advantages and features of the various embodiments of the present invention, a more specific description of the various embodiments of the present invention will be presented with reference to the accompanying drawings. It is to be understood that these drawings depict only typical embodiments of the invention and are therefore not intended to limit its scope. In the drawings, identical or corresponding parts will be indicated by identical or similar reference numerals for clarity.

[0030] Figure 1 The diagram shows a flowchart of a lunar calibration method for single-axis control according to an embodiment of the present invention.

[0031] Figure 2 A schematic diagram showing the relationship between the solar vector and the lunar vector during a full moon;

[0032] Figure 3 A schematic diagram showing the motion of the sun and moon relative to the satellite;

[0033] Figure 4 A schematic diagram illustrating the calculation of the center rolling angle according to an embodiment of the present invention is shown;

[0034] Figure 5 This diagram illustrates a lunar calibration using detector rolling control according to an embodiment of the present invention; and

[0035] Figure 6This diagram illustrates a comparison of lunar trajectories calibrated using only the center roll angle and the real-time roll angle, according to an embodiment of the present invention. Detailed Implementation

[0036] In the following description, the invention is described with reference to various embodiments. However, those skilled in the art will recognize that the embodiments may be practiced without one or more specific details or in conjunction with other alternatives and / or additional methods. In other instances, well-known methods or operations are not shown or described in detail so as not to obscure the inventive points of the invention.

[0037] In this specification, references to "an embodiment" or "this embodiment" mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. The phrase "in one embodiment" appearing throughout this specification does not necessarily refer to the same embodiment in all instances.

[0038] Furthermore, the numbering of the steps in the methods of the present invention does not limit the execution order of the method steps. Unless otherwise specified, the method steps may be executed in different orders.

[0039] This invention is based on the inventor's insight that most existing lunar calibration methods rely on attitude maneuvers via three-axis pointing. However, in situations with weak control capabilities or abnormal spacecraft conditions, such as a gyroscope failure, high-precision angular velocities can only be determined using star-sensitive differential methods, which limit the required range of attitude variations. This restricts the calibration requirements, rendering conventional lunar calibration methods unsuitable.

[0040] To meet the specific requirements of lunar calibration, the inventors proposed a method for lunar calibration using only the roll angle. This method allows for the payload's lunar calibration orientation to be controlled via single-axis adjustment, enabling on-orbit lunar calibration of spacecraft under constrained conditions. The following description, in conjunction with the accompanying drawings, further illustrates the solution of this invention.

[0041] Since the lunar calibration method described above adjusts only the roll angle, the detector's observation direction must be along the satellite's own system. In the axial direction, to achieve better calibration results, the spacecraft should be able to maneuver and maintain a target attitude pointing only at the roll angle, and the attitude accuracy stability should meet the payload calibration requirements. Specifically, the satellite's roll attitude maneuvering capability should ensure stability within a maneuvering range of at least ±90° to ±180° (determined based on the sign of the beta angle; if beta is positive, the roll angle is negative). Furthermore, the satellite's attitude response capability needs to meet the pointing change requirements. Specifically, the satellite should have three-axis stabilization control capability. However, this invention does not limit the specific attitude control actuators and / or specific attitude control methods and / or specific attitude measurement means and / or the method of obtaining the orbital coordinate system and / or the process and manner of roll attitude maneuvering. Furthermore, this invention does not limit the size of the payload detector for on-orbit calibration.

[0042] Figure 1 This diagram illustrates a flowchart of a lunar calibration method for single-axis control according to an embodiment of the present invention. Figure 1 As shown, a lunar calibration method suitable for single-axis control includes:

[0043] First, in step 101, the timing is selected. To ensure compliance with lunar calibration interference and lunar phase requirements, in this embodiment of the invention, the angle between the Sun, Earth, and Moon needs to be >150°. According to common knowledge in the art, near a full moon, i.e., near the 15th day of the lunar month, the angle between the solar vector and the lunar vector is approximately 180°, that is, approximately in opposite directions. Figure 2 As shown, this means that in the orbital coordinate system, the lunar vector is located at its apex or apex. Therefore, in embodiments of the present invention, a time near the full moon is selected as the timing for lunar calibration. In one embodiment of the present invention, the timing can be directly estimated based on the lunar calendar date, i.e., the time point that differs from the 15th day of the lunar calendar by a specified amount of time is used as the timing. In another embodiment of the present invention, the timing is determined by calculating the solar-Earth-Moon intersection angle. Specifically, a time when the solar-Earth-Moon intersection angle is >150° is selected as the timing. The solar-Earth-Moon intersection angle is calculated by consulting the solar and lunar ephemeris, specifically including the following steps:

[0044] Once the calculation time is determined, the corresponding solar ephemeris is consulted, and the right ascension and declination in the ephemeris are converted into the first angle. Second angle ;

