Satellite-borne microwave radar tracking beam on-orbit correction method

Abstract

The invention discloses a satellite-borne microwave radar tracking wave beam on-orbit correction method, which comprises the following steps: an on-orbit calibration step: acquiring high-precision relative angle information through GNSS differential positioning by using two cooperative satellites equipped with GNSS receivers, and making a difference between the high-precision relative angle information and a tracking measurement angle of a satellite-borne microwave radar to a target satellite, obtaining a pointing deviation of a radar tracking beam; and an on-orbit correction step: injecting the pointing deviation into the spaceborne microwave radar in a ground injection mode, and adjusting a radar tracking algorithm to compensate the pointing deviation so as to realize on-orbit correction of tracking beam pointing. According to the invention, the problem of deterioration of radar product tracking precision caused by inconsistency of the on-orbit state and the ground state can be effectively solved, and the anti-risk capability of the load system function is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of spaceborne microwave radar signal processing, in particular to a method for in-orbit calibration of a spaceborne microwave radar tracking beam. BACKGROUND

[0002] With the rapid development of space technology, the application field of microwave radar has been extended from reconnaissance, early warning, and surveillance of ground (sea) and air targets to reconnaissance, identification, and surveillance (tracking) of space targets. In some application scenarios, the angle tracking accuracy of a spaceborne microwave radar determines the success or failure of the entire mission. Currently, the methods for improving the tracking accuracy of a spaceborne microwave monopulse radar mainly include: a) Reducing the radar beam width through frequency band and antenna design within the scope allowed by the task; b) Improving the signal-to-noise ratio of the target echo by increasing the radar transmit power and improving the signal processing method; c) Optimizing the antenna design to reduce the phase error of the channels before the sum-and-difference device and increase the null depth; d) In a mechanically scanned radar, optimizing the mechanism design to improve the pointing accuracy and reduce the noise of the servo control system; e) In system joint testing, measuring the tracking fixed error of the product by means of the theodolite and industrial camera, and compensating for it. SUMMARY

[0003] The present application is mainly used to solve the problem of in-orbit angle tracking accuracy calibration of a spaceborne microwave radar. In view of the problem that the difference between the in-orbit working condition of a spaceborne microwave radar and the ground test condition causes the tracking accuracy of the radar to decrease, the in-orbit calibration and correction technology is used to realize the in-orbit calibration of the tracking beam of the spaceborne microwave radar, so as to ensure that the in-orbit tracking accuracy index of the product meets the task requirements.

[0004] In order to achieve the above purpose, the present application proposes a method for in-orbit calibration of a tracking beam of a spaceborne microwave radar, which comprises the following steps: An in-orbit calibration step: using two cooperative satellites equipped with GNSS receivers, obtaining high-precision relative angle information through GNSS differential positioning, and subtracting the tracking measurement angle of a target star by the spaceborne microwave radar to obtain a pointing deviation of the radar tracking beam; An in-orbit calibration step: injecting the pointing deviation into the spaceborne microwave radar through ground number injection, adjusting the radar tracking algorithm to compensate for the pointing deviation, and realizing the in-orbit calibration of the pointing of the tracking beam.

[0005] Optionally, in the in-orbit calibration step, the two cooperative satellites include a body satellite carrying a microwave radar and a target satellite, and the two satellites track navigation satellites synchronously through GNSS receivers and collect measurement data, and high-precision relative position information is obtained after data exchange and differential processing, and the relative angle information is calculated.

[0006] Optionally, the pointing deviation is obtained by recording the yaw angle and the pitch angle fed back by radar telemetry after the microwave radar stably tracks the target satellite, and performing difference operation on the yaw angle and the pitch angle calibrated by GNSS differential positioning and the radar telemetry angle to obtain the pointing deviation including the yaw angle deviation and the pitch angle deviation.

[0007] Optionally, in the in-orbit correction step, the pointing deviation is uploaded to a signal processor of the on-board microwave radar as a parameter of a ground-based command, and the signal processor controls the radar tracking mechanism to adjust the pointing of the tracking beam from the zero position of the antenna to an angle position after compensating the pointing deviation.

