On-orbit unloading system and method for residual moment and residual angular momentum of spacecraft active payloads

Abstract

The present invention provides an on-line unloading system and method for residual torque and residual angular momentum of a spacecraft active payload, belonging to the field of on-line unloading of residual torque and residual angular momentum. The on-line unloading system of the present invention includes two single-frame control moment gyros and two flywheels. The frame axes of the two single-frame control moment gyros are installed in parallel along the positive x direction to unload the torque along the z-axis and y-axis or the single z-axis residual torque. The two flywheels are respectively installed on the negative half-axis of x and the positive half-axis of y to unload the residual torque on the x-axis and y-axis. The on-line unloading method of the present invention is for the system to operate, sending the residual torque information generated by the current tracking and pointing device to the on-board control computer for mode screening, and comparing and analyzing the collected residual torque signals. The present invention uses fewer gyros, which can reduce the system weight and save financial and material resources; by analyzing the generation of angular momentum and torque for the active payload, fewer gyros are selected to achieve the same function.

Description

Technical Field

[0001] The present invention relates to an on-line unloading system and method for residual moment and residual angular momentum of a spacecraft movable payload, belonging to the field of on-line unloading of moment and residual angular momentum. Background Art

[0002] The paper "High-precision attitude control method for large remote sensing satellites based on MSCMG" (Journal of Chinese Inertial Technology, Vol. 25, No. 4, 2017, Shu Shi, Article No. 1005 - 6734(2017)04 - 0421 - 11) proposed a high-precision attitude control method for large remote sensing satellites based on closed-loop compensation of magnetic suspension control moment gyroscopes. This article applied it to the motion compensation control system of an earth observation remote sensing imaging camera, carried out motion modeling and magnetic suspension control moment gyroscope compensation scheme design for two types of cameras: a scanning camera with one-dimensional motion and a staring camera with two-dimensional motion, improved the traditional method, and optimized the accuracy and stability of the control system. Although the paper "High-precision attitude control method for large remote sensing satellites based on MSCMG" (Journal of Chinese Inertial Technology, Vol. 25, No. 4, 2017, Shu Shi, Article No. 1005 - 6734(2017)04 - 0421 - 11) improved the traditional method, carried out modeling and simulation for specific movable payloads and was able to compensate for the residual moment, it only applied the control moment gyroscope for moment compensation on the axis of the maximum component of the residual moment, and the moments generated by coupling on other axes were not compensated.

[0003] The patent "On-orbit real-time compensation method for large interference moment of payload scanning mechanism" (invention patent, Yu Jie, 201611045964.3) described the steps of real-time compensation using a moment compensation flywheel group, and finally could ensure the synchronization between the interference moment of the payload and the feedforward moment compensation, and could achieve high-precision and high-reliability attitude stability control of the satellite. The patent "On-orbit real-time compensation method for large interference moment of payload scanning mechanism" (invention patent, Yu Jie, 201611045964.3) used two compensation flywheels to compensate for the moments of two axes, but due to the limited output capacity of the flywheels, it was not applicable to devices that generated relatively large residual moments, and at the same time, only the moments of two axes were compensated, and the moment of the third axis was not compensated.

[0004] Based on the above technologies and problems, for a spacecraft with a tracking and pointing device, this patent proposes a combined actuator that applies two single-frame control moment gyros and two flywheels to unload the residual torque of the tracking and pointing device with two-dimensional motion. First, a two-dimensional motion description of the tracking and pointing device is given, and the torque magnitudes of the torque principal axis and other component axes generated are analyzed. Secondly, according to the above torque analysis, the manipulation mode of configuration selection is judged: Manipulation mode 1, when the payload torque is concentratedly distributed within two axes and there is a coupling torque on the third axis, select manipulation mode 1, apply two CMGs to cancel the planar torque and one flywheel to cancel the torque on the third axis; when the payload torque is concentratedly distributed on a single axis and there are coupling torques on the other two axes, select manipulation mode 2, apply two CMGs to cancel the component of the axis with the largest torque, and apply two flywheels to compensate for the torque on the remaining two axes. For the two cases, the configurations of the dual control moment gyros that can unload the main torque generation plane and the expressions of the manipulation laws are given respectively, and flywheels are installed on the axis with the minimum output torque to ensure the unloading of the residual torque on the three axes. Summary of the Invention

[0005] The object of the present invention is to solve the problems existing in the above-mentioned prior art, and further provide a system and method for on-line unloading of residual torque and residual angular momentum of a spacecraft active payload.