[0045] According to the first angle Second angle Find the direction vector from Earth to Sun in the J2000 system at the given solution time. :

[0046] ;

[0047] Look up the corresponding lunar ephemeris and convert the right ascension and declination in the ephemeris into third angles. Fourth angle ;

[0048] According to the third angle Fourth angle Find the direction vector from Earth to Moon in the J2000 system at the given solution time. :

[0049] ;as well as

[0050] Find the angle between the direction vector of Earth pointing towards the Sun and the direction vector of Earth pointing towards the Moon. :

[0051] ;

[0052] Next, in step 102, select the window. In an embodiment of the present invention, if the lunar calibration method is to be used for lunar calibration, the satellite's orbit is preferably located in the shadow region. Secondly, in the orbital coordinate system, both the solar vector and the lunar vector are conical, representing two opposite cones, such as... Figure 3 As shown, the position where the lunar vector passes overhead is the same as the position where the solar vector passes under, which is the shadow area. Therefore, in this embodiment of the invention, the time when the lunar vector passes overhead is selected as the window for lunar calibration. At this time, the lunar vector's projection on the orbital system's Z-axis is at its maximum, and the lunar vector lies on the orbital system's YOZ plane, allowing for lunar calibration simply by rolling.

[0053] Finally, in step 103, the angle is calculated. The angle refers to the detector's roll angle, which is calculated geometrically, such as... Figure 4 The diagram shows the transformation of the lunar vector in the J2000 coordinate system to the orbital coordinate system for description. Specifically, it includes:

[0054] Calculate the spacecraft's position vector in the inertial coordinate system within the window. Velocity vector and lunar direction vector As mentioned earlier, the lunar orientation vector should be located within the YOZ plane of the orbital system at this time. Therefore, according to the aforementioned position vector... and velocity vector It can solve for the attitude transformation matrix from the J2000 coordinate system to the orbital coordinate system. :

[0055] ,

[0056] in,

[0057] ,

[0058] ,as well as

[0059] ,

[0060] The lunar direction vector in the orbital coordinate system can then be represented as: ,

[0061] Based on the description of the lunar direction vector in the orbital coordinate system, the angle between the lunar direction vector and the orbital system's Z-axis can be further defined. It can be represented as:

[0062] ,

[0063] The time when the lunar vector passes through the zenith is selected as the window for lunar calibration; that is, the time when the lunar vector passes through the zenith is selected. The moment when the value is minimum For calibration window; At this time, the lunar direction vector and orbital system The included angle of the axis.

[0064] Therefore, the magnitude of the center roll angle required for lunar calibration at this time is: The sign of the roll angle needs to be determined based on the sign of the beta angle; if beta is positive, the roll angle is negative. By controlling the roll angle of the detector to change according to the central roll angle, lunar calibration can be achieved.

[0065] However, if the probe is large enough that it rotates only according to the central roll angle, the trajectory of the moon sweeping across the probe will be a curve, such as... Figure 6 As shown by line a in the diagram. To ensure that the moon sweeps across the exact center of the probe at any given moment during each mission, as... Figure 6 As shown by line b, the roll angle needs to be adjusted in real time according to the size of the detector, and the roll angle of the detector needs to be controlled to change according to the real-time roll angle to achieve lunar calibration. Therefore, in one embodiment of the present invention, a method for calculating the real-time roll angle is further provided, specifically including:

[0066] First, determine the direction vector of the satellite pointing towards the moon. The direction vector of the satellite pointing to the corresponding point on the centerline of its respective detector. The angle between the two vectors is The angle between the two vectors pointing from the satellite to the center of the detector and the corresponding point on the center line of the detector. :

[0067] ,

[0068] ,

[0069] ,

[0070] ,

[0071] in, The angular velocity of the probe during lunar sweep is given. For detector The field of view in the direction, The position vector of the spacecraft in the inertial coordinate system. The transformation matrix from the satellite's own system to its orbital system when the satellite is pointing towards the center of the detector (i.e., the Euler angles of the 312 transformation order). (corresponding transformation matrix), and The window time determined in step 102; and next, based on the included angle and the lunar direction vector relative to the orbital system Minimum included angle of the axis Determine the real-time scroll angle. :

[0072] ,

[0073] In embodiments of the present invention, the waiting time also needs to be determined based on factors such as the size of the probe and the motion of the lunar vector in the orbital system. Typically, the time it takes for the probe to photograph the moon... It should meet the following requirements:

[0074] ,

[0075] To ensure the successful completion of the mission, in one embodiment of the present invention, the range of maneuver time is expanded by extending it slightly before and after the maneuver. Waiting, the satellite attitude was adjusted in advance. Similarly, the position corresponding to that moment, After a certain point, the satellite's attitude is temporarily maintained before it performs another maneuver. Therefore, the actual time required for lunar calibration should meet the following requirements:

[0076] .