[0008] Optionally, the adjustment of the radar tracking algorithm includes calculating an angle error according to the amplitude comparison angle measurement principle of the microwave radar, calculating an angular velocity based on the angle error calculation mechanism, and compensating the pointing deviation into the mechanism control angular velocity, so that the mechanism points to the target position every frame.

[0009] Optionally, the relative position information obtained by the GNSS differential positioning is based on the phase center of the GNSS receiving antenna, and the radar measurement is based on the radar reference coordinate system, and the position vectors in different coordinate systems are converted to the orbit coordinate system through coordinate conversion, and the conversion process involves the transfer matrix between the body coordinate system, the device reference coordinate system and the orbit coordinate system.

[0010] Optionally, in the coordinate conversion, the relative measurement vector is represented as a vector from the origin of the radar reference coordinate system to the geometric center of the target satellite, and the GNSS differential positioning vector is a vector of the phase center of the GNSS receiving antenna of the two satellites, and the position vector relationship between the radar reference coordinate system and the GNSS antenna phase center obtained by ground precise measurement is combined to complete the coordinate unification between the vectors.

[0011] Optionally, the amplitude comparison angle measurement principle is single-pulse and difference amplitude comparison angle measurement, and the angle error is calculated to drive the mechanism control by performing digital down-conversion and quadrature decomposition on the sum signal and the difference signal.

[0012] Optionally, in the in-orbit calibration step, when the distance between the two satellites is greater than 10 km, a high-precision star sensor is used to realize angle-second level attitude measurement, and the reference error of the radar and the star sensor is controlled within 0.001°.

[0013] Optionally, the spaceborne microwave radar is a monopulse radar, equipped with a ground-based signal processor and a tracking mechanism controller, wherein the tracking mechanism adjusts the beam direction according to the compensated control angular velocity.

[0014] This invention can effectively address the problem of radar product tracking accuracy deterioration caused by inconsistencies between on-orbit and ground conditions, and improves the resilience of the payload system. Attached Figure Description

[0015] Figure 1 This is a schematic diagram illustrating the definition of relative measurement data in the equipment's reference coordinate system. Figure 2 It is the relationship between the relative measurement vector and the GNSS differential positioning vector.

[0016] Figure 3 This is a schematic diagram of radar tracking beam correction.

[0017] Figure 4 Workflow of spaceborne microwave monopulse radar and differential amplitude angle measurement. Detailed Implementation

[0018] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a further detailed explanation of the on-orbit correction method for a spaceborne microwave radar tracking beam proposed in this invention. The advantages and features of this invention will become clearer from the following description. It should be noted that the accompanying drawings are in a very simplified form and use non-precise proportions, used only to facilitate and clearly illustrate the embodiments of this invention. Please refer to the accompanying drawings to make the objectives, features, and advantages of this invention more apparent and understandable. It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings are only for illustrative purposes to aid those skilled in the art and are not intended to limit the implementation conditions of this invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to the size, without affecting the effects and objectives achieved by this invention, should still fall within the scope of the technical content disclosed in this invention.

[0019] The present invention provides an on-orbit correction method for tracking beams of a spaceborne microwave radar, comprising: On-orbit calibration of tracking accuracy for spaceborne microwave radar: The on-orbit calibration process for the tracking accuracy of a spaceborne microwave radar requires the cooperation of two satellites, including the main satellite. Specifically, the two satellites use GNSS receivers to synchronously track the navigation satellite, collect measurement data, exchange data via inter-satellite links, or synchronously transmit data to the ground for differential data processing to reduce receiver error variance and achieve high-precision positioning, thereby calculating relative angle information.

[0020] Optionally, when the distance between the two satellites is more than 10 km, a high-precision star sensor is used to achieve an attitude measurement accuracy of angle-second level; by using a common reference installation and precise temperature control, the reference error between the relative measurement device and the star sensor can be controlled within 0.001°. When the star-borne microwave radar enters a working state, it tracks another cooperative satellite, and the relative angle between the two satellites is calculated through radar angle measurement telemetry data and GNSS differential positioning. The difference between the angle measured by the star-borne microwave radar and the angle calculated by the GNSS differential positioning is the pointing deviation of the radar tracking beam. The deviation of the radar tracking angle (the yaw angle deviation is , and the pitch angle deviation is ) can be calculated, which is the tracking error of the microwave radar.

