11:00 AM - 1:00 PM
[PCG18-P12] Attitude Control System Using Geomagnetic Sensor and Magnetic Torquer
Keywords:Microsatellite, ACS, Kanazawa SAT3
Kanazawa University is developing a nano-satellite "KOYOH". The observation mission of "KOYOH" is to detect the direction and time of arrival of X-rays generated simultaneously with gravitational waves, and to report them to the ground. This will make it possible to identify the source of the X-rays, which is expected to lead to the elucidation of the mechanism of black hole formation. In order to observe X-rays in space, it is necessary to point the observation equipment in the direction of deep space. This requirement is realized by a system that controls the attitude of the satellite.
The attitude control system consists of a sensor that detects the information necessary to determine the attitude of the satellite and an actuator that generates the control force. The attitude control system calculates how much to rotate the satellite's body based on the information read by the sensors, and drives the actuators appropriately to control the satellite's attitude. "KOYOH" is equipped with STT (Star Tracker), GAS (Geomagnetic Aspect Sensor), GYR (Gyro Sensor), FSS (Fine Sun Sensor), CSS (Coarse Sun Sensor), and GPS (Global Positioning System) as sensors, and RW (Reaction Wheel) and MTQ (Magnetic Torquer) as actuators. The GAS is a device that detects the geomagnetic vector, and the MTQ is a device that generates a magnetic moment by applying a voltage and passing a current through its internal coil. The control torque is generated by the interference between this magnetic moment and the earth's magnetic field.
The OBC calculates the voltage to be applied to the MTQ based on the received data, and sends the value to the MC. The OBC generates PWM signals from the received values and controls the MTQ. The MC generates PWM signals from the received values and controls the MTQ. This is the sequence of attitude control using MTQ and GAS. However, since the GAS also detects the magnetic field generated by the MTQ, they cannot be used at the same time, and it takes up to 150 msec for the GAS detection value to stabilize after the MTQ drive is stopped. In addition, there is noise and outliers in the detected values of GAS. To deal with these problems, the control design of each device was defined in this study. The control cycle is required to be realized within 2000msec from the viewpoint of attitude accuracy. Therefore, the execution time of PWM control was set to 1600 msec, the waiting time to 170msec, the reading time of the GAS detection value to 20 msec, and the data was designed to be acquired multiple times for filter processing. For the filter for noise removal, we compared the performance evaluation of an IIR-type first-order low-pass filter and a moving average, and adopted the moving average.
Furthermore, the temperature characteristics of the equipment used for attitude control were evaluated. The control voltage of MTQ was proportional to the temperature, and the rate of change of the control voltage was 1.4% in the test environment. The output value of GAS was proportional to the temperature and decreased by about -15nT per 1degC.
In the future, it will be necessary to develop software to integrate with the systems of other instruments and to control the attitude autonomously in space.
The attitude control system consists of a sensor that detects the information necessary to determine the attitude of the satellite and an actuator that generates the control force. The attitude control system calculates how much to rotate the satellite's body based on the information read by the sensors, and drives the actuators appropriately to control the satellite's attitude. "KOYOH" is equipped with STT (Star Tracker), GAS (Geomagnetic Aspect Sensor), GYR (Gyro Sensor), FSS (Fine Sun Sensor), CSS (Coarse Sun Sensor), and GPS (Global Positioning System) as sensors, and RW (Reaction Wheel) and MTQ (Magnetic Torquer) as actuators. The GAS is a device that detects the geomagnetic vector, and the MTQ is a device that generates a magnetic moment by applying a voltage and passing a current through its internal coil. The control torque is generated by the interference between this magnetic moment and the earth's magnetic field.
The OBC calculates the voltage to be applied to the MTQ based on the received data, and sends the value to the MC. The OBC generates PWM signals from the received values and controls the MTQ. The MC generates PWM signals from the received values and controls the MTQ. This is the sequence of attitude control using MTQ and GAS. However, since the GAS also detects the magnetic field generated by the MTQ, they cannot be used at the same time, and it takes up to 150 msec for the GAS detection value to stabilize after the MTQ drive is stopped. In addition, there is noise and outliers in the detected values of GAS. To deal with these problems, the control design of each device was defined in this study. The control cycle is required to be realized within 2000msec from the viewpoint of attitude accuracy. Therefore, the execution time of PWM control was set to 1600 msec, the waiting time to 170msec, the reading time of the GAS detection value to 20 msec, and the data was designed to be acquired multiple times for filter processing. For the filter for noise removal, we compared the performance evaluation of an IIR-type first-order low-pass filter and a moving average, and adopted the moving average.
Furthermore, the temperature characteristics of the equipment used for attitude control were evaluated. The control voltage of MTQ was proportional to the temperature, and the rate of change of the control voltage was 1.4% in the test environment. The output value of GAS was proportional to the temperature and decreased by about -15nT per 1degC.
In the future, it will be necessary to develop software to integrate with the systems of other instruments and to control the attitude autonomously in space.