Robert Halverson

Spacecraft are often equipped with lightweight, flexible appendages, such as large solar panels, antennas, or robotic arms to assist in spacecraft docking or on-orbit assembly. There are well-established control methods for attitude control of the rigid spacecraft hub equipped with flexible appendages, however attitude control of the end of the flexible appendage or payload attachment using a torque applied to the rigid spacecraft hub is a much more challenging problem. In this project, parallel feedforward control methods are applied to a spacecraft with a large payload attached to the end of a flexible appendage. A 2D dynamic model of this spacecraft is considered with a torque applied directly to the hub of the spacecraft, where the control objective is to track a desired angular velocity of the payload. This setup leads to a noncolocated relationship between the spacecraft hub torque and the payload angular velocity output. Numerical simulations demonstrate that implementing the parallel feedforward controller simplifies the choice of a stabilizing feedback controller. These results are expanded to an experimental rotary flexible joint manipulator, which is used as a physical analog to the flexible-appendage spacecraft. The experimental results confirm the findings from the numerical results, demonstrating the practical nature of the proposed control method. Both results include a comparison to a state-of-the-art control mu-tip method, where it is shown that parallel feedforward control is implementable in situations where mu-tip control is not. Furthermore, preliminary simulations are being implemented on a 3D model of a spacecraft equipped with a flexible appendage.