[0021] In-orbit correction of the tracking accuracy of the star-borne microwave radar: According to the amplitude comparison angle measurement principle of the star-borne microwave single-pulse radar, the signal processing method of the radar is to calculate the azimuth angle error and the pitch angle error through the sum-difference amplitude comparison, and to control the mechanism to point to the target through the angle error driving mechanism controller. In order to correct the pointing of the in-orbit tracking beam, the tracking error factors of the microwave radar are added to the angular velocity calculation formula of the driving mechanism during the design of the radar, and the parameter is set as a ground-annotated parameter. During the in-orbit correction, the tracking error (the yaw angle deviation is , ) of the microwave radar is annotated through the ground annotation, and the tracking beam of the radar signal processing machine is controlled to move from the original antenna zero tracking to the (the yaw angle deviation is , ) angle tracking, so as to realize the correction of the pointing of the radar tracking beam. That is, the pointing deviation is injected into the star-borne microwave radar through the ground annotation, the radar tracking algorithm is adjusted to compensate for the pointing deviation, and the in-orbit correction of the pointing of the tracking beam is realized.

[0022] During the in-orbit calibration of the tracking error of the star-borne microwave radar, the measurement coordinate system of the star-borne relative measurement device is established on the detection sensor, and the reference coordinate system is established on the installation reference (generally, a prism is installed on the product as the reference). Before the product is delivered, precision calibration is performed, and the two coordinate systems are unified through the cross-multiplication conversion matrix in the software, and the measurement coordinate system data is unified to the reference coordinate system.

[0023] During the relative navigation, the relative measurement data of the target needs to be transmitted to the spacecraft body coordinate system and the orbit coordinate system through the reference coordinate system. The data is generally in the form of polar coordinates, and the conversion sequence is pitch first and then yaw. The reference coordinate system is defined as shown in Figure 1 . Wherein is the measurement device reference coordinate system, points to the flight direction of the spacecraft, points to the opposite direction of the orbit normal of the spacecraft, is obtained according to the right-hand rule, For the target to be tested, For the goal Projection of a plane The relative distance to the target. To measure the pitch angle of the target, Measure the yaw angle for the target.

[0024] Assume the spaceborne microwave radar (measuring equipment) is located on satellite A, and satellite B is the target satellite. The relationship between the spaceborne microwave radar's measurement vector of the target and the GNSS differential positioning vector is as follows: Figure 2 As shown. Satellite A performs relative measurements with satellite B, measuring the vector... One end is the origin of the microwave radar reference coordinate system of satellite A, and the other end is the geometric center of the side of satellite B facing satellite A. Relative measurement vector It can be represented as: (1) The two GNSS receivers determine their absolute positions separately, and then, with the aid of differential positioning technology, provide high-precision relative position information, thus determining the vector relationship between the phase centers of the two GNSS receiving antennas. Differential positioning technology refers to using two or more GNSS receivers, placed at both ends of a baseline, to simultaneously observe the same GNSS satellites and determine the baseline vector representing the relative position of the baseline in a protocol Earth coordinate system. The position vector between the microwave radar reference coordinate system of satellite A and the phase center of the GNSS receiving antenna. And the position vectors of the phase center and the lateral geometric center of the B-satellite GNSS receiving antenna. It can be obtained through precise ground-based measurements.

[0025] The reference coordinate system is a coordinate system based on the mounting plane of the measuring equipment, generally referring to the coordinate system of the prism installed on the equipment; the body coordinate system refers to the coordinate system of the entire satellite on which the measuring equipment is installed, with the origin at the satellite's center of mass. Due to errors during the installation of the measuring equipment, the two coordinate systems are rotated, and the transformation matrix is ​​determined through calibration before the entire satellite leaves the factory.

