Ground Experimental Method for Sun-Orientation of Cubesat Solar Wings Based on Gravity Vector Tracking

Abstract

The present invention proposes a ground experiment method for the sun-oriented orientation of a cube satellite's solar wing based on gravity vector tracking. By introducing a constant gravity vector that can be analogized to the solar vector as the vector tracking source, without the need for complex dedicated equipment such as solar simulators, and only using general test equipment such as a three-axis turntable, the simulation and test of the sun-oriented orientation function of the solar wing can be achieved. This method has fewer test steps, simple procedures, high speed, does not require complex modeling, is suitable for the testing of solar wings and ground experiments in general laboratory environments, is used to verify its sun-oriented orientation function and accuracy, and is more in line with the characteristics of cube satellite research and development, such as fast speed, simple structure, and low cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of CubeSat solar wings, and particularly relates to a ground experiment method and device for CubeSat solar wing solar orientation based on gravity vector tracking. Background Art

[0002] CubeSats (hereinafter referred to as CubeSats) have the advantages of small size, light weight, low cost, fast development, and the ability to launch multiple satellites simultaneously, making them suitable for conducting technology exploration and verification in the space field and receiving increasing attention. One of the main factors restricting the application of CubeSats is their energy supply capacity. The working energy of CubeSats is provided by solar photovoltaic cells. In the traditional body-mounted scheme, the photovoltaic cells are installed on the outer surface of the CubeSat, and the power generation capacity is limited due to the limited surface area of the CubeSat. The deployable solar wing uses an expandable photovoltaic cell sailboard installed in a folded manner, and improves the photovoltaic power generation by increasing the area of the photovoltaic cells. The basic deployable solar wing only realizes the deployment of the photovoltaic cell sailboard, and the solar wing cannot change the angle relative to the CubeSat body. Therefore, the incident angle of sunlight is affected by the satellite attitude. The photoelectric conversion efficiency of the photovoltaic cell is directly related to the incident angle of the light relative to the solar wing. The closer to the perpendicular irradiation, the higher the electric energy conversion efficiency. Therefore, improving the photovoltaic power generation of the deployable solar wing mainly depends on its solar orientation ability. Subsequently, single-axis tracking and double-axis tracking methods were developed to enable the solar wing to rotate in one or two degrees of freedom to track sunlight, improving the photovoltaic conversion efficiency and power generation. In order to improve the control accuracy and working efficiency of the solar wing for solar orientation, it is of great significance to verify the orientation effect and orientation accuracy of the solar wing during the ground test stage.

[0003] Considering the ground experimental environment, the following reasons make it difficult to directly use sunlight as the light source for solar vector tracking: (1) If sunlight is introduced, the indoor experimental environment must be modified, adding a complex indoor-outdoor light transmission system, which is costly, and the sunlight changes angles continuously over time, making it difficult to be used as a stable reference light source; (2) If an indoor simulation light source is used, the general lighting method cannot produce a parallel light source, and a special solar simulator is needed to simulate parallel sunlight. It is expensive and the size of the irradiation spot it generates is small, making it difficult to irradiate the entire solar wing; (3) When the CubeSat conducts a ground attitude control simulation experiment, the position of the solar wing changes continuously with the movement of the CubeSat attitude, and it is difficult for sunlight or the simulation light source to accurately point to and irradiate the solar wing; (4) Other stray light, reflected light, indoor lighting, etc. in the indoor environment will interfere with the experimental results. The above factors bring difficulties to the ground verification and testing of the solar orientation function and accuracy of the solar wing, and a more simple and accurate method is needed to conduct the ground experimental verification of the solar orientation function of the solar wing.

[0004] Currently, most of the ground experiment methods for solar arrays are in the form of large-scale hardware-in-the-loop simulation, mainly targeting large flexible solar arrays. For the small rigid solar arrays of CubeSats, it is expected to complete their ground tests with relatively simple experimental methods and general experimental instruments. The methods with complex technology, high equipment requirements, and troublesome experimental verification processes are not fully applicable. The literature "Key Technologies of the Hardware-in-the-loop Test Bench for the Sun-pointing Device of the Space Station, Journal of Astronautics, 2019, Vol.40(5): 596-603" proposed a ground test method for the sun-pointing device of the solar array. This method combines two ways of large-scale physical test bench and MATLAB modeling and simulation, and uses special equipment such as complex simulation units, high-precision loading units, and large driving devices to complete the test. The results show that the sun-pointing device of the solar array can stably track the given signal. This method has good practicability for large flexible solar arrays, but considering the deficiencies such as the complexity of the test system, the test conditions of software and hardware combination, high test environment cost, and long test cycle, it is not applicable to the ground experiment of the sun-pointing of the small rigid solar arrays of CubeSats. Summary of the Invention

[0005] To solve the deficiencies in the ground test capabilities of the sun-pointing of CubeSat solar arrays and overcome the problems brought by traditional methods, such as complex test systems, high equipment requirements, cumbersome steps, and long test cycles, the present invention proposes a ground experiment method and device for the sun-pointing of CubeSat solar arrays based on gravity vector tracking.