[0006] The object of the present invention is achieved by the following technical solutions:

[0007] A system for on-line unloading of residual torque and residual angular momentum of a spacecraft active payload includes an on-board control computer, a tracking and pointing device, a residual torque measuring device, and a device for unloading the residual torque of the spacecraft active payload. The on-board control computer performs mission planning and control on the spacecraft active payload according to mission requirements. When the tracking and pointing device rotates, torques around the Z-axis and Y-axis and a coupling torque on the X-axis are generated. The residual torque measuring device measures the residual torque and transmits the result to the on-board computer through a feedback signal. The on-board control computer analyzes the measurement signal and finally transmits a residual torque unloading command signal to the device for unloading the residual torque of the spacecraft active payload. This process continues until the residual torque drops to a reasonable value. The device for unloading the residual torque of the spacecraft active payload includes two single-frame control moment gyros and two flywheels. The frame axes of the two single-frame control moment gyros are installed in parallel along the positive x-direction to unload the torques along the z-axis and y-axis or the single z-axis residual torque. The two flywheels are respectively installed on the negative x-semi-axis and the positive y-semi-axis to unload the residual torque on the x-axis and y-axis.

[0008] For the system for on-line unloading of residual torque and residual angular momentum of the spacecraft active payload of the present invention, the reasonable value is set according to different mission requirements, and usually takes a value of 3% - 5%.

[0009] Unloading method of the on-line unloading system for residual moment and residual angular momentum of the spacecraft's moving payload. The specific unloading method is as follows:

[0010] Step 1: The system operates, and the residual moment information generated by the current tracking and pointing device is sent to the on-board control computer.

[0011] Step 2: The on-board control computer performs mode screening, and compares and analyzes the collected residual moment signals: comparing the magnitudes of the residual moments of the three axes, and combining the actual residual moment distribution of the moving payload, generally divided into two cases: the concentrated z-axis and y-axis case where the residual moments of the z-axis and y-axis are larger but the x-axis is smaller, and the concentrated single z-axis case where only the residual moment of the z-axis is larger but the residual moments of the z-axis and y-axis are smaller. Then, the distribution form of the payload moment is obtained, and the corresponding control signals are sent to the on-line unloading system. The on-line unloading system then drives the corresponding control moment gyroscopes and flywheels to unload the residual moments of the three axes according to the received mode selection signal and residual moment measurement signal.

[0012] For the unloading method of the present invention, the actual residual moment distribution form of the moving payload in Step 2 is: when the generated moment is concentrated on the z-axis and y-axis, Mode 1 is applied, and the generated three-dimensional disturbance moment is divided into two parts. The first part applies the pseudo-inverse control law to cancel the disturbance moment in the zoy plane, and the second part applies the flywheel FW1. According to to cancel the coupling moment of the x-axis, thereby realizing the real-time compensation of the payload disturbance moment.

[0013] When the generated moment is concentrated on a single z-axis, Mode 2 is applied. At this time, the frame angles of the two moment gyroscopes rotate in opposite directions, and only the moment on the z-axis is generated. According to the scissor configuration, the control law is applied to cancel the z-axis moment, and at the same time, the disturbance moments generated on the x and y axes are cancelled by the flywheel FW1 and the flywheel FW2.

[0014] For the on-line unloading system and method of the residual moment and residual angular momentum of the spacecraft's moving payload of the present invention, compared with the traditional method that only uses control moment gyroscopes to form a gyro group configuration, the number of gyroscopes used is less, which can reduce the system weight and save financial and material resources; by analyzing the generation of angular momentum and moment for this moving payload, fewer gyroscopes are selected to achieve the same function. The same configuration can select different working modes according to different working conditions requirements, broadening the application range.

[0015] Compared with using flywheels to unload the payload moment, it can output a larger moment, and is suitable for unloading the moment of payloads with relatively large residual moments.

[0016] Compared with the torque compensation only for the main axis of torque generation, the torque generated by the three axes can be compensated, optimizing the control accuracy and stability of the system. Description of the Drawings

[0017] Figure 1 It is a schematic structural diagram of the on-line unloading system for residual torque and residual angular momentum of the spacecraft active payload of the present invention.