[0026] In summary, relative measurement vector It can be represented as: (2) The four vectors in the formula are established in different coordinate systems, and they need to be uniformly transformed to the orbital coordinate system. The transformation equation is: (3) In the formula: This is the transition matrix between the body coordinate system of satellite A and the orbital coordinate system; This is the transfer matrix of satellite A relative to the microwave radar reference coordinate system and relative to the satellite A body coordinate system; is the transfer matrix of the B-star body coordinate system relative to the orbit coordinate system.

[0027] When only considering the A-star microwave radar measurement error, the calibration result calculated by formula (3) is subtracted from the microwave radar measurement result calculated by formula (1), and the following formula (4) can be obtained: (4) In the formula: is the A-star relative measurement error; is the microwave radar measurement result calculated by formula (1). By collecting multiple groups of data, error calibration can be realized, and the error calibration formula is as follows: (5) In the formula: n is the number of data collection. i represents the i-th data collection.

[0028] During on-orbit calibration, the target star is searched and tracked by the satellite-borne microwave radar, and after stable tracking, the target relative distance , target measurement pitch angle and target measurement yaw angle fed back by the microwave radar telemetry are recorded. The relative measurement vector is calculated by formula (1); the relative measurement error is calculated according to formula (5) by performing GNSS differential positioning calibration on-orbit according to the above method; and the final measurement error measurement result is obtained through multiple measurements. Finally, the yaw angle deviation angle and the pitch angle deviation angle are obtained from the measurement error result , which are used for on-orbit correction of the satellite-borne microwave radar tracking beam.

[0029] After on-orbit calibration of the satellite-borne microwave radar tracking accuracy, the actual tracking pointing deviation of the satellite-borne microwave radar can be obtained. According to the actual tracking pointing deviation, the antenna beam tracking pointing angle is corrected by adjusting the two-dimensional driving mechanism angular velocity algorithm. The schematic diagram of radar tracking beam correction is shown in Figure 3 .

[0030] The single-pulse radar adopts sum-difference amplitude comparison angle measurement mechanism, calculates the yaw angle error and pitch angle error through sum-difference amplitude comparison, and controls the mechanism pointing to the target through the angle error driving mechanism controller. The sum-difference amplitude comparison angle measurement workflow is shown in Figure 4 .

[0031] Taking the pitch axis as an example, the sampling frequency is , and the signal center frequency is , the radar echo and the radar echo and road and pitch difference digital intermediate frequency signal of the ADC output of the radar signal processor are respectively: (6) (7) wherein, , are the amplitude modulation components of the sum and difference signals respectively; , are the phase modulation components of the sum and difference signals respectively, is the signal carrier frequency, and is expressed as .

[0032] After the sum and difference signals are subjected to the quadrature decomposition, filtering and decimation shown in the figure, the outputs are expressed as follows: Figure 4 (8) (9) Then, the calculated angular error result is as follows in the ideal case: (10) After the angular error is calculated, the maximum tracking angular velocity V of the mechanism is calculated according to the maximum tracking angular velocity required by the system, max and then the control angular velocity of the mechanism is calculated as: (11) According to the pitch angle pointing deviation obtained through the above steps, the pitch axis angular velocity of the mechanism is adjusted, and the above formula can be adjusted as: (12) Similarly, the angular velocity for controlling the yaw axis angular velocity of the mechanism is: (13) After each frame of radar signal processing, the calculated pitch axis and yaw axis are transmitted to the two-dimensional driving mechanism controller, so that the mechanism tracks the target position, that is, the tracking accuracy of the microwave radar is corrected on orbit.

[0033] The existing background technology all guarantees the tracking accuracy of the spaceborne microwave radar at the design and ground test level, and ignores the influence of the launch environment and the on-orbit operation environment on the tracking accuracy of the product. In some application scenarios sensitive to this index, there is a great technical risk. The present application provides a spaceborne microwave radar tracking beam on-orbit calibration method, which can effectively cope with the risk of deterioration of the tracking accuracy of the radar product caused by the inconsistency between the on-orbit state and the ground state, thereby affecting the function of the load system.

[0034] ​Optionally, in the on-orbit calibration step, the two cooperative satellites include a body satellite carrying a microwave radar and a target satellite, both of which track navigation satellites synchronously through GNSS receivers and collect measurement data, and high-precision relative position information is obtained after data exchange and differential processing, and the relative angle information is calculated.