[0006] The inventive concept of the present invention is as follows:

[0007] The actual working process of the solar array tracking sunlight can be described as the accurate tracking of a spatial vector by the solar array. When conducting ground tests on the sun-pointing of CubeSat solar arrays, we can consider using another vector that can reliably simulate the characteristics of the sunlight constant vector as the tracking object, avoiding the use of complex special equipment such as solar simulators.

[0008] In view of the characteristics of CubeSats, such as small solar array area and large stiffness, the present invention introduces a constant gravity vector that can be analogized to the solar vector as the vector tracking source. Without complex special equipment such as solar simulators, only general test equipment such as a three-axis turntable is used to realize the simulation and test of the sun-pointing function of the solar array. This method has fewer test steps, simple links, high speed, does not require complex modeling, and is suitable for the testing and ground experiments of solar arrays in general laboratory environments, used to verify its sun-pointing function and accuracy, and is more in line with the characteristics of CubeSats, such as fast R & D, simple structure, and low cost.

[0009] The technical solution of the present invention is as follows:

[0010] The method is characterized in that: the method uses the method of the solar wing tracking a constant gravity vector when the cubic satellite body is rotating to replace the actual working condition of the solar wing tracking the change of the solar vector when the cubic satellite body is stationary, and controls the solar wing to rotate in the pitch and roll directions by adopting the control method and servo mechanism to be verified, tracks the relative direction change between the solar wing and the gravity vector caused by the change of the cubic satellite body posture, and equivalently simulates the process of the solar wing tracking the solar vector in two degrees of freedom under the actual working condition, realizes the closed-loop control function and accuracy verification of the solar wing performing two-dimensional angular tracking of the solar vector, and achieves the purpose of verifying the two-dimensional solar orientation effect of the solar wing under ground indoor conditions.

[0011] Furthermore, the ground experiment method for the solar orientation of a cubic satellite solar wing based on gravity vector tracking is characterized in that: a three-axis accelerometer is installed on the solar wing to replace the original sun sensor to obtain the azimuth information of the measured vector; the measured vector is the gravity vector during the ground experiment; the cubic satellite body posture is driven to change relative to the gravity vector by the movement of the three-axis turntable, simulating the change in the illumination azimuth of the solar vector relative to the cubic satellite body when in orbit, and the solar wing is manipulated to rotate in the pitch and roll directions by adopting the control method and servo mechanism to be verified, and the relative direction change between the solar wing and the gravity vector caused by the change in the posture of the cubic satellite body is tracked, which is equivalent to simulating the process of the solar wing tracking the solar vector in two degrees of freedom under actual working conditions, so as to realize the closed-loop control function and accuracy verification of the two-dimensional angular tracking of the solar vector of the solar wing.

[0012] Furthermore, the ground experiment method for the orientation of a cubic satellite solar wing towards the sun based on gravity vector tracking is characterized by comprising the following steps:

[0013] Step 1: Use the three-axis accelerometer on the solar wing to measure the current gravity vector orientation, and then transmit the obtained information to the solar wing follower controller;

[0014] Step 2: The solar wing follower device controller uses the control method to be verified to control the solar wing to rotate in the pitch and roll directions to achieve the tracking of the gravity vector by the solar wing;

[0015] Step 3: By changing and measuring the pitch angle and roll angle of the cubic satellite body attitude, the two-dimensional angle between the normal direction of the solar wing and the direction of the gravity vector is adjusted. Then the solar wing follower device uses the control method and servo mechanism to be verified to control the solar wing to rotate in the pitch and roll directions, so as to achieve two-dimensional tracking of the gravity vector by the solar wing, simulating the tracking process of the solar wing to the sun vector when the actual in-orbit satellite body attitude is stationary and the sun vector rotates.

[0016] Further, the control method to be verified is as follows: According to the current gravity vector orientation measured by the triaxial accelerometer, calculate the angles between the current gravity direction and the solar array normal direction on the pitch and roll axes, and accordingly control the servo mechanism to drive the two-dimensional rotation of the solar array to reduce the angular deviation in the two axes until the gravity vector direction coincides with the solar array normal direction.

[0017] Further, in step 3, the pitch angle and roll angle of the CubeSat body attitude are changed by using a triaxial turntable to control the two-dimensional angle between the gravity vector direction and the solar array normal direction to simulate the two-dimensional angle between the solar vector direction and the solar array normal direction when the CubeSat is in orbit.

