Design and Test of an Attitude Determination and Control System for a 6U CubeSat using AFIT's CubeSat Testbed

Abstract : The design and test of a 6U CubeSat Attitude Determination and Control System (ADCS) are explored to establish single-axis control using AFIT's CubeSat testbed consisting of a Helmholtz cage and hemi-spherical air bearing. The Helmholtz cage produces a near-uniform magnetic eld inside the cage while the air bearing provides a near-frictionless surface for ADCS testing. The ADCS testbed includes a four wheel pyramid reaction wheel array (RWA) for actuation and an inertial measurement unit (IMU) for attitude determination. Along with the ADCS hardware, the ADCS testbed also includes an Electrical Power System (EPS) and Command and Data Handling (CDH) for power and wireless telemetry, respectively. Attitude estimation is performed using the QUEST algorithm with magnetometer and accelerometer sensor data to estimate a current quaternion. A Proportional-Integral-Derivative (PID) controller is used for control of the ADCS testbed while each reaction wheel motor is controlled by a proportional gain. After calibration, the static estimation accuracy improved from 3o to 0.02o (3 ). The RWA is characterized as a 1st order system with a systemic 0.2 second time delay. The ADCS testbed controller demonstrates linear time response characteristics at small angle slews. Through this research e ort, the pointing accuracy was improved from 20o to 0.07o (3 ). External torques caused by air currents and inherent magnetic moments were explored and characterized. The inherent magnetic moment of the ADCS testbed was calculated. Simulated time response characteristics of the model showed similar behavior to the ADCS testbed results.

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