Fast calibration method for micro-nano satellite magnetometer

Abstract

A method for rapidly calibrating a micro-nano satellite magnetometer involves rotating the micro-nano satellite around the X, Y, and Z axes of the celestial body. Four static points are collected for each axis, with multiple sets of data collected each time. The average is taken as the magnetometer measurement value for that point. The hard iron magnetic field component error to be eliminated on each axis is calculated using the least squares method, thereby correcting the center of the sphere to the origin. This method utilizes the fact that the direction and magnitude of the Earth's magnetic field are constant. When the sensor rotates arbitrarily in space, the trajectory of the Earth's magnetic field theoretically lies on a sphere. An uncalibrated magnetometer would measure a sphere whose center is not at the origin of the coordinate system. In this case, the magnetometer data would not accurately reflect the direction and magnitude of the magnetic field. This method allows for rapid calibration of the micro-nano satellite magnetometer using the satellite itself after the satellite enters full-satellite testing, without the need for other high-precision magnetometers.

Description

Technical Field

[0001] The present invention relates to a technology in the field of micro-nano satellite control, in particular to a method for rapid calibration of a micro-nano satellite magnetometer. Background Art

[0002] Magnetic properties are crucial for satellite attitude control and stabilization. The output accuracy of magnetometers in micro- and nanosatellites is primarily affected by two factors. First, the magnetometer's inherent sensor errors, including zero offset, sensitivity error, and orthogonality error. Second, environmental magnetic interference errors. Micro- and nanosatellites are small, and the electromagnetic environment surrounding onboard equipment is complex. This can generate strong hard and soft magnetic interference, leading to magnetometer measurement errors. Eliminating and mitigating the impact of these errors on the magnetometer is key to improving the output accuracy of micro- and nanosatellite magnetometers.

[0003] Conventional magnetometer calibration methods require a zero-magnetic laboratory or a standard high-precision magnetometer. After measuring the residual magnetism, magnetic blocks are placed inside the satellite to offset the residual magnetism. However, the internal space of the micro-nano satellite is limited. Using this method for testing is costly, time-consuming, and difficult to implement, and it cannot achieve the rapid production and deployment of micro-nano satellites. Summary of the Invention

[0004] The present invention addresses the problems that existing micro-nano satellite magnetometer calibration requires the cooperation of multiple sensors, resulting in high costs, long testing cycles, and a difficult calibration process. A rapid calibration method for micro-nano satellite magnetometers is proposed. The method utilizes the fact that the direction and magnitude of the Earth's magnetic field are constant. When the sensor rotates arbitrarily in space, the trajectory of the Earth's magnetic field is theoretically on a spherical surface. The magnetic field measured by an uncalibrated magnetometer will be a sphere whose center is not at the origin of the coordinate system. In this case, the magnetometer data cannot accurately reflect the direction and magnitude of the magnetic field. Rapid calibration of the micro-nano satellite magnetometer can be achieved using the satellite itself after the satellite enters full-satellite testing, without the need for other high-precision magnetometers.

[0005] The present invention is achieved through the following technical solutions:

[0006] The present invention relates to a rapid calibration method for a micro-nano satellite magnetometer. The micro-nano satellite is rotated around the three axes X, Y, and Z of the celestial body, and four static points are collected on each axis. Multiple groups of data are collected each time, and the average value is taken as the measurement value (M) of the magnetometer at that point. xi , M yi , M zi ), the hard iron magnetic field component error to be eliminated on each axis (M′) is calculated by the least squares method. x , M′ y , M′ z ), thereby correcting the center of the sphere to the origin.

[0007] The least squares method is: Find A T B, where: a, b, c represent i=10, 11, 12, M xi -M x(i+1) =ΔM xi(i+1) ,i=1,3,5,7,9,11,

[0008] The hard iron field is an interfering magnetic field generated by devices and ferromagnetic materials with high coercivity. Its direction and magnitude relative to the celestial body generally remain constant. The magnetic heading deviation caused by the hard iron field is called hard magnetic compass. Because the soft iron field is much smaller than the hard iron field and varies erratically, only hard magnetic compass correction is considered.

[0009] Technical Effects

[0010] Compared with the existing technology, the present invention is based on the trajectory theory of the geomagnetic field. It can quickly and cheaply obtain the hard iron magnetic field deviation of micro-nano satellites for micro-nano satellites. Through software modification, it can realize the calibration of micro-nano satellite magnetometers, thereby realizing the rapid production and deployment of micro-nano satellites. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 Flowchart of the present invention;

[0012] Figure 2 Schematic diagram of the rotation of the micro-nano satellite during the calibration process of the present invention.