[0018] Further, in step 3, the variation rules of the pitch angle and roll angle of the CubeSat body attitude controlled by the triaxial turntable are as follows:

[0019]

[0020]

[0021]

[0022]

[0023]

[0024]

[0025] where θ z is the pitch angle of the CubeSat body attitude controlled by the triaxial turntable, and δ z is the roll angle of the CubeSat body attitude controlled by the triaxial turntable; θ s is the elevation angle of the solar vector in the Earth inertial system; δ s is the azimuth angle of the solar vector in the Earth inertial system, T s is the time calculated from the vernal equinox; is the rotation matrix from the Earth inertial coordinate system to the orbital coordinate system; ω is the argument of perigee, f is the true anomaly, i is the orbital inclination, Ω is the right ascension of the ascending node, C x 、C y and C z correspond to the rotation matrices of the x, y, and z axes in the orbital coordinate system respectively; is the solar unit vector [1 0 0] T at the vernal equinox, s x 、s y and s z respectively represent the components of the solar vector on the x, y, and z axes. After the CubeSat orbit is determined, the description of the solar vector in the orbital system is known.

[0026] A ground experiment device for solar wing orientation of a cubic satellite based on gravity vector tracking, characterized by comprising a cubic satellite body, a solar wing, a solar wing controller, a three-axis accelerometer, a pitch channel driving device, a roll channel driving device, a pitch channel angle sensor, a roll channel angle sensor, and a three-axis turntable motion table;

[0027] The CubeSat body is used to install solar wings and solar wing controllers, wherein the solar wings are composed of solar panels and are connected to the CubeSat body through a solar wing two-dimensional rotation mechanism;

[0028] The solar wing controller is used to control the pitch channel driving device and the roll channel driving device of the solar wing;

[0029] The three-axis accelerometer is installed on the solar wing and is used to measure the direction of the gravity vector;

[0030] The pitch channel driving device and the roll channel driving device drive the solar wing to rotate the pitch and roll channels according to the signal of the solar wing controller;

[0031] The pitch channel angle sensor is used to measure the real-time rotation angle of the solar wing in the pitch channel; the roll channel angle sensor is used to measure the real-time rotation angle of the solar wing in the roll channel;

[0032] The cubic satellite body is fixedly mounted on a three-axis turntable motion table. The three-axis turntable motion table drives the cubic satellite body to rotate by rotating itself, so that the angle between the normal direction of the solar wing and the direction of the gravity vector deviates.

[0033] Beneficial Effects

[0034] The beneficial effects of the present invention are:

[0035] (1) The experimental instruments and equipment used are common laboratory instruments and equipment, the experimental cost is low, the experimental system and experimental plan design are simpler, and the implementation is convenient and fast;

[0036] (2) The gravity vector is used to replace the sun vector, and no special instruments or equipment are required. The vector's own orientation does not change, and it is not affected by external disturbances such as ambient light, making the feedback state more stable and uninterrupted, easy to obtain measurements, and not easily disturbed;

[0037] (3) The satellite's body attitude movement replaces the rotation of the sun vector, making it easy to control and measure the azimuth relationship between the star and the tracked vector on the ground, reducing the requirements for experimental equipment and experimental environment;

[0038] (4) Replacing the sun sensor with a triaxial accelerometer can achieve the equivalent replacement of the measurement element during ground experiments, with good measurement stability, reduced experimental difficulty, and improved experimental reliability;

[0039] (5) It is applicable to the two-dimensional sun-pointing ground experiments of various satellites such as CubeSats, and can also be used for the one-dimensional sun-pointing ground experiments of CubeSat rigid solar wings after simplification.

[0040] The additional aspects and advantages of the present invention will be partially given in the following description, partially become apparent from the following description, or be understood through the practice of the present invention. Brief Description of the Drawings

[0041] The above and / or additional aspects and advantages of the present invention will become apparent and easy to understand from the description of the embodiments in conjunction with the following drawings, where:

[0042] Figure 1 It is a schematic diagram of a two-axis tracking and following solar wing.

[0043] Reference numerals in the figure: 1 is the CubeSat body, 2 is the solar wing, 3 is the sun sensor, 4 is the solar wing controller, 5 is the solar wing pitch rotation arm, 6 is the solar wing roll axis, 7 is the pitch channel drive motor, and 8 is the roll channel drive motor.

[0044] Figure 2 It is a schematic diagram of the rotation of the measurement coordinate system for solar vector tracking.

[0045] Figure 3 It is a schematic diagram of the rotation of the body coordinate system for gravity vector tracking.

[0046] Figure 4 It is a schematic diagram of a two-degree-of-freedom gravity vector tracking ground experiment.

[0047] Reference numerals in the figure: 1 is the CubeSat body, 2 is the solar wing, 3 is the sun sensor, 5 is the solar wing pitch rotation arm, 6 is the solar wing roll axis, 10 is the triaxial accelerometer, 11 is the moving table surface of the triaxial turntable, 12 is the pitch channel angle sensor, and 13 is the roll channel angle sensor.

[0048] Figure 5 It is a flow chart of the equivalent analysis of the two-dimensional vector tracking algorithm for the solar wing.