[0018] Figure 2 It is a schematic diagram of the output plane torque of the single-frame control moment gyro in the present invention.

[0019] Figure 3 It is a schematic diagram of the output single-axis torque of the single-frame control moment gyro in the present invention.

[0020] Figure 4 It is the torque tracking situation of the simulation in Mode 1 of the Second Embodiment.

[0021] Figure 5 It is the torque tracking situation of the simulation in Mode 2 of the Second Embodiment.

[0022] Figure 6 It is the torque generation situation of the actual tracking and pointing device in the Second Embodiment of the present application.

[0023] Figure 7a It is the torque compensation situation of the single-frame control moment gyro in Mode 1 of the Second Embodiment of the present application.

[0024] Figure 7b It is the torque compensation situation of the flywheel in Mode 1 of the Second Embodiment of the present application.

[0025] Figure 8 It is a schematic diagram of the two-dimensional tracking and pointing system in the Third Embodiment.

[0026] Figure 9 It is the working process of the residual torque unloading device for the spacecraft active payload.

[0027] Figure 10 It is a flow chart of signal judgment and working mode. Detailed Embodiments

[0028] The present invention will be further described in detail below with reference to the drawings: This embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation manners are given, but the protection scope of the present invention is not limited to the following embodiments.

[0029] Embodiment 1: The on-line unloading system and method for residual torque and residual angular momentum of the spacecraft active payload involved in this embodiment. The on-line unloading system for residual torque and residual angular momentum of the spacecraft active payload with a tracking and pointing device is composed of two single-frame control moment gyros and two flywheels. The specific installation method is as follows Figure 1As shown, the specific working steps are as follows: Step 1, the system operates, and the torque information generated by the current tracking device is sent to the control computer; Step 2, the control computer performs mode screening, compares and analyzes the collected torque signals to obtain the distribution form of the payload torque, and sends the corresponding control signals to the torque unloading device. When the generated torque is concentratedly distributed on two axes, Mode 1 is applied. The generated three-dimensional disturbance torque is divided into two parts. The first part applies the pseudo-inverse control law , (where C is the torque matrix expressed as , are the gimbal angles of two CMGs, T c is the control command torque, and h is the initial angular momentum of the gyro) can cancel the disturbance torque in the zoy plane. The second part applies the flywheel FW1. According to (where is the moment of inertia of the flywheel, is the flywheel speed) can cancel the coupling torque on the x-axis, thereby realizing real-time compensation of the payload disturbance torque; when the generated torque is concentratedly distributed on a single z-axis, Mode 2 is applied. At this time, the gimbal angles of the two CMGs rotate in opposite directions, and only the torque on the z-axis is generated. According to the scissor configuration, the control law is applied, (T z is the current residual torque on the z-axis) can cancel the z-axis torque. At the same time, for the disturbance torques generated on the x and y axes, FW1 and FW2 are used to cancel the torques. The following gives the specific ways to compensate for the disturbance torque in the two working modes of Step 2.

[0030] The working principles of the single-gimbal control moment gyro and the flywheel. The basic working principle of the SGCMG can be described as follows: When the flywheel rotor in the gimbal rotates at a high speed, if the direction of the angular momentum is changed at this time, due to the gyroscopic inertia, it will precess in order to maintain its original state, and thus generate a gyroscopic torque. At this time, the direction of the gyroscopic torque is perpendicular to the plane formed by the gimbal axis and the angular momentum. When the SGCMG rotates a certain gimbal angle , the gimbal angular velocity will affect the output torque , which can be expressed as

[0031] (1)

[0032] where is the unit vector in the direction of the gimbal axis, is the unit vector in the direction of the flywheel angular momentum, is the unit vector in the direction of the output torque and is perpendicular to and It forms a right - hand system. The flywheel is obtained by removing the outer frame from the CMG and generates a control torque by changing the rotor speed. Thus, it only generates a torque in the x - axis direction. Similarly, due to the limitation of speed saturation, there is a limit to the torque output capacity. The output torque of the flywheel can be expressed as

[0033] (2)

[0034] Secondly, the control laws of two single - gimbal control moment gyros in two modes are given. The schematic diagram of the plane angular momentum generated by two CMGs is as follows Figure 2 as shown. From Figure 2 it can be known that the output angular momentum of the two gyros can be expressed as

