Design and verification of the LEAP attitude control system

Gravity gradient control is the simplest and most commonly used passive control technique for micro-satellite's attitude stabilization. This technique is valuable as it requires little power for stabilization. The limitation of the gravity gradient stabilization, however, lies in the lack of accuracy and pointing capability as the amount and direction of the torque is restricted. Further, the pure passive gravity gradient method cannot prevent satellite attitude from flipping. In this paper, the design and verification of the attitude control system of the LEAP, a micro-satellite being developed at National Cheng Kung University, is described. The LEAP utilizes a passive gravity gradient stabilization scheme together with an active control method by using magnetic torques to decrease angular velocity after the satellite is released from the launcher or while the satellite cannot maintain pointing accuracy. When the satellite detect that the direction of the z-axis in body frame points to earth, the satellite would deploy the gravity gradient boom in applicable timing to process passive gravity gradient control without flipping. In this work, the model of the environment in space is set up, and the complete process of deploying the boom is simulated. Numerical and hardware in the loop simulation results demonstrate that the proposed method can effectively control the satellite attitude to maintain the pointing accuracy and ensure normal operation.