[0049] Figure 6 It is a flow chart of the ground experiment test. Detailed Embodiments

[0050] For CubeSats with deployable solar arrays, there are problems such as insufficient ground test capabilities for solar array sun-pointing, complex test systems, high equipment requirements, cumbersome procedures, and long test cycles in traditional methods. The present invention proposes a ground experiment method and corresponding device for CubeSat solar array sun-pointing based on gravity vector tracking. This method uses the gravity vector, which has a constant vector direction, is easily obtained indoors, and is not easily disturbed, to replace the solar vector, whose vector direction changes constantly, is inconvenient to measure, is difficult to stably obtain indoors, and is easily affected by ambient light, as the tracking object; the movement of the CubeSat body attitude relative to the gravity vector is used to replace the rotation of the solar vector relative to the CubeSat body in space, enabling the convenient acquisition of accurate, controllable, and easily measurable vector direction changes; in terms of the experimental device, a triaxial accelerometer is used to replace the sun sensor as the measurement element when the solar array performs vector tracking, and the body attitude angle rotation is realized through a triaxial turntable and the rotation angle measurement value is given. The required measurement elements and instrumentation have strong versatility and are easily obtained.

[0051] The core idea of this experimental method is to use the gravity vector, which has a constant direction and is not easily disturbed, to replace the solar vector, whose direction changes and is easily disturbed, as the measured vector during ground experiments. By installing a triaxial accelerometer on the solar array to replace the original sun sensor to obtain the azimuth information of the measured vector, and using the movement of the triaxial turntable to drive the satellite attitude to change relative to the gravity vector, simulating the change in the illumination azimuth of the solar vector relative to the satellite during on-orbit operation, thereby verifying the closed-loop control function and accuracy of the solar array for two-dimensional angular servo tracking of the solar vector.

[0052] For Figure 1 the double-axis tracking servo (two-dimensional sun-pointing) solar array shown, first use the triaxial accelerometer on the solar array to measure the current gravity vector azimuth, and then transmit the obtained information to the solar array servo device controller. Calculate the angles between the current gravity direction and the solar array normal direction on the pitch and roll axes, and accordingly drive the two-dimensional rotation of the solar array to reduce the angular deviation in the two axes until the gravity direction coincides with the solar array normal direction, thereby realizing the servo tracking of the solar array for the gravity vector. At the same time, by changing and measuring the pitch angle and roll angle of the CubeSat body attitude, the two-dimensional angle between the solar array normal direction and the gravity direction can be adjusted, and then the two-dimensional servo tracking of the gravity vector can be carried out by the solar array, thereby simulating the servo tracking process of the solar array for the solar vector when the actual on-orbit flying satellite body attitude remains unchanged and the solar vector rotates. This method can effectively verify the servo control algorithm and servo tracking ability of the solar array for the solar vector, and overcome the problem that it is difficult to obtain a constant solar vector in the indoor environment, which affects the verification of the two-dimensional sun-pointing function and accuracy of the solar array.

[0053] The following gives the principle analysis and specific experimental process of the present invention:

[0054] (1) Sensor equivalent replacement

[0055] A triaxial accelerometer is used to replace the sun sensor, and both are devices fixedly connected to the illuminated surface of the solar panel. The sun sensor is used to measure the two-degree-of-freedom angular orientation of the sun vector relative to the sensor body, so as to determine the orientation of the sun vector relative to the solar panel. The triaxial accelerometer is used to measure the triaxial gravitational acceleration, and then calculate the two-degree-of-freedom angular orientation of the solar panel relative to the gravity vector. Both of these sensors determine the pitch and roll channel angles between the solar panel and the vector by measuring the two-dimensional relative angular relationship between a certain vector and the sensor body, and use this as the feedback measurement value to achieve the follow-up tracking of the solar panel to the vector. At the same time, since the measurement result is the angle between the measured vector and each coordinate axis of the sensor, it has nothing to do with the specific installation position of the sensor on the solar panel. Therefore, it is feasible to use a triaxial accelerometer to replace the sun sensor for vector angular orientation measurement in the present invention, and the designed and verified follow-up tracking control algorithm is also fully applicable to the two-dimensional sun-pointing tracking of the solar panel. The specific algorithm is shown in the following equivalent analysis.

[0056] (2) Equivalent analysis of the two-dimensional vector follow-up tracking control algorithm of the solar panel

[0057] ① Coordinate system definition

[0058] Satellite body coordinate system Ox b y b z b : The origin O is at the centroid of the satellite, and Ox b , Oy b , Oz b The three axes are respectively fixed on the satellite body to form a right-handed rectangular coordinate system.

[0059] Solar panel measurement coordinate system Ox m y m z m : The origin O is located at the centroid of the solar panel, and x m , Oy m The plane is in the solar panel plane, and Oy m The axis points to the extension direction of the pitch rotating arm of the solar panel, and Oz m The axis is perpendicular to the solar panel plane and forms a right-handed rectangular coordinate system with Ox m , Oy m .

[0060] Both of the above coordinate systems are shown in Figure 1 .