[0035] (3)

[0036] Similarly, the output torque can be obtained as

[0037] (4)

[0038] Writing the angular momentum and torque in the form of and the corresponding A and B matrices can be obtained as follows

[0039] (5)

[0040] (6)

[0041] According to the above principle, when selecting Mode 1, that is, two CMGs rotate in a plane to output a plane torque, the form of the pseudo - inverse control law is designed as follows

[0042] (7)

[0043] At the same time, in the direction perpendicular to the torque output plane, only one flywheel FW1 can complete the compensation task of the residual torque of the three - axis payload. When selecting Mode 2, that is, when a larger torque is to be output on the z - axis, the corresponding control law form of the scissor configuration is adopted as follows

[0044] (8)

[0045] The way of outputting angular momentum and torque at this time is as follows Figure 3 as shown. The gimbal angular velocity directions of the two CMGs are opposite and equal in magnitude, which can cancel the torque in the direction perpendicular to the torque output direction, and then achieve the ability of single - axis large - torque output. At the same time, FW1 and FW2 are applied to meet the compensation tasks of the smaller residual torques of the other two axes.

[0046] Example 2: For an on-line unloading system and method for residual torque and residual angular momentum of a spacecraft active payload involved in this example, simulations are carried out for the two working modes in step 2. For Mode 1: Assume that the torque in the main output torque plane of the tracking and pointing device is sinusoidal, and the maximum torque amplitudes are , . Select a CMG with an initial angular momentum of 50 Nms, and select an initial gimbal angle of . The following simulation results can be obtained Figure 4 as shown.

[0047] It can be seen that the system can track the specified sinusoidal signal well, with almost no torque error. At this time, selecting an appropriate flywheel can sufficiently cancel the coupling torque on the x-axis.

[0048] For Mode 2: Assume that the main output torque of the tracking and pointing device is concentrated on the z-axis, with a maximum value of 50 Nm, and the initial gimbal angle is . The output torque results of two SGCMGs with an initial angular momentum of 50 Nms are as follows Figure 5 as shown. It can be seen that the system can track the 50 Nm sinusoidal torque signal well. At this time, selecting an appropriate flywheel can sufficiently cancel the coupling torques on the x and y axes.

[0049] The following is a simulation analysis for the actual working motion of the camera: The torque generated when the tracking and pointing device moves is as follows Figure 6 as shown. Corresponding to the control computer selecting Mode 1, the following simulation results can be obtained as shown in Figure 7 below. It can be seen that in Mode 1, the system can track the payload torque well, that is, it can cancel the residual torque of the tracking camera well.

[0050] Example 3: For an on-line unloading system and method for residual torque and residual angular momentum of a spacecraft active payload involved in this example,

[0051] Taking a two-degree-of-freedom tracking and pointing device as an example, the two-degree-of-freedom tracking and pointing device can rotate around the Z-axis and the Y-axis to track and point at a specific target in real time. Assume that the coordinate system O c Z c Y c X c of the two-degree-of-freedom tracking and pointing device and the spacecraft body coordinate system O b Z b Y b X bIf there is no relative rotation between them (if there is rotation, only multiply by a certain rotation matrix), the characteristics of the residual torque generated on the spacecraft are as follows: the torques around the Z-axis and Y-axis are large, while the coupling torque around the X-axis is relatively small. For the moving load with such residual torque characteristics, a residual torque unloading device in the following form is designed. At the same time, in order to make full use of the configuration function, a residual torque unloading method for an additional working condition is designed, that is, the configuration can also unload the residual torque distribution with a large torque around the Z-axis and small torques around the Y-axis and X-axis.

[0052] The process of the residual torque measurement device for the spacecraft moving load is described as follows: The on-board control computer conducts mission planning and control on the spacecraft moving load (hereinafter taking the two-degree-of-freedom tracking device as an example) according to the mission requirements. During this process, the rotation of the two-degree-of-freedom tracking device will generate torques around the Z-axis and Y-axis and the coupling torque around the X-axis. The residual torque measurement device can measure this residual torque and return the result to the on-board computer. The on-board control computer analyzes the measurement signal and finally transmits the residual torque unloading instruction signal to the residual torque unloading device of the spacecraft moving load, and continues this process until the residual torque drops to a reasonable value. The flowchart of this process is as Figure 9 shown.