[0013] Figure 3 This is a comparison diagram of the magnetometer before and after calibration in the embodiment;

[0014] In the figure: (a) rotation around the x-axis; (b) rotation around the y-axis; (c) rotation around the z-axis. DETAILED DESCRIPTION

[0015] like Figure 1 As shown, this embodiment relates to a method for rapid calibration of a micro-nano satellite magnetometer, comprising the following steps:

[0016] The first step is to power on the entire satellite so that the calibration environment of the magnetometer is close to the working environment during the operation of the micro-nano satellite.

[0017] The second step is Figure 2 As shown in the figure, the micro-nano satellite is rotated around the XYZ axis of the star body, and multiple sets of magnetometer data are collected every 90° rotation. The average value is taken to obtain the magnetometer measurement value (M) at each static position. xi , M yi , M zi ), where: i = 1, 2, ..., 12, i represents the i-th position.

[0018] The third step is to calculate the error (M′) caused by the hard iron magnetic field using the recursive least squares method. x , M′ y , M′ z ), specifically: Find in: a, b, c represent i=10, 11, 12, M xi -M x(i+1) =ΔM xi(i+1) ,i=1,3,5,7,9,11,

[0019] Step 4: Calculate the magnetometer data after removing the hard iron magnetic field

[0020] Step 5: Modify the onboard software code to correct the magnetometer output.

[0021] The sixth step is to verify the magnetometer output results. Rotate around the three axes to determine whether the data of the other two axes are circles with the center near the origin. If so, the calibration is complete; if not, recalibration is required.

[0022] Preferably, ferromagnetic objects, such as keys and cell phones, should not be placed near the CubeSat during calibration. Calibration should also be conducted away from areas with strong magnetic fields, such as magnetic mines, parking lots, and construction areas with underground rebar.

[0023] Preferably, the magnetic heading meter needs to be recalibrated when the following situations occur.

[0024] 1) Magnetometer data anomalies, including: data deviating too much from the theoretical value of the local magnetic field, obvious bad points, etc.

[0025] 2) The mechanical structure of micro-nano satellites has changed;

[0026] 3) During the calibration process, a strong magnetic field approaches the micro-nano satellite.

[0027] After specific actual experiments, taking the "Siyuan" No. 1 Student 3U CubeSat of Shanghai Jiao Tong University as an example, the above calibration method was carried out on the lawn of the School of Electrical Engineering of Shanghai Jiao Tong University Minhang Campus at 02:30 on the morning of September 21, 2021. The magnetometer model used by the CubeSat is MTI-600. After calibration, the three-axis measurement values ​​of the magnetometer all form an approximate circle around the origin, which is significantly improved compared to the measurement values ​​before calibration. Specifically, the comparison results of the magnetometer measurement values ​​before and after calibration are as follows: Figure 3 As shown, compared with the prior art, this method has significant improvements in speed and low cost.

[0028] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principles and purpose of the present invention. The scope of protection of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. All implementation schemes within its scope shall be subject to the constraints of the present invention.

Claims

1. A method for rapid calibration of a micro-nano satellite magnetometer, characterized in that: The micro-nano satellite rotates around the XYZ axis of the star, and collects four static points on each axis. Multiple sets of data are collected each time, and the average value is taken as the measurement value of the magnetometer at that point. , the hard iron magnetic field component error to be eliminated on each axis is calculated by the least squares method , thereby correcting the center of the sphere to the origin; The least squares method is: , find , , , a, b, c represent 10, 11, 12 respectively, , .

2. The micro-nano satellite magnetometer rapid calibration method according to claim 1 is characterized in that: include: The first step is to power on the entire satellite so that the magnetometer calibration environment is close to the working environment during the operation of the micro-nano satellite; The second step is to rotate the micro-nano satellite around the XYZ axis of the star. Collect multiple sets of magnetometer data, take the average value, and obtain the magnetometer measurement value at each static position ,in: , i represents the i-th position; The third step is to calculate the error caused by the hard iron magnetic field using the recursive least squares method. , specifically: , find , , , a, b, c represent 10, 11, 12 respectively, , ; Step 4: Calculate the magnetometer data after removing the hard iron magnetic field ; Step 5: Modify the onboard software code to correct the magnetometer output; The sixth step is to verify the magnetometer output results. Rotate around the three axes to determine whether the data of the other two axes are circles with the center near the origin. If so, the calibration is complete; if not, recalibration is required.

3. The micro-nano satellite magnetometer rapid calibration method according to claim 2, characterized in that: During the calibration process, do not place ferromagnetic materials near the CubeSat and avoid strong magnetic field areas when testing.

4. The micro-nano satellite magnetometer rapid calibration method according to claim 2, characterized in that: The magnetic heading gauge needs to be recalibrated when the following situations occur: 1) Abnormal magnetometer data; 2) The mechanical structure of micro-nano satellites has changed; 3) During the calibration process, a strong magnetic field approaches the micro-nano satellite.

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