[0061] ② Description of space sun vector tracking

[0062] When the satellite is in orbit, taking the satellite body as the reference point, the sun vector rotates relative to the satellite body. For the two-degree-of-freedom solar panel, the solar panel measurement coordinate system Ox fixedly connected to the solar panel my m z m Measure the elevation angle and azimuth angle of the solar vector in real time, and calculate the solar vector. The solar wing controller adjusts the rotation angle of the solar wing according to the direction of the solar vector, so as to achieve the solar wing's orientation towards the sun.

[0063] In the solar wing measurement coordinate system Ox m y m z m under, the elevation angle and azimuth angle of the solar vector in the measurement coordinate system can be obtained according to the sun sensor, and the solar vector is determined by using the relationship between the included angles of unit vectors. Assume that at time t, the solar wing has completed orientation towards the sun, that is, the solar vector is perpendicular to the solar wing plane. At this time, the measured elevation angle θ0 = 90°. At the next moment, the solar vector rotates, and the elevation angle and azimuth angle change. At this time, the elevation angle and azimuth angle measured by the sun sensor are θ and It can be obtained that the solar vector coordinates in the solar wing measurement coordinate system Ox m y m z m are:

[0064]

[0065] To make the solar wing achieve orientation towards the sun again, it is necessary to rotate the solar wing so that its normal is parallel to the solar vector, as Figure 2 shown, Ox m y m z m needs to rotate by an angle β around the Ox m axis to obtain the Ox m y m ′z m ′ coordinate system, and then rotate by an angle γ around the Oy m ′ to obtain the Ox m ″y m ″z m ′ coordinate system. Therefore, the rotation matrix of the solar wing measurement coordinate system Ox m y m z m is:

[0066]

[0067] When the solar wing completes orientation towards the sun again, [x m y m z m T In the Ox m ″y m ″z m ″ coordinate system should be expressed as [0 0 -1] T , that is:

[0068] ​

[0069] The expressions for the pitch angle β and the roll angle γ are as follows:

[0070]

[0071]

[0072] ③ Description of ground gravity vector tracking

[0073] During ground experiments, the CubeSat is fixed on a horizontally placed three-axis turntable. At this time, the turntable plane is always parallel to the xOy plane of the satellite body coordinate system. When the three-axis turntable works, the CubeSat will rotate together with it, and the representation of the gravity vector in the solar panel measurement coordinate system Ox y z will also change accordingly. To make the three-axis turntable simulate the rotation law of the solar vector, the specific motion law of the three-axis turntable is given below: b y b z b of x b Oy b plane. When the three-axis turntable works, the CubeSat will rotate together with it, and the representation of the gravity vector in the solar panel measurement coordinate system Ox y z will also change accordingly. To make the three-axis turntable simulate the rotation law of the solar vector, the specific motion law of the three-axis turntable is given below: m y m z m When the satellite orbit is determined, the description of the solar vector in the orbit system can be obtained. To make the three-axis turntable simulate the orbital state of the satellite in orbit, the method for calculating its rotation angle is as follows:

[0074] When the satellite orbit is determined, the solar vector in the orbit system can be obtained. To make the three-axis turntable simulate the orbital state of the satellite in orbit, the method for calculating its rotation angle is as follows:

[0075]

[0076] where, θ s is the elevation angle of the solar vector in the Earth inertial system; δ s is the azimuth angle of the solar vector in the Earth inertial system, T s is the time calculated from the vernal equinox point; is the rotation matrix from the Earth inertial coordinate system to the orbit coordinate system, and ω is the argument of perigee, f is the true anomaly, i is the orbital inclination, Ω is the right ascension of the ascending node, C x , C y and C z correspond to the rotation matrices of the x, y, and z axes respectively; is the solar unit vector at the vernal equinox point [1 0 0] T , s x , s y and s z represent the components of the solar vector s on the x, y, and z axes respectively. Since the gravity vector in the yaw direction of the three-axis turntable remains constant in direction during ground experiments, the pitch angle of the three-axis turntable is controlled according to θ z , and the roll angle of the three-axis turntable is controlled according to δ z .

[0077] After the three-axis turntable rotates according to the above rotation law, the gravity vector expression can be obtained according to the three-axis gravity acceleration components. The solar wing controller adjusts the pitch angle and roll angle of the solar wing in real time based on the gravity vector azimuth to make its normal direction coincide with the gravity vector direction, so as to realize the gravity vector tracking in the ground experiment.