[0053] The analysis process of the on-board computer for the residual torque measurement signal is described as follows: For the configuration design of the spacecraft residual torque unloading device, it can select the control mode according to the characteristics of the feedback signal (or determine the residual torque distribution of the load). ① If the residual torque around the X-axis in the feedback signal is significantly smaller than the residual torques around the Z-axis and Y-axis (such as the two-degree-of-freedom tracking device), then select working mode one (that is, the SGCMG group outputs a planar torque), and two SGCMGs and FW1 work to complete the residual torque unloading. ② If the residual torque around the Z-axis in the feedback signal is significantly larger than the residual torques around the X-axis and Y-axis, then select working mode two (that is, the SGCMG group outputs a single-axis torque), and two SGCMGs and FW1, FW2 work to complete the residual torque unloading. The specific flowchart is as Figure 10 shown.

[0054] As mentioned above, only the preferred specific embodiments of the present invention are described. These specific embodiments are all different implementation manners based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. On-orbit unloading system for residual moment and residual angular momentum of spacecraft active payloads, comprising an on-board control computer, a tracking and pointing device, a residual moment measuring device, and an on-orbit unloading device for residual moment of spacecraft active payloads. The on-board control computer conducts mission planning and control for the spacecraft active payload according to mission requirements. When the tracking and pointing device rotates, it generates moments around the Z-axis and Y-axis and a coupling moment around the X-axis. The residual moment measuring device measures the residual moment and sends the result to the on-board computer through a feedback signal. The on-board control computer analyzes the measurement signal and finally transmits a residual moment unloading command signal to the on-orbit unloading device for residual moment of spacecraft active payloads, and this process continues until the residual moment drops to a reasonable value. It is characterized in that, The residual torque unloading device for the spacecraft's active payload includes two single-frame control moment gyros and two flywheels. The frame axes of the two single-frame control moment gyros are installed in parallel along the positive x-direction to unload the torques along the z-axis and y-axis or the single z-axis residual torque. The two flywheels are respectively installed on the negative half-axis of x and the positive half-axis of y to unload the residual torques on the x-axis and y-axis.

2. The on-line unloading system for residual moment and residual angular momentum of the spacecraft's movable payload according to claim 1, wherein The reasonable value is set according to different mission requirements and usually takes a value of 3% - 5%.

3. The unloading method of the on-line unloading system for the residual moment and residual angular momentum of the spacecraft's active payload as described in any one of claims 1-2, characterized in that, The specific unloading method is as follows: Step 1: The system operates, and sends the residual torque information generated by the current tracking and pointing device to the on-board control computer. Step 2: The on-board control computer conducts mode screening, and compares and analyzes the collected residual torque signals: comparing the magnitudes of the residual torques of the three axes, and combining the actual residual torque distribution of the active payload, generally divided into two cases: the concentrated z-axis and y-axis case where the residual torques of the z-axis and y-axis are larger but the x-axis is smaller, and the concentrated single z-axis case where only the residual torque of the z-axis is larger but the residual torques of the z-axis and y-axis are smaller, so as to obtain the distribution form of the payload torque, and send the corresponding control signals to the on-line unloading system. The on-line unloading system then drives the corresponding control moment gyros and flywheels to unload the residual torques of the three axes according to the received mode selection signal and residual torque measurement signal.

4. The unloading method according to claim 3, characterized in that The actual residual moment distribution form of the active load in the second step is as follows: when the generated moment is concentrated in the z-axis and y-axis, apply Mode 1. Divide the generated three-dimensional disturbance moment into two parts. The first part applies the pseudo-inverse control law to cancel the disturbance moment in the zoy plane. The second part applies the flywheel FW1. According to to cancel the coupling moment in the x-axis, thereby realizing the real-time compensation of the payload disturbance moment; When the generated torque is concentrated and distributed on a single z-axis, Application Mode 2 is applied. At this time, the gimbal angles of the two torque gyros rotate in opposite directions, only generating torque on the z-axis. According to the scissor configuration, the control law is applied to cancel the z-axis torque. At the same time, for the disturbance torques generated on the x and y axes, the flywheels FW1 and FW2 are used to cancel the torques.

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