[0077] Furthermore, to avoid the disadvantages of detection in the case of dawn / dusk orbits, in one embodiment of the present invention, the orbital beta angle is required to be within [ ] in the case of low Earth orbit. , Within the range, Corner of Earth's occlusion:

[0078] ,

[0079] in, For the Earth's radius, and This represents the satellite's orbital altitude.

[0080] This invention provides a lunar calibration method applicable to single-axis control, which can complete the lunar calibration orientation of the spacecraft payload through single-axis adjustment control, thereby realizing on-orbit lunar calibration of spacecraft with limited conditions. It provides a feasible method for spacecraft with degraded functions and limited angles, and at the same time provides a new lunar calibration approach for normal spacecraft.

[0081] Although various embodiments of the invention have been described above, it should be understood that they are presented by way of example only and not as limitations. It will be apparent to those skilled in the art that various combinations, modifications, and alterations can be made without departing from the spirit and scope of the invention. Therefore, the breadth and scope of the invention disclosed herein should not be limited by the exemplary embodiments disclosed above, but should be defined solely by the appended claims and their equivalents.

Claims

1. A lunar calibration method suitable for single-axis control, characterized in that, Including the following steps: Select the time window for monthly calibration; The lunar vector is described in the orbital frame to obtain the description result, wherein the description result includes the projection of the lunar vector on the orbital frame-Z axis and the angle between the lunar direction vector and the orbital frame-Z axis; The moment when the lunar vector's projection onto the orbital coordinate system's Z-axis is at its maximum, or when the angle between the lunar direction vector and the orbital coordinate system's Z-axis is at its minimum, is used as the calibration window to calculate the center roll angle; and The roll angle of the detector is controlled according to the central roll angle.

2. The lunar calibration method as described in claim 1, characterized in that, Also includes: If the size of the detector is larger than a preset value, the real-time roll angle of the detector is calculated based on the center roll angle, and the roll angle of the detector is controlled to change based on the real-time roll angle.

3. The lunar calibration method as described in claim 1, characterized in that, Selecting the time window includes: The estimation is based on the lunar calendar date, including using a time window that is a specified time difference from the 15th day of the lunar calendar.

4. The lunar calibration method as described in claim 1, characterized in that, Selecting a time window includes selecting a time window where the Earth-Sun intersection angle is greater than 150° and the Moon passes overhead.

5. The lunar calibration method as described in claim 4, characterized in that, The solar-Earth-Moon intersection angle is calculated by consulting the solar and lunar ephemeris, including: Once the calculation time is determined, the corresponding solar ephemeris is consulted, and the right ascension and declination in the ephemeris are converted into the first angle. Second angle ; According to the first angle Second angle Find the direction vector from Earth to Sun in the J2000 system at the given solution time. : ； Look up the corresponding lunar ephemeris and convert the right ascension and declination in the ephemeris into third angles. Fourth angle ; According to the third angle Fourth angle Find the direction vector from Earth to Moon in the J2000 system at the given solution time. : ;as well as Find the angle between the direction vector of Earth pointing towards the Sun and the direction vector of Earth pointing towards the Moon. : 。 6. The lunar calibration method as described in claim 1, characterized in that, The calculation of the center roll angle includes: The direction vector pointing to the moon in the J2000 system is obtained from the lunar ephemeris. ; Transforming the direction vector into the orbital frame, we obtain the angle alpha between the lunar direction vector and the orbital frame's Z-axis. The angle min(alpha) between the lunar direction vector and the orbital frame's Z-axis at the moment of lunar overpass is also given. The center rolling angle is determined to be (180-min(alpha))° based on the included angle min(alpha). The direction of the center rolling angle is determined according to the sign of the track beta angle. If the track beta is positive, then the center rolling angle is negative.

7. The lunar calibration method as described in claim 2, characterized in that, Calculating the real-time roll angle includes: Based on the angle ph between any point on the centerline of the satellite pointing to the detector and the center of the detector, the angle deta between the direction vector of the satellite pointing to the moon and the direction vector of the satellite pointing to the corresponding point on the centerline of the detector, and the angle min(alpha) between the direction vector of the moon and the orbital system -Z axis, the roll angle of the satellite is determined to be (180-min(alpha)+deta)°.

8. The lunar calibration method as described in any one of claims 1 to 7, characterized in that, The spacecraft's orbit lies within a shadowed region where the angle between the Sun, Earth, and Moon is greater than 150°, and the spacecraft's orbital beta angle is [ ] in low Earth orbit. , Within the range, To shield the Earth from view.

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