[0078] In the solar wing measurement coordinate system Ox m y m z m , the gravitational acceleration is denoted as g, and the three-axis accelerometer directly measures the three-axis components of the gravitational acceleration. As Figure 3 shown, assuming that the gravity vector is perpendicular to the solar wing plane at time t, at this time it can be represented by the unit vector [0 0 -1] T in the measurement coordinate system. At the next moment, the three-axis turntable rotates, and the rotation angles given based on the body coordinate system are: pitch angle θ1, roll angle yaw angle δ1. According to the rotation information of the three-axis turntable, the rotation matrix of the body coordinate system Ox b y b z b is:

[0079]

[0080] After the three-axis turntable rotates, the three-axis components of the gravity vector measured by the three-axis accelerometer change. At this time, it can be represented as the unit vector [a x a y a z T . Combining the gravity vector direction at time t, it is simply considered that the body coordinate system Ox b y b z b is relatively stationary with the measurement coordinate system Ox m y m z m during the rotation of the three-axis turntable. The measurement coordinate system rotates with the three-axis turntable, then there is:

[0081]

[0082] At the next moment, the solar wing normal tracks the gravity vector direction. When the two coincide again, in the solar wing measurement coordinate system Ox m y m z m there is:

[0083]

[0084] It can be known that:

[0085] L b = L m ​T (10)

[0086] That is, in ground experiments, the pitch angle β′ and roll angle γ′ of the satellite solar panel can be described as follows:

[0087]

[0088] Considering the equivalent effects of the sun sensor and the triaxial accelerometer, the unit gravity vector is expressed as the triaxial components and the elevation angle and azimuth angle forms respectively, where the elevation angle and azimuth angle are θ′ and Then there are the triaxial components:

[0089]

[0090] Also, from equations (7) and (8), we can get:

[0091]

[0092] Obviously, equation (12) is equal to equation (13). Combining with equation (11), we can get:

[0093]

[0094] Therefore, we can obtain:

[0095]

[0096]

[0097] By comparing equations (4), (5), (15), and (16), it can be seen that the pitch angle β′ and roll angle γ′ of the solar panel tracking the gravity vector during ground experiments are equivalent to the pitch angle β and roll angle γ of the solar panel tracking the sun vector when the satellite is in orbit.

[0098] To sum up, the output of the triaxial accelerometer is equivalent to the output of the sun sensor during ground experiments, and the calculation of the rotation pitch angle and roll angle of the solar panel is consistent with that during sun vector tracking. Therefore, the core idea of this experiment is feasible: during ground experiments, the gravity vector is used to replace the sun vector, and the movement of the triaxial turntable drives the change of the satellite attitude, so as to simulate the change of the illumination azimuth of the sun vector relative to the satellite body in orbit with the change of the azimuth of the gravity vector relative to the satellite body; the triaxial accelerometer is installed on the solar panel to replace the original sun sensor to obtain the azimuth information of the measured vector, and the equivalent simulation of the solar panel tracking the variable azimuth vector can be carried out when the rotation attitudes are the same. The equivalent analysis flow chart is as Figure 5 shown.

[0099] ④ Main experimental process

[0100] After the three-axis turntable starts, the attitude of the satellite changes following the rotation of the moving tabletop of the turntable. The three-axis accelerometer measures the changes in the three-axis components of the gravity vector in real time, and then transmits the information to the solar panel controller. The pitch angle β′ and roll angle γ′ required for the normal of the solar panel to coincide with the gravity vector are calculated in real time, and then the motor is controlled to drive the solar panel to rotate, so that it can track the changes of β′ and γ′ in time to achieve the orientation control of the solar panel. During this process, the actual pitch angle β r and roll angle γ r of the solar panel rotation measured by the pitch channel angle sensor and roll channel angle sensor installed on the CubeSat body can be used to calculate the tracking accuracy of the solar panel. The response time of the solar panel tracking can be obtained according to the difference between the starting time t of the turntable rotation and the ending time t r of the solar panel rotation.

[0101] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0102] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.

[0103] In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Therefore, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality" means two or more unless otherwise specifically defined.

[0104] (1) Introduction to the composition and functions of each component in the ground experiment

[0105] Main component composition: CubeSat body 1, solar panel 2, solar panel controller 4, three-axis accelerometer 10, pitch channel drive motor 7, roll channel drive motor 8, pitch channel angle sensor 12, roll channel angle sensor 13, three-axis turntable moving tabletop 11.

[0106] The CubeSat body 1 is used to install the solar wing 2 and the solar wing controller 4. The solar wing 2 consists of solar panels and is connected to the CubeSat body 1 by a solar wing pitch rotation arm 5 and a solar wing roll rotation shaft 6. The solar wing controller 4 is used to control the pitch channel drive motor 7 and the roll channel drive motor 8 of the solar wing. The three-axis accelerometer 10 is used to measure the direction of the gravity vector. The pitch channel drive motor 7 and the roll channel drive motor 8 drive the solar wing 2 to rotate in the pitch and roll channels according to the signals of the solar wing controller 4. The pitch channel angle sensor 12 is used to measure the real-time rotation angle of the solar wing 2 in the pitch channel. The roll channel angle sensor 13 is used to measure the real-time rotation angle of the solar wing 2 in the roll channel. The rotation of the three-axis turntable moving table 11 drives the CubeSat body 1 to rotate, causing a deviation in the angle between the normal of the solar wing 2 and the gravity vector.

[0107] (2) Ground experiment process

[0108] Verification of the two-degree-of-freedom rotation closed-loop control function of the solar wing 2 when the three-axis accelerometer 10 replaces the sun sensor 3.

[0109] Mainly test whether the solar wing 2 can rotate normally in the pitch and roll degrees of freedom, confirm whether the signal polarities are the same when the sun sensor 3 and the three-axis accelerometer 10 are installed according to the measurement coordinate system of the solar wing 2; confirm whether the pitch channel drive motor 7 and the roll channel drive motor 8 start and drive the solar wing 2 to rotate within two degrees of freedom after the rotation of the three-axis turntable moving table 11 causes an angle between the normal of the solar wing 2 and the gravity vector, and preliminarily verify the completion effect of the vector tracking closed-loop control of the solar wing 2 with the three-axis accelerometer 10 as the feedback sensor.

[0110] Considering the two installation methods of the sun sensor 3 on the solar wing 2 or the CubeSat body 1, the present invention describes the more complex installation method of the sun sensor 3 on the solar wing 2. If the sun sensor 3 is installed on the CubeSat body 1, align the sensitive main axis of the sun sensor 3 with the positive directions of the three axes of the satellite body coordinate system Ox b y b z b to be consistent, and the solar vector in the satellite body coordinate system can be directly obtained. When installing the three-axis accelerometer 10, with the same signal polarity as the sun sensor 3 as the standard, the gravity vector in the satellite body coordinate system can also be directly obtained, that is, the two are still equivalent, and the control algorithm used in the present invention is also applicable.

[0111] Single-channel tracking gravity vector test of the solar wing 2.

[0112] Set the motion plane 11 of the three-axis turntable to be horizontal, set the plane where the solar panel 2 is located to be horizontal with the lower end face of the CubeSat body 1, and fix the lower end face of the CubeSat body 1 on the motion tabletop 11 of the three-axis turntable. At this time, the relative position between the motion tabletop 11 of the three-axis turntable and the satellite body coordinate system Ox b y b z b is determined. All subsequent rotation operations of the motion tabletop 11 of the three-axis turntable are described in terms of the satellite body coordinate system. Start the three-axis turntable. First, control the motion tabletop 11 of the three-axis turntable to only change the pitch angle θ z . During this process, the three-axis accelerometer 10 measures the direction of the gravitational acceleration in real time, and transmits the angle signal generated by the normal direction of the solar panel 2 and the gravitational vector to the solar panel controller 4. The solar panel controller 4 determines whether there is an angular deviation between the normal direction of the solar panel 2 and the gravitational vector direction. If there is, it controls the pitch channel drive motor 7 to run, drives the solar panel pitch rotating arm 5 to rotate, and performs deviation correction until the gravitational vector direction coincides with the normal direction of the solar panel 2, completing the test of the solar panel 2 tracking the gravitational vector in the pitch channel.

[0113] After the motion tabletop 11 of the three-axis turntable returns to the horizontal position, control the motion tabletop 11 of the three-axis turntable to only change the roll angle δ z . The three-axis accelerometer 10 measures the direction of the gravitational acceleration in real time. If there is an angular deviation between the normal direction of the solar panel 2 and the gravitational vector direction, control the roll channel drive motor 8 to run, drive the solar panel roll rotating shaft 6 to rotate to drive the solar panel 2 to rotate, and perform deviation correction until the gravitational vector direction coincides with the normal direction of the solar panel 2, completing the test of the solar panel 2 tracking the gravitational vector in the roll channel.

[0114] Two-channel vector tracking test of the pitch and roll of the solar panel 2.

[0115] Based on the single-channel tracking gravitational vector test of the solar panel 2 in the second step, the experimenter controls the motion tabletop 11 of the three-axis turntable to rotate to simulate the rotation law of the solar vector, that is, simultaneously change the pitch angle θ z and the roll angle δ z of the motion tabletop 11 of the three-axis turntable. Then, the changed angles of the motion tabletop 11 of the three-axis turntable in the body coordinate system are recorded as the pitch angle θ1, the roll angle δ1, and the yaw angle , and the corresponding data are recorded. At the same time, record the starting time t of the rotation of the motion tabletop 11 of the three-axis turntable. According to the pitch channel angle sensor 12 and the roll channel angle sensor 13 installed on the CubeSat body 1, measure the actual rotation pitch angle β r and the roll angle γ r of the solar panel 2, as well as the ending time t r of the rotation of the solar panel 2, and calculate the accuracy and response time of the two-channel gravitational vector tracking of the pitch and roll of the solar panel 2. The calculation formulas are as follows:

[0116]

[0117]

[0118] Δt = t r -t (19)

[0119] The entire test process is as Figure 6 shown. It can be seen that the experimental method of using the movement table 11 of the three-axis turntable to operate and simulate the azimuth relationship between the CubeSat body 1 and the measured vector, using the gravity vector to simulate the solar vector, and using the three-axis accelerometer 10 to simulate the solar wing of the sun sensor 3 to replace the vector tracking experiment proposed by the present invention can test and verify the correctness and working performance of the two-dimensional sun-pointing function of the solar wing 2 in the ground experiment stage.

[0120] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention. The content not described in detail in the present invention belongs to the prior art well-known to those of ordinary skill in the art.

Claims

1. A ground experiment method for sun-pointing of a cube satellite solar wing based on gravity vector tracking, characterized in that: It includes the following steps: Step 1: Measure the current gravity vector orientation using the three-axis accelerometer on the solar wing, and then transmit the obtained information to the solar wing follow-up device controller; Step 2: The solar wing follow-up device controller uses the control method to be verified to manipulate the solar wing to rotate in the pitch and roll directions, so as to achieve the tracking of the solar wing for the gravity vector; Step 3: By changing and measuring the pitch angle and roll angle of the CubeSat body attitude, the two-dimensional angle between the normal direction of the solar wing and the gravity vector direction is adjusted. Furthermore, the solar wing follow-up device uses the control method to be verified and the servo mechanism to manipulate the solar wing to rotate in the pitch and roll directions, so as to achieve the two-dimensional follow-up tracking of the solar wing for the gravity vector, and simulate the follow-up tracking process of the solar wing for the solar vector when the CubeSat body attitude remains unchanged and the solar vector rotates during actual on-orbit flight; The control method to be verified is: According to the current gravity vector orientation measured by the three-axis accelerometer, calculate the angles between the current gravity direction and the normal direction of the solar wing on the pitch and roll axes, and accordingly control the servo mechanism to drive the two-dimensional rotation of the solar wing to reduce the angular deviation in the two axes until the gravity vector direction coincides with the normal direction of the solar wing; Use a three-axis turntable to change the pitch angle and roll angle of the CubeSat body attitude, and control the two-dimensional angle between the gravity vector direction and the normal direction of the solar wing to simulate the two-dimensional angle between the solar vector direction and the normal direction of the solar wing during the on-orbit operation of the CubeSat; The variation law of the pitch angle and roll angle of the CubeSat body attitude controlled by the three-axis turntable is: where θ z is the pitch angle of the cubic satellite body attitude controlled by the three-axis turntable, and δ z is the roll angle of the cubic satellite body attitude controlled by the three-axis turntable; θ s is the elevation angle of the sun vector in the Earth inertial system; δ s is the azimuth angle of the sun vector in the Earth inertial system, T s is the time calculated starting from the vernal equinox point; is the rotation matrix from the Earth inertial coordinate system to the orbital coordinate system; ω is the argument of perigee, f is the true anomaly, i is the orbital inclination, Ω is the right ascension of the ascending node, C x , C y and C z correspond to the rotation matrices of the x, y, and z axes in the orbital coordinate system respectively; is the vernal equinox sun unit vector [100] T , s x , s y and s z represent the components of the sun vector on the x, y, and z axes respectively. After the cubic satellite orbit is determined, the description of the sun vector s in the orbital system is known; According to the pitch angle β′ and roll angle γ′ required for the normal of the solar wing to coincide with the gravity vector obtained by calculation, and the actually measured pitch angle β r and roll angle γ r of the solar wing rotation, calculate the tracking accuracy of the solar wing; according to the difference between the start time t of the three-axis turntable rotation and the end time t r of the solar wing rotation, obtain the response time of the solar wing tracking.

2. A ground experimental device for the solar panel of a cube satellite to orient towards the sun based on gravity vector tracking, characterized in that: It includes a CubeSat body, a solar wing, a solar wing controller, a three-axis accelerometer, a pitch channel driving device, a roll channel driving device, a pitch channel angle sensor, a roll channel angle sensor, and a three-axis turntable moving tabletop; The experimental device conducts experiments according to the method described in Claim 1; The CubeSat body is used to install the solar wing and the solar wing controller. The solar wing is composed of solar panels and is connected to the CubeSat body through a solar wing two-dimensional rotation mechanism; The solar wing controller is used to control the pitch channel driving device and the roll channel driving device of the solar wing; The three-axis accelerometer is installed on the solar wing and is used to measure the gravity vector direction; The pitch channel driving device and the roll channel driving device drive the solar wing to rotate in the pitch and roll channels according to the signals of the solar wing controller; The pitch channel angle sensor is used to measure the real-time rotation angle of the solar wing in the pitch channel; The roll channel angle sensor is used to measure the real-time rotation angle of the solar wing in the roll channel; The CubeSat body is fixedly installed on the three-axis turntable moving tabletop. The three-axis turntable moving tabletop drives the CubeSat body to rotate through its own rotation, so that the angle between the normal direction of the solar wing and the gravity vector direction deviates.

3. The ground experimental device for the solar wing of the cube satellite to face the sun based on gravity vector tracking according to claim 2, characterized in that: The three-axis turntable moving tabletop drives the CubeSat body to rotate through its own rotation, and controls the two-dimensional angle between the gravity vector direction and the normal direction of the solar wing to simulate the two-dimensional angle between the solar vector direction and the normal direction of the solar wing during the on-orbit operation of the CubeSat.

Images