[0035] Optionally, the pointing deviation is obtained by recording the yaw angle and pitch angle of radar telemetry feedback after the microwave radar stably tracks the target satellite, and performing difference operation on the yaw angle and pitch angle calibration values calculated by GNSS differential positioning and the radar telemetry angle to obtain the pointing deviation including the yaw angle deviation and the pitch angle deviation.

[0036] Optionally, in the on-orbit correction step, the pointing deviation is uploaded to the signal processor of the satellite-borne microwave radar as a parameter of the ground injectable number, and the signal processor controls the radar tracking mechanism to adjust the pointing of the tracking beam from the antenna zero position to the angle position after compensating the pointing deviation.

[0037] Optionally, the adjustment of the radar tracking algorithm includes calculating the angle error according to the amplitude comparison angle measurement principle of the microwave radar, calculating the angular velocity based on the angle error calculation mechanism, and compensating the pointing deviation into the mechanism control angular velocity, so that the mechanism points to the target position every frame.

[0038] Optionally, the relative position information obtained by the GNSS differential positioning is based on the GNSS receiving antenna phase center, and the radar measurement is based on the radar reference coordinate system, and the position vectors in different coordinate systems are converted to the orbit coordinate system through coordinate conversion, and the conversion process involves the transfer matrix between the body coordinate system, the device reference coordinate system and the orbit coordinate system.

[0039] Optionally, in the coordinate conversion, the relative measurement vector is represented as the vector from the origin of the radar reference coordinate system to the geometric center of the target satellite, and the GNSS differential positioning vector is the vector of the GNSS receiving antenna phase center of the two satellites, and the position vector relationship between the radar reference coordinate system and the GNSS antenna phase center obtained by ground precise measurement is combined to complete the coordinate unification between vectors.

[0040] Optionally, the amplitude comparison angle measurement principle is single pulse and difference amplitude comparison angle measurement, and the angle error is calculated to drive the mechanism control by digital down-conversion and quadrature decomposition of sum signal and difference signal.

[0041] Optionally, the satellite-borne microwave radar is a single pulse radar equipped with a signal processor and a tracking mechanism controller which can be ground-injected, and the tracking mechanism adjusts the beam pointing according to the compensated control angular velocity.

[0042] In summary, the prior art is to ensure the tracking accuracy of the satellite-borne microwave radar at the design and ground test level, ignoring the influence of the launch environment and the on-orbit operation environment on the tracking accuracy of the product. In some application scenarios sensitive to this indicator, there is a great technical risk. The present application provides an on-orbit calibration method for the tracking beam of a satellite-borne microwave radar, which can effectively cope with the problem of deterioration of the tracking accuracy of the radar product caused by the inconsistency between the on-orbit state and the ground state, thereby improving the risk resistance ability of the load system function.

[0043] It should be noted that in this document, the terms "comprise", "comprise", or any other variant thereof are intended to cover non-exclusive inclusion, so that processes, methods, articles or devices that include a series of elements not only include those elements, but also include other elements not explicitly listed, or include elements inherent to such processes, methods, articles or devices. Without more limitations, the element defined by the statement "comprises a" does not exclude the presence of additional identical elements in the process, method, article or device that includes the element.

[0044] In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "center", "height", "thickness", "upper", "lower", "vertical", "horizontal", "top", "bottom", "inner", "outer", "axial", "radial", "circumferential" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0045] In the description of the present application, unless otherwise specified and limited, the terms "mounting", "connection", "connection", "fixing" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0046] In the present application, unless specifically stated and limited otherwise, the "on" or "under" of a first feature to a second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, the "on", "above" and "on top of" of a first feature to a second feature includes that the first feature is directly above and obliquely above the second feature, or only means that the first feature is horizontally higher than the second feature. The "under", "below" and "underneath" of a first feature to a second feature includes that the first feature is directly below and obliquely below the second feature, or only means that the first feature is horizontally lower than the second feature.

[0047] Although the present application has been described in detail by the foregoing preferred embodiments, it should be recognized that the foregoing description is by way of example only and that various modifications and substitutions can be made by those skilled in the art without departing from the scope of the present application. Accordingly, the scope of the present application should be limited only by the appended claims.

Claims

1. A method for on-orbit correction of a tracking beam in a spaceborne microwave radar, characterized in that, Includes the following steps: On-orbit calibration steps: Using two cooperative satellites equipped with GNSS receivers, high-precision relative angle information is obtained through GNSS differential positioning, and the difference between this information and the tracking measurement angle of the target star by the onboard microwave radar is calculated to obtain the pointing deviation of the radar tracking beam. On-orbit correction steps: The pointing deviation is injected into the spaceborne microwave radar via ground-based data injection, and the radar tracking algorithm is adjusted to compensate for the pointing deviation, thereby achieving on-orbit correction of the tracking beam pointing.

2. The on-orbit calibration method as described in claim 1, characterized in that, In the on-orbit calibration step, the two cooperating satellites include a main satellite carrying a microwave radar and a target satellite. The two satellites synchronously track the navigation satellite and collect measurement data through a GNSS receiver. After data exchange and differential processing, high-precision relative position information is obtained, and then the relative angle information is calculated.

3. The on-orbit calibration method as described in claim 1 or 2, characterized in that, The pointing deviation is obtained by the following method: after the microwave radar stably tracks the target star, the yaw angle and pitch angle fed back by the radar telemetry are recorded; the yaw angle and pitch angle calibration values ​​calculated by GNSS differential positioning are compared with the radar telemetry angles to obtain the pointing deviation including the yaw angle deviation and the pitch angle deviation.

4. The on-orbit calibration method as described in claim 1, characterized in that, In the on-orbit correction step, the pointing deviation is used as a parameter that can be ground-monitored. The ground-monitored data is then uploaded to the signal processor of the spaceborne microwave radar. The signal processor controls the radar tracking mechanism to adjust the tracking beam from the antenna zero position to the angle position after compensating for the pointing deviation.

5. The on-orbit calibration method as described in claim 4, characterized in that, The adjusted radar tracking algorithm includes: calculating the angular error based on the amplitude-to-angle measurement principle of microwave radar, controlling the angular velocity based on the angular error calculation mechanism, and compensating the pointing deviation into the angular velocity controlled by the mechanism, so that the mechanism tracks and points to the target position in each frame.

6. The on-orbit calibration method as described in claim 2, characterized in that, The relative position information obtained by the GNSS differential positioning is based on the phase center of the GNSS receiving antenna, and the radar measurement is based on the radar reference coordinate system. The position vectors under different coordinate systems are uniformly transformed to the orbit coordinate system through coordinate transformation. The transformation process involves the transfer matrix between the body coordinate system, the equipment reference coordinate system and the orbit coordinate system.

7. The on-orbit calibration method as described in claim 6, characterized in that, In the coordinate transformation, the relative measurement vector is represented as the vector from the origin of the radar reference coordinate system to the geometric center of the target star, and the GNSS differential positioning vector is the vector of the phase center of the two GNSS receiving antennas. By combining the position vector relationship between the radar reference coordinate system and the GNSS antenna phase center obtained by ground precision measurement, the coordinate unification between the vectors is completed.

8. The on-orbit calibration method as described in claim 5, characterized in that, The amplitude-comparison angle measurement principle is a single-pulse sum-difference amplitude-comparison angle measurement. By performing digital down-conversion and orthogonal decomposition on the sum and difference signals, the angle error is calculated to drive the mechanism for control.

9. The on-orbit calibration method as described in claim 1, characterized in that, In the on-orbit calibration step, when the distance between the two satellites is greater than 10km, a high-precision star sensor is used to achieve arcsecond-level attitude measurement, and the reference error between the radar and the star sensor is controlled within 0.001°.

10. The on-orbit calibration method as described in claim 1, characterized in that, The spaceborne microwave radar is a monopulse radar, equipped with a ground-based signal processor and a tracking mechanism controller. The tracking mechanism adjusts the beam direction according to the compensated control angular